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A complication probability study for a definitive-intent, moderately hypofractionated image-guided intensity-modulated radiotherapy protocol for anal sac adenocarcinoma in dogs


Meier, Valeria; Besserer, Jürgen; Roos, Malgorzata; Rohrer Bley, Carla (2019). A complication probability study for a definitive-intent, moderately hypofractionated image-guided intensity-modulated radiotherapy protocol for anal sac adenocarcinoma in dogs. Veterinary and Comparative Oncology, 17(1):21-31.

Abstract

Previous trials showed the importance of administering radiation therapy (RT) with small doses per fraction in canine pelvic tumours to maintain acceptable toxicity levels. With increased accuracy/precision of RT, namely intensity-modulated RT (IMRT), this approach might be challenged. Theoretical toxicity calculations for a new definitive-intent moderately hypofractionated RT protocol for canine anal sac adenocarcinomas (ASAC) were performed, focussing on the risk of toxicity in pelvic organs at risk (OAR). Computed tomography datasets of 18 dogs with stage 3b ASAC were included. Re-planning with margins for daily image-guidance/IMRT was performed and a new protocol isoeffective to previously described definitive-intent protocols was computed. Dose-volume information were derived from individual plans and used for normal tissue complication probability (NTCP) computations. A 12 × 3.8 Gy protocol was computed for risk estimation. Tumour volumes ranged from 27.9 to 820.4 cm3 (mean 221.3 cm3 ± 188.9). For late rectal toxicity/bleeding ≥grade 2, median risk probability was 2.3% inter quartile range (IQR: 5.9; 95% confidence interval (CI): 1.2, 8.4) (rho = 0.436) and 3.4% (IQR: 0.96; 95%CI: 3.1, 4.0) (rho = 0.565), respectively. Median late toxicities in urinary bladder, kidneys and small bowel were <1%, except in one kidney. Myelopathy/myelonecrosis had a median risk probability of 4.1% (IQR: 23.5; 95%CI: 2.1, 25.2) (rho = 0.366) and 5.6% (IQR: 13.5; 95%CI: 3.1, 14.1) (rho = 0.363), respectively. However, graded risk showed a probability estimate for late spinal cord toxicity of ≥5% in 8/18 patients. The daily-imaging IMRT 12 × 3.8 Gy protocol for canine ASAC seems tolerable for most cases, even in advanced disease. Theoretical dose computations serve as estimate, but are safe measures before implementing new protocols into clinical use.

Abstract

Previous trials showed the importance of administering radiation therapy (RT) with small doses per fraction in canine pelvic tumours to maintain acceptable toxicity levels. With increased accuracy/precision of RT, namely intensity-modulated RT (IMRT), this approach might be challenged. Theoretical toxicity calculations for a new definitive-intent moderately hypofractionated RT protocol for canine anal sac adenocarcinomas (ASAC) were performed, focussing on the risk of toxicity in pelvic organs at risk (OAR). Computed tomography datasets of 18 dogs with stage 3b ASAC were included. Re-planning with margins for daily image-guidance/IMRT was performed and a new protocol isoeffective to previously described definitive-intent protocols was computed. Dose-volume information were derived from individual plans and used for normal tissue complication probability (NTCP) computations. A 12 × 3.8 Gy protocol was computed for risk estimation. Tumour volumes ranged from 27.9 to 820.4 cm3 (mean 221.3 cm3 ± 188.9). For late rectal toxicity/bleeding ≥grade 2, median risk probability was 2.3% inter quartile range (IQR: 5.9; 95% confidence interval (CI): 1.2, 8.4) (rho = 0.436) and 3.4% (IQR: 0.96; 95%CI: 3.1, 4.0) (rho = 0.565), respectively. Median late toxicities in urinary bladder, kidneys and small bowel were <1%, except in one kidney. Myelopathy/myelonecrosis had a median risk probability of 4.1% (IQR: 23.5; 95%CI: 2.1, 25.2) (rho = 0.366) and 5.6% (IQR: 13.5; 95%CI: 3.1, 14.1) (rho = 0.363), respectively. However, graded risk showed a probability estimate for late spinal cord toxicity of ≥5% in 8/18 patients. The daily-imaging IMRT 12 × 3.8 Gy protocol for canine ASAC seems tolerable for most cases, even in advanced disease. Theoretical dose computations serve as estimate, but are safe measures before implementing new protocols into clinical use.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Epidemiology, Biostatistics and Prevention Institute (EBPI)
05 Vetsuisse Faculty > Veterinary Clinic > Department of Small Animals
Dewey Decimal Classification:570 Life sciences; biology
630 Agriculture
Uncontrolled Keywords:anal sac adenocarcinoma; dog; image-guided radiation therapy; intensity-modulated radiation therapy; normal tissue complication probability; radiation therapy
Language:English
Date:1 March 2019
Deposited On:16 Nov 2018 16:12
Last Modified:26 Feb 2020 14:05
Publisher:Wiley-Blackwell Publishing, Inc.
ISSN:1476-5810
OA Status:Closed
Publisher DOI:https://doi.org/10.1111/vco.12441
PubMed ID:30136336

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