ESTRO 2020 Abstract Book

S607 ESTRO 2020

Paolo II, UO di Fisica Sanitaria, Campobasso, Italy ; 3 Dipartimento di Medicina Specialistica Diagnostica e Sperimentale- DIMES- Azienda Ospedaliera-Universitaria S.Orsola-Malpighi, UO di Radioterapia, Bologna, Italy ; 4 PO ‘Veneziale’, UO di Oncologia Medica, Isernia, Italy ; 5 PO ‘Cardarelli, UO di Urologia, Campobasso, Italy ; 6 Università Cattolica S. Cuore- Fondazione Giovanni Paolo II, UO di Radiologia, Campobasso, Italy ; 7 Fondazione Policlinico Universitario A. Gemelli- IRCCS, UOC di Radioterapia- Dipartimento di Scienze Radiologiche- Radioterapiche ed Ematologiche, Roma, Italy Purpose or Objective To determine the efficacy and safety of stereobody radiosurgery (SRS) in the treatment of isolated bone metastases (mts) in prostate cancer (PC) patients (pts). Material and Methods Data from PC patients with <3 bone mts undergone single fraction stereotactic radiosurgery (SRS-DESTROY-2 phase I clinical trial) as exclusive treatment, or boost (SRS- vertebra phase I clinical trial) after conformal external beam radiotherapy (3D-CRT), were collected and analyzed. From October 2010 to December 2018, as per trials design, PC pts received SRS according to skeletal site (vertebral versus other bone lesions). In particular, vertebral mts received a 3D-CRT dose of 25 Gy in 10 fractions followed by a SRS dose of 8 Gy, 10 Gy, or 12 Gy, in subsequent escalated cohorts; other bone lesions were treated by subsequent escalated SRS doses ranging from 12 Gy to 24 Gy. Best radiologic response to SRS was evaluated by computed tomography (CT) scan, Magnetic Resonance (MR) or positron tomography (PET) scan, and classified according to the RECIST or PERCIST criteria. Objective response rate included complete response (CR) and partial response. Actuarial local control (LC) was defined as the time interval between the date of SRS and the date of inside SRS field relapse/progression of disease or the last follow-up visit. Toxicity was evaluated by CTC-AE scale. Results Forty-six pts carrying a total of 68 bone mts were selected for the enrolment. The median age was 73 years (range: 56-86), and the majority of patients (96%) presented Eastern Cooperative Oncology Group performance status 0-1. The most frequent anatomical districts were the pelvis (40%) followed by vertebral mts (35%), and a miscellanea of other sites, mainly ribs, sternum and scapula (17,25%). Overall, dose prescription to the Planning Target Volume ranged from 12 to 37 Gy (median dose: 24 Gy) and all lesions were treated with a volumetric arc radiotherapy technique. With a median follow-up of 18 months (1-66) no severe (> grade 3) acute or late toxicities were recorded, with only 3 pts reporting G2 toxicity (2 esophagitis and 1 ematological). The overall objective response rate was 75.0% (CI 95%:60.1-84.8) with a CR rate of 62%. The 2-years actuarial LC was 94% (median not reached). Conclusion This study confirms the activity and safety of SRS in the treatment of bone metastases in oligometastatic PC pts. Optimal SRS schedules should be defined taking into account the need to guarantee the best personalized radiation dose. PO-1154 Assessing the potential gains of a decision support system for primary treatment of prostate cancer Y. Van Wijk 1 , B. Ramaekers 2 , C. Oberije 3 , J. Van Roermund 4 , B. Vanneste 5 , P. Lambin 3 1 Maastricht university, School for Oncology and Developmental Biology, Maastricht, The Netherlands ; 2 Maastricht university medical centre+, Clincial Epidemiology and Medical Technology Assessment, Maastricht, The Netherlands ; 3 Maastricht University,

Department of Precision medicine the D-lab, Maastricht, The Netherlands ; 4 Maastricht university medical centre+, Oncologiecentrum, Maastricht, The Netherlands ; 5 Maastricht university medical centre+, Department of Radiation Oncology MAASTRO Clinic, Maastricht, The Netherlands Purpose or Objective As primary treatment for prostate cancer (PCa), radical prostatectomy (RP) and external beam radiotherapy (EBRT) are two of the main treatment choices. Studies have found that survival after either treatment is similar, but the risks of different toxicity outcomes are not the same (Hamdy 2016). We hypothesized that there is a clinically relevant increase in cost-effectiveness (CE) when using a multifactorial decision support system (mDSS) (Lambin 2013) to choose treatment compared to randomized treatment selection (i.e. choice between RP and EBRT based on coincidence). This would lead to improved patient quality of life and be a step toward individualized care. The aim of this study was to develop a model-based mDSS that compares patient specific outcomes in terms of quality adjusted live years (QALYs) between RP and EBRT and to perform an initial CE analysis comparing the mDSS to randomized treatment selection. Material and Methods We developed a state transition model to calculate the CE of RP compared to EBRT (Figure 1). The transition probabilities from healthy to recurrence and from healthy to toxicity (impotence, urinary incontinence and rectal bleeding) were calculated from prediction models. These models use clinical parameters (such as age, BMI, pre- treatment PSA, Gleason score) to predict the probability of an event after a set period of time. The toxicity models all predict long term side effects, and we assumed them to be life-long. The time horizon was taken to be 10 years, with a cycle time of one month. We performed analyses on a synthetic dataset of 1500 patients, with realistic clinical parameters. For the CE analyses, we compared patient treatment allocation based on the mDSS versus random allocation. For the mDSS arm, we selected the treatment with the highest number of QALYs. We conducted a multivariate probabilistic sensitivity analysis to assess model uncertainty, using a Monte-Carlo simulation. From this simulation, we calculated the CE acceptability curve.

Figure 1: The structure of the state transition model