by Helen A. Shih, M.D. & Jay S. Loeffler, M.D.
NEPTCC Newsletter MGH Neuroendocrine Center Bulletin Vol 12, Issue 1, Fall/Winter 2006
Preface: If radiation therapy has been recommended to you for treatment of a pituitary adenoma, you have probably already considered and/or tried other types of medical therapies or surgery with inadequate results. Remember, a tumor is a tissue mass, typically not normally present in the body. It can be either benign or cancerous. Pituitary adenomas are a type of benign tumor with many subtypes. Radiation therapy can be a very effective treatment for both hormonally active (such as Cushing’s disease or acromegaly) and inactive (“non-functioning”) pituitary adenomas. The decision to use radiation therapy should be balanced with an understanding of its associated risks. Treatment recommendations are tailored by specific type of pituitary tumor, size, boundaries of the tumor if large, response to initial therapies, and other patient health concerns. Compiled here are common questions raised by patients with pituitary adenomas regarding radiation therapy.
1. What is radiation therapy? Radiation therapy is the use of ionizing radiation to treat and control benign or cancerous tumors. Ionizing radiation is a form of high energy that can be directed as beams to treat targets. It can effectively reduce or stop excessive tumor growth or activity. The most common form of radiation therapy used is called photon beam. Photon beams can be either generated from machines and are called X-rays or from naturally radioactive substances and are called gamma rays. The photon beams applied in radiation therapy are most often X-rays and are similar to those used for chest X-rays but are of higher energy.
2. How does radiation work? Ionizing radiation causes injury to the most actively growing cells. Abnormally growing cells will frequently die over a period of days to months following radiation treatment. Truly normal cells can frequently repair radiation injury.
3. What type of radiation therapy is best for me? I’ve heard of terms such as intensity modulated radiation therapy (IMRT), 3D conformal radiation therapy, stereotactic radiosurgery (SRS), and stereotactic radiotherapy (SRT).
This is a complex question and requires the training and expertise of your doctor to select the treatment delivery system that is best suited for you. All of these terms refer to radiation treatment techniques. They all use photon radiation. Frequently, there is more than one good choice.
4. How do I get treatment? What are the practical things that I need to know for my schedule?
Radiation therapy comes in many forms but all types of radiation therapy involve a planning process referred to as the “simulation”. The first part of the simulation is to establish a reproducible set up position that you will assume for each treatment. A mask or frame for your head will be custom made such that you will be able to get into the same position with great accuracy for each radiation treatment. The simulation session usually takes about one hour to complete and most commonly involves a CT scan or X-ray pictures of your head in the treatment position. These pictures are used to design the appropriate radiation beams for your treatment.
Daily treatments are usually about 10-15 minutes within the treatment room with most of that time allotted to setting you up accurately. Treatments are delivered by radiation therapists, highly skilled technologists who currently go through four years of training to obtain their radiation therapist license. The radiation beams are usually on for 1-2 minutes per day once the patient is inthe correct position. Treatments are usually given daily, Monday through Friday, for five treatments per week. The total number of treatments most commonly ranges between 25-30 treatments, meaning a total of 5-6 weeks. Most centers have some amount of waiting time preceding treatment so it is best to be flexible and expect up to an hour’s time with each daily visit until you are familiar with your treatment center’s pattern
5. Does this treatment hurt? Will I be sick? What does it feel like? This treatment does not hurt. In fact, most people do not feel anything and cannot detect when the radiation beam is on. Others can either smell a scent described as ozone or see colors while the radiation beam is on. There are no detectable side effects immediately after treatment. It is not known to make people feel sick.
6. What are my daily restrictions if any?
There are typically no restrictions to your activity or diet.
7. What are the common side effects while on radiation therapy? While on treatment, you may notice a little fatigue that slowly appears over the weeks of treatment. Sometimes patches of hair loss and skin redness and dryness are experienced. These occur in the radiation beam paths. Much less common are headaches or nausea. Even less common are neurological symptoms like seizures.
8. What are the risks of me going blind from radiation? Risks are individualized so you should ask your radiation oncologist. However, for most people, this risk is very low because it is taken into careful consideration during the planning of your radiation treatment. It is one of the main reasons why the protracted 5-6 week course of radiation is preferred over the single dose of stereotactic radiosurgery. The nerves involved with vision are able to absorb a fair amount of radiation without risk of injury to their function.
9. Am I or my body fluids radioactive? For practical purposes, you are not radioactive while you are receiving your radiation treatment. However, for a few minutes immediately after each treatment, there does remain extremely low residual radioactivity in the tissues that have directly received radiation. This is not dangerous to others and no activity restrictions are needed.
10. Can I take medications while receiving radiation therapy? Yes, generally there are no changes to medications while on radiation therapy.
11. Can I work during my treatments? If not, when can I return to work? This is up to you and your doctor. Some people prefer to relax and may consider returning to work after a few weeks from completion of radiation treatment. Others choose to work while under treatment and
are able to do so without difficulty.
12. How fast will the treatment be effective? How do I know if the radiation has worked? Treatment response varies. Some patients feel that they begin to have a response even while on radiation treatment, but most experience gradual responses ranging over many months between 2-3 years from the completion of radiation treatment. However, responses do continue to evolve for many years beyond that. Depending upon the nature of your pituitary adenoma, response is measured by imaging the head (MRI or CT), blood or urine tests, and how you feel.
13. What is stereotactic radiosurgery? How does it differ from other radiation used for pituitary adenomas? Stereotactic radiosurgery (SRS) is a type of radiation therapy that delivers high dose radiation in a single treatment. The most commonly used form of SRS for pituitary tumors is known as “gamma-knife”. At Massachusetts General Hospital, SRS is given as either “proton beam” or “photon beam” radiation. SRS is a convenient treatment because it takes only one day and is frequently associated with a quicker response than the protracted alternative of daily radiation treatments over several weeks. However, SRS can also be associated with increased risk of side effects, such as injury to the nerves which transmit vision. Risk of injuries varies depending upon the nature of your tumor. Details of the size, shape, and location of your pituitary adenoma determine which form of radiation delivery is best suited for you. If SRS has been recommended, then the risk of serious injury is felt to be very low.
Because a high radiation dose will be given at one setting, the highest precision is very important with SRS. A special head frame is used to keep your head still during treatment. Most people tolerate this treatment very well.
14. What is the chance of the tumor reappearing after radiation treatment? There is roughly a 95% chance of controlling your tumor’s growth and 60-80% chance of controlling activity of hormonally active tumors although this does vary depending on the details of your tumor. If the tumor is controlled, it is unlikely for it to recur.
15. What are the long-term side effects of radiation treatment? Radiation can decrease levels of one or more hormones produced by the pituitary gland. The risk of hormone deficiencies is very low immediately following radiation, but gradually increases over the years. Some patients develop hormone deficiencies a year or two after radiation, while others may have normal levels for 10 or 20 years and then develop low hormone levels. These deficiencies are treatable with replacement hormones. Because of this, it is important that you continue under close care with your endocrinologist. It is uncommon to develop injury to the brain or vision and even more rare to develop a radiation-induced tumor. All of these unlikely but serious events typically require years to occur.
At MGH, proton radiation is also available and offers unique advantages to photon radiation in some conditions. Some common inquires about this resource are addressed below:
16. What is proton radiation therapy? How is it different from photon radiation? Protons, like photons, are another form of high energy ionizing radiation. Unlike photons, protons are particles with significant mass and a positive charge. These properties of protons make proton beams easier to shape than photon beams during treatment. All radiation beams give off energy as they travel through tissue. Proton beams travel a finite short length. Proton beams are designed to stop in the target so that there is no additional radiation deposited downstream, on the other side of the target. In comparison, photon beams are radiation beams that go on and on like a beam of light and will deposit energy to the tissues beyond the target. This is a lower dose than the dose delivered to the target but sometimes even this low dose can be harmful.
17. Why is proton radiation more appropriate for me? When considering options within radiation, protons are often better suited for large pituitary tumors that extend beyond the sella, the bony cup that holds the normal pituitary gland. Larger tumors generally require a wider and larger radiation beam. Proton treatment in this situation will deliver significantly less radiation to the surrounding normal tissues. Small tumors that overproduce hormones (such as in Cushing’s or acromegaly) can also be ideal for proton beam treatment. There are some data to suggest that control of hormone overproduction may be faster with stereotactic radiosurgery than with conventional radiation.
18. Will there be any side effects to proton radiation? Side effects of radiation associated with photon radiation can also be seen with proton radiation. The risk of most of these side effects is reduced but still include injury to the neighboring brain or other tissues. Sometimes the risk of hair loss and skin irritation is higher with proton radiation.
19. How often will I see my Radiation
Oncologist after the treatment has been given? Initially, visits are annually, then just as needed. It is very important that head scans (MRI or CTs) be performed regularly. It is essential to see your endocrinologist every 6-12 months to monitor pituitary hormones.