ABSTRACT
Objective To compare the single-shot fields irradiated by three focusing modes of γ-knife and explore the approaches for improving the quality of stereotactic radiosurgery.Methods GAFCHROMIC(R) EBT3 mode flushing-free film was used to measure the single-shot fields irradiated by multi-source static focusing modes,multi-source single-axis rotating focusing mode and single-source double-axis rotating focusing mode of γ-knife.Also the uniformity and penumbra of the single-shot fields were compared.Results The 2D dose distribution of the single-shot fields irradiated by three focusing modes of γ-knife was different.In the axis (x,y,z),the rang of penumbra axial length ratios of multisource static focusing modes,multi-source single-axis rotating focusing mode and single-source double-axis rotating focusing mode were 0.13-0.48,0.17-0.33 and 0.28-0.54,in the diagonal direction of the wings plane (NSD,PSD),were 0.31-0.39,0.38-0.43 and 0.54-0.72,respectively;the penumbra axial length ratio of single-source double-axis rotating focusing mode was bigger than in multi-source static focusing modes and multi-source single-axis rotating focusing mode.On the no-wings plane,the area ratios of 80％ dose curve enveloped and 50％ dose curve enveloped(A80％/A50％)were 0.40,0.47 and 0.19,on the wings plane,were 0.61,0.53 and 0.35,respectively.The field uniformity of multi-source static focusing modes and multi-source single-axis rotating focusing mode were superior to single-source doubleaxis rotating focusing mode.Conclusions Considering dose distribution of the single-shot fields,the multi-source static focusing modes devices and the multi-source single-axis rotating focusing mode devices should be preferred,when important tissues and organs are adjacent to the target areas.Compared with single-source double-axis rotating focusing mode,both multi-source static focusing modes and multi-source single-axis rotating focusing mode could make more target areas to be surrounded by high dose region.
ABSTRACT
Objective To investigate the patients' radiation dose received in digital radiography (DR) and provide basic data for developing diagnostic reference levels.Methods The patient' s ESD was estimated using the TLDs and DAP was measured by the dose-area product meter.The E values were then calculated by the DAP using Monte Carlo data and RefDose software.Measurements were made for twelve types of examination:skull PA,skull LAT,chest PA,chest LAT,abdomen AP,pelvis AP,cervix spine PA,cervix spine LAT,thoracic spine PA,thoracic spine LAT,lumber spine PA and lumber spine LAT.Results Both kV and mAs varied in the same type of examination for ESD,DAP and E(F =33.47,24.68,43.19,P ＜ 0.05).The dose each time for lumber spine LAT was the highest,reached 4.62 mGy in ESD and 2.26 Gy·cm2 in DAP,respectively.The E of abdomen AP averaged as 0.59 mSv,higher than that of lumber spine LAT.Even for the same type of examination,the dose from each equipment was different.Conclusions DR has the potential to reduce the patients' radiation doses.The guidance levels suitable for Chinese population should be established as soon as possible.
ABSTRACT
Objective To study the method of measuring the position accuracy and the step distance accuracy of afterloading system with192Ir source by using flushing-free film.Methods The position accuracy and the step distance accuracy of a China-made afterloading system with192Ir source was measured by using GAFCHROMIC (R) EBT3 flushing-free film.The film was scanned to proper image format,required by dose analysis software,by EPSON PREFACTION V700 PHOTO scanner.Then images are analyzed by using film dose analysis software in SNC Patient 5.2.Results With focus on the center of active section of source,the position accuracy of this afterloading system with192Ir source was-0.75 mm.Using film analysis could make the step point to tell apart if the step distance was 5 mm away by the method of film analysis,but couldnot make it to tell apart if the step distance was 2.5 mm away.The 2.5 mm step distance accuracy could be judged if the distance between the 1 st point and the 3rd point was 5 mm,then the 2.5 mm step distance could be deemed to no deviation.The 5 mm step distance of this afterloading system had no deviation in continuous 9 step points measured by flushing-free film.The indirect measuring results of the 2.5 mm step distance had no deviation as well.The position accuracy of this afterloading system measured with the flushing-free film accorded with the national standards.Conclusions The method of measuring the position accuracy and the step distance accuracy of the afterloading system with192Ir source by using flushing-free film is technically feasible.