James S. Welsh MD, MS, Presenter: Board Member, Coqui Radiopharmaceuticals Corporation Officer, Radion, Inc Co-founder, Radion, Inc

Daniel Javorsek, Abstract Co-Author: Nothing to Disclose

George J. Buse MD, Abstract Co-Author: Nothing to Disclose

Ephraim Fischbach, Abstract Co-Author: Nothing to Disclose

Nicholas Flores, Abstract Co-Author: Nothing to Disclose

J. Thomas Gruenwald, Abstract Co-Author: Nothing to Disclose

Jere H Jenkins, Abstract Co-Author: Nothing to Disclose

Robert H Lee, Abstract Co-Author: Nothing to Disclose

Daniel W Mundy, Abstract Co-Author: Nothing to Disclose

Peter A Sturrock, Abstract Co-Author: Nothing to Disclose

Contrary to the assumed absolute consistency of the nuclear decay law, recent observations in the measured decays of some radionuclides have demonstrated anomalous variations in decay rate. These interesting but unexpected observations raise the possibility that such variations could be clinically relevant for temporary brachytherapy (both LDR and HDR), teletherapy and Gamma Knife radiosurgery treatments if the actual activity at the time of treatment differs from what is expected..

Several independent sources were used to initially document the anomalous nuclear decay variations. Data was prospectively collected from 2Dec 06 – 3Jan 07 at Purdue University (54Mn). Datasets acquired at Brookhaven National Laboratory (32Si, 36Cl), Physikalisch-Technische Bundesanstalt (152Eu, 154Eu, 226Ra) and Children’s Nutrition Research Center (56Mn, 137Cs) were analyzed. Finally, published data (3H, 54Mn, 60Co, 90Sr/90Y, 238Pu) was critically reviewed.

Unanticipated variations, deviating slightly from the anticipated exponential decay curve, were found. These variations have been characterized by 1.) oscillations with a strong annual periodicity and 2.) short-duration deviations from expected measured decay rates. Annual periodicity has been observed in 14 separate nuclides while short-duration deviations have been observed in 4 so far. The annual oscillation amplitude varies by nuclide and is typically less than 0.5%. The short-duration deviations result in apparent decay rate changes persisting hours to days.  Short-duration deviations for 54Mn have exhibited a nearly 6-fold transient change in the apparent half-life  persisting for up to two days.

An annual periodicity has been observed in 14 separate radionuclides thus far. Among these, several are important in Radiation Oncology (60Co, 90Sr/90Y, 137Cs and 226Ra). Short-duration deviations have been observed in 4 radionuclides thus far including the clinically important isotopes,  60Co, 90Sr/90Y and 226Ra. Additional investigations, including analysis of archived data and careful examination of existing calibration data from active clinics that have been sampled at sufficient frequencies are underway. Potential dosimetric consequences are being estimated.

Short-duration variations might have important clinical consequences if  treatments are delivered during a period in which the activity deviates significantly from what is expected.

Welsh, J, Javorsek, D, Buse, G, Fischbach, E, Flores, N, Gruenwald, J, Jenkins, J, Lee, R, Mundy, D, Sturrock, P, Clinical Implications of Anomalous Variations in the Nuclear Decay Law.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12043885.html