_____________________________________________________________________________________________________ *Corresponding author: E-mail: gunes@gazi.edu.tr; Journal of Scientific Research & Reports 6(4): 287-293, 2015; Article no.JSRR.2015.154 ISSN: 2320-0227 SCIENCEDOMAIN international www.sciencedomain.org The Stopping Powers of Water and Lung for Protons in Radiotherapy Güneş Tanır 1* , Rıza Dilek 2 and M. Hicabi Bölükdemir 1 1 Department of Physics, Faculty of Sciences, Gazi University, 06500-Ankara, Turkey. 2 Biomedical Equipment Technology Program, Vocational School, Gedik University, 34913-Istanbul, Turkey. Authors’ contributions This work was carried out in collaboration between all authors. All authors read and approved the final manuscript. Article Information DOI: 10.9734/JSRR/2015/15979 Editor(s): (1) Zhaohui Feng, Department of Radiation Oncology, Department of Pharmacology, The Cancer Institute of New Jersey, University of Medicine and Dentistry of New Jersey, USA. (2) Francisco Torrens, Institut Universitari de Ciència Molecular, Universitat de València, Edifici d'Instituts de Paterna, València, Spain. (3) Amit Balakrishnan, School of Pharmacy, University of Maryland, Baltimore, USA. (4) Luigi Rodino, Dipartimento di Matematica, Università di Torino, Italy. Reviewers: (1) Anonymous, France. (2) Steven Feigenberg, Radiation Oncology, University of Maryland, USA. Complete Peer review History: http://www.sciencedomain.org/review-history.php?iid=965&id=22&aid=8383 Received 30 th December 2014 Accepted 27 th February 2015 Published 9 th March 2015 ABSTRACT Aims: This study aims to calculate the energy losses in unit length of protons during their movement within water and lung by using two analytical equations. Study Design: One of the equations used in this study is the mass stopping power equation suggested by Bethe-Bloch (1930-1933) and modified by Tsoulfanidis (1995) and a new approach has been suggested in the other one. Methodology: The suggested new approach was obtained by substituting effective z*, Z* and I* values into the equation reported by Tsoulfanidis. Although the energy range of protons used in the radiotherapy is 75-250 MeV, in this study 0.001-250 MeV energy ranges were performed to identify the stopping power. In addition, a new empirical relation was given to simplify the expressions for stopping power. The results were compared with the other researcher’s results. Results: The suggested approach for the mass stopping power (Equation 2) can be used for both high- and low energy protons. Stopping power values of protons should be especially useful in such medical fields as radiobiology, biomedical applications, radiotherapy and so on. Short Research Article