固定型腔内后装施源器治疗宫颈癌的剂量分布特点

Dose Distribution Trait of Fixed Intrauterine Tee Source Applicator

目的:研究固定型腔内后装施源器及标准腔内后装施源器的剂量分布特点,评价固定型腔内施源器是否符合临床剂量学要求。方法:比较固定型腔内后装施源器和标准型腔内施源器的等剂量曲线分布图,并根据腔内近距离放疗中剂量分布与距离平方成反比的剂量学特点,按照施源器材料中的指数衰减及吸收系数,计算出两种施源器x和y轴两个方向上的剂量比。结果:标准Ⅲ通腔内施源器和固定Ⅲ通腔内施源器等剂量曲线分布图通过TPS优化,图形基本一致:在冠状面上等剂量曲线呈扁梨行,宫颈、阴道剂量大于宫体剂量,在横断面上等剂量曲线呈扁椭圆形;且固定型扁平腔内施源器源中心到模表面距离为0.5 cm,而标准Ⅲ通腔内施源器从源中心到模表面距离为1 cm,通过计算可知当r=0.5 cm,l=1.0 cm时其剂量比大于l=1.5 cm时的剂量比,因此给予A点相同剂量所需要的时间较标准腔内后装施源器要短,由于治疗时间短,膀胱直肠所受剂量就小,通过优化,直肠剂量只有A点剂量的70%,而宫颈粘膜表面剂量比经典施源器剂量要高出45%。结论:固定型腔内后装施源器剂量分布符合临床剂量学要求,且优于标准施源器,同时由于使用简单方便,不用模拟机拍片,剂量计算模式也固定,更适合宫颈癌患者多的治疗中心使用。

This study was aimed to research the dose distribution of the intrauterine fixed tee source applicator and traditional one, and evaluate whether or not this applicator meet the requirement of clinical dosimetry. Methods： The isodose curve cattergram of fixed intrauterine tee source applicator was compared with standard apparatus. Dose distribution was the inverse to the square of the distance in intracavitary brachytherapy, so the dose ratios in x- and y-direction of the two applicator were calculated by the coefficient of the exponential decay and the absorption. Results： The isodose curve cattergram of standard and fixed intrauterine tee source applicator, optimized by TPS, were nearly accordant. They displayed a fiat pearl pattern in coronal plane, and flat oval pattern in cross section. The dose in cervix uteri and vagina was greater than that in corpus uteri. The 0.5 cm distance from the center of the source to the surface was applied in fixed applicator, and 1.0 cm in standard apparatus, and larger dose ratio were calculated when r =0.5 cm,ι=1.0 cm than ι=1.5 cm. The lapse of time to reach the same dosage in point A of the fixed applicator was much shorter than traditional one. It had saddle form dose distribution, with high dosage in the cervix and low dosage in the bladder. When optimized by the fixed applicator, dose adopted in the rectum wasonly 70% of the A point, and was 45% higher in the cervix membrane surface than that in the classic one. Conclusions： Dose distribution of fixed tee source applicator is more rational than traditional device, and this apparatus is more suitable for caner centers with a lot of patients.