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1. Stereotactic Body Radiation Therapy (SBRT) for the Primary Treatment of Localized Prostate Cancer M. Bernetich4, C. Oliai6, R. M. Lanciano1,2,3, A. Hanlon5, J. Lamond1,2,3, S. Arrigo1,2,3 J. Yang1,2,3, M. Good1, J. Feng1, B. Garber1, M. Mooreville1, L. Brady1,3 1Philadelphia CyberKnife, 2Delaware County Memorial Hospital / Crozer Keystone Healthcare System, 3Drexel University, Philadelphia, PA, 4Rowan University School of Osteopathic Medicine, Stratford, NJ , 5University Of Pennsylvania, Philadelphia, PA, 6California Pacific Medical Center, San Francisco, CA Introduction The American Society of Radiation Oncology (ASTRO) model policy update, published 4-17-13, acknowledges that Stereotactic Body Radiation Therapy (SBRT) is equivalent to standard radiation modalities used to treat prostate cancer such as Intensity Modulated Radiation Therapy (IMRT). Furthermore, ASTRO supports the treatment of low and intermediate risk prostate cancer with SBRT where it has excellent biochemical control rates with correspondingly low rates of severe toxicity. However, only recently has five year data been published with limited sample size. We report an update of our previously published experience for primary treatment of prostate cancer with CyberKnife SBRT, assessing efficacy and toxicity. Figure 1. CyberKnife SBRT treatment plan (36.25 Gy × 5 fractions prescribed to the 81 % isodose line (white) with a 44.75 Gymaximum dose). Shown are the prostate (43.6 cm3, red) and PTV (77.8 cm3, orange). A bladder (green) volume of 1.66 cm3 received 37 Gyand 0.4 cm3 of the rectum (yellow) received 36 Gy. METHODS From 2007 to 2012, 143 localized prostate cancer patients were treated with primary SBRT using the CyberKnife system. Risk groups analyzed ranged from very low/low (43%), intermediate (43%), and high (14%). Various dose levels were used over the years of treatment, and for the purpose of this study have been categorized into low dose (35Gy, n=5 or 36.25Gy, n=108) and high dose (37.5Gy, n=30). All treatments were delivered in five fractions. 28% of the patients received androgen deprivation therapy, usually administered to intermediate and high risk patients. Genitourinary (GU) Toxicity was assessed using Radiation Therapy Oncology Group criteria; acute toxicity occurred within 3 months and late toxicity >3 months following treatment. Freedom From Biochemical FailureProbability RESULTS At a median follow-up time of 35 months, the median PSA value was 0.30 ng/mL. The 5-year freedom from biochemical failure (FFBF) was 94.1%, 93.8% and 86.2% for very low/low, intermediate, and high-risk patients, respectively. A dose response was observed between the low and high dose groups for all patients with FFBF of 85.2% vs. 100.0% (p=0.058), respectively. Of the 143 patients treated, 97 patients had follow-up times of at least 2 years, with a median follow-up of 47 months and median PSA value of 0.20 ng/mL. The 5-year FFBF for this group was 94.1%, 92.9%, and 85.7% for very low/low, intermediate, and high-risk patients, respectively. A dose response was also observed in this group between the low and high dose groups with FFBF of 84.1% and 100.0% (p=0.046), respectively. For all treated patients, severe GU toxicities (Grade 3 and 4) included 2% acute and 3% late; however, at most recent follow-up, severe GU toxicity was 0.7%. One grade 4 GU toxicity was observed. No grade 3 or 4 gastrointestinal toxicities were observed. At last follow-up, 12% of hormone naïve patients lost the ability to achieve erections strong enough for penetration and required ED medication for intercourse. No hormone naïve patient who was potent before SBRT developed ED refractory to medical treatment. Years of Freedom From Relapse Figure 2. Freedom From Biochemical Failure(All Patients) Freedom From Biochemical FailureProbability • CONCLUSION • Our experience with CyberKnife SBRT for localized prostate cancer demonstrates favorable efficacy with less toxicity compared to the outcome for IMRT as reported in literature. Years of Freedom From Relapse Figure 3.Freedom From Biochemical Failure (All Patients) - High Dose vs. Lose Dose