In these situations, however, local treatment is limited by the dose already received during previous irradiation sessions by healthy tissue adjacent to the tumour. To deliver a new dose that will be effective against the tumour without generating severe toxicity, proton therapy may be proposed. This makes it possible to limit the irradiation of healthy tissues to medium or low doses.
Proton therapy significantly limits the intermediate doses to pre-radiated healthy tissue, a restrictive factor, to deliver a curative dose for a second time. Proton therapy can provide substantial tissue savings and avoid toxicity, while sometimes performing a dose escalation.
For example, in the special case of radiation-induced sarcomas occurring after childhood irradiation for retinoblastoma, reirradiation may be the only local treatment approach. In this situation where there is a predisposition towards radiation-induced tumours, proton therapy is to be preferred.