Establishment of trigger levels to steer the follow-up of radiation effects in patients undergoing fluoroscopically-guided interventional procedures in Belgium.

The accumulated dose to the skin of the patient during fluoroscopically-guided procedures can exceed the thresholds for tissue reactions. In practice, interventionalists have no direct information about the local procedure-related skin doses in their patient, causing suboptimal or delayed treatment. In current study, the accumulated Kerma-Area-Product (KAP) values were registered, as well as the reference air kerma (Ka,r) values, if available, for almost 200 cases undergoing seven different procedures. A sheet filled with 50 thermoluminescent dosemeters was wrapped around each patient to measure the peak skin dose. In a significant part of the Transjugular Intrahepatic Portosystemic Shunt (TIPSS) procedures, chemo-embolizations of the liver and cerebral embolizations, the threshold values for deterministic skin damage (2 Gy) were attained. Trigger values in terms of KAP, corresponding to a peak skin dose of 2 Gy, were determined. In general, our results comply reasonably well with the values proposed in the NCRP 168 report, with a KAP value of 425 Gy cm² and a Ka,r value of 3 Gy, corresponding to a peak skin dose of 3 Gy. Only for the TIPSS procedure a considerably lower value of 2 Gy was obtained at the published Ka,r and for the RF ablations we obtained a considerably lower value of 250 Gy cm² in terms of KAP.

Gafchromic film dosimetry: four years experience using FilmQA Pro software and Epson flatbed scanners.

PURPOSE: s: To assess performance of FilmQA Pro software for pre-treatment patient-specific quality assurance (QA), using radiochromic films and two commercial flatbed scanners. To evaluate a novel multichannel approach compared to the classical red channel evaluation. MATERIAL AND METHODS: Patient films (mostly EBT2 films, one box of EBT3) were digitalized using successively two flatbed scanners: the A4-size Epson V750 and the A3-size Epson 10000XL. Prior to patient dose verification, basic characteristics of films and scanners were investigated. Patient films were analyzed using FilmQA Pro software, which enables to use the signal from all three colour channels (Red, Green, Blue). RESULTS: Compared to the red channel evaluation, multichannel evaluation presents better passing rates with regard to local gamma index. As expected, we obtained better results using A3-size scanner compared to A4-size scanner, especially when considering large region of interest. An observation of great interest was made for both scanners: after intensive use, a tilting in the blue transmittance profiles appeared in the lamp direction, making multichannel analysis unsuitable for accurate dose evaluation.

A study of the correlation between dose area product and effective dose in vascular radiology.

The purpose of the multi-centre study was to assess dose area product (DAP) and effective dose of patients undergoing angiography of the lower limbs in Belgium and to investigate the correlation between DAP and effective dose. DAP values were measured in 12 centres and compared with the national diagnostic reference levels (DRLs). The effective dose (E) was estimated by multiplying the DAP with case-specific conversion coefficients (CCs) that were calculated with Monte Carlo software MCNP5. As a model for the patient, a mathematical hermaphrodite phantom was used. Calculations showed that tube configurations and extra Cu filtration have a large influence on these CCs. Due to the use of Cu filtration, effective dose can be twice as high for comparable DAP values. Also the use of an over-couch tube configuration is a disadvantage when compared with the under-couch tube configuration. For centres working under-couch without the use of extra Cu-filtration, the DAP values correlate very well with effective dose (Spearman's rank correlation rho ; = 0.97). For these conditions, general CCs between DAP and E were calculated. They were 0.083 mSv Gy(-1) cm(-2) (ICRP 60) and 0.065 mSv Gy(-1) cm(-2) (ICRP 103).

Diagnostic reference levels in angiography and interventional radiology: a Belgian multi-centre study.

The purpose of this study was to determine diagnostic reference levels (DRLs) for common angiographic and interventional procedures in Belgium. Dose Area Product (DAP) measurements were performed on 21 systems, (13 angiography and 4 vascular surgery centres). Type of procedure, total DAP, patient weight and height were collected on a daily basis during 1 y. The 75th percentile of the distribution of DAP values was defined as DRL. Preliminary DRLs were calculated for the three most frequent procedures for the whole population, for a weight class of patients (65-80 kg) and normalised to the standard size patient. Among them, the DRL for angiography of the lower limbs (30% of the procedures) from the whole population was 74.6 and 63.2 Gycm2 for the size corrected. The mean DAP values of each room was then compared to these DRLs.

[Benign diseases in radiotherapy: a practice survey in Belgium. Peer review of radiotherapy in Belgium]. / Affections bénignes et radiothérapie: une enquête de la pratique en Belgique. Peer review de radiothérapie de Belgique.

In 1996 and 2000, a survey of radiation practice in Belgium was performed by sending a questionnaire to the different centers asking their opinion and number of patients treated. There was a great similarity between the two surveys both for indications and total number of patients irradiated. For the most common indications (prevention of cheloids, heterotopic bone formation, hyperthyroidy ophthalmopathy), there was a trend to use similar radiation technique following recent publications. In contrast, if the number of cases of macular degeneration is declining, the prevention of vessels restenosis is becoming more and more an indication.

Radiotherapy of pelvic malignancies: impact of two types of rigid immobilisation devices on localisation errors.

BACKGROUND AND PURPOSE: To determine the distribution of set-up errors for patients treated with and without two rigid partial immobilisation devices for pelvic malignancies. MATERIALS AND METHODS: 30 patients receiving pelvic irradiation with a four field technique underwent a total of 524 portal films. The patients are divided into 3 cohorts of 10 patients. The first cohort is treated on a standard treatment couch without immobilisation device (NI); the second and third cohorts are treated with a custom-made immobilisation device used in an attempt to improve set-up accuracy: an Alpha-Cradle mattress (AM) or an Orfit cast (OC). Set-up deviations are analysed in the X, Y, Z directions of a fixed coordinate system, corresponding to the lateral, cranio-caudal and antero-posterior direction, respectively. RESULTS: Considering the percentage of discrepancies < or = 5 mm between the simulation films and the portal films as a measure of set-up accuracy, immobilisation devices seem to increase accuracy: 88.5% (X) 79% (Y) and 100% (Z) with AM; 84% (X-Y), 97.5% (Z) with OC and only 76.5% (X), 40% (Y) and 65.5% (Z) for NI. The distribution of the systematic set-up errors for the three patient cohorts, defined as the mean patient displacement for the treatment course, had a mean and a standard deviation of (0.7 +/- 2.7) mm in the X-axis, (-5.5 +/- 2.6) mm in the Y-axis and (-0.9 +/- 2.2) mm in the Z-axis when no immobilisation is added; (0.8 +/- 1.7) mm, (-2 +/- 2.7) mm and (0.3 +/- 0.4) mm for the Alpha-Cradle group; (0.3 +/- 1.4) mm, (0.5 +/- 1.1) mm and (0.5 +/- 0.6) mm for the Orfit cast group. The distribution of random errors about the mean approximated a normal distribution and the standard deviations are 4.4 mm (X), 4.2 mm (Y) and 4.8 mm (Z) for NI; 3.3, 3.5 and 2.5 mm for the AM; 3.4, 3.3 and 2.7 mm for the OC. CONCLUSIONS: The two rigid immobilisation devices improve the reproducibility of a given pelvic field but there is a small benefit comparative to the cost and the cumbersome place of the devices.

Build-up modification of commercial diodes for entrance dose measurements in 'higher energy' photon beams.

BACKGROUND AND PURPOSE: Several commercially available p-type diodes do not provide sufficient build-up for in-vivo dosimetry in 'higher' energy photon beams, and only limited information could be found in the literature describing the correction factor variation and/or the achievable accuracy for in-vivo dosimetry methods in this energy range. The first aim of this study is to assess and analyze the variation of diode correction factors for entrance dose measurements at higher photon energies. In a second step the total build up thickness of the diode has been modified in order to minimize the correction factor variation. MATERIALS AND METHODS: Diode correction factors accounting for non-reference conditions (field size, source surface distance, tray, wedge, and block) are determined in 18-25 MV photon beams provided by different treatment units for Scanditronix p-type diodes recommended for higher energy photon beams: old type and new type EDP-20, and EDP-30 diodes. Hemispherical build-up caps of different materials (copper, iron, lead) are used to increase the total build-up thickness. Perturbation effects with and without additional build-up caps are assessed for the three diode types. RESULTS: For unmodified diodes field size correction factors (C(FS)) vary between 1.7% and 6%, dependent on diode type and treatment unit. For example, for an old type EDP-20 the C(FS) variation at 18 MV is much higher on a GE linac (5%) as compared to the Philips machine (1.7%). Depending on diode type, this variation can be reduced to 1-2% when adding additional build-up. The variation of source to surface distance correction factors is almost independent of build-up thickness. By adding additional build-up the influence of trays and blocks can be almost eliminated. CONCLUSIONS: The correction factor variation of unmodified diodes reflects the variation of the electron contamination with treatment geometry. A total build-up thickness of 30 mm is found to be the 'best compromise' for the three types of diodes investigated when measuring entrance doses in the energy range between 18 and 25 MV.

A dosimetric quality audit of photon beams by the Belgian Hospital Physicist Association.

Since 1987, a dosimetric standardization process has been started by the Belgian Hospital Physicist Association (BHPA). As part of this project, on-site visits were performed by a voluntary team, by request of the local physicist. They included mechanical checks on treatment machines and simulators and a dosimetric intercomparison of photon beams, following the EORTC methodology. Until now 16 centres have participated. Dose measurements were performed in order to evaluate the uniformity in dosimetry after the adoption by the BHPA members of the Nederlandse Commissie voor Stralingsdosimetrie (NCS) code of practice for photon beams. Doses were measured with an ionization chamber in water under NCS reference conditions and under other conditions in 13 cobalt beams and 24 high energy X-ray beams from 4 to 25 MV. Under reference conditions, the mean ratio of measured to stated dose is 0.999 (+/- 0.010) and 1.006 (+/- 0.23) for cobalt and X-ray beams, respectively, with a difference between the extreme values (delta) of 0.042 for cobalt beams and 0.084 for X-ray beams. In other conditions, the spread is a little larger for all beams. The results are comparable, but with a smaller dispersion, with those of other national and international similar dose intercomparisons and show the importance of applying a common protocol. The results of mechanical checks show some large deviations in digital displays and indicate the need for a systematic mechanical and beam alignment quality assurance programme.