ESTRO 2025 - Abstract Book

S1023

Clinical – Head & neck

ESTRO 2025

2329

Digital Poster Effects of scheduled replanning during dose painting on organs at risk for head and neck squamous cell carcinoma Anna Liza MP de Leeuw 1 , Simon R van Kranen 1 , Jordi Giralt 2 , Yungan Tao 3 , Sergi Benavente 2 , Thanh-Vân F Nguyen 3 , Frank JP Hoebers 4 , Ann Hoeben 5 , Chris HJ Terhaard 6 , Lip Wai Lee 7 , Signe Friesland 8 , Roel JHM Steenbakkers 9 , Harry Bartelink 1 , Coen RN Rasch 10 , Jan-Jakob Sonke 1 , Olga Hamming-Vrieze 1 1 Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, Netherlands. 2 Department of Radiation Oncology, Hospital General Vall d’Hebron, Barcelona, Spain. 3 Department of Radiation Oncology, Institut Gustave Roussy, Villejuif, France. 4 Department of Radiation Oncology (Maastro), GROW School for Oncology and Reproduction, Maastricht University Medical Centre+,, Maastricht, Netherlands. 5 Division of Medical Oncology, Department of Internal Medicine, GROW-School of Oncology and Developmental Biology Maastricht University Medical Center+, Maastricht, Netherlands. 6 Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, Netherlands. 7 Department of Radiation Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom. 8 Department of Oncology and Pathology, Karolinska Institutet , Department of Head, Neck, Lung and Skin Tumors, Karolinska University Hospital, Stockholm, Sweden. 9 Department of Radiation Oncology, University Medical Center Groningen, Groningen, Netherlands. 10 Department of Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands Purpose/Objective: Dose painting (DP) utilizes nonuniform dose distribution and subvolume dose escalation that may lead to increased dose to organs at risk (OAR) in the presence of anatomical changes. In a prospective trial investigating DP in locally advanced head and neck squamous cell carcinoma (LAHNSCC), adaptive radiotherapy (ART) was scheduled after two weeks of treatment to account for anatomical changes (1). This study investigates whether ART limited OAR delivered dose in patients with LAHNSCC treated with DP. Material/Methods: This is a secondary analysis of 76 patients who were prospectively treated with DP+ART. Deformable image registration between cone beam computed tomography (CBCT) or replanning (rePLAN) CT and the baseline planning (bPLAN) CT was performed before accumulating the rePLAN and/or bPLAN dose. To eliminate the effect of ART timing or additional ad-hoc replanning, we compared two simulations: (a) accumulating bPLAN doses given over all 35 fractions (bPLANacc) and (b) an ART simulation, where rePLAN doses were accumulated from the 12 th fraction onwards (ARTacc). Dose differences between bPLANacc and ARTacc were evaluated using the Wilcoxon match pair tests. We further assessed the predictive value of dose differences at 10 fractions on dose increase ≥3Gy using the area under the ROC curve (AUC) and evaluated whether selecting patients for ART after 10 fractions would enhance ART efficacy in limiting OAR dose. Results: No significant dose differences were seen between ARTacc and bPLANacc simulations (P≥0.06, Table 1). In bPLANacc, 42% of patients had accumulated doses ≥3Gy in any of the OAR, primarily in the parotid glands (14% contra-, 24% ipsilateral) followed by the larynx (7%). With ART, delivered doses decreased in 18% of patients, but increased dose in 9% of patients (Figure 1). Accumulated dose at 10 fractions was predictive of dose increases ≥3Gy for all OAR (AUC≥0.93). Selecting patients for ART after 10 fractions significantly improved larynx dose (P=.02), but did not significantly improve dose to the parotids (P≥.18).