# Proton Therapy

> Citation bundle for Proton Therapy on The Treatment Registry.
> URL: https://thetreatmentregistry.com/procedures/proton-therapy
> Bundle URL: https://thetreatmentregistry.com/api/citations/procedures/proton-therapy

- Category: oncology

## Description

In medicine, proton therapy, or proton radiotherapy, is a type of particle therapy that uses a beam of protons to irradiate diseased tissue, most often to treat cancer. The chief advantage of proton therapy over other types of external beam radiotherapy is that the dose of protons is deposited over a narrow range of depth; hence in minimal entry, exit, or scattered radiation dose to healthy nearby tissues.

## Overview

Proton therapy, also called proton radiotherapy, is a type of particle therapy that uses a beam of protons to irradiate diseased tissue, most often to treat cancer. Its defining advantage over other forms of external-beam radiotherapy comes from the physics of how protons deposit energy: the dose is released over a narrow range of depth, an effect known as the Bragg peak, so there is minimal entry, exit or scattered radiation to the healthy tissue around the target. This allows a higher radiation dose to be delivered to a tumour while significantly reducing the dose to nearby organs at risk. Physicians may therefore choose proton therapy when sparing the surrounding normal tissue cannot be adequately achieved with conventional photon-based radiotherapy and doing so would benefit the patient. Like photon radiation therapy, proton therapy is often used in conjunction with surgery and/or chemotherapy to treat cancer most effectively. There are two main delivery methods. In passive scattering, the earliest commercially available approach, the beam is spread out by scattering devices and then shaped to the tumour with items such as collimators and compensators. In the newer pencil-beam scanning method, a thin beam is swept magnetically across the target so the dose closely conforms to the tumour's shape without custom-milled hardware; many older scattering systems have since been upgraded to pencil-beam scanning. Proton therapy has been in clinical use for over 40 years and is a mature technology, although, as with all radiation, understanding of how it interacts with tumour and normal tissue remains imperfect.

## FAQs

### What is proton therapy?

Proton therapy is a form of particle therapy that uses a beam of protons to irradiate diseased tissue, most often to treat cancer. It is a type of external-beam radiotherapy.

### How is it different from standard radiotherapy?

Protons deposit their dose over a narrow range of depth, an effect called the Bragg peak, with little entry, exit or scattered radiation. This lets a higher dose reach the tumour while reducing radiation to nearby healthy organs compared with conventional photon therapy.

### What is pencil-beam scanning?

Pencil-beam scanning is the newest form of delivery. A thin proton beam is swept magnetically across the target so the dose closely conforms to the tumour's shape. The older method, passive scattering, spreads a wider beam and shapes it with collimators and compensators.

### When is proton therapy chosen?

Physicians may choose it when it is important to deliver a higher dose to the tumour while sparing nearby organs at risk, particularly when adequate sparing of normal tissue cannot be achieved with photon-based radiotherapy and the patient would benefit.

### Is proton therapy used on its own?

Not always. Like photon radiation therapy, proton therapy is often used together with surgery and/or chemotherapy in order to treat cancer most effectively.

### Is proton therapy new or experimental?

No. Proton therapy has been in use for over 40 years and is described as a mature technology, though, as with all radiation treatment, the understanding of how it interacts with tumour and normal tissue is still imperfect.

## Alternative treatments

- **Photon (X-ray) radiotherapy** — Established, widely available alternative; less precise dose conformity to organs at risk.
- **Chemotherapy alone** — When systemic disease dominates the clinical picture.

## Sources

- [NCCN Clinical Practice Guidelines in Oncology](https://www.nccn.org/guidelines/category_1) — National Comprehensive Cancer Network (accessed 2026-06-29)