Thulani Nyathi, Student no: 0413256X, MSc thesis, Physics, Faculty of science. 2006. Supervisor: Prof D van der Merwe. / This study aims to calculate tumour control probabilities (TCP) and normal tissue complication probabilities (NTCP) using radiobiological models and correlate these probabilities with clinically observed treatment outcome from follow-up records. These radiobiological calculations were applied retrospectively to thirty-nine paediatric patients who were treated with radiation at Johannesburg Hospital during the period January 1990 to December 2000 and had histologically proven rhabdomyosarcoma. Computer software, BIOPLAN, was used to calculate the TCP and NTCP arising from the dose distribution calculated by the treatment planning system and characterized by dosevolume histograms (DVHs). There was a weak correlation between the calculated TCP and the observed 5-year overall survival status. Furthermore, potential prognostic factors for survival were examined. Statistical analysis was performed using the Cox proportional hazards regression model. The 5-year overall survival rate was 55 %. The findings of this study are a yardstick against which more aggressive radiotherapy fractionation regimes can be compared.