Session Item

Radiation-induced lumbo-sacral radiculopathy is an under-reported long-term side effect of external pelvic radiation therapy.  It consists of a variety of symptoms that can have a serious and significant impact on the quality of life of patients after cancer treatment.
Our aim is to evaluate a correlation between this clinical syndrome and the doses received at the lumbo-sacral plexus.  

Patients selection :
First, we used the Medical Outcome Study Short Form 36 (MOSSF36) to evaluate symptomatic lumbosacral radiculopathy in 150 patients, who have been currently cancer free and under follow-up after being treated with  pelvic radiotherapy in our department.
Target volume delineation :
Delineation of the lumbosacral plexus was performed on the same dosimetric scan used to treat these symptomatic patients. 
For this study, the same radiation oncologist had delineated the lumbosacral plexus on each dosimetric scan from the L4-L5 interspace to the level of the sciatic nerve, with the assistance of a neuroradiologist using registration tools with pelvic MRI when available, and anatomy textbooks.
Planning procedure and statistical analysis:
All plans used the anisotropic analytical algorithm (AAA version 10.0.28) for dose calculation with a 2.5-mm calculation grid and heterogeneity correction.We collected dosimetric data from the treatment plans, to assess correlation with clinical analysis using spearman rank correlation
All our results were compared and analyzed using SPSS software, version 10.0, and a statistical significance level of 0.05 was used (p < 0.05).

The mean age at treatment was 51.3 years, 43% of these patients were female, median follow-up time was 87 months. Out of the 150 patients: 34,2% had cervical cancer, 43,3% had prostate cancer, intensity-modulated radiation therapy was used in 31,7% of the cases. 3,5% had stereotactic pelvic radiotherapy. The mean prescribed radiation dose was 64.3 +5.8Gy (EQ2D), conventional fractionation was used for 95,4% of the patients.
The average maximum dose to the lumbosacral plexus (average Dmax) was 49Gy+ 13,5, the average volume receiving 50 Gy (V50Gy) was 15.6%.
only 8% of the patients had clinical symptoms of lumbo-sacral plexopathy (all Grade 3).  LS doses exceeded 70Gy in 41.7% of patients with neurologic toxicity. All symptomatic  patients were associated with  LS doses above 70Gy. The median and mean LS doses in patients with neurological toxicity (73.9 Gy and 72.5 Gy respectively) were significantly higher than the median and mean LS doses in patients without neurological toxicity (63.9 Gy and 59.1 Gy respectively ( p=O.0015).  Gender and diabetes were significant predictors of radiation induced plexopathy.

Given this high correlation between dosimetric data and radiation-induced lumbo sacral plexopathy in symptomatic patients, we encourage the documentation of lumbo sacral plexus doses by systematically delineating it during pelvic irradiations.