A study of multi-modality imaging for three-dimensional radiotherapy treatment planning of brain tumors

Abstract

Integration of information from multiple imaging modalities like CT/MRI/SPECT/PET helps in management of cancer, from tumor detection to assessment of treatment efficacy since each imaging modality provides unique information about the tumor and normal structures. This Ph.D. study has been aimed at evaluation of multi-modality imaging in target localization and radiation treatment planning in patients with malignant glioma undergoing radiotherapy. Variations of gross tumor and the edema volumes delineated by a radiologist on CT and MRI scans were addressed. These scans were registered and transferred to the treatment planning system (TPS) using Windows based automatic image registrationsoftware developed in house using AIR routines (Roger Woods, UCLA). QA tests were designed and tested for the 3D automatic target expansion algorithm of the treatment planning system. The influences of variation of target volumes in CT and MRIimages on cumulative dose distribution were also analyzed.Software for quantitative analysis of DVHs has been developed (for Isis-3D TPS) and results showed the importance of incorporation of targets from multiple imaging modalities. A novel approach to study the radiation-induced changes in normal appearing white matter (NAWM) using T2 and magnetization transfer ratio (MTR) maps was developed. The study demonstrated dose-dependent changes of the MTR values and reversal of MTR values seen for doses Gy . However, the T2 maps did not show any dose depended changes within the time period studied. The following in-house software tools were developed to accomplish various tasks of the thesis work: (a) Windows based automatic image registration (AIR) of multi-modality images suitable for radiotherapy planning, (b) to preprocess “bitmap” images from film scanner suitable for AIR software, (c) to transfer registered “tiff” images into the Isis-3D planning system, (d) quantitative analysis of DVH curves generated by the Isis-3D system, and (e) quantitative analysis of sequential MRI scans to generate and analyze T2, MTR, and ADC maps. These software tools, along with source codes, can be freely supplied upon request to the author.