Radiotherapy of small intracranial tumours with different advanced techniques using photon and proton beams: a...

The potential benefits and limitations of five different radiation techniques, 3D conformal radiotherapy (3DCRT), stereotactic arc therapy (SRS/T), intensity modulated radiotherapy with photons (IMRT), and radiotherapy with protons (spot scanning (SSp) or passive scattering (PSp)), have been assessed using comparative treatment planning methods in a cohort of patients presenting with 'benign' brain tumours.

Plans for five acoustic neurinomas, five meningiomas, and two pituitary adenomas were computed for all modalities using computed tomography (CT) scans to delineate planning target volume and organs at risk (OARs) and to predict dose distributions. Dose-volume histograms were used for physical and simple biological evaluation.

Proton techniques were shown to be superior to all photon approaches for the irradiation of small brain lesions in terms of target dose uniformity and conformity and in terms of sparing OARs. No major differences were observed between the results of the photon techniques, which were generally good for target coverage. Minimum target doses ranged from 81% with SRS/T to 93% with IMRT. The volume receiving more than 95% of the dose ranged from 95% (SRS/T) to 99% (PSp). No clear patterns of coverage dependence upon target shape were observed. Maximum brain stem irradiation ranged from 60% with IMRT to 26% with protons and the conformity index from 4.4 with IMRT to 2.5 with protons. Considering the rather long life expectancy of the patients suffering from meningiomas, neurinomas, and pituitary adenomas, the most important aspect to be considered, other than target coverage, is toxicity and in the long term, the possibility of secondary tumour induction. Considering these aspects, proton irradiation should be the irradiation technique of choice, when available. If not, IMRT, or even 3DCRT, techniques can provide an acceptable compromise, even without recurring to unconventional treatments like SRS/T, which require complex installations and high machine occupancy.