ESTRO 2023 - Abstract Book

S825

Monday 15 May 2023

ESTRO 2023

For each patient, a traditional plan was generated in the planning scenario (pCT) using 5 mm as PTV margin; a “MultipleCT plan” was created using 3mm as CTV-to-PTV margin and by including 5 additional CTs (Figure 1), four simulating the shift of PTV by 5 mm in anterior, posterior, superior and inferior direction, and one (CT75) simulating an expansion of bladder and rectum by 0.24 and 0.27mm, respectively. These values represent the 75th percentile of collected variations of these OARs in a subgroup of RADIOSA-enrolled pts. Both plans simulated a 30Gy/3fx VMAT treatment optimized in Raystation v11.0 according to Timmerman constraints and doses calculated with CCC algorithm. The two strategies were compared (i) on the nominal scenario (sCT) in terms of target coverage, PTV homogeneity index (HI), and constraints compliance; (ii) in terms of robustness, simulating a 0.52 mm shift of the patient in all the directions; (iii) on the CT75, in terms of variations in bladder/rectum D1.

Results Median value in the considered parameters on pCT and in the worst scenario (WS) across all pts can be seen in Table 1 for both strategies. Despite the smaller margin used, the proposed optimization method provided plans that can meet all constraints and clinical goals. In addition, at the robustness evaluation, aRO plans showed smaller variations between pCT and WS for all the considered parameters, pointing the increased robustness of the novel optimization method. Interestingly, HI variations resulted smaller for aRO plans, as well as rectum and bladder D1 variations at the dose recalculation on CT75.

Conclusion These preliminary data suggest that inclusion of synthetic CTs as additional scenarios in the optimization process provides plans that can meet clinical goals despite the smaller PTV margins. In addition, aRO plans resulted more robust against changes in PTV position and anatomical variations, thus increasing the confidence in treatment delivery and potentially allowing for future dose escalation approaches. PD-0977 Automation of prostate treatment planning with template dose mimicking constraints R. Vauclin 1 , J. Prunaretty 2 , N. Bus 1 , E. Mengin 1 , R. Marini Silva 1 , H. Kallala 1 , N. Paragios 3 , P. Fenoglietto 2 1 Therapanacea, Physics, Paris, France; 2 Institut du Cancer de Montpellier, Department of Radiation Oncology, Montpellier, France; 3 Therapanacea, CEO, Paris, France

Purpose or Objective