S1883
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Keywords: RapidArcDynamic Breast Dosimetry
Material/Methods: Datasets of 32 patients with left-sided breast cancer and treated with 26 Gy in 5 fractions (19 in free breathing (FB), and 13 with deep inspiration breath hold (DIBH)) were included in the present study. For each case, three plans were generated: IMRT, VMAT, and RAD. PTV coverage and organs at risk dose distribution were calculated and compared between techniques for both FB and DIBH. Results:
Digital Poster 2360 Delivered dose reconstruction with differential motion for the DESTINATION trial Björn Eiben 1 , Alex Dunlop 1 , Alison C. Tree 2 , Emilia Persson 3,4 , Simeon Nill 1 , Uwe Oelfke 1 1 Joint Department of Physics, The Royal Marsden NHS Foundation Trust and The Institute of Cancer Research, London, United Kingdom. 2 Department of Radiotherapy, The Royal Marsden HNS Foundation Trust and The Institute of Cancer Research, London, United Kingdom. 3 Department of Hematology, Oncology, and Radiation Physics, Skåne University Hospital, Lund, Sweden. 4 Department of Translational Medicine, Lund University, Malmö, Sweden Purpose/Objective: The prostate trial DESTINATION1 combines hypo- fractionation, margin reduction, dose de-escalation, and focal boost to a dominant intra-prostatic lesion (DIL) in one study protocol. This was enabled by daily treatment adaptation to inter-fractional anatomical changes using the Unity MR-Linac workflow (Elekta AB, Stockholm, Sweden) resulting in increased dose delivery precision. In DESTINATION the primary endpoint is defined as the coverage of the DIL (D90%(GTV+4mm) ≥ 42Gy) assessed on the anatomy captured with a post-treatment MR image (pMRI). However, this strategy does not evaluate the actually delivered dose since the pMRI represents only one time-point2. Here we evaluate a delivered-dose reconstruction framework that utilises treatment logfiles and cine-MR images (cMRI) to compute an accurate reconstruction of the delivered dose to individual structures with differential motion. Material/Methods: We analysed 66/70 fractions from 14 patients enrolled in DESTINATION. Patients were prescribed 45Gy/5f to the GTV+4mm and 30Gy/5f to the prostate including the proximal SV.The reconstruction framework integrates with the research TPS Monaco v6.09.01 (Elekta AB, Stockholm, Sweden) and accounts for differential motion by representing each ROI by a cloud of dose-reconstruction points (CDRP). Such CDRPs are individually translated according to cMRI- derived motion3. The delivered dose is reconstructed using treatment logfiles and the Monte-Carlo dose engine GPUMCD (Elekta AB, Stockholm, Sweden) using a shape-sampling strategy4.To quantify the effect of differential motion between the prostate and rectum, the delivered dose was also reconstructed with an iso- centre shift method (ISO-shift) which assumes the complete patient anatomy moves with the target, and, to generate a zero-motion baseline dose, we
PTV coverage (D95% ≥ 95%; acceptable D90% ≥ 95%) goals were met by all 3 techniques. For FB plans, compared to IMRT and VMAT, RAD allowed a better sparing of maximum dose to the left anterior descending artery (LADMax) (respectively for RAD, IMRT and VMAT: mean 5.3 vs 14.6 vs 8.3Gy p <0.01) and heart volume receiving 7 Gy (VH7Gy) (0.3% vs 3.7% vs 2.6% p<0.01); the Dmean to the heart was comparable with IMRT and RAD and lower compared to VMAT plans (1.1Gy vs 1.3Gy vs 1.9Gy p<0.01). For DIBH plans, IMRT achieved an optimal sparing of heart and lung with doses to LADMax comparable to RAD and VMATplans (5.4Gy vs 4.3 Gy vs 3Gy p>0.1). Contralateral doses to lung and breast were better for IMRT plans in both FB and DIBH. Conclusion: This study showed that in ultrahypofractionated left- sided breast radiotherapy, RAD provides superior sparing of the V7Gy heart and LADMax doses compared to IMRT and VMAT. Those differences are especially visible in FB. For DIBH plans those differences are smaller and IMRT remains the preferred technique offering minimal irradiation of the heart and controlateral organs. References: Hubley, E., Koger, B., Salerno, M., Scheuermann, Characterization of a treatment plan optimization algorithm for VMAT with integrated static-angle ports. Medical Physics 120, e139, 1.10.2024Clark, R., Magliari, A., Rosa, L., Li, T., Beriwal, S., & Cozzi, L, Comparison of advanced dynamic arc therapy with collimator rotation and fixed integrated gantry positions to the standard of care across five treatment sites. Department of Medical Affairs, Varian, Palo Alto, USA, 18.06.2025Hubley, E., Archibald-Heeren, B., Koivumäki, T., Baron, B., Billaudeau, A., Costa, Rethinking breast irradiation using volumetric modulated arc therapy with the integration of static angle ports and dynamic collimator. Medical Physics 120, S217, 1.10.2024
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