# Radiation-Induced Lumbosacral Radiculopathy: A Comprehensive Clinical and Dosimetric Study

## TL;DR

This study finds that higher radiation doses to the lumbosacral plexus are linked to neurological symptoms after pelvic radiotherapy, suggesting the need for dose constraints.

## Contribution

The study identifies radiation dose distribution to the lumbosacral plexus as a significant predictor of radiation-induced radiculopathy.

## Key findings

- RILP was observed in 13% of patients, all classified as Grade 3.
- Median maximum plexus dose was 72.1 Gy in patients with toxicity versus 60.2 Gy in those without.
- Gender and pre-existing diabetes were identified as predictive factors for RILP.

## Abstract

Background: Radiation-induced lumbosacral radiculopathy is an under-reported late complication of pelvic radiotherapy and may result in persistent neurological symptoms with a substantial impact on long-term quality of life. The primary objective of this study was to evaluate the association between radiation dose distribution to the lumbosacral plexus (LSP) and the occurrence of radiation-induced lumbosacral plexopathy (RILP).

Methods: A total of 175 cancer-free patients under long-term follow-up after pelvic radiotherapy were evaluated for lumbosacral radicular symptoms using the Oswestry Disability Index (ODI). The LSP was delineated retrospectively on planning CT scans from the L4-L5 interspace to the level of the sciatic nerve, with neuroradiologist support and pelvic MRI when available. Dosimetric parameters were extracted from treatment plans calculated using the anisotropic analytical algorithm. Correlations between dosimetric variables and clinical outcomes were analyzed using Spearman's rank correlation, with statistical significance set at p<0.05.

Results: The mean patient age was 63.3 years, with 48% female, and the median follow-up was 81.7 months. Gynecological and prostate cancers accounted for 49% and 28% of cases, respectively. Intensity-modulated radiation therapy (IMRT) was used in 35.4% of patients, and 21.1% received stereotactic pelvic radiotherapy. RILP was observed in 13% of patients, all classified as Grade 3. The median maximum dose (Dmax) to the LSP was 69 Gy, and the mean V50 Gy was 72.4%. The mean LSP volume overlapping the planning target volume was significantly higher in symptomatic patients (54.5%) compared with asymptomatic patients (18.4%). Median maximum plexus dose was 72.1 Gy in patients with neurological toxicity versus 60.2 Gy in those without toxicity (p=0.0015).

Conclusion: Higher radiation doses to the LSP, particularly Dmax and high-dose volume exposure, were significantly associated with radiation-induced lumbosacral radiculopathy. Gender and pre-existing diabetes also emerged as predictive factors. These findings support the inclusion of the LSP as an organ at risk and highlight the importance of individualized dose constraints to reduce neurological toxicity in pelvic radiotherapy.