Meigooni A S, Zhu Y, Williamson J F, Myerson R J, Teague S, Löffler E, Nussbaum G H, Klein E E, Kodner I J
Radiation Oncology Center, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
Int J Radiat Oncol Biol Phys. 1996 Mar 15;34(5):1153-63. doi: 10.1016/0360-3016(95)02201-5.
An applicator is described for endocavitary treatment of rectal cancers using a high dose rate (HDR) remote afterloading system with a single high-intensity 192Ir source as an alternative to the 50 kVp x-ray therapy contact unit most frequently used in this application.
The applicator consists of a tungsten-alloy collimator with a 45 degree beveled end, placed in a protoscope with an elliptical cross-section. The resultant 3 cm diameter circular treatment aperture, located in the beveled face of the proctoscope, is irradiated by circular array of dwell positions located about 6.5 mm from the applicator surface. This beveled end allows patients with posterior wall tumors to be treated in the dorsal lithotomy position. The dose-rate distributions about the applicator were determined using a combination of thermoluminescent dosimetry (TLD-100 detectors) and radiochromic film dose measurement techniques along with Monte Carlo dosimetry calculations. TLD-100 (3 x 3 x 0.9 mm3 chips) measurements were used to measure the distribution of dose over the proctoscope surface as well as the central axis dose-rate distribution. Relative radiochromic film measurements were used to measure off-axis ratios (flatness and penumbra width) within the treatment aperture. These data were combined with Monte Carlo simulation results to obtain the final dose distribution.
The tungsten collimator successfully limits the dose to the tissue in contact with the proctoscope walls to less than 12% of the prescribed dose. These results indicate that the HDR applicator system has slightly more penetrating depth-dose characteristics than the most widely used contact therapy x-ray machine. Flatness characteristics of the two treatment delivery systems are comparable, although the HDR endocavitary applicator has a significantly wider penumbra. Finally, the HDR applicator has a lower surface dose rate (1.5-4 Gy/min of dwell time) compared to 9-10 Gy/min for the x-ray unit.
An applicator system has been developed for endocavitary treatment of early stage rectal carcinoma that uses a single-stepping source HDR remote afterloading system as a radiation source. The advantages of the HDR-based system over x-ray therapy contact units currently used in this clinical application are (a) enhanced flexibility in applicator design and (b) widespread availability of single-stepping source HDR remote afterloading systems.
描述一种用于直肠癌腔内治疗的施源器，该施源器使用带有单个高强度铱 - 192源的高剂量率（HDR）遥控后装系统，作为此应用中最常用的50 kVp X射线治疗接触装置的替代方案。
施源器由一个钨合金准直器组成，其一端呈45度斜面，放置在一个具有椭圆形横截面的直肠镜中。位于直肠镜斜面上的最终直径为3 cm的圆形治疗孔径，由距离施源器表面约6.5 mm的驻留位置圆形阵列进行照射。这个斜面端使得后壁肿瘤患者能够在膀胱截石位接受治疗。使用热释光剂量测定法（TLD - 100探测器）和放射变色胶片剂量测量技术相结合的方法，并结合蒙特卡罗剂量学计算，来确定施源器周围的剂量率分布。TLD - 100（3×3×0.9 mm³芯片）测量用于测量直肠镜表面的剂量分布以及中心轴剂量率分布。相对放射变色胶片测量用于测量治疗孔径内的离轴比（平坦度和半值层宽度）。这些数据与蒙特卡罗模拟结果相结合，以获得最终的剂量分布。
钨准直器成功地将与直肠镜壁接触的组织剂量限制在规定剂量的12%以下。这些结果表明，HDR施源器系统的深度剂量穿透特性比使用最广泛的接触治疗X射线机略强。两种治疗输送系统的平坦度特性相当，尽管HDR腔内施源器的半值层明显更宽。最后，与X射线装置的9 - 10 Gy/min相比，HDR施源器的表面剂量率较低（驻留时间为1.5 - 4 Gy/min）。
已开发出一种用于早期直肠癌腔内治疗的施源器系统，该系统使用单步源HDR遥控后装系统作为辐射源。基于HDR的系统相对于目前在此临床应用中使用的X射线治疗接触装置的优势在于：（a）施源器设计的灵活性增强；（b）单步源HDR遥控后装系统广泛可用。
