The Princess Margaret - Radiation Therapy Centre
Intensity-modulated radiation therapy (IMRT) is an advanced mode of precision radiotherapy that allows for the radiation dose to conform more precisely to the shape of the tumor. It can modulate the strength and the intensity of the radiation beam in multiple small volumes. The treatment planning is usually performed by using tomography (CT scan) of the patient in conjunction with computerized dose calculations to determine the dose intensity pattern that will best conform to the prostate gland. When IMRT is combined with a radiation treatment planning system called "inverse planning", it provides radiation oncologists with a tool of unique accuracy for delivering high doses of radiation to the prostate while minimizing the dose to adjacent normal structures thus causing fewer side effects.
VMAT is a variation of the IMRT technique that is also available at PMH. It is an advanced radiation therapy solution that increases the number of beamlets by continuously rotating the treatment unit while modulating the radiation beam. It potentially improves treatment conformality as compared to the standard IMRT and reduces daily treatment times.
Image-guided radiation therapy (IGRT) is the frequent use of imaging techniques during a course of radiation therapy in order to improve the precision and accuracy of the treatment. The prostate gland and adjacent organs can move between different treatment fractions due to differences in organ filling or other factors. The machines that deliver radiation, called linear accelerators, are equipped with imaging technologies (e.g. cone-beam CT, ultrasound or stereoscopic X-rays) so that the exact position of the target can be monitored immediately before or even during the time radiation is delivered. Using specialized computer software, these images are then compared to the images taken during simulation (CT simulation). Any necessary adjustments are then made to the patient's position and/or radiation beams in order to accurately deliver the prescribed dose of radiation. All patients treated at Princess Margaret Hospital will have a cone-beam CT done before each treatment.
In order to help localize the prostate during IGRT, some patient may also have three small gold seeds implanted in the prostate, called fiducial markers. This is performed under the guidance of a trans-rectal ultrasound, in a procedure similar to the biopsy performed for diagnosis.