Intrafraction motion compensation by highly constrained iterative deconvolution of organ motion.

This short paper investigates highly constrained organ-motion deconvolution in the context of the delivery of radiotherapy. Whereas unconstrained and unphysical deconvolution of regular intrafraction motion can generate a dose distribution exactly matching the plan (made on a supposedly static object), the addition of fluence-positivity, fluence-smoothing and fluence-capping constraints to create constrained, physically valid, deconvolution reduces the goodness of fit. However, the generated modulations are physically acceptable and essentially are 'for free', no added delivery technology being needed and they improve on the 'do nothing about motion' strategy. This technique cannot ever rival gating, breath-hold or tracking and is not intended to.