22 research outputs found
Dosimetric Investigation of Electron Arc Therapy Delivered Using Siemens Electron Arc Applicator with a Trapezoidal Aperture
Get PDFThis study investigated the delivery of electron arc treatment with a trapezoidal aperture. The aim of the investigation is to reduce the nonuniformity of the dose distribution, which is caused by the variation of the patient contour from superior to inferior. The characteristics of static electron beam were first investigated. Then a measurement-based algorithm was developed and implemented as a computer program called EarcMU to calculate the monitor units required for delivering the prescribed dose with a trapezoidal aperture. The central axis percentage depth dose was found to be independent of source-to-surface distance (SSD) and the width of the aperture. The inplane profiles of a trapezoidal aperture show that the dose decreases longitudinally from the wide to the narrow end of the trapezoidal aperture. The EarcMU program was verified using two cylindrical water phantoms. The measured dose and the dose calculated by the program agreed within 2.1% in the typical clinical conditions. A simple method was also proposed for determining the trapezoidal aperture for an individual patient. Under the same conditions, the trapezoidal apertures calculated by this method along with the open aperture were used to deliver treatments to several conical phantoms. Significant improvement in the uniformity of dose distribution was observed. On average, the flatness index of the longitudinal dose distribution from superior to inferior decreases dramatically from 8% for open aperture down to 0.58% for trapezoidal aperture. The results are clinically significant, indicating that delivering the electron arc treatment using a trapezoidal aperture can bring more uniform dose to the patient regardless of the change of patient contour from superior to inferior
An accuracy assessment of different rigid body image registration methods and robotic couch positional corrections using a novel phantom
No full textDose calibration of EPIDs for segmented IMRT dosimetry
Get PDFThe purpose of this study was to investigate the dose response of amorphous silicon (a-Si) electronic portal imaging devices (EPIDs) under different acquisi-tion settings for both open jaw defined fields and segmented intensity-modulated radiation therapy (IMRT) fields. Four different EPIDs were used. Two Siemens and one Elekta plus a standalone Perkin Elmer research EPID. Each was operated with different acquisition systems and settings. Dose response linearity was measured for open static jaw defined fields and ‘simple ’ segmented IMRT fields for a range of equipment and system settings. Six ‘simple ’ segmented IMRT fields were used. The segments of each IMRT field were fixed at 10 × 10 cm2 field size with equal MU per segment, each field having a total of 20 MU. Simultaneous measurements with an ionization chamber array (ICA) and EPID were performed to separate beam and detector response characteristics. Three different pixel calibration meth-ods were demonstrated and compared for an example ‘clinical IMRT field’. The dose response with the Elekta EPID for ‘simple ’ segmented IMRT fields versus static fields agreed to within 2.5 % for monitor unit (MU) ≥ 2. The dose respons
An algorithm to calculate a collapsed arc dose matrix in volumetric modulated arc therapy
No full textA comprehensive tool to analyse dynamic log files from an Elekta-Synergy accelerator
No full textThis study presents the development of a software tool 'Treat Check' to analyse the dynamic log files from an Elekta - Synergy accelerator. The software generates formatted output in the form of a plot presenting errors in various treatment delivery parameters such as gantry angle, Multi Leaf Collimator (MLC) leaf position, jaw position and Monitor Units (MU) for each of the control-points (CP) of the treatment beam. The plots are automatically saved in Portable Document Format (pdf). The software also has the functionality to introduce these treatment delivery errors into the original plan in the Pinnacle (Philips) treatment planning system (TPS) in order to assess the clinical impact of treatment delivery errors on delivered dose
Dose calibration of EPIDs for segmented IMRT dosimetry
No full textThe purpose of this study was to investigate the dose response of amorphous silicon (a-Si) electronic portal imaging devices (EPIDs) under different acquisition settings for both open jaw defined fields and segmented intensity-modulated radiation therapy (IMRT) fields. Four different EPIDs were used. Two Siemens and one Elekta plus a standalone Perkin Elmer research EPID. Each was operated with different acquisition systems and settings. Dose response linearity was measured for open static jaw defined fields and 'simple' segmented IMRT fields for a range of equipment and system settings. Six 'simple' segmented IMRT fields were used. The segments of each IMRT field were fixed at 10 x 10 cm 2 field size with equal MU per segment, each field having a total of 20 MU. Simultaneous measurements with an ionization chamber array (ICA) and EPID were performed to separate beam and detector response characteristics. Three different pixel calibration methods were demonstrated and compared for an example 'clinical IMRT field'. The dose response with the Elekta EPID for 'simple' segmented IMRT fields versus static fields agreed to within 2.5% for monitor unit (MU) ≥ 2. The dose response for the Siemens systems was difficult to interpret due to the poor reproducibility for segmented delivery, at MU ≤ 5, which was not observed with the standalone research EPID nor ICA on the same machine. The dose response measured under different acquisition settings and different linac/EPID combinations matched closely (≤ 1%), except for the Siemens EPID. Clinical IMRT EPID dosimetry implemented with the different pixel-to-dose calibration methods indicated that calibration at 20 MU provides equivalent results to implementing a ghosting correction model. The nonlinear dose response was consistent across both clinical EPIDs and the standalone research EPID, with the exception of the poor reproducibility seen with Siemens EPID images of IMRT fields. The nonlinear dose response was relatively insensitive to acquisition settings and appears to be primarily due to gain ghosting effects. No additional ghosting correction factor is necessary when the pixel-to-dose calibration factor at small MU calibration method is used
Dose discrepancy between planning system estimation and measurement in spine stereotactic body radiation therapy: A case report
No full textBenchmarking the gamma pass score using ArcCHECK for routine dosimetric QA of VMAT plans
No full textA minimum expected gamma (gamma) pass rate for VMAT plan verification using ArcCHECK was established based on the RTTQA, TG119 test cases and 10 clinical plans with varying levels of complexity. The impact of the 'Measurement Uncertainty' parameter as available in the ArcCHECK software on gamma pass rate was studied for both global and local gamma analysis. Our results show that excluding measurement uncertainty adds tighter tolerance in local gamma comparison. From the verification of our benchmark cases we established minimum expected gamma pass rates of 85% and 88% for 2%/2mm global and 3%/3mm local tolerance criteria
Validation of 3DVH estimated DVH metrics for prostate VMAT plans
No full textThe accuracy of 3DVH (Sun Nuclear Corporation, USA) reported DVH metrics for target volumes and Organs at Risk (OARs) for two Prostate Volumetric Modulated Arc Therapy (VMAT) plans was studied. The accuracy of 3DVH estimated DVH metrics in the presence of Multi Leaf Collimator (MLC) systematic errors was also tested with error introduced plans calculated in Pinnacle. The results of the study show that the DVH metrics estimated by 3DVH for error-free plans agree with the TPS calculation within 3%. The D95 to PTV was shown to be sensitive in detecting studied MLC errors. However the accuracy of 3DVH estimated DVH metrics for Target Volumes and OARs in the presence of MLC errors for VMAT prostate plans has limitations with this small data set. Although for most situations values matched within 3% for small MLC errors, there was up to a 9.8% difference between the TPS and 3DVH in the presence of a simulated 5mm MLC positioning error. Further study with more plans including other treatment sites is required to fully assess the performance of 3DVH in detecting potential clinical delivery errors
Three dimensional dose verification of VMAT plans using the Octavius 4D dosimetric system
No full textThe Octavius 4D dosimetric system generates a 3D dose matrix based on a measured planar dose and user supplied Percentage Depth Dose (PDD) data. The accuracy of 3D dose matrices reconstructed by the Octavius 4D dosimetric system was systematically studied for an open static field, an open arc field and clinical VMAT plans. The Octavius reconstructed 3D dose matrices were compared with the Treatment Planning System (TPS) calculated 3D dose matrices using 3D gamma (gamma) analysis with 2%/2mm and 3%/3mm tolerance criteria. The larger detector size in the 2D detector array of the Octavius system resulted in failed voxels in the high dose gradient regions. For the open arc fields mean (1 sigma) gamma pass rates of 84.5(8.9) % and 94.2(4.5) % were observed with 2%/2mm and 3%/3mm tolerance criteria respectively and for clinical VMAT plans mean (1 sigma) gamma pass rates of 86.8(3.5) % and 96.7(1.4) % were observed
