OC-0483: ISIORT-Europe Data Registry: main characteristics of IORT treatments

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5. Analysis of differences between doses calculated and measured during irradiation with mantle fields

PurposeThe aim of this work is to analyse differences between doses calculated and measured in-vivo during irradiation of patients with Hodgkin disease.Materials and Methods76 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.ResultsAll 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]]ConclusionMean 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

314. How the implementation of an in-vivo dosimetry protocol improved the dose delivery accuracy in radiotherapy?

The aim of this study was to check if the implementation of the institutional in-vivo dosimetry protocol improved the accuracy of the dose delivery in Radiotherapy.Material and MethodsThe dose evaluation was performed for the two groups of patients. First group consisted 812 patients treated from January 1st until June 30th, 2001. Composition of targets was: head and neck – 285 patients, breast – 138, gynaecology – 251 and the lung – 26. The second group consisted 1571 patients irradiated from February 1st, 2002 and included respectively: head and neck – 407, breast – 309, gynaecology – 681 and the lung – 309. Doses were calculated with the use of the Cadplan planning system and measured with semiconductor detectors: PTW Freiberg for photons 6–12 MV, Sun Nuclear Insured for photons 1–4 MV and 15–20 MV. The detectors were placed in a central axis at the entry. The institutional protocol implemented during the period between two evaluated groups of patients required that doses had to be measured during the first week of the treatment. The next measurement was performed in the middle of the radiotherapy course. Additional dose checks were done after any modification of the fields and on the request of the clinician or physicist. All fields were measured excluding the certain specific procedures. Measured doses were recalculated to the reference ICRU point using standard formulas. The following parameters were evaluated: N – the mean number of dose checks per patients, mean difference (in the groups) between measured Dm and calculated Dc doses: R=(Dm-Dc)/Dc*100% and SD – standard deviation (for one measurement).ResultsN= 4.9 vs. 6.0 (for the Ist vs. IInd group). The Mean R was respectively: −1.5% vs. −0.5% for head and neck; 3.4% vs. 2.2% for breast; 3.4% vs. 2.2% for gynaecology and −2.1% vs. 2.5% for the lung. The SD was respectively: 6.1% vs. 5.6% for head and neck; 5.8% vs. 5.4% for breast; 7.4% vs. 6.8% for gynaecology and 6.9% vs. 9.0% for the lung. The Shapiro-Wilk and Kolmogorov-Smirnov tests shoved for not normal distributions. Kolmogorov-Smirnov and Mann-Whitney U tests detected a significant difference between 1st and the IInd groups on the p=0.005 for head and neck, gynaecology and the lung while only at p=0.05 for the breast respectively.ConclusionsThe implementation of the institutional in-vivo dosimetry protocol increased significantly the compliance between measured and calculated doses excluding for the lung region

Clinical and technical characteristics of intraoperative radiotherapy. Analysis of the ISIORT-Europe database

A joint analysis of clinical data from centres within the European section of the International Society of Intraoperative Radiation Therapy (ISIORT-Europe) was undertaken in order to define the range of intraoperative radiotherapy (IORT) techniques and indications encompassed by its member institutions