A Dosimetric Parameter Reference Look-Up Table for GRID Collimator-Based Spatially Fractionated Radiation Therapy

Abstract

Computations of heterogeneity dose parameters in GRID therapy remain challenging in many treatment planning systems (TPS). To address this difficulty, we developed reference dose tables for a standard GRID collimator and validate their accuracy. The .decimal Inc. GRID collimator was implemented within the Eclipse TPS. The accuracy of the dose calculation was confirmed in the commissioning process. Representative sets of simulated ellipsoidal tumours ranging from 6–20 cm in diameter at a 3-cm depth; 16-cm ellipsoidal tumours at 3, 6, and 10 cm in depth were studied. All were treated with 6MV photons to a 20 Gy prescription dose at the tumour center. From these, the GRID therapy dosimetric parameters (previously recommended by the Radiosurgery Society white paper) were derived. Differences in D5 through D95 and EUD between different tumour sizes at the same depth were within 5% of the prescription dose. PVDR from profile measurements at the tumour center differed from D10/D90, but D10/D90 variations for the same tumour depths were within 11%. Three approximation equations were developed for calculating EUDs of different prescription doses for three radiosensitivity levels for 3-cm deep tumours. Dosimetric parameters were consistent and predictable across tumour sizes and depths. Our study results support the use of the developed tables as a reference tool for GRID therapy.

Automated target placement for VMAT lattice radiation therapy: enhancing efficiency and consistency

“…A common and straightforward method of delivering SFRT is to use single static fields in combination with commercially available blocks with divergent apertures (Buckey et al 2010, Zhang et al 2022. However, this approach may not be optimal in all clinical scenarios as the highest dose may not be delivered within the tumor and considerable exit dose may exist beyond it.…”

“…The purpose of this paper is to describe the development and implementation of a fully automated algorithm which addresses the challenges associated with manual placement of spherical lattice structures for VMAT LRT. Notably, the algorithm distinguishes itself from earlier work that maximized the number of lattice points with the GTV or utilized a regular arrangement of targets (Duriseti et al 2021, Zhang et al 2022. While sphere packing is a well-known mathematical problem, the placement of spherical lattice structures for LRT plans differs from traditional packing problems due to the therapeutic intentions of SFRT.…”

Dosimetric characterization for GRID collimator‐based spatially fractionated radiation therapy: Dosimetric parameter acquisition and machine interchangeability investigation

“…18,19 Because both types of GRID collimators use similar aperture designs, their dose profiles are similar and reproducible. Therefore, Zhang et al 20 developed the dosimetric parameter reference tables of the brass block collimator, including the peak/valley dose ratios (PVDRs) and output factors (OFs) across different depths and field sizes for 6 MV GRID fields. The lookup table enabled GRID therapy planning without the treatment planning system (TPS).…”

“…With the intent of using higher energy beams for more complicated treatments, corresponding dosimetric parameters of the GRID fields must be verified before implementing the lookup table method. 20 As the TPS can also be used for GRID therapy planning, a proper commissioning and experimental verification becomes crucial for ensuring TPS calculation accuracy.…”

“…23 Zhang et al reported more detailed dosimetric characteristics for the GRID beam of 6MV, including PDD, PVDR, and OFs for various field sizes and depths. 20 However, there is lack of detailed comprehensive commissioning report of GRID collimator for newer model linacs and high energies.…”