ESTRO 37 Abstract book

S847

ESTRO 37

Purpose or Objective The aim of this retrospective study was to analyze the outcomes of patients with castration-resistant prostate cancer (CRPC) that were treated with proton therapy at a single institution. Material and Methods Between 2003 and 2014, 43 consecutive CRPC patients without distant metastasis were irradiated locally with proton therapy at Hyogo Ion Beam Medical Center. Biochemical failure was defined using the Phoenix consensus definition. Late toxicities were graded according to Common Terminology Criteria for Adverse Events, version 4.0. Freedom from biochemical relapse (FFBR), clinical progression free survival (CPFS), cause specific survival (CSS), overall survival (OS) and rate of late toxicities were calculated using the Kaplan-Meier method and compared using the Log-rank test. Results The median follow-up period was 68 months (range, 13- 134 months). Forty-two patients (98%) received 74 Gy (RBE) in 37 fractions. Twenty-seven patients (63%) patients experienced biochemical relapse. Median time to biochemical relapse was 23 months (range, 1-107 months). Seventeen patients (40%) experienced clinical recurrence. Among them, two patients experienced local recurrence. Thirteen patients (30%) died of prostate cancer. Five-year FFBR, CPFS, CSS and OS were 38%, 72%, 75%, 67%, respectively. T3b, T4 and PSA ≥ 10 were prognostic factors for biochemical relapse, clinical recurrence and death from prostate cancer. Five-year grade 2 or greater late gastrointestinal and genitourinary toxicities were 11% and 8.1%, respectively. Conclusion As far as we could search, this is the first results of CRPC patients treated with PT. PT showed better results compared to other treatments. However, as some patients experienced early recurrence, it is considered important to select appropriate patients for PT. S.S. Nanda 1 , M. Rastogi 1 , A. Gandhi 1 , R. Khurana 1 , K. Sahni 1 , R. Hadi 1 , S.P. Mishra 1 , A. Srivastava 1 , S. Farzana 1 , M.L.B. Bhatt 2 1 Ram Manohar Lohia Institute of Medical Sciences, Radiation Oncology, Lucknow UP, India 2 King George Medical University, Radiation Oncology, Lucknow, India Purpose or Objective Image guided intensity modulated radiotherapy (IG-IMRT) enables dose escalation, while minimizing the treatment related toxicities in the management of carcinoma prostate. Localization using gold markers and online treatment verification could potentially reduce the planning target volume (PTV) which may translate in to reduction of radiation toxicity. We aim to retrospectively evaluate the effect of PTV reduction on acute as well as late radiation toxicity and compare the biochemical control. Material and Methods The present study is a single institution retrospective evaluation. Histopathologically proven adenocarcinoma of prostate, T1c-T3bN0M0, age ≥ 18 years, karnofsky performance status (KPS) of ≥70 treated definitively with RT were evaluated. Patients were staged as per AJCC 7 th and risk stratification done by the D’Amico criteria. A week prior to simulation, 3 fiducial gold markers were inserted under transrectal ultrasound guidance. Contrast EP-1569 Impact of reduced PTV margins on toxicity in prostate carcinoma treated with image guided IMRT

included. There were no significant differences in patient characteristics between the two arms. The radiotherapy (RT) treatment parameters differed significantly between CRT and HRT (all p < 0.001). Use of androgen deprivation therapy (ADT) varied from 0-100% in both groups, (mean ± SD: 43.3% ± 43.6 ; CRT vs. HRT: p : ns). The odds ratio (OR), risk ratio (RR) and risk difference (RD) between CRT and HRT for BF, BCF, OM, PCaSM, acute GU, late GU and GI toxicities were all nonsignificant (Table). However, acute GI toxicities were 9.1% less with CRT (RD = 0.091, OR = 1.687, RR = 1.470, all p < 0.001). Subgroup analyses were carried out for key variables that could influence acute GI toxicity. These include %ADT use, %patients with full volume of seminal vesicle (SV) in clinical target volume (CTV) and biological effective dose of HRT for acute GI effects (BED 10 ). Using median values of the respective variables as a cut-off, subgroups of ≤ vs. > 66.8% ADT (RD : 0.052 vs. 0.136 ; p = 0.008) and < vs. ≥ 76% full volume of SV in CTV (RD : 0.034 vs. 0.108 ; p < 0.001) significantly influenced the acute GI toxicity with HRT. A higher proportion of high-risk group patients with the entire SVs in CTV were treated with neoadjuvant ADT (r = 0.959, p = 0.001). For BED 10 , the RD significantly favored CRT for individual subgroups of < 62.95Gy 10 (RD: 0.124, p < 0.001) and ≥ 62.95Gy 10 (RD : 0.069, p = 0.016). However, no significant difference was noted on comparing these subgroups based on BED 10 (< vs. ≥ 62.95Gy 10 , RD : 0.091, p : ns).

Conclusion The meta-analysis reaffirms HRT as a viable alternative therapeutic approach to CRT in LLPaC. HRT could shorten treatment duration, require fewer hospital visits and reduce the costs for health care providers. However, the significantly higher acute GI toxicities with HRT need careful evaluation. Reducing the SV volume in the CTV in low / intermediate risk patients and using ADT in high- risk patients to induce prostate shrinkage, could minimize the irradiated rectal volumes and thereby mitigate acute GI toxicity. M. Takagi 1 , Y. Demizu 2 , N. Fuwa 2 , K. Terashima 2 , O. Fujii 3 , D. Jin 4 , Y. Niwa 4 , M. Hareyama 1 , T. Okimoto 2 1 Sapporo Teishinkai Hospital, Proton Therapy Center, Sapporo-city, Japan 2 Hyogo Ion Beam Medical Center, Department of Radiology, Tatsuno, Japan 3 Hakodate Goryoukaku Hospital, Department of Radiation Oncology, Hakodate, Japan 4 Tsuyama Chou Hospital, Department of Radiology, Tsuyama, Japan EP-1568 Results of proton therapy for castration resistant prostate cancer