Improving total bone marrow and lymphoid irradiation: feasibility of intensity-modulated proton therapy (IMPT) and dosimetric comparison with helical tomotherapy (HT).

Background and purpose: This study aims to develop and validate a novel whole-body intensity-modulated proton therapy (IMPT) approach for total marrow/lymphatic irradiation (TMI/TMLI) and compare its efficacy to helical tomotherapy (HT).

Materials and methods: Whole-body IMPT plans were designed using five isocenters and fifteen fields for adult and three isocenters and eight fields for pediatric. Overlapping sub-PTVs were optimized to ensure robust and homogeneous dose distribution across consecutive isocenters and across CT datasets. Dosimetric benefits were compared to HT, safety and accuracy were verified using an in-house algorithm and planar dosage measurement.

Results: The average cranio-caudal and lateral whole-body PTV dimensions were 169.24 cm and 46.41 cm for five adults; 95.2 cm and 28.86 cm for one pediatric patient. IMPT plans provided adequate and homogeneous dose to all sub-PTVs, upper and lower body PTVs, with mean D95% ≥ 11.4 GyRBE. In comparison to HT, IMPT plans reduced mean integral dosage to normal tissue by 38%, OARs by a factor of 1.32 to 3.94, and V107% by 520.97 cc for sub-PTVs and 1166 cc for upper-body PTVs. For 38 pairs of planned and measured dosage planes at three depths, the average (± SD) gamma value was 96.77% (± 2.45%). Radiation ON time of 76 and 28 min for the tallest adult and pediatric patient plan was almost double HT plan of 39.9 and 14.1 min.

Conclusion: The presented whole-body IMPT approach for TMI/TMLI patients of any physical build-up is dosimetrically superior, safe and feasible to implement. Nevertheless, detailed robustness evaluation and cost-benefit analyses should guide its clinical implementation.