Williamson J F, Coursey B M, DeWerd L A, Hanson W F, Nath R, Rivard M J, Ibbott G
Radiation Oncology Center, Washington University, St. Louis, Missouri 63110, USA.
Med Phys. 2000 Apr;27(4):634-42. doi: 10.1118/1.598923.
The National Institute of Standards and Technology (NIST) introduced a national standard for air kerma strength of the ThreaSeed Model 200 103Pd source (the only 103Pd seed available until 1999) in early 1999. Correct implementation of the NIST-99 standard requires the use of dose rate constants normalized to this same standard. Prior to the availability of this standard, the vendor's calibration procedure consisted of intercomparing Model 200 seeds with a 109Cd source with a NIST-traceable activity calibration. The AAPM undertook a comprehensive review of 103Pd source dosimetry including (i) comparison of the vendor and NIST-99 calibration standards; (ii) comparison of original Task Group 43 dosimetry parameters with more recent studies; (iii) evaluation of the vendor's calibration history; and (iv) evaluation of administered-to-prescribed dose ratios from the introduction of 103Pd sources in 1987 to the present. This review indicates that for a prescribed dose of 115 Gy, the administered doses were (a) 124 Gy for the period 1988-1997 and (b) 135 Gy for the period 1997-1999. The AAPM recommends that the following three steps should be undertaken concurrently to implement correctly the 1999 dosimetry data and NIST-99 standard for 103Pd source: (1) the vendor should provide calibrations in terms of air kerma strength traceable to NIST-99 standard, (2) the medical physicist should update the treatment planning system with properly normalized (to NIST-99) dosimetry parameters for the selected 103Pd source model, and (3) the radiation oncologist in collaboration with the medical physicist should decide which clinical experience they wish to duplicate; the one prior to 1997 or the one from 1997 to 1999. If the intent is to duplicate the experience prior to 1997, which is backed by the long-term follow-up and published outcome studies, then the prior prescriptions of 115 Gy should be replaced by 124 Gy to duplicate that experience.
美国国家标准与技术研究院（NIST）于1999年初推出了针对ThreaSeed Model 200 103Pd源空气比释动能强度的国家标准（该源是1999年之前唯一可用的103Pd籽源）。正确实施NIST - 99标准需要使用根据该同一标准归一化的剂量率常数。在该标准出台之前，供应商的校准程序包括将Model 200籽源与具有可溯源至NIST的活度校准的109Cd源进行比对。医学物理师协会（AAPM）对103Pd源剂量测定进行了全面审查，包括：（i）供应商校准标准与NIST - 99校准标准的比较；（ii）原始任务组43剂量测定参数与近期研究的比较；（iii）供应商校准历史的评估；以及（iv）从1987年引入103Pd源到目前的实际给予剂量与处方剂量之比的评估。该审查表明，对于115 Gy的处方剂量，实际给予剂量为：（a）1988 - 1997年期间为124 Gy，（b）1997 - 1999年期间为135 Gy。AAPM建议应同时采取以下三个步骤，以正确实施1999年103Pd源的剂量测定数据和NIST - �9标准：（1）供应商应以可溯源至NIST - 99标准的空气比释动能强度提供校准；（2）医学物理师应以针对所选103Pd源模型正确归一化（至NIST - 99）的剂量测定参数更新治疗计划系统；以及（3）放射肿瘤学家应与医学物理师合作，决定他们希望复制哪种临床经验；是1997年之前的还是1997 - 1999年期间的。如果意图是复制1997年之前的经验，该经验有长期随访和已发表的结果研究作为支撑，那么应将115 Gy的先前处方替换为124 Gy以复制以复制该经验。
