Friday, August 19, 2011

Radiation Oncology


Radiation Oncology  has been in use as a cancer treatment for more than 100 years, with its earliest roots traced from the discovery of x-rays in 1895 by Wilhelm Roentgen The field of radiation therapy began to grow in the early 1900s largely due to the groundbreaking work of Nobel Prize-winning scientist Marie Curie, who discovered the radioactive elements polonium and radium. This began a new era in medical treatment and research.Radium was used in various forms until the mid-1900s when cobalt and caesium units came into use. Medical linear accelerators have been used too as sources of radiation since the late 1940s.
With Godfrey Hounsfield’s invention of computed tomography (CT) in 1971, three-dimensional planning became a possibility and created a shift from 2-D to 3-D radiation delivery; CT-based planning allows physicians to more accurately determine the dose distribution using axial tomographic images of the patient's anatomy. Orthovoltage and cobalt units have largely been replaced by megavoltage linear accelerators, useful for their penetrating energies and lack of physical radiation source.
The advent of new imaging technologies, including magnetic resonance imaging (MRI) in the 1970s and positron emission tomography (PET) in the 1980s, has moved radiation therapy from 3-D conformal to intensity-modulated radiation therapy (IMRT) and image-guided radiation therapy (IGRT) Tomotherapy. These advances allowed radiation oncologists to better see and target tumors, which have resulted in better treatment outcomes, more organ preservation and fewer side effects.
Thirty or forty years ago, the ability to diagnose and treat an individual with a brain tumor was limited by crude surgical and radiological tools. Modern neurosurgical tools and techniques and advanced imaging modalities such as CT and MRI now allow brain tumors to be identified much earlier in the course of the disease. Even when a cure is not possible, an earlier diagnosis can result in an improved outcome for the patient through more appropriate utilization of radiation therapy.
Radiation therapy uses high energy light beams (X-rays or gamma rays) or charged particles (electron beams or proton beams) to damage critical biological molecules in tumor cells. If enough damage is done to the chromosomes of a cell, it will spontaneously die or it will die the next time it tries to divide into two cells. Radiation therapy is usually done on an outpatient basis with treatment occurring each workday for a period of several weeks. If the patient has had surgery for the tumor, radiation therapy typically begins a week or two after surgery.
Radiation therapy is an effective cancer therapy. In surgery, a surgeon may be constrained in resecting the cancer by the presence of critical structures that cannot be removed. The side effects of chemotherapy on normal tissues far away from the brain may limit the ability of a medical oncologist to deliver appropriately intensive treatment to a brain tumor. In radiation therapy, a non-invasive treatment can be given repetitively over several weeks to months and can be aimed specifically at the area where treatment is needed, minimizing side effects for uninvolved normal tissues.
This repetitive treatment is called fractionation because a small fraction of the total dose is given in each treatment. The skills of the radiation oncologist, physicist and dosimetrist allow complex plans to be devised to minimize side effects for normal tissues. Radiotherapy can only be performed with linear accelerator technology.
Conventionally administered external beam radiation therapy gives a uniform dose of radiation to the entire region affected by the tumor. There is only a small variation of the dose delivered to various parts of the tumor. Radiation therapy may not be as effective as stereotactic radiosurgery, which can give higher doses of radiation to the tumor itself.
Treatment of brain tumors with external beam radiation therapy has been an area of intense research activity over the past several decades. Through clinical research, conducted on patients, much has been learned about how to appropriately use radiation therapy for various types of brain tumors. External beam radiation therapy is a valuable component of therapy for nearly all brain tumors; treatment can be delivered to any part, or all, of the central nervous system. The ability to assure uniform doses of radiation to the areas being treated is one of the major strengths of modern external beam radiation therapy.


  •     External Beam Therapy (EBRT or XRT)
External beam therapy (EBT) is a method for delivering a beam of high-energy x-rays to a patient's tumor. The beam is generated outside the patient (usually by a linear accelerator, see below) and is targeted at the tumor site. These high energy x-rays can deposit their dose to the area of the tumor to destroy the cancer cells and, with careful treatment planning, spare the surrounding normal tissues. No radioactive sources are placed inside the patient's body.

  •   Brachytherapy  or  Unsealed Source Radiotherapy
Brachytherapy is an advanced cancer treatment. Radioactive seeds or sources are placed in or near the tumor itself, giving a high radiation dose to the tumor while reducing the radiation exposure in the surrounding healthy tissues. The term "brachy" is Greek for short distance. Brachytherapy is radiation therapy given at a short distance: localized, precise, and high-tech.

  •    Particle Therapy

using beams of energetic protons, neutrons, or positive ions for cancer treatment. The most common type of particle therapy as of 2009 is proton therapy. Although a photon, used in x-ray or gamma ray therapy, can also be considered a particle, photon therapy is not considered here. Additionally, electron therapy is generally put into its own category. Because of this, particle therapy is sometimes referred to, more correctly, as hadron therapy (that is, therapy with particles that are made of quarks).


Radiation therapy has been in use as a cancer treatment for more than 100 years, with its earliest roots traced from the discovery of x-rays in 1895 by Wilhelm Röntgen.[8]

The field of radiation therapy began to grow in the early 1900s largely due to the groundbreaking work of Nobel Prize-winning scientist Marie Curie, who discovered the radioactive elements polonium and radium. This began a new era in medical treatment and research.[8] Radium was used in various forms until the mid-1900s when cobalt and caesium units came into use. Medical linear accelerators have been used too as sources of radiation since the late 1940s.

  With Godfrey Hounsfield’s invention of computed tomography (CT) in 1971, three-dimensional planning became a possibility and created a shift from 2-D to 3-D radiation delivery; CT-based planning allows physicians to more accurately determine the dose distribution using axial tomographic images of the patient's anatomy. Orthovoltage and cobalt units have largely been replaced by megavoltage linear accelerators, useful for their penetrating energies and lack of physical radiation source.

The advent of new imaging technologies, including magnetic resonance imaging (MRI) in the 1970s and positron emission tomography (PET) in the 1980s, has moved radiation therapy from 3-D conformal to intensity-modulated radiation therapy (IMRT) and image-guided radiation therapy (IGRT) Tomotherapy. These advances allowed radiation oncologists to better see and target tumors, which have resulted in better treatment outcomes, more organ preservation and fewer side effects.


Intensity Modulated Radiation Therapy (IMRT)

Intensity-modulated radiation therapy (IMRT) is an advanced form of three-dimensional conformal radiotherapy (3DCRT). It uses sophisticated software and hardware to vary the shape and intensity of radiation delivered to different parts of the treatment area. It is one of the most precise forms of external beam radiation therapy available.
Like conventional 3DCRT, IMRT links CT scans to treatment planning software that allows the cancerous area to be visualized in three dimensions. However, regular 3DCRT and IMRT differ in how the pattern and volume of radiation delivered to the tumor is determined. In conventional 3DCRT, clinicians input delivery patterns into the computer. In IMRT, the physician designates specific doses of radiation (constraints) that the tumor and normal surrounding tissues should receive. The physics team then uses a sophisticated computer program to develop an individualized plan to meet the constraints. This process is termed "inverse treatment planning." Treatment with IMRT is slightly longer that with 3DCRT, but generally produces fewer side effects.
IMRT uses the same medical linear accelerators that deliver x-ray beams in conventional 3DCRT.
As a unique feature, it also involves dynamic multi-leaf collimators (DMLCs), computer-controlled devices that use up to 120 movable "leaves" to conform the radiation beam to the shape of the tumor from any angle, while protecting normal adjacent tissue as much as possible.
DMLCs allow the dose of radiation to vary within a single beam – in other words, to deliver higher radiation in some areas and lower radiation in others. Earlier technology could also shape radiation beams but could deliver them only at a single, constant dose. The ability to vary the radiation dose with DMLCs is accomplished by "sliding windows" of radiation beams across the target cancerous area.
To more easily picture how DMLCs work, imagine a shower head with many nozzles, with the water representing radiation. Standard radiation techniques only allow a constant flow of water to be delivered through all nozzles. But with DMLCs, individual nozzles may be turned off and on, or set to deliver water at different intensities. In radiation therapy, the net effect is that radiation doses can be "wrapped" around tumors, or "painted" within tumors, far more precisely than was previously possible.
Treatment process and side effects for IMRT are similar to those for 3DCRT.

Image-Guided Radiotherapy (IGRT)

Image-guided radiation therapy (IGRT) is the process of frequent two and three-dimensional imaging, during a course of radiation treatment, used to direct radiation therapy utilizing the imaging coordinates of the actual radiation treatment plan. The patient is localized in the treatment room in the same position as planned from the reference imaging dataset. An example of Three-dimensional (3D) IGRT would include localization of a cone-beam computed tomography (CBCT) dataset with the planning computed tomography (CT) dataset from planning. Similarly Two-dimensional (2D) IGRT would include matching planar kilovoltage (kV) radiographs fluoroscopy or megavoltage (MV) images with digital reconstructed radiographs (DRRs) from the planning CT.
This process is distinct from the use of imaging to delineate targets and organs in the planning process of radiation therapy. However, there is clearly a connection between the imaging processes as IGRT relies directly on the imaging modalities from planning as the reference coordinates for localizing the patient. The variety of image gathering hardware used in planning includes Computed Tomography(CT), Magnetic Resonance Imaging (MRI), and Positron Emission Tomography (PET) among others. Through advancements in imaging technology, combined with a further understanding of human biology at the molecular level, the impact of IGRT on radiotherapy treatment continues to evolve.

Stereotactic Radiosurgery (SRS)

Stereotactic radiosurgery works the same as all other forms of radiation treatment. It does not remove the tumor or lesion, but it distorts the DNA of the tumor cells. The cells then lose their ability to reproduce and retain fluids. The tumor reduction occurs at the rate of normal growth for the specific tumor cell. In lesions such as AVMs (a tangle of blood vessels in the brain), radiosurgery causes the blood vessels to thicken and close off. The shrinking of a tumor or closing off of a vessel occurs over a period of time. For benign tumors and vessels, this will usually be 18 months to two years. For malignant or metastatic tumors, results may be seen in a few months, because these cells are very fast-growing.

Stereotactic Body Radiation Therapy (SBRT)

Stereotactic body radiation therapy (SBRT) is a technique designed to deliver radiation therapy very precisely to tumors anywhere in the body.  The word stereotactic pertains to the precise positioning of a tumor in relationship to the body.  The technology used in SBRT allows external beam radiation to be delivered with pinpoint accuracy.  With SBRT the physician can even take into account movement of a tumor based on a patient’s breathing pattern.  Such advancement in accuracy of radiation treatments allows higher doses of radiation to be delivered, thus potentially improving the likelihood of killing the cancer cells of a tumor.  Another benefit to improved accuracy is that treatments can be completed in a short period of time.  Typically, SBRT consists of 3 to 5 treatments carried out over the course of 1 to 2 weeks.  The precision associated with SBRT simultaneously helps reduce the dose of radiation to normal tissue around a tumor, thus helping to reduce side effects for patients.

3-Dimensional Conformal Radiotherapy

Three-dimensional conformal radiotherapy (3DCRT) is a complex process that begins with the creation of individualized, 3D digital data sets of patient tumors and normal adjacent anatomy. These data sets are then used to generate 3D computer images and to develop complex plans to deliver highly "conformed" (focused) radiation while sparing normal adjacent tissue. Because higher doses of radiation can be delivered to cancer cells while significantly reducing the amount of radiation received by surrounding healthy tissues, the technique should increase the rate of tumor control while decreasing side effects.

3DCRT is used to treat tumors that in the past might have been considered too close to vital organs and structures for radiation therapy. For example, 3DCRT allows radiation to be delivered to head and neck tumors in a way that minimizes exposure of the spinal cord, optic nerve, salivary glands and other important structures.

            SIDE EFFECTS

  • Side effects of radiation therapy will depend on the type of radiation received, the amount of the surface of the brain targeted, the site targeted, and the total dose of radiation. In general, there will be hair loss, skin irritation, possible hearing problems, nausea, vomiting, loss of appetite, and neurologic effects. The most prevalent side effect is fatigue which is may last through treatment and for many months afterwards. The neurologic effects most affecting quality of life are eventual permanent memory and speech problems. These are just a few of the problems that can develop.
          Some specific indications for radiation therapy are discussed below.

Brain Metastases  

Cancers arising outside the brain in such diverse organs as the lung or breast can travel through the blood vessels to grow in the brain. Tumors that have spread in this fashion are known as metastases. Metastases may be discovered before or after they cause symptoms; a CT scan or an MRI are the tests most frequently used to diagnose brain metastases. Brain metastases may develop at different times (early or late) in the course of the disease in different patients.
Whole brain irradiation is frequently prescribed for patients with brain metastases. This treatment uses radiation to treat the visible lumps of tumor and the presumed invisible tumor deposits that are so small they may not be seen on even a sensitive MRI scan. Therefore, large areas of the brain may be treated to stop the spread of the tumors.
Symptoms caused by tumors metastatic to the brain usually respond to whole brain radiation therapy; different studies have reported response rates of 50 to 70 percent.
The Radiation Therapy Oncology Group (RTOG) performed randomized studies that showed a course of 10 treatments over two weeks to give a total dose of 30 Gray (the same as 3000 centiGray or 3000 rads, to use older terms) was as good as more extended courses of radiation therapy that give higher doses. In some situations, a shorter or longer course of treatment than two weeks may be preferable. For patients who have a single brain metastasis that is removed surgically, whole brain radiation therapy was found in a randomized study to give great improvements in preventing cancer from regrowing in the brain and in prolonging survival.
Stereotactic radiosurgery can be combined with whole brain radiation therapy for brain metastases. The whole brain radiation therapy will treat the visible metastases and any presumed microscopic tumor deposits as well. This is possible because whole brain radiation therapy is given as a low dose to a larger volume and targeted to the tumor and the area of possible tumor spread, while stereotactic radiosurgery is a high dose given to a very small volume and targeted only within the tumor itself. The two treatment techniques can be thought of as complementary in achieving control of metastases to the brain.
Whole brain radiation therapy can cause shrinkage of visible brain metastases, sometimes making them more amenable to stereotactic radiosurgery or microsurgery. The addition of whole brain radiation therapy to stereotactic radiosurgery can decrease the possibility of additional metastatic lesions and decrease the chance that visible lesions treated with radiosurgery may have recurrences after radiosurgical treatment. Omission of whole brain radiation therapy for brain metastases is slightly controversial, but this is an area of ongoing intensive research.
Recently, some investigators have tried stereotactic radiosurgery alone without whole brain radiation therapy for selected patients with brain metastases to avoid causing the side effects of whole brain radiotherapy. Because whole brain radiation therapy can be given at a later date to these patients if their metastases are not controlled by the radiosurgery, this strategy may relieve symptoms effectively while not adversely affecting survival.
There is a widely accepted belief that for melanoma, kidney cancer and sarcomas that spread to the brain, stereotactic radiosurgery may be more effective at controlling the lesions than whole brain radiation therapy. The Eastern Cooperative Oncology Group (ECOG) is evaluating radiosurgery as a solitary treatment for patients with one to three brain metastases of these types of tumors.




Meningiomas are tumors arising from the meninges, one of the protective layers surrounding the brain and its cushioning cerebrospinal fluid. They are usually slow-growing tumors that do not spread to other places in the brain or elsewhere in the body.
It is generally acknowledged that an operation that completely removes a meningioma does not require radiation therapy afterwards to prevent regrowth. An operation in an area where it is difficult for the surgeon to completely remove the meningioma from the surface of the brain can leave tumor cells behind that can lead to tumor regrowth.
For meningiomas that are completely removed, approximately 20 percent will regrow in 10 years and 33 percent by 15 years's time. Up to one third of patients with meningiomas who undergo an operation will be left with obvious residual tumor. More than half of patients with residual tumor after an operation will have regrowth of the tumor by 10 years's time and about 10 percent will not have had regrowth by 15 years's time.
Patients with meningiomas that are unresectable because of the extent or location of the tumor may be offered radiation therapy to try to prevent its further growth. There have been no randomized controlled (phase III) trials evaluating the effectiveness of a course of irradiation in preventing meningiomas from recurring after an operation, but radiation therapy is recognized as helpful in this role. Various researchers have found the control rates for incompletely resected meningiomas treated with radiation therapy as being in the range of 75 to 90 percent at 10 years. A significant decrease in post-radiation recurrences occurred when radiation oncologists started using MRI and CT scans to plan the radiation therapy. It was then possible to avoid accidentally missing the meningiomas when administering treatment! The University of California San Francisco has reported that the five-year recurrence rate for incompletely resected meningiomas after radiotherapy in the modern era is only 2 percent.



Pituitary Adenomas   

There has been less of a role for radiation therapy in the management of pituitary tumors in recent years because of progress in multidisciplinary medical management of the benign tumors arising in this important endocrine organ.
Improved neurosurgical technology and microsurgical techniques have also led to less of a need for postoperative radiation therapy to prevent regrowth of incompletely removed tumors. High resolution MRI imaging and sensitive hormone analyses can help assess the completeness of resection of tumors. Medications can help suppress hormone hypersecretion from some pituitary adenomas.
Many patients who have pituitary tumors that cannot be completely removed with surgery are offered stereotactive radiosurgery to try to prevent recurrence or further growth of the tumor. This is sometimes not possible because of proximity of the optic nerves to the pituitary tumor and because treating the tumor with an effective dose of irradiation may cause damage to the optic nerves, resulting in a loss of vision. A five- to six-week course of external beam radiation therapy has been shown to be effective in preventing further growth of these tumors with a low risk of damage to vision and has even been shown to improve vision when unresectable tumor is pressing on the optic nerves.
There have been no randomized controlled (phase III) trials evaluating the effectiveness of radiation therapy to prevent regrowth of pituitary tumors and there have been no similar trials to comparatively evaluate stereotactic radiosurgery and external beam radiation therapy. Stereotactic radiosurgery with its precise targeting may offer a good alternative after surgery for these types of tumors. As with meningiomas, it is most common to use either radiosurgery or radiation therapy for a pituitary adenoma, reserving the other treatment technique for any failures to control the pituitary tumor.
Radiation therapy for pituitary tumors has been associated with delayed side effects. The normal pituitary gland can produce decreased hormone levels following a course of radiation therapy, resulting in the need for hormone supplementation. It has been argued that this results from the radiation being given to the hypothalamic region of the brain (just above the pituitary). Follow-up of patients currently being treated with stereotactic fractionated radiotherapy may help determine whether this technological advance decreases these late side effects by more precise irradiation of the pituitary gland. Long-term follow-up has shown that patients treated with radiation therapy for residual pituitary tumors have a slightly increased risk of developing second tumors a decade or more after their irradiation. More precise, modern irradiation techniques may decrease the incidence of second tumors.



Gliomas and Malignant Tumors  

This group of tumors arises from the cells supporting the neurons in the brain. Some of these tumors initially present as low-grade, slowly -growing masses and can eventually progress to more aggressive, high-grade tumors. There are also tumors that are more aggressive and malignant at their outset.
This group includes astrocytoma and oligodendroglioma as well as tumors in which these cell types are combined oligoastrocytomas or mixed gliomas. More aggressive tumors have the word anaplastic in their descriptive name. The most aggressive type of glioma is called glioblastoma multiforme. Anaplastic gliomas and glioblastoma multiforme are termed malignant gliomas and represent approximately 40 percent of all brain tumors.
Malignant gliomas will spread from the site of origin to other areas in the brain but will almost never spread outside the brain. There is typically a gradient of infiltrating tumor cells that decreases as the distance from the margin increases. Most commonly, the tumor will recur at the same location that it started or immediately adjacent thereto. Radiation therapy treatment recommendations for malignant gliomas currently advise that several centimeters of apparently normal brain tissue around the tumor be treated to try to prevent these tumors from recurring at the edge of the area where the radiation is given.
A current study being run by the RTOG is using 3D conformal treatment and dose escalation to evaluate whether this promising technology can safely deliver higher doses of radiation to the tumor in patients who have had an operation for glioblastoma multiforme. Prior studies have not shown any benefit from higher doses of radiation than is conventionally given over six weeks's time, but it is hoped that modern technology may help limit the dose of radiation to normal brain tissue to a greater extent than was previously possible. If this can be safely done, one outcome may be improved survival from lower failure rates, but this remains to be proven.
Current trials are underway evaluating the role of chemotherapy in the treatment of malignant gliomas and low-grade gliomas. Oligodendrogliomas seem to be more responsive to chemotherapy than other gliomas. There have been promising initial results. New drugs active against gliomas will be found through these trials and physicians will learn how best to integrate them with surgery and radiation therapy.

  • Radiation treatments affect all cells that are targeted. This means where normal healthy cells are targeted along with tumor cells, there will be injury to the healthy cells. The Merck Manual states the following:
          Radiation Injury to the Nervous System: The nervous system can be damaged by radiation therapy.      Acute and subacute transient symptoms may develop early, but progressive, permanent, often disabling nervous system damage may not appear for months to years. The total radiation dose, size of the fractions, duration of therapy, and volume of [healthy brain] nervous tissue irradiated influence the likelihood of injury. Considerable variation in individual susceptibility complicates the effort to predict safe radiation doses. (Source: The Merck Manual of Diagnosis and Therapy, Section 14, Neurologic Disorders.)
Side-effects of radiation are caused by the radiation treatment’s affect on normal cells with some being minimal and other being permanent. Additionally, the effects may occur quickly (acute) or months and years after treatment.
Acute reactions occur during or immediately after radiation. They are normally caused by swelling and can be easily controlled with medications. Delayed or late reactions are normally permanent and can be progressive. They can vary from mild to severe and may include decreased intellect, memory impairment, confusion, personality changes among other changes. All symptoms would be dependent on the amount of healthy tissue targeted with radiation.
Oncogenesis, the development of another tumor from the radiation treatment to the brain, is now a recognized, although rare, possible long-term side-effect of radiation to the brain. When another tumor occurs it is rare, and is most often associated with whole brain radiation or with fractionated radiotherapy. Each of these target more healthy brain tissue than one-session radiosurgery.

Wednesday, August 17, 2011

Enhanced Radiation Warhead

Enhanced Radiation Warhead ( ERW ) also known as Neutron bomb, is a type of tactical nuclear weapon designed specifically to release a large portion of its energy as energetic neutron radiation rather than explosive energy. An ERW explosion is typically about one-tenth as powerful as that of a comparable fission-type atomic bomb because standard thermonuclear weapons create increased explosive yield by capturing their neutron radiation. Although their extreme blast and heat effects are not eliminated, the increased radiation released by ERWs is meant to affect biological material (which may otherwise be protected from the heat of an explosion) rather than material infrastructure. ERWs are still much more destructive than conventional bombs. They were formerly built mainly by the United States.  


Sam Cohen is considered the father of the neutron bomb. In the summer of 1958 he began investigating the possibility of large thermonuclear weapons. In his research, Cohen argued that if the uranium casing of a hydrogen bomb were removed, the neutrons released would travel great distances, penetrating even well-shielded structures with lethal doses of radiation and harming anyone inside.
Neutron bombs could be used as strategic anti-ballistic missile weapons or as tactical weapons intended for use against armored forces; in fact, the neutron bomb was originally conceived as a weapon that could stop Soviet armored divisions from overrunning Western Europe without destroying Western Europe in the process.

As an anti-ballistic missile weapon, an ER warhead was developed for the Sprint missile system as part of the Safeguard Program to protect United States cities and missile silos from incoming Soviet warheads by damaging their electronic components with the intense neutron flux.

Tactical neutron bombs are primarily intended to kill soldiers who are protected by armor. Armored vehicles are extremely resistant to blast and heat produced by nuclear weapons, so the effective range of a nuclear weapon against tanks is determined by the lethal range of the radiation, although this is also reduced by the armor. By emitting large amounts of lethal radiation of one of the most penetrating kinds, ER warheads maximize the lethal range of a given yield of nuclear warhead against armored targets.

At the same time, modest fallout shelters of ordinary design will protect civilian populations. According to Sam Cohen's book, one of the best kept secrets is that the bomb is an effective defensive weapon against an armor attack.

One problem with using radiation as a tactical anti-personnel weapon is that to bring about rapid death of the individuals targeted, a radiation dose that is many times the lethal level must be administered. A radiation dose of 6 Gy is normally considered lethal. It will kill at least half of those who are exposed to it, but no effect is noticeable for several hours. Neutron bombs were intended to deliver a dose of 80 Gy to quickly kill targets. A 1 kt ER warhead can do this to a T-72 tank crew at a range of 690 m, compared to 360 m for a pure fission bomb (the blast would likely destroy it, however). For a 6 Gy dose, the distances are 1100 m and 700 m respectively, and for unprotected soldiers 6 Gy exposures occur at 1350 m and 900 m. The lethal range for tactical neutron bombs exceeds the lethal range for blast and heat even for unprotected troops, which is likely the reasoning for the idea that a neutron bomb destroys life and not infrastructure. If a neutron bomb were detonated at the correct altitude, deadly levels of radiation would blanket a wide area with minimal heat and blast effects when compared to a nuclear weapon of conventional design.

The neutron flux can induce significant amounts of short-lived secondary radioactivity in the environment in the high flux region near the burst point. The alloys used in steel armor can develop radioactivity that is dangerous for 24–48 hours. If a tank exposed to a 1 kt neutron bomb at 690 m (the effective range for immediate crew incapacitation) is immediately occupied by a new crew, they will receive a lethal dose of radiation within 24 hours.

One significant drawback of the weapon is that not all targeted troops will die or be incapacitated immediately. After a brief bout of nausea, many of those hit with about 5-50 Sv of radiation will experience a temporary recovery (the latent or "walking ghost phase") lasting days to weeks. Moreover, these victims would likely be aware of their inevitable fate and react accordingly.

3  Types  ERW :

W66 Thermonuclear Warhead

was used on the Sprint anti-ballistic missile system, designed to be a short range interceptor to shoot down incoming ICBM warheads. The W66 was a low yield (details not declassified, but reportedly a few kilotons) thermonuclear bomb, which was the first Neutron bomb (technically Enhanced Radiation weapon) fielded anywhere in the world. It was designed to destroy or disable an incoming warhead using neutron flux, and to a lesser extent X-ray and blast effects.
The W66 was 18 inches in maximum diameter and 35 inches long, with a weight of around 150 pounds.
Retired soon thereafter, along with the missile system.

W70 Mod 3 warhead

W70 is the designation for a tactical nuclear warhead developed by the United States in the early 1970s. The Lawrence Livermore National Laboratory designed W70 was used on the MGM-52 Lance. About 1250 were built in total. The warhead had a variable yield of between 1 and 100 kilotons, selectable by the user. The design dates from 1973.
The W70-3 was a modified version of the W70 and one of the first warheads to be battlefield-ready with an "enhanced radiation" (i.e. neutron bomb) feature. It had an explosive yield of about 1 kt., was manufactured during 1981-83, and retired by 1992; 380 were built. Note that using the explosive yield of a neutron weapon to measure its destructive power can be deceptive: most of the injuries inflicted by a neutron weapon are caused by its intense pulse of ionising radiation, not from heat and blast.
The inventor of the neutron bomb, Samuel Cohen, has criticized the description of the W70 as a "neutron bomb"  W70 Mod 3 warhead was dismantled in 1996.

W79 Mod Warhead

The W79 was produced in two models, the "W79 Mod 0" and "W79 Mod 1". Both were a plutonium-based linear-implosion, nuclear weapon. The "Mod 0" was a variable yield device with three yields, ranging from 100 tons up to 1.1 kiloton and an enhanced-radiation (popularly known as Neutron bomb) mode which could be turned on or off.
The "Mod 1" was fission only, without the enhanced-radiation option, and had a fixed 0.8 kiloton yield (800 tons of TNT). This probably corresponds with the maximum pure-fission yield of the "Mod 0".
Both models were 8 inches (203 mm) in diameter, 44 inches (112 cm) long and weighed 200 pounds (90 kg).
The W79 was produced  in 1981 and continuing into 1986. All units were retired from active service by the end of 1992.

                        FATHER OF NEUTRON BOMB

Samuel T. Cohen, the physicist who invented the small tactical nuclear weapon known as the neutron bomb, a controversial device designed to kill enemy troops with subatomic particles but leave battlefields and cities relatively intact.
Samuel Theodore Cohen was born in Brooklyn on Jan. 25, 1921, to Lazarus and Jenny Cohen, Austrian Jews who had migrated to the United States by way of Britain. His father was a carpenter and his mother a housewife who rigidly controlled family diets and even breathing habits (believing it unhealthy to breathe through the mouth). The boy had allergies, eye problems and other ailments, and for years was subjected to daily ice-water showers to toughen him up. 
The family moved to Los Angeles when he was 4. He was a brilliant student at public schools and U.C.L.A., where he graduated in 1943 with a physics degree. He joined the wartime Army and was posted to the Massachusetts Institute of Technology for advanced training in mathematics and physics.
In 1944 he was tapped for the Manhattan Project to analyze radioactivity in nuclear fission. He worked on Fat Man, the bomb dropped on Nagasaki in 1945, days after Little Boy destroyed Hiroshima.
Mr. Cohen was married twice. His first marriage, to Barbara Bissell in 1948, ended in divorce in 1952. In 1960, he married Margaret Munnemann. She survives him, as do their three children, Carla Nagler, Paul and Thomas, and three grandchildren.
Mr. Cohen joined RAND in Santa Monica in 1947 and 11 years later designed the neutron bomb as a consultant to the Lawrence Livermore National Laboratory. Many technical features of what the Pentagon called an “enhanced radiation weapon” had been known for years, and scientists had theorized about a nuclear device that would release most of its energy as radiation.
All nuclear explosions produce a rain of potentially lethal neutrons, uncharged particles from an atom’s nucleus, and Mr. Cohen, by adjusting components and reshaping the bomb shell, limited the blast and released more energy as neutrons — so tiny they passed easily through solid inanimate objects, but killed all living things in their path.
The military successfully tested the bomb, and over the next two decades Mr. Cohen campaigned for its deployment without success. He left RAND in 1969, but continued writing about the bomb. His articles appeared in The Washington Post, The New York Times, The Wall Street Journal and other publications. He was featured in a 1992 segment of the BBC-TV series “Pandora’s Box.”
His books included “Tactical Nuclear Weapons: An Examination of the Issues” (1978); “The Neutron Bomb: Political, Technological and Military Issues” (1978); “Checkmate on War” (1980); “The Truth About the Neutron Bomb” (1983); “We Can Prevent World War III” (1985); and “Nuclear Weapons, Policies and the Test Ban Issue” (1987). His memoir, “Shame: Confessions of the Father of the Neutron Bomb,” was published on the Internet in 2000.
In recent years, Mr. Cohen prominently warned of a black market substance called red mercury, supposedly capable of compressing fusion materials to detonate a nuclear device as small as a baseball — ideal for terrorists.
Most scientists call the substance mythical, and stories about it, many circulating on the Internet, are widely regarded as spurious.

Samuel T. Cohen died on Sunday at his home in Los Angeles. He was 89.
The cause was complications of stomach cancer, his son Paul said.
Unlike J. Robert Oppenheimer and Edward Teller, the respective fathers of the atomic and hydrogen bombs, Mr. Cohen was not well known outside government and scientific circles, although his work for years influenced the international debate over the deployment and potential uses of nuclear arms.
In contrast to strategic warheads, which can kill millions and level cities, and smaller short-range tactical nuclear arms designed to wipe out battlefield forces, the neutron bomb minimized blast and heat. Instead, it maximized a barrage of infinitesimal neutrons that could zip through tanks, buildings and other structures and kill people, usually by destroying the central nervous system, and all other life forms.
While doubters questioned the usefulness, logic and ethics of killing people and sparing property, Mr. Cohen called his bomb a “sane” and “moral” weapon that could limit death, destruction and radioactive contamination, killing combatants while leaving civilians and towns unscathed. He insisted that many critics misunderstood or purposely misrepresented his ideas for political, economic or mercenary reasons.
A specialist in the radiological effects of nuclear weapons, he relentlessly promoted the neutron bomb for much of his life, writing books and articles, conferring with presidents and cabinet officials, taking his case to Congressional committees, scientific bodies and international forums. He won many converts, but ultimately failed to persuade the United States to integrate the device into its tactical nuclear arsenal.
The Reagan administration developed but never deployed the weapons in the 1980s. France, Israel and the Soviet Union were believed to have added versions of the bomb to their arsenals. Western military planners rejected their use in the Vietnam War and regarded them only as a possible deterrent to superior Soviet tank forces in Europe. But the end of the cold war obviated even that purpose.
A graduate of the University of California, Los Angeles, Mr. Cohen was recruited while in the Army in World War II for the Manhattan Project, which developed the first atomic bomb at Los Alamos, N.M. After the war, he joined the RAND Corporation and in 1958 designed the neutron bomb as a way to strike a cluster of enemy forces while sparing infrastructure and distant civilian populations.
Fired via a missile or an artillery shell and detonated a quarter-mile above ground, his bomb limited death to an area less than a mile across, avoiding wider indiscriminate slaughter and destruction. It was not a radioactively “clean” bomb, but its neutrons dissipated quickly, leaving no long-term contamination that could render entire regions uninhabitable for decades.
But many military planners scoffed at the idea of a nuclear bomb that limited killing and destruction, and insisted that deployment would escalate the arms race and make nuclear war more likely. The device was anathema to military contractors and armed services with vested interests in nuclear arsenals. Even peace activists denounced it as “a capitalist weapon” because it killed people but spared the real estate.
Washington rejected the bomb repeatedly. The Kennedy administration said it might jeopardize a test-ban moratorium. The Johnson administration said its use in Vietnam might raise the specter of Hiroshima — Asians again slaughtered by American nuclear bombs — drawing worldwide condemnation. In 1978, President Jimmy Carter said development might impede disarmament prospects.
In 1981, President Ronald Reagan ordered 700 neutron warheads built to oppose Soviet tank forces in Europe. He called it “the first weapon that’s come along in a long time that could easily and economically alter the balance of power.” But deployment to the North Atlantic alliance was canceled after a storm of antinuclear protests across Europe. President George Bush ordered the stockpile scrapped.
By 1982, Mr. Cohen had abandoned his deployment quest. But he continued for the rest of his life to defend the bomb as practical and humane.
“It’s the most sane and moral weapon ever devised,” he said in September in a telephone interview for this obituary. “It’s the only nuclear weapon in history that makes sense in waging war. When the war is over, the world is still intact.”

Source :

Past interview of Cohen for the Tribune review :
Confessions of the Father of Neutron bomb
By Christopher Ruddy

LOS ANGELES - For most of Sam Cohen's life, he has struggled against politicians who, in his opinion, have sacrificed good sense when it comes to the nation's defenses. Cohen is the physicist who invented the neutron bomb, the one that kills people but leaves things like tanks and buildings intact. Plans to deploy his creations in Europe during the '70s and '80s awakened the "peace movement" across that continent, stopping its deployment.
With that and other battles lost, the 76-year-old Cohen finds solace in his Brentwood home, nestled high on a hill overlooking Los Angeles. There the world is far more peaceful, or so it seems. Just down the road is the Rockingham estate of one O.J. Simpson. Cohen would pass there often during his morning walks, and occasionally see the former football star. "He was always pleasant," Cohen recounted.
Cohen would probably be unfazed if confronted by a knife-wielding mugger - a threat insignificant in the scheme of things. What worries him are weapons of mass destruction - nuclear ones that destroy whole cities.
The politicians tell us that our security has never been better. Cohen describes the present situation as "scary, more scary than ever before." He's concerned that the Clinton administration has decided it is politically incorrect to even think about the design and development of nuclear weapons. The head of the division of the Livermore National Laboratories in charge of such weapon development has threatened to resign if he is ordered to develop new weapons, Cohen noted in a recent interview.
The government doesn't want people to even think about nuclear weapons, which is like telling Sam Cohen he is no longer permitted to breathe.
As a kid from Brooklyn who graduated with a physics degree from UCLA, he enlisted in the Army after Pearl Harbor. In 1944 Cohen was assigned to the top-secret Manhattan Project to develop atomic weapons at Los Alamos, N.M. Cohen had the mundane job of calculating how neutrons behaved in "Fat Man" - the nickname of the bomb dropped on Nagasaki. (The bomb dropped on Hiroshima three days earlier was nicknamed "Little Boy.")
The boring work was all worthwhile because Cohen eventually stood in the Nevada desert and witnessed something on par with the Transfiguration: an atomic explosion. Cohen saw firsthand the awesome power of the unleashed atom as human history entered a new age. "Awesome spectacle" is how Cohen still describes the event. Puffing on a cigar as he relaxed in his easy chair wearing a T-shirt and jogging pants, Sam remembered that day vividly.
World War II flying hero Jimmy Doolittle stood next to him when the bomb went off. "The little guy was blown down," Cohen recalled.
After the war ended, Cohen joined the Rand Corp. where he was paid to continue thinking about nuclear weapons. He was obsessed with the idea of a neutron bomb, one that would make use of the lethal particles he had observed so studiously at Los Alamos.
The earliest bombs had used nuclear fission, splitting heavy atoms to release energy. Later bombs used nuclear fusion, which fused hydrogen atoms to release energy. Both designs produced tremendous blasts that could level whole cities, and left them uninhabitable for long periods because of lingering radiation.
Cohen's neutron bomb would use nuclear fusion, but in a different way. The detonation of a neutron bomb would still produce an explosion, but one much smaller than a standard nuclear weapon's. The main effect of a neutron bomb would be the release of high-energy neutrons that would take lives far beyond the blast area. The result: fewer buildings, cars, tanks, roads, highways and other structures destroyed.
And unlike standard nuclear bombs that leave long-term contamination of the soil and infrastructure, the neutron radiation quickly dissipates after the explosion.
For Cohen, the neutron bomb is the ultimate sane weapon. It kills humans, or as he puts it "the bad guys," but doesn't produce tremendous collateral damage on civilian populations and the infrastructure a civilian population needs to survive.
This meant, in Cohen's mind, that a conventional war could escalate without immediately leading to an all-out nuclear holocaust. If regular nuclear weapons were used across Europe, the radioactive fallout could turn the continent into a wasteland for decades. That wouldn't be the case if neutron bombs were used.
Between 1958 and 1961 the neutron bomb idea was tested successfully, but the politicians in Washington nixed development and deployment of the weapon. Cohen persisted. As the Vietnam War began and festered in the 1960s, Cohen became an advocate of using neutron bombs there. To Cohen, his weapon was "a perfect fit" for dealing with the Viet Cong hidden in the jungles and rice paddies.
Again, the politicians had other ideas. Secretary of Defense Robert McNamara ruled that no nuclear weapons of any type would be used in the war. The use of the small neutron bombs would have brought the war to a quick end, Cohen still argues, and saved the loss of more than 50,000 American lives.
In 1969, Cohen was fired from the Rand Corp. for continuing to advocate the use of tactical neutron bombs to end the conflict. "I lost all my battles," Cohen says today.
In 1979, he was in Paris helping the French build their own arsenal of neutron bombs when presidential candidate Ronald Reagan came through on a European tour. Cohen met with Reagan to brief him on the neutron bomb. Reagan grasped the idea of neutron weaponry immediately, and made a pledge to Cohen, and later a public pledge, that he would reverse Carter administration policy by building and deploying a large number of neutron bombs.
As president, Reagan fulfilled that pledge and approximately a thousand weapons were constructed. But criticism from European allies kept the weapons from being deployed across Europe.
With the fall of the Berlin Wall and the end of communism as we knew it, the Bush administration moved to dismantle all of our tactical nuclear weapons, including the Reagan stockpile of neutron bombs. In Cohen's mind, America was brought back to Square One. Without tactical weapons like the neutron bomb, America would be left with two choices if an enemy was winning a conventional war: surrender, or unleash the holocaust of strategic nuclear weapons.
Other nation's haven't been afflicted by the U.S. blindness regarding neutron bombs. According to Cohen:
Evidence exists that China has neutron bombs stockpiled, and that the United States gave the Chinese the technology to build them.
Russia has a large quantity of such weapons, as well as the world's largest arsenal of nuclear weapons.
Israel has hundreds of neutron weapons. The neutron bombs would allow Israel to stop advancing Arab armies and tank columns - even one on Israeli soil - without permanently contaminating the land.
South Africa, which constructed a cache of neutron weapons before the end of white rule, claimed it dismantled those weapons before handing over power to the Nelson Mandela government. Cohen, however, claims to have it on good authority that white military leaders still control the secret stockpile as "an insurance policy."
Most frightening for Cohen is the relative ease by which neutron bombs can be created with a substance called red mercury. Red mercury is a compound containing mercury that has undergone massive irradiation. When exploded, it creates tremendous heat and pressure - the same type needed to trigger a fusion device such as a mini-neutron bomb.
Before, an obstacle to creating a nuclear bomb was the need for plutonium, which when exploded could create a fusion reaction in hydrogen atoms. But red mercury has changed that. The cheap substance has been produced in Russia, Cohen said, and shipped on the black market throughout the world.
Cohen said that when U.N. inspectors went to Iraq to examine the Iraqis' nuclear weapons capabilities, the U.N. team found documents showing that they had purchased quantities of red mercury. The material means a neutron bomb can be built "the size of baseball" but able to kill everyone within several square blocks.
The public isn't being warned about this development because the politicians have little desire to combat the menace or to confront nations like Iraq, Iran and Libya that likely would use such weapons, Cohen said.
Cohen has little faith in the politicians anyway. "Every president since Truman, with the possible exception of Eisenhower, would have sold the country out if it came down to a nuclear confrontation," he said.
Cohen on nation security issues
In a recent interview, Sam Cohen, the father of the neutron bomb, offered his views on several national security issues:
RUSSIA: Though the Cold War is over and Russia appears in disarray, Cohen suggested that the situation remains dangerous because Russia has "far and away substantially more nuclear weapons than we do." While U.S. policy makers have been busy dismantling our nuclear arsenal, Russia continues to modernize.
The United States has been paying billions of dollars for the leftover plutonium from Russia's dismantled weapons, but evidence indicates that the Russians have not been turning over weapons-grade plutonium. Instead, the United States has been paying for, and not objecting to, material from their nuclear power plants - a strong sign the Russians are not dismantling their weapons.
MISSILE DEFENSES: Calling a ballistic missile defense system "absolutely necessary," Cohen said American space-based plans so far have been a "debacle" that have cost taxpayers more than $50 billion.
Cohen argued that the "Star Wars" plan envisioned by President Ronald Reagan was inherently flawed. Politicians, once again fearing the "n" word, promised that nuclear weapons would not be used in any missile defense system. Cohen contends Reagan received misleading advice that technology was advanced enough to create a non-nuclear missile defense system.
Almost 15 years have passed since Reagan's call for a missile defense system, and still no weapons have been deployed. Cohen said that, had nuclear weapons been used, a fairly inexpensive system could already have been deployed. In such a system, nuclear weapons are exploded high in the atmosphere to either destroy or knock off trajectory incoming missiles. While the radioactive fallout from such explosions would pose some threat to civilian populations, it would be infinitely less harmful than having enemy missiles hit their targets.
Already, Cohen reported, the Russians have a sophisticated nuclear-based missile defense system around Moscow and possibly elsewhere. According to published intelligence reports, in the late 1980s the Russians began developing a "plasma weapon" for missile defenses. The plasma weapon uses nuclear energy to ionize the atmosphere, destroying or rendering inoperable any missiles passing through the plasma field.
SEAPOWER: Cohen said navies have become "obsolete" in terms of global warfare using nuclear weapons, and he described floating ships as "sitting ducks" for nuclear weapons. The U.S. Navy depends on AEGIS missile defense systems to protect its fleets, but Cohen said AEGIS has failed all of its tests, and there is no proof that it could fend off a multi-missile strike against a fleet, let alone a country.
Cohen said the U.S. Navy should put more resources into nuclear-powered submarines because of the difficulty any enemy might have in destroying them in a first strike.
For years, the nuclear submarines were the most important part of our deterrent against surprise nuclear attack, primarily because the submarine captain and crew did not need special codes, known as permissive action links or PALs, to fire their weapons. Thus, if a surprise attack disabled our military communications, the submarine could still counterattack.
In recent years, Cohen said, the Clinton administration has instituted the use of PALs on nuclear missile submarines, limiting their deterrence value.
CHINA: Cohen thinks China will soon be in position to blackmail the United States into reneging on promises to defend Taiwan. Already China has made overt threats about hitting the U.S. mainland with nuclear weapons. "China has said, `OK, if you defend Taiwan, we'll drop a nuclear weapon on Los Angeles,'" Cohen said.
In a trip to Taiwan, Cohen spoke before the military leadership there and strongly advised them to begin their own nuclear weapons program. The United States will not defend you because the politicians don't care about you, he told them.

Source : 



Summer 1958
While conducting researching on developing a large thermonuclear weapon, Sam Cohen introduces the idea of removing the uranium casing from a hydrogen bomb to allow neutrons to travel great distances and penetrate even heavily shielded armor and structures.

The Kennedy administration decides against the idea of developing a neutron bomb and introducing it into the US nuclear arsenal because it may jeopardize the moratorium on nuclear testing being observed by the US and Soviet Union.

The Soviet Union breaks the moratorium on nuclear testing allowing the US to proceed with developing the neutron bomb.

The first neutron device is successfully tested.

The Carter administration proposes modernizing the US nuclear arsenal by installing neutron warheads on the Lance missiles and artillery shells planned for deployment in Europe.

West Germans realize their country will likely be the battleground for use of the neutron bomb and begin hotly debating whether or not the weapon should be allowed on their soil.

Succumbing to international and domestic pressure, President Carter decides to defer deployment of the neutron bomb, conditional to Soviet restraint in military production and force deployments.

France announces that it has tested a neutron device.

President Reagan re-authorizes the production of neutron warheads for the Lance missile and an 8-inch artillery shell, but because of strong opposition in Europe, he orders that all neutron weapons be stored in the US with the option to deploy overseas in the event of war. The USSR announces that it too has tested neutron weapons, but has no plans of deploying them.

France begins production of the neutron warhead.

France announces it will abandon the production of neutron warheads because of internal and external political pressure.




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