How effectively to use biophysical models in treatment planning?

Abstract

Introduction

The potential of biophysical models is rarely used in clinical practice. Calculations are time consuming, tedious which deter of clinicians to use them. There is a challenge to develop a suitable computer support system for flexible evaluation of radiobiological consequences of radiation therapy.

Materials & Methods

A computer program (RADBIO) based on the linear quadratic model (LQM) with an involvment of the, 4Rs” of radiobiology (repopulation, repairing, reoxygenation and redistribution) has been developed. The biologically equivalent dose (BED), the predictive values of NTCP – F (BED, DVH) and tumour control probability (TCP) are calculated simultanously for all tissues of interest. A total biological effect is a result combined courses of external beam therapy and brachytherapy. The data base contains all current available radiobiologic data of tumours and normal tissues. Entries of individual patient data are simple and take 1–2 minutes of clinicians time. The output obtains a complex radiobiologic report and a graphical picture with a, Terapeutic Ratio” for a relevant protocol.

Results

Comparison of rivals protocols for Ca of Uterine Cervix IIB, III (2 LDR insertions/20 Gy + EBRT 40,8 Gy versus 4 HDR insertions + EBRT 40.8 Gy) follows to an isoeffeetive HDR dose/fr = 6.65 Gy. Critieal % doses (related to NTCP _{rectum, bladder}-5%) are 65% and 80% respectively. It correlates with a maximum, Benefit function” defined as BF-TCP (1-NTCP).

Conclusion

The contribution shows a simple and potentially useful approach for computing more realistic isoeffect relations for tumour, early and late responding tissues when comparing different radiotherapeutic protocols. It offers a real chance to optimize a, Therapeutic gain” as a final goal of radiation therapy.