Photon versus Proton Therapy: Systematic Review of Energy Transfer and Dose Distribution
Abstract
Radiation therapy is a key part of modern cancer care, and is needed by about half of all people with cancer at some point during their treatment. Photon therapy is the most common modality used today. It is derived from X-rays and gamma rays. It is the most common because it is available and cost effective. Proton therapy, however, is a sophisticated approach using charged particles based on precision. A systematic review was conducted following PRISMA guidelines, by searching for peer-reviewed sources published between 2014 and 2025 to compare the physical and biological characteristics of both modalities, with particular emphasis on energy transfer mechanisms and dose distribution. Results indicate that photon therapy is associated with indirect ionization and an unavoidable exit dose, thus energy is deposited in healthy tissues outside the tumor, increasing the risk of toxicity in normal tissues. Proton therapy on the other hand has a unique Bragg Peak that allows maximum deposition of energy at a specific depth with minimal or no dose beyond the target, thus sparing organs at risk such as the heart and lungs. However, clinical data shows an exception with lower endocrine toxicity with photon therapy than proton therapy in patients with craniopharyngioma (13.7% vs 27.8%). In conclusion, although proton therapy has definite biophysical and dosimetric advantages over photon therapy, treatment selection has to be individualized according to tumor type, anatomical location…
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