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HyTEC Editorial Editorial - Editorial (2021)

Category: HyTEC Editorial

The 1991 “Emami paper”1 summarized dose/volume/outcome estimates for normal tissues as part of a full issue of the International Journal of Radiation Oncology, Biology, Physics (IJROBP) dedicated to the report of an NCI-funded Collaborative Working Group on Evaluation of High Energy Photon External Beam Treatment Planning. It guided and informed many providers and helped countless patients in the early years of 3D planning. The Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC) project aimed to update Emami based on reported normal tissue outcomes during the following decades of clinical implementation of 3D planning.2 QUANTEC received financial assistance from the American Association of Physicists in Medicine (AAPM) and the American Society for Radiation Oncology (ASTRO) but worked independently of either organization’s structure. QUANTEC was published in a supplementary issue of IJROBP in 2010.2

Given the explosive growth of stereotactic body radiation therapy (SBRT, also known as stereotactic ablative body radiotherapy or SABR), it is timely to have a similar literature-based project on dose/volume outcomes for both normal tissues and tumors treated with SBRT. AAPM led this effort through the Working Group on Biological Effects of Hypofractionated Radiotherapy/SBRT (WGSBRT) under the Biological Effects Subcommittee (BESC). The WG, which has chosen the acronym HyTEC (“Hy”-dose per fraction, Hypofractionated Treatment Effects in the Clinic), consists of AAPM physicists and guest members who are physicians, physicists, radiobiologists, biostatisticians, and biomathematicians. While AAPM made significant contributions to the QUANTEC effort, it oversaw HyTEC much more closely, and the scientific review process was conducted through the AAPM committee structure. Given the highly clinical nature of the HyTEC reviews, the articles will be published in IJROBP, with AAPM members having full and free access via the “Publications” section of the AAPM website.

A special HyTEC issue of IJROBP will be published on May 1, 2021. The issue covers the main anatomic sites treated with SBRT—cranial, head and neck, thoracic, abdominal, pelvic and spinal—including nine disease sites and multiple associated normal tissues. There are also several introductory and “vision” papers that address topics related to underlying radiobiology, immunologic, and mathematical outcome modeling. The basic strategy of Emami1 and its companion modeling paper3 and of QUANTEC2 is continued by HyTEC: to provide risk organ tolerances for treatment planning, based on both published clinical dose-outcome data and statistical dose-response modeling. As with QUANTEC, the HyTEC introductory article features a table summarizing the major dose/volume outcome findings from each site-specific report.4

Similar dose/volume guidance for SBRT treatment planning has been previously provided by AAPM’s Task Group 101 and by other works.5-7 Although the growing availability of clinical data prompted the HyTEC effort, these data remain suboptimal. Problems with sparsity and quality of the published data that were reported by QUANTEC8, 9 unfortunately persist in the era of SBRT, and HyTEC is similarly limited by them. The last section of each site-specific HyTEC paper includes a reporting standards wishlist aimed to improve future publications. Physicists, in particular, are strongly encouraged to ensure that when they author or review a paper concerning radiation therapy outcomes, sufficient detail is included (in the supplementary material if necessary) to facilitate future analyses. Ideally, all SBRT outcome-related reports would clearly define the prescription dose and fractionation, along with doses received by the critical anatomical structures. The QUANTEC lessons8 and data pooling articles,9 and the HyTEC introduction and site-specific reporting standards, provide useful suggestions to promote more comprehensive data reporting.

Clinical adoption of SBRT has outpaced outcomes analyses, especially considering the strong impact of fraction size on late effects. We hope that HyTEC provides a useful analysis and summary of the published outcomes to improve treatment planning in clinical practice.

Medical Physics

Jimm Grimm, Andrew Jackson, Brian D. Kavanagh, Lawrence B. Marks, Ellen Yorke, Jinyu Xue

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