头肩体垫固定下乳腺癌的放疗摆位误差

目的 探讨头肩体垫固定的乳腺癌的放疗摆位误差，并计算合适的临床靶区（CTV）外扩边界。方法 53例乳腺癌患者均接受头肩体垫固定，采用千伏级锥形束CT（CBCT）扫描并分析左右（X）、头脚（Y）、上下（Z）3个轴方向的线性误差（X、Y、Z），及绕此3个轴的旋转误差（Xr、Yr、Zr）。统计误差数据，评价头肩体垫的优劣，并根据公式MPTV=2.5∑+0.7δ计算CTV外扩为计划靶区（PTV）的范围（MPTV）。结果 53例患者共得到265次摆位误差的数据。265组线性误差绝对值的均值为2.50 mm、2.40 mm、2.20 mm，旋转误差为1.13°、1.11°、0.94°，Z轴方向与X、Y轴方向误差的差异有统计学意义（P<0.05）。X、Y、Z 轴3个方向的线性群体系统误差为2.5 mm、2.3 mm、1.9 mm，随机误差为2.5 mm、2.20 mm、2.20 mm；旋转群体系统误差分别为1.03°、1.10°、0.95°，随机误差为0.79°、1.15°、0.72°。建议外扩边界为8.00 mm，7.30 mm、6.30 mm。结论 头肩体垫具有较好的摆位精度，利用CBCT测量乳腺癌放疗的摆位误差，为乳腺癌放疗CTV外扩为PTV提供参考依据，提高了乳腺癌放疗的精准性。

Analysis of radiotherapy setup errors of breast cancer sufferers immobilized by head-shoulder-truncus vac-uum bags

Objective To analyze radiotherapy setup errors of breast cancer sufferers immobilized by head-shoulder-truncus vacuum bags and calculate the clinical target volume （CTV） enlarging to the planning target volume（PTV）. Methods Fifty-three patients were immobilized by the head-shoulder-truncus vacuum bags. Setup errors were analyzed using kilovoltage cone beam computed tomography （CBCT）. The data of the linear （X， Y and Z） and rotational （Xr，Yr and Zr） setup errors were collected. The statistics were used to estimate the performance of head-shoulder-truncus vacuum bags. According to the formula Mptv=2.5∑+0.7δ， the Mptvwas calculated. Results A total of 265 CBCT scans from 53 patients were done. The average absolute value of 265 linear errors were 2.50 mm， 2.40 mm and 2.20 mm at X， Y and Z axes，rotation errors were 1.13°， 1.11°and 0.94°at Xr， Yr and Zr axes， and the errors of X and Y axes compared with Z axis had statistical significance （P<0.05）. For the linear setup errors， the group systematic errors were 2.50 mm， 2.30 mm and 1.90 mm， and the group random errors were 2.50 mm， 2.20 mm and 2.20 mm at X， Y and Z axes. For the rotational errors， the group systematic errors were 1.03°， 1.10°and 0.95°at Xr， Yr and Zr axes， and the random errors were 0.79°， 1.15° and 0.72° at Xr， Yr and Zr axes. In accordance with formula， the Mptv were recommended as 8.00 mm， 7.30 mm and 6.30 mm at X， Y and Z axes. Conclusion The head-shoulder-truncus vacuum bag has good setup accuracy. The data of setup errors which measured by CBCT provide references for CTV enlarging to PTV， and increase the precision in breast cancer radiotherapy.