S1815
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
respectively, between 2 cm and 20 cm depths. In the evaluation of MLC aperture width, the calculated MLC tr remained unchanged with depth for fully closed to ≤ 1 cm aperture widths but varied with depth for aperture widths ≥ 1.5 cm (Fig. 2).
carcinoma – A feasibility study. Int J Hyperthermia. 2018;34(7):994–1001. doi:10.1080/02656736.2018.1454610[3] Hasgall PA et al. IT’IS Database for thermal and electromagnetic parameters of biological tissues. Feb 2022. Available: https://itis.swiss/database Keywords: Hyperthermia, Uncertainty analysis, robustness Digital Poster 1074 Evaluation of calculation accuracy of MLC transmission for depth Moe Tsujimura 1 , Yusuke Saeki 2,1 , Okihiro Motoda 2 , Makiko Higuchi 2 , Kiyona Aramaki 1 , Mana Sugimoto 1 , Sayaka Yamashita 1 , Tetsukazu Kiriyama 3 , Kuniaki Katsui 4 , Yoshinori Tanabe 5 1 Radiological Technology, Okayama University, Okayama, Japan. 2 Radiological Technology, Kawasaki Medical School Hospital, Kurashiki, Japan. 3 Radiology, Uwajima City Hospital, Uwajima, Japan. 4 Radiology, Kawasaki Medical School, Kurashiki, Japan. 5 Radiological Technology, Graduate School of Health Sciences, Okayama, Japan Purpose/Objective: In Intensity Modulated Radiation Therapy, MLC transmission (MLC tr) and leaf-end transmission influence the administered dose, even at low levels. The registered MLC tr and dosimetry leaf gap at 10 cm depth in the treatment planning system (TPS) may differ between the calculated and actual dose at different depths. This study evaluates the calculation accuracy of MLC tr in the depth direction. Material/Methods: MLC tr was evaluated at five depths (2, 5, 10, 15 and 20 cm) using 6 MV and 10 MV photon beams, two calculation algorithms (Anisotropic Analytical Algorithm [AAA] and Acuros XB [AXB]), three linear accelerators (TrueBeam and Clinac), and two versions of the TPS Eclipse (ver.16 and ver.18). The difference in calculated MLC tr between versions was evaluated at 2.5 cm off-axis in a completely closed half field (10 × 5 cm ² ) at five depths, with a source-to-chamber distance (SCD) of 100 cm. In the completely closed irradiation field at 5 cm off-axis, MLC tr along the isocenter axis was measured using a Farmer chamber and calculated in the TPS. For irradiation field sizes of 10 cm × 0.1, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0 cm (MLC aperture width) at 5 cm off-axis, MLC tr was calculated in the TPS at the five depths. Results: In the half-field evaluation, the calculated MLC tr showed a strong correlation (> 0.99) between Eclipse ver.16 and ver.18 (Fig. 1). The difference in measured MLC tr for 6 MV and 10 MV was 13.1% and 4.1%,
Conclusion: The trend of MLC tr with depth showed a strong correlation between Eclipse ver.16 and ver.18. In the fully closed aperture field width, the measured MLC tr changed with depth, whereas the calculated MLC tr did not change. TPS-calculated MLC tr may be inaccurate for very small aperture widths (approximately 0–2 cm). Keywords: MLC transmission, MLC parameter, RTPS Digital Poster 1075 Feasibility of EMBRACE II external-beam dose constraints for cervical cancer Ida Jacobsson 1 , Niina Rintelä 1 , Jeanette Wolke 1 , Åsa Carlsson Tedgren 1,2 , Kristina Hellman 2,3 , Eva Onjukka 1,2 1 Department of Nuclear Medicine and Medical Physics, Karolinska University Hospital, Stockholm, Sweden. 2 Department of Oncology-Pathology, Karolinska Institutet, Stockholm, Sweden. 3 Department of Gynaecologic Cancer, Theme Cancer, Karolinska University Hospital, Stockholm, Sweden Purpose/Objective: The purpose of this study was to investigate the feasibility of meeting external-beam (EBRT) dose constraints from the EMBRACE II protocol for cervical cancer patients. Material/Methods: EMBRACE II-based EBRT dose constraints were introduced for rectum and bladder in our clinic in 2024, complementing the pre-existing constraint for bowel bag. As the hard constraints in the protocol are considered compulsory, the focus of the evaluation was on the compliance with the soft constraints (listed in the table). The bowel, as defined in the protocol,
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