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Comparison of dosimetry from bowel bag and individual bowel loop contouring for patients receiving pelvic Stereotactic Ablative Radiotherapy (SABR)
EP30646
Poster Title: Comparison of dosimetry from bowel bag and individual bowel loop contouring for patients receiving pelvic Stereotactic Ablative Radiotherapy (SABR)
Submitted on 25 Sep 2019
Author(s): Eleanor Clarke, Rhiannon Howells, Matthew Beasley, Louise Murray
Affiliations: University of Leeds, Leeds Cancer Centre
This poster was presented at NCRI 2019, BIR Annual Congress 2019
Poster Views: 75
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Poster Information
Abstract: Background
Current practice for patients receiving SABR for pelvic oligometastases is to delineate individual bowel loops (BL) on planning CT; a time-consuming process. A bowel bag (BB) structure outlines the peritoneal cavity, allowing estimation of bowel dose.

This study investigated whether contouring only restricted BL in close tumour proximity, with the BB contoured to cover the remaining volume, would provide a more efficient contouring method without sacrificing valuable information.

Methods
Planning CTs with contoured BL for twenty patients who received SABR for pelvic oligometastatic nodal recurrence were included. BB was delineated. Planning target volume (PTV) was expanded 3 cm laterally and 2 cm superio-inferiorly (PTV3+2), to include BL closest to the tumour. Maximum doses to BL (0.5 cm3 (Dmax0.5cm3) and 5 cm3 (Dmax5cm3)) inside and beyond the PTV3+2 were evaluated.

Results
Dmax0.5cm3 and Dmax5cm3 for BL within PTV3+2 were consistently higher than doses to BL beyond PTV3+2 (both p<0.001).

The median difference in Dmax0.5cm3 of BL outside the PTV3+2 (BL_outside_PTV3+2) and BB outside the PTV3+2 (BB_outside_PTV3+2) was 0.4 Gy (range:-0.2 to +7.0). In 17/20, dose to BB_outside_PTV3+2 was higher.

Median difference in Dmax5cm3 of BL_outside_PTV3+2 and BB_outside_PTV3+2 was 1.0 Gy (range:-0.1 to +7.1), with dose to BB_outside_PTV3+2 higher in all.

Conclusions
Contouring individual BL in close proximity to the target provides the relevant structures to limit high dose to individual BL during planning using Dmax constraints. Contouring BB only beyond PTV3+2 does not result in any meaningful under-estimation of dose to BL within this region. This process offers time-saving implications.
Summary: This study aimed to compare dosimetry for bowel bag and individual bowel loop contouring for patients receiving Stereotactic Ablative Radiotherapy for pelvic oligometastatic recurrence. Report abuse »
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