Purpose: Radiodynamic therapy (RDT) uses Cerenkov light induced by photon beams to treat deep-seated tumors that photodynamic therapy cannot perform due to the low penetration depth of laser beams. The purpose of this study was to investigate the therapeutic effect of RDT with 15MV photon beams combined with 5-aminolevulinic acid (5-ALA) using a mouse model.
Methods: A subcutaneous murine KP1 small-cell lung cancer model using male C57 black mice was used. The tumors (n=18) were randomly assigned into four groups, including control (untreated, n=4), radiation treatment (RT) only (n=4), 5-ALA only (n=4), and RDT (n=6), to observe individual and synergistic effects of 5-ALA and radiation treatment. For mice treated with radiation, 4 Gy in a single fraction was delivered to the tumors using 15MV photons on a Varian Clinac iX accelerator. For the RDT group, 5-ALA was injected at a dosage of 100mg/kg by tail-vein 4 hours prior to RT. Tumor volumes were measured using a 1.5T MR scanner on the treatment day and weekly post-treatment. Tumor growth for each tumor was quantified as the ratio of tumor volume one and two weeks after treatment to the tumor volume on the treatment day.
Results: RDT achieved a decrease in tumor volume by 27.5±11.4% and 26.9±11.4% at one- and two-week post-treatment, respectively, compared to the tumor volume on the treatment day. The tumor growth in the RDT group was delayed by 73.1±25.4%, 82.6±28.9%, and 81.2±19.4% two weeks after treatment compared to 5-ALA only (P<0.05), RT only (P<0.01), and control group (P<0.01), respectively. There were no significant differences in tumor growth between 5-ALA only, RT only, and the control group.
Conclusion: Radiation treatment with 5-ALA resulted in a significant tumor growth control compared to the other groups. The preliminary (hypothesis-generating) results advocate a further investigation into larger sample sizes.