Evaluation of Optical Surface Scanning of Breast Cancer Patients for Improved Radiotherapy

Abstract

Patients with breast cancer often receive radiotherapy and it is crucial that the positioning of the patient is reproduced accurately at each treatment fraction. An optical surface scanning (OS) system can automatically and in real-time provide corrections for patient posture and also couch corrections to position the patient as planned, without giving any dose of ionizing radiation to the patient. In addition, the system can monitor the respiratory motion, used for deep-inspiration breath-hold (DIBH) radiotherapy, by tracking a small predefined area on the patient’s surface. The objective of the present PhD study was to investigate if OS-systems can lead to improved radiotherapy for breast cancer patients. Potential improvement of radiotherapy was investigated by evaluating (i) the accuracy of the patient setup, (ii) the dose coverage of the target, and (iii) the accuracy of the respiratory motion monitoring. In regard to respiratory motion monitoring, the feasibility of moving the gating area during the treatment course was also investigated. In a prospective study with 39 left-sided breast cancer patient, the treatment position was evaluated after conventional setup (kilo- and megavoltage X-ray imaging (kV-MV)) for patients with (n = 19) and without (n = 20) arm posture correction using cone beam computed tomography (CBCT) as ground truth. No indications of improved kV-MV based setup with arm posture correction were found. Nonetheless, it was found that the initial patient setup is significantly improved based on surface scans rather than in-room lasers. In a pilot study, involving three out of the 39 patients, it was found that incorrect arm posture led to reduced dose coverage of the target breast. The reduction was however small and based on a limited number of patients. In a phantom study it was concluded that the OS-system can be used for respiratory motion monitoring. Compared to an alternative external marker- based system, the amplitude estimates from the OS-system are more accurate with no angle-dependency of the patient surface. In a patient study (n = 194), the feasibility of moving the gating area from an area above the xiphoid process to the target breast was investigated. Based on simultaneous monitoring of the respiratory motion at the xiphoid process and the target breast, it was concluded that the gating area in general should not be moved. Overall it can be concluded that the OS-system can improve radiotherapy for breast cancer patients, as the system can be used for respiratory motion monitoring with more accurate amplitude estimates. The system can also be used for posture corrections where data indicated that arm posture correction can improve dose coverage of the breast. In addition it was concluded, that with the current technology patient setup can not solely be based on OS. Conventional x-ray based imaging of internal anatomy therefore remains an essential part of the clinical workflow. However, the initial patient setup is improved if based on surface scans rather than laser.