New insights into x-ray sterilization: Dose rate matters

Radiation sterilization technology destroys the DNA and cellular structures of bacteria and microorganisms using electromagnetic waves with far higher energy than ultraviolet radiation. This technique has become indispensable for sterilization in various fields, including medical devices (e.g., disposable syringes, catheters, artificial joints), pharmaceuticals (e.g., raw materials, tissue grafts), and food products (e.g., sprout inhibition in potatoes).

Traditionally, it has been believed that the effectiveness of radiation sterilization depends solely on the total irradiation dose. However, this assumption has now been challenged by a research team led by Professor Matsumoto and Associate Professor Iwata at Nagoya City University.

In their study, the team varied the X-ray dose rate significantly while keeping the total irradiation dose constant, using Escherichia coli as a model organism. The results revealed striking differences depending on the nutritional environment of the bacteria:
(a) In a nutrient-poor environment, long-term irradiation at a low dose rate (i.e., low-intensity X-rays) was more effective than short-term irradiation at a high dose rate.
(b) Conversely, in a nutrient-rich environment, short-term irradiation at a high dose rate achieved more than ten times the sterilization efficiency compared to long-term irradiation at a low dose rate.

These findings were further analyzed using stochastic differential equations—a cutting-edge mathematical tool—enabling a quantitative understanding of the mechanisms by which radiation damages bacterial and cellular structures.

This research not only provides a scientific foundation for optimizing sterilization and disinfection protocols using radiation, but also introduces a novel framework for designing irradiation strategies that can selectively eliminate rapidly proliferating lesion cells (e.g., cancer cells) while minimizing damage to healthy tissue. These insights hold great promise for the development of safer, more effective, and patient-friendly radiation therapies using X-rays and proton beams.