Author: Nebi Demez, Noufal Manthala Padannayil, Shyam Pokharel, Suresh Rana, Umesh Rana, Nishan Shrestha, Somol Sunny 👨🔬
Affiliation: Florida Atlantic University, Lynn Cancer Institute, Boca Raton Regional Hospital, Baptist Health South Florida 🌍
Purpose: DynamicARC is an advanced proton therapy technique that leverages pencil beam scanning to deliver dose to the patient while the gantry rotates around the patient. This study investigates the impact of varying spot spacing on dosimetric outcomes in DynamicARC treatment planning for lung cancer cases.
Methods: This retrospective study analyzed three anonymized lung cancer cases. Treatment plans were generated with a total prescribed dose of 5000 cGy(RBE) in 5 fractions, optimized with spot spacings ranging from 0.2 cm to 0.8 cm in increments of 0.1 cm. A single partial arc was utilized in all cases. Other dosimetric parameters were kept constant during robust optimization, and plans were evaluated against clinical goals to assess the variability and consistency of dose metrics.
Results: Dose results across varying spot spacings showed variability in achieving clinical goals. For CTV_D99% ≥ 4950 cGy(RBE), patient 1 exhibited a 5.7% change, while patient 3 showed a 4.9% change. For CTV_D95% ≥ 5000 cGy(RBE), patient 1 consistently met the clinical goal, but patient 3 showed greater fluctuations, with a least dose of 4918 cGy(RBE) compared to 5057 cGy(RBE) for patient 1 and 4981 cGy(RBE) for patient 2. For CTV_Dmax ≤ 5200 cGy(RBE), dose metrics varied modestly, with up to 3.2% difference across patients. The CTV_D1% exhibited the greatest variability; patient 2 had the highest variance (3,562 cGy²(RBE)), while patient 3 showed the lowest (1,428 cGy²(RBE)).
Conclusion: The spacing of proton spots impacts dosimetric outcomes in DynamicARC treatment planning for lung cancer. Adjusting spot spacing is crucial to minimizing variability and achieving consistency with clinical goals. Future studies should include a larger cohort of patients and investigate the effects of proton spot spacing on organs at risk (OARs).