Wolthaus Jochem W H, Sonke Jan-Jakob, van Herk Marcel, Belderbos José S A, Rossi Maddalena M G, Lebesque Joos V, Damen Eugène M F
Department of Radiation Oncology, The Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
Int J Radiat Oncol Biol Phys. 2008 Mar 15;70(4):1229-38. doi: 10.1016/j.ijrobp.2007.11.042.
To discuss planning target volumes (PTVs) based on internal target volume (PTVITV), exhale-gated radiotherapy (PTVGating), and a new proposed midposition (PTVMidP; time-weighted mean tumor position) and compare them with the conventional free-breathing CT scan PTV (PTVConv).
Respiratory motion induces systematic and random geometric uncertainties. Their contribution to the clinical target volume (CTV)-to-PTV margins differs for each PTV approach. The uncertainty margins were calculated using a dose-probability-based margin recipe (based on patient statistics). Tumor motion in four-dimensional CT scans was determined using a local rigid registration of the tumor. Geometric uncertainties for interfractional setup errors and tumor baseline variation were included. For PTVGating, the residual motion within a 30% gating (time) window was determined. The concepts were evaluated in terms of required CTV-to-PTV margin and PTV volume for 45 patients.
Over the patient group, the PTVITV was on average larger (+6%) and the PTVGating and PTVMidP smaller (-10%) than the PTVConv using an off-line (bony anatomy) setup correction protocol. With an on-line (soft tissue) protocol the differences in PTV compared with PTVConv were +33%, -4%, and 0, respectively.
The internal target volume method resulted in a significantly larger PTV than conventional CT scanning. The exhale-gated and mid-position approaches were comparable in terms of PTV. However, mid-position (or mid-ventilation) is easier to use in the clinic because it only affects the planning part of treatment and not the delivery.
探讨基于内部靶区体积（PTVITV）、呼气门控放疗（PTVGating）以及新提出的中位位置（PTVMidP；时间加权平均肿瘤位置）的计划靶区体积，并将它们与传统自由呼吸CT扫描的计划靶区体积（PTVConv）进行比较。
呼吸运动导致系统和随机的几何不确定性。它们对临床靶区体积（CTV）到计划靶区体积边界的贡献因每种计划靶区体积方法而异。使用基于剂量概率的边界公式（基于患者统计数据）计算不确定性边界。通过肿瘤的局部刚性配准确定四维CT扫描中的肿瘤运动。纳入了分次间摆位误差和肿瘤基线变化的几何不确定性。对于PTVGating，确定30%门控（时间）窗口内的残余运动。根据45例患者所需的CTV到PTV边界和PTV体积对这些概念进行评估。
在患者组中，使用离线（骨性解剖结构）摆位校正方案时，PTVITV平均比PTVConv大（+6%），而PTVGating和PTVMidP比PTVConv小（-10%）。使用在线（软组织）方案时，与PTVConv相比，PTV的差异分别为+33%、-4%和0。
内部靶区体积法导致的计划靶区体积比传统CT扫描显著更大。呼气门控和中位位置方法在计划靶区体积方面相当。然而，中位位置（或中位通气）在临床上更易于使用，因为它仅影响治疗的计划部分，而不影响治疗的实施。
