Clinical RT has developed rapidly over the past decades. Treatment planning was initially 2D, based on radiographs or external features. Technological advances including MRI and CT imaging, inverse planning, and IMRT first realized with patient-specific compensators, which varied the intensity within beam apertures, and later multi-leaf collimators (MLCs) that arbitrarily shape/modulate fields, radically improved the conformality of dose to diseased tissues and reduced complications. The precision provided by IMRT has enabled more effective treatment methods such as simultaneous integrated boosts (SIB) to radioresistant regions within a given tumor. Modern developments in functional imaging techniques, including PET, SPECT, and MRI offer potential to identify radioresistant tissue regions by probing pathophysiological features of tumor tissues such as metabolism, tumor cell proliferation, hypoxia, and perfusion. Molecular imaging methods are being applied to study tumor biology at the genotype and phenotype level to further unravel tumor heterogeneity. This wealth of new information presents a tremendous opportunity to identify regions within a tumor volume with differing sensitivity to radiation dose. The dose-painting hypothesis suggests local control could be improved by treating biologically defined target volumes with a nonuniform dose by sub-volume boosting or dose-painting-by numbers as opposed to the current paradigm of uniform treatments to anatomically defined targets. Preclinical studies are warranted to test this hypothesis. Unfortunately, preclinical irradiators are currently limited to open field treatments making them unsuitable for dose-painting precise tumor sub-regions due to poor dose conformality.

Our work has developed techniques for developing IMRT treatment plans for small animals, developing models of compensators to achieve the necessary fluence modulation suitable for rapid fabrication with 3D printing using metal loaded plastics.  This cutting edge approach enables a range of preclinical studies, of which our group has a specific interest in personalized radiation therapy plans developed using functional imaging to address local variations in tumor physiology and microenvironment, see our other work on oxygen guided radiation therapy.

Planning study results showing the conformity index is shown for IMRT and conformal techniques. Dose conformity about the hypoxic volume to be boosted was highly significantly improved with use of IMRT versus CRT.