Open AccessComparing measurement‐derived (3DVH) and machine log file‐derived dose reconstruction methods for VMAT QA in patient geometries
Author(s) -
Tyagi Neelam,
Yang Kai,
Yan Di
Publication year - 2014
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1120/jacmp.v15i4.4645
Subject(s) - isocenter , nuclear medicine , ionization chamber , medicine , mathematics , algorithm , computer science , physics , imaging phantom , ion , quantum mechanics , ionization
The purpose of this study was to compare the measurement‐derived (3DVH) dose reconstruction method with machine log file‐derived dose reconstruction method in patient geometries for VMAT delivery. A total of ten patient plans were selected from a regular fractionation plan to complex SBRT plans. Treatment sites in the lung and abdomen were chosen to explore the effects of tissue heterogeneity on the respective dose reconstruction algorithms. Single‐ and multiple‐arc VMAT plans were generated to achieve the desired target objectives. Delivered plan in the patient geometry was reconstructed by using ArcCHECK Planned Dose Perturbation (ACPDP) within 3DVH software, and by converting the machine log file to Pinnacle 3 9.0 treatment plan format and recalculating dose with CVSP algorithm. In addition, delivered gantry angles between machine log file and 3DVH 4D measurement were also compared to evaluate the accuracy of the virtual inclinometer within the 3DVH. Measured ion chamber and 3DVH‐derived isocenter dose agreed with planned dose within 0 . 4 % ± 1 . 2 % and ‐ 1 . 0 % ± 1 . 6 % , respectively. 3D gamma analysis showed greater than 98% between log files and 3DVH reconstructed dose. Machine log file reconstructed doses and TPS dose agreed to within 2% in PTV and OARs over the entire treatment. 3DVH reconstructed dose showed an average maximum dose difference of 3% ± 1.2% in PTV, and an average mean difference of ‐ 4 . 5 % ± 10 . 5 % in OAR doses. The average virtual inclinometer error (VIE) was ‐0.65° ± 1.6° for all patients, with a maximum error of ‐5.16° ± 4.54° for an SRS case. The time averaged VIE was within 1°–2°, and did not have a large impact on the overall accuracy of the estimated patient dose from ACPDP algorithm. In this study, we have compared two independent dose reconstruction methods for VMAT QA. Both methods are capable of taking into account the measurement and delivery parameter discrepancy, and display the delivered dose in CT patient geometry rather than the phantom geometry. The dose discrepancy can be evaluated in terms of DVH of the structures and provides a more intuitive understanding of the dosimetric impact of the delivery errors on the target and normal structure dose. PACS number: 87.55