Adaptive radiotherapy, promises and pitfalls

Abstract

Adaptive radiotherapy is a technique that adapts the radiotherapy to the changes of the patient's anatomy and tumour volume by using repeated images acquired during the treatment course. Adaptive radiotherapy aims to optimize the dose distribution, ensure that the tumour remains in the treatment volume and spare the organs at risk. Adaptive radiotherapy can be applied at three timescales: between fractions (offline), immediately before a fraction (online) or real-time (online, during a fraction). Over the last decade, manufacturers have developed linear accelerators dedicated to online adaptive radiotherapy, based on either computed tomography or magnetic resonance imaging. These systems allow for treatment plan adaptation according to deformable, registration-based segmentation and physicist-driven plan optimization. This has led to a rapid rise of this technique on a larger scale, although robust data on its benefits remains scarce. Adaptive radiotherapy has demonstrated dosimetric benefits, such as improved lesion coverage and sparing of organs at risk, in various tumour sites. However, the clinical benefit, in terms of toxicity reduction or improved tumour control, remains to be demonstrated in many disease sites. Furthermore, the implementation of adaptive radiotherapy requires careful planning, increased time, logistics and security, which represents an extra burden and impacts the cost-efficiency of the approach.