USE OF V(EFF) AND ISO-NTCP IN THE IMPLEMENTATION OF DOSE-ESCALATION PROTOCOLS

Purpose: This report investigates the use of a normal tissue complicat ion probability (NTCP) model, 3-D dose distributions, and a dose volum e histogram reduction scheme in the design and implementation of dose escalation protocols for irradiation of sites that are primarily limit ed by the dose to a normal tissue which exhibits a strong volume effec t (e.g., lung, liver). Methods and Materials: Plots containing iso-NTC P contours are generated as a function of dose and partial volume usin g a parameterization of a NTCP description. Single step dose volume hi stograms are generated from 3-D dose distributions using the effective -volume (V(eff)) reduction scheme. In this scheme, the value of V(eff) for each dose volume histogram is independent of dose units (Gy, %). Thus, relative dose distributions (%) may be used to segregate patient s by V(eff) into bins containing different ranges of V(eff) values bef ore the assignment of prescription doses (Gy). The doses for each bin of V(eff) values can then be independently escalated between estimated complication levels (iso-NTCP contours). Results and Conclusion: Give n that for the site under study, an investigator believes that the NTC P parameterization and the V(eff) methodology at least describe the ge neral trend of clinical expectations, the concepts discussed allow the use of patient specific 3-D dose/volume information in the design and implementation of dose escalation studies. The result is a scheme wit h which useful prospective tolerance data may be systematically obtain ed for testing the different NTCP parameterizations and models.