A proposal for process QA in modern radiation therapy

Conformal and intensity modulated radiation therapy (IMRT) have become the standard of care for radiation treatment in modern radiation therapy; in most centres these therapies are used with image guidance (with the acronym TGRT) to ensure target localization for precise treatment. These developments have also enabled the move to adaptive approaches (often designated IGART) where a patient treatment can be modified at various points taking advantage of information acquired during the process. A simple example would be patient setup modification immediately prior to dose delivery resulting from imaging at the treatment unit. These processes require considerable data processing for image registration and analysis. More sophisticated approaches envisage adaptation over each fraction. The proposals for inter-fraction IGART are not limited to corrections for tissue geometry. The potential for on-line dosimetry (perhaps via exit beam dosimetry with portal images or tomotherapy CT detectors) during each treatment raises the feasibility of dose delivery monitoring with subsequent correction as fractions continue through the treatment course. This implies that each fraction may delivery slightly different doses via slightly different MLC sequencing