A service evaluation of the use of VMAT with CBCT imaging for Ca Cervix patients – evaluating the margin needed for target volume coverage with bone-registration matching



Bradford, S and Kirby, MC ORCID: 0000-0001-9765-5641
(2017) A service evaluation of the use of VMAT with CBCT imaging for Ca Cervix patients – evaluating the margin needed for target volume coverage with bone-registration matching. [Poster]

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Abstract

Sarah Bradford - Clatterbridge Cancer Centre, Wirral, Merseyside and Mike Kirby - Department of Medical Imaging and Radiotherapy, School of Health Sciences, University of Liverpool Background: VMAT techniques for Ca cervix patients offers the potential for improved conformity and reduced toxicity compared with standard CRT. On-treatment verification based upon the soft-tissue of the uterine cervix is both difficult, requiring specific training and complex, given the large internal motion of the uterus. But accurate verification is necessary, especially given the high dose gradients involved with VMAT This service evaluation examined whether a set CTV-PTV margin could still provide adequate coverage, when using more practical bone-registration matching using CBCT. Method: Retrospective CBCT scan data for 17 patients (240 scans) was analysed using off-line review tools to visually assess (in all three principal planes) appropriate coverage of the uterine cervix for a range of CTV-PTV margins, when simple bone-registration matching was used. The dosimetric consequences of the variation in required margin was examined in three of the 17 patients. Results: A large variation in CTV-PTV margin was needed for adequate coverage across all patients; maximum margins ranged from 1-4 cm; mean margins 1-2.7 cm for all patients. Variation across the treatment course was high, ranging from no change to 3 cm. No single margin could be used with straightforward bone-registration. Significant changes were seen in the OAR DVH data for the three patients examined – but noting that even in the original plans, dose constraints were compromised. Conclusion: Straightforward bone-registration matching is not suitable with a standardised margin for these patients. Adaptive solutions are needed e.g. combining bone-registration with plan-of-the-day approaches, integrity verified by further dosimetric analysis

Item Type: Poster
Depositing User: Symplectic Admin
Date Deposited: 08 Aug 2017 06:48
Last Modified: 09 Jan 2021 06:37
URI: https://livrepository.liverpool.ac.uk/id/eprint/3008859