Verification using in vivo optically stimulated luminescent dosimetry of the predicted skin surface dose in patients receiving postmastectomy radiotherapy

Johnathon R Wake; Feng Qin Chen; Simon Ashworth; Karen Byth; Wei Wang; Kirsty E Stuart

doi:10.1016/j.meddos.2020.10.001

Verification using in vivo optically stimulated luminescent dosimetry of the predicted skin surface dose in patients receiving postmastectomy radiotherapy

Med Dosim. 2021;46(2):e1-e6. doi: 10.1016/j.meddos.2020.10.001. Epub 2020 Oct 24.

Authors

Johnathon R Wake¹, Feng Qin Chen¹, Simon Ashworth¹, Karen Byth², Wei Wang³, Kirsty E Stuart⁴

Affiliations

¹ Department of Radiation Oncology, Crown Princess Mary Cancer Centre, Westmead, New South Wales, Australia.
² NHMRC Clinical Trials Centre, The University of Sydney, New South Wales, Australia; Research and Education Network, Western Sydney Local Health District, New South Wales, Australia.
³ Department of Radiation Oncology, Crown Princess Mary Cancer Centre, Westmead, New South Wales, Australia; Westmead Breast Cancer Institute, Westmead, New South Wales, Australia; Western Clinical School, The University of Sydney, New South Wales, Australia.
⁴ Department of Radiation Oncology, Crown Princess Mary Cancer Centre, Westmead, New South Wales, Australia; Westmead Breast Cancer Institute, Westmead, New South Wales, Australia; Western Clinical School, The University of Sydney, New South Wales, Australia. Electronic address: [email protected].

PMID: 33941320
DOI: 10.1016/j.meddos.2020.10.001

Abstract

The purpose of this study was to evaluate whether dose to the skin surface underneath bolus, was accurately predicted by a 3D treatment planning system (TPS) in patients receiving 50 Gy/25# postmastectomy radiotherapy (PMRT) using optically stimulated luminescent dosimetry (OSLD) for verification. In vivo dosimetry using OSLDs was performed in 20 consecutive patients receiving PMRT. An array of 9 OSLDs were applied to the chest wall or neobreast in a grid arrangement. Dosimetry data were recorded on 3 separate treatment fractions, averaged, and extrapolated to 25 fractions. On the 3D TPS, the predicted dose was calculated using the departmental planning algorithm at points corresponding to the OSLDs. The mean within patient difference between the planned and measured dose at each of the 9 points was calculated and Bland-Altman limits of agreement used to quantify the extent of agreement. Paired t-tests were used to test for evidence of systematic bias at each point. The coefficient of variation of the 3 OSLD readings per patient at each of the 9 points was low for 8 points (≤4.4%) demonstrating comparable dose received per fraction at these points. The mean ratio between the in vivo measured extrapolated OSLD (IVME OSLD) dose and the planned TPS dose ranged between 0.97 and 0.99 across all points (standard deviation range 0.05 to 0.08). The mean within patient difference between the IVME OSLD and planned TPS was <1 Gy at 7 of the 9 points and the t-test for evidence of systematic bias was significant (p = 0.03) at only 1 of the 9 points. Our commercially available 3D TPS closely predicted PMRT skin surface dose underneath bolus as verified by OSLDs. At all sites, the average ratio of delivered to predicted dose was >0.97 but <1. This practical and feasible OSLD assessment of only 3 of 25 fractions facilitates quality assurance of a TPS in predicting skin surface dose under bolus.

Keywords: Bolus; Breast neoplasm; Dosimetry; OSLD; Skin surface; postmastectomy radiotherapy.

MeSH terms

Breast Neoplasms* / radiotherapy
Female
Humans
Mastectomy
Optically Stimulated Luminescence Dosimetry*
Radiometry
Radiotherapy Planning, Computer-Assisted