Pruitt Amy F, Thrall Donald E
Department of Molecular Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606, USA.
Vet Radiol Ultrasound. 2004 Sep-Oct;45(5):471-5. doi: 10.1111/j.1740-8261.2004.04081.x.
To compare changes in dose distribution in irregularly shaped volumes treated using fields with noncoincident isocenters compared with fields with coincident isocenters. The hypothesis was that use of fields with noncoincident isocenters would result in improved homogeneity of dose distribution. We chose to test the hypothesis in canine nasal tumors because of the increased dorsoventral thickness of the caudal compared with the rostral nasal cavity. Computed tomography images from eight dogs with nasal tumors were selected. A tissue-contouring program was used to outline contours, including the mandible as a normal tissue structure and the planning target volume (PTV), divided into a rostral and caudal volume. A traditional computerized treatment plan consisting of two parallel-opposed fields was constructed for each dog. A second treatment plan using a third caudally located field having a different isocenter was constructed for comparison. Dose-volume histograms were generated and compared for each contoured structure in both plans. In all dogs the use of noncoincident fields resulted in increased dose to the ethmoid region through the caudal field. Minimum dose in the caudal tumor PTV increased as well. At the same time, dose delivered to the mandible, prone to develop significant side effects, was lower in all dogs with the use of noncoincident fields, as it was possible to reduce the dose delivered from the ventral field. Use of photon fields with noncoincident isocenters can improve the dose distribution in irregularly shaped volumes in comparison with fields with coincident isocenters. Improved tumor dose distribution was achieved with the addition of a smaller field having a different isocenter.
比较使用非重合等中心野与重合等中心野治疗不规则形状体积时剂量分布的变化。假设是使用非重合等中心野会导致剂量分布的均匀性得到改善。由于犬尾侧鼻腔与头侧鼻腔相比背腹厚度增加，我们选择在犬鼻肿瘤中检验该假设。选取了8只患有鼻肿瘤的犬的计算机断层扫描图像。使用组织轮廓程序勾勒轮廓，包括将下颌骨作为正常组织结构以及规划靶区（PTV），PTV分为头侧和尾侧体积。为每只犬构建了一个由两个平行相对野组成的传统计算机化治疗计划。构建了第二个治疗计划，使用第三个位于尾侧且等中心不同的野进行比较。生成两个计划中每个勾勒结构的剂量体积直方图并进行比较。在所有犬中，使用非重合野通过尾侧野导致筛骨区域剂量增加。尾侧肿瘤PTV中的最小剂量也增加了。同时，在所有使用非重合野的犬中，下颌骨因易产生显著副作用而接受的剂量较低，因为可以减少来自腹侧野的剂量。与重合等中心野相比，使用非重合等中心的光子野可改善不规则形状体积中的剂量分布。通过添加一个等中心不同的较小野实现了肿瘤剂量分布的改善。
