S1939
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
1 Radiation Oncology, UANL, Monterrey, Mexico. 2 Faculty of Medicine, UANL, Monterrey, Mexico. 3 Obstetrics, UANL, Monterrey, Mexico Purpose/Objective: To evaluate dosimetric differences among the three techniques and the total treatment time. Material/Methods: Retrospective study evaluating three patients with a diagnosis of non-melanoma skin cancer using three different techniques: helicoidal-mode VMAT, electron radiotherapy (RT Ē ), and HDR-BT with Iridium-192 using customized molds. Results: Three male patients with non-melanoma skin cancer at different anatomical sites were analyzed. Basal cell carcinoma was observed in two patients (one with a tumor on the left ear lobe and one with a tumor in the left maxillary region), and squamous cell carcinoma in one patient (fourth digit of the right hand). As shown in Table 1, dosimetric analysis demonstrated CTV coverage >100% and PTV coverage ranging from 91– 100% across all three techniques. The primary difference was observed in total treatment time, with VMAT requiring longer machine time and overall treatment duration. Conclusion: For skin cancer treatment, all three techniques analyzed provided adequate coverage of the target volume. Technique selection should take into consideration patient volume at each center to reduce machine time, as well as patient age and functional status. References: 1. Wills, R. J., Lowe, G., Jones, C. L., & Hoskin, P. J. (2021). Dosimetric comparison of volumetric modulated arc therapy (VMAT) and high-dose-rate brachytherapy (HDR-BT) for superficial skin irradiation with significant curvature in one or more planes. Strahlentherapie Und Onkologie, 197(6), 547-554. https://doi.org/10.1007/s00066-021-01759-42. Boman, E. L., Paterson, D. B., Pearson, S., Naidoo, N., & Johnson, C. (2018). Dosimetric comparison of surface mould HDR brachytherapy with VMAT. Journal Of Medical Radiation Sciences, 65(4), 311-318.
Digital Poster 3552 Dosimetric performance of Fixed and MLC collimators in robotic stereotactic radiosurgery for brain metastases Anna Pederzoli 1 , Stefano Riga 1 , Lanfranco Chirico 1,2 , Stefania Nici 1 , Martina Camilla Daniotti 1 , Francesco Puglia 1 , Martina Peretti 1,3 , Valeria Cardamuro 2,1 , Cristian Toraci 1 , Sara Pedretti 4 , Davide Tomasini 4 , Michela Buglione di Monale 4,5 , Luigi Spiazzi 1,5 1 Medical Physics Department, ASST Spedali Civili, Brescia, Italy. 2 Postgraduate School of Medical Physics, University of Milan, Milan, Italy. 3 Postgraduate School of Medical Physics, University of Padua, Padua, Italy. 4 Department of Radiation Oncology, ASST Spedali Civili, Brescia, Italy. 5 Centro per lo Studio della Radioterapia guidata dalle Immagini e dai Biomarkers (BIO-RT), University of Brescia, Brescia, Italy Purpose/Objective: CyberKnife® Stereotactic Radiosurgery (SRS) can be delivered using Fixed/Iris collimators or the InCise™ multileaf collimator (MLC). Evidence suggests that Fixed collimators may improve dose fall-off for small lesions, whereas MLC increases delivery efficiency on larger or multiple targets. This study aims to compare plans generated with Fixed vs MLC collimators in terms of conformity index (CI), heterogeneity index (HI), maximum dose (Dmax), and the absolute volume of healthy brain tissue (WB-GTV) receiving ≥ 10 Gy. Material/Methods: A retrospective analysis of CyberKnife SRS plans for brain metastases was conducted. Fifty clinical treatment plans (15 MLC and 35 Fixed) were analysed, corresponding to 75 targets, all treated within the last year at our Istitution. All treatments delivered 24 Gy in a single fraction, with 99% of the lesion volume covered by the prescription isodose, in accordance with the institutional clinical protocol. For each target, CI, HI, Dmax, and WB-GTV ≥ 10 Gy (absolute volume of healthy brain receiving ≥ 10 Gy) were extracted from Accuray iDMS (Accuray Inc., Madison, Wisconsin, USA). No replanning was performed: the aim was to capture real-world clinical decision-making in collimator selection. Statistical comparison was performed using the Mann–Whitney U test. Results: MLC plans were associated with significantly larger lesion volumes (Fixed: 0.88±1.02 cc vs MLC 2.99 ±2.96 cc; p < 0.001). Despite this, conformity (CI: Fixed 1.18±0.18 vs MLC 1.19±0.14; p = 0.535) and homogeneity (HI: Fixed 1.36±0.10 vs MLC 1.30±0.16, p=0.112) remained equivalent between the two approaches. A statistically significant difference emerged for irradiation of healthy brain tissue WB- GTV V10Gy (Fixed 5.6±3.2 cc vs MLC 7.9± 2.4; p = 0.0085). Dmax was comparable (Fixed 32.5±2.4 Gy vs
https://doi.org/10.1002/jmrs.301 Keywords: SKIN, PLANEATION,
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