Nihon Hoshasen Gijutsu Gakkai zasshi · 2026
[Impact of the Number of Subfields in an Automatic Field-in-field Technique on Dose Distribution and Delivery Efficiency in Tangential Whole-breast Irradiation].
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Miura Hideharu, Ochi Masanori, Kenjo Masahiro, Ozawa Shuichi
Аннотация
PURPOSE: This study aimed to evaluate the impact of increasing the number of automatic field-in-field (FIF) subfields per tangential beam on dose distribution and delivery efficiency in tangential whole-breast irradiation.
METHODS: Ten women with left-sided early breast cancer treated under deep inspiratory breath-hold were retrospectively selected, and tangential whole-breast irradiation plans were generated using the RayStation treatment planning system. Beam arrangement and dose normalization conditions were kept identical, while only the number of Auto FIF subfields per beam was varied from 0 to 4 (FIF0-FIF4). To ensure coverage of the evaluation clinical target volume (CTV_eval), dose was normalized to an open tangential plan. Evaluated dosimetric parameters were CTV_eval, homogeneity index (HI), body maximum dose and D1cc, absolute V40Gy of the left lung, and total monitor units (MUs). Pairwise comparisons between adjacent FIF levels were performed using Wilcoxon's signed-rank tests.
RESULTS: CTV_eval dose remained stable for all FIF settings. HI improved stepwise from FIF0 through FIF3, with no further significant improvement at FIF4. The body maximum dose decreased significantly from FIF0 to FIF1, and body D1cc showed significant improvement up to FIF2. Absolute left lung V40Gy decreased markedly from FIF0 to FIF1. Total MUs increased monotonically with each additional subfield, with significant stepwise increases through FIF3 but no further significant increase at FIF4.
CONCLUSION: Increasing the number of Auto FIF subfields improved whole-breast dose homogeneity, but using more than three subfields per beam yielded minimal additional dosimetric benefit while increasing MU. A setting of approximately two to three Auto FIF subfields per beam appears to offer a reasonable balance between plan quality and delivery efficiency.
METHODS: Ten women with left-sided early breast cancer treated under deep inspiratory breath-hold were retrospectively selected, and tangential whole-breast irradiation plans were generated using the RayStation treatment planning system. Beam arrangement and dose normalization conditions were kept identical, while only the number of Auto FIF subfields per beam was varied from 0 to 4 (FIF0-FIF4). To ensure coverage of the evaluation clinical target volume (CTV_eval), dose was normalized to an open tangential plan. Evaluated dosimetric parameters were CTV_eval, homogeneity index (HI), body maximum dose and D1cc, absolute V40Gy of the left lung, and total monitor units (MUs). Pairwise comparisons between adjacent FIF levels were performed using Wilcoxon's signed-rank tests.
RESULTS: CTV_eval dose remained stable for all FIF settings. HI improved stepwise from FIF0 through FIF3, with no further significant improvement at FIF4. The body maximum dose decreased significantly from FIF0 to FIF1, and body D1cc showed significant improvement up to FIF2. Absolute left lung V40Gy decreased markedly from FIF0 to FIF1. Total MUs increased monotonically with each additional subfield, with significant stepwise increases through FIF3 but no further significant increase at FIF4.
CONCLUSION: Increasing the number of Auto FIF subfields improved whole-breast dose homogeneity, but using more than three subfields per beam yielded minimal additional dosimetric benefit while increasing MU. A setting of approximately two to three Auto FIF subfields per beam appears to offer a reasonable balance between plan quality and delivery efficiency.