Overview and Recommendations for Prospective Multi-institutional Spatially Fractionated Radiation Therapy Clinical Trials

Abstract

Purpose: The highly heterogeneous dose delivery of spatially fractionated radiation therapy (SFRT) is a profound departure from standard radiation planning and reporting approaches. Early SFRT studies have shown excellent clinical outcomes. However, prospective multi-institutional clinical trials of SFRT are still lacking. This NRG Oncology/American Association of Physicists in Medicine working group consensus aimed to develop recommendations on dosimetric planning, delivery, and SFRT dose reporting to address this current obstacle toward the design of SFRT clinical trials.

Methods and materials: Working groups consisting of radiation oncologists, radiobiologists, and medical physicists with expertise in SFRT were formed in NRG Oncology and the American Association of Physicists in Medicine to investigate the needs and barriers in SFRT clinical trials.

Results: Upon reviewing the SFRT technologies and methods, this group identified challenges in several areas, including the availability of SFRT, the lack of treatment planning system support for SFRT, the lack of guidance in the physics and dosimetry of SFRT, the approximated radiobiological modeling of SFRT, and the prescription and combination of SFRT with conventional radiation therapy.

Conclusions: Recognizing these challenges, the group further recommended several areas of improvement for the application of SFRT in cancer treatment, including the creation of clinical practice guidance documents, the improvement of treatment planning system support, the generation of treatment planning and dosimetric index reporting templates, and the development of better radiobiological models through preclinical studies and through conducting multi-institution clinical trials.

Fig. 1.

Commercially available GRID collimator by (a) high-dose radiation grid (Radiation Products Design) and (b) dot decimal. (c) Dot decimal GRID versus open percent depth dose. (d) Dot decimal GRID dose profiles at different depths.

Fig. 2.

(a) Multileaf collimator (MLC) step-and-shoot design of single-field GRID therapy treatment. (b) The corresponding Electronic Portal Imaging Device images of the treatment field.

Fig. 3.

(a) Three-dimensional multileaf collimator fitting and (b) dose distribution of multileaf collimator–based 3-dimensional conformal spatially fractionated radiation therapy (15 Gy in 1 fraction) for a deep-seated bulky mass of a 10.0-cm diameter tumor in a right pelvis–malignant neoplasm of the connective and soft tissue of trunk.

Fig. 4.

LATTICE radiation therapy (LRT) as a 3-dimensional extension of GRID. (a) Two-dimensional GRID. (b) Three-dimensional LRT with focused photon beams. (c) Three-dimensional LRT with charged particle beams.

Fig. 5.

Typical planning parameters of a LATTICE radiation therapy plan.