Ash Dan, Al-Qaisieh Bashar, Bottomley David, Carey Brendan, Joseph Joji
Regional Cancer Treatment Center, Cookridge Hospital, Leeds, UK.
Radiother Oncol. 2006 May;79(2):185-9. doi: 10.1016/j.radonc.2006.04.004. Epub 2006 May 15.
In 1998 Stock and Stone demonstrated a dose response relationship correlating D90 with probability of biochemical control and showed that a D90 of 140 Gy is a highly significant factor in predicting PSA relapse free survival (PSA-RFS). Although, a mean D90 of over 140 Gy was achieved in our series, there is nevertheless a normal distribution with 20% of patients achieving a D90 of less than 120 Gy. We have analysed the possible causes for the low D90 and the impact on outcome.
Prospective data from 667 patients treated between 1995 and 2001 by I-125 seeds prostate implant as monotherapy were analysed. Post-implant dosimetry was performed on 413 patients. D90 and other indices were calculated for each patient. Statistical analysis was performed on D90 dose to identify the correlation that would predict the 8.2 years PSA relapse free survival as defined by the American Society for Therapeutic Radiology and Oncology (ASTRO).
Correlation between D90 and outcome shows no significant difference for the whole population between those who receive greater or less than 140 Gy (P=0.43) and there was also no difference for those receiving more or less than 130 Gy (P=0.14). Subgroup analysis by risk group, however, showed that for low risk patients there was a significant correlation between D90 and PSA control (P<0.01). Although, post-implant dosimetry was performed 6-8 weeks after brachytherapy, post-implant CT still showed variable levels of oedema compared with the pre-implant ultrasound. A statistically significant relationship was shown between D90 and the ratio between CT and ultrasound volume (P<0.01) which suggests that some low D90s may be related to persistent oedema at the time of calculation. Segmental analysis of a subgroup of 32 patients showed that the dose was most often deficient in the anterior basal segment of the gland.
D90 was found to be a good discriminator for those with low risk where failure to achieve local control is likely to be the dominant cause of PSA failure. No significant dose response relationship between D90 and PSA was found in the intermediate and high-risk population of patients. This could be due to (1) the presence of oedema or discrepancy between pre- and post-implant volumes causing a low D90, (2) the possibility that the underdosed area could be situated where there is unlikely to be tumour, (3) the fact that biochemical control does not equate to local control because some patients fail outside the prostate, particularly in the high and intermediate risk patients, (4) if D90 is a good discriminator only for low risk patients, the absence of a dose response correlation in this series which contained 53.8% intermediate and high risk patients could be related to case mix.
1998年，斯托克和斯通证明了D90与生化控制概率之间存在剂量反应关系，并表明140 Gy的D90是预测无前列腺特异性抗原（PSA）复发存活期（PSA-RFS）的一个高度显著因素。尽管在我们的系列研究中，平均D90超过了140 Gy，但仍呈正态分布，20%的患者D90低于120 Gy。我们分析了D90较低的可能原因及其对治疗结果的影响。
分析了1995年至2001年间接受碘-125粒子前列腺植入单一疗法治疗的667例患者的前瞻性数据。对413例患者进行了植入后剂量测定。计算了每位患者的D90和其他指标。对D90剂量进行统计分析，以确定能预测美国放射治疗与肿瘤学会（ASTRO）定义的8.2年无PSA复发存活期的相关性。
对于接受大于或小于140 Gy的患者，D90与治疗结果之间的相关性在总体人群中无显著差异（P = 0.43），接受大于或小于130 Gy的患者之间也无差异（P = 0.14）。然而，按风险组进行的亚组分析显示，对于低风险患者，D90与PSA控制之间存在显著相关性（P < 0.01）。尽管近距离放射治疗后6至8周进行了植入后剂量测定，但与植入前超声相比，植入后CT仍显示出不同程度的水肿。D90与CT和超声体积之比之间存在统计学显著关系（P < 0.01），这表明一些较低的D90可能与计算时的持续性水肿有关。对32例患者亚组的节段性分析表明，剂量最常不足的部位是腺体的前基底部。
发现D90对于低风险患者是一个很好的判别指标，在这类患者中，未能实现局部控制可能是PSA失败的主要原因。在中、高风险患者群体中，未发现D90与PSA之间存在显著的剂量反应关系。这可能是由于：（1）水肿的存在或植入前后体积的差异导致D90较低；（2）剂量不足的区域可能位于不太可能有肿瘤的部位；（3）生化控制并不等同于局部控制，因为一些患者在前列腺外出现失败，尤其是在中、高风险患者中；（4）如果D90仅对低风险患者是一个很好的判别指标，那么在本系列中（其中53.8%为中、高风险患者）缺乏剂量反应相关性可能与病例组合有关。
