Companison of dose distribution and setup error of two different positions and immobilization techniques in breast cancer radiotherapy / 中华放射医学与防护杂志

ABSTRACT

Objective To compare the dose distribution and setup error of angled breast board position ( ABB) with plain breast board position ( PBB) in breast cancer radiotherapy. Methods Twenty consecutive postoperative left breast cancer patients in the First Affiliated Hospital, Zhejiang University were enrolled from March 2017 to January 2018. All cases were assigned into the ABB and PBB groups according to positions and there were 10 cases in each groups respectively. The target volume, heart and lung structures were defined on the CT images of the localized scan. The plan was designed using the field in field ( FIF) technique to compare the dosimetric parameters of the PTV, lung, and heart treatments, and the setup errors for the two different positions. Results The ipsilateral lung V20[ABB(11.2 ±3.2)％, PBB(15.9 ±5.3)％, t= -2.47,P< 0.05], and V30[ABB(9.8 ±1.5)％, PBB(12.9 ±2.2)％, t= -4.46,P<0.05] were both statistically significant for the two different position and immobilization. Heart dose V25[ABB (1.9 ± 0.2)％, PBB (2.8 ± 0.4)％, t = -8.28, P <0.05], V30 [ABB(1.8 ±0.1)％, PBB (2.7 ± 0.3)％, t = -8.34,P < 0.05], and Dmean of heart [ABB (3.0 ±0.5)Gy, PBB(5.3 ± 1.2)Gy, t=5.58,P<0.05] were all statistically significant for the two different positions. The translational errors of ABB and PBB on LR, SI, and AP were ( 3.23 ± 2.63 ) , ( 5.42 ± 3.22), (4.58 ± 2.30) mm, and (2.35 ± 1.22), (2.17 ± 1.29), (2.27 ± 1.58) mm, respectively. The rotation errors of pitch(θ), yaw(Φ) and roll(ψ) for ABB and PBB were (1.60 ± 0.56)°, (3.40 ± 1.65)°, (2.50 ± 1.72)°, and (1.37 ± 0.43)°, (1.79 ± 0.71)°, (2.06 ± 0.63)°, respectively. Meanwhile, the in-and out-SI, anterior and posterior AP, yaw rotation error (Φ) were also statistically significant(t=3.06, 2.80, 3.33,P<0.05). Conclusions There is no statistically significant difference in the tumor target between the two position and immobilization techniques. However, the ABB is better than the PBB in normal tissue sparing while the setup accuracy of PBB is better than the ABB.