Application of optical surface monitoring system(OSMS) during postoperative radiotherapy for breast cancer patients immobilized with neck and thorax thermoplastic mask / 中华放射医学与防护杂志

ABSTRACT

Objective:To build patient setup workflow based on the optical surface monitoring system (OSMS) in postoperative radiotherapy for breast cancer, and compare the setup accuracy and PTV margin between OSMS based setup and conventional skin marker based method.Methods:The setup data of 20 cases of postoperative radiotherapy for breast cancer were retrospectively analyzed and divided into two groups OSMS setup group and conventional skin marker setup group with 10 patients in each group. All CBCT rigid registration values in six dimensions ( x, y, z, Rtn, Pitch, Roll) were obtained, and the absolute value and distribution of errors were statistically analyzed by single sample t-test and χ2-test respectively. Finally, the CTV-PTV margins were compared using the extension formula. Results:The mean values in OSMS setup group and conventional skin marker setup group in sixdirections were 0.18 and 0.18 cm, 0.12 and 0.13 cm, 0.13 and 0.23 cm, 0.55° and 0.74°, 0.63° and 0.99°, 0.67° and 0.68°, respectively, while the standard deviations were 0.13 and 0.12 cm, 0.09 and 0.09 cm, 0.11 and 0.16 cm, 0.37° and 0.55°, 0.53° and 0.65°, 0.42° and 0.55°, respectively. The setup error differed in both z and Pitch directions( t=3.53, 2.98, P<0.05), while the error distribution rate difference was statistically significant between two groups in z direction( χ2=11.090, P<0.05). The CTV-PTV margins in OSMS setup group and conventional skin marker setup group were 0.28 and 0.26 cm, 0.21 and 0.20 cm, 0.24 and 0.35 cm, respectively. Conclusions:The proposed OSMS-based patient setup work flow is better than the conventional skin marker based method in setup accuracy, with significant setup error differences in z and Pitch directions. The proposed OSMS workflow is of potential clinical benefit.