ESTRO 2024 - Abstract Book

S4271

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

1592

Digital Poster

Dosimetric comparison of adaptive and scheduled plans in adaptive teletherapy of prostate cancer

András Herein 1 , Domonkos Szegedi 1,2 , Ádám Gáldi 1,3 , Tamás Pócza 1 , Csilla Pesznyák 1,2 , László Gesztesi 1 , Kliton Jorgo 1,4 , Péter Ágoston 1,4 , Zoltán Takácsi-Nagy 1,4 , Tibor Major 1,4 1 National Institute of Oncology, Centre of Radiotherapy, Budapest, Hungary. 2 Budapest University of Technology and Economics, Institute of Nuclear Techniques, Budapest, Hungary. 3 Semmelweis University, Doctoral School of Theoretical and Translational Medicine, Budapest, Hungary. 4 Semmelweis University, Department of Oncology, Budapest, Hungary

Purpose/Objective:

At online adaptive treatments, in each fraction you can choose from two plans for that day's irradiation: the scheduled plan is the recalculated version of the original irradiation plan for that day's anatomy and contours, while the adaptive irradiation plan is dosimetrically optimized for that day's anatomy and contours [1]. Our aim was to compare the adaptive and scheduled radiation plans for prostate cancer patients treated with online adaptive radiation therapy, with special focus on the dose coverage of the target volume.

Material/Methods:

Five prostate cancer patients treated in 2022-2023 with Varian Ethos linear accelerator after radical prostatectomy were selected for our dosimetry study. We imported the data of all treatment fractions of these patients from the Ethos to the Varian Eclipse system. The dosimetric data of the different treatment plans were collected by an in house developed script in Eclipse system. For all patients, only the tumour bed was treated. The fractionation used during the treatment was 37x2 Gy for four patients, and 35x2 Gy for one patient, so a total of 183 fractions were analysed. For both plans of all fractions of the five patients, retrospective collection of dosimetric data was performed on the target volumes (CTV, PTV) and the most important organs at risk (bladder, rectum). The investigated parameters were the V95, V98, V100, D50 and D max for the target volumes, D50, V 30Gy , V 40Gy , V 50Gy and V 60Gy for the bladder and rectum. After testing the data series for normality, statistical analysis was performed using the Wilcoxon signed rank test.

Results:

There were significant differences in the dose coverage of the target volumes. On average, the PTV coverage of the adaptive plans was higher than that of the scheduled plans (V95: 99.91% vs. 97.47%, p<0.0001, V98: 99.32% vs. 94.09%, p<0.0001, V100: 96.19% vs. 76.96%, p<0.0001), while the maximum doses were similar (D max : 105.67% vs. 105.04%, p=0.1909). The median dose of PTV was higher for adaptive plans (101.52% vs. 100.79%, p=0.0033). Similar to PTV, for CTV, adaptive plans had on average higher coverage parameters (e.g. V100: 99.91% vs. 85.69%, p<0.0001), while the maximum value within CTV was also similar (D max : 103.37% vs. 102.95%, p=0.7295). The D50 parameter of the bladder and the rectum were significantly lower for adaptive plans (D50 B : 5.62% vs. 6.5%, p<0.001, D50 R : 10.26% vs. 14.03%, p=0.0423). All of the examined V xx parameters were significantly lower for adaptive plans except for the V 30Gy for rectum, which was similar in the two types of plans.