Author: Eduardo Florian, Osmar Obdulio Hernandez, Otto Hurtarte, Milton Ixquiac, Erick Orlando Montenegro, Franky Eduardo Reyes, Edgar Aparicio Ruiz, Kevin Vega, Vicky de Falla 👨🔬
Affiliation: Liga Nacional Contra el Cancer, Liga Nacional Contra el Cancer/INCAN, Liga Nacional Contra el Cancer / INCAN, Liga Nacional Contra el Cancer and Universidad de San Carlos de Guatemala, Liga Nacional Contra el Cáncer / INCAN 🌍
Introduccion:
Lattice Radiation Therapy (LRT) is a form of spatially fractionated radiation therapy (SFRT) designed to improve control of large tumors by delivering ablative doses while minimizing toxicity. LRT utilizes advanced 3D radiation planning to create alternating high-dose "vertices" and low-dose "valleys" within the tumor. This inhomogeneous dose targets the tumor core while sparing surrounding organs at risk (OARs), making LRT valuable for treating tumors that are not suitable for SBRT.
Background/Purpose:
Ring gantry linacs are limited in their ability to produce non-coplanar radiation beams due to the lack of couch angulation, which results in excessive dose delivery outside the intended vertices and a reduced dose gradient for LRT.
This study proposes an optimization method that achieves the required dose gradient in this type of treatment while considering the mechanical constraints of a ring gantry linac.
Methods:
The proposed method involves rotating the lattice of vertices. A 30° rotation was applied in both the sagittal and coronal planes. The resulting dose distributions were analyzed for the same target volume in treatment plans with and without lattice rotation. These plans were generated using Eclipse V16.2 and delivered on a Halcyon Elite V3.2 system. The prescription for this study involved a single fraction of 15 Gy to the vertices, with efforts made to maintain a dose of 3 Gy to the remaining tumor volume.
Results:
To assess the achieved dose gradient in each case, the isodose volumes outside the vertices were compared. When a 30° rotation was applied, the 7.5 Gy isodose volume (250% prescription dose) decreased by 12% to 40%, while the 12 Gy isodose volume showed a reduction of 11% to 15%.
Conclusion:
These findings demonstrate the impact of lattice rotation on reducing high-dose regions outside the target vertices.