Surface guided radiotherapy

Abstract: AbstractModern radiotherapy aims to treat the decease while minimizing the radiation dose to the adjacent normal tissue, to minimize acute and late effects of the treatment. The foremost technological approaches have been intensity modulated radiotherapy (IMRT) and intensity modulated proton therapy (IMPT) in combination with image guided radiotherapy (IGRT). IMRT and IMPT is characterized by a more conform dose distribution, often accompanied by steep dose gradients. In turn, accurate patient localization and motion management becomes more important. Several image guidance systems are available for radiotherapy (RT), with 3-dimensional (3D) volumetric images with cone beam computed tomography (CBCT) as a gold standard. In recent years, surface imaging (SI) using an optical surface scanning system has been included in the IGRT toolbox. The SI system CatalystTM (C-rad Positioning AB, Uppsala Sweden) visualize 3D surface images of the patient topography, and direct correlate the patient localization to the initial planned position. SI offers the largest field-of-view in RT, does not contribute to radiation exposure, provides real-time feedback and sub-millimeter spatial resolution. These characteristics are suitable for both patient positioning and motion management during RT.Integration with the linac provides beam control and automatic couch shifts, which imposes rigorous attention to quality assurance (QA) of the SI systems. In order to integrate the beam control, beam latency times (beam-on and beam-off) should be characterized, which required the development PIN diode circuit as a QA tool. Of extra importance was the measurements of the beam-off latency time, since it represents the time the linac continues to irradiate after the beam hold signal was sent from the SI system. The automatic couch shift is calculated by a deformable image registration (DIR) algorithm, unique for the CatalystTM surface scanning system. Positioning accuracy is dependent on the image registration, and hence, a deformable thorax phantom was developed to investigate accuracy of the DIR with anatomical realistic deformations present as a QA tool.Compared to traditional 3-point localization for patient positioning, this thesis has shown that SI improve the positioning for both breast and prostate cancer patients. Also, the SI workflow has shown to be time efficient for positioning of prostate cancer patients. A respiratory motion management technique is deep inspiration breath hold (DIBH), where the patient is instructed to hold his/her breath during the treatment delivery. The aim using DIBH, is to create an anatomical distance between the treatment volume and surrounding organs-at-risk (OARs). Comparative treatment planning studies, within the work of this thesis, showed that DIBH can be an effective method for both left sided breast cancer and Hodgkin’s lymphoma (HL) in order to spare dose to the heart. For HL, the combination of IMPT and DIBH was found to spare dose to OARs, however, due to the spread in target localization individual deviations from this treatment technique were observed. The real-time feedback from the surface image system was used to investigate the reproducibility of the DIBH to ensure correct dose distribution during the treatment delivery. High reproducibility of the isocenter position during DIBH was observed, however, for a few breath holds larger deviations occurred which urges the need to use beam control tolerance for the isocenter. The overall conclusion is that optical imaging systems, developed within the work of this thesis, can be used as an imaging tool for accurate and faster patient setup, intrafractional motion monitoring and reduced dose to OARs during treatment in DIBH.