ESTRO 36 Abstract Book

S722 ESTRO 36 _______________________________________________________________________________________________

Purpose or Objective Prostate movement is unrelated to pelvic lymph nodes (PLN) location. Therefore, for High-Risk Prostate Cancer radiotherapy, set-up corrections based on image-guided localisation of the prostate might not guarantee that the other nodal PTV receives the intended dose. The aim was to evaluate the impact that couch shifts applied for prostate motion correction have on the dose delivered to the PLN CTV and to determine their ideal PTV margins. Material and Methods Retrospective analysis of 21 VMAT treatments was realized using the interfraction prostate-based couch shifts as new isocentre coordinates in a verification plan. Then each fraction dose was recalculated and the dose coverage of the PLN CTV was assessed with DVHs. To reduce the geometric miss new PLN PTV margins were proposed using the Van Herk formula. Finally treatment plans using current and proposed margins were compared based on the dose to OARs and PTVs. Results The verification plans reported a mean PLN CTV D 99% of 91.7% and this reduced between 4.8% and 9.0% (p<0.001) compared to the mean of the original plans. 51.3% of the verification plans did not meet the criteria, these showed a prostate vector displacement larger than 0.62 cm. The proposed margins: AP 0.91, SI 0.57, and RL 0.26 cm, reported no significant difference in the dose to OARs and PTVs compared to the current treatment plans margins. Conclusion When daily position correction is made considering only the prostate there is potential dose degradation to the PLN CTV. The proposed new recommended margins, however, are expected to improve dose coverage of the PLN CTV, without significantly affecting the associated OAR doses. EP-1346 Oligorecurrent nodal prostate cancer: long- term results of an elective nodal irradiation approach S. Tran 1 , S. Jorcano 2 , T. Falco 1 , G. Lamanna 1 , R. Miralbell 1 , T. Zilli 1 1 Hôpitaux Universitaires Genève, Radiation Oncology, Geneva, Switzerland 2 Instituto Oncológico Teknon, Radiation Oncology, Barcelona, Spain Purpose or Objective The best strategy to irradiate oligorecurrent nodal prostate cancer (PCa) remains debated with both elective nodal radiotherapy (ENRT) and SBRT considered valid alternatives. Aim of this study is to report long-term results of ENRT in PCa patients (pts) with oligorecurrent nodal disease after primary treatment. Material and Methods Data of 53 oligorecurrent PCa pts (N1 and/or M1a) with ≤ 5 nodal metastases (n=108) treated with ENRT combined with androgen deprivation (AD) between 2004 and 2016 were retrospectively reviewed. Median age and PSA at diagnosis were 62 yrs (range, 47-77) and 8.6 ng/ml (range, 3.4-92.9 ng/ml), respectively. The primary treatment was RT, radical prostatectomy (RP), RP + postoperative RT and RT + salvage RP in 9 (17%), 23 (43%), 20 (38%) and 1 (2%) pts, respectively. At recurrence (median time after primary treatment of 34 mo, range 2-129 mo), all but one patient were re-staged with 18F-choline PET-CT studies. Median PSA and PSA doubling time (DT) were 3.4 ng/ml (0.2-48.9 ng/ml) and 5 mo (range, 1-35 mo), respectively. At restaging, 45.3% (n=24) of the pts presented a single nodal metastasis, while 2, 3, 4 and 5 nodal metastases were found in 30% (n=16), 7.5% (n=4), 9.5% (n=5) and 7.5% (n=4) of the pts, respectively. Recurrences were mainly located in the pelvis (n=38). A combined N1 and M1a oligorecurrence or extrapelvic nodal progression (M1a) was observed in 10 and 5 pts, respectively. All pts

underwent ENRT between 45 and 50.4 Gy with a boost on positive nodes (median 64.4 Gy, 54-69 Gy) using mainly VMAT (n=24) or IMRT (n=21) techniques. Concomitant AD was administered to all pts for a median time of 6mo (range, 3-30 mo). Results After a median follow-up (FU) after ENRT of 44 mo (range, 2-133), 27 pts (51%) showed PSA progression, with a 5-yr biochemical disease free-survival of 43±8.3%. The 5-yr distant progression-free survival (DPFS) rate was 58.2±8.5% (n=19 pts with clinical progression). Pts with a PSA DT at relapse <3 mo showed a worse 5-yr DPFS compared to pts with a PSA DT ≥ 3mo (36.8% vs. 63.6%, p=0.029), while a trend towards significance was observed for pts with 1 vs ≥ 2 recurrent nodes (71.8% vs. 44.9%, p=0.089). Overall survival rate at 5-yr was 86.4±6.9% (2 over 4 pts died from PCa). Ten of 19 clinically relapsing pts presented a new oligometastatic progression (7 nodal/2 bone/1 combined). One patient presented a local relapse in the previously untreated prostate bed. Eight out 10 pts were treated with a new RT course, with 3 pts in complete remission at last FU. Only 2 pts presented with a CTCAE v3.0 Grade ≥2 genitourinary toxicity. Conclusion ENRT combined with concomitant short-course AD is a safe and effective salvage modality for patients with oligorecurrent nodal PCa, able to better delay distant progression compared to historical series using focal SBRT. Prospective randomized studies comparing focal SBRT vs ENRT are warranted to define the best treatment strategy for oligorecurrent nodal PCa. EP-1347 Treatment outcomes with hypofractionated high-dose radiation therapy for prostate cancer D. Candini 1 , F. López Campos 1 , C. Vallejo Ocaña 1 , M. Martín Martín 1 , A. Hervás Morón 1 1 Hospital Ramon y Cajal, Radiation Oncology, Madrid, Spain Purpose or Objective To report treatment results, genitourinary (GU) and lower gastro-intestinal (GI) toxicity of a retrospective cohort of prostate cancer patients treated with hypofractionated radiotherapy (hypo-RT) with a high equivalent biological From April 2014 to October 2015, 35 patients with histologically confirmed intermediate risk prostate cancer defined by National Comprehensive Cancer Network (NCCN) risk group were assigned to receive hypo-RT with a total dose of 63,4 Gy/20 fractions. Use of image-guided techniques (IGRT) with fiducial markers was required. All patients were given radiotherapy with 6 months of neoadjuvant and concurrent androgen suppression. GI and GU toxicity were prospectively evaluated according to modified RTOG criteria. Toxicity was considered “acute” if occurred during and/or within 3 months after the treatment and “sub-acute” if occurred between 3 and 12 months after the treatment. Biochemical recurrence was defined as a PSA concentration superior than nadir plus 2 35 patients with a median age of 76 years (range 61-86 years) were treated in the defined period receiving hypo- RT. The median follow-up was 20.3 months (range 12 – 30 months). Acute GU toxicity grade I occurred in 20 patients (57.1%), grade II in 2 patients (5.7%). Acute GI toxicity grade I were observed in 6 patients (17.1%), grade II in 3 patients (8.6%). None developed acute GU or GI toxicity grade III or IV. Sub-acute GU toxicity occurred as follows: grade I in 9 patients (25.7%) and grade II in 1 patients (2.9%). Sub- effective dose (BED). Material and Methods ng/mL. Results