What Is Proton Therapy — And How Is It Different from Regular Radiation?

All radiation therapy uses high-energy particles to damage cancer cell DNA enough that the cells can no longer divide and eventually die. Conventional radiation uses photons — X-rays, essentially — to do this. Proton therapy uses protons. The physics of these two particles behave differently inside the body, and that difference matters in specific clinical situations.

Understanding the difference requires a short detour into physics, but not a complicated one.

The Physics — Why Protons Behave Differently

When a beam of X-rays enters the body, it deposits dose continuously as it travels — the dose is highest just under the skin, decreases gradually, and then exits the other side. This "exit dose" — the radiation that passes through the tumour and continues into healthy tissue beyond it — is unavoidable with photon therapy. Oncologists minimise it by using multiple beam angles that cross at the tumour, but they cannot eliminate it entirely.

Protons behave differently. As a proton beam travels through tissue, it deposits relatively little energy at first, then releases most of its energy in a sharp burst at a predictable depth — the Bragg peak — and then stops. There is almost no exit dose.

The depth of the Bragg peak is controlled by adjusting the energy of the beam. Point it at the correct depth for the tumour and the maximum dose goes to the tumour. Beyond the tumour: almost nothing.

This sounds like an obvious advantage. Why would anyone use conventional radiation if proton therapy exists? Because for most cancers, in most locations, the clinical difference in outcomes is small. The additional cost of proton therapy — both in equipment (a proton centre costs several times what a conventional radiation machine costs) and in treatment — is not justified for every case.

When Proton Therapy Has a Clear Advantage

1. Paediatric cancers. Children's bodies are developing, and radiation damage to developing tissue — bone growth, neurological development, endocrine glands — can cause permanent effects that matter over a lifetime of decades. Reducing radiation dose to healthy tissue in a child treated for a brain tumour or solid cancer has long-term consequences that are genuinely meaningful. Proton therapy is now widely considered the preferred approach for many paediatric cancers where it is accessible.

2. Brain tumours and skull base cancers. Brain tumours sit among the most sensitive structures in the body — the brainstem, optic nerves, cochlea, pituitary gland. When a tumour is adjacent to these structures, reducing the radiation that crosses them is clinically important. Proton therapy's lack of exit dose reduces the risk of damage to these structures.

3. Head and neck cancers. Cancers of the nasopharynx, oropharynx, salivary glands, and paranasal sinuses are treated with radiation that must cover lymph node regions while sparing the spinal cord, salivary glands (damage causes permanent dry mouth), cochleae, and eyes. Proton therapy allows more precise dose shaping.

4. Spine and paraspinal tumours. Where the tumour is adjacent to the spinal cord, the Bragg peak's precision prevents the beam from irradiating the cord.

5. Re-irradiation. Patients who have previously received radiation and need a second course in the same area face cumulative dose limits in surrounding normal tissue. Proton therapy's reduced exit dose can make re-irradiation technically feasible in some cases where conventional radiation would exceed safe limits.

6. Left-sided breast cancer. The heart — particularly the left anterior descending coronary artery — sits in the radiation field for left-sided breast treatment. Long-term cardiac damage from radiation is a real clinical concern in women who will live decades after treatment. Proton therapy reduces cardiac dose.

Where Proton Therapy Is Available

Proton therapy requires specialised infrastructure — a cyclotron or synchrotron to generate and accelerate protons, a complex beam delivery system, and shielded treatment rooms. This equipment is expensive and not widely available.

Apollo Proton Cancer Centre (APCC) in Chennai is South Asia's only proton therapy facility. It opened in 2019 and is where international patients from East Africa, the Middle East, and South Asia access proton therapy in India. The centre operates an IBA Proteus One compact proton therapy system.

Dr. Rakesh Jalali — Medical Director and Lead of Neuro Oncology at Apollo Proton Cancer Centre — is a key opinion leader in proton therapy with over 300 peer-reviewed publications and 28 years of experience in oncology. His publications appear in The Lancet, JAMA Oncology, and Journal of Clinical Oncology.

Dr. Sapna Nangia, also at Apollo Proton Cancer Centre, is a radiation oncologist working alongside Dr. Jalali in the proton therapy programme.

Dr. Prasad E at the same centre covers cancer care coordination for international patients.

How Long Does Proton Therapy Take?

Treatment is delivered in daily fractions — one session per day, Monday to Friday. The number of sessions depends on the cancer type and protocol:

• Brain tumours: typically 25 to 33 fractions over five to seven weeks
• Paediatric cancers: 20 to 30 fractions over four to six weeks
• Head and neck cancers: 30 to 35 fractions over six to seven weeks
• Left-sided breast cancer: 15 to 25 fractions
• Spinal/paraspinal tumours: 20 to 30 fractions

Each session takes 30 to 45 minutes including setup time. Actual beam delivery is minutes. Patients do not feel anything during treatment.

Is Proton Therapy Right for Your Case?

Not for every cancer. Proton therapy is specifically advantageous for the indications above. For many common cancers — straightforward early-stage breast cancer on the right side, localised prostate cancer with standard anatomy, colorectal cancer — the clinical benefit over modern conventional radiation is small and the added cost is usually not justified.

The honest assessment is done by the radiation oncologist reviewing the specific tumour location, its proximity to critical structures, the patient's age, and whether the reduction in exit dose translates to a meaningful clinical benefit for this particular case.

For patients from Addis Ababa, Dar es Salaam, Kampala, Banjul, and across Africa who want to know whether proton therapy is relevant to their cancer diagnosis: share biopsy reports and imaging with Prime Medical Solutions. Dr. Rakesh Jalali's team at Apollo Proton Cancer Centre reviews within 48 hours and provides an honest opinion on whether proton therapy would benefit the specific case.

To book a consultation, call the number on our website.