ABSTRACT
ObjectiveTo compare the accuracy of enhanced dynamic wedge (EDW) models of adaptive convolution algorithm (ACA) in Pinnacle3 9.0 and anisotropic analytical algorithm (AAA),and pencil beam convolution (PBC) algorithms in Eclipse7.3 treatment planning systems (TPS).MethodsTo evaluate the accuracy of the three algorithm models,we compared actual measurement values with TPS calculation values of EDW wedge factors under for different fields in which Varian-21EX 6 MV X-ray was applied,and also compared the actual dose distribution profile with that of TPS.ResultsThe deviations of EDW wedge factors of symmetry fields and asymmetric fields are within 2.8％ and 19.4％ for ACA in Pinnacle3 9.0.Meanwhile,the deviations are 1.0％ and 2.0％ for AAA,1.2％ and 3.0％ for PBC in Eclipse7.3.The deviations between measurement and calculation of all fields profile for ACA is within 3％ and within 2.7％ for AAA within 4.0％ for PBC in wedge direction.For the dose distributions,we evaluated the pass rates of three algorithms using gamma analysis.The gamma pass rates among all the three algorithms in symmetry and asymmetric fields are above 87％ and 85％ respectively.After the removal of the penumbra zone,the pass rates among all the three algorithms are above 96％ in symmetry fields,and above 95％ in asymmetric fields,respectively.Conclusions AAA and PBC algorithms in symmetric and asymmetric fields can meet the need of clinical applications.While,wedge factor of ACA should not be used in clinical due to its greater error in asymmetric fields.
ABSTRACT
Objective To investigate the correction of manual monitor unit calculation for asymmetric fields using the Varian enhanced dynamic wedge.Methods Monitor unit (MU) was calculated when the field sizes ranged from 6 cm × 6 cm to 20 cm × 20 cm at a depth of 5 cm using Varian Eclipse and both 6 MV and 10 MV X-rays data from Varian Clinac 23EX for all seven available EDW angles,including 10°15°,20°,25°,30°,45°and 60° The field size was kept fixed,and the distance between geometry center of field and isocenter was increased in increments of 1 cm,ranging from -9 cm to 4 cm.When the field size was the same,the correction factor was defined as the ratio of MU calculated for asymmetric field to monitor unit calculated for symmetric field.To ensure the correction factors obtained above could be used in routine manual calculation for EDW fields,measurements were made at a depth of 5 cm for 30°and 45°EDW with field size of 10 cm × 10 cm using 6 MV X-rays.Results The correction factor was independent of field dimensions,so the average value was adopted to make practical calculation.Without correction,the maximum error was 18% for 30°,and 30% for 45.After the results of monitor unit calculation were corrected,the largest error was - 1.8% and - 1.7% for 30° and 45°EDW,respectively.The magnitude of errors was within the clinical tolerance limits.Conclusions For asymmetric EDW fields,there is very large difference between the prescribed dose by manual calculation using EDW factors measured for symmetric fields and that delivered during treatment in order to obtain correct dose to reference point.The errors are decreased to be acceptable after correction.The method of correction is simple and independent of machine specific beam parameters.
ABSTRACT
In order to evaluate the radio-protective advantage of an enhanced dynamic wedge (EDW) over a physical wedge (PW), we measured peripheral doses scattered from both types of wedges using a 2D array of ion-chambers. A 2D array of ion-chambers was used for this purpose. In order to confirm the accuracy of the device, we first compared measured profiles of open fields with the profiles calculated by our commissioned treatment planning system. Then, we measured peripheral doses for the wedge angles of 15 degrees, 30 degrees, 45 degrees, and 60 degrees at source to surface distances (SSD) of 80 cm and 90 cm. The measured points were located at 0.5 cm depth from 1 cm to 5 cm outside of the field edge. In addition, the measurements were repeated by using thermoluminescence dosimeters (TLD). The peripheral doses of EDW were (1.4% to 11.9%) lower than those of PW (2.5% to 12.4%). At 15 MV energy, the average peripheral doses of both wedges were 2.9% higher than those at 6MV energy. At a small SSD (80 cm vs. 90 cm), peripheral dose differences were more recognizable. The average peripheral doses to the heel direction were 0.9% lower than those to the toe direction. The results from the TLD measurements confirmed these findings with similar tendency. Dynamic wedges can reduce unnecessary scattered doses to normal tissues outside of the field edge in many clinical situations. Such an advantage is more profound in the treatment of steeper wedge angles, and shorter SSD.
Subject(s)
Heel , Silver Sulfadiazine , ToesABSTRACT
For clinical implementation of Enhanced Dynamic Wedge (EDW), it is necessary to adequately analyze and commission its dosimetric properties in comparison to common physical metal wedge (MTW). This study was implemented with the essential measurements of parameters for clinical application, such as percentage depth dose, peripheral dose, surface dose, effective wedge factor, and wedge profile. In addition, through the comparison study of EDW with open and MTW, the analysis was performed to characterize the EDW. We also compared EDW dose profiles of measured values using chamber array 24 (CA24) with calculated values using radiation treatment planning system. PDDs of EDW showed good agreements between 0.2~0.5% of open beam, but 2% differences with MTW. In the result of the measurements of peripheral dose, it was shown that MTW was about 1% higher than open field and EDW. The surface doses of 60degrees MTW showed 10% lower than the others. We found that effective wedge factor of EDW had linear relationships according to Y jaw sizes and was independent of X jaw sizes and was independent of X jaw sizes and asymmetric Y jaw opening. In comparison with measured values and calculate values from Golden-STT based radiation treatment planning system (RTP system), it showed very good agreement within difference of 1%. It could be concluded that EDW is a very reliable and useful tool as a beam modification substitute for conventional MTW.