ESTRO 2020 Abstract Book

S243

ESTRO 2020

Oncology, Waco, USA ; 4 Mayo Clinic, Radiation Oncology, Rochester, USA ; 5 Mayo Clinic, Radiation Oncology, Phoenix, USA Purpose or Objective We instituted a prospective registry to capture provider- and patient-reported clinical outcomes in a large, multi- site radiation oncology practice. Herein, we evaluate the association between proton vs. photon therapy and adverse events as (AEs) assessed by the Patient-Reported Outcomes version of the Common Terminology Criteria for Adverse Events (PRO-CTCAE TM ). Material and Methods PRO-CTCAE questionnaires were administered at baseline, end-of-treatment, 3, 6, 12 months, then annually. Eligible patients were treated with radiation therapy with curative intent and completed selected PRO-CTCAE items based on cancer type between 2013 and 2019. A patient was considered to have patient-reported treatment-related symptomatic AEs if he/she had a score of 3 or 4 for any PRO-CTCAE item that was higher than baseline. Artificial neural network analysis with 4-fold cross-validation was utilized to predict patient-reported AEs with local interpretable model-agnostic explanations (LIME) to approximate clinical effect. All data was analyzed to determine the predictive power of the artificial neural network. Inherent differences in the proton vs. photon patient populations mandated a propensity score analyses utilizing inverse probability of treatment weighting (IPTW) to assess the effect of modality on patient-reported AEs. Artificial neural networks were utilized to predict proton vs. photon treatment assignment to create the inverse weights, while logistic regression models assessed the effect of modality for patient-reported AEs. Results 1,930 patients were eligible; 695 received proton and 1481 received photons. The median time from treatment to last survey was 33.6 mos. Site-specific patient-reported AE rates include(N): 44.2% Prostate (821), 6.7% Breast (624), 20.0% Esophagus (129), 11.2% Pancreas (106), 30.8% Colorectal (91), 37.3% Head & Neck (76), 26.4% Sarcoma (71), and 58.3% Gynecologic (12). Overcoming the subjective nature of patient-reported AEs, the artificial neural network correctly predicted 76.6% (95% CI: 74.5%, 79.6%) of AEs. Prostate cancer and higher total doses were associated with increased risk of patient-reported AEs while breast cancer, pancreas cancer, and hypo- fractionation were associated with lower risk of patient- reported AEs (Fig.1A). Artificial neural networks and the resulting LIMEs showed deterministic factors for modality (Fig.1B). Subsequently, propensity score analysis demonstrated that patients treated with proton therapy had significantly less patient-reported AEs (p=0.045) with an odds’ ratio of 0.79 (95% CI: 0.63, 0.99) when accounting for baseline differences. Conclusion This large, multi-site prospective registry demonstrates a significant benefit of proton therapy in reducing patient- reported AEs. Based on patient characteristics and treatment, artificial neural networks can predict patient- reported AEs after treatment completion. Utilizing multi- level modelling an adjusting for confounding, the direct treatment effect of proton therapy can be predicted. OC-0441 An interim analysis of outcome data from the UK Proton Overseas Programme S. Gaito 1 , N. Burnet 1,2 , M. Aznar 3 , P. Foden 4 , C. Howell 4 , S. Pan 1 , D. Saunders 1 , G. Whitfield 1,2 , A. Crellin 5 , E. Smith 1,2,4

1 The Christie, Proton Beam Therapy Centre, Manchester, United Kingdom ; 2 The University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom ; 3 The University of Manchester, Radiotherapy Related Research, Manchester, United Kingdom ; 4 The Christie, Proton Clinical Outcomes Unit, Manchester, United Kingdom ; 5 NHS England, National Clinical Lead Proton Beam Therapy, Manchester, United Kingdom Purpose or Objective The Proton Overseas Program (POP) was launched in 2008 by the National Health Service (NHS) to deliver high energy Proton Beam Therapy (PBT) abroad to UK patients until this became available in the UK (in 2018). The NHS used a systematic evidence based and prioritised approach. More than 10 years since its inception, we report the long term outcomes on patient groups who have accessed this programme; results compare favourably with other studies (1). Material and Methods Between 2008 and 2018, 1352 patients with eligible indications, from 46 centres across the UK, were referred for consideration of PBT. A national expert panel, adhering to approved criteria, established the appropriateness of PBT in each case. All cases were of sufficient performance status to travel, were appropriately staged and received treatment in experienced PBT centres. 1264 patients were approved (93.5 % of the referrals), 1096 (86.7%) were treated in North America and 168 (13.3%) were treated in Europe. Patient, tumour, treatment and follow-up data were collated in a centralised database. A Proton Clinical Outcomes Unit (PCOU) has been established to monitor this patient cohort as well as standardise and improve prospective outcome data collection for UK PBT patients going forward. Systematic follow-up data was available for 979 patients (77.1% of those approved for PBT). Mirroring the National Institute for Health and Care Excellence’s (NICE) definition of children, and Teenagers and Young adults (TYA), analysis has been conducted on the subgroups ≤25 vs >25 years old (y). Patients, disease and treatment characteristics are listed in Table 1. Results After a median follow-up of 34 months (range 6-123), the Local Control (LC) rate for the whole cohort is 85.3%; by age (≤25 y vs >25 y) LC rates are 87% for the younger group vs 78.8% for the older group. For tumours of the central nervous system (CNS), the LC rate is 84.1% (86.2% ≤ 25 y vs 79.2% > 25 y). For tumours outside the CNS the LC rate is 87.3% (88.1% in ≤ 25 y vs 75% in > 25 y). Further analysis on the major histological subgroups is listed in Table 1. The data show that LC is highest for craniopharyngioma (97.7%) in the CNS subgroup and for Ewing’s sarcoma (88.2%) in the body subgroup. Figure 1 illustrates the Kaplan-Meier survival estimates (95% Confidence Intervals) for the main groups. Conclusion The outcome of patients treated through the POP compares favourably with that reported in the literature (1). The POP has facilitated equitable access to PBT abroad for patients with complex needs from across the UK without disadvantaging patient outcome. The PCOU continues to collect data from these patients, as well as from patients who have been treated at the now established PBT service in UK. This prospective data registry will, over time, inform us further of the outcomes of patients treated with PBT to improve patient care. 1.Indelicato, DJ, et al Pediatr Blood Cancer . 2017; 64:12.