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4 | Oncology Advances Dana-Farber/Brigham and Women's Cancer Center (DF/BWCC) was the first center in Massachusetts and one of the first in the United States to use an innovative technique for preserving rectal tissue while increasing the effectiveness of radiation ther- apy for treating adenocarcinoma of the prostate. "This opens up radiation to a whole set of patients who previ- ously had no viable treatment options, and gives them a sec- ond chance at cure," said Paul L. Nguyen, MD, Director of Prostate Brachytherapy at DF/BWCC. The technique uses an FDA-approved biocompatible, ab- sorbable hydrogel (SpaceOAR) that is injected into the space between the posterior portion of the prostate and the anterior wall of the rectum. The extra space separates the rectum from the prostate and allows for delivery of radiation to the prostate with less spill of dose to the sensitive tissues of the rectum, ex- plained Peter F. Orio, III, DO, Medical Director of Radiation Oncology, DF/BWCC at Milford Regional Medical Center and DF/BWCC in clinical affiliation with South Shore Hospital. Radiation Therapy for Prostate Cancer, Innovative BWH Technique Preserves Rectal Tissue sure, or the need to re-treat the prostate with salvage thera- pies, then rectal sparing techniques become much more im- portant," said Dr. Orio. Radiation oncologists at DF/BWCC use high-precision variants of intensity modulated radiation therapy (IMRT), including image-guided radiation therapy and volumetric arc therapy (RapidArc Radiotherapy Technology), which delivers a precisely shaped 3-D dose distribution pattern to the tumor with a 360- degree rotation of the gantry in a single, multi-arc treatment. Dr. Orio explained, "Because we use these techniques, we are not delivering large doses of radiation to the rectum, or are at least we are giving doses that are well tolerated. But the ques- tion is, can we improve on what we're doing with dose esca- lation while still maintaining that margin of safety?" More Space, Fewer Side Effects Injecting the hydrogel components requires a degree of skill, Dr. Orio said. The product consists of a precursor and acceler- ator solution that are prepared and loaded into dual syringes with a Y-adapter with an 18 gauge, 15 cm needle attached. The solution is injected into the perirectal space via a perineal approach under ultrasound guidance. Once in place, the com- ponent materials mix and form a hydrogel that maintains its shape and spacing for approximately three months, and is ab- sorbed safely into the body by approximately six months, al- lowing sufficient time for radiation planning and delivery. Dr. Orio noted that in a pivotal multicenter randomized, controlled clinical trial of the SpaceOar gel system in 222 pa- tients (Int J Radiat Oncol Biol Phys. 2015 Aug 1;92(5):971-7), the mean perirectal space for patients who received injections of the hydrogel was 12.6 + 3.9 mm, compared with 1.6 + 2.0 mm for controls. DF/BWCC researchers were not part of this clinical trial. "This difference is important because the radiation dose falls off quickly over distance. You lose about 10 percent of the dose per millimeter, so having those extra few millimeters can decrease the dose to the rectum significantly," he commented. The trial also met its primary efficacy endpoint of the propor- tion of patients achieving a more than 25 percent reduction in rectal volume receiving at least 70 Gray due to spacer place- ment. This endpoint was chosen because it represents the dif- ference in dose reduction to the rectum seen between conventional external beam radiation and IMRT. In all, 12.4 percent of patients in the hydrogel group met the primary end- point, compared with 3.3 percent of controls (P = .0001). Radiation oncologists Peter F. Orio, III, DO, and Paul L. Nguyen, MD, are using an innovative technique to preserve rectal tissue while increasing the effectiveness of radiation therapy for the treatment of adenocarcinoma of the prostate. "With the advanced radiation delivery technologies that we use at Dana-Farber/Brigham and Women's Cancer Center, the toxicity profile is fairly low, but there are times when, because of the patient's anatomy, previous surgery or radiation expo-

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