Hao Chang¹, Jun Liang², Dequan Yu², Yanjun Zhang², Yuhong Qi², Dongjie He², Hong Gao²

¹Department of Radiotherapy, TangDu Hospital, Fourth Military Medical University, Fourth Military Medical University, TangDu Hospital

Objective: To simplify the craniospinal irradiation planning and the treatment process without loss of dose homogeneous. Describes a simple and effective way to improve the dose distribution at the junctions. Method: Six patients were selected for retrospective planning at our department with a prescription of 36Gy in 20 fractions. Two or three isocenter were made depending on the length of PTV. The spinal PTV of the IMRT technique was planned using five posterior coplanar fields. In those tall patients which two spinal PTV was needed. The fields targeted the two PTV volumes overlapped each other and the junctions has the same optimization objectives but a small weights priority. The cranial part of the target volume was planned with lateral opposing fields. The angle of collimator was set to approximately 85°and 95° so that we could set a few millimeters apart to optimize the dose coverage of craniospinal junction and to limit the penumbra. Result: The HI values for craniospinal axis with IMRT and 3D-CRT were a little difference (0.09±0.01vs 0.12±0.02, P>0.05), especially for the spinal cord volume (0.09±0.02 vs 0.20±0.04, P<0.05). More dose homogeneity was achieved for IMRT in craniospinal junctions (0.21±0.01 vs 0.36±0.06, P<0.05) and spinal-spinal junctions (0.08 vs 0.40±0.14, P<0.05). Spinal-spinal junctions was more outstanding than craniospinal junctions in IMRT approach (0.08 vs 0.21±0.01, P<0.05). The field collimator rotation technique reduced max lens dose about 0.3Gy to 0.5Gy compared with conventional 3D-CRT plans. Conclusion: The new IMRT plans resulted in better homogeneity than the conventional plan in spinal-spinal junction for CSI and craniospinal junction region also has a high dose improvement than conventional method.

Key Words: Craniospinal irradiation  Field junctions  IMRT