Quantifying early pelvic radiation-induced bone injury with dual-energy CT: a rabbit model study of dynamic bone mineral and marrow adiposity changes.

PURPOSE: Dual-energy computed tomography (DECT) has been applied to tumor radiotherapy planning but has rarely been used in post-treatment toxicity assessment. This study assesses the feasibility of using DECT to detect early pelvic radiation-induced bone injury (pRIBI).

METHODS: Thirty mature female New Zealand White rabbits were allocated at random into five distinct cohorts: one non-irradiated control group and four experimental groups subjected to a single 30-Gy radiation exposure, with euthanasia performed at 1, 2, 3, or 4 weeks following irradiation. All rabbits underwent DECT before and after radiotherapy and contents of calcium (Ca), hydroxyapatite (HAP) and fat at the seventh lumbar vertebra (L7) and femoral neck (FN) were measured. Postmortem quantitative analysis utilized hematoxylin and eosin (HE)-stained with adipocyte-area-ratio (%) to measure fat content, while Ca content was measured via muffle furnace. Statistical evaluation was conducted via one-way analysis of variance (ANOVA) accompanied by post-hoc comparisons, alongside Pearson correlation assessments. The DECT-derived Ca concentration was validated using a phantom study.

RESULTS: Phantom validation confirmed high DECT Ca quantification accuracy (R 2 = 0.995). DECT revealed progressive demineralization at L7 and FN, with significant reductions in Ca and HAP (P < 0.05) following a triphasic trajectory: initial slow decline (weeks 0-1), accelerated loss (weeks 1-3), and late attenuation (weeks 3-4). Muffle furnace Ca measurements strongly correlated with DECT values (r 2 = 0.949, P < 0.05). Fat peaked at week 1 (P < 0.05) and progressively declined thereafter, aligning with histopathology.

CONCLUSION: DECT enables non-invasive detection of early pRIBI, characterized by Ca and HAP loss, and dynamic fat remodeling. These findings underscore its potential for unveiling early pRIBI.