Impact of dynamic jaw width adjustment in tomotherapy on hippocampus sparing and treatment efficiency in whole-brain radiotherapy.

The aim of this study is to evaluate the impact of dynamic jaw width adjustment in tomotherapy on hippocampal sparing, target dose conformity, and treatment efficiency in hippocampal-avoidance whole-brain radiotherapy (HA-WBRT), in accordance with RTOG 0933 guidelines. A retrospective study of 60 patients treated with HA-WBRT was conducted. CT-MRI fusion facilitated accurate hippocampal delineation. Treatment plans were created using Accuray Precision TPS and delivered on the Radixact Tomotherapy system with three jaw widths (1 cm, 2.5 cm, and 5 cm), fixed pitch (0.215), and modulation factor (3.0). The prescription dose was 30 Gy in 10 fractions. Evaluation metrics included PTV coverage (D98%, V95%, D2%, Dmax), homogeneity index (HI), conformity index (CI), hippocampal and lens doses, and beam-on time (BOT). Plan verification was performed with ArcCHECK using 3%/3 mm and 3%/2 mm gamma criteria. The 1 cm jaw achieved the best PTV coverage (D98% = 29.22 Gy, V95% = 98.71%), with HI = 0.09, CI = 0.99, and superior hippocampal sparing (Dmax = 14.91 Gy, Dmin = 7.57 Gy), but had the longest BOT (1165 s). Wider jaws (2.5 cm, 5 cm) reduced BOT (480 s, 280 s) but slightly compromised conformity and increased OAR doses, all within limits. Jaw width selection in Helical Tomotherapy influences dose distribution characteristics and treatment delivery efficiency in hippocampus-sparing WBRT. A 1 cm jaw width provides superior dosimetric conformity and enhanced hippocampal sparing, albeit at the cost of increased BOT. In contrast, wider jaw widths (2.5 cm and 5 cm) improve delivery efficiency but result in modest reductions in dose precision and organ-at-risk sparing. Therefore, jaw width selection should be carefully individualized based on clinical objectives, balancing the trade-off between organ preservation and treatment efficiency.