Analysis of utility of optical surface imaging system for patients who received radiotherapy with active breath control

Objective To analyze the precision and stability of optical surface imaging system for patients who received radiotherapy with active breath control. Methods Eighteen radiotherapy patients with lung metastasis were managed by active breath control (ABC). The difference error detected by optical surface imaging system and CBCT were defined as the precision of optical surface imaging system. The variation among the error of optical surface imaging positioning the value of correction of treatment position and the error detected by optical surface imaging again were defined as the stability of optical surface imaging system. Intrafractional errors were analyzed by optical surface imaging system through whole treatment process (including breath hold and free breath). Results The optical surface imaging system had precision (systematic (Σ) and random errors (σ)) of 1.78/3.42 mm 2.54/6.57 mm and 2.79/3.22 mm respectively and stability of2.12/2.54 mm 3.09/4.02 mm and 1.37/3.55 mm respectively in lateral-medial superior-inferior and anterior-posterior directions. The intrafractional errors (Σ and σ) were 0.42/0.85 mm 0.41/1.47 mm and 0.41/1.47 mm respectively for breath hold duration and 4.76/4.16 mm 6.54/7.78 mm and 3.13/5.92 mm for free breath duration in lateral-medial superior-inferior and anterior-posterior directions. Conclusions As an effective method for validate breath hold; Optical surface imaging system can improve the precision and safety of active breath control. However, the factors that affect the accuracy and stability of the optical surface imaging system in patients undergoing radiotherapy with ABC are not clear; it cannot replace the CBCT for positioning verification. Key words: Tomography, X-ray computed, three-dimensional; Active breath control; Systematic error; Setting error