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Investigation of Variability and Standardization in Normal Tissue Dose Limits Across Multi-Institutional Clinical Trials

S Quirk1*, T Ritter2, M Ebert3, W Smith4, P Taylor5, J Sohn6, M Matuszak7, (1) University of Calgary, Calgary, AB, Canada, (2) VCU Health System, Chesterfield, VA, (3) The University of Western Australia, Nedlands, Australia, (4) University of Washington, Seattle, WA, (5) UT MD Anderson Cancer Center, Houston, TX, (6) Allegheny Health Network, Pittsburgh, PA, (7) University of Michigan, Ann Arbor, MI

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To quantify variability in normal tissue dose limits in multi-institutional cooperative group clinical trials across major tumor sites.

Methods: Normal tissue dose limits were reviewed for 32 trials: six breast, eight brain, eight prostate, five lung, and five head and neck. Protocols reviewed included published, multi-institutional, phase I/II/III protocols from NRG, Canadian Cancer Trials Group (CCTG), Trans-Tasman Radiation Oncology Group (TROG), Radiation Therapy Oncology Group (RTOG), and ClinicalTrials.gov. Trials currently accruing (n=18) or closed within last 48 months (n=14) were included.

Results: Within a tumor site, even limiting to comparable prescriptions, normal tissue limits varied both in the number of normal tissues specified and the metrics prescribed. Brain and head and neck trials demonstrated consistency for optic nerves, chiasm, brachial plexus, and parotids. Head and Neck varied in the structures contoured, with some studies including dose limits to multiple substructures related to swallowing function. Both breast and prostate demonstrated variation across commonly delineated structures such as heart and rectum, respectively. Across breast trials, there were six unique dose limiting metrics for heart (left) including mean dose of 3 to 5 Gy, limiting heart-in-field to 1.5 cm, and V10%<25Gy. For prostate trials with the same fractionation, the rectal limit ranged from D35%=65Gy to V65Gy=8%. Lung trials included the most unique fractionations leading to challenges in comparing metrics; however, there were few commonalities even in limit type (maximum, mean doses, DVH-specific) for the same normal tissue (e.g. healthy lung limits of V5Gy, V20Gy, and D1000cc).

Conclusions: Normal tissue limits in clinical trials both within and between tumor sites vary largely and few commonalities exist, even when the radiotherapy regimen is not the focus of the trial. The variation in trial design and dose reporting leads to challenges in result pooling, meta-analysis, and normal tissue constraint recommendations for standard practice.

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Keywords

Not Applicable / None Entered.

Taxonomy

TH- External Beam- Photons: General (most aspects)

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