Prevention of radiation induced normal tissue damage by cytokines and hyperbaric oxygen

Purpose/Objective: Radiation therapy (XRT) is an effective cancer treatment. A goal of therapy is minimization of side effects. Bone growth after XRT of children is one limiting normal tissue tolerance. The goal of the current experiment is to identify the possible protective effect of hyperbaric oxygen (HBO) and basic fibroblast growth factor (FGF) on bone growth after lower extremity radiation. Material and Methods: 170 five weeks old female C3H mice were divided into 17 study groups. Groups 1-4 are controls which received XRT at 0, 10, 20, and 30 Gy single fraction without subsequent HBO. Groups 5-7 had XRT at 10 Gy with HBO at weeks 1-4, weeks 5-8, and weeks 9-12 after XRT. Groups 8-10 had XRT at 20 Gy with HBO at weeks 1-4, weeks 5-8, and weeks 9-12 after XRT. Groups 11-13 had XRT at 30 Gy with HBO at weeks 1-4, weeks 5-8, and weeks 9-12 after XRT. Groups 14-17 had XRT at 30 Gy and iv FGF with or without HBO at weeks 1-4 (groups 14, 15), and at weeks 5-8 (groups 16, 17) after XRT. Using fluoroscopy, the animals were positioned so that the beam was directed to irradiate the entire right hindlimb, including the majority of the femur. Dosimetry was confirmed by TLD in mouse phantoms. HBO treatments were given 5 days per week for 4 weeks to each study group using 2 ATA (max. 15 PSI) of 100% oxygen for 3 hours/day. FGF was given intravenously at 6 μg twice a week for 4 weeks. X-ray films were taken to measure the leg (tibia and femur) length of animals before and 18 weeks after radiation. The acute and chronic side effects of skin in the irradiated area were checked daily according to standard criteria. The leg bones and soft tissue were collected at the end of experiment for histologic study. Result: HBO significantly reduces the retardation of bone growth induced by XRT for 10 and 20 Gy groups. For example, at the 18th week, leg length discrepancy is 0.0±1.6% for control, 4.2±1.3% for 10 Gy, and 8.2±1.8% for 20 Gy. HBO in 10 Gy groups decreased these discrepancies to 2.2±1.8% (P=0.013) in weeks 1-4, 1.9±1.9% (P=0.004) in weeks 5-8, and 2.4±1.3% (P=0.007) in weeks 9-12. In the 20 Gy groups, HBO decreased these discrepancies to 7.0±2.3% (P=0.20) in weeks 1-4, 5.0±1.6% (P=0.003) in weeks 5-8, and 4.0±2.4% (P=0.001) in weeks 9-12. Interestingly HBO delayed till weeks 9-12 still had substantial benefit. At the highest radiation dose (30 Gy), HBO did not have any measurable protective effect at any time period. Leg length discrepancy was 10.7±3.0% at 30 Gy without any treatment. Interestingly, FGF did improve leg length discrepancy with or without HBO. With HBO, leg length discrepancy was 6.5±1.8% (P=0.009) in weeks 1-4 group, and 7.3±2.1% (P=0.005) in weeks 5-8 group. In the groups that had FGF without HBO, leg length discrepancy was 6.8±1.4% (P=0.009) in weeks 1-4 group, and 7.6±1.4% (P=0.007) in weeks 5-8 group. HBO did not show any protective effect on acute and chronic skin reactions. In group 15, 50-75% of the irradiated area showed epilation after FGF treatment (given at 1-4 week after 30 Gy XRT). All other groups which received 30 Gy XRT showed close to 100% epilation in the irradiated area. Conclusion: HBO raises normal tissue oxygen level and both HBO and FGF can stimulates neovasculature. These effects might, in turn, counteract radiation induced anti-angiogenesis. The current experiment shows that radiation induced normal tissue damage can be significant reduced by HBO and FGF treatment. Planed preventive therapies such as HBO or FGF may make bone growth retardation less severe in pediatric patients requiring high dose bone irradiation