Author: Hao Gao, Yuting Lin, Nimita Shinde, Weijie Zhang 👨🔬
Affiliation: Department of Radiation Oncology, University of Kansas Medical Center 🌍
Purpose: LATTICE, a form of spatially fractionated radiation therapy (SFRT), delivers high-dose peaks and low-dose valleys to the target volume and has been clinically used for large target volumes. However, its application to small-to-medium target volumes remains challenging. In this study, we introduce a novel proton LATTICE modality (pLATTICE) using minibeams, termed minibeam-pLATTICE, which extends the LATTICE approach to small-to-medium target volumes.
Methods: We propose three methods to implement minibeam-pLATTICE: M0 with a fixed minibeam collimator orientation (i.e., 0º) for all beam angles; M1 with alternating minibeam collimator orientation between 0º and 90º for consecutive beam angles; M2 with both minibeam collimator orientations (i.e., 0º and 90º) for each beam angle. The goal of using different collimator orientations is to address the anisotropic dose distribution at lattice peaks caused by the planar spatial modulation of minibeams. Specifically, the M2 approach uses orthogonal minibeam collimators per beam angle to mitigate peak dose anisotropy.
Results: We compared and cross-validated the three methods in two head and neck (HN) cases. For HN01, M2 provided the best plan quality compared to M0 and M1. Notably, M2 resulted in a peak-to-valley dose ratio (PVDR) of 5.89, which was higher than the PVDRs for conventional pLATTICE (4.13), M0 (4.87), and M1 (4.7). Additionally, the maximum dose delivered to the brainstem was lower with M2 (5.8 Gy) compared to conventional pLATTICE (16.75 Gy), M0 (6.54 Gy), and M1 (7.04 Gy).
Conclusion: We present the novel minibeam-pLATTICE approach, which enables the generation of lattice dose patterns for small-to-medium target volumes, a capability not achievable with conventional pLATTICE. The correction of peak dose anisotropy is achieved through inverse treatment planning, utilizing orthogonal minibeam collimators per beam angle.