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
Highlights
Since the introduction of intensity-modulated radiotherapy (IMRT), the physical measurements and patient-specific QA procedures to validate each IMRT plan before treatment have been considered an integral component of this delivery technique.[1,2] The comprehensive QA is essential for IMRT due to the complex nature of treatment planning and multitude of interfaces between the treatment planning system (TPS) and treatment delivery
Monte-Carlo–based independent dose calculations have been suggested for routine IMRT verification[14] and even to replace the dosimetric verification in phantom.[15]. In addition to research and clinical interest, the commercial interest in independent dose calculation for IMRT is growing and tools have become commercially available.[19,20] Recently there is still a debate to evaluate the necessity and effectiveness of dosimetric validation of each individual IMRT treatment plan with dosimetric plan before delivery.[12]. The machine log file analysis has been proposed as an alternative for IMRT QA by several groups.[16]. Log files have been used to study step-and-shoot and dynamic MLC deliveries.[17,18] A commercial software that automatically verifies delivery accuracy for patient treatment using the machine log files has become available
Treatment plans In the present study, 16 IMRT plans have been evaluated by experimental methods and by an independent dose calculation method followed by machine log file analysis
Summary
Since the introduction of intensity-modulated radiotherapy (IMRT), the physical measurements and patient-specific QA procedures to validate each IMRT plan before treatment have been considered an integral component of this delivery technique.[1,2] The comprehensive QA is essential for IMRT due to the complex nature of treatment planning and multitude of interfaces between the treatment planning system (TPS) and treatment delivery. Traditional measurement-based QA verification techniques may not be sensitive enough to detect many types of failures (such as plan transfer errors, beam delivery error, dose calculations errors) in the IMRT process.[10,11] Traditional IMRT QA processes rely on dose verification measurements in water equivalent plastic phantoms, which do not represent patient geometry or tissue heterogeneities. This oversimplification may not be able to identify calculation errors in some treatment sites. Log file analysis has been a routine component of patient-specific IMRT QA procedure for several years.[21]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
