Hamilton R J, Kuchnir F T, Sweeney P, Rubin S J, Dujovny M, Pelizzari C A, Chen G T
Department of Radiation and Cellular Oncology, University of Chicago, IL, USA.
Int J Radiat Oncol Biol Phys. 1995 Dec 1;33(5):1221-8. doi: 10.1016/0360-3016(95)00275-8.
Compare the use of static conformal fields with the use of multiple noncoplanar arcs for stereotactic radiosurgery or stereotactic radiotherapy treatment of intracranial lesions. Evaluate the efficacy of these treatment techniques to deliver dose distributions comparable to those considered acceptable in current radiotherapy practice.
A previously treated radiosurgery case of a patient presenting with an irregularly shaped intracranial lesion was selected. Using a three-dimensional (3D) treatment-planning system, treatment plans using a single isocenter multiple noncoplanar arc technique and multiple noncoplanar conformal static fields were generated. Isodose distributions and dose volume histograms (DVHs) were computed for each treatment plan. We required that the 80% (of maximum dose) isodose surface enclose the target volume for all treatment plans. The prescription isodose was set equal to the minimum target isodose. The DVHs were analyzed to evaluate and compare the different treatment plans.
The dose distribution in the target volume becomes more uniform as the number of conformal fields increases. The volume of normal tissue receiving low doses (> 10% of prescription isodose) increases as the number of static fields increases. The single isocenter multiple arc plan treats the greatest volume of normal tissue to low doses, approximately 1.6 times more volume than that treated by four static fields. The volume of normal tissue receiving high (> 90% of prescription isodose) and intermediate (> 50% of prescription isodose) doses decreases by 29 and 22%, respectively, as the number of static fields is increased from four to eight. Increasing the number of static fields to 12 only further reduces the high and intermediate dose volumes by 10 and 6%, respectively. The volume receiving the prescription dose is more than 3.5 times larger than the target volume for all treatment plans.
Use of a multiple noncoplanar conformal static field treatment technique can significantly reduce the volume of normal tissue receiving high and intermediate doses compared with a single isocenter multiple arc treatment technique, while providing a more uniform dose in the target volume. Close conformation of the prescription isodose to the target volume is not possible using static uniform conformal fields for target shapes lacking an axis of rotational symmetry or plane of mirror symmetry.
比较立体定向放射外科或立体定向放射治疗颅内病变时，静态适形野与多个非共面弧的使用情况。评估这些治疗技术提供与当前放射治疗实践中认为可接受的剂量分布相当的剂量分布的疗效。
选择一例先前接受过放射外科治疗的患者，其颅内病变形状不规则。使用三维（3D）治疗计划系统，生成使用单等中心多个非共面弧技术和多个非共面适形静态野的治疗计划。计算每个治疗计划的等剂量分布和剂量体积直方图（DVH）。我们要求所有治疗计划中80%（最大剂量）等剂量面包围靶体积。处方等剂量设定为等于最小靶等剂量。分析DVH以评估和比较不同的治疗计划。
随着适形野数量的增加，靶体积内的剂量分布变得更加均匀。接受低剂量（>处方等剂量的10%）的正常组织体积随着静态野数量的增加而增加。单等中心多弧计划使接受低剂量的正常组织体积最大，比四个静态野治疗的体积大约多1.6倍。随着静态野数量从四个增加到八个，接受高剂量（>处方等剂量的90%）和中等剂量（>处方等剂量的50%）的正常组织体积分别减少29%和22%。将静态野数量增加到12仅进一步使高剂量和中等剂量体积分别减少10%和6%。所有治疗计划中接受处方剂量的体积比靶体积大3.5倍以上。
与单等中心多弧治疗技术相比，使用多个非共面适形静态野治疗技术可显著减少接受高剂量和中等剂量的正常组织体积，同时在靶体积内提供更均匀的剂量。对于缺乏旋转对称轴或镜面对称平面的靶形状，使用静态均匀适形野不可能使处方等剂量与靶体积紧密适形。
