McLaughlin Patrick, Narayana Vrinda, Pan Charlie, Berri Sally, Troyer Sara, Herman Joseph, Evans Vicki, Roberson Peter
Department of Radiation Oncology, University of Michigan Medical Center, Ann Arbor, MI 48109-0010, USA.
Int J Radiat Oncol Biol Phys. 2006 Jan 1;64(1):144-50. doi: 10.1016/j.ijrobp.2005.06.044. Epub 2005 Oct 21.
To determine, using MRI-based dosimetry (Day 0 and Day 14), whether clinically significant changes in the dose to the prostate and critical adjacent structures occur between Day 0 and 14, and to determine to what degree any changes in dosimetry are due to swelling or its resolution.
A total of 28 patients with a permanent prostate implant using 125I rapid strands were evaluated at Days 0 and 14 by CT/MRI fusion. The minimal dose received by 90% of the target volume (prostate D90), percentage of volume receiving 100% of prescribed minimal peripheral dose (prostate V100), external sphincter D90, and 4-cm3 rectal volume dose were calculated. An acceptable prostate D90 was defined as D90 >90% of prescription dose. Prostate volume changes were calculated and correlated with any dosimetry change. A paradoxic dosimetric result was defined as an improvement in D90, despite increased swelling; a decrease in D90, despite decreased swelling; or a large change in D90 (>30 Gy) in the absence of swelling.
The D90 changed in 27 of 28 patients between Days 0 and 14. No relationship was found between a change in prostate volume and the change in D90 (R2 = 0.01). A paradoxic dosimetric result was noted in 11 of 28 patients. The rectal dose increased in 23 of 28 patients, with a >30-Gy change in 6. The external sphincter D90 increased in 19 of 28, with a >50-Gy increase in 6.
The dose to the prostate changed between Days 0 and 14 in most patients, resulting in a change in clinical status (acceptable or unacceptable) in 12 of 28 patients. Profound increases in normal tissue doses may make dose and toxicity correlations using Day 0 dosimetry difficult. No relationship was found between the prostate volume change and D90 change, and, in 11 patients, a paradoxic dosimetric result was noted. A differential z-axis shift of stranded seeds vs. prostate had a greater impact on final dosimetry and dose to critical adjacent tissues than did prostate swelling. These findings challenge the model that swelling is the principal cause of dosimetric changes after implantation. Stranded seeds may have contributed to this outcome. On the basis of these findings, a change in technique to avoid placement of stranded seeds inferior to the prostate apex has been adopted. These results may not apply to implants using single seeds within the prostate.
运用基于磁共振成像的剂量测定法（第0天和第14天），确定前列腺及临近关键结构的剂量在第0天至第14天之间是否发生具有临床意义的变化，并确定剂量测定的任何变化在多大程度上归因于肿胀或肿胀消退。
共有28例接受125I快速链状永久前列腺植入的患者在第0天和第14天通过CT/磁共振成像融合技术进行评估。计算90%靶体积所接受的最小剂量（前列腺D90）、接受规定最小周边剂量100%的体积百分比（前列腺V100）、外括约肌D90以及4立方厘米直肠体积剂量。可接受的前列腺D90定义为D90＞处方剂量的90%。计算前列腺体积变化，并将其与任何剂量测定变化相关联。矛盾的剂量测定结果定义为：尽管肿胀增加，但D90改善；尽管肿胀减轻，但D90降低；或者在无肿胀情况下D90发生较大变化（＞30 Gy）。
28例患者中有27例在第0天至第14天之间D90发生变化。未发现前列腺体积变化与D90变化之间存在相关性（R2 = 0.01）。28例患者中有11例出现矛盾的剂量测定结果。28例患者中有23例直肠剂量增加，其中6例变化＞30 Gy。28例患者中有19例外括约肌D90增加，其中6例增加＞50 Gy。
大多数患者在第0天至第14天之间前列腺剂量发生变化，导致28例患者中有12例临床状态发生改变（可接受或不可接受）。正常组织剂量的大幅增加可能使使用第0天剂量测定法进行剂量与毒性相关性分析变得困难。未发现前列腺体积变化与D90变化之间存在相关性，并且在11例患者中观察到矛盾的剂量测定结果。与前列腺肿胀相比，链状籽源与前列腺在z轴上的差异移位对最终剂量测定及关键临近组织的剂量影响更大。这些发现对肿胀是植入后剂量测定变化的主要原因这一模型提出了挑战。链状籽源可能促成了这一结果。基于这些发现，已采用一种改变技术的方法以避免将链状籽源放置在前列腺尖下方。这些结果可能不适用于前列腺内使用单粒籽源的植入情况。
