Improved dose compensation model owing to short irradiation interruption time for hypoxic tumor using a microdosimetric kinetic model.

BACKGROUND

The objective was to enhance the biological compensation factor related to irradiation interruption in a short time (short irradiation interruption) in hypoxic tumors using a refined microdosimetric kinetic model (MKM) for photon radiation therapy.

MATERIALS AND METHODS

The biological dose differences were calculated for CHO-K1 cells exposed to a photon beam, considering interruptions of (τ) of 0-120 min and pO at oxygen levels of 0.075-160 mm Hg. The interrupted dose fraction (IDF) was defined as the percentage ratio of the dose delivered before short irradiation interruption to the total dose, which ranged from 10-90%. The compensated dose was calculated based on an IDF of 10-90% for a dose of 2-8 Gy and oxygen levels of 0.075-160 mm Hg.

RESULTS

The Δ with and without short irradiation interruption was more pronounced with a higher dose and increased pO. It exceeded 3% between IDF of 50% and either 10% or 90% and occurred more than τ = 50 min at 0.075 mm Hg, τ = 20 min at 3 mm Hg, τ = 20 min at 8 mm Hg, τ = 20 min at 15 mm Hg, τ = 20 min at 38 mm Hg, and τ = 20 min at 160 mm Hg. The dose compensation factor was greater at higher IDF rates.

CONCLUSION

The biological dose decreased with longer interruption times and higher oxygen concentrations. The improved model can compensate for the biological doses at various oxygen concentrations.

ADVANCES IN KNOWLEDGE

The current study improved the dose compensation method for the decrease in the biological effect owing to short irradiation interruption by considering the oxygen concentration.