Purpose: The variability of relative biological effectiveness (RBE) of a proton beam with spatial distribution is well known. It is dependent on the proton beam characteristics, type of tissue and biological indices. A computational model based on a proton spectrum and LET is used for the estimation of the biological dose. Methods: The depth dose curve of the pristine beam is divided into two regions: the proximal region from the surface to the Bragg peak and the distal region beyond the peak. Knowing the beam energy at the surface in the proximal region, and using the published energy‐range tables, we estimated the effective proton energy at any depth proximal to the Bragg peak. Based on the energy, the LET and RBE is estimated. In the distal region, we assume that the effective beam energy changes monotonically from the value calculated at the peak to the final energy of about 3MeV at the 3% dose level on the distal edge. Applying the calculated RBE factor to the measured depth dose profile we obtain the biological dose in the pristine beam. The method can easily be applied to modulated beams. Results: Our computation model shows that it is possible to predict the biological dose for any combination of beam energy, and for SOBP size based on the available RBE data. Our results showed that the biological dose for a SOBP has finite slope rising to higher values close to distal edge of the peak. Conclusions: A computational model provides an unique tool to estimate the biological dose in any combination of beam energy and SOBP size. If the RBE vs LET data for a tissue is know our computational approach could provide the biological dose accurately in a clinical beam.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging