Hadley Austin, Ding George X
Department of Radiation Oncology, Vanderbilt University School of Medicine, Nashville, TN.
Department of Radiation Oncology, Vanderbilt University School of Medicine, Nashville, TN.
Med Dosim. 2014 Winter;39(4):314-9. doi: 10.1016/j.meddos.2014.05.004. Epub 2014 Jun 7.
Craniospinal irradiation (CSI) requires abutting fields at the cervical spine. Junction shifts are conventionally used to prevent setup error-induced overdosage/underdosage from occurring at the same location. This study compared the dosimetric differences at the cranial-spinal junction between a single-gradient junction technique and conventional multiple-junction shifts and evaluated the effect of setup errors on the dose distributions between both techniques for a treatment course and single fraction. Conventionally, 2 lateral brain fields and a posterior spine field(s) are used for CSI with weekly 1-cm junction shifts. We retrospectively replanned 4 CSI patients using a single-gradient junction between the lateral brain fields and the posterior spine field. The fields were extended to allow a minimum 3-cm field overlap. The dose gradient at the junction was achieved using dose painting and intensity-modulated radiation therapy planning. The effect of positioning setup errors on the dose distributions for both techniques was simulated by applying shifts of ± 3 and 5mm. The resulting cervical spine doses across the field junction for both techniques were calculated and compared. Dose profiles were obtained for both a single fraction and entire treatment course to include the effects of the conventional weekly junction shifts. Compared with the conventional technique, the gradient-dose technique resulted in higher dose uniformity and conformity to the target volumes, lower organ at risk (OAR) mean and maximum doses, and diminished hot spots from systematic positioning errors over the course of treatment. Single-fraction hot and cold spots were improved for the gradient-dose technique. The single-gradient junction technique provides improved conformity, dose uniformity, diminished hot spots, lower OAR mean and maximum dose, and one plan for the entire treatment course, which reduces the potential human error associated with conventional 4-shifted plans.
全脑全脊髓照射（CSI）需要在颈椎处相邻野衔接。传统上使用野衔接位移来防止因摆位误差在同一位置导致的剂量过量/剂量不足。本研究比较了单梯度野衔接技术与传统多野衔接位移在颅颈交界处的剂量学差异，并评估了摆位误差对两种技术在一个疗程和单次分割治疗中剂量分布的影响。传统上，全脑全脊髓照射使用2个侧脑野和1个后脊柱野，每周野衔接位移1厘米。我们回顾性地对4例全脑全脊髓照射患者进行重新计划，采用侧脑野与后脊柱野之间的单梯度野衔接。野进行了扩展，以允许至少3厘米的野重叠。通过剂量描绘和调强放射治疗计划实现野衔接处的剂量梯度。通过施加±3毫米和5毫米的位移来模拟两种技术的摆位误差对剂量分布的影响。计算并比较了两种技术在野衔接处的颈椎剂量。获取了单次分割和整个疗程的剂量分布曲线，以纳入传统每周野衔接位移的影响。与传统技术相比，梯度剂量技术导致更高的剂量均匀性和对靶区的适形性、更低的危及器官（OAR）平均剂量和最大剂量，以及在治疗过程中因系统摆位误差导致的热点减少。梯度剂量技术的单次分割热点和冷点得到改善。单梯度野衔接技术提供了更好的适形性、剂量均匀性、热点减少、更低的危及器官平均剂量和最大剂量，以及整个疗程的单一计划，这减少了与传统4次位移计划相关的潜在人为误差。
