Division of Radiation Oncology, The Ottawa Hospital Cancer Centre, The University of Ottawa, Ottawa, Ontario, Canada.
Int J Radiat Oncol Biol Phys. 2012 Jul 15;83(4):1160-8. doi: 10.1016/j.ijrobp.2011.09.039. Epub 2012 Jan 21.
Postoperative radiotherapy (XRT) increases survival in high-risk prostate cancer patients. Approximately 50% of patients on long-term follow-up relapse despite adjuvant XRT and the predominant site of failure remains local. Four consensus guidelines define postoperative clinical target volume (CTV) in prostate cancer. We explore the possibility that inadequate CTV coverage is an important cause of local failure. This study evaluates the utility of preoperative magnetic resonance imaging (MRI) in defining prostate bed CTV.
Twenty prostate cancer patients treated with postoperative XRT who also had preoperative staging MRI were included. The four guidelines were applied and the CTVs were expanded to create planning target volumes (PTVs). Preoperative MRIs were fused with postoperative planning CT scans. MRI-based prostate and gross visible tumors were contoured. Three-dimensional (3D) conformal four- and six-field XRT plans were developed and dose-volume histograms analyzed. Subtraction analysis was conducted to assess the adequacy of prostate/gross tumor coverage.
Gross tumor was visible in 18 cases. In all 20 cases, the consensus CTVs did not fully cover the MRI-defined prostate. On average, 35% of the prostate volume and 32% of the gross tumor volume were missed using six-field 3D treatment plans. The entire MRI-defined gross tumor volume was completely covered in only two cases (six-field plans). The expanded PTVs did not cover the entire prostate bed in 50% of cases. Prostate base and mid-zones were the predominant site of inadequate coverage.
Current postoperative CTV guidelines do not adequately cover the prostate bed and/or gross tumor based on preoperative MRI imaging. Additionally, expanded PTVs do not fully cover the prostate bed in 50% of cases. Inadequate CTV definition is likely a major contributing factor for the high risk of relapse despite adjuvant XRT. Preoperative imaging may lead to more accurate CTV definition, which should result in further improvements in survival for patients with high-risk prostate cancer.
术后放疗（XRT）可提高高危前列腺癌患者的生存率。尽管接受了辅助 XRT，但约有 50%的长期随访患者复发，且失败的主要部位仍然是局部。四项共识指南定义了前列腺癌术后临床靶区（CTV）。我们探讨了CTV 覆盖不足是局部复发的重要原因的可能性。本研究评估了术前磁共振成像（MRI）在定义前列腺床 CTV 中的作用。
本研究纳入了 20 例接受术后 XRT 治疗且有术前分期 MRI 的前列腺癌患者。应用四项指南，并对 CTV 进行扩展以创建计划靶区（PTV）。将术前 MRI 与术后计划 CT 扫描融合。对 MRI 定义的前列腺和大体可见肿瘤进行轮廓勾画。制定了三维（3D）适形四野和六野 XRT 计划，并分析剂量-体积直方图。进行了减影分析，以评估前列腺/大体肿瘤覆盖的充分性。
18 例可见大体肿瘤。在所有 20 例患者中，共识 CTV 均未完全覆盖 MRI 定义的前列腺。使用六野 3D 治疗计划，平均有 35%的前列腺体积和 32%的大体肿瘤体积未被覆盖。仅在 2 例（六野计划）中完全覆盖了整个 MRI 定义的大体肿瘤体积。50%的情况下，扩展后的 PTV 未完全覆盖整个前列腺床。前列腺基底和中区是覆盖不足的主要部位。
基于术前 MRI 成像，目前的术后 CTV 指南不能充分覆盖前列腺床和/或大体肿瘤。此外，50%的情况下，扩展后的 PTV 不能完全覆盖前列腺床。CTV 定义不足可能是尽管辅助 XRT 仍有高复发风险的主要原因之一。术前影像学可能导致更准确的 CTV 定义，从而进一步提高高危前列腺癌患者的生存率。
