Radiation-Enhanced Diffusion As a Physical Mechanism of Radiation Treatment of Osteoarthritis and Related Disorders
Abstract
Purpose
Osteoarthritis (OA) is a progressive disorder affecting over 30 million Americans. OA is the second-most costly health condition in the US responsible for over 4% of all total hospitalization costs. OA results from the degeneration of articular cartilage between bones in the joint. That degradation is not capable of self-healing due to lack of efficient transport in cartilages, which are avascular and alymphatic tissues, where the primary mode of transport is by diffusion. Low dose radiation treatment (LDRT) of OA, utilized in Europe for decades, is gradually getting clinically accepted in US. While the reason for its effectiveness is not well understood, attributed mostly to biological causes, revealing the role of radiation-enhanced diffusion (RED) as a possible physical mechanism is the main purpose of our study.
Methods
We consider RED in the framework of the vacancy and interstitial diffusion modes showing how radiation can increase the cartilage diffusivity by tens orders of magnitude. Additionally, we explore the charging effect of cartilages under irradiation, which opens a venue to nontrivial radiation treatment planning. We show that given the amplified RED the characteristic healing times may become the treatment bottleneck.
Results
Our emphasis shifts from fast radiation delivery to a much slower healing process that requires continuous supply of materials. The radiation induced charge build-up becomes a natural means of creating long-lasting transport mode, which suggests a carefully chosen chemical doping of cartilages (perhaps by direct injection) prior to LDRT.
Conclusion
We have proposed RED as a physical mechanism behind the observed positive effects of osteoarthritis LDRT. In addition, we have identified the effect of radiation induced electric charge build-up as a means of creating long-lasting diffusion flux of nutrients and other species in cartilages, potentially resulting in curative rather than palliative endpoint.