On the parameter describing the generalised equivalent uniform dose (gEUD) for tumours

Søvik, Åste; Ovrum, Jostein; Olsen, Dag Rune; Malinen, Eirik

doi:10.1016/j.ejmp.2007.09.001

« Previous Next »Physica Medica: European Journal of Medical Physics
Volume 23, Issue 3 , Pages 100-106, December 2007

On the parameter describing the generalised equivalent uniform dose (gEUD) for tumours

Åste Søvik
- Department of Medical Physics, The Norwegian Radium Hospital, Montebello, 0310 Oslo, Norway
- Department of Physics, University of Oslo, 0316 Oslo, Norway
Jostein Ovrum
- Department of Physics, University of Oslo, 0316 Oslo, Norway
- Department of Radiation Biology, The Norwegian Radium Hospital, Montebello, 0310 Oslo, Norway
Dag Rune Olsen
- Department of Physics, University of Oslo, 0316 Oslo, Norway
- Department of Radiation Biology, The Norwegian Radium Hospital, Montebello, 0310 Oslo, Norway
Eirik Malinen
- Department of Medical Physics, The Norwegian Radium Hospital, Montebello, 0310 Oslo, Norway
- Department of Physics, University of Oslo, 0316 Oslo, Norway
- Corresponding author. Department of Medical Physics, The Norwegian Radium Hospital, Montebello, 0310 Oslo, Norway.

Received 26 July 2007; received in revised form 16 September 2007; accepted 19 September 2007. published online 26 October 2007.

Abstract

The purpose of the present work was to estimate the parameter ‘a’ describing the generalised equivalent uniform dose (gEUD) for tumours and its dependence on radiobiological parameters. The consequences of uncertainties in a on the gEUD were also studied. An estimate of a was found by requiring that, for a given target dose distribution, the mechanistic EUD (based on radiobiological linear quadratic modelling) equals gEUD. The estimate of a was found to depend on the dose distribution, and decreased with factors that increase the slope of the cell survival curve (i.e. decreasing α/β values and increasing α values). Furthermore, the parameter a was estimated for 35 prostate cancer IMRT plans of varying dose distributions, for two sets of previously published radiobiological parameters: (1) α=0.15Gy⁻¹ and α/β=3Gy, and (2) α=0.26Gy⁻¹ and α/β=10Gy. The estimated values of a ranged from −25.6 to −22.4 for all combinations of dose distributions and parameter sets. Uncertainties in a were found to give only small uncertainties in gEUD. Although the current work shows limitations of the gEUD model for tumours, gEUD may still be preferable for biological treatment plan optimization, evaluation and reporting.