Measuring dose in lung identifies peripheral tumour dose inaccuracy in SBRT audit

Maddison Shaw; Jessica Lye; Andrew Alves; Joerg Lehmann; Masoumeh Sanagou; Moshi Geso; Rhonda Brown

doi:10.1016/j.ejmp.2023.102632

Measuring dose in lung identifies peripheral tumour dose inaccuracy in SBRT audit

Phys Med. 2023 Aug:112:102632. doi: 10.1016/j.ejmp.2023.102632. Epub 2023 Jul 3.

Authors

Maddison Shaw¹, Jessica Lye², Andrew Alves³, Joerg Lehmann⁴, Masoumeh Sanagou⁵, Moshi Geso⁶, Rhonda Brown³

Affiliations

¹ Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia; School of Health and Biomedical Sciences, RMIT University, Melbourne, Australia. Electronic address: maddison.shaw@arpansa.gov.au.
² Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia; Olivia Newton John Cancer Wellness and Research Centre, Austin Health, Australia.
³ Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia.
⁴ Department of Radiation Oncology, Calvary Mater Newcastle, Newcastle, Australia; School of Science, RMIT University, Melbourne, Australia; School of Mathematical and Physical Sciences, University of Newcastle, Australia; Institute of Medical Physics, University of Sydney, Australia.
⁵ Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia.
⁶ School of Health and Biomedical Sciences, RMIT University, Melbourne, Australia.

PMID: 37406592
DOI: 10.1016/j.ejmp.2023.102632

Abstract

Purpose: Stereotactic Body Radiotherapy (SBRT) for lung tumours has become a mainstay of clinical practice worldwide. Measurements in anthropomorphic phantoms enable verification of patient dose in clinically realistic scenarios. Correction factors for reporting dose to the tissue equivalent materials in a lung phantom are presented in the context of a national dosimetry audit for SBRT. Analysis of dosimetry audit results is performed showing inaccuracies of common dose calculation algorithms in soft tissue lung target, inhale lung material and at tissue interfaces.

Methods: Monte Carlo based simulation of correction factors for detectors in non-water tissue was performed for the soft tissue lung target and inhale lung materials of a modified CIRS SBRT thorax phantom. The corrections were determined for Gafchromic EBT3 Film and PTW 60019 microDiamond detectors used for measurements of 168 SBRT lung plans in an end-to-end dosimetry audit. Corrections were derived for dose to medium (D_m,m) and dose to water (D_w,w) scenarios.

Results: Correction factors were up to -3.4% and 9.2% for in field and out of field lung respectively. Overall, application of the correction factors improved the measurement-to-plan dose discrepancy. For the soft tissue lung target, agreement between planned and measured dose was within average of 3% for both film and microDiamond measurements.

Conclusions: The correction factors developed for this work are provided for clinical users to apply to commissioning measurements using a commercially available thorax phantom where inhomogeneity is present. The end-to-end dosimetry audit demonstrates dose calculation algorithms can underestimate dose at lung tumour/lung tissue interfaces by an average of 2-5%.

Keywords: Algorithm; Dose calculation; Dosimetry audit; Film dosimetry; Lung; Monte Carlo; QA; SABR; SBRT; Stereotactic.

MeSH terms

Algorithms
Humans
Lung
Lung Neoplasms* / radiotherapy
Lung Neoplasms* / surgery
Monte Carlo Method
Phantoms, Imaging
Radiometry / methods
Radiosurgery* / methods
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Thorax