The treatment we recommend at Sloan Kettering is dependent upon which subtype of Intermediate-Risk a patient’s cancer falls into (see Appendices I and II). For example, in patients with Favorable Intermediate-Risk prostate cancer who are eligible, we tend to prefer permanent seed implants alone. On the other hand, the Unfavorable Intermediate-Risk subtype tends to behave more like High-Risk. In these men we recommend using a combination of seed radiation and intensity modulated radiation therapy (IMRT).
The distinction between permanent and temporary seeds lies in the rate at which radioactivity is deposited into the prostate. There is no evidence that either type of seed implant is superior to the other in terms of cancer cure rates. When combined with seeds, IMRT is usually delivered over an approximately four to five-week period and may commence several weeks prior to or after the seed implant. At Sloan Kettering, our preference is to perform the seed implant prior to the IMRT. The total course of combined therapy with seeds plus IMRT is usually completed over two months.
Compared to using either type of radiotherapy by itself, there is a two-fold rationale for using them in combination: 1) delivery of a significantly higher dose of radiation to the tumor within the prostate; 2) the addition of IMRT to seed placement allows for the treatment of microscopic prostate cancer that may have spread through the capsule but still remains closely adjacent to the prostate. By expanding the size of the radiation field so it includes the area just outside the edge of the prostate IMRT allows for a more robust “halo” of treatment. Studies demonstrate that, when compared to IMRT alone, the combination of HDR seeds and IMRT reduces the chance of the prostate cancer’s return.
When treating with IMRT alone, studies show that adding a short course of hormone therapy improves overall survival. Although there is no data to guide us, with the high radiation doses achieved using combination therapy, the anticancer effects may be sufficient enough so that the added boost from hormone therapy may no longer be necessary. However, because combination radiation therapy does not target prostate cancer that has spread outside the prostate to distant areas of the body, a certain proportion of patients with Unfavorable Intermediate-Risk prostate cancer—those who may have microscopic and thus undetected prostate cancer cells that have traveled to distant sites—may still benefit by receiving a short course of hormone therapy. It is for this reason that we will consider adding four to six months of hormone therapy in Unfavorable Intermediate-Risk prostate cancer patients receiving combination therapy. What would trigger such a recommendation in these patients? We routinely obtain an multiparametric MRI of the prostate. Should that detect a larger-sized tumor that is pushing through the prostate capsule or into the seminal vesicles we would typically recommend the addition of hormone therapy.
Ultimately, if the toxicities of combination therapy were excessive, we could not in good conscience recommend using seeds and beam radiation together if the cure rates were only marginally better. However, studies indicate that combination therapy provides a 20 percent improvement in cure rates. It is true that the side effects of seeds and beam radiation are increased in the short term and are marginally increased in the long term. The risk of serious disruptions to urinary and bowel function, however, is equivalent to either seeds or beam alone and, more importantly, quite low. The rates of urinary incontinence (the inability to control urine flow) are dramatically less than the rates that are typical after prostatectomy.
Sean M. McBride, MD, MPH is a board-certified radiation oncologist with an expertise in treating primary genitourinary (prostate, bladder, kidney, and testicular) and head and neck (oral cavity, base of tongue, tonsil, larynx, hypopharynx, sinus, nasopharynx, and thyroid) malignancies. Dr. McBride works with a dedicated team of medical oncologists, surgeons, and medical physicists to help deliver individualized care using sophisticated radiation therapy techniques including image-guided, stereotactic radiosurgery (IGRT), intensity modulated radiation therapy (IMRT), and brachytherapy.
Michael Zelefsky, MD is Chief of Memorial Sloan Kettering’s Brachytherapy Service. In addition, he was instrumental in pioneering the use of IMRT and IGRT for prostate cancer. He is Editor-in-Chief of Brachytherapy, Chairman of the National Patterns of Care Study for Genitourinary Cancers, and past president of the American Brachytherapy Society. He has received several awards including the Boyer Award for Excellence in Clinical research, the Outstanding Teaching Award in the Department of Radiation Oncology at Memorial Sloan Kettering, the 2009 Henschke Medal, and the 2009 Emanuel Van Descheuren Award for Excellence in Translational Research.