ESTRO 2022 - Abstract Book

S232

Abstract book

ESTRO 2022

Dose distributions from 10 anonymized and previously treated patients were adjusted, using the in-house developed tool, and re-imported to the clinical treatment planning system (TPS). A paired blinded observer study was performed with two oncologists set to choose which of the two treatment plans, they would prefer, see Figure 1 for an example where A1 is the adjusted treatment plan and B1 the clinical. The oncologists were also asked to do graded comparisons of the treatment plans with regards to homogeneity, planning target volume (PTV) coverage and organ-at-risk (OAR)/normal tissue sparing on a five step Likert scale. The treatment plans were compared on their dosimetric indices, the dose that 90% of the PTV receives ( D 90% ); the volume in the PTV that receive 100% ( V 100% ) and 200% ( V 200% ) of the prescription dose and the dose that the hottest 0.1 cm 3 volume of urethra is receiving ( D 0.1cc ). The homogeneity of the treatment plans was compared using the size of the four largest contiguous areas of dose higher than 200% of the prescription

dose.

Results The adjusted treatment plan was preferred in 15 of 20 cases. The observer study showed that PTV coverage and OAR/normal tissue sparing was considered equal for the clinical treatment plan compared to the adjusted. For homogeneity, there was a tendency in the observer study that the adjusted treatment plan was considered better. The dosimetric indices showed small differences in PTV coverage ( D 90% and V 100% ) and urethra sparing ( D 0.1cc ). The adjusted treatment plan had significantly smaller V 200% than the clinical treatment plan 9,5 cm 3 compared to 10,4 (p=0.002). The four largest contiguous areas of dose higher than 200% of the prescription dose was on average at least 69% smaller for the adjusted treatment plan compared to the clinical. Conclusion The in-house adjustment tool improves the clinical treatment plans upon homogeneity. The study will be expanded to include more observers and more prostate cases during 2021.

OC-0275 Incorporating control of contiguous high-dose volumes in automated optimization for prostate BT

J.L. Commandeur 1 , A. Bouter 1 , L.R. Dickhoff 2 , D.L. Barten 3 , H. Westerveld 3 , B.R. Pieters 3 , T. Alderliesten 2 , P.A. Bosman 1

1 Centrum Wiskunde & Informatica, Life Sciences and Health, Amsterdam, The Netherlands; 2 Leiden University Medical Center, Radiation Oncology, Leiden, The Netherlands; 3 Amsterdam UMC University of Amsterdam, Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective In 2020, ‘BRachytherapy via artificially Intelligent GOMEA-Heuristic based Treatment planning’ (BRIGHT) for prostate HDR BT was clinically introduced. BRIGHT is a bi-objective treatment planning method that finds a set of high-quality, patient- specific treatment plans (TPs) with different trade-offs between clinical target coverage and organ sparing, by directly optimizing the dose volume indices (DVIs) in the clinical protocol. However, in the clinic, manual adjustments of BRIGHT TPs are still done to meet additional patient specific aims. Particularly, this includes minimization of contiguous high-dose volumes, i.e., hotspots (HSs). We therefore aim to incorporate control of HS volumes in BRIGHT, while minimally impacting obtainable DVI values. Materials and Methods We augment BRIGHT with a third objective to minimize HSs. For this, we define an HS as ‘a contiguous volume of >0.1 mL outside catheters receiving >300% in target volumes: prostate and seminal vesicles, or >200% in normal-tissue around target volumes of the prescribed dose’. We tailored a graph-based method, which uses a connected component algorithm (Afforest), to determine HSs. The graph consists of dose calculation points (DCPs) as nodes and edges between close ( ≤ 0.5 mm) neighbouring DCPs. DCPs are randomly sampled locations where the dose is calculated (to compute the DVIs). The third objective in tri-objective BRIGHT is the sum of HS volumes (metric 1). For comparison, we also consider as third objective a more efficiently computable metric, which however ignores whether the high-dose volume is contiguous: the sum of V 300% of the target volumes and V 200% of normal tissue (metric 2). We compare bi-objective BRIGHT with both tri-objective BRIGHT versions on a data set of 11 prostate cancer patients by

retrospectively planning single-dose HDR BT with

Results