Proton Therapy and Variable Relative Biological Effectiveness:Overview of Suggested Radiobiological Models

Background: Regarding to the increasing advantages of particle therapy methods such as proton therapy (PT) due to having unique characteristics that cannot be achieved with photons, such as Bragg peak and appropriate dose distribution in tumors and the organs at risk (OARs), radiobiological investigations of this therapeutic approaches are more important ۱. According to the recent recommendation of international Commission on Radiation Units and Measurements (ICRU), the amount of relative biological effectiveness (RBE) in PT is considered to be ۱.۱ ۲, but actually this depends on various factors such as dose, linear-energy transfer (LET), α/β ratio of the tissue, oxygen concentration and end-point ۳,۴. The purpose of this review is to update the contents related to RBE and LET in the approach of PT to reduce normal tissue complications probability (NTCP) in healthy tissues around tumors which has become a discrepancy.Methods: This study is a systematic review based on articles, books and studies available in scientific databases such as MEDLINE, PubMed, Scopus, Google Scholar, Cochrane Library, Web of Science and EMBASE .Results: Totally, the dose distribution has been improved in PT but RBE is increase when the α/β ratio and absorbed dose decreases and LET increases, particularly in areas between OARs receiving almost no dose and OARs absorbing low dose of the proton that the reasons for this phenomenon are because of ۱) different DNA repair pathways which were found in many cancers and normal tissues and ۲) dependence on LET at the distal edge of the spread-out Bragg peak (SOBP). Based on studies, to solve this challenge, it is suggested to use some radiobiological models such as Carabe-Fernandez, Wedenberg and Scholz. All of the studies indicated and agreed with conformal PT that can have higher RBE and NTCP in OARs surrounding the tumors, but with modifications in planning, this treatment approach will be accomplished as possible as optimized ۵-Conclusion: Neglecting the variable RBE and its uncertainties might lead to underestimations of the variation in the RBE-weighted doses to the clinical target volume (CTV) and OARs. Accounting for this in an optimization of the physical dose may generate plans with satisfying worst-case CTV doses and acceptable OAR doses that for this to happen, radiobiological models need to be added to the treatment planning system (TPS) to optimize dose delivery and treatment .

کلیدواژه ها:

Proton Therapy ، RBE ، LET ، Radiobiology and Modeling