ESTRO 36 Abstract Book

S714 ESTRO 36 2017 _______________________________________________________________________________________________

12 months and yearly thereafter. The highest score of both was used to identify toxicity. Between 2010-2013, validated self-assessment questionnaires, EORTC QLQ-C30 for health-related QoL and EORTC PR-25 for PCa-specific QoL, were yearly sent to all patients. All C30 functioning domains, global health and fatigue and pain symptoms were evaluated. The evaluated PR25 domains were sexual activity and functioning, urinary and bowel symptoms, and incontinence aid use. Raw scores of each domain were linearly transformed into 0-100 scales. Higher functional scores indicate higher functioning and better QoL, while higher symptom scores indicate lower QoL. Patients with toxicity were compared to patients without late toxicity. A multi-level linear model was used to statistically assess the QoL differences between the 2 groups over 6-10 years FU. Covariates were included in the analysis to control for their influence: age, PSA, prostate volume and FU time. Clinical relevance of the differences was assessed by means of the minimally important difference (MID): toxicity group mean scores ≥0.5 standard deviation different from the non-toxicity group, were considered clinically relevantly different. Results Late grade ≥2 toxicity was reported by 79 patients (46.2%), of whom 57 (33.3%) had GU and 30 (17.5%) had GI symptoms. Of both C30 and PR25, 364 questionnaires were analysed (mean 2.1 per patient). Generic QoL (C30)domains did not show any statistically significant differences (Table 1). PR25 PCa-specific QoL for both urinary and bowel symptoms showed clinically relevant worse QoL scores for patients with grade ≥2 toxicity (p<0.001 and p=0.01, respectively). Of sexually active patients, patients with toxicity reported better sexual function (p=0.001); which was also clinically relevant. The included covariates did not show any associations with QoL score differences.

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

Conclusion For patients treated with EBRT and HDR-BT boost, late grade ≥2 toxicity was not associated with decreased QoL for generic QoL domains, but associations between toxicity and decreased PCa-specific QoL scores were observed. The higher sexual functioning scores in the toxicity group are hard to explain and worth more investigation. EP-1345 Dosimetric effect of seed-based prostate localisation on Pelvic Lymph Nodes in High-Risk Prostate Ca R. Valentine 1 , E. Miguel Chumacero 2 1 NHS greater glasgow and clyde, Department of Radiotherapy Physics, glasgow, United Kingdom 2 NHS greater glasgow and clyde- University of Glasgow, Department of Radiotherapy Physics, Glasgow, United Kingdom 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