McNeely Lee K, Stone Nelson N, Presser Joseph, Chircus Jeffrey H, Stock Richard G
Department of Radiation Oncology, Boulder Community Hospital, Boulder, CO, USA.
Int J Radiat Oncol Biol Phys. 2004 Jan 1;58(1):292-9. doi: 10.1016/s0360-3016(03)00783-1.
Achieving a minimal dose of 140 Gy to 90% of the prostate (D90) on postimplant dosimetry has been shown to yield improved biochemical control by 125I brachytherapy, and a D90 >180 Gy can be associated with increased long-term toxicity of seed implantation. Significant enlargement of the prostate on postimplant CT compared with the ultrasound (US) volume at implantation (CT/US ratio) has been associated with lower dose results, but other factors predicting for high or low doses are not well established. We determined whether the prostate size at implantation influenced the CT/US ratio results affecting postimplant dosimetry or predicted for D90 values <140 or >180 Gy in patients implanted with 125I in a community hospital setting.
The dosimetry results from 501 patients from 33 community hospitals were analyzed after full dose 125I implantation. Implant radioactivity was obtained from reference tables relating millicuries to prostate volume (PV). Seeds were placed under real-time US guidance with peripheral weighting in a uniform method for all prostate sizes. CT-based dosimetry was performed 1 month after implantation. Dose-volume histogram parameters were analyzed for volume effects, including D90, the dose to 10% and 30% of the rectal wall, and the dose to 30% of the urethra and bladder. The PV was defined as small (<25 cm3), medium (25 to <40 cm3), or large (> or =40 cm3).
The PV ranged from 9 to 79 cm3 (median 32.7). A D90 > or =140 Gy was achieved in 452 patients (90%). The median D90 was 164 Gy (range 90-230) and increased from 149.5 Gy in small prostates to 164 Gy in medium (p <0.001) and 176 Gy in large (p <0.001) prostates. A D90 <140 Gy occurred in 20% of small vs. 9% of medium and 3% of large prostates (p = 0.003). A D90 >180 Gy occurred in 7% of small and 10% of medium vs. 25% of large glands (p <0.001). The rectal dose increased significantly with an enlarging PV. The bladder and urethral doses increased from the small to medium PVs, although did not increase further in the large glands. The median CT/US ratios showed a significant volume relationship, decreasing with enlarging PVs, but were not associated with a D90 <140 or >140 Gy. The D90 results for <140 Gy and >140 Gy occurred at equal activities per volume.
Ninety percent of patients implanted by community-level practitioners using reference tables and real-time US-guided implantation achieved a D90 outcome of > or =140 Gy. Significant differences in dose outcomes <140 Gy and >180 Gy occurred related to PV. Those with prostates <25 cm3 had a 20% frequency of D90 <140 Gy, unrelated to excessive postimplant volume enlargement or insufficient activity per reference table, suggesting that the activity-to-volume recommendations may not allow for much variance in final seed position. Such seed displacement may contribute to lower doses, most commonly in small glands. One may consider increasing the activity implanted in small prostates, because a D90 >180 Gy occurred in only 7% of these cases. Patients with glands >40 cm3 were 25% likely to have a D90 result >180 Gy and were at only 3% risk of a D90 <140 Gy. These patients may benefit from intraoperative dosimetry or a reduction in implant activity.
植入后剂量测定显示，对90%的前列腺实现140 Gy的最小剂量（D90）可通过¹²⁵I近距离放射疗法改善生化控制，而D90>180 Gy可能与种子植入的长期毒性增加有关。与植入时超声（US）测量的前列腺体积相比，植入后CT显示前列腺显著增大（CT/US比值）与较低的剂量结果相关，但预测高剂量或低剂量的其他因素尚未明确确立。我们确定在社区医院环境中，植入时的前列腺大小是否会影响CT/US比值结果，进而影响植入后剂量测定，或者是否能预测¹²⁵I植入患者的D90值<140或>180 Gy。
分析了33家社区医院501例患者在¹²⁵I全剂量植入后的剂量测定结果。植入放射性活度根据将毫居里与前列腺体积（PV）相关联的参考表获得。在实时超声引导下，对所有前列腺大小均采用外周加权的统一方法放置种子。植入后1个月进行基于CT的剂量测定。分析剂量体积直方图参数的体积效应，包括D90、直肠壁10%和30%的剂量以及尿道和膀胱30%的剂量。PV被定义为小（<25 cm³）、中（25至<40 cm³）或大（≥40 cm³）。
PV范围为9至79 cm³（中位数32.7）。452例患者（90%）实现了D90≥140 Gy。D90中位数为164 Gy（范围90 - 230），从小前列腺的149.5 Gy增加到中前列腺的164 Gy（p<0.001）和大前列腺的176 Gy（p<0.001）。小前列腺中20%的患者D90<140 Gy，中前列腺为9%，大前列腺为3%（p = 0.003）。小前列腺中7%、中前列腺中10%以及大腺体中25%的患者D90>180 Gy（p<0.001）。直肠剂量随PV增大而显著增加。膀胱和尿道剂量从小PV增加到中PV，但在大腺体中未进一步增加。CT/US比值中位数显示出显著的体积关系，随PV增大而降低，但与D90<140或>140 Gy无关。D90<140 Gy和>140 Gy的结果在每单位体积的相同活度下出现。
社区水平的从业者使用参考表和实时超声引导植入，90%的患者实现了D90≥140 Gy的结果。D90<140 Gy和>180 Gy的剂量结果因PV不同而存在显著差异。前列腺<25 cm³的患者中20%的频率出现D90<140 Gy，这与植入后体积过度增大或参考表中每单位活度不足无关，表明活度与体积的推荐可能无法在最终种子位置上有太大差异。这种种子移位可能导致剂量降低，最常见于小腺体。可以考虑增加小前列腺植入的活度，因为这些病例中只有7%的患者D90>180 Gy。腺体>40 cm³的患者有25%的可能性D90结果>180 Gy，而D90<140 Gy的风险仅为3%。这些患者可能从术中剂量测定或降低植入活度中受益。
