A treatment planning inter-comparison of proton and intensity modulated photon radiotherapy

Purpose: A comparative treatment planning study has been undertaken between standard photon delivery techniques, b intensity modulated photon methods and spot scanned protons in order to investigate the merits and limitations of each of these treatment approaches. Methods: Plans for each modality were performed using CT scans and planning information for nine patients with varying indications and lesion sites an d the results have been analysed using a variety of dose and volume based p arameters. Results: Over all cases, it is predicted that the use of protons could lead to a reduction of the total integral dose by a factor three compared to st andard photon techniques and a factor two compared to IM photon plans. In a ddition, in all but one Organ at Risk (OAR) for one case, protons are predi cted to reduce both mean OAR dose and the irradiated volume at the 50% mean target dose level compared to both photon methods. However, when consideri ng the volume of an OAR irradiated to 70% or more of the target dose, littl e difference could be shown between proton and intensity modulated photon p lans. On comparing the magnitude of dose hot spots in OARs resulting from t he proton and IM photon plans, more variation was observed, and the ranking of the plans was then found to be case and OAR dependent. Conclusions: The use of protons has been found to reduce the medium to low dose load (below about 70% of the target dose) to OARs and all non-target t issues compared to both standard and inversely planned photons, but that th e use of intensity modulated photons can result in similar levels of high d ose conformation to that afforded by protons. However, the introduction of inverse planning methods for protons is necessary before general conclusion s on the relative efficacy of photons and protons can be drawn. (C) 1999 El sevier Science Ireland Ltd. All rights reserved.