S802
Clinical - Lung
ESTRO 2026
Purpose/Objective: After chemoradiotherapy for lung cancer, various maintenance therapies have been implemented, increasing the importance of reducing radiation pneumonitis (RP). The correlation between dose- volume histogram (DVH) parameters for total lung, such as V20% (percentage of volume receiving ≥ 20 Gy), and RP is well established. The lower lobes play a predominant role in pulmonary ventilation and perfusion. Our recent analysis demonstrated that the absolute irradiated volume of the lower lobes receiving ≥ 20 Gy (Low-V20cc) independently predicted RP. Considering the physiological dominance of the right lower lobe, we hypothesized that right-lower- lobe-specific dose parameters might further improve the accuracy of RP prediction. Material/Methods: We retrospectively analyzed 146 patients with unresectable non-small cell lung cancer who underwent definitive radiotherapy (excluding stereotactic body radiotherapy) at our institution between August 2018 and September 2023. In the treatment planning system, the lungs were contoured by dividing them into the upper/middle lobes and lower lobes, using the major fissure as the boundary. Total lung values of V20, V5, and mean lung dose (MLD) were calculated. Additionally, the volume receiving ≥ 20 Gy was defined as RL-V20cc for the right lower lobe. RP was graded according to CTCAE v5.0, and the correlation between Grade ≥ 2 RP and each parameter was analyzed. Results: Grade ≥ 2 RP was observed in 60 patients (41%). Receiver operating characteristic (ROC) analysis revealed that the area under the curve (AUC) was highest for RL-V20cc (0.615), followed by V20 (0.612). In univariate analysis, significant correlations were observed for V20 (p < 0.01), MLD (p = 0.02), and RL- V20cc (p < 0.01). In multivariate analysis including V20, V5, MLD, RL-V20cc, age, and sex, RL-V20cc was identified as an independent predictor of Grade ≥ 2 RP (p < 0.01). To further evaluate the associations of V20 and RL-V20cc with RP, patients were stratified into three groups based on ROC-derived cut-off values: Group A (low V20 and low RL-V20cc), Group B (either low V20 with high RL-V20cc or high V20 with low RL- V20cc), and Group C (high V20 and high RL-V20cc). A significant difference was observed between Group C and the other groups (p < 0.01). Conclusion: Right-lower-lobe-specific dose parameters may serve as strong predictors of Grade ≥ 2 RP. References: Tsujino K, et al. Int J Radiat Oncol Biol Phys. 2003; 55: 110-115.Seppenwoolde Y, et al. Int J Radiat Oncol Biol Phys. 2004; 60: 748-758.Defraene G, et al. Radiother Oncol. 2017; 122: 300-306.
Conclusion: Implementing a limit to the CAA successfully reduced dose to the heart-base without significantly affecting doses to other thoracic organs. Overall, AE profiles were low and largely unchanged between cohorts, except for a numerical increase in grade 2 oesophagitis. This reflects the use of advanced radiotherapy techniques, although higher oesophagus and lung doses remained associated with an increased reporting of AEs. References: 1Fornacon-Wood I, Holley R, Crawford H, Banfill K, Marchant T, Morgan C, Turner-Uaandja H, Walker A, Kontopantelis E, van Staa T, Devaney S, Holm S, Price G, Faivre-Finn C. Developing a prospective rapid- learning methodology to evaluate the survival impact of changing radiotherapy practice to include a new heart dose limit for patients with lung cancer in a UK specialist cancer centre (RAPID-RT): a protocol. BMJ Open. 2025 Aug 27;15(8):e105519 Keywords: radiotherapy adverse event, cardiac avoidance area
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Role of right-lower-lobe-specific DVH parameters in predicting radiation pneumonitis risk after definitive radiation therapy for lung cancer Sachiko Miura, Nobuhide Wakai, youhei Kanamori, Mei Nikimoto, Nobuyoshi Inooka, Kaori Yamaki, Tetsuro Tamamoto, Fumiaki Isohashi Radiation Oncology, Nara Medical University, Kashihara, Japan
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