What is radiation therapy?
Radiation therapy is a form of cancer treatment that uses radiation (strong beams of energy) to kill cancer cells or keep them from growing and dividing. Radiation therapy is often used with chemotherapy and surgery to treat cancer.
Radiation therapy is individualized to your individual diagnosis and needs. Your radiation oncologist will work in partnership with your medical team to determine the best treatment plan for you.
What type of radiation therapies are offered at the QMG Cancer Institute?
3-Dimensional radiotherapy is the working platform for the vast majority of modern-day radiation treatments. The fundamental principle of “3-D” radiotherapy is to customize the radiation treatment machine (a “linear accelerator”) to the specific anatomy of any individual. This is accomplished by performing a specialized “CT” scan or Computer Tomography Scan.
A CT scan is a specialized radiation machine capable of capturing detailed images of the body. The CT table which you will you lay on exactly matches the treatment table of the linear accelerator. During this study, the Radiation Therapists will position you on the CT Table in the “treatment position”. This position exactly matches the position you will be placed in on the actual treatment table of the linear accelerator.
The therapists will fabricate a number of molding devices which will help you relax and maintain this positioning in a comfortable and reproducible manner. These molding devices are specific for each individual patient and are “indexed” into the CT table to allow for accurate positioning. The CT machine has a set of lasers which crisscross the your body at a specific point in space. The therapists will place special “markers’ on the your body highlighting the location of the laser “crosshairs” on the your skin. You and the table are then moved through the CT, enabling the imaging component of the CT to “scan” or capture hundreds of images of your body. Using this data, the computer then re-constructs your anatomy 3 dimensionally – in the “treatment” position – to produce a “virtual patient”. On the same computer, the physicist maintains all of the X-ray data for the linear accelerator treatment machine. The physicist will undertake a number of calculations to “conform” the opening of the linear accelerator to “fit” the 3-dimensional shape of your tumor. These calculations will allow the Radiation Oncologist to assess the amount of radiation delivered to the tumor as opposed to the surrounding normal organs. The Physicist and Radiation Oncologist will calibrate the treatment machine to ensure delivery of a maximum amount of radiation to the cancerous tumor while minimizing the amount received by the surrounding normal organs. This process allows the Radiation Oncologist to assess different treatment plans virtually (and 3 dimensionally!) on the computer screen prior to exposing you to radiation.
On any given treatment day, the Radiation Therapists will replicate the virtual plan on the treatment machine. Utilizing the previously fabricated molding devices and skin marks of the CT laser crosshairs, they will align you on the treatment table to within 1-2 mm of their CT position. They will then “upload” the conformal shaping information and radiation dose parameters of the virtual plan to the treatment machine. Once activated, the machine will rotate around you, delivering radiation in a precise and accurate manner so as to maximize exposure to the tumor while minimizing radiation dose to healthy tissue. A typical treatment will last 12-15 minutes.
Intensity Modulated Radiation, better known as “IMRT”, is an evolutionary off-shoot of 3-D radiation. IMRT is a radiation dose delivery technique which effectively sub divides each radiation beam into small “beamlets”. This allows the Radiation Oncologist to “intensely modulate” the shape of the radiation beam as the treatment machine rotates around the patient. The result is a highly conformal delivery of radiation to the tumor while avoiding critical structures, such as the spinal cord. In some instances, such tight conformality of the radiation dose has been shown to minimize the risk of long-term injury of normal tissue. This has been very helpful in the treatment of certain cancers such as esophageal, pancreatic, and prostate cancers.
Stereotactic Body Radiotherapy is a form of radiation treatment which aims to delivery a high dose of radiation on a daily basis, thereby shortening the overall course of your treatment. SBRT can be undertaken utilizing the beam conformality and dose delivery techniques of either 3D or IMRT. The main difference with SBRT is the amount of radiation delivered on any given treatment day. In many ways, the biology of radiation is similar to that of medication. Rather than taking a whole bottle of medication, patients take one pill a day over a certain period of time. Similarly, standard radiation treatment consists of small dose of radiation given each day over, on average, a 5-6 week period. With SBRT, the defining characteristic is the high dose of radiation you will receive on a daily basis. These doses can be 6 times greater than standard radiation doses. The benefit of SBRT is the shorter overall treatment course – 4-5 days as opposed to 5-6 weeks. Some cautionary footnotes of SBRT are:
- Daily Treatment Time are often 30 – 40 minutes as opposed to 12-15 minutes
- Short-term side effects are more common and often require some form of medication to effectively manage.
- Long-term side effects are more problematic – high doses of radiation are more likely to scar normal tissue resulting in a small but real risk of symptomatic organ damage.
Image Guided Radiotherapy, or IGRT, is a radiation technique designed to accommodate the motion of an individual’s internal organs. Every organ of the body exhibits some degree of motion regardless of how motionless a person tries to be. While radiation therapy using 3 Dimension techniques have proven a major advance in accurately defining the location of a tumor, studies have shown small variations in the day-to-day position of a tumor due to the inherent functions of an organ ( example – the effects of bladder filling on the prostate or breathing on the position of the breast). Even the brain, completely surrounded by the boney structures of the skull, will exhibit internal motion due to breathing and heart rate. To accommodate such internal organ motion, Radiation Oncologist will often request the Surgeon or Radiologist to place a small metal marker (termed “fiducial” marker) in or close to the tumor. The fiducial marker will be visualized during the CT scan and is then incorporated into the calibration of the treatment machine. The position of the marker is correlated with the position of the tumor and both tumor and marker are then reconciled to the center of the treatment machine. Thus, on any given day, the therapists can take a quick picture of the patient, localized the metal marker, and adjust the treatment table so the tumor is back in the crosshairs of the machine. In essence, the fiducial marker serves as a surrogate “target”, enabling “image guidance” of the machine to compensate for the day-to-day variation in the tumor’s location.
What radiation therapy technology is used at the QMG Cancer Institute and what are its benefits?
At the QMG Cancer Institute, our goal is to provide you with the best possible treatment while keeping you comfortable. We utilized Varian VitalBeam Linear Accelerator, also known as a “linac”, to deliver your radiation therapy. Our linac is a versatile radiation therapy machine that can treat cancers throughout the body using advanced methods such as image guidance, radiosurgery, intensity-modulated radiotherapy, stereotactic body radiotherapy, and RapidArc beam delivery.
By combining respiratory gating, real-time tracking, imaging, and high-dose rate treatment delivery, the Varian VitalBeam linear accelerator treats tumors with advanced speed and accuracy.
What should you expect during your treatment?
Every patient is unique. Radiation treatment is individualized depending on many factors including your overall health, the size and location of your cancer, and your prior treatment. Radiation treatment is tailored to meet your specific needs.