Estimation of a radiation weighting factor for 99mTc

Area of Science:

• Medical Physics
• Radiation Biology
• Nuclear Medicine

Background:

• Technetium-99m ((99m)Tc) emits gamma rays and low-energy electrons.
• The short range of these electrons complicates radiation weighting factor determination.
• Ultrasoft X-rays are used for comparison due to similar energy deposition mechanisms.

Purpose of the Study:

• To simulate DNA damage induced by (99m)Tc decay electrons.
• To compare DNA damage from (99m)Tc with that from ultrasoft X-rays.
• To evaluate the radiation weighting factor for (99m)Tc.

Main Methods:

• Monte Carlo computer codes for electron emission spectra of (99m)Tc.
• Track structure calculations to simulate DNA damage.
• Modeling ultrasoft X-rays using carbon K photons (270 eV).

Main Results:

• An average of four electrons are emitted per (99m)Tc decay.
• Simulations showed nearly identical primary DNA strand break spectra for (99m)Tc and carbon K radiation.
• (99m)Tc radiation weighting factor was determined to be 1.2.

Conclusions:

• Low-energy electrons from (99m)Tc decay induce DNA damage comparable to ultrasoft X-rays.
• The calculated radiation weighting factor of 1.2 is based on simulated DNA damage.
• This study provides a method for assessing the biological impact of (99m)Tc radiation.