Optimizing radiotherapy (RT) techniques for neoadjuvant treatment of locally advanced rectal cancer (LARC) requires a balance among target dose quality, organ-at-risk (OAR) sparing, and delivery efficiency. Although hybrid IMRT/VMAT strategies have been explored in several disease sites, evidence regarding proportion-based hybrid planning in LARC, particularly on the Halcyon platform, remains limited. Seventeen patients with LARC treated with neoadjuvant chemoradiotherapy were retrospectively analyzed. For each patient, five plans were generated: IMRT, RapidArc (a VMAT technique), and three hybrid IMRT/RapidArc plans with IMRT/RapidArc dose weightings of 30%/70%, 50%/50%, and 70%/30%. Target coverage, homogeneity index (HI), conformity index (CI), treatment delivery time, monitor units (MUs), gamma passing rates, and OAR dosimetric parameters were compared using the paired Wilcoxon signed-rank test with Bonferroni correction. All plans achieved adequate planning target volume coverage. Varying the IMRT/RapidArc weighting in the hybrid plans resulted in systematic trade-offs among dose homogeneity, OAR sparing, and delivery efficiency. For example, the 70%-IMRT/30%-RapidArc plan achieved bladder and small-intestine sparing comparable to standalone IMRT while providing shorter delivery times and lower MUs. Increasing the RapidArc proportion further improved delivery efficiency but was associated with higher OAR exposure. Proportion-based hybrid IMRT/RapidArc planning on the Halcyon platform effectively integrates the dosimetric advantages of IMRT with the delivery efficiency of RapidArc. Hybrid strategies allow flexible trade-offs between target quality, OAR protection, and workflow efficiency, which may support personalized RT planning in LARC. Further validation in larger cohorts is warranted.
Li et al. (Thu,) studied this question.