Abstract
<h3>Purpose/Objective(s)</h3> Few studies have investigated glioblastoma (GBM) changes during chemoradiotherapy (chemoRT). Many lesions grow and many post-operative resection cavities (RC) shrink when comparing pre- and post-treatment MRI. MRI-Linac offers the opportunity to investigate tumor dynamics during chemoRT without standalone MRI. The purpose of this study was to investigate intracranial changes during chemoRT using imaging from MRI-Linac for future prospective trials. <h3>Materials/Methods</h3> Using an IRB-approved prospective cohort of 34 GBM patients undergoing 30 fractions of chemoRT to 60 Gy on a 0.35T MRI-Linac, tumor/edema (lesion) and RC dynamics throughout treatment were analyzed on T2-weighted treatment set-up scans. RC/lesion change was measured for weekly time points (W1-W6). Absolute and relative volume (>1 indicates growth, <1 indicates shrinkage) changes compared to the planning scan (PL) and migration distance, the largest linear distance that RC/lesion migrated from PL, were calculated. Target margins required through treatment to avoid lesion growth out of margins and how much normal brain can be saved by adapting to shrinking RC were investigated. <h3>Results</h3> 8 patients had RC only, 10 had lesion only, and 16 had both RC and lesion. The volumes and migration distances (median (range)) for RCs and lesions, are shown (table). The treatment margin required to avoid the average lesion from growing out of margins at any point during chemoRT from PL (i.e., migration distance) is 1.30 cm (max 4.1 cm). Adapting to a shrinking RC (RC only or RC with small lesion <20 ml (n=11)), assuming a 2 cm CTV adapted at W5, saves 26.92 ml (9.66 – 58.63 ml) of normal appearing brain from full RT dose. <h3>Conclusion</h3> Clinically significant anatomic changes were seen in GBM patients during chemoRT. Patients with unresected lesions require large RT margins or volume expansions for growth during RT. As RCs shrink, margins can be reduced to save normal brain. Limited volume GBM boost trials should strongly consider adaptive RT given the significant interfractional variability.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: International Journal of Radiation Oncology*Biology*Physics
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
