Abstract Purpose This study aimed to determine an appropriate frequency of image‐guided (IG) schedules for left‐sided postmastectomy radiotherapy by comprehensively evaluating dosimetric, radiobiological, imaging dose, and imaging‐related cost outcomes. Methods A retrospective analysis of 20 patients treated with volumetric modulated arc therapy (VMAT) was conducted. Virtual CT images were generated by deforming the pCT to daily cone‐beam computed tomography (CBCT) using deformable image registration. Accumulated dose, tumor control probability (TCP), normal tissue complication probability (NTCP), imaging dose, and imaging‐related cost were compared among six IG schedules: no image‐guided (NIG), weekly image‐guided (WIG), twice‐weekly image‐guided (TIG), thrice‐weekly image‐guided (THRIG), initial 3 days then weekly image‐guided (3D + WIG), and daily image‐guided (DIG). Results Increasing the frequency of IG schedules significantly improved planning target volume (PTV) dose coverage (D 95 ) and TCP (P < 0.001), with DIG achieving optimal target dose delivery. Although no statistically significant differences were observed in dose to organs at risk (OARs) or NTCP, higher‐frequency schedules showed a trend toward reduced variability. However, cumulative imaging dose increased linearly with the frequency of IG schedules (e.g., contralateral breast: 1.26–31.50 mGy; ipsilateral lung: 2.85–71.25 mGy), and imaging‐related cost increased substantially from NIG to DIG, with differences of approximately 1.7‐ to 25‐fold. THRIG demonstrated a favorable balance, with minimal deviations in PTV D 95 (1.38%) and TCP (0.83%) relative to DIG, while reducing imaging dose and cost to approximately 60% of DIG. Conclusion While high frequency IG schedules improve target dose coverage, they are associated with increased imaging dose and imaging‐related cost. Within the CBCT‐guided VMAT workflow evaluated in this study, THRIG may provide a balanced trade‐off between treatment precision, safety, and cost.
Liu et al. (2026) studied this question.