S1726
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
and neck cancer. Radiother Oncol. 2011;101(3):351- 355.3. Welz et al. Dose escalation to hypoxic subvolumes in head and neck cancer: A randomized phase II study using dynamic [18F]FMISO PET/CT. Radiother Oncol. 2022;171:30-36.4. Mesny et al. Towards tumour hypoxia imaging: Incorporating relative oxygen extraction fraction mapping of prostate with multi-parametric quantitative MRI on a 1.5T MR-linac. J Med Imaging Radiat Oncol. 2024;68(2):171-176. Keywords: dose escalation, proton therapy, hypoxia
proton therapy (IMPT) and proton arc therapy (PAT) plans with prescription doses of 70 Gy(RBE) and 54.25 Gy(RBE) to the high-risk and low-risk CTV (IMPTConv and PATConv) and with a 10% prescription dose escalation in hypoxic sub-volumes (IMPTEsc and PATEsc). Treatment plan evaluation included target and organ-at-risk (OAR) doses as well as tumor control probabilities (TCPs) calculated conventionally (TCPConv) and under consideration of hypoxia- induced radioresistance (TCPHyp). TCP calculations were repeated with up to 405 reported model parameter value sets to account for considerable uncertainties in model parameter values.
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Towards consensus on practical probabilistic evaluation metrics for clinical decision-making Jenneke I de Jong 1,2 , Steven J.M. Habraken 3,2 , Erik W Korevaar 4 , Mirko Unipan 5 , Alejandra Méndez Romero 1,2 , Edwin Oldehinkel 4 , Michiel Kroesen 2,1 , Roel J.H.M. Steenbakkers 4 , Yvonne L.B. Klaver 2,3 , Sebastiaan Breedveld 1 , Mischa S Hoogeman 1,2
Results: Results: During IMPT and PAT, dose escalation increased hypoxic sub-volume TCPConv by (4.6±1.2) percentage points (pp) and (4.1±0.5) pp, respectively (both p=0.002). Dose escalation increased TCPHyp by (8.6±0.7) pp during IMPT and (8.0±0.5) pp during PAT (both p=0.002). Compared to the patients’ clinical photon therapy treatment plans, mean OAR doses were reduced by (13.6±9.3)Gy(RBE) by IMPTConv, (14.4±10.5)Gy(RBE) by PATConv, (9.9±10.5)Gy(RBE) by IMPTEsc, and (10.4±12.9)Gy(RBE) by PATEsc (all p=0.002). TCP and OAR data for all patients is shown in Figure 2.
1 Radiotherapy, Erasmus MC Cancer Institute, Rotterdam, Netherlands. 2 Medical Physics &
Informatics, HollandPTC, Delft, Netherlands. 3 Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands. 4 Radiation Oncology, University Medical Center Groningen, Groningen, Netherlands. 5 Radiation Oncology, Maastro, Maastricht, Netherlands Purpose/Objective: Previous research has shown that probabilistic planning in IMPT improves the trade-off between target coverage and OAR sparing [1]. However, several challenges remain before clinical implementation: (1) the difficulty of presenting extensive probabilistic evaluation data in a form that supports clinical decision-making, and (2) the need to calibrate probabilistic CTV goals with respect to current clinical practice, with a lack of consensus on optimal calibration method. In this study, we compared calibration methods for the probabilistic CTV goal and develop practical probabilistic evaluation metrics with clinicians. Material/Methods: 20 neuro-oncological IMPT patients from center 1 and 20 curative HNC IMPT patients from center 2 were included. For each clinical plan, polynomial chaos expansion was applied to simulate 10,000 fractionated treatments, deriving probability distributions for relevant DVH parameters. First, probabilistic CTV goal calibration was performed using both a volumetric (volume receiving at least 0.95Dpres with 90% probability) and a dosimetric approach (dose received by 98% of the CTV volume with 90% probability).Second, four different probabilistic evaluation metrics were developed for all clinical goals
Conclusion: Conclusion: During IMPT and PAT, dose escalation improved TCPs while reducing healthy tissue doses compared to the patients’ clinical photon therapy treatment plans. MRI-informed hypoxia-based dose escalation was therefore found to be feasible and is expected to partially counteract hypoxia-induced radioresistance. References: 1. Nordsmark et al. Prognostic value of tumor oxygenation in 397 head and neck tumors after primary radiation therapy. An international multi- center study. Radiother Oncol. 2005;77(1):18-24.2. Madani et al. Maximum tolerated dose in a phase I trial on adaptive dose painting by numbers for head
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