Purpose: A planning study is presented in order to compare the suitability of intensity modulated photon radiotherapy (IMXT), helical tomotherapy (HTT) and intensity modulated protontherapy (IMPT) for dose painting.
Methods: For three HNC patients, nine different treatment plans were generated. Firstly, a uniform dose escalation (uniDE) of 10% was applied to the FDG PET positive region with step-and-shoot IMXT, HTT and IMPT. Secondly, dose painting by numbers (DPBN) was performed based on dose escalation maps determined from dynamic FMISO PET data for all three treatment modalities. Thirdly, the maximum PTV dose was not constrained while maximizing TCP, whereas the same organ at risk constraints as used for conventional IMXT had to be fulfilled. The dose distributions in spinal cord and parotids were optimized with equivalent uniform dose (EUD) constraints, expressing the risk of late reactions.
Results: The target coverage obtained with IMPT and HTT was more conformal regarding the inhomogeneous prescriptions than with IMXT for both uniDE and DPBN. IMPT allowed significantly higher levels of sparing normal tissues. In addition, the study showed that using IMXT, HTT or IMPT theoretically allows dose escalations of up to 50% under late reaction iso-toxicity conditions.
Conclusion: The quality of dose painting treatment plans created for IMXT, HTT and IMPT is comparable. More accurate target coverage can be reached with HTT and IMPT, whereas IMPT allows to significantly reduce the dose to normal tissues.