A study on clinical applications of kilovoltage cone beam computed tomography in image guided radiotherapy

Abstract

Radiotherapy has undergone rapid changes in the last decade including advanced image based treatment planning and intensity modulated delivery with modern dose calculation and verification methods. The need to improve targeting in high precision radiation therapy has spurred a deluge of research activities in image-guided radiotherapy (IGRT). Of all IGRT solutions, cone beam computed tomography (CBCT) is being installed at the fastest pace. This thesis work is an overview of clinical applications of Varian kV-CBCT system in radiotherapy. The impact of target motion in kV-CBCT imaging was investigated using an in-house built dynamic phantom. The dynamic phantom was designed to move with a period of 4 seconds and two different amplitudes (PA1 and PA2). The targets of well defined geometries were made using wax. A reference image of the static target was obtained with fan beam CT. This study suggests that non-gated CBCT imaging of the moving targets can lead to significant loss of volumetric information and lesser distortion of shape. The dosimetric results of CBCT-based plans were comparable to CT-based plans, but it is necessary to validate the dosimetric data for inhomogeneous tissue regions. Our study infers that a tapered CTV-to-PTV margin based RapidArc plan incurs significant improvement in sparing OAR under strict bladder and rectum preparation regimens. The preliminary investigation showed that a double arc plan results in reduction of dose to OAR and healthy tissues with better target coverage. The PTV1 and PTV2 volumes enclosed by 95% isodose in adaptive plans were 93.51 ± 1.17% and 94.59 ± 1.43% respectively. The lung V10Gy, V20Gy and mean dose in Adap_RA plan was reduced significantly by 17.43%, 34.64% and 16.50% respectively compared to Clin_RA plan. The Adap_RA plan reduces heart D35% and mean dose by 17.35% and 17.16% respectively. No significant reduction in spinal cord and liver doses were observed. Normal tissue complication probability (NTCP) for the lung and heart was reduced significantly in a