Feasibility study on the application of accelerator MV CBCT images in adaptive radiation therapy

Objective: To investigate whether the accelerator image beam line (IBL) full scan and extend field of view(EFOV) scan mode megavoltage cone beam CT(MV CBCT) images can be used for dose calculation in adaptive radiotherapy. Methods: The large aperture CT and MV CBCT were used to scan the CIRS 062M electron density modules, the CT value was established to electron density curves in the Pinnacle treatment planning system. Also, CT and MV CBCT were used to scan the head and neck, chest, abdomen and pelvis phantom. The intensity modulated radiotherapy(IMRT) plans were made with CT images and transplanted to MV CBCT images. The dose of targets and organs with their electron density curves was calculated, and two type IMRT plans with different CT images were compared. Results: The dose distribution of head and neck phantom was acceptable, compared with the reference plan, the difference was within 3%. The dose distribution of chest and pelvis was significantly reduced from reference plans, and the difference was 5% and 10% separately. This difference was beyond the scope of clinical acceptance. Conclusions: MV CBCT images of accelerator IBL full scan mode in patients with head and neck site scan could be used for dose calculation in adaptive radiotherapy, chest and pelvic sites in EFOV mode scanning MV CBCT images could only be used for image guidance. (authors)