What is it?
Radiation is a form of photon energy, much like light, and the high energy radiation used to treat pituitary tumors and other cancers is generated from a linear accelerator (LINAC). The radiation beam deposits energy in the tissue through which it passes, causing chemical and biologic damage. In the treatment of pituitary tumors, this energy is focused in the region of the tumor, using multiple radiation beams, akin to directing many spotlights onto one spot. Radiation causes DNA damage. The surrounding normal brain tissue has a greater capacity to repair this damage as compared to cancerous cells or the cells in growing benign tumors.
The word “fractionated” means that the treatment is delivered over the course of many days. Each treatment of radiation is called a “dose fraction.” Though radiation can be delivered in one dose, with a specialized procedure called stereotactic radiosurgery, many pituitary tumors are treated with fractionated radiation. One of the reasons to deliver the radiation over many fractions is because over the course of several weeks, the cells within the tumor cycle through different phases of their growth cycle; also the tumor itself changes with respect to its blood flow. These changes allow the radiation to be more effective against the tumor. Another reason is that the normal tissues are more capable of repairing radiation damage if the dose is delivered in smaller daily treatments.
What is its goal?
Radiation damages cellular DNA and to some extent the lipid membrane of the cells. Normal tissues are more apt to repair this damage, while cancerous cells are more susceptible to radiation damage. The goal of fractionated radiation is to kill the cancer cells, while minimizing the risk of damage to the surrounding tissues.
How is it done?
Prior to radiation treatments, the patient undergoes what is called a simulation. The purpose of the simulation is to map the coordinates of where the radiation is to be delivered. At the time of simulation, a plastic mask is custom made for the patient while the patient lies comfortably on a CT scan table. The mask serves to keep the patient as still as possible. The mask is intentionally tightly fitting so as to minimize any movement. Patients can breathe through the mask very easily. With the mask in place, a CT scan is obtained. A radiation therapist (RTT) is a licensed professional who carries out the simulation under the direction of the physician. While the patient is undergoing CT imaging, the doctor maps out where the radiation is to go.
After the CT scan, the physician, along with a licensed radiation dosimetrist, devise a radiation plan specifically catered to the patient. The doctor and dosimetrist use the CT scan from the simulation as well as previous MRI and CT scans to define the radiation target as well as critical areas in the brain and head to avoid with radiation. With the assistance of a computer planning system, the radiation treatment is designed.
The radiation treatments are delivered after the plan has been finalized. Licensed radiation therapists (RTT) run the LINAC machine under the supervision of the physician. Radiation is given once (and occasionally twice) a day, Monday through Friday. The weekends are important for recovery of the normal tissues.
While radiation can be given if a patient is hospitalized, it is mostly an outpatient treatment. If a patient does not have access to reliable transportation to the Cancer Center on a daily basis, the Wilmot Cancer Center social workers may be able to assist in this matter.
During radiation therapy, the doctor and nurse see the patient at least once a week, and more frequently if necessary.
What is the success rate?
The success at controlling the tumor depends on many factors, including what type of tumor is being treated, where the tumor is located and what other treatments, such as surgery or chemotherapy, are given. Your doctor can discuss this in much more detail with you since every patient’s case is unique. Despite being able to tell a patient the odds of success, no physician can tell a patient with certainty whether or not radiation will be successful for that patient.
What are the risks?
Most patients tolerate radiation quite well. Hair loss on the scalp is quite common, but is generally only temporary. Occasionally patients experience mild headache, nausea, scalp irritation or earache. While radiation can impact vision, strength and sensation, every attempt is made to minimize these risks. The risk of symptomatic necrosis- a form of tissue breakdown from radiation exposure – is low. The risk of radiation causing a cancer years or decades later is also low.
Since the tumors treated are typically near or in the pituitary gland, there is also the risk that over time the pituitary gland may stop functioning properly. This risk is difficult to predict because it really depends on the location of the tumor treated. However, since the consequences of this effect can be prevented with hormonal replacement, patients with radiation near the pituitary gland should be followed closely with hormonal testing every one to 2 years. The risk of developing pituitary failure continues to increase over time, so patients receiving this treatment should be followed in a Multidisciplinary Neuroendocrine clinic for the rest of their life.
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