Potential of intensity-modulated radiotherapy to escalate doses to head-and-neck cancers: What is the maximal dose?

To investigate the potential of intensity-modulated radiotherapy (IMRT) to escalate doses to head-and-neck cancer and find the maximal dose that could be prescribed to the target volume with IMRT while doses to critical organs were maintained at their currently acceptable levels. The secondary goal was to search for limits in current IMRT technology. For a group of 12 head-and-neck cancer patients with different tumor locations and shapes, we performed IMRT planning using a simultaneous integrated boost strategy, that is, the gross tumor volume (GTV), clinical target volume (CTV), and electively treated nodes were treated simultaneously at different dose levels. The critical structures involved in the treatment field that needed to be spared included the brainstem, spinal cord, and parotid glands, depending on the disease site. Nine coplanar 6-MV photon beams were used for planning with the IMRT system developed at our institution, and dose–volume criteria were used for optimization. By varying the optimization parameters, we gradually increased the dose to the GTV while keeping the dose to the critical structures at less than the acceptable tolerance level. The criteria for accepting the plan included the following: ( 1) the prescription dose to the GTV had to cover 99% of the volume, and the dose homogeneity of the GTV needed to be