Radiation Therapy Overview
Radiation can be delivered from a machine outside the body (external radiation therapy) or from inserting internal radiation therapy seeds (brachytherapy) or a combination of both. Current types of radiation include IMRT (Intensity-Modulated Radiation Therapy), Proton Beam, and Robotic Radiosurgery Systems such as the Cyberknife and Novalis. The treatments have important differences including side effects and results.
IMRT (Intensity modulated radiation therapy) is external radiotherapy using Photons from a linear accelerator directed at the prostate and surrounding tissues through multiple beams aimed at the prostate and not the surrounding tissues. Increasing the dose of radiation improves cure but had been limited in the past with conventional external beam radiation therapy (delivered by a single beam) by the toxicity of treatment to surrounding tissue. Our new MRI-based treatment planning allows precision contouring of the radiation beam to shape the dose just to the prostate and not to the surrounding tissues like bladder and rectum. The latest generation three dimensional reconstruction software not only contours the beam to the shape of the prostate, but also modifies the number, orientation and intensity of the beam. IGRT (image guided radiation therapy) precisely aims each beam with CT scan just milliseconds before the radiation dose is delivered with each daily treatment. This is a very important distinction from beams that cannot be aimed (e.g. older conventional external radiation machines), which must increase the size of the radiation target and lower the dose to compensate for normal variation in the position of the prostate on a daily basis. The treatments are given over 9 weeks with daily “fractions” of the total planned dose.
Radioactive Seed implantation (Brachytherapy)
Radioactive seeds act as a source of radiation directly placed into the prostate. Brachytherapy delivers a high dose of radiation with minimal impact on surrounding healthy tissues. Two types of radioactive source seeds are used in our practice: Iodine and Palladium. Both deliver the radiation at a low dose rate. Brachytherapy is an outpatient procedure that takes less than 45 minutes under anesthesia. The radioactive seeds are implanted through the perineum (area below scrotum and above anus) with ultrasound guidance. Each seed is precisely using the “real-time” seed implant technique in locations determined by a computer programmed to maximize the prostate dose but minimize the radiation to the rectum, bladder and urethra. Our center specializes in the ‘real time’ technique which allows customization of the radiation dose to maximize cancer control and minimize side effects. The procedure to insert the seeds is often not as invasive as the original biopsy.
BRACHYTHERAPY AS MONOTHERAPY
When seeds are given as monotherapy (i.e. no additional radiation), the type of radiation isotope is Iodine (I125). A radioactive iodine seed delivers radiation of about one inch in diameter and emits radiation for about 10 months. This procedure is also known as a “permanent low dose-rate (LDR) implant”.
Combination IMRT and Radioactive Seeds
Combination therapy (real time Palladium seed implantation followed by IMRT/ IGRT) is the cornerstone of our radiation program. Palladium seed (Pd103) implants delivers radiation to an area about 3/8 of an inch in diameter over 90 days. Sixty days after the palladium seed implant, IMRT/IGRT is started for 5 weeks. A palladium seed has a much smaller area of radiation and shorter lifespan than the Iodine seed. A Palladium implant delvers a higher dose to the prostate with less rectum, bladder and urethra exposure. The combination therapy has a 96% 10-year PSA cure rate at our center.
Proton Beam Radiation
Proton beam radiation therapy is available at only a few centers worldwide. Proton therapy differs from other forms of radiation because it uses beams of protons instead of beams of photons. Theoretically, the proton beam has properties that make it ideal for treating the prostate since the deposit most the energy at the end of the beam. However, for a proton to do this properly, its pinpoint beam would have to move across the prostate much like a Pac-man moving across the screen. This would take hours. Therefore, a gold foil is placed in front of the proton beam which changes the pinpoint beam into a flashlight beam. The proton beam is a single beam (unlike multiple beams of the IMRT). These factors limit the dose to the prostate or risk severe radiation toxicity. This reduced dose has a similar reduction in clinical results. To date, no 10-year data and very limited 5-year data is available for review. Our center does not provide proton therapy for prostate cancer.
Robotic Radiosurgery Systems
Robotic Radiosurgery delivers beams of high dose radiation (similar to IMRT) to the prostate and include the CyberKnife and Novalis Systems. Prior to the procedure, the patient is imaged with a CT scan to determine the size, shape and location of the prostate. Computer software generates a treatment plan to match the desired IMRT radiation dose while limiting radiation exposure to the surrounding healthy tissue. The CyberKnife System’s computer-controlled robot slowly moves around the patient to the various locations from which it will deliver radiation to the tumor over 5- (sometimes less), 30-, and 90-minute sessions. In the Novalis System, CT images are used to position the patient on a robotic table that manipulates the patient to a fixed radiation beam. Through Terk Oncology, radiosurgery can be considered for low risk tumors.
Radiation Damages DNA – but our bodies are exposed to damaging radiation from the sun every day. Nature can heal the damage in less than an hour. But the radiation dose is high enough that 1-2% of the cells can’t keep up with the fractions and the dose accumulates to kill them. Radiation kills cancer cells easier than normal cells because they are rapidly growing and using their DNA to grow.
Radiation is often used by our center to treat prostate cancer. We have published our treatment data on a very large number of patients using radiation demonstrating a 10-year PSA cure rate over 80% for high risk cancer and 96% for intermediate to low-risk cancers using brachytherapy or a combination of brachytherapy with IMRT. This is through our partnership with Terk Oncology.
To learn more about Terk oncology- visit www.terkoncology.com