Characterization and clinical evaluation of a novel IMRT quality assurance system

Abstract

Intensity‐modulated radiation therapy (IMRT) is a complex procedure that involves the delivery of complex intensity patterns from various gantry angles. Due to the complexity of the treatment plans, the standard care is to perform measurement‐based, patient‐specific quality assurance (QA). IMRT QA is traditionally done with film for relative dose in a plane and with an ion chamber for absolute dose. This is a laborious and time‐consuming process. In this work, we characterized, commissioned, and evaluated the QA capabilities of a novel commercial IMRT device, Delta4, (ScandiDos, Uppsala, Sweden). This device consists of diode matrices in two orthogonal planes inserted in a cylindrical acrylic phantom that is 22 cm in diameter. Although the system has detectors in only two planes, it provides a novel interpolation algorithm that is capable of estimating doses at points where no detectors are present. Each diode is sampled per beam pulse so that the dose distribution can be evaluated on segment‐by‐segment, beam‐by‐beam, or as a composite plan from a single set of measurements. The end user can calibrate the system to perform absolute dosimetry, eliminating the need for additional ion chamber measurements. The patient's IMRT plan is imported into the device over the hospital LAN and the results of the measurements can be displayed as gamma profiles, distance‐to‐agreement maps, dose difference maps, or the measured dose distribution can be superimposed on the patient's anatomy to display an as‐delivered plan. We evaluated the system's reproducibility, stability, pulse‐rate dependence, dose‐rate dependence, angular dependence, linearity of dose response, and energy response using carefully planned measurements. We also validated the system's interpolation algorithm by measuring a complex dose distribution from an IMRT treatment. Several simple and complex isodose distributions planned using a treatment planning system were delivered to the QA device; the planned and measured dose distributions were then compared and analyzed. In addition, the dose distributions measured by conventional IMRT QA, which uses an ion chamber and film, were compared. We found that the Delta4 device is accurate and reproducible and that its interpolation algorithm is valid. In addition, the supplied software and network interface allow a streamlined IMRT QA process.PACS number: 87.56Fc

Clinically evaluating directional dependence of 2D seven29 ion-chamber array with different IMRT plans

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] In the study 'characterization of the response of the seven29 2D array detector' 11 by Syam et al, the detector's directional dependence was measured as a function of the beam angles and verified by delivering an open field. In the present study, we clinically investigated the angular dependence of a 2D ion-chamber array for IMRT dose verification and quantified the influence of the directional dependence on the effectiveness of the treatment with different IMRT plans.…”

“…Here, the fluence profile along the moving direction of a leaf pair is created by sweeping the leaf pair with different openings over the field while the beam is always on. [1][2][3][4][5][6][7] IMRT is a complicated procedure that involves the delivery of complex intensity patterns from various gantry angles. Owing to the complexity of the treatment plans, IMRT requires their dosimetric verification, as it produces a steep gradient inside tumors.…”

A retrospective analysis for patient-specific quality assurance of volumetric-modulated arc therapy plans

“…8 Many types of dosimeters have been used for patientspecific quality assurance (QA), such as ion chamber, film, 9,10 2-dimensional (2D) diode or ion chamber matrix detectors, [10][11][12][13][14] electronic portal imaging devices, 15 gel dosimetry, 16 and 3D diode arrays. 17,18 3D diode arrays are easy to use and provide 3D dose distributions and QA results, while measurements are being performed. Published studies provide evidence that 3D diode journal homepage: www.meddos.org arrays are accurate and reliable tools for dose verification of VMAT treatment.…”

Advantage of 3D volumetric dosemeter in delivery quality assurance of dynamic arc therapy: comparison of pencil beam and Monte Carlo calculations

“…These have been verified by many researchers, and these dose evaluation methods are still in use today. 11,[27][28][29][30][31][32][33][34] In addition, the evaluation of an absolute isocenter dose and 2D dose distribution are considered to be adequate for delivery QA of arc therapy, such as IMAT or VMAT. 35,36 Wagner and Vorwerk 35 reported that the use of a 2D ionization chamber (MatriXX™; IBA Dosimetry GmbH, Schwarzenbruck, Germany) for VMAT plan verification is reasonable in clinical routine use.…”