S1923
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
6 Department of Medical Physics, Wellbeing Services County of Central Finland, Jyväskylä, Finland
Purpose/Objective: The use of deep-inspiration breath hold (DIBH) aims to reduce lung toxicity for right-sided node positive breast cancer patients [1][2]. While DIBH often reduces the lung dose parameters compared to free breathing (FB), quantifying this benefit is challenging due to the non-uniform expansion of the lung. This has been shown to slightly diminish the benefit of DIBH in volumetric modulated arc therapy (VMAT) [3], but currently no such evaluation exists for intensity- modulated radiation therapy (IMRT), which is also commonly used for node-positive breast cancer. Therefore, this study evaluates the impact of non- uniform lung expansion on DIBH lung dose in IMRT using deformable image registration (DIR). Material/Methods: IMRT treatment plans were generated in both DIBH and FB CT images covering the right breast, supraclavicular and internal mammary nodes for 19 patients. The plans were optimized to achieve identical dosimetric quality criteria. A DIR between the ipsilateral lung in DIBH and FB images was generated. First, DVH parameters (V16Gy, V8Gy and V4Gy) were compared between the DIBH and FB plans. Second, DIR was used to transform these DIBH isodose volumes to FB anatomy, generating DIR-corrected DVH values, thereby bypassing the confounding effect of non-uniform lung expansion. Finally, DIR-corrected DVH values were compared with the corresponding FB values. Wilcoxon test was used for statistical testing between DIBH, FB and DIR parameters. Results: Compared to FB, DIBH initially reduced the DVH parameters by a median of 14-16% (Table 1, Figure 1). When accounting for the non-uniform lung expansion with DIR, the median relative reduction was between 6-8%. A similar effect was previously observed with VMAT [3].Table 1: Relative differences in lung DVH parameters for DIBH and DIR-correction compared to FB. Bolded values and asterisks (*) denote a statistical significance versus FB values (p < 0.05) and DIBH values (p < 0.01), respectively. VMAT values for this cohort were adopted from previous work [3].
Figure 1: Ipsilateral lung DVH parameters in DIBH, DIR- corrected DIBH and FB with IMRT. Conclusion: DIBH reduces ipsilateral lung dose in IMRT for right- sided breast cancer with nodal involvement. However, the apparent benefit of DIBH is reduced to approximately half when accounting for the non- uniform lung expansion. DIR enables a more accurate assessment of the true dosimetric impact of DIBH. The future steps aim to increase the cohort size and model the clinical impact of this dose reduction on the incidence of pneumonitis. References: [1] Desai N et al. Nationwide Trends in Heart-Sparing Techniques Utilized in Radiation Therapy for Breast Cancer. Adv Radiat Oncol 2019;4:246-52[2] Chiril ă M et al. Organ-sparing techniques and dose-volume constrains used in breast cancer radiation therapy - Results from European and Latin American surveys. Clin Transl Radiat Oncol 2024;46:100752[3] Mankinen M et al. The benefit of DIBH on irradiated lung volume is overestimated in right-sided breast cancer VMAT with node involvement. Phys Med 2025;137:105095 Keywords: treatment planning, pulmonary toxicity Evaluating the potential of a one-field-per-fraction approach to achieve ultra-high dose rates (UHDR) with very high-energy electrons (VHEE) Flaminia Quattrini 1 , Till T Böhlen 2 , Alberto Burattini 3 , Gaia Franciosini 4 , Laura Frassi 1 , Michela Marafini 5 , Raphaël Moeckli 2 , Vincenzo Patera 4 , Angelo Schiavi 4 , Luana Testa 1 , Marco Toppi 4 , Giacomo Traini 6 , Arianna Vannucci 5 , Alessio Sarti 4 1 Department of Physics, Sapienza University of Rome, Rome, Italy. 2 Institute of Radiation Physics, Lausanne University Hospital and Lausanne University, Lausanne, Switzerland. 3 Specialty School in Medical Physics, Sapienza University of Rome, Rome, Italy. 4 Department of Basic and Applied Sciences for Engineering, Sapienza University of Rome, Rome, Italy. 5 Historical Museum and Research Center “E. Fermi”, Historical Museum and Research Center “E. Fermi”, Proffered Paper 3208
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