Effect of low-level laser therapy on repair of the bone compromised by radiotherapy.

Radiotherapy (RDT) is commonly used for cancer treatment, but high doses of ionizing radiation can directly affect healthy tissues. Positive biological effects of low-level laser therapy (LLLT) on bone repair have been demonstrated; however, this effect on surgical defects of bone previously compromised by radiotherapy has not been evaluated. The aim of this study was to investigate the influence of LLLT (λ = 830 nm) in femur repair after ionizing radiation. Twenty Wistar rats were divided into four groups: control group (GC, n = 5) creation of bone defects (BDs) only; laser group (GL), with BD and LLLT (n = 5); radiotherapy group (GR), submitted to RDT and BD (n = 5); and radiotherapy and laser group (GRL), submitted to RDT, BD, and LLLT (n = 5). GL and GRL received punctual laser application (DE = 210 J/cm(2), P = 50 mW, t = 120 s, and beam diameter of 0.04 cm(2)) immediately after surgery, with 48-h interval during 7 days. Animals were euthanized at 7 days after surgery, and bone sections were evaluated morphometrically with conventional microscopy. Bone repair was only observed in nonirradiated bone, with significant improvement in GL in comparison to GC. GR and GRL did not present any bone neoformation. The result demonstrated a positive local biostimulative effect of LLLT in normal bone. However, LLLT was not able to revert the bone metabolic damage due to ionizing radiation.