S2002
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Muñiz 1 , Ana M. Vilchez-Simó 1 , Daniela Medal- Francesh 2 , Victor Muñoz-Garzón 1 , Patricia Willisch- Santamaría 1 1 Radiation Oncology, Hospital Meixoeiro, Vigo, Spain. 2 Medical Physics, Hospital Meixoeiro, Vigo, Spain
45° and 15° (p-adj = 0.05), indicating superior coverage at 45°. Additionally, D2% of the spinal cord showed a moderate negative correlation with PTV coverage at 45° (r = -0.55, p = 0.01), suggesting this angle may allow simultaneous high PTV coverage and better spinal sparing. Parotid D2% values showed weak, non- significant correlations with PTV coverage at all angles (|r| < 0.2), indicating parotid sparing was largely unaffected by collimator rotation.Considering conformity and homogeneity indices, 45° maintained comparable plan quality to 5° and 30°. 15° occasionally showed slightly reduced conformity.Overall, 45° provided robust PTV coverage and potential dosimetric benefits to the spinal cord without compromising other OARs. Conclusion: This analysis demonstrates that 45° achieves statistically significant and clinically superior PTV coverage while simultaneously reducing spinal cord D2%. The negative correlation between PTV coverage and spinal cord dose at 45° implies advantageous geometric modulation supporting both coverage and sparing. Clinical decisions should therefore weigh marginal gain in PTV coverage at 45° against individual OAR proximity or tolerance concerns. Future work should expand to explementary angles (summing to 360°) and investigate potential optimisation automation to further individualise collimator angle selection for complex cases. References: [1] G. Murtaza et al., “Optimal VMAT delivery for ELEKTA MLC beam modulator: A study of collimator rotation for head and neck planning,” vol. 51, no. 2, pp. 289–298, 2020. [Online]. Available: https://www.jmirs.org/article/S1939-8654(20)30009- 6/abstract[2] Y. H. Kim et al., “Effect of collimator angles on the dosimetric results of volumetric modulated arc therapy planning for patients with a locally-advanced nasopharyngeal carcinoma,” Journal of the Korean Physical Society, vol. 70, no. 5, pp. 5399- 5444, 2017. [Online] Available: https://link.springer.com/article/10.3938/jkps.70.539 Keywords: optimisation, collimator angle, VMAT
Purpose/Objective: Ultra-hypofractionation (26 Gy/5 fractions) is
increasingly adopted for adjuvant breast radiotherapy. This study aimed to perform a dosimetric analysis of mean heart dose (MHD) in breast cancer patients and to describe ipsilateral lung dose metrics in patients with and without boost. Material/Methods: We conducted a retrospective single-center study of breast cancer patients treated with adjuvant ultra- hypofractionated radiotherapy. Clinical, pathological, and dosimetric data were collected. Dose metrics for the heart and ipsilateral lung were obtained. MHD was compared according to laterality and the presence of a simultaneous integrated boost (SIB) using the Mann– Whitney U test. Results: A total of 116 patients (median age 63 years, range 43– 87) were included; 68.1% had right-sided disease. Most patients had early-stage tumors: pT1–T2 in 89% and pN0 in 89%. The cohort included mainly invasive tumors, with 25 patients having Ductal Carcinoma In Situ (DCIS). The majority of tumors were hormone receptor–positive, predominantly Luminal A (n=84, 72.4%). Conservative surgery was performed in 99.1% of cases, with only one mastectomy. Systemic therapy was administered according to clinical indications, including neoadjuvant chemotherapy (n=6), adjuvant chemotherapy (n=7), and adjuvant targeted therapy (n=5). Radiotherapy was predominantly delivered using 3D conformal techniques (94.8%), and a simultaneous integrated boost (SIB) was administered in 51.7% of patients (n=60). Of the 60 patients who received a simultaneous integrated boost (SIB), 46 were treated to 30 Gy and 14 to 29 Gy. Mean PTV V95% was 96.94% (range 94.68–100%). Median MHD was significantly higher in left-sided compared with right-sided irradiation: 1.41 Gy (range 0.63–2.7 Gy) vs 0.46 Gy (range 0.24–1.70 Gy), p < 0.001 (Mann– Whitney U test). No significant difference in MHD was observed between patients with and without SIB (p = 0.286). Regarding ipsilateral lung exposure, in patients without boost, the median V8 was 13.47 cc (range 3.17–18.77 cc), whereas in patients with boost, the median V12 was 12.75 cc (range 3.37–19.40 cc). Patients completed the 5-fraction regimen in a median of 5 days (range 5–9). Severe (grade 3 or higher) skin reactions were not observed. Conclusion: Adjuvant ultra-hypofractionated breast radiotherapy provides adequate target coverage with low mean
Digital Poster 4532
Dosimetric evaluation of cardiac exposure in ultra- hypofractionated adjuvant breast radiotherapy Beatriz Vázquez-Barreiro 1 , M. Luisa López-Louzara 1 , Aldara Candal-Meléndrez 1 , Xeila Bernárdez-Martínez 1 , Marta Vázquez-Lorenzo 1 , Diego A. Expósito- Rodríguez 1 , Pilar Marcos-Pérez 1 , Sara Montemuiño-
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