What is a 5 day course of treatment? It is a five-day, non-invasive treatment for prostate cancer (called “stereotactic body radiation therapy” or “SBRT”). SBRT is a specialized form of IMRT (intensity modulated radiation therapy) that delivers high doses of radiation over a period of five days. Instead of giving small doses of radiation each day for several weeks, SBRT involves delivery of very focused beams of high-dose radiation. Several beams are aimed at the tumor from different angles. When for other cancers it is delivered in a single fraction it is known as stereotactic body radiosurgery. Like other forms of external radiation, these treatments are painless.
TOTAL TREATMENT TIME: 45 minutes on CyberKnife vs. 20 minutes on Elekta Infinity.
TREATMENT PLANNING: Both CyberKnife and Elekta Inifinity use Monte Carlo based dose calculations. Unlike other planning software programs that use theory models to calculate dose, Monte Carlo is statistical planning and the most accurate. Because Elekta Infinity utilizes a multileaf collumater, which can change shape instantaneously we can mimic the shape of the prostate as seen from different beam angles better, compared to the circular aperture in a CyberKnife system. This will reduce the normal tissue being irradiated from various gantry angles. Thus we can achieve better DVH (Dose Volume Histogram) with LINAC based prostate SRT compared to CyberKnife.
TARGETING THE PROSTATE: None of these machines can track the motion of the prostate throughout treatment AND adjust delivery accordingly. The CyberKnife System uses invasively implanted fiducials as reference points to identify the exact location of the prostate. Patients will wait approximately one week after insertion of the fiducials before CyberKnife treatment planning can begin to ensure that fiducial movement has stabilized.
At The Farber Center for Radiation Oncology we have a completely non-invasive approach to targeting the prostate. We use a RadiaDyne balloon. The balloon acts primarily as an immobilizer reducing the daily variations in location of the prostate, and allowing the rectum and prostate to be positioned in a more predictable and reproducible location during the treatment course. Because of the decreased probability of the prostate moving out of the treatment fields, smaller treatment margins around the prostate may be used. This will have the effect of lowering the radiation dose to the normal tissue surrounding the prostate and lowering the incidence of potential side effects to normal tissues. We also take a second Cone Beam CT Scan in the middle of treatment to verify the position of the prostate. This together with the placement of the RadiaDyne ballon ensures consistency in the location and motion of the prostate during the course of treatment. Due to the fact that we can complete a entire treatment including setup and imaging in under 20 minutes, the amount of prostate motion documented from studies (Both, et al) is kept at a clinical minimum.
KEY POINTS with Elekta Infinity:
5 Day Treatment
No need for surgical procedure
Better bladder DVH
Higher Rate of Erectile Function Preservation
CBCT to see prostate/rectum interface
In my opinion, the most important factors in selecting the right team are the reputation, training and experience of the radiation oncologists and their support staff (physicists, dosimetrists, therapists, nurses, etc.) in treating prostate cancer using SBRT.