NRG Oncology and Particle Therapy Co-Operative Group Patterns of Practice Survey and Consensus Recommendations on Pencil-Beam Scanning Proton Stereotactic Body Radiation Therapy and Hypofractionated Radiation Therapy for Thoracic Malignancies

Abstract

Stereotactic body radiation therapy (SBRT) and hypofractionation using pencil-beam scanning (PBS) proton therapy (PBSPT) is an attractive option for thoracic malignancies. Combining the advantages of target coverage conformity and critical organ sparing from both PBSPT and SBRT, this new delivery technique has great potential to improve the therapeutic ratio, particularly for tumors near critical organs. Safe and effective implementation of PBSPT SBRT/hypofractionation to treat thoracic malignancies is more challenging than the conventionally fractionated PBSPT because of concerns of amplified uncertainties at the larger dose per fraction. The NRG Oncology and Particle Therapy Cooperative Group Thoracic Subcommittee surveyed proton centers in the United States to identify practice patterns of thoracic PBSPT SBRT/hypofractionation. From these patterns, we present recommendations for future technical development of proton SBRT/hypofractionation for thoracic treatment. Among other points, the recommendations highlight the need for volumetric image guidance and multiple computed tomography-based robust optimization and robustness tools to minimize further the effect of uncertainties associated with respiratory motion. Advances in direct motion analysis techniques are urgently needed to supplement current motion management techniques.

Fig. 1.

The summarized counts of (a) limit of maximum tumor diameter allowed, (b) prescription for primary lung cancer, (c) computed tomography scan slice thickness, and (d) number of beams used for treatment planning from different proton centers.

Fig. 2.

Summary of different robust optimization and robustness evaluation configurations: (a) patient setup uncertainty magnitude, (b) proton range uncertainty, and (c) combining patient setup and proton range uncertainties, in robust optimization and robustness evaluation respectively, of different proton centers.

Fig. 3.

Summary of different (a) targets for nominal plan coverage evaluation, (b) inhomogeneity dose allowed in targets, and (c) dose volume criterion for target evaluation for robust analysis from different proton centers. “BW” is the bandwidth of dose-volume histogram indices from the dose-volume histogram family for all uncertainty scenarios.

Fig. 4.

Answers to questions: (a) How can we increase the use of proton stereotactic body radiation therapy in lung cancer treatment? (b) What are the 3 most important technologies to improve lung treatment quality?