ESTRO 2020 Abstract book

S25 ESTRO 2020

Conclusion UI recovery after prostatectomy strongly depends on TTRT, with no further improvement starting from about 8- 9 months after surgery: this result strongly suggests that no additional benefit in terms of baseline UI recovery derives from waiting longer to deliver PORT. Higher levels of neuroticism lead to an overestimation of UI. PD-0060 Treatment-related toxicity of hypofractionated radiation therapy for prostate cancer M. Parry 1 , A. Sujenthiran 2 , J. Nossiter 2 , P. Cathcart 3 , N. Clarke 4 , H. Payne 5 , A. Aggarwal 6 1 London School of Hygiene and Tropical Medicine, Department of Health Services Research and Policy, London, United Kingdom ; 2 The Royal College of Surgeons of England, Clinical Effectiveness Unit, London, United Kingdom ; 3 Guy’s and St Thomas’ NHS Foundation Trust, Department of Urology, London, United Kingdom ; 4 The Christie and Salford Royal NHS Foundation Trusts, Department of Urology, London, United Kingdom ; 5 University College London Hospitals, Department of Oncology, London, United Kingdom ; 6 King’s College London, Department of Cancer Epidemiology- Population- and Global Health, London, United Kingdom Purpose or Objective Randomised controlled trials (RCTs) have demonstrated comparable early oncological outcomes after hypofractionated (H-RT) and conventionally fractionated radiation therapy (C-RT) in the radical treatment of prostate cancer (PCa). Data from these studies on the effect of hypofractionation on treatment-related (gastrointestinal) GI and (genitourinary) GU toxicity remains uncertain, and the effect of H-RT on older men with locally advanced PCa is under-reported. Material and Methods Population-based study of all patients treated with radical C-RT (n=9,106) and H-RT (n= 3,027) in all radiotherapy centres in the English National Health Service between 2014 – 2016. We identified severe GI and GU toxicity using a validated coding-framework and compared C-RT and H- RT using a competing-risks proportional hazards regression analysis. Results There was no difference in GI toxicity (C-RT: 5.0 events/100 person-years; H-RT: 5.2 events/100 person- years; adjusted sHR: 1.00, 95%CI: 0.89-1.13; p=0.95) or GU toxicity (C-RT: 2.3 events/100 person-years; H-RT: 2.3 events/100 person-years; adjusted sHR: 0.92, 95%CI: 0.77 -1.10; p=0.35) between patients who received C-RT and H- RT . Conclusion This national cohort study has demonstrated the use of H- RT in the radical treatment of PCa does not increase rates of severe GI or GU toxicity. Our findings also support the use of H-RT in elderly men and those with locally advanced PCa. PD-0061 Does the dose to penile bulb/internal pudendal arteries matter for erectile dysfunction post- SBRT? G. Lamanna 1 , S. Jorcano 2 , S. Bral 3 , C. Rubio 4 , A. Oliveira 5 , M. Bottero 1 , U. Abacioglu 6 , V. Achard 1 , H. Minn 7 , Z. Symon 8 , T. Zilli 1 , R. Miralbell 1,2 1 HUG, Radiotherapy, Genève, Switzerland ; 2 Teknon Oncologic Institute, Radiotherapy, Barcelona, Spain ; 3 Onze-Lieve-Vrouwziekenhuis- Aalst- Belgium, Radiotherapy, Aalst, Belgium ; 4 HospitalUniversitario HM Sanchinarro- Madrid- Spain, Radiotherapy, Madrid, Spain ; 5 Portuguese Institut of Oncology- Porto- Portugal, Radiotherapy, Porto, Portugal ; 6 Neolife Medical Center, Radiotherapy, Istanbul, Turkey ; 7 University Hospital Turku, Radiotherapy, Turku, Finland ; 8 Sheba Medical Center, Radiotherapy, Ramat Gan, Israel

Purpose or Objective Stereotactic body radiotherapy (SBRT) is an emerging treatment option for localized prostate cancer(PCa) patients that,despite the overall low toxicity profile, lead to erectile dysfunction (ED) as a common side effect. The dose to the penile bulb (NTD 2Gy D 2% <50 Gy and D mean <20 Gy, Rasmusson et al. ASTRO 2019) and to the internal pudendal arteries (IPA)/crura (NTD 2Gy ≤ 36/30 Gy, Spratt DE et al. Eur Urol 2017) have been strongly correlated with ED. In this study we aimed to assess the correlation between the dose to the penile bulb and IPA with the development of ED after extreme hypofractionation as part of a phase II randomized trial of once-a-week (QW) versus every-other- day (EOD) urethra sparing prostate SBRT (NCT01764646). Material and Methods Between 2012 and 2015, 170 patients with localized PCa from 9 centers were randomized to receive 36.25Gy in 5 fractions (6.5Gy x 5 to the urethra) delivered either EOD (arm A, n=84), or QW (arm B, n=86) with 25% of them receiving 6 months of androgen deprivation therapy. At baseline, 87 patients aged between 50 and 80 yo (median 69) presented with grade 0-1 ED (CTCAE v4.0 grading scale). The penile bulb, the crura, and the IPA D mean and D 2% were recorded to find a correlation with an eventual development of ED.The impact on QoL ( i.e. , difficulty getting or maintaining an erection based on the EORTC PR- 25 questionnaire) was also assessed. Results After a median follow-up of 36 months (range 15-49), only 19.5% (n=17) of patients developed a grade 2-3 ED with no differences regarding age (years ≤ 65 vs. > 65) or penile base structure and prostate PTV volumes. D mean and D 2% of IPA were: 13.3 Gy vs . 13.9 Gy and 19.9 Gy vs. 21.7 Gy for grade 0-1 ED (ED-) vs. grade 2-3 ED (ED+), respectively; for the crura: 4.7 Gy vs. 4.8 Gy and 12 Gy vs. 14.1 Gy for ED- vs. ED+, respectively; and for the penile bulb: 6 Gy vs. 6.8 Gy and 21.4 Gy vs. 20.3 Gy, for ED- vs. ED+, respectively (p=NS). At last follow-up, 70% of the patients (n=44/63) reported moderate to high ED based on the EORTC PR-25 QoL patient self-evaluation questionnaire, with no dose- volume-effect correlations too. Conclusion ED rates following urethra sparing SBRT in our study seem to be promising. The low doses delivered to penile base structures, below published threshold constraints predictive of ED, may explain the minimal impact of SBRT on erectile function and the lack of dose-volume-effect correlation differences between patients with or without severe ED. Longer follow-up is needed to confirm these findings.

IPA

IPA Penile Bulb Penile Bulb Crura Crura

Dmean D2% Dmean

D2% 21.4 20.3

Dmean D2%

ED - 13.3 19.9 6 ED + 13.9 21.7 6.8

4.7 4.8

12

14.1 Table: Dmean and D2% (in Gy) to the internal pudendal arteries (IPA), the penile bulb, and the crura and erectile dysfunction (ED)

Poster discussion: Radiobiology

PD-0062 Clinical modulation of tumour immune infiltrates and plasma cytokines by ATR inhibition ± radiation M. Dillon 1 , M. McLaughlin 1 , E. Patin 1 , P. Malin 1 , C. Ragulan 1 , F. Elisa 1 , A. Wilkins 1 , A. Melcher 1 , K. Harrington 1 1 Institute of Cancer Research, Chester Beatty Laboratories, London, United Kingdom