Dosimetric evaluation and clinical application of collimated apertures with proton beam line scanning in stereotactic radiotherapy.

Purpose: Stereotactic radiotherapy (SRT) is a highly effective treatment with precision for small, localized lesions. Proton therapy, characterized by the Bragg peak, offers superior dose conformity compared to photon-based approaches. However, challenges remain in minimizing lateral penumbra and optimizing dose delivery, particularly for small targets. This study presents the first clinical application of collimated apertures integrated with the proton line scanning technique for proton stereotactic radiotherapy (PSRT). The aim was to evaluate the dosimetric advantages and clinical feasibility of this innovative approach.

Methods: Over a 1-year period, 30 patients with small lesions, including choroid melanoma and arteriovenous malformations, were treated using proton line scanning. Two planning strategies were evaluated: uncollimated proton line scanning (UPLS) and collimated proton line scanning (CPLS), incorporating patient-specific apertures. Dosimetric comparisons were conducted using the Homogeneity Index (HI), Paddick Conformity Index (CI_Paddick), Gradient Index (GI), and R50%. Treatment accuracy was validated using absolute dose measurements and Gamma Passing Rate (GPR) analysis under the criteria of 3%/3 and 2%/2 mm.

Results: Plans incorporating customized collimated apertures showed significant improvements in dose conformity, with higher CI_Paddick values (p < 0.001), and exhibited steeper dose fall-off, as reflected in lower GI and R50% values (p < 0.001). A trend toward more homogeneous dose distributions was also observed (p < 0.001). GPR analysis confirmed high treatment accuracy, with an average value of 99.00 ± 1.83% (3%/3 mm) and 91.06 ± 4.91% (2%/2 mm).

Conclusions: Integrating customized collimated apertures with proton beam line scanning is clinically feasible, improving precision, dose conformity, and healthy tissue sparing in PSRT. These findings support adopting this novel approach to advance precision proton therapy for small lesions.