Is current technology improving outcomes with radiation therapy for gliomas?

Radiotherapy (RT) remains the principal component of glioma treatment, and three-dimensional conformal RT (3DCRT) is the current standard of RT delivery. Advances in imaging and in RT technology have enabled more precise treatment to defined targets combined with better means of avoiding critical normal structures, and this is complemented by intensive quality assurance, which includes on-treatment imaging. The refinements of 3DCRT include intensity modulated RT (IMRT), arcing IMRT, and high-precision conformal RT, formerly described as "stereotactic," which can be delivered using a linear accelerator or other specialized equipment. Although proton therapy uses heavy charged particles, the principal application can also be considered as refinement of 3DCRT. The technologies generally improve the dose differential between the tumor and normal tissue and enable more dose-intensive treatments. However, these have not translated into improved survival outcome in patients with low- and high-grade gliomas. More intensive altered fractionation regimens have also failed to show survival benefit. Nevertheless, novel technologies enable better sparing of normal tissue and selective avoidance of critical structures, and these need to be explored further to improve the quality of life of patients with gliomas. Principal clinical advance in RT has been the recognition that less intensive treatments are beneficial for patients with adverse prognosis high-grade gliomas. We conclude that the principal gain of modern RT technology is more likely to emerge as a reduction in treatment related toxicity rather than as an improvement in overall survival; the optimal avoidance strategies remain to be defined.