5. Analysis of differences between doses calculated and measured during irradiation with mantle fields
Abstract
Purpose
The aim of this work is to analyse differences between doses calculated and measured in-vivo during irradiation of patients with Hodgkin disease.
Materials and Methods
76 patients were included into study. Measurements were made from the beginning of September 1999 until the end of December 2000 (each patient had made measurement once or two or three times). Semiconductor detectors (with DPD 510 by Scanditronix) were used during in-vivo dosimetry. Doses were calculated and measured in (1) the centre of the irradiation field; (2) supraclavicular region; (3) mediastinum; (4) lower edge of the field and (5) neck. Patients were irradiated at various accelerators, most of them at Neptun with photons 9 MeV.
Results
All patients were divided into three groups. The criterion of inclusion was the per cent difference between calculated and measured doses average for all dosimetrical points. The ranges for the groups were: 0–5%, 510% and over 10%. The mean per cent differences in the first group of 43 patients was 3.1%, in second of 27 patients – 6.3%, and in third of 6 patients – 17.6% respectively. There was no clear reason, beside an accidental error why for the certain patient difference was much larger than for the another. Mean difference for all groups was equal to 5.3%.
In the table mean per cent differences between doses calculated and measured and their standard deviations (SD) in the whole group of patients are shown for central axis, mediastinum and supraclavicular region.[[tgroup cols="6"]][[colspec colname="col1"/]][[colspec colname="col2"/]][[colspec colname="col3"/]][[colspec colname="col4"/]][[colspec colname="col5"/]][[colspec colname="col6"/]][[tbody]][[row]][[entry namest="col1" nameend="col2" align="center"]]central axis[[/entry]][[entry namest="col3" nameend="col4" align="center"]]mediastinum[[/entry]][[entry namest="col5" nameend="col6" align="center"]]supraclavicular region[[/entry]][[/row]][[row]][[entry align="center"]]Mean diff.[[/entry]][[entry align="center"]]SD[[/entry]][[entry align="center"]]Mean diff.[[/entry]][[entry align="center"]]SD[[/entry]][[entry align="center"]]Mean diff.[[/entry]][[entry align="center"]]SD[[/entry]][[/row]][[row]][[entry align="center"]]1.5%[[/entry]][[entry align="center"]]4.1%[[/entry]][[entry align="center"]]−0.3%[[/entry]][[entry align="center"]]4.6%[[/entry]][[entry align="center"]]2.0%[[/entry]][[entry align="center"]]5.7%[[/entry]][[/row]][[/tbody]][[/tgroup]]
Conclusion
Mean difference in the whole group of patients shows good agreement between pre-calculated and measured doses, especially for three clinically important regions (table). It is accompanied by low standard deviation which is an indicator of small deviations between doses inside the whole group.