For decades, experts at Memorial Sloan Kettering have been pioneering sophisticated ways to safely and effectively deliver powerful doses of radiation directly to a person’s tumor with incredible precision. One recent example of these ongoing efforts is an innovative technique called stereotactic hypofractionated accelerated radiation to the prostate (SHARP).
Also known as stereotactic radiosurgery, SHARP is a form of external beam radiation that uses sophisticated imaging technologies combined with an advanced computer system to deliver very high doses of radiation to tumors with an accuracy of under a millimeter.
Another advantage of SHARP is that patients require only five treatment sessions, with the entire course being completed in a little over a week, compared with close to 50 sessions over ten weeks using the conventional approach.
In addition, each SHARP treatment session takes three to four minutes, whereas patients treated with other forms of stereotactic radiosurgery, such as CyberKnife®, are required to spend nearly an hour on the treatment table for each session.
Three small gold markers are implanted into the prostate to enable doctors to track the precise coordinates of the prostate in real time right before the treatment starts and during the actual radiation session. The markers act as guides to allow the radiation oncologists to determine the prostate’s exact location. If the prostate moves outside of a very tight margin, the radiation treatment can be stopped and adjustments made.
This kind of missile technology helps us and our medical physics colleagues localize the target with an accuracy akin to the sharpness of a surgeon’s scalpel, sculpt a high dose of radiation around the prostate, and effectively minimize the amount of normal tissue that’s included in that margin.
Memorial Sloan Kettering is the only hospital in the world currently offering the SHARP treatment approach and one of only a few academic medical centers in the world doing it within the context of an ongoing clinical trial. (1)
Over the past eight years we have been employing this form of external beam radiotherapy. As of May 2017 we have treated approximately 900 patients with the SHARP treatment. Our results so far indicate excellent tolerance of the treatment with the risk of significant urinary or rectal problems resulting from the treatment observed in less than two percent of patients. We have also noted that a significant percentage of patients treated with our current dose regimen of 40 Gray in 5 fractions have had negative prostate biopsies which we routinely perform two years after the treatment.
Existing Options in Radiation Therapy for Prostate Cancer
Radiation therapy is one of several options available to men with prostate cancer, which, after skin cancer, is the most common cancer among men in the United States. More than 180,000 men are diagnosed with prostate cancer every year, the majority of whom are age 65 and over.
Radiation therapy can be delivered to the prostate in several ways. Brachytherapy is an internal form of radiation therapy, also pioneered at MSK, in which radioactive seeds are implanted near the site of the tumor.
Another commonly used method is external beam radiation therapy, which involves aiming radiation directly at the prostate from outside the body using a machine called a linear accelerator, a device that forms beams of fast-moving subatomic particles.
MSK has particular expertise in the use of intensity-modulated radiation therapy, which targets tumors with multiple beams at different angles and intensities. That experience has served as an important foundation for the development of new approaches, such as SHARP, to treat men with prostate cancer.
SHARP, the Latest MSK Innovation
Our SHARP program is not simply stereotactic radiosurgery; it incorporates a number of critical components, making it a unique treatment program for patients with localized prostate cancer. In addition to sophisticated image-guidance techniques tracking the prostate in real time during the several-minute treatment, we are utilizing MRI mapping — without the need for CT scans — to accurately target the prostate gland. MRI mapping allows for superior visualization of the prostate and surrounding normal tissues, providing unprecedented accuracy of treatment delivery.
Another important component of the SHARP program is the use of a biodegradable gel that is inserted between the prostate and the rectum at the time of the marker placement (see Figure 1). This creates a buffer between the prostate and the rectum, pushing the rectum out of the way of the high dose of radiation and further reducing the risk of bowel side effects.
What makes the prostate program at MSK unique is the availability of the comprehensive package of options we can offer our patients. Our expertise and the array of choices at our disposal enables us to tailor radiation therapy based on the characteristics and location of the tumor, as well as important physical, emotional, and psychological factors that take into account the entire individual and his quality of life.
Candidates for SHARP treatment
The radiation therapy approach we recommend depends on the unique characteristics of a man’s disease. SHARP is generally recommended for men who have localized prostate cancer that has not spread beyond the prostate and who have relatively good urinary function.
For men with more aggressive disease, we may combine SHARP with other treatments such hormone therapy or radioactive seed implants, also known as brachytherapy.
Side effects of SHARP treatment
Despite the application of high radiation doses, patients receiving SHARP at our institution have tolerated the treatment well and experience similar or lesser side effects compared with more conventional external radiation techniques. After treatment, patients are closely followed with MRIs and a prostate biopsy two years after the treatment is completed.
Some patients may experience urinary or bowel changes, sexual health problems, or fatigue, among other side effects. However, advances in the precision of radiation therapy have lessened the risk of complications, so some men don’t experience any of these symptoms.
We believe that SHARP will likely replace the standard way of delivering external radiation therapy for prostate cancer if continued research and patient follow-up show that it is equally or more effective.