Proton Radiation Therapy vs. Photon Radiation Therapy

When facing a cancer diagnosis, one of the most important decisions a patient will make involves selecting the right treatment approach. Radiation therapy has long been a cornerstone of cancer treatment, with multiple techniques available. In general, there are two main types: photon-based therapy and proton-based therapy. Both work by damaging the DNA inside cancer cells, interfering with their ability to reproduce and ultimately causing the cells to die. However, each type uses a distinct form of ionizing radiation. 

Photon therapy uses high-energy X-rays produced by a machine called a linear accelerator.

Proton therapy uses positively charged particles called protons which are accelerated to high speeds using a cyclotron. 

Understanding the differences between photon therapy and proton therapy can help a patient make more informed decisions about their care. When coupled with expert guidance from a radiation oncologist familiar with the case, this information can help the patient choose the optimal treatment strategy to achieve the best possible outcome and quality of life.

How do photon therapy and proton therapy differ?

The most common type of radiation therapy for cancer is photon therapy, which uses high-energy X-rays produced by an external machine (linear accelerator). Like rays of light, X-rays do not have physical mass. Therefore, when directed at a tumor, a photon beam will pass through the body and leave at an exit point; it will not stop inside the tumor. As a result, the surrounding organs and tissues will likely be exposed to some level of radiation.

Through ongoing research and development, photon therapy is continually improving. Radiation oncologists can now control the photon beam and delivery angle to precisely match the size and shape of a tumor. However, even though exposure to neighboring healthy structures can be minimized, it cannot be completely avoided with photon therapy.

Proton therapy, though not brand-new, offers a different way to deliver radiation treatment. Protons are positively charged subatomic particles which—unlike photons—have physical mass. This is significant for cancer treatment because a physician can stop a proton beam at a certain depth before it exits the body, thereby confining its energy within the tumor and eliminating the exit dose. As a result, the surrounding organs and tissues will be spared, reducing the risk of treatment side effects and complications.

Advantages of proton therapy

For certain patients, proton therapy may offer significant benefits over standard photon radiation, including:

• Minimal impact on healthy tissues – A proton beam can be halted at the tumor site, eliminating the exit dose and greatly reducing radiation exposure to nearby organs and tissues. For this reason, proton therapy may be a particularly good option for a patient who requires reirradiation.
• Lower risk of long-term side effects – Compared to photon therapy, proton therapy is associated with fewer radiation-related side effects, making it particularly advantageous for tumors located near critical structures, such as the brain, eyes, heart, lungs, kidneys and liver, as well as developing tissues in pediatric patients.
• Potential for higher radiation doses – Proton therapy allows for a higher radiation dose to be concentrated directly on a tumor while sparing the neighboring healthy tissues, which may improve cancer control in some cases.

Advantages of photon radiation therapy

While proton therapy offers several distinct advantages, photon-based radiation therapy remains an excellent, time-tested and often more practical choice for many patients. Compared to proton therapy, the potential benefits of photon therapy include:

• Proven effectiveness – Used widely for decades to effectively treat various cancers, photon radiation has been extensively studied and refined over time to enhance its precision and reduce any related side effects.
• Wider availability and accessibility – Photon radiation is more readily available than proton therapy, making it a more convenient option for many patients.
• Comparable outcomes for certain cancers – Modern photon-based radiation delivery techniques, such as intensity-modulated radiation therapy (IMRT), can precisely shape the radiation beam to the contours of the tumor, potentially achieving a result similar to proton therapy.
• Lower cost – Due to the highly specialized expertise and equipment required to administer proton therapy, it is generally more expensive than traditional photon radiation therapy, and not all health insurance plans cover the cost of treatment.

Choosing the best treatment option at Moffitt Cancer Center

While Moffitt Cancer Center currently delivers world-class photon (X-ray) radiation therapy, patients in the Tampa Bay area will soon have access to another advanced cancer-fighting tool: proton therapy.

Moffitt is installing the Proteus®ONE proton therapy system, the most precise and FDA-cleared proton technology available, targeting tumors with accuracy measured in millimeters at its new SPEROS FL campus. The 55-ton cyclotron and 100-ton gantry have already begun their installation journey, with patient treatment expected to begin in 2026. The system’s rotating gantry delivers proton therapy from multiple directions while minimizing exposure to healthy tissue. That means more comfortable treatment sessions and fewer long-term side effects, especially for hard-to-reach tumors.

Moffitt will be the first health system in the Tampa Bay area to offer this transformative option, placing it at the forefront of next-generation cancer care.

Every patient’s cancer journey is unique. Our Radiation Oncology Program is designed to offer the most advanced and comprehensive treatment options,  and each patient benefits from a personalized strategy tailored to their specific needs. Our team of radiation oncologists, advanced practice professionals and physicists conduct weekly peer reviews to collaboratively assess and refine our patients’ treatment plans. These reviews take place in an academic setting where experts are encouraged to exchange ideas, request feedback and critique their strategies to ensure the highest level of care.

Additionally, Moffitt holds weekly multidisciplinary tumor board meetings, where specialists across various fields—including medical oncology, surgical oncology and radiation oncology—come together to discuss complex cases and collectively determine the best course of action. This collaborative approach ensures that every patient receives a well-rounded, carefully considered treatment plan.

Making an informed decision

Ultimately, the decision between proton therapy and standard radiation therapy depends on various factors, including the type, location and stage of the cancer, as well as the patient’s overall health. At Moffitt, we are committed to guiding our patients through their treatment choices and delivering the highest standard of care.

If you have been diagnosed with cancer and are considering radiation therapy, our team is here to help. To request a consultation with a Moffitt radiation oncologist to explore your options and determine the best treatment plan for you, call 1-888-663-3488 or submit a new patient registration form online. We do not require referrals.