Abstract
The first quality assurance process for validating dose‐volume histogram data involving brachytherapy procedures in radiation therapy is presented. The process is demonstrated using both low dose‐rate and high dose‐rate radionuclide sources. A rectangular cuboid was contoured in five commercially available brachytherapy treatment planning systems. A single radioactive source commissioned for QA testing was positioned coplanar and concentric with one end. Using the brachytherapy dosimetry formalism defined in the AAPM Task Group 43 report series, calculations were performed to estimate dose deposition in partial volumes of the cuboid structure. The point‐source approximation was used for a 125I source and the line‐source approximation was used for a 192Ir source in simulated permanent and temporary implants, respectively. Hand‐calculated, dose‐volume results were compared to TPS‐generated, dose‐volume histogram (DVH) data to ascertain acceptance. The average disagreement observed between hand calculations and the treatment planning system DVH was less than 1% for the five treatment planning systems and less than 5% for 1 cm≤r≤5 cm. A reproducible method for verifying the accuracy of volumetric statistics from a radiation therapy TPS can be employed. The process satisfies QA requirements for TPS commissioning, upgrading, and annual testing. We suggest that investigations be performed if the DVH%VolTPS “actual variance” calculations differ by more than 5% at any specific radial distance with respect to %VolTG−43, or if the “average variance” DVH DVH%VolTPS calculations differ by more than 2% over all radial distances with respect to %VolTG−43.PACS numbers: 87.10.+e, 87.55.‐x, 87.53.Jw, 07.05.Tp
Highlights
111 Gossman et al.: Brachytherapy dose-volume histogram (DVH) commissioning which is qualitatively represented in the form of isodose lines superimposed on the images, depicts which anatomical part of the patient is estimated to receive a certain dose
The report states that DVH validation depends on many factors including the dose calculation grid, volumetric region-of-interest grid, accuracy of object segmentation, bin size of the histogram, and any plan normalization.[3,4] Since it is important to have accurate DVH results for clinical use, we have tasked ourselves to examine the accuracy of the DVH output in the computerized treatment planning system (TPS) against independent hand calculations
Brachytherapy dose calculations The Association of Physicists in Medicine (AAPM) Task Group 43 (TG-43) report from 1995 and updates TG-43U1 and TG-43U1S1 are currently recognized as the worldwide standard for low-energy, photon-emitting brachytherapy dose calculations.[11,12,13] The high-energy, photon-emitting brachytherapy dosimetry protocol is described by the joint AAPM/ESTRO High Energy Brachytherapy Dosimetry Working Group Report.[14]. A detailed description of the formalism involved is available in that literature
Summary
111 Gossman et al.: Brachytherapy DVH commissioning which is qualitatively represented in the form of isodose lines superimposed on the images, depicts which anatomical part of the patient is estimated to receive a certain dose. The DVH carries no spatial information, it can differentiate the percentage of the prescribed dose received to any organ or structure being considered.[1] Clinical interpretation of organ-specific DVH data is a deciding factor in whether a treatment plan is acceptable.[2] DVH metrics reported by TPSs need to be examined routinely to ensure the calculations are correct. The report states that DVH validation depends on many factors including the dose calculation grid, volumetric region-of-interest grid, accuracy of object segmentation, bin size of the histogram, and any plan normalization.[3,4] Since it is important to have accurate DVH results for clinical use, we have tasked ourselves to examine the accuracy of the DVH output in the computerized TPS against independent hand calculations
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