Clinical Application of CTVision Images-guided Precise Radiotherapy in Breast Cancer Patients with Postoperative

Abstract

By applying kilovolt (KV) level computerized tomography (CT) in Image-Guided Radiation Therapy system (IGRT) – CTVision, setup errors of postoperative breast cancer patients after breast bracket with thermoplastic molding in precise radiotherapy is studied, advantages and disadvantages of manual osseous registration and skin tag tumor bed area registration are compared, it is verified that breast bracket with thermoplastic phantom is the best fixing mode for postoperative breast cancer patients and then clinically possible extended value of CTV (Clinical Target Volume) and PRV (Planning Organ at Risk Volume) are discussed. Materials and methods: Siemens CTVision image-guided system is adopted for 10 cases of postoperative breast cancer patients, including 7 patients with modified radical mastectomy and 3 breast-conserving surgery patients which is using breast bracket with thermoplastic molding and scaned by Large aperture CT of CTVision image-guided system. Image guidance is respectively conducted 3 continuous times three days before treatment and once weekly during treatment, osseous manual registration and skin tag tumor bed area registration are conducted for verification image and planned image of postoperative breast cancer patients, setup error data of two different registration modes is measured, displacement error difference in direction of horizontal (X-axis), vertical (Y-axis) and longitudinal (Z-axis) is analyzed, and error effect on CTV and PRV extended boundary is explored. Results: 10 cases of postoperative breast cancer patients received 80 scans, average displacement errors in horizontal (X-axis) direction of osseous manual registration and skin tag tumor bed region registration are 0.7 ± 2.4 mm and -1.3 ± 5.6 mm respectively; displacement errors in vertical (Y-axis) direction are 0.5 ± 2.6 mm and -0.3 ± 4.4 mm respectively; displacement errors in longitudinal (Z-axis) direction are 0.7 ± 1.1 mm and 1.9 ± 2.0 mm respectively. Extended boundary of CTV of osseous manual registration and skin tag tumor bed area registration are 4.79 mm and 13.62 mm, 5.81 mm and 8.52 mm, 1.46 mm and 3.71 mm respectively in X-, Y-, Z-axis direction; extended boundary of organs at risk (PRV) are 2.62 mm and 7.28 mm, 3.13 mm and 4.50 mm, 0.80 mm and 2.04 mm respectively in X-, Y-, Z-axis direction. Re-setup or online mobile treatment couch calibration is conducted for the above osseous manual registration displacement error value over 5 mm in three-dimensional direction, and corrected INT. J. BIOAUTOMATION, 2019, 23(3), 369-386 doi: 10.7546/ijba.2019.23.3.000627 370 displacement errors in X, Y, and Z directions are lower than those before correction, with resetup or online correction rate at 3.8%. Discussion: (1) Setup error of intensity modulated radiotherapy of postoperative breast cancer patients with large aperture CT scan imaging of CTVsion image guided radiation therapy system is within an acceptable range, osseous manual registration is superior to skin tag tumor bed region registration, and therefore, intensity modulated radiotherapy of postoperative breast cancer patients with osseous manual registration to decide set-up errors is a more realistic option. (2) Fixing mode of breast bracket joint thermoplastic phantom is with good repeatability and stability, low positioning failure rate, and thermoplastic phantom can effectively control error caused by respiratory movement in longitudinal direction. Breast bracket joint thermoplastic phantom is one of the best fixing mode for postoperative breast cancer patients. (3) Based on the study on systemic error and random error in two registration modes of intensity modulated radiotherapy of postoperative breast cancer patients, CTV and PRV extended value obtained by setup errors of osseous manual registration mode is more realistic, extension of 5 mm of postoperative breast cancer plan is clinically feasible, and extension of organs at risk PRV should be decided by patients’ tumor site and treatment plan design, etc.