Application of the inverse Monte Carlo treatment planning system IKO for an inhomogeneous dose prescription in the sense of dose painting.

Biological imaging (PET SPECTJfMRI, MRS, etc.) is able to provide tri-dimensional biological information, i.e. proliferation, cell density, hypoxia or choline/citrate ratio. The implementation of this information in a treatment plan can be utilised to escalate the dose in target subvolumes. For this purpose, a treatment planning system has to be able to realise an inhomogeneous dose prescription with sufficient spatial resolution. The present study investigated to which extent the inverse Monte Carlo treatment planning system IKO (inverse kernel optimization), developed at our department, can modulate an inhomogeneous dose prescription. As a qualifier to describe this ability, we defined in analogy to imaging a modulation transfer function for treatment planning systems. In addition two clinical cases, a prostate case and a head-and-neck case, were set up with different dose prescriptions in different subtargets. The modulation transfer function revealed that IKO is able to modulate structures larger than 1.3 cm with sharp dose gradients. Also, IKO is able to modulate several subtargets inside a prostate with different escalated doses. The dose-volume histograms of the head-and-neck case showed a good dose coverage of the target volumes, as well as a good protection of the organs at risk according to the dose constraints. As a result, IKO is able to realise a heterogeneous dose prescription in the sense of "dose painting".