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Reducing margins for abdominopelvic tumors in dogs: impact on dose‐coverage and normal tissue complication probability


Meier, Valeria; Staudinger, Chris; Radonic, Stephan; Besserer, Jürgen; Schneider, Uwe; Walsh, Linda; Rohrer Bley, Carla (2020). Reducing margins for abdominopelvic tumors in dogs: impact on dose‐coverage and normal tissue complication probability. Veterinary and Comparative Oncology:Epub ahead of print.

Abstract

Image‐guided, intensity modulated radiation therapy (IG‐IMRT) reduces dose to pelvic organs at risk without losing dose coverage to the planning target volume (PTV) and might permit margin reductions potentially resulting in lower toxicity. Appropriate PTV margins have not been established for IG‐IMRT in abdominopelvic tumours in dogs, and herein we explore if our usual PTV 5 mm margin can be reduced further. Datasets from dogs that underwent IG‐IMRT for non‐genitourinary abdominopelvic neoplasia with 5 mm‐PTV expansion were included in this retrospective virtual study. The clinical target volumes and organs at risk (OAR) colon, rectum, spinal cord were adapted to each co‐registered cone‐beam computed tomography (CBCT) used for positioning. New treatment plans were generated and smaller PTV margins of 3 mm and 4 mm evaluated with respect to adequate dose coverage and normal tissue complication probability (NTCP) of OAR. Ten dogs with a total of 70 CBCTs were included. Doses to the OAR of each CBCT deviated mildly from the originally planned doses. In some plans, insufficient build‐up of the high dose‐area at the body surface was found due to inadequate or missing bolus placement. Overall, the margin reduction to 4 mm or 3 mm did not impair dose coverage and led to significantly lower NTCP in all OAR except for spinal cord delayed myelopathy. However, overall NTCP for spinal cord was very low (<4%). PTV‐margins depend on patient immobilization and treatment technique and accuracy. IG‐IMRT allows treatment with very small margins in the abdominopelvic region, ensuring appropriate target dose coverage, while minimizing NTCP.

Abstract

Image‐guided, intensity modulated radiation therapy (IG‐IMRT) reduces dose to pelvic organs at risk without losing dose coverage to the planning target volume (PTV) and might permit margin reductions potentially resulting in lower toxicity. Appropriate PTV margins have not been established for IG‐IMRT in abdominopelvic tumours in dogs, and herein we explore if our usual PTV 5 mm margin can be reduced further. Datasets from dogs that underwent IG‐IMRT for non‐genitourinary abdominopelvic neoplasia with 5 mm‐PTV expansion were included in this retrospective virtual study. The clinical target volumes and organs at risk (OAR) colon, rectum, spinal cord were adapted to each co‐registered cone‐beam computed tomography (CBCT) used for positioning. New treatment plans were generated and smaller PTV margins of 3 mm and 4 mm evaluated with respect to adequate dose coverage and normal tissue complication probability (NTCP) of OAR. Ten dogs with a total of 70 CBCTs were included. Doses to the OAR of each CBCT deviated mildly from the originally planned doses. In some plans, insufficient build‐up of the high dose‐area at the body surface was found due to inadequate or missing bolus placement. Overall, the margin reduction to 4 mm or 3 mm did not impair dose coverage and led to significantly lower NTCP in all OAR except for spinal cord delayed myelopathy. However, overall NTCP for spinal cord was very low (<4%). PTV‐margins depend on patient immobilization and treatment technique and accuracy. IG‐IMRT allows treatment with very small margins in the abdominopelvic region, ensuring appropriate target dose coverage, while minimizing NTCP.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Physics Institute
05 Vetsuisse Faculty > Veterinary Clinic > Department of Small Animals
Dewey Decimal Classification:530 Physics
Scopus Subject Areas:Health Sciences > General Veterinary
Uncontrolled Keywords:General Veterinary
Language:English
Date:28 December 2020
Deposited On:14 Jan 2021 16:56
Last Modified:16 Feb 2021 10:54
Publisher:Wiley-Blackwell Publishing, Inc.
ISSN:1476-5810
OA Status:Hybrid
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1111/vco.12671
Project Information:
  • : FunderSNSF
  • : Grant ID320030_182490
  • : Project TitleChallenging traditional radiation dose homogeneity: using normal tissue tolerance for heterogeneous dose escalation and better tumor control

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