A simple dosimetric approach to spatially fractionated GRID radiation therapy using the multileaf collimator for treatment of breast cancers in the prone position

Abstract

The purpose of this study was to explore the treatment planning methods of spatially fractionated radiation therapy (SFRT), commonly referred to as GRID therapy, in the treatment of breast cancer patients using multileaf collimator (MLC) in the prone position. A total of 12 patients with either left or right breast cancer were retrospectively chosen. The computed tomography (CT) images taken for the whole breast external beam radiation therapy (WB‐EBRT) were used for GRID therapy planning. Each GRID plan was made by using two portals and each portal had two fields with 1‐cm aperture size. The dose prescription point was placed at the center of the target volume, and a dose of 20 Gy with 6‐MV beams was prescribed. Dose‐volume histogram (DVH) curves were generated to evaluate dosimetric properties. A modified linear‐quadratic (MLQ) radiobiological response model was used to assess the equivalent uniform doses (EUD) and therapeutic ratios (TRs) of all GRID plans. The DVH curves indicated that these MLC‐based GRID therapy plans can deliver heterogeneous dose distribution in the target volume as seen with the conventional cerrobend GRID block. The plans generated by the MLC technique also demonstrated the advantage for accommodating different target shapes, sparing normal structures, and reporting dose metrics to the targets and the organs at risks. All GRID plans showed to have similar dosimetric parameters, implying the plans can be made in a consistent quality regardless of the shape of the target and the size of volume. The mean dose of lung and heart were respectively below 0.6 and 0.7 Gy. When the size of aperture is increased from 1 to 2 cm, the EUD and TR became smaller, but the peak/valley dose ratio (PVDR) became greater. The dosimetric approach of this study was proven to be simple, practical and easy to be implemented in clinic.

An International Consensus on the Design of Prospective Clinical–Translational Trials in Spatially Fractionated Radiation Therapy

“…In addition, dosimetric and geometric characteristics of the heterogeneous dose distribution, such as dose volume histogram characteristics (D10, D50, D90) and peak-to-peak distance, should be reported according to guidelines further described in the recent GRID physics and dosimetry white paper. 22 Owing to the different SFRT technologies (eg, collimator-based and MLC-based GRID) with different dose distributions, 34 the equivalent uniform dose (EUD) for H&N squamous cell carcinoma (using α/β = 10 Gy) and for normal tissues (generally α/β = 3 Gy) must be determined for any trial regimen. Principles of EUD computation in SFRT, which favor the modified linear quadratic model, and tumor cell sensitivity considerations are described in the recent SFRT physics guideline publications.…”

“…Because of the different SFRT technologies (e.g. collimator-based and MLC-based GRID) with different dose distributions 34 , the equivalent uniform dose (EUD) for H&N squamous cell carcinoma (employing α/β=10 Gy) and for normal tissues (generally α/β=3 Gy) must be determined for any trial regimen. Principles of EUD computation in SFRT, which favor the modified linear quadratic model, and tumor cell sensitivity considerations are described in the recent SFRT physics guideline publications 22 25 .…”

Radiobiological and Treatment-Related Aspects of Spatially Fractionated Radiotherapy

“…Their simulation demonstrated that the 3D conformal MLC-based GRID resulted in enhanced target coverage with reduced skin and organs at risk toxicity. Using a similar approach in a cohort of patients consistently with breast cancer, Murphy et al demonstrated that the dosimetric qualities of MLC-based GRID plans were comparable with block-based GRID with the added advantage of superior conformity for MLC-based plans [ 88 ]. Plan evaluations were conducted in terms of the EUD and TR using DVH curves.…”

Three discipline collaborative radiation therapy (3DCRT) special debate: FLASH radiotherapy needs ongoing basic and animal research before implementing it to a large clinical scale

“…GRID and FLASH therapies have in common a highly heterogeneous dose distribution, very high prescription doses and an overall lack of experience among physicists and clinicians. 16 , 17 …”