P092: Estimating the dosimetric benefit of involved-node radiotherapy in comparison to involved-field radiotherapy - implications from the GHSG HD 17 trial

Table 1: Size of the planning targe volume (PTV) and dose exposure to organs at risks in comparison between involved-field (IFRT) radiotherapy and involved-node radiotherapy (INRT). Gy: Gray Question: The HD17 trial of the German Hodgkin Study Group evaluated the value of consolidative involved-node (IN)RT for patients with PET-positivity after chemotherapy and enabled a comparison between INRT and involved-field (IF)RT [1]. The present work analyzes the organs at risk (OAR) exposure of the performed RT. Methods/Material: For dosimetric evaluation, all INRT-plans in the HD 17 trial were requested and compared to a random selection of IFRT-cases in the standard arm. Dose-volume histograms (DVH), either paper-based or digital, were analyzed using SPSS (version 28, IBM, Armonk, NY, USA). For comparisons between the two RT concepts, a two-sided t-test or a Mann-Whitney U test was used with a p-value < 0.05 considered as significant. Results: In total, 148 DVH (INRT: 112, IFRT: 36) could be evaluated. Details on planning target volume (PTV) size and OAR exposure are shown in table 1. The introduction of INRT decreased the PTV size without reaching statistical significance. There was a consistent decrease in OAR-doses with INRT except for V5 in both lungs and V10 and Dmean in the right lung. Despite the dosimetric advantages, significant differences in favor of INRT could only be found for the spinal cord and thyroid. Conclusion: INRT, in comparison to IFRT, decreases PTV-size and OAR exposure and may help to comply with modern dose constraints [2]. Literature 1. Lancet Oncol. 2021 Feb;22(2):223-234. 2. Blood. 2019 Mar 21;133(12):1384-1385.