Statement

For microbial inactivation, total absorbed dose determines lethality regardless of dose rate across a 5-order-of-magnitude range (0.37 to 36,000 kGy/h). "Dose is dose."

Evidence

"Hansen et al. 2020", Biomedical Instrumentation & Technology 54(S1):45–52. DOI: 10.2345/0899-8205-54.s3.45

• D₁₀ values for Bacillus pumilus: 1.2–1.5 kGy across all conditions
• No significant difference in microbial inactivation (ANOVA p > 0.05)
• Tested range: 0.37 kGy/h (low gamma) to 36,000 kGy/h (high e-beam) = ~100,000× range

McEvoy et al. 2023, Radiation Physics and Chemistry 208:110915. DOI: 10.1016/j.radphyschem.2023.110915

• Extended comparison across X-ray, gamma, and electron beam at industrial dose rates
• D-values: 1.46–1.61 kGy with no statistically significant differences
• Confirms "dose is dose" for sterilization endpoints

Caveat

G21 uses ~3.8 Gy/hr, which is ~260× below the lowest tested rate in McEvoy et al. (1 kGy/h) and ~100× below the lowest tested rate in Hansen et al. (370 Gy/hr). The principle holds across a 2,000× range in McEvoy and a 100,000× range in Hansen with no inflection point, supporting extrapolation downward, but direct validation at G21's dose rate has not been performed.

Argument

A1: Two independent studies confirm dose-rate independence. Hansen et al. (100,000× range) and McEvoy et al. (2,000× range) both show D₁₀ values statistically indistinguishable across their tested ranges.

A2: Mechanism supports extrapolation. DNA damage from ionizing radiation is cumulative. For desiccated and frozen spores (the relevant MSR analog), there is no active DNA repair during irradiation.

A3: Trend is monotonic with no inflection. Across both datasets, D₁₀ values show no systematic trend with dose rate.

Implication

Supports applying higher-dose-rate laboratory sterilization data to the low-dose-rate in-situ scenario for biological inactivation endpoints. Phase II studies recommended for organic chemistry dose-rate effects.

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