Abstract
Purpose: There is a clinical need for novel effective local therapies to treat spinal metastases at significant risk for fracture. Photodynamic therapy (PDT) is a promising cancer treatment that employs wavelength specific light combined with a photosensitizing agent to induce localized tumour destruction by photochemical generation of singlet oxygen. Using minimally invasive techniques developed for vertebroplasty to deliver light within the vertebral body, PDT is proposed as a potential new treatment for spinal metastases; however, the effects of PDT on bone are largely unknown. This study aims to determine if PDT affects the structural integrity of normal vertebral bone.
Methods: Sixteen Wistar rats were randomly assigned to control, 1-week treatment or 6-week treatment groups. Rats treated with PDT received an intracardiac injection of 2mg/kg BPD-MA activated at 15 minutes post-injection through administration of a non-thermal 690nm diode laser positioned adjacent to the L3 vertebral body via fluoroscopic guidance (150J at 150mW). Rats were sacrificed at 1-week or 6-weeks following a single treatment. |In vitro & #956;CT scans were taken of L2-L4 and 3D stereological quantities measured using a semiautomated volume shrinkage thresholding technique within the trabecular bone centrum. L2, L3 and L4 vertebral bodies were individually tested biomechanically to failure in axial compression. Yield stress and stiffness were calculated from generated load displacement curves.
Results: Bone surface area and bone volume significantly increased with treatment, through trabecular thickening, at both 1-week and 6-weeks vs. control group. The treated group demonstrated an increase in yield stress at 6-weeks vs. control (27%, p=0.023). An increase in stiffness (45%, p=0.010) was found in the 1-week treatment group vs. control, but was not maintained in the 6-week group.
Conclusions: PDT is a promising new treatment for spinal metastases that appears to strengthen vertebral bone. Further research must determine the mechanism of this action and verify if similar effects will occur in metastatically-involved vertebrae. If PDT proves to be effective in both destroying tumour cells and in strengthening remaining bone, it may provide a very attractive minimally invasive treatment option for patients with spinal metastases.
Funding : Other Education Grant
Funding Parties : Canadian Breast Cancer Foundation, Ontario Chapter
Correspondence should be addressed to Cynthia Vezina, Communications Manager, COA, 4150-360 Ste. Catherine St. West, Westmount, QC H3Z 2Y5, Canada
