Anderson L L, Moni J V, Harrison L B
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021.
Int J Radiat Oncol Biol Phys. 1993 Sep 1;27(1):129-35. doi: 10.1016/0360-3016(93)90430-4.
103Pd is being substituted for 125I in permanent implants for which it is desired to deliver a higher initial dose rate while maintaining readily achieved radiation protection. We have constructed a nomograph to assist in determining both the total seed strength required and the appropriate needle spacing for 103Pd implants. We have calculated the "matched peripheral dose" (MPD), that is, the dose for which the isodose contour volume is equal to the target volume, for 64 125I and 13 103Pd actual implants as if 103Pd had been used for all of them, employing a computer lookup table based on single-seed dose distribution measurements in solid water. The calculated data were used to obtain a least-squares fit to a linear relationship between the logarithm of the total seed strength for a given MPD and the logarithm of the average dimension, da (cm). We found that, for a nominal MPD of 11,500 cGy, total seed strength (in mCi) is given by 3.2 da2.56. A 103Pd nomograph has been constructed on the basis of this power function relationship. Our nomographic guide for planning 103Pd implants calls for total seed strength to increase significantly faster as a function of target volume average dimension than is the case for 125I. This nomograph will facilitate the application of 103Pd seeds in permanent implants.
在永久性植入物中，¹⁰³Pd正被用于替代¹²⁵I，因为人们希望在保持易于实现辐射防护的同时，提供更高的初始剂量率。我们构建了一个列线图，以帮助确定¹⁰³Pd植入所需的总籽源强度和合适的针间距。我们计算了64个¹²⁵I和13个¹⁰³Pd实际植入物的“匹配周边剂量”（MPD），即等剂量线轮廓体积等于靶体积时的剂量，就好像所有植入物都使用了¹⁰³Pd一样，使用基于固体水中单籽源剂量分布测量的计算机查找表。计算数据用于对给定MPD下总籽源强度的对数与平均尺寸da（厘米）的对数之间的线性关系进行最小二乘拟合。我们发现，对于标称MPD为11500 cGy，总籽源强度（以mCi为单位）由3.2da².⁵⁶给出。基于这种幂函数关系构建了一个¹⁰³Pd列线图。我们用于规划¹⁰³Pd植入的列线图指南要求，总籽源强度作为靶体积平均尺寸的函数，其增加速度比¹²⁵I的情况要快得多。这个列线图将便于¹⁰³Pd籽源在永久性植入物中的应用。
