ESTRO 36 Abstract Book

S459 ESTRO 36 _______________________________________________________________________________________________

Material and Methods 42 patients with inoperable, stage II-III NSCLC were treated with (chemo)radiotherapy as part of the (NCT01024829) PET-boost trial. Patients received escalated doses (≥ 72 Gy) in 24 fractions consisting of either a homogenous boost to the PTV, or an inhomogeneous boost to FDG avid (≥50% SUV max ) areas. Patients whom could not be boosted received 66 Gy in 24 fractions. All patients received an FDG PET/CT scan 3 months post-treatment, which was registered to the planning CT. The lung contours minus the GTV were compared between the SUV on FDG PET and the planning CT dose. The planning CT dose was adjusted to equivalent doses in 2 Gy fractions, assuming an α/β = 3 Gy, and then binned per 5 Gy increments. The SUV was averaged over all patients per dose bin and a dose response sigmoid was fit (SUV vs Gy ) to determine upper and lower asymptotes, as well as the EC50. The linear portion of the sigmoid fit (17.6%-82.4% asymptotes difference) was applied to individual patients for linear fitting, yielding the correlation coefficient and the SUV response to an increase in dose (slope). All values were reported as median[interquartile range (IQR)]. All fits were considered significant with an alpha of 0.05. Results A positive relationship was found between SUV and post- treatment dose. A sample patient with post-treatment grade 1 pneumonitis is shown in figure 1. The sigmoidal fit (figure 2) over all patients was significant (chi-squared = 0.01) with an EC50 at 39 Gy, and lower and upper asymptotes at 0.60 SUV and 1.31 SUV, respectively. The linear portion of the sigmoidal fit (15- 60 Gy) was found to be significantly (p ≤ 0.05), highly linear in individual patients with a median correlation coefficient of 0.93[0.79-0.97]. Four patients did not have significant linear fits (p-values ranging from 0.05 to 0.13). The median SUV response per increase in dose (slope) was heterogeneous with a median of 0.0083[0.005-0.018] SUV/Gy, implying a 55 Gy to 200 Gy increase needed per SUV increase within the IQR.

increase of lung damage up to a certain threshold (60 Gy), before adopting an asymptotic relationship. Patient response in the linear fitting was heterogeneous with a greater than 3 fold difference found in the IQR. These findings may aid in post-treatment response assessment and toxicity modeling in NSCLC patients undergoing escalated dosing regimens. PO-0848 Predictors of patient-reported incontinence after prostate cancer RT: results from a cohort study C. Cozzarini 1 , N. Bedini 2 , E. Garibaldi 3 , D. Balestrini 4 , P. Franco 5 , G. Girelli 6 , I. Improta 7 , F. Palorini 8 , V. Vavassori 9 , T. Rancati 8 , R. Valdagni 2,8 , C. Fiorino 7 1 San Raffaele Scientific Institute, Radiotherapy, Milano, Italy 2 Fondazione IRCCS Istituto Nazionale dei Tumori, Radiation Oncology 1, Milano, Italy 3 Istituto di Candiolo- Fondazione del Piemonte per l'Oncologia IRCCS, Radiotherapy, Candiolo, Italy 4 Ospedale Bellaria, Radiotherapy, Bologna, Italy 5 Ospedale Regionale U.Parini-AUSL Valle d’Aosta, Radiotherapy, Aosta, Italy 6 Ospedale ASL9, Radiotherapy, Ivrea, Italy 7 San Raffaele Scientific Institute, Medical Physics, Milano, Italy 8 Fondazione IRCCS Istituto Nazionale dei Tumori, Prostate Cancer Program, Milano, Italy 9 Cliniche Gavazzeni-Humanitas, Radiotherapy, Bergamo, Italy Purpose or Objective To assess clinical and dose factors affecting the incidence of patient-reported urinary incontinence (INC) at three years after radical radiotherapy (RT) for prostate cancer of a large group of patients enrolled in a prospective, multi-centric trial in the period 2010-2014. Material and Methods Enrolled patients were treated in seven Institutions at different prescribed doses with conventional (74-80 Gy at 1.8-2 Gy/fr, CONV) or moderately hypo-fractionated RT (65-75.2 Gy at 2.2-2.7 Gy/fr, HYPO) in 5 fractions/week. Several clinical factors were collected for each patient: comorbidities, drugs, hormone therapies, previous surgeries, smoking, alcohol, age, and body mass index. In addition, the prescribed 2Gy equivalent dose (EQD2) was considered by applying an alpha-beta ratio of 0.8, 3 and 5Gy, according to values recently reported in the literature. INC was evaluated through the International Consultation on Incontinence Modular Questionnaire short form (ICIQ) filled in by the patients at start/end of RT and every 6 months until 5 years of follow up. In the current analysis, patients with ICIQ available at 30 and/or 36 months were considered (n=298;); the incidence of INC at 3 years was defined as the occurrence of an ICIQ value >12 at least once between 6 and 36 months. Univariable and backward multivariable logistic analyses were performed to build a predictive model. Results In total, 298 patients had the required minimum follow- up; patients with baseline ICIQ>12 (n=3) were excluded restricting the analysis to 295 patients (CONV: 149; HYPO: 146, 86% treated with IMRT). The median number per patients of completed questionnaires was 5 (range: 2-6): the incidence of ICIQ>12 was 5.1% (n=15) with a prevalence at 30/36 months equal to 4.1%. Main predictors at univariable analysis were age (p=0.01,OR=1.19), baseline ICIQ>0 (p=0.056, OR=2.9), previous TURP (p=0.04, OR=3.8) and EQD2 (p=0.003-0.02, OR=1.12-1.17 depending on alpha-beta). EQD2 calculated with alpha- beta=0.8Gy showed the best performances in terms of calibration plot and p-value and was included in the multi- variable analysis. Final results suggested a two-variable model including EQD2 (p=0.005,OR=1.13; 95%CI:1.04-1.24) and age (p=0.011,OR=1.19; 95%CI:1.04-1.37); the model showed good performances in terms of goodness of fit

Conclusion Strong linear and sigmoidal relationships were found between post-treatment SUV and planned dose. These results suggest that increasing dose leads to a highly linear