ABSTRACT
Objective@#To investigate the Offset values of different applicators in afterloading brachytherapy.@*Methods@#Six types of applicators were selected in this study which included stainless steel interstitial needle (Part#083.062), proguide round needle (Part#189.608), proguide sharp needle (Part#189.601), vaginal multi-channel applicator (Part#110.800), fletcher CT/MR applicator (Part#189.745) and henschke titanium applicator (Part#110.437). According to the sources imaging in the fluorography film, the distance of applicators between the first dwell position and the top could be measured. Marker was pasted on the surface of applicator corresponding to the first dwell position. And then the applicator was put into the pelvic phantom for a CT scan. During applicator reconstruction in the treatment planning system, the Offset values of all applicators could be acquired through adjusting the value of offset to superimpose the first dwell and the marker images. On account of the density of plastic material applicators were similar to human tissues, it was difficult to reconstruct the top of the applicator. With the help of stopper or simulation source, the value of offset could be acquired for plastic material applicators. Based on the measurement results, the differences were analyzed among different applicators.@*Results@#The Offset values significantly differed among various applicators. The Offset value for stainless steel interstitial needle was -11.4 mm, -4.1 mm for proguide round needle, -3.5 mm for proguide sharp needle, 0 mm or -5.0 mm for vaginal multi-channel applicator, -6.5 mm for fletcher CT/MR applicator and -7.5 mm for henschke titanium applicator, respectively.@*Conclusion@#To adapt to the rapid development of precise radiotherapy, it is necessary to verify the Offset value in afterloading brachytherapy.
ABSTRACT
Objective To investigate the Offset values of different applicators in afterloading brachytherapy.Methods Six types of applicators were selected in this study which included stainless steel interstitial needle (Part#083.062),proguide round needle (Part#189.608),proguide sharp needle (Part# 189.601),vaginal multi-channel applicator (Part # 110.800),fletcher CT/MR applicator (Part # 189.745)and henschke titanium applicator (Part#110.437).According to the sources imaging in the fluorography film,the distance of applicators between the first dwell position and the top could be measured.Marker was pasted on the surface of applicator corresponding to the first dwell position.And then the applicator was put into the pelvic phantom for a CT scan.During applicator reconstruction in the treatment planning system,the Offset values of all applicators could be acquired through adjusting the value of offset to superimpose the first dwell and the marker images.On account of the density of plastic material applicators were similar to human tissues,it was difficult to reconstruct the top of the applicator.With the help of stopper or simulation source,the value of offset could be acquired for plastic material applicators.Based on the measurement results,the differences were analyzed among different applicators.Results The Offset values significantly differed among various applicators.The Offset value for stainless steel interstitial needle was-11.4 mm,-4.1 mm for proguide round needle,-3.5 mm for proguide sharp needle,0 mm or-5.0 mm for vaginal multi-channel applicator,-6.5 mm for fletcher CT/MR applicator and-7.5 mm for henschke titanium applicator,respectively.Conclusion To adapt to the rapid development of precise radiotherapy,it is necessary to verify the Offset value in afterloading brachytherapy.
ABSTRACT
Objective To report a simple method for determination of dwell position offset of ring applicator using GafchromicTM EBT3 film and ImageJ software. Methods In the dummy plan, this study reconstructed the ring applicator point by point manually according to the MR line marker, the most distal reconstruction point was at the end of marker, set the offset to zero. The first, eleventh, and twenty-third dwell positions were activated with the step length of 2. 5 mm. A setup image was designed to immobilize the ring applicator. The setup image was composed of two perpendicular thin lines and a circular with a diameter of 16 mm. GafchromicTM EBT3 film was fixed behind the setup image by plastic tapes. After irradiation, a ruler was put on the bottom of the irradiated film as a plotting scale. Photos were taken with the help of a vertical camera using a tripod. The file was imported into ImageJ software and the coordinate values were obtained by semi-automatic recognition of the center of exposure area. The test was repeated five times at one week interval to evaluate the uncertainty. For every time, each dwell position was measured five times. Results The angle between the radius of the first dwell position and the x-axis was 43° in the dummy plan, and (46. 8 ± 0. 9)° for actual measurement. The offset was 0. 9 mm for the ring applicator combined with the MR according to calculation. The distances between the first,the eleventh and the twenty-third dwell positions and the center of the ring were ( 12. 9 ± 0. 1 ) mm, ( 12. 5 ± 0. 1 ) mm, (12. 4 ± 0. 1) mm, respectively. Conclusions Using GafchromicTM EBT3 film and the ImageJ software is a simplified method to validate the dwell position offset of the ring applicator.