Merrick G S, Butler W M, Dorsey A T, Lief J H
Schiffler Oncology Center, Wheeling Hospital, WV 26003-6300, USA.
Int J Radiat Oncol Biol Phys. 1999 Jun 1;44(3):717-24. doi: 10.1016/s0360-3016(99)00067-x.
Postoperative CT-based dosimetric analysis provides detailed information regarding the coverage and uniformity of an implant, but the assessment of implant quality remains an unanswered and controversial issue. There is no disagreement that a good implant should cover the target volume with an adequate dose, but there is no consensus as to what represents an adequate dose.
The American Brachytherapy Society has recently proposed that prostate brachytherapy quality be measured in terms of the following parameters: D90, V100, and V150 where D90 is defined as the minimal dose covering 90% of the prostate volume and V100 and V150 are defined as the percent volume of the prostate receiving at least 100% or 150% of the prescribed minimal peripheral dose (mPD), respectively. We report detailed day 0 dosimetric evaluation for 60 consecutive prostate brachytherapy patients implanted via a standard transperineal ultrasound guided approach in terms of D90, D100, V90, V100, and V150 and also the maximal and average rectal and urethral dose.
Dosimetric evaluation resulted in a V100 greater than 80% of the prostate volume and a D90 greater than 90% of the mPD in the entire patient population. There was a statistically significant difference between the quality scores of 125I implants and 103Pd implants with the 125I mean V100 and D90 at 95.3% volume and 109.9% mPD, respectively, vs. 103Pd at 91.8% volume and 103.7% mPD. Likewise, the rectal and urethral doses as a fraction of mPD were significantly lower in 103Pd than in 125I implants. This occurred despite the fact that palladium implants were typically preplanned with significantly better coverage and hotter V150 than iodine implants. We consider V150 to be an important parameter for determining dose homogeneity although the clinical utility of dose homogeneity remains unknown. The mean V150 was 45.6 +/- 9.6% volume. There was no additional dosimetric utility from a determination of V90 while D100 was found to be overly sensitive to steep dose gradients at the periphery of the prostate.
This report represents the first detailed postimplant day 0 dosimetric evaluation comparing ABS recommended quality parameters used to evaluate prostate brachytherapy. At the present time, no long-term clinical outcomes are available because of short follow-up. As PSA based follow-up data becomes available, however, this report may help define what represents an adequate implant.
基于术后CT的剂量学分析可提供有关植入物覆盖范围和均匀性的详细信息，但植入物质量的评估仍是一个未解决且存在争议的问题。对于一个良好的植入物应使用足够剂量覆盖靶体积这一点并无异议，但对于什么是足够的剂量却没有达成共识。
美国近距离放射治疗学会最近提议，前列腺近距离放射治疗质量应根据以下参数来衡量：D90、V100和V150，其中D90定义为覆盖90%前列腺体积的最小剂量，V100和V150分别定义为接受至少100%或150%规定最小周边剂量（mPD）的前列腺体积百分比。我们报告了60例连续接受前列腺近距离放射治疗患者在植入当天基于D90、D100、V90、V100和V150以及最大和平均直肠及尿道剂量的详细剂量学评估，这些患者通过标准经会阴超声引导方法进行植入。
剂量学评估显示，在整个患者群体中，V100大于前列腺体积的80%，D90大于mPD的90%。125I植入物和103Pd植入物的质量得分存在统计学显著差异，125I的平均V100和D90分别为95.3%体积和109.9% mPD，而103Pd分别为91.8%体积和103.7% mPD。同样，103Pd植入物中作为mPD一部分的直肠和尿道剂量显著低于125I植入物。尽管钯植入物通常在预先规划时覆盖范围明显更好且V150更高，但仍出现这种情况。我们认为V150是确定剂量均匀性的一个重要参数，尽管剂量均匀性的临床效用仍不明确。平均V150为45.6±9.6%体积。确定V90没有额外的剂量学效用，而发现D100对前列腺周边陡峭的剂量梯度过于敏感。
本报告是首次对用于评估前列腺近距离放射治疗的美国近距离放射治疗学会推荐质量参数进行详细的植入后第0天剂量学评估比较。目前，由于随访时间短，尚无长期临床结果。然而，随着基于PSA的随访数据可用，本报告可能有助于确定什么代表一个足够的植入物。
