脊柱图像引导放射治疗方案优化的实验研究

Experimental study of spinal image guided radiotherapy scheme optimization

目的：观察脊柱图像引导放射治疗（image guided radiation therapv，IGRT）不同方案放疗过程中放疗区域脊髓MRI弥散加权成像（diffusion—weighted imaging．DWI）的表观扩散系数（apparent diffusion eoeffieient．ADC），为IGRT优化提供实验依据。方法：选用雄性成年比格犬36只，根据放疗方案中照射野数（A，5、7、9野）、单次剂量（B，16、20Gy）、放射剂量率（C，4、6Gy／min）及照射角度（D，等角度、不等角度）4个l临床放疗常用冈素，按L12（3x2，）正交实验表共12种方案对T7～T12椎体及其附件进行IGRT，每周1次，总剂量均为80Gv。每种方案3只犬。分别于放疗前、开始放疗后每2周进行放疗区域脊髓ADC值检测，并对所测得ADC值进行正交实验的方差分析，从而得出脊柱IGRT的较优方案。结果：放疗前各方案组间ADC值无统计学差异（P〉0．05）。经过不同方案的放疗后，各方案组ADC值均出现升高，开始放疗后6周出现ADC最大值，至放疗结束后第3个月时所测ADC值均仍高于放疗前自身水平。相同时间点不同放疗方案脊髓ADC值存在差异（P〈0．05），各时间点照射野5野、单次剂量20Gy，放射剂量率6Gy／min、等角度照射时的ADC最大，而照射野9野、单次剂量16Gy，放射剂量率4Gy／min、等角度照射时的ADC值最小。照射野数、单次剂量和放射剂量率对放疗区域脊髓ADC值的影响有统计学意义（P〈0．05），照射角度对ADC值的影响无统计学意义（P〉0．05）：且各因素对脊髓损伤影响的主效应排序为单次剂量〉放射剂量率〉照射野数。结论：照射野数、单次剂量、放射剂量率及照射角度会影响脊柱IGRT放疗区域脊髓的损伤程度．应用IGRT时应选择优化方案。

Objectives： To observe the effects of different spinal image guided radiation therapy（IGRT） during radiotherapy treating area of spinal cord MRI diffusion-weighted imaging（DWI） apparent diffusion coefficient （ADC）, and to provide experimental basis for IGRT optimization. Methods： 36 male adult Beagles were divid- ed according to the irradiation schemes as 4 common factors of clinical radiotherapy of the wild（A, 5, 7, 9）, single dose（B, 16, 20Gy）, radiation dose rate（C, 4, 6Gy/min） and irradiation angle（D, angle, unequal angle） and fractionated radiotherapy as L12（3x23） orthogonal table IGRT in T7-T12, once a week, total dose was 80Gy. Each scheme was performed in 3 dogs. ADC of radiation region of spinal cord was tested every 2 weeks before radiotherapy and after radiotherapy started, the measured data were analyzed by using statistical software SPSS 17.0, the optimum scheme was obtained by spinal IGRT. Results： Groups showed no signifi- cant difference as for the values of ADC （P〉0.05） before radiotherapy. After different radiotherapy schemes, ADC values elevated; ADC value reached maximum at 6 weeks after radiotherapy. Until the third month after radiotherapy, the ADC values were still higher than the level before radiotherapy. At the same time with dif- ferent schemes of spinal cord, ADC values were different（P〈0.05）, each time point of 5 wild field, a single dose of 20Gy radiation rate, 6Gy/min and equal angle had the maximum ADC value, and the radiation field of 9 wild, a single dose of 16Gy, dose rate of 4Gy/min and equal angle had the minimum ADC value. Sta- tistically significant influence of irradiation field, single dose, dose rate of radiotherapy on regional spinal cord ADC value （P〈0.05）, and the contribution of each factor to spinal cord injury was s single dose〉 dose rate〉 radiation field. Conclusions： The radiation field, single dose, dose rate and angle will impact the size of the damage of spinal IGRT radiotherapy regions of the spinal cord, the the optimization scheme should be cautioned when choosing spinal IGRT.