Different treatment planning protocols can lead to large differences in organ at risk sparing.

BACKGROUND AND PURPOSE Different planning protocols may define varying planning target volume (PTV) dose criteria. We investigated the hypothesis that this could result in differences in organ-at-risk (OAR) sparing. MATERIAL AND METHODS Volumetric modulated arc therapy plans were created for ten locally advanced head and neck cancer patients following PTV criteria specified by the RTOG, EORTC and institutional (VUmc) protocols. Resulting plans were evaluated on the basis of the homogeneity index, calculated for the boost/elective PTVs as HIB/HIE=100%*(D2%-D98%)/D50% and mean dose to individual and composite salivary (compsal) and swallowing (compswal) OARs. RESULTS RTOG plans were the most homogeneous, with mean HIB of 8.2±0.9%, compared to 9.5±1.0%/11.6±1.5% for the VUmc/EORTC plans. EORTC plans provided most OAR sparing, with compsal/compswal doses of 24.6±7.7/22.9±4.2Gy, compared to 32.2±9.7/29.9±4.2Gy and 28.4±8.1/24.7±5.3Gy for RTOG and VUmc, respectively. EORTC provided 7.2/7.7Gy mean dose reductions to the contra/ipsilateral parotid glands compared to RTOG. CONCLUSIONS Different planning protocols resulted in different levels of PTV dose homogeneity. We observed differences of up to ⩾7Gy in composite and individual mean OAR doses. This could influence rates of toxicity and should be taken into account when comparing clinical studies. A consensus should be reached between major trial groups on appropriate PTV parameters.