Therapy—Radiation Oncology

In December 1940 (age 12 months), I had a birthmark on the back of my neck that was "removed" using some kind of heavy, surface (I'd hope) radiation. What kind of radiation might have been used for this purpose? What kind of device? How deeply might it have penetrated? What dose might have been used at that time? Was this experimental, unusual, new, or customary treatment to remove a birthmark? What risks might follow? The treatment left a one-inch oval burn scar, odd stippled markings, and a skin depression that's still there, though faded.

The treatment you described probably involved the use of ²²⁶Ra (radium-226) for a hemangioma (Lundell et al. 1990). Treatments may have involved the use of superficial x rays, but I would assume that it involved the use of ²²⁶Ra. It was a common treatment and, in the paper cited, 14,647 children were treated from 1909 to 1959. Without knowing the exact treatment, estimates can be made for a typical dose of 8 Gy using radium needles. Mean doses to specific organs include 0.03 Gy to the brain, 0.04 Gy to the eye lens, parotid gland, and gonads, 0.06 Gy to the thyroid, and 0.08 Gy to the breast anlage. While these doses are high, the values are lower than those seen in other populations of children irradiated for tinea capitis and thymus enlargement, where the main detriment was the development of thyroid cancer. I do not know of any studies in which radiation resulted in any autoimmune or allergy responses.

Reference
Lundell M, Fürst CJ, Hedlund B, Holm L-E. Radium treatment for hemangioma in early childhood: Reconstruction and dosimetry of treatments, 1920—1959. Acta Oncologica 29; 5, 551—556; 1990.

Can you tell me about ⁶⁰Co (cobalt-60) and its use in cancer treatment?

⁶⁰Co is a gamma-emitting radionuclide with a physical half-life of 5.27 years. When it decays to stable nickel, it emits two relatively high-energy gamma rays at 1.17 and 1.33 MeV, respectively. These properties make ⁶⁰Co an excellent gamma source for external-beam radiation therapy of cancer. The ⁶⁰Co gamma source is shielded when it is not in use. For patient cancer treatment, the ⁶⁰Co source is moved to a position where, through an open port in the shielded unit, it can irradiate the tumor at a distance of about 95 cm. The ⁶⁰Co source is rotated on an axis around the tumor to maximize the tumor dose and minimize the skin-entry dose. The gamma rays are collimated to reduce radiation scatter to unwanted places. A shielded counterbalance absorbs radiation that passes through the patient. The counterweight is fitted with a transit dose ionization chamber to measure the attenuation of gamma rays by the patient. ⁶⁰Co radiation therapy units in hospitals have been largely replaced by more-modern electron beam radiation therapy systems, but are still widely used in less-developed countries. Since the ⁶⁰Co sources must be replaced about every six or seven years, the safeguarding of surplus expended sources is an important practice in radiation protection to prevent inadvertent radiation exposures to members of the public.

Many years ago removable lead shields were adapted over the teeth in an attempt to protect them from radiation during oral cancer therapy. Presently, is that procedure still used in modern treatment?

The lead shield mentioned was used many years ago when the treatment energy was very low-orthovoltage energies of 150 kVp or so. With that energy the lead furnished a partial shielding effect and protected the mucosal tissues from excessive doses. Given the 6 MV energies typically used today for head and neck cancer treatment, the lead would act as a buildup material and would enhance the dose to the mucosal tissues. What is used on occasion today is a fluoride stent, which bathes the teeth in the fluoride ion and protects them partially from cavity formation due to the lack of saliva, a radiation consequence. Also used on occasion are spacer devices, which separate the lower and upper jaw so the radiation field can more easily spare one or the other depending on the tumor location. If the tumor is superficial and low-energy orthovoltage x rays are the treatment energies of choice, then the use of a wax-coated stint may still be used with some benefit to the patient. However, few facilities have the orthovoltage capability anymore.

Please explain Stereotactic Radiation.

The following website addresses should be of help:

• The University of Florida Radiosurgery Website. It has both a reference list and some practical day-to-day patient information.
• The website for the Elekta Corporation, the developers of the GammaKnife. No radiosurgery reading would be complete without some GammaKnife reading.
• The Harvard/MGH website is also a good resource.

And also a book titled Linac Radiosurgery: A Practical Guide, authors W.A. Friedman, J.M. Buatti, F.J. Bova, and W.M. Mendenhall.

What photon energies are produced by linear accelerators used in radiation therapy?

Linear accelerators commonly used in radiation therapy are grouped into three broad energy ranges. "Low" energy accelerators produce a beam in the 4-6 MV range. Some "high"-energy machines can deliver a beam up to 25 MV, but most are about 18 MV. "Medium"-energy machines are in the 10 MV range. Some machines offer dual energies to cover a wider range of tissue depths. Please note that these comments are limited to "off the shelf" accelerators produced by the major manufacturers. There may be other highly specialized accelerators operated in other energy ranges for experimental therapies.

What methods are used to prevent scattering when radiotherapy is being done? I mean how do they make sure that only the tumors are being bombarded?

Conventional radiation therapy involves aiming a source of radiation toward the diseased portion of the patient's body. In order to be sure that the diseased part of the body is treated, the radiation beam is collimated by the use of collimators, blocks, and wedges. However, some healthy tissues will be irradiated because the tumor is almost always surrounded by normal tissue. The objective in radiation therapy is to deliver as much radiation to the tumor (the higher the dose, the higher the probability of cure) while minimizing damage to surrounding health tissues.

There are other techniques used in radiation therapy called interstitial radiotherapy and intercavitary radiotherapy. In these procedures, radioactive material is inserted directly into the diseased tissue or cavity. This can be very effective in delivering a high radiation dose to the tumor while sparing surrounding healthy tissue.

My best friend told me she has cancer. A few days after I found out, she said she started treatment (radiation). However, she doesn't seem sick and don't you get "marked" when you get radiation? What side effects will she have?

The effects of radiation treatment for cancers depends quite a bit on the types of radiation treatment delivered. It may be in the form of:

1. External beam irradiation (the person is placed in a radiation beam for less than a few minutes several times over a multiweek period),
2. Injected or ingested radionuclides (radionuclides are put into the body, where they distribute in desirable ways to affect the cancer), or
3. Implanted radionuclides (this is called "brachytherapy" and involves the temporary insertion of small containers or "seeds" of radionuclides into body cavities or in thin tubes; these are removed from the patient before release from the hospital).

External beam irradiation is very common for a wide variety of cancers and may be used when any particular cancer has spread. It is often accompanied with chemotherapy, which carries additional side effects. The most common therapeutic use of injected radionuclides is for therapy of thyroid disorders. Implanted radionuclides are used for uterine, prostrate, or (less commonly) breast cancer, but other situations are possible.

While undergoing external beam radiation treatments, patients may be visibly marked to assist with their appropriate alignment in the radiation field. With all types of radiation, patients may experience hair loss, but hair usually grows back. Note that hair loss is not a symptom for lower exposures to radiation and may be caused by something other than radiation (e.g., chemotherapy). Some radiation therapies may result in nausea and vomiting in patients, overall not feeling well, serious fatigue, and other effects. The visible signs of radiation therapy, however, may be very dependent upon the individual patient.

What are the effects of artificial radiation on humans? Are there any alternatives for curing a disease without the use of x rays?

The use of therapeutic radiation is now limited to treatment of malignant disease (cancer) with very few exceptions. It is one of three classical modalities of cancer treatment, along with surgery and chemotherapy. Several new and experimental modalities are now being added to this arsenal, including such things as stimulation of the immune system, stem cell transplants, etc. The selection of the modality of treatment for a given patient is based on giving that patient the best chance of cure of the cancer. Frequently several modalities are used in combination. There are risks to therapeutic radiation, just as there are with other modalities of cancer treatment-or with any medical treatment. Patients occasionally die from surgery. Chemotherapeutic drugs are very toxic and can damage healthy tissue. Every patient who gets therapeutic radiation has some damage to healthy tissue. That damage usually appears as nonspecific inflammation. Great care is taken to hold the level of that damage to what the healthy tissue can tolerate and recover. There is also concern that the radiation may induce a second cancer in the patient. However, if that happens it will be years to decades before the second cancer appears. Patients are willing to trade cure of a current cancer for the chance of getting another at a later date.

Recently, my dad received radioactive seed implants for prostate cancer treatment. Afterwards, the doctor advised him to stay six feet away from others for four hours, then three feet away from others for two weeks. After two weeks there is no distance requirement. The radioactive seeds are permanent. The radiation is supposed to last for a year. Is this amount of radiation dangerous? And if so, what can my dad do to lessen the danger?

One method of treating prostate cancer uses the placing of small sealed radioactive sources, called "seeds," within the prostate tissue during a surgical procedure. These seeds are approximately ½ the length of a straight pin, with approximately the same width as the pin. Most of these procedures can be done using same-day surgery. There are two radionuclides in common use: ¹⁰³Pd (palladium-103) with a half-life of 21 days and ¹²⁵I (iodine-125) with a half-life of 60 days. The half-life is the amount of time required for one-half of the initial amount implanted to decay. Since you mention one year in your question, I will assume that the radionuclide used was ¹²⁵I. Both of the radionuclides in common use emit low-energy radiations. For ¹²⁵I, a substantial portion of the radiation is attenuated within the patient's body. For most normal-sized patients, there would be no measurable exposure rate at 1 meter (approx. 3.3 ft.) from the surface of the patient's body. If someone is in intimate or direct contact with the patient, they would be exposed to a small amount of radiation. As an example, it may be recommended that the implanted patient not hold children on his lap for an extended period of time.

Most often, the instructions given to a patient are tailored to his individual situation. It is the goal of these instructions to limit the doses to persons in the vicinity of the patient to levels allowed for the general public. However, for a general view of typical instructions, you can visit the Chicago Prostate Cancer Center Website. Literally thousands of men have been treated with seed implants. You should also be able to speak with the facility where your father was treated to clear up any questions that may persist.

My husband was treated for prostate cancer four years ago with a radioactive seed implant. Could this radiation cause a tremor of his hand now?

There are three possible biologic effects from the seed implants:

1. Scarring in the vicinity of the seeds. This is an unavoidable result of the acute inflammatory response occurring immediately after seed placement. However, it causes no (or only minor) clinically significant problems in virtually all patients.
2. A second cancer. This is a very rare possibility and would require several decades to develop.
3. Genetic effects, even rarer, in subsequent generations. If the patient has no more children, this effect cannot occur.

Your husband's hand tremor is almost certainly not caused by the seed implants.

I would like to know what happens to the destroyed parts of the tumor or cancer that was treated by radiation in the body.

Cancer cells (or any cells) that are killed by radiation break apart and are destroyed by a process known as phagocytosis. Large cells called macrophages (which are part of our immune system) literally engulf fragments of these dead cells and digest them. This is the same process by which the body eliminates any dead cells, whether killed by radiation, infection, injury, or whatever.

I've had treatments for prostate cancer. I asked what the frequency was and was told "S-band microwave 3000 MHz klystron rating 300 pulses/sec." I thought I was getting an x ray. Am I missing something here?

Indeed, the radiation that is being employed to treat your cancer (and which is used in most radiotherapy treatments) is in the form of x rays. X rays are made in linear accelerators (usually inside the gantry or treatment head that is aimed at the treatment area) by taking very energetic electrons (accelerated through an equivalent voltage of 6 to 20 million volts) and having them hit an irradiator (often tungsten is used). In the course of interacting with the nuclei and atoms in the tungsten irradiator, the electrons slow down and stop and along the way they emit lots of very high-energy photons known as x rays. These x rays can penetrate deep into tissue and disrupt the tumor cells' growth. So, now we need high energy-electrons. How do we get them? They have to be accelerated by passing them through segmented tubes (called acceleration cavities) that have very large voltage that pass through them. These large voltages are provided by microwaves and those microwaves are generated by devices called klystrons. (3000 MHz is the frequency of the microwaves.) Klystrons come in many varieties and operate over a range of frequencies and, coupled with these segmented acceleration cavities, can deliver "bunches" of fast electrons at specified rates (like 300 pulses/sec).

 

Ask the Experts is posting information using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.