Comparative dosimetric analysis of base dose and gradient-based optimization in overlapping regions of extended target volumes using an anthropomorphic phantom.

This study compares the dosimetric performance of Base Dose Optimization (BDO) and Gradient-Based Optimization (GBO) for extended target volumes in Total Body Irradiation (TBI). The focus is on overlapping regions using the Rando Phantom. The study evaluates dose distribution, conformity, homogeneity, and sensitivity to positional deviations. The Rando Phantom was used for treatment planning with both BDO and GBO plans. Positional shifts of ± 5 mm and ± 10 mm were introduced to assess uncertainties. Dosimetric metrics included mean dose, minimum dose, maximum dose, homogeneity index (HI), and conformity index (CI). Positional deviations and their impact on dose variations were analyzed. Quality assurance was performed using OSLDs and an array detector. The BDO plan delivered higher mean doses (103.6%-108.7%) and hotspot values, with a maximum of 133.7%. In contrast, the GBO plan produced a more uniform dose distribution (99.6%-100.3%) with lower hotspots, peaking at 112%. The BDO plan achieved better uniformity (HI 0.025-0.103) and higher conformity (CI 0.938-0.981). The GBO plan showed greater variability (HI 0.143-0.253) and slightly lower conformity (CI 0.941-0.964). Positional shifts revealed that the BDO plan was highly sensitive, with overdoses of + 46.60% and underdoses of - 47.29%. The GBO plan showed smaller deviations (+ 11.62% overdose, - 11.73% underdose). Gamma analysis demonstrated higher pass rates for the GBO plan. The BDO plan excels in target coverage and conformity but is sensitive to positional shifts. The GBO plan offers better uniformity and robustness, supporting its use in complex clinical scenarios. Further refinement of both approaches could improve clinical applicability and patient outcomes.