自主呼吸控制对保乳术后全乳调强放疗靶区剂量分布的影响

目的 探讨保乳术后自主呼吸控制(ABC)辅助全乳调强放疗(IMRT)过程中分次内及分次间靶区位移对剂量分布的影响.方法 ABC辅助CT模拟定位,获得3个呼吸状态的5套CT图像,分别为自主呼吸(FB)1套、适度深吸气呼吸控制(mDIBH)2套、深呼气呼吸控制(DEBH)2套.放疗10～15次后,ABC辅助重复CT模拟定位,并获得与初次定位相同的5套CT图像.在Pinnacle3治疗计划系统中,以初次定位的第1套mDIBH状态下CT图像制定正向IMRT计划,将此计划分别复制到初次定位的第2套及重复定位的第1套mDIBH状态下的CT图像上,保持射野角度、方向、大小、形状及处方剂量等参数不变,比较计划中某一子野中高剂量区所覆盖的乳腺体积变化.结果 初次定位的第1套mDIBH状态下CT图像制定的IMRT计划中,多叶准直器(MLC)遮挡后,挡高剂量线子野内接受103%高剂量照射的平均乳腺体积为(1.16±0.39)cm3,同一IMRT计划复制到初次定位的第2套mDIBH状态下的CT图像上,挡高剂量线子野内接受103%高剂量照射的平均乳腺体积为(3.88±1.07)cm3,两者差异无统计学意义(P=0.103).同一IMRT计划复制到重复定位的第1套mDIBH状态下的CT图像上,挡高剂量线子野内接受103%高剂量照射的乳腺体积为(51.66±8.68)cm3,两者差异有统计学意义(P<0.01).结论 如果保持相同的mDIBH阈值,单次放疗中,靶区位移对IMRT照射剂量分布无明显影响;如果不进行摆位误差校正,分次照射间IMRT计划中挡高剂量区子野位置会发生明显变化,从而导致照射剂量分布的明显变化.

Influence of active breathing control on the dose distribution in the target of forward whole-breastintensity-modulated radiotherapy after breast conserving surgery

Objective To explore the influence of intrafraction and interfraction target displacement on the dose distribution in the target of forward whole-breast intensity-modulated radiotherapy (IMRT) assisted by active breathing control (ABC). Methods Each of the selected patient who had received breast conserving surgery was immobilized and received the primary CT simulation assisted by ABC device to get five sets of CT images in three different breathing status, including free breathing (FB) ( one set), moderate deep inspiration breathing hold (mDIBH) (two sets) and deep expiration breathing hold (DEBH) (2 sets). After 10 to 15 fractions of radiation, the repeated CT simulation was completed and the same five sets of CT images were obtained at FB, mDIBH, and DEBH, respectively. In the Pinnacle3 treatment planning system, the forward IMRT planning was completed on the first set of mDIBH CT images from the primary CT simulation, and the planning was separately copied by the special system order to the second set of CT images from the primary CT simulation and to the first set of CT images from the repeated CT simulation, keeping the primary angle, direction, size and shape of the MLC field and prescribed dose un-changed, the volumes covered by selected high dose area in the selected segment were compared. Results In the planning based on the first set of mDIBH CT images from the primary CT simulation, the volume irradiated by equal and more than 103% of prescribed dose in the segment was (1.16±0.39) cm3, and the volumes were (3.88±1.07) cm3 and (51.66 ± 8.68) cm3 in the plannings copied from the first set of mDIBH CT images from the primary CT simulation respectively to the second set of CT images from the primary CT simulation and first set of CT images from the repeat CT simulation, the difference of the volume in the two plannings based on the two set mDIBH CT image from the primary CT simulation was not statistically significant (t = -1. 672, P =0. 103). The difference of the volume in the two plannings based on the two sets of mDIBH CT images respectively from the primary and repeat CT simulations had a significant difference (t = - 5. 728, P < 0.01 ). Conclusion If the same threshold of mDIBH is maitained during IMRT after breast conserving surgery, the influence of the intrafraetion target displacement on the dose distribution is not significant. However, if set-up error is not adjusted, the interfraction change of position of the segment given to cover the high dose area in the IMRT planning will be significant, resulting in a significant change of dose distribution in the breast.