Protons and heavy ions (usually carbon) are both particle therapies: the beam deposits most of its energy at a planned depth (the Bragg peak) and then falls off sharply, sparing normal tissue behind the target. The difference is that heavy ions have a higher relative biological effectiveness (RBE), which is more damaging to radioresistant tumours.
Common indications
- Proton often preferred: paediatric and adolescent tumours, skull-base and paraspinal lesions, recurrent head-and-neck disease, targets adjacent to the brainstem or optic nerve, liver and selected lung lesions.
- Heavy ion often advantageous: chordoma, chondrosarcoma and other radioresistant tumours, salivary gland cancer, selected pancreatic and recurrent rectal cancers.
Course length and cost
Proton therapy is usually delivered once daily, five days a week, over 4–7 weeks; heavy ions, with higher RBE, can shorten some regimens to 3–4 weeks. Cost depends on target volume and dose — proton courses commonly fall in the RMB 250,000–350,000 range, heavy ion somewhat higher. The hospital quotes after planning.
Three decision points
- Whether the tumour sits where photons cannot be delivered safely (skull base, next to spinal cord or optic nerve).
- Whether prior radiotherapy means a second course must avoid cumulative toxicity.
- Age and life expectancy: in children, second malignancies and growth effects decades later take priority.
Particle therapy is not appropriate for every tumour. In widely metastatic disease requiring systemic treatment, systemic therapy takes precedence over the choice of local modality. Suitability must be assessed by radiation oncology with imaging and dosimetry.