Verification of dynamic and segmental IMRT delivery by dynamic log file analysis

The purpose of this study was to compare the MLC error sensitivity of various measurement devices for VMAT pre‐treatment quality assurance (QA). This study used four QA devices (Scandidos Delta4, PTW 2D‐array, iRT systems IQM, and PTW Farmer chamber). Nine retrospective VMAT plans were used and nine MLC error plans were generated for all nine original VMAT plans. The IQM and Farmer chamber were evaluated using the cumulative signal difference between the baseline and error‐induced measurements. In addition, to investigate the sensitivity of the Delta4 device and the 2D‐array, global gamma analysis (1%/1, 2%/2, and 3%/3 mm), dose difference (1%, 2%, and 3%) were used between the baseline and error‐induced measurements. Some deviations of the MLC error sensitivity for the evaluation metrics and MLC error ranges were observed. For the two ionization devices, the sensitivity of the IQM was significantly better than that of the Farmer chamber (P < 0.01) while both devices had good linearly correlation between the cumulative signal difference and the magnitude of MLC errors. The pass rates decreased as the magnitude of the MLC error increased for both Delta4 and 2D‐array. However, the small MLC error for small aperture sizes, such as for lung SBRT, could not be detected using the loosest gamma criteria (3%/3 mm). Our results indicate that DD could be more useful than gamma analysis for daily MLC QA, and that a large‐area ionization chamber has a greater advantage for detecting systematic MLC error because of the large sensitive volume, while the other devices could not detect this error for some cases with a small range of MLC error.

Section: Introductionmentioning

confidence: 99%

Comparison of MLC error sensitivity of various commercial devices for VMAT pre‐treatment quality assurance

Saito

Sano

Shibata

et al. 2018

“…The log files analysis will also report delivered dose errors due to dropped segments, leaf over/under shoot, faulty leaf motors, tongue‐and‐grove effect, rounded leaf ends, and communication delays between the controller and the workstation. In addition, they also tell us if the MLC gain calibration is set appropriately 8 , 11 …”

Section: Introductionmentioning

confidence: 99%

Comparing measurement‐derived (3DVH) and machine log file‐derived dose reconstruction methods for VMAT QA in patient geometries

Tyagi

Yang

Yan

2014

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 Pinnacle3 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%.15em±.15em1.2% and ‐1.0%.15em±.15em1.6%, 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%.15em±.15em10.5% 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

“…Methods for analysis and presentation of machine log files have been previously reported for linear accelerator‐(linac‐) based external beam radiation therapy (EBRT) treatments 9 , 10 , 11 , 12 , 13 . The MLC dynamic log files are available on Varian linac treatment machines (14) and have been utilized at the authors' institution and by other groups to validate the accuracy and completeness of the treatment deliveries 15 , 16 , 17 , 18 , 19 , 20 , 21 .…”

Section: Introductionmentioning

confidence: 99%

A software tool to automatically assure and report daily treatment deliveries by a cobalt‐60 radiation therapy device

Yang

Wooten

Green

et al. 2016

The aims of this study were to develop a method for automatic and immediate verification of treatment delivery after each treatment fraction in order to detect and correct errors, and to develop a comprehensive daily report which includes delivery verification results, daily image‐guided radiation therapy (IGRT) review, and information for weekly physics reviews. After systematically analyzing the requirements for treatment delivery verification and understanding the available information from a commercial MRI‐guided radiotherapy treatment machine, we designed a procedure to use 1) treatment plan files, 2) delivery log files, and 3) beam output information to verify the accuracy and completeness of each daily treatment delivery. The procedure verifies the correctness of delivered treatment plan parameters including beams, beam segments and, for each segment, the beam‐on time and MLC leaf positions. For each beam, composite primary fluence maps are calculated from the MLC leaf positions and segment beam‐on time. Error statistics are calculated on the fluence difference maps between the plan and the delivery. A daily treatment delivery report is designed to include all required information for IGRT and weekly physics reviews including the plan and treatment fraction information, daily beam output information, and the treatment delivery verification results. A computer program was developed to implement the proposed procedure of the automatic delivery verification and daily report generation for an MRI guided radiation therapy system. The program was clinically commissioned. Sensitivity was measured with simulated errors. The final version has been integrated into the commercial version of the treatment delivery system. The method automatically verifies the EBRT treatment deliveries and generates the daily treatment reports. Already in clinical use for over one year, it is useful to facilitate delivery error detection, and to expedite physician daily IGRT review and physicist weekly chart review.PACS number(s): 87.55.km