基于锥形束CT的保乳术后调强放疗在线校正前后分次间位移规律分析

目的 基于锥形束CT（CBCT）探讨乳腺癌保乳术后调强放疗（IMRT）疗程中在线校正分次间位移变化规律。方法 选择保乳术后行全乳IMRT患者18例，共获取452次CBCT图像，获取CBCT校正前后分次间三维方向位移及摆位误差，分析分次间三维方向位移曲线。 结果 患者分次间位移幅度变化较大，同一患者不同方向的分次间位移幅度差异也较大。疗程中左右（LR）、前后（AP）和头脚（SI）方向分次间位移差异最大为0.22、0.49和0.48 cm，CBCT校正后LR、AP和SI方向位移差异最大为0.16、0.21和0.17 cm，CBCT在线校正降低了放疗疗程中患者SI方向的分次间位移（-0.08 cm 和0.03 cm，t=-2.373，P<0.05）和LR、AP、SI方向的随机误差（t=5.302、6.689、4.812，P<0.05），系统误差差异无统计学意义。CBCT校正前后放疗疗程中患者分次间位移无明显规律性。结论 对于保乳术后IMRT患者，通过自动像素-解剖结构密度配准实施CBCT在线校正降低了放疗过程中患者头脚方向的分次间位移和三维方向的随机误差；由于个体差异性的存在，CBCT在线校正前后患者分次间三维方向位移离散度较大。

Assessment of inter-fractional displacement during the breast intensity modulated radiotherapy based on the on-line Cone Beam CT corrections

Objective To explore the inter-fractional geometric uncertainties in breast cancer patients receiving intensity modulated radiotherapy (IMRT) using cone beam CT (CBCT), and to quantify the inter-fractional motion of breast cancer patients. Methods Eighteen breast cancer patients were included in this study, who had received whole breast IMRT after breast conserving surgery. A total of 452 CBCT scans were acquired. Three dimensional inter-fractional motion and setup errors before and after on-line CBCT-based corrections were quantitatively analyzed. The magnitude trends of inter-fractional motion during the treatment were also assessed. Results The magnitudes of the inter-fractional displacements varied among the 18 patients. For the same patient, the disparities in three directions were also different. The maximum inter-fractional variability prior to CBCT-based corrections in the lateral (LR),anteroposterior (AP) and superoinferior (SI) directions were 0.22,0.49 and 0.48 cm respectively, while 0.16, 0.21 and 0.17 cm respectively after on-line CBCT-based corrections. On-line CBCT-based corrections decreased the displacement in SI direction (-0.08 cm vs 0.03 cm, t=-2.373, P<0.05) and random error(t=5.302, 6.689, 4.812,P<0.05), but there were no significant differences for systematic errors. No trends in inter-fractional motion before and after on-line CBCT-based corrections were observed. Conclusions For breast cancer patients who received IMRT, both inter-fractional displacement in SI direction and mean population random errors in three dimensions were reduced after on-line CBCT-based corrections using automatic greyscale match. As a result of individual differences, no significant trend of inter-fractional displacement was identified.