ESTRO 2020 Abstract book

S117 ESTRO 2020

symptoms after prostate cancer radiotherapy. These subregions have been identified in a cohort of 272 patients treated with IMRT/IGRT at 70/80 Gy (2 Gy/fr), for 2 acute toxicities (retention and incontinence) and for 3 late toxicities (retention, dysuria and hematuria) (Mylona et al., IJROBP 2019). The prediction capability of the subregions needs to be validated in an external cohort, before being used in the clinical practice. The objective of this study was to validate, in a large independent dataset, the capabilities of these subregions for predicting the corresponding side effects.

Conclusion External validation confirms that three subregions, located in the posterior bladder part and the urethra, are predictive of acute incontinence, late dysuria and late retention, while the dose received by the whole bladder was less or not predictive. In addition to prediction, the dose to the subregions may also be considered at the planning step in order to reduce toxicity. OC-0212 Patient-reported functional outcomes after hypofractionated radiation for prostate cancer J. NossiteR 1 , A. Sujenthiran 1 , T. Cowling 2 , M. Parry 1 , S. Charman 1 , P. Cathcart 3 , N. Clarke 4 , H. Payne 5 , J. Van der Meulen 2 , A. Aggarwal 6 1 The Royal College of Surgeons of England, Clinical Effectiveness Unit, London, United Kingdom ; 2 London School of Hygiene and Tropical Medicine, Department of Health Services Research and Policy, London, United Kingdom ; 3 Guy's and St Thomas' NHS Foundation Trust, Department of Urology, London, United Kingdom ; 4 Salford Royal NHS Foundation Trust and The Christie NHS Foundation Trust, Department of Urology, Manchester, United Kingdom ; 5 University College London Hospitals, Department of Oncology, London, United Kingdom ; 6 Guy's and St Thomas' NHS Foundation Trust, Department of Clinical Oncology, London, United Kingdom Purpose or Objective To determine patient‐reported functional outcomes (PROs) in men with prostate cancer (PCa) undergoing moderately hypofractionated (H‐RT) or conventionally fractionated radiotherapy (C‐RT) in a national cohort study. Material and Methods All men diagnosed with PCa between April 2014 and September 2016 in the English National Health Service undergoing C‐RT or H‐RT were identified in the National Prostate Cancer Audit and mailed a questionnaire at least 18 months after diagnosis. Differences in patient‐reported urinary, bowel, sexual, and hormonal function (EPIC‐26 domain scores on a 0‐100 scale) and health‐related quality of life (EQ5D5L on a 0‐1 scale) were estimated using linear regression with adjustment for patient, tumour and treatment‐related factors in addition to gastrointestinal (GI) and genitourinary (GU) baseline function with higher scores representing better outcomes. Results Of the 17,058 men in the cohort, 77% responded: 8,432 men had C‐RT (64.2%) and 4,699 H‐RT (35.8%). Men in the H‐RT group were older (≥70 years: 67.5% versus 60.9%), fewer men had locally advanced disease (56.5% versus 71.3%), were less likely to receive ADT (79.5% versus 87.8%) and slightly more men had pre‐treatment GU

Material and Methods For the external validation of the subregions, a dataset of 501 patients from the TROG 03.04‐RADAR trial was considered (Denham et al., RO 2012). Patients were treated with 3DCRT at a total dose of 66, 70 or 74 Gy (1.8‐ 2 Gy/fraction). Urinary toxicity was scored using LENT/SOMA and the International Prostate Symptom Score (IPSS) questionnaire. The five subregions were propagated from the template‐patient (where they were previously identified) to the native space of each patient in the validation cohort (planning CT). The intra‐prostatic urethra was also segmented automatically on the CT images using an in‐house developed algorithm (Acosta et al., RO 2017). For each patient, DVHs were computed for the whole bladder, the urethra and the 5 subregions. The prediction capability of the DVH and the mean dose in the corresponding structures was assessed using logistic regression and the area under the ROC curve (AUC) for acute toxicities and using the Cox proportional hazard model and the time‐dependent AUC for late toxicities. Results The toxicity prediction capabilities of the mean dose and the DVHs of the five subregions, the whole bladder and the urethra are shown in Table 1. Considering the five symptoms, the dose was predictive in the whole bladder for two of them (acute incontinence; AUC=0.65 and late retention; AUC=0.62), in the urethra for only one symptom (acute incontinence; AUC=0.70) and in the subregions for three symptoms (acute incontinence (AUC=0.70), late dysuria (AUC=0.65) and late retention (AUC= 0.69). The localization of the three subregions in the anatomy of the template‐patient is displayed Figure 1B. Acute retention and late hematuria subregions were not predictive.