Evaluation of the efficiency and effectiveness of independent dose calculation followed by machine log file analysis against conventional measurement based IMRT QA

Abstract

Experimental methods are commonly used for patient‐specific IMRT delivery verification. There are a variety of IMRT QA techniques which have been proposed and clinically used with a common understanding that not one single method can detect all possible errors. The aim of this work was to compare the efficiency and effectiveness of independent dose calculation followed by machine log file analysis to conventional measurement‐based methods in detecting errors in IMRT delivery. Sixteen IMRT treatment plans (5 head‐and‐neck, 3 rectum, 3 breast, and 5 prostate plans) created with a commercial treatment planning system (TPS) were recalculated on a QA phantom. All treatment plans underwent ion chamber (IC) and 2D diode array measurements. The same set of plans was also recomputed with another commercial treatment planning system and the two sets of calculations were compared. The deviations between dosimetric measurements and independent dose calculation were evaluated. The comparisons included evaluations of DVHs and point doses calculated by the two TPS systems. Machine log files were captured during pretreatment composite point dose measurements and analyzed to verify data transfer and performance of the delivery machine. Average deviation between IC measurements and point dose calculations with the two TPSs for head‐and‐neck plans were 1.2±1.3% and 1.4±1.6%, respectively. For 2D diode array measurements, the mean gamma value with 3% dose difference and 3 mm distance‐to‐agreement was within 1.5% for 13 of 16 plans. The mean 3D dose differences calculated from two TPSs were within 3% for head‐and‐neck cases and within 2% for other plans. The machine log file analysis showed that the gantry angle, jaw position, collimator angle, and MUs were consistent as planned, and maximal MLC position error was less than 0.5 mm. The independent dose calculation followed by the machine log analysis takes an average 47±6 minutes, while the experimental approach (using IC and 2D diode array measurements) takes an average about 2 hours in our clinic. Independent dose calculation followed by machine log file analysis can be a reliable tool to verify IMRT treatments. Additionally, independent dose calculations have the potential to identify several problems (heterogeneity calculations, data corruptions, system failures) with the primary TPS, which generally are not identifiable with a measurement‐based approach. Additionally, machine log file analysis can identify many problems (gantry, collimator, jaw setting) which also may not be detected with a measurement‐based approach. Machine log file analysis could also detect performance problems for individual MLC leaves which could be masked in the analysis of a measured fluence.PACS numbers: 87.53.Bn, 87.55.Qr, 87.55.km, 87.57.Uq

Process‐based quality management for clinical implementation of adaptive radiotherapy

“…Although not based on direct dosimetric measurements, post-treatment or real-time monitoring of MLC log files is a simpler solution. This approach has been demonstrated by several groups 16,22 and log-file QA software is now commercially available for use in the clinic (Modus Medical Devices, Inc.). It has been suggested that supplementing MLC log file analysis with independent dose calculations may be a better QA method than traditional measurement-based approaches due to increased sensitivity to dose calculation errors, heterogeneity errors, and beam modeling errors.…”

“…Comparison of machine delivery log files to planned patterns could reveal failures-a practice that has been shown to be both feasible and effective for postdelivery verification. 16 This approach is also much less resource intensive than physical measurement-based QA. Retrospective post-treatment QA (simulated or physical phantom-based) could be adequate for delivery systems that demonstrate time-tested stability.…”

Predicting Delivery Error Using a DICOM-RT Plan for Volumetric Modulated Arc Therapy

“…Several groups have proposed the use of machine log file analysis as an alternative for IMRT and VMAT QA [8]- [10]. However, log file evaluation must be performed after VMAT delivery.…”

Desenvolvimento e avaliação de um sistema de cálculo de dose independente para controle de qualidade de IMRT do tipo jaws-only

“…Nosúltimos anos, o cálculo de dose independente do SPT vem sendo apresentado como uma forma de realizar o CQ de IMRT com uma redução da carga de trabalho [38,39,32,40,41]. A propostaé substituir a dosimetria por esse cálculo, como forma de verificar as previsões dosimétricas do SPT.…”

“…O cálculo independente não verifica a entrega da dose, portanto, esse método deve ser acompanhado de uma outra forma de verificar o funcionamento da máquina de tratamento. Essa verificação pode ser realizada por meio de um arquivo (log file) que possui informações, adquiridas pelos sistemas de detecção do acelerador linear, de parâmetros usados na irradiação, como o posicionamento do MLC [39]. Diferentes algoritmos de cálculo são usados na implementação dos sistemas de cálculo independente, sendo os métodos baseados em simulações de Monte Carlo os que proporcionam maior exatidão.…”