A dosimetric analysis of interstitial intensity modulated implants for pelvic recurrences, base of tongue and orbita tumors with specific references to the ICRU-58

Background and purposeIn this article the conversion of the dosimetry of three different kinds of IMBT (intensity modulated brachytherapy) implants into ICRU-58 formalism is presented. The results allow an inter-study comparison of relative reference doses between different sites.Patients and methodsThe evaluation included 76 patient plans: (a) 31 pelvic recurrences, (b) 30 base of tongue tumors, and (c) 15 orbita tumors were analysed retrospectively and the mean central doses (MCD) and relative reference doses were evaluated.ResultsThe reference doses Dref normalized to the mean central doses of three subgroups resulted in (a) 66%, (b) 68%, and (c) 52%. This is in contrast to the generally proposed standard reference dose of 85% of the Paris system.ConclusionsReduction of the reference dose yields to higher dose inhomogeneities and affects the positive local tumor control. It was found that in IMBT implants the 85% reference dose of the Paris system is suitable for reporting purposes but not necessarily for dose prescription. Consequently, in IMBT implants the prescription dose of 85% should be critically used.