Deveau Michael A, Gutiérrez Alonso N, Mackie Thomas R, Tomé Wolfgang A, Forrest Lisa J
School of Medicine and Public Health, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53792, USA.
Vet Radiol Ultrasound. 2010 Jan-Feb;51(1):90-6. doi: 10.1111/j.1740-8261.2009.01629.x.
Intensity-modulated radiation therapy (IMRT) can be employed to yield precise dose distributions that tightly conform to targets and reduce high doses to normal structures by generating steep dose gradients. Because of these sharp gradients, daily setup variations may have an adverse effect on clinical outcome such that an adjacent normal structure may be overdosed and/or the target may be underdosed. This study provides a detailed analysis of the impact of daily setup variations on optimized IMRT canine nasal tumor treatment plans when variations are not accounted for due to the lack of image guidance. Setup histories of ten patients with nasal tumors previously treated using helical tomotherapy were replanned retrospectively to study the impact of daily setup variations on IMRT dose distributions. Daily setup shifts were applied to IMRT plans on a fraction-by-fraction basis. Using mattress immobilization and laser alignment, mean setup error magnitude in any single dimension was at least 2.5 mm (0-10.0 mm). With inclusions of all three translational coordinates, mean composite offset vector was 5.9 +/- 3.3 mm. Due to variations, a loss of equivalent uniform dose for target volumes of up to 5.6% was noted which corresponded to a potential loss in tumor control probability of 39.5%. Overdosing of eyes and brain was noted by increases in mean normalized total dose and highest normalized dose given to 2% of the volume. Findings suggest that successful implementation of canine nasal IMRT requires daily image guidance to ensure accurate delivery of precise IMRT distributions when non-rigid immobilization techniques are utilized. Unrecognized geographical misses may result in tumor recurrence and/or radiation toxicities to the eyes and brain.
调强放射治疗（IMRT）可用于产生精确的剂量分布，通过生成陡峭的剂量梯度紧密贴合靶区并减少对正常组织的高剂量照射。由于这些陡峭的梯度，每日摆位变化可能会对临床结果产生不利影响，导致相邻正常组织可能接受过量照射和/或靶区可能接受剂量不足。本研究详细分析了在缺乏图像引导而未考虑每日摆位变化时，其对优化的犬鼻肿瘤IMRT治疗计划的影响。回顾性重新规划了10例先前使用螺旋断层放疗治疗的鼻肿瘤患者的摆位历史，以研究每日摆位变化对IMRT剂量分布的影响。每日摆位偏移逐分次应用于IMRT计划。使用床垫固定和激光定位，任何单一维度的平均摆位误差幅度至少为2.5毫米（0 - 10.0毫米）。纳入所有三个平移坐标后，平均复合偏移向量为5.9 +/- 3.3毫米。由于这些变化，靶区体积的等效均匀剂量损失高达5.6%，这相当于肿瘤控制概率潜在损失39.5%。通过平均归一化总剂量和给予2%体积的最高归一化剂量增加，发现眼睛和大脑出现过量照射。研究结果表明，当采用非刚性固定技术时，成功实施犬鼻IMRT需要每日图像引导，以确保精确的IMRT分布准确递送。未识别的摆位偏差可能导致肿瘤复发和/或对眼睛和大脑的放射毒性。
