The dosimetric and radiobiological effects of rotational errors in breast cancer radiotherapy

This study aimed to assess the dosimetric and radiobiological consequences of rotational errors in breast cancer radiotherapy.

A retrospective analysis involving 80 breast cancer patients was performed. We simulated 124 rotational scenarios across three axes (yaw, pitch, and roll) to generate rotated dose distributions, then evaluated their dosimetric effects alongside tumor control probability (TCP) and normal tissue complication probability (NTCP) for the target and organs at risk (OARs).

Rotational errors caused significant dose deviations. The D95 for PTV, heart, ipsilateral lung, contralateral breast, and left anterior descending artery (LAD_V40) in rotated dose distributions showed statistical significance compared to the original dose (p < 0.05), except for LAD_V40 in the whole-breast radiation therapy (WBRT) _left4005 cohort (p = 0.058). LAD_V40 and PTV_sc were primarily affected in left-sided breast cancer, while PTV_sc and PTV_cw were predominantly affected in right-sided breast cancer. TCP decreased from 0.91 to 0.81 in the WBRT₄₀₀₅ cohort, from 0.95 to 0.70 in the WBRT₅₀₀₀ cohort, and from 0.87 to 0.23 in postmastectomy radiation therapy (PMRT)₅₀₀₀ cohort. NTCP for the heart increased from 2.08 × 10^-14 to 5.78 × 10^-10, and NTCP for the lung increased from 1.82 × 10^-3 to 1.37 × 10^-2. When single-axis rotations were involved, the pitch direction was more likely to cause dose deviations. For multi-axis (≥2) rotations, opposite-direction yaw and pitch rotations in left-sided breast cancer and same-direction yaw and pitch rotations in right-sided breast were more prone to exceeding dose limits.

The dosimetric and radiobiological analysis of rotational errors demonstrated that rotational errors (particularly in pitch and yaw) induce significant dosimetric deviations, compromising tumor control probability and increasing normal tissue complication probability. It identifies rotational axes requiring correction during multi-axis rotations and provides recommendations for prioritizing targets versus organs at risk during image-guided registration. Implementing these corrections and prioritization strategies is essential for optimizing therapeutic efficacy in breast radiotherapy.