Author: Awens Alphonse, Nebi Demez, Noufal Manthala Padannayil, Shyam Pokharel, Suresh Rana, Lauren A. Rigsby, Gagandeep Saini, Nishan Shrestha, Somol Sunny 👨🔬
Affiliation: Lynn Cancer Institute, Boca Raton Regional Hospital, Baptist Health South Florida 🌍
Purpose: This study examined the impact of varying the pitch factor in hippocampal-avoidance whole-brain (HP-WB) radiotherapy treatments, utilizing the newly introduced VOLO Ultra optimization for Helical Tomotherapy (HT) plans.
Methods: Patients previously treated with HP-WB radiotherapy at 30 Gy in 10 fractions were selected. Treatment plans were re-optimized by varying pitch values from 0.1 mm to 0.5 mm in 0.1 mm increments, with a constant field width of 1 cm and fixed optimization parameters. Ten HT plans were created for two patients using the Precision Treatment Planning System and VOLO Ultra optimization. All plans were normalized to ensure consistent target coverage. Plan quality was evaluated using various metrics for organs at risk (OARs). Beam delivery metrics, including beam-on time, gantry period, active rotations, and modulation factor (MF), were also analyzed.
Results: All plans met the clinical objectives outlined in the NRG protocol CC001, achieving D98% of the planning target volume (PTV) ≥28 Gy. While smaller pitch values resulted in slightly lower D0.03cc and D100% doses to the hippocampus, these differences were not clinically significant. Increasing pitch values did not compromise OAR sparing but substantially reduced beam-on time—from 1696.5±51 seconds at a pitch of 0.1 mm to 1163.45±78.5 seconds at 0.5 mm. The MF was highest at 0.1 mm and stabilized with minimal variations for pitches above 0.2 mm.
Conclusion: Increasing pitch values enhances treatment efficiency by significantly reducing beam-on time while maintaining target coverage and OAR sparing. This demonstrates that higher pitch values can optimize beam delivery in HP-WB radiotherapy without negatively impacting dosimetric outcomes.