A BSTRACT Purpose: Iso-center placement is a key determinant of dosimetric accuracy and workflow efficiency in intensity-modulated radiotherapy (IMRT). While the anatomical iso-center (AIP) is conventionally used, high-volume centers increasingly consider the virtual iso-center (VIP) defined during CT simulation to streamline patient setup. This study evaluates the dosimetric impact and workflow benefits of VIP relative to AIP in IMRT planning. Materials and Methods: A retrospective planning analysis was performed for 40 IMRT patients. For each case, two plans were generated: one centered on the AIP and the other on the VIP. Dosimetric indices, including conformity index (CI), homogeneity index (HI), target coverage, organ-at-risk (OAR) doses, monitor units (MUs), and iso-center displacement were compared. Workflow efficiency was assessed by estimating setup time saved through omission of couch shifts. Results: VIP-based plans demonstrated a statistically significant increase in MUs (mean + 4.4%, P 0.15). The VIP approach eliminated couch shifts, reducing average setup time by approximately 4.2 min per patient, translating into the potential to treat 5–6 additional patients per month. Larger displacements (>6 cm) were associated with greater MU penalties. Conclusions: VIP planning enhances workflow efficiency without compromising target coverage or OAR sparing. However, the consistent MU increase, particularly with large displacements, supports selective use and vigilant quality assurance.
Khan et al. (Thu,) studied this question.