28. Comparison of doses measured by thermolumi-nescent and semiconductor detectors during total body irradiation at Cobalt-60 and 15 meV linear accelerator

Abstract

In-vivo dosimetry is an important way of dose verification during total body irradiation (TBI).

Aim

The aim of this paper was to compare the doses measured in-vivo with two types of detectors: thermoluminescent (TLD) and semiconductor (SEM) during TBI.

Patients

Since 1993, 38 patients have TBI performed, out of them – 22 on Cobalt-60 and 16 on 15 MeV linear accelerator. Total dose of 12,6 Gy was prescribed and delivered in 8 fractions during 4 days. Combination of lateral and anterior-posterior fields, with lung shields was used. Doses were measured with the aim to verify primarily calculated doses (in ten reference points in the body).

Methods

Measured doses were normalised to those pre-calculated. Mean doses and their standard deviations (SD) were calculated separately for each of ten sections, for doses measured with TLD and SEM detectors respectively. Analysis was carried out for doses measured in points lying on the beam to the body entry during irradiation at lateral fields.

Results

Mean dose for the whole group of patients treated on Cobalt-60, for all ten sections together, measured with TLD detectors was equal to 1,05 (normalised to calculated dose) with standard deviation (SD) of 3,4% and for SEM was equal to 0,98 with SD = 2,5%. Respectively, for 15 MeV linear accelerator mean dose for TLD was 1,05 with SD = 3,1% and 1,02 with SD = 3,1%.

Conclusions

Mean differences between doses measured with TLD and SEM dosimeters at beam entry at lateral fields were equal to 6,8% for Cobalt-60 and 3,1% for 15 MeV.