An automated Monte Carlo QC system for volumetric modulated arc therapy: Possibilities and challenges

R Chakarova; R Cronholm; M Krantz; P Andersson; A Hallqvist

doi:10.1016/j.ejmp.2018.03.010

An automated Monte Carlo QC system for volumetric modulated arc therapy: Possibilities and challenges

Phys Med. 2018 Jul:51:32-37. doi: 10.1016/j.ejmp.2018.03.010. Epub 2018 Mar 21.

Authors

R Chakarova¹, R Cronholm², M Krantz³, P Andersson³, A Hallqvist⁴

Affiliations

¹ Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden; Department of Radiation Physics, Sahlgrenska Academy at the University of Gothenburg, Sweden. Electronic address: roumiana.chakarova@vgregion.se.
² Department of Radiation Physics, Skåne University Hospital, Lund, Sweden.
³ Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden.
⁴ Department of Oncology, University of Gothenburg, Sweden.

PMID: 29572112
DOI: 10.1016/j.ejmp.2018.03.010

Abstract

Purpose: To develop and implement an automated Monte Carlo (MC) system for patient specific VMAT quality control in a patient geometry that generates treatment planning system (TPS) compliant DICOM objects and includes a module for 3D analysis of dose deviations. Also, the aims were to recommend diagnose specific tolerance criteria and an evaluation procedure.

Methods: The EGSnrc code package formed the basis for development of the MC system. The workflow consists of a number of modules connected to a TPS by means of manual DICOM exports and imports which were executed sequentially without user interaction. DVH comparison was performed in the TPS. In addition, MC- and TPS dose distributions were analysed by applying the normalized dose difference (NDD) formalism. NDD failure maps and a pass rate for a certain threshold were obtained. 170 clinical plans (prostate, thorax, head-and-neck and gynecological) were selected for analysis.

Results: Agreement within 1.5% was found between clinical- and MC data for the mean dose to the target volumes and within 3% for parameters more sensitive to the shape of the DVH e.g. D_98% PTV. Regarding the NDD analysis, tolerance criteria 2%/3 mm were established for prostate plans and 3%/3 mm for the rest of the cases.

Conclusions: An automated MC system was developed and implemented. Evaluation procedure is recommended with NDD-analysis as a first step. For pass rate < 95%, the evaluation continues with comparison of DVH parameters. For deviations larger than 2%, a visual inspection of the clinical- and MC dose distributions is performed.

Keywords: Monte Carlo; Normalized dose difference; Patient specific VMAT QC.

MeSH terms

Automation
Humans
Monte Carlo Method*
Quality Control
Radiotherapy Dosage
Radiotherapy, Intensity-Modulated*