S1807
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Med Biol. 2013;58(9):2841-2859. doi:10.1088/0031- 9155/58/9/28412. Kawrakow I, Mainegra-Hing E, Rogers DWO, et al. The EGSnrc code system: Monte Carlo simulation of electron and photon transport. Tech. Rep. PIRS-701, National Research Council Canada, 2019. Keywords: Dose calculation, Macro Monte Carlo, VHEE Digital Poster 700 DIBH for Right Breast-Only Radiotherapy: Worth the Extra Minutes? Sara Poeta 1 , Antoine Desmet 2 , Daphne Van Kampen 2 , Nicolas Jullian 2 , Younes Jourani 1 1 Medical Physics, Institut Jules Bordet, Brussels, Belgium. 2 Radiation Oncology, Institut Jules Bordet, Brussels, Belgium Purpose/Objective: A recent European survey ¹ showed that 61% of centers use Deep Inspiration Breath Hold (DIBH) for left breast-only treatment, while only 16% apply it for both sides. However, published data demonstrate that this technique also benefits right-sided breast-only treatment, reducing not only lung dose but also exposure to the heart and liver ² - ⁵ . In this work, we analyzed our own data to evaluate the benefits of DIBH for right breast-only radiotherapy and to quantify its impact on treatment time. Material/Methods: In the first part of the study, CT scans in free-breathing (FB) and DIBH were retrieved from fifteen patients previously treated with radiotherapy for left-sided breast cancer and retrospectively replanned for irradiation of the right breast only. Dose-volume parameters for the ipsilateral lung, heart, and liver were evaluated. All plans were generated using the VMAT butterfly technique and normalized so that 95% of the PTV received 95% of the prescribed dose (40 Gy in 15 fractions). In the second part, treatment delivery times were collected for 20 patients (10 treated in FB and 10 in DIBH) from Mosaiq. Differences for dosimetric parameters and treatment time between FB and DIBH plans were assessed using Mann– Whitney tests, with p < 0.05 considered statistically significant.
simulated monoenergetic VHEE (50-250 MeV) impinging perpendicularly on homogeneous and heterogeneous academic phantoms using pencil, spot (0.1 cm radius), or squared (5 x 5 cm2) broad beams (Fig. 1). All simulations had statistical uncertainties <1%. 3D gamma evaluations with 2%/1 mm (global) and 2%/2 mm (global) criteria and a 10% dose threshold of the maximum dose were used to compare MMC against EGSnrc calculated doses, for homogeneous and heterogeneous phantoms, respectively. Computation times were recorded.
Results: For homogeneous phantoms (Fig. 1a), gamma passing rates were >99% (2%/1 mm (global)). For heterogenous phantoms with slab inserts forming transversal interfaces (Fig. 1b), and phantoms forming inline interfaces with split slab insert (Fig. 1c), gamma passing rates were 100% (2%/2 mm (global)). MMC was 8-20 times faster compared to EGSnrc. Conclusion: We developed and validated an MMC approach for dose calculation of VHEE beams and using academic phantoms of different materials. MMC achieved good agreement compared to EGSnrc, with efficiency gain in dose calculation by one order of magnitude.Supported by the Swiss Cancer Research Foundation (KFS-5948- 08-2023). Dose calculations were performed on UBELIX (www.id.unibe.ch/hpc), the high-performance cluster at the University of Bern. References: 1. Fix MK, Cygler J, Frei D, et al. Generalized eMC implementation for Monte Carlo dose calculation of electron beams from different machine types. Phys
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