Establishment of a Fast Quality Assurance Method for Three-dimensional Afterloading Treatment Plan

Objective:To study the correlation between tumor size,radiation source intensity,prescription dose,and source dwell time in afterloading treatment plan,and to establish a rapid quality control method for afterloading treatment plan.Methods:A total of 181 patients with gynecological tumor were enrolled in our hospital.A total of 84 patients were installed with three tubes of Fletcher'applicator,58 patients with single uterine tube and 39 patients with vaginal applicator.Each patient was scanned with CT before treatment,and the target area and organs were delineated by doctors.The treatment plan was optimized by IPSA.The planned source intensity,prescription dose,source residence time and tumor volume of each case were recorded and the CI,RV,and k value were calculated,The CI distribution characteristics and the relationship with RV value were analyzed.In addition,46 cases of gynecological tumor patients'afterloading plan used this method for quality control verification.Results:The CI of the three kinds of applicators was normal distribution.The average Ci of Fletcher applicator was 0.720±0.067,k=1394,r=0.894,the average CI of Fletcher applicator was 0.697±0.076,k=1428,r=0.940,the average CI of vaginal applicator was 0.742±0.067,k=1362,r=0.909.Conclusion:Using this method,we could quickly evaluate the target volume,radiation source intensity,prescription dose and treatment time,to determine the cause of deviation according to the feedback results,ensuring that the afterloading treatment plan can be implemented efficiently quickly,and accurately in accordance with the clinical requirements.

Attenuation properties of 3D-printed materials for an Ir-192 high dose rate source using Valencia skin applicators

Objective:To evaluate the physical properties of commonly used 3D-printed materials and the dose attenuation around a high-dose-rate ^(192)Ir source,in order to provide a reference for selecting appropriate 3D-printed materials for brachytherapy.Methods:Fifteen 3D-printed materials(12 non-metallic material and 3 metallic material)were assessed.Each material was fabricated into a wafer with a diameter of 30 mm and thickness of 3 mm using 3D printing.The CT number of each material was measured,and attenuation measurements were conducted with a Valencia skin applicator and well-type ionization chamber.192Ir was used as the radioactive source,and the attenuated ionization charges were normalized against that obtained in the presence of a solid water phantom at the same depth.Results:The CT number of nylon was(-7.78±3.36)HU,closest to water among all materials.The CT numbers of the other 11 non-metallic materials were below 300 HU.Moreover,the CT number of the Al alloy was(1,350.89±374.55)HU,while the CT numbers of the Ti alloy and stainless steel exceeded 2,976 HU,reaching the upper limit of the CT number range.The results of the attenuation measurements were normalized with the solid water phantom.The average attenuation coefficients of a polyamide,epoxy resin,photosensitive resin,carbon fiber,silica gel,Al alloy,Ti alloy,and stainless steel were 1.003,0.994,0.992,0.995,0.995,0.967,0.939,and 0.866,respectively.Conclusions:Among the common 3D-printed materials with a density similar to that of water,nylon exhibited the best performance,while the metallic materials caused significant dose attenuation and exhibited CT number distortion.As a result,care should be taken when metallic materials are used as 3D-printed materials for brachytherapy.