TUMOR DOSE ESTIMATION USING AUTOMATED TLD TECHNIQUES

Lithium fluoride (TLD-700) dosimeters were used to measure exit surfac e absorbed doses in external beam radiotherapy using an automated TLD reader. Delivered tumour absorbed doses were derived from these measur ements for head and neck, pelvis and breast treatments. For the head a nd neck treatments (first fraction only), the mean percentage differen ce between prescribed and delivered tumour absorbed doses was - 0.15 /- 3.0% (+/- 1 SD), for the pelvic treatments - 0.83 +/- 2.8% and for the breast treatments + 0.26 +/- 2.9%. The spread of results is approx imately +/- 3% (+/- 1 SD). This is comparable with the estimated uncer tainty in a single TLD absorbed dose measurement in phantom (+/- 2%; /- 1 SD). Thus, ICRU recommended tolerances for absorbed dose delivery of +/- 5% may not be unequivocally detectable using this method. An a ction level of +/- 10% is suggested, allowing investigation of possibl e gross errors in treatment delivery at an early stage, before the cou rse of treatment has progressed to a point at which absorbed dose comp ensation is impossible.