Wu Trudy C, Xiang Michael, Nickols Nicholas G, Tenn Stephen, Agazaryan Nzhde, Hegde John V, Steinberg Michael L, Cao Minsong, Kishan Amar U
Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, California.
Department of Radiation Oncology, VA Greater Los Angeles Healthcare System, Los Angeles, California.
Adv Radiat Oncol. 2022 Mar 16;7(4):100944. doi: 10.1016/j.adro.2022.100944. eCollection 2022 Jul-Aug.
To determine the effect of daily shifts based on rigid registration to intraprostatic markers on coverage of boost doses delivered to gross nodal disease for prostate cancer.
Seventy-five cone beam computed tomographies (CBCTs) from 15 patients treated with definitive radiation for clinically node-positive prostate cancer underwent fiducial-based and pelvic bony-based registration to the initial planning scans. Gross tumor volumes of nodal boost targets were contoured directly on each CBCT registration. The nodal displacement (3-dimensional translation from the node centroid on planning CT to node centroid on registered CBCT) and dose coverage (minimum dose [Dmin], mean dose [Dmean], dose delivered to 95% of the gross tumor volumes [D95]) were calculated for each registration on all nodal targets. All doses for each node were normalized to its intended prescription dose (dose covering 95% of a 3 mm planning target volume [PTV] expansion).
Forty-one gross nodal targets were analyzed. Most boosted nodes (80.5%, 33/41) were treated with conventional fractionation using volumetric-arc radiation therapy, and 19.5% (8/41) underwent stereotactic body radiation therapy (SBRT). Dmin, Dmean, and D95 were all significantly lower with fiducial-based registration compared with bony-based registration ( < .0001). Nodal displacement was significantly higher for fiducial-based registrations ( < .0001). The 3-dimensional translation between the fiducial-based and bony-based registrations (bony-to-fiducial vector) was the most significant predictor of nodal displacement ( < .0001). On fiducial-based registrations, a 3 to 5 mm gross nodal PTV margin is sufficient in most directions; however, superior and posterior margins of 8 to 9 mm are required as a result of asymmetrical prostatic motion.
Large and anisotropic PTV margins are likely needed to adequately dose gross nodal targets when patient setup is based on rigid registration to intraprostatic markers. Alternative approaches such as adaptive replanning may be required to overcome these limitations.
基于对前列腺内标志物的刚性配准，确定每日分次放疗对前列腺癌大体淋巴结转移灶高剂量照射覆盖范围的影响。
对15例临床淋巴结阳性前列腺癌患者进行根治性放疗，获取75次锥形束计算机断层扫描（CBCT），将基于基准点和骨盆骨的配准应用于初始计划扫描。在每次CBCT配准上直接勾勒出淋巴结增强靶区的大体肿瘤体积。计算所有淋巴结靶区每次配准的淋巴结位移（从计划CT上的淋巴结质心到配准CBCT上的淋巴结质心的三维平移）和剂量覆盖范围（最小剂量[Dmin]、平均剂量[Dmean]、给予大体肿瘤体积95%的剂量[D95]）。每个淋巴结的所有剂量均根据其预期处方剂量进行归一化（覆盖3 mm计划靶体积[PTV]扩展区95%的剂量）。
分析了41个大体淋巴结靶区。大多数增强淋巴结（80.5%，33/41）采用容积弧形放疗的常规分割方式治疗，19.5%（8/41）接受立体定向体部放疗（SBRT）。与基于骨的配准相比，基于基准点的配准的Dmin、Dmean和D95均显著更低（<0.0001）。基于基准点的配准的淋巴结位移显著更高（<0.0001）。基于基准点和基于骨的配准之间的三维平移（骨到基准点向量）是淋巴结位移的最显著预测因子（<0.0001）。在基于基准点的配准中，在大多数方向上3至5 mm的大体淋巴结PTV边界就足够了；然而，由于前列腺运动不对称，需要8至9 mm的上缘和后缘边界。
当患者体位基于对前列腺内标志物的刚性配准时，可能需要较大且各向异性的PTV边界来充分照射大体淋巴结靶区。可能需要诸如自适应重新计划等替代方法来克服这些限制。
