Quantification of radiation damage for proton craniospinal irradiation using magnetic resonance imaging

Abstract

Radiation doses delivered to entire vertebral bodies are current standard practice for the growing pediatric proton craniospinal irradiation (CSI) patients who are growing children. This procedure prevents patients from developing radiation-induced growth impairment, but it will cause hematopoietic marrow suppression. We aim to develop a noninvasive method to verify radiation damage to the marrow in spine vertebrae during fractional treatment using multiple magnetic resonance imaging (MRI) scans. We identified five pediatric patients who received proton CSI treatment with prescription relative biological effectiveness doses of 36 Gy for the spine. Each patient underwent multiple MRI scans during the treatment using T1-weighted sequences. Sagittal MR images were analyzed and focused on lumbar spine regions. Multi-Gaussian models were used to fit histograms from different MR images to quantify the radiation-induced damage to the bone marrow. MR images acquired before the treatment served as the reference to ensure no radiation-induced damage was found. After the treatment started, radiation-induced fatty marrow filtration showed in the vertebral bodies. We defined the radiation-induced damage based on the ratio between fatty marrow imaging pixels and total pixels in spine marrow, L1-L5 level. Damage fractions increased rapidly when the vertebral bodies received doses between 14 Gy and 34 Gy. The maximum damage happened approximately 40 days from the treatment start. After that, bone marrow regeneration was observed, and the damage fractions decreased. The proposed method can potentially achieve adaptative proton plan modification on the fly.