应用机载千伏级CBCT研究鼻咽癌IMRT的摆位误差及其对受照剂量的影响
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摘要
目的:应用机载千伏级CBCT监测鼻咽癌调强放疗患者疗程中摆位误差的变化和影响因素,分析摆位误差对物理剂量的影响,以达到减少和/或消除摆位误差对放疗的影响。
方法:本实验选取病理学确诊的鼻咽癌早期患者15例,行调强放疗。患者每周按治疗计划标志点摆位,利用机载KV-CBCT扫描获取摆位误差,将摆位误差代入治疗计划,模拟出未使用IGRT时,实际摆位位置中剂量分布情况。计算在相同治疗阶段所有患者三维线性方向和水平面旋转方向摆位误差平均值、标准差及95%可信区间(CI);分析随疗程进行摆位误差的变化情况;探讨体重指数和体重变化对摆位误差的影响;研究不同方向的摆位误差对危及器官剂量影响;分析三维移动矢量和旋转误差对靶区剂量影响,并探讨本科室鼻咽癌患者靶区外放边界范围。
结果:患者在腹背、头脚、左右三个坐标轴和水平面旋转方向的摆位误差均值分别为-0.1833cm、-0.0322cm、0.0967cm和-0.8333°,95%的可信区间分别为[-0.2117cm,-0.1549cm],[-0.0768cm,0.0124cm],[0.0563cm,0.1371cm]和[-1.0987°,-0.5687°]。随疗程进行,摆位中心点向腹侧偏移。BMI≥25患者在左右方向及水平面旋转方向首次摆位误差绝对值较BMI<25患者明显增大;BMI≥25患者在左右方向及水平面旋转方向的系统误差较BMI<25患者明显;患者体重下降会引起摆位中心点往腹侧偏移和水平面逆时针旋转。摆位中心点向背侧偏移0.2cm,脑干D1和脊髓D1cc增高率均值分别为6.58%和4.70%,摆位中心点向头侧偏移0.2cm,视交叉D1增高率均值为8.94%,摆位中心点向左侧偏移0.2cm,同侧腮腺D50增高率均值为4.95%。CTV2 D95、GTVnd D98与三维移动矢量和旋转误差有相关性(P<0.05,|r|>0.4);CTV1 D95和GTVnx D98与旋转误差无明显相关性(P>0.05);而GTVnx D98与三维移动矢量无明显相关性(P=0.077,|r|=0.187)。BMI≥25患者各个方向的MPTV值较BMI<25患者明显增大。
结论:在鼻咽癌调强放疗中:1、BMI≥25患者有必要进行自适应放疗;2放疗疗程中体重减少超过7.10%时,需要及时调整放疗计划;3、摆位中心点偏移应尽量控制在0.2cm以内;4、GTVnd和CTV2剂量较GTVnx、CTV1剂量对线性误差和旋转误差敏感;5、BMI≥25患者可通过机载千伏级CBCT在线或离线纠正摆位误差,缩小CTV至PTV外放边界而获益。
Objective: Using KV-cone beam CT (CBCT) on IGRT to study the setup errors for nasopharyngeal carcinoma treated by fractionated intensity-modulated radiation therapy (IMRT) and to explore the effects on dose distributions in order to reduce and/or eliminate the effects on radiotherapy.
Methods: Fifteen patients diagnosed with early nasopharyngeal carcinoma by pathology were selected. They were treated by fractionated IMRT. During the treatment courses, patients were posed by the original positions every week in order to get fractional setup errors with on-board KV-CBCT. We applied setup errors into the TPS to acquire dose distributions when patients posed at actual setup positions without image guided radiotherapy (IGRT). The mean values, standard deviations, 95% confidence intervals (CI) of three dimensional and the horizontal rotation errors were calculated. Analyzed the effects of body mass index and weight loss on setup errors. Explored the impact of the setup errors on the dose distributions for targets and organs at risk. And defined margins for planning target volume definition.
Results: The mean values of setup errors on ventral-dorsal, cranial-caudal, medio-lateral directions and the horizontal rotation were -0.1833cm, -0.0322cm, 0.0967cm, -0.8333°and 95% confidence intervals were [-0.2117cm, -0.1549cm], [-0.0768cm, 0.0124cm ], [0.0563cm, 0.1371cm] and [-1.0987°, -0.5687°] respectively. The displacements increased with the treatment progress along the ventral-dorsal direction. Absolute values of the first setup errors, the system errors of the medio-lateral direction and the horizontal rotation in the patients with BMI≥25 are more apparent than those with BMI<25. Weight loss can obviously result in the center of actual setup position shifting to the ventral direction and the horizontal rotation counterclockwise. The center of actual setup position shifting to the dorsal direction 0.2cm is able to meanly increase brain stem D1 and spinal cord D1cc, with 6.58% and 4.70%. The center of actual position shifting to the cranial direction 0.2cm resulted in 8.94% dose meanly increasing of optic chiasm D1. The center of actual setup position shifting to the left direction 0.2cm resulted in left parotid D50 meanly increasing with 4.95%. The variations of CTV2 D95 and GTVnd D98 are relevant to 3-dimensional shift vector and the rotation setup error (P<0.05, |r|>0.4); the variations of CTV1 D95 and GTVnx D98 are not relevant to the rotation setup error (P>0.05); the variation of GTVnx D98 is not relevant to 3-dimensional shift vector (P=0.077, |r|=0.187). Patients with BMI≥25 of MPTV values were significantly increased in all directions.
Conclusion: 1. The nasopharyngeal carcinoma patients with BMI≥25 should be treated by adaptive radiation therapy; 2. The treatment planning should be adjusted when the weight lost over than 7.10% during the treatment course; 3. The effective measures should be adopted to control isocenter point deviation of three directions within 0.2cm in nasopharyngeal carcinoma with IMRT; 4. The doses of GTVnd and CTV2 are more sensitive than that of GTVnx and CTV1 in translational and rotational setup error; 5. The patients with BMI≥25 might benefit from KV-CBCT online or offline correcting fractional setup errors to reduce margins for the PTV.
方法:本实验选取病理学确诊的鼻咽癌早期患者15例,行调强放疗。患者每周按治疗计划标志点摆位,利用机载KV-CBCT扫描获取摆位误差,将摆位误差代入治疗计划,模拟出未使用IGRT时,实际摆位位置中剂量分布情况。计算在相同治疗阶段所有患者三维线性方向和水平面旋转方向摆位误差平均值、标准差及95%可信区间(CI);分析随疗程进行摆位误差的变化情况;探讨体重指数和体重变化对摆位误差的影响;研究不同方向的摆位误差对危及器官剂量影响;分析三维移动矢量和旋转误差对靶区剂量影响,并探讨本科室鼻咽癌患者靶区外放边界范围。
结果:患者在腹背、头脚、左右三个坐标轴和水平面旋转方向的摆位误差均值分别为-0.1833cm、-0.0322cm、0.0967cm和-0.8333°,95%的可信区间分别为[-0.2117cm,-0.1549cm],[-0.0768cm,0.0124cm],[0.0563cm,0.1371cm]和[-1.0987°,-0.5687°]。随疗程进行,摆位中心点向腹侧偏移。BMI≥25患者在左右方向及水平面旋转方向首次摆位误差绝对值较BMI<25患者明显增大;BMI≥25患者在左右方向及水平面旋转方向的系统误差较BMI<25患者明显;患者体重下降会引起摆位中心点往腹侧偏移和水平面逆时针旋转。摆位中心点向背侧偏移0.2cm,脑干D1和脊髓D1cc增高率均值分别为6.58%和4.70%,摆位中心点向头侧偏移0.2cm,视交叉D1增高率均值为8.94%,摆位中心点向左侧偏移0.2cm,同侧腮腺D50增高率均值为4.95%。CTV2 D95、GTVnd D98与三维移动矢量和旋转误差有相关性(P<0.05,|r|>0.4);CTV1 D95和GTVnx D98与旋转误差无明显相关性(P>0.05);而GTVnx D98与三维移动矢量无明显相关性(P=0.077,|r|=0.187)。BMI≥25患者各个方向的MPTV值较BMI<25患者明显增大。
结论:在鼻咽癌调强放疗中:1、BMI≥25患者有必要进行自适应放疗;2放疗疗程中体重减少超过7.10%时,需要及时调整放疗计划;3、摆位中心点偏移应尽量控制在0.2cm以内;4、GTVnd和CTV2剂量较GTVnx、CTV1剂量对线性误差和旋转误差敏感;5、BMI≥25患者可通过机载千伏级CBCT在线或离线纠正摆位误差,缩小CTV至PTV外放边界而获益。
Objective: Using KV-cone beam CT (CBCT) on IGRT to study the setup errors for nasopharyngeal carcinoma treated by fractionated intensity-modulated radiation therapy (IMRT) and to explore the effects on dose distributions in order to reduce and/or eliminate the effects on radiotherapy.
Methods: Fifteen patients diagnosed with early nasopharyngeal carcinoma by pathology were selected. They were treated by fractionated IMRT. During the treatment courses, patients were posed by the original positions every week in order to get fractional setup errors with on-board KV-CBCT. We applied setup errors into the TPS to acquire dose distributions when patients posed at actual setup positions without image guided radiotherapy (IGRT). The mean values, standard deviations, 95% confidence intervals (CI) of three dimensional and the horizontal rotation errors were calculated. Analyzed the effects of body mass index and weight loss on setup errors. Explored the impact of the setup errors on the dose distributions for targets and organs at risk. And defined margins for planning target volume definition.
Results: The mean values of setup errors on ventral-dorsal, cranial-caudal, medio-lateral directions and the horizontal rotation were -0.1833cm, -0.0322cm, 0.0967cm, -0.8333°and 95% confidence intervals were [-0.2117cm, -0.1549cm], [-0.0768cm, 0.0124cm ], [0.0563cm, 0.1371cm] and [-1.0987°, -0.5687°] respectively. The displacements increased with the treatment progress along the ventral-dorsal direction. Absolute values of the first setup errors, the system errors of the medio-lateral direction and the horizontal rotation in the patients with BMI≥25 are more apparent than those with BMI<25. Weight loss can obviously result in the center of actual setup position shifting to the ventral direction and the horizontal rotation counterclockwise. The center of actual setup position shifting to the dorsal direction 0.2cm is able to meanly increase brain stem D1 and spinal cord D1cc, with 6.58% and 4.70%. The center of actual position shifting to the cranial direction 0.2cm resulted in 8.94% dose meanly increasing of optic chiasm D1. The center of actual setup position shifting to the left direction 0.2cm resulted in left parotid D50 meanly increasing with 4.95%. The variations of CTV2 D95 and GTVnd D98 are relevant to 3-dimensional shift vector and the rotation setup error (P<0.05, |r|>0.4); the variations of CTV1 D95 and GTVnx D98 are not relevant to the rotation setup error (P>0.05); the variation of GTVnx D98 is not relevant to 3-dimensional shift vector (P=0.077, |r|=0.187). Patients with BMI≥25 of MPTV values were significantly increased in all directions.
Conclusion: 1. The nasopharyngeal carcinoma patients with BMI≥25 should be treated by adaptive radiation therapy; 2. The treatment planning should be adjusted when the weight lost over than 7.10% during the treatment course; 3. The effective measures should be adopted to control isocenter point deviation of three directions within 0.2cm in nasopharyngeal carcinoma with IMRT; 4. The doses of GTVnd and CTV2 are more sensitive than that of GTVnx and CTV1 in translational and rotational setup error; 5. The patients with BMI≥25 might benefit from KV-CBCT online or offline correcting fractional setup errors to reduce margins for the PTV.
引文
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1.于金明,李宝升.调强放射治疗的临床应用现状与存在的问题[J].中华肿瘤杂志, 2005, 27(3): 188-190.
2. Huiaenga H, Levendag PC, De Porre P. M. Z. R. et al. Accuracy in radiation field alignment in head and neck cancer: A prospective study [J]. Radiother Oncol, 1988, 11(2): 1871-1872.
3. Shih HA, Jiang SB, Aljarrah KM, et al. Internal target volume determined with expansion margins beyond composite gross tumor volume in three dimensional conformal radiotherapy for lung cancer [J]. Int J Radiation Oncology Biol. Phys, 2004, 60(2): 613-622.
4. Chin LM, Kijewski PK, Svensson GK, et al. Dose optimization with computer controlled gantry rotation, collimator motion and dose-rate variation [J]. Int J Radiat Oncol Biol Phys, 1983, 9(5): 723-729.
5. McBain CA, Henry J, Sykes A, et al. X ray volumetric imaging in image-guided radiotherapy;the new standard in on treatment imaging [J]. Int J Radiat Oncol Biol Phys, 2006, 64(2): 625-634.
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