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S Vynckier

Publications and source records attributed to S Vynckier.

At least 37 records · Page 2Linked to original sources
PubMed1996

Proton dosimetry intercomparison.

BACKGROUND AND PURPOSE: Methods for determining absorbed dose in clinical proton beams are based on dosimetry protocols provided by the AAPM and the ECHED. Both groups recommend the use of air-filled ionization chambers calibrated in terms of exposure or air kerma in a 60Co beam when a calorimeter or Faraday cup dosimeter is not available. The set of input data used in the AAPM and the ECHED protocols, especially proton stopping powers and w-value is different. In order to verify inter-institutional uniformity of proton beam calibration, the AAPM and the ECHED recommend periodic dosimetry intercomparisons. In this paper we report the results of an international proton dosimetry intercomparison which was held at Loma Linda University Medical Center. The goal of the intercomparison was two-fold: first, to estimate the consistency of absorbed dose delivered to patients among the participating facilities, and second, to evaluate the differences in absorbed dose determination due to differences in 60Co-based ionization chamber calibration protocols. MATERIALS AND METHODS: Thirteen institutions participated in an international proton dosimetry intercomparison. The measurements were performed in a 15-cm square field at a depth of 10 cm in both an unmodulated beam (nominal accelerator energy of 250 MeV) and a 6-cm modulated beam (nominal accelerator energy of 155 MeV), and also in a circular field of diameter 2.6 cm at a depth of 1.14 cm in a beam with 2.4 cm modulation (nominal accelerator energy of 100 MeV). RESULTS: The results of the intercomparison have shown that using ionization chambers with 60Co calibration factors traceable to standard laboratories, and institution-specific conversion factors and dose protocols, the absorbed dose specified to the patient would fall within 3% of the mean value. A single measurement using an ionization chamber with a proton chamber factor determined with a Faraday cup calibration differed from the mean by 8%. CONCLUSION: The adoption of a single ionization chamber dosimetry protocol and uniform conversion factors will establish agreement on proton absorbed dose to approximately 1.5%, consistent with that which has been observed in high-energy photon and electron dosimetry.

Calibration↗
PubMed1996

Entrance and exit dose measurements with semiconductors and thermoluminescent dosemeters: a comparison of methods and in vivo results.

BACKGROUND AND PURPOSE: In order to compare diodes and TLD for in vivo dosimetry, systematic measurements of entrance and exit doses were performed with semiconductor detectors and thermoluminescent dosemeters for brain and head and neck patients treated isocentrically with external photon beam therapy. MATERIAL AND METHODS: Scanditronix EDP-20 diodes and 7LiF thermoluminescent chips, irradiated in a 8 MV linac, were studied with similar build-up cap geometries and materials in order to assure an equivalent electronic equilibrium. Identical calibration methodology was applied to both detectors for the dose determination in clinical conditions. RESULTS: For the entrance dose evaluation over 249 field measurements, the ratio of the measured dose to the expected dose, calculated from tabulated tissue maximum ratios, was equal to 1.010 +/- 0.028 (1 s.d.) from diodes and 1.013 +/- 0.041 from thermoluminescent crystals. For the exit dose measurements, these ratios were equal to 0.998 +/- 0.049 and 1.016 +/- 0.070 for diodes and TLDs, respectively, after application of a simple inhomogeneity correction to the calculation of the expected exit dose. CONCLUSIONS: Thermoluminescence and semiconductors led to identical results for entrance and exit dose evaluation but TLDs were characterised by a lower reproducibility inherent to the TL process itself and to the acquisition and annihilation procedures.

Brain Neoplasms↗
PubMed1996

Response analysis of TLD-300 dosimeters in heavy-particle beams.

In vivo dosimetry is recommended as part of the quality control procedure for treatment verification in radiation therapy. Using thermoluminescence, such controls are planned in the p(65) + Be neutron and 85 MeV proton beams produced at the cyclotron at Louvain-La-Neuve and dedicated to therapy applications. A preliminary study of the peak 3 (150 degrees C) and peak 5 (250 degrees C) response of CaF2:Tm (TLD-300) to neutron and proton beams aimed to analyse the effect of different radiation qualities on the dosimetric behaviour of the detector irradiated in phantom. To broaden the range of investigation, the study was extended to an experimental 12C heavy ion beam (95 MeV/nucleon). The peak 3 and 5 sensitivities in the neutron beam, compared to 60Co, varied little with depth. A major change of peak 5 sensitivity was observed for samples positioned under five leaves of the multi-leaf collimator. While peak 3 sensitivity was constant with depth in the unmodulated proton beam, peak 5 sensitivity increased by 15%. Near the Bragg peak, peak 3 showed the highest decrease of sensitivity. In the modulated proton beam, the sensitivity values were not significantly smaller than those measured in the unmodulated beam far from the Bragg peak region. The ratio of the heights of peak 3 and peak 5 decreased by 70% from the 60Co reference radiation to the 12C heavy-ion beam. This parameter was strongly correlated with the change of radiation quality.

Carbon↗
PubMed1996

Radioiodine treatment of thyroid carcinoma in patients on maintenance hemodialysis.

To deliver optimal radioiodine activity in hemodialyzed patients with thyroid carcinoma, the behavior of radioiodine was followed during six treatments. During hemodialysis, blood activity decreases with a half-life of 3.4 +/- 0.5, (1SD) h. The whole body dose was calculated from the total activity determined during 10 days after 131I administration. A reasonable strategy may consist in delivering 25% of the currently prescribed activity (925 MBq-25 mCi) and to perform the first dialysis session after 24 h to reduce total body irradiation.

Adult↗
PubMed1996

Water calorimetry and ionization chamber dosimetry in an 85-MeV clinical proton beam.

In recent years, the increased use of proton beams for clinical purposes has enhanced the demand for accurate absolute dosimetry for protons. As calorimetry is the most direct way to establish the absorbed dose and because water has recently been accepted as standard material for this type of beam, the importance of water calorimetry is obvious. In this work we report water calorimeter operation in an 85-MeV proton beam and a comparison of the absorbed dose to water measured by ionometry with the dose resulting from water calorimetric measurements. To ensure a proper understanding of the heat defect for defined impurities in water for this type of radiation, a relative response study was first done in comparison with theoretical calculations of the heat defect. The results showed that pure hypoxic water and hydrogen-saturated water yielded the same response with practically zero heat defect, in agreement with the model calculations. The absorbed dose inferred from these measurements was then compared with the dose derived from ionometry by applying the European Charged Heavy Particle Dosimetry (ECHED) protocol. Restricting the comparison to chambers recommended in the protocol, the calorimeter dose was found to be 2.6% +/- 0.9% lower than the average ionometry dose. In order to estimate the significance of chamber-dependent effects in this deviation, measurements were performed using a set of ten ionization chambers of five different types. The maximum internal deviation in the ionometry results amounted to 1.1%. We detected no systematic chamber volume dependence, but observed a small but systematic effect of the chamber wall thickness. The observed deviation between calorimetry and ionometry can be attributed to a combination of the value of (Wair/e)p for protons, adopted in the ECHED protocol, the mass stopping power ratios of water to air for protons, and possibly small ionization chamber wall effects.

Calorimetry↗
PubMed1994

Supplement to the code of practice for clinical proton dosimetry. ECHED (European Clinical Heavy Particle Dosimetry Group).

The 'Code of Practice for Clinical Proton Dosimetry' (Vynckier, S., Bonnett, D.E. and Jones, D.T.L. Code of practice for clinical proton dosimetry. Radiother. Oncol. 20: 53-63, 1991) was published in 1991, but since then new data for mass stopping powers have been reported and consideration has been given to the specification of absorbed dose in water instead of the original recommendation of absorbed dose in tissue. This supplement summarises the basic recommendations of the original Code of Practice and incorporates the new stopping power data for dose specification in water.

Absorption↗
PubMed1994

Verification of absorbed doses determined with thimble and parallel-plate ionization chambers in clinical electron beams using ferrous sulphate dosimetry.

Absorbed dose values determined with the commonly applied NACP and PTW/Markus parallel-plate chambers and the cylindrical NE2571 Farmer chamber were compared to values obtained with ferrous sulphate dosimetry in a number of electron beams. For the ionometry with the parallel-plate chambers the dose-to-air chamber factor ND (or Ngas) was derived from a 60Co beam calibration free in air with an additional buildup layer of 0.54 g cm-2 graphite as proposed by the protocol for electron dosimetry published by the Netherlands Commission on Radiation Dosimetry. For the product kattkm in this calibration geometry values of 0.980 +/- 0.003 [1 standard deviation (s.d.)] and 0.993 +/- 0.004 (1 s.d.) were obtained for the parallel-plate NACP and PTW/Markus chambers, respectively. The behavior of the fluence perturbation correction factor pf versus the mean electron energy at depth was deduced for the flat PTW/Markus and cylindrical NE2571 chamber by comparison with the NACP chamber, for which pf was assumed unity. Our results show a small but significant energy dependence of pf for the PTW/Markus chamber. The absorbed dose values, determined ionometrically with the different chambers considered in the study using the experimentally determined kattkm and pf values, are systematically 0.5% higher than those obtained with ferrous sulphate dosimetry adopting 352 x 10(-6) m-2 kg-1 Gy-1 for epsilon mG. The performed comparative study confirms also that for the NACP chamber pf is unity independent of the electron energy down to a mean energy at depth of 2 MeV.

Biophysical Phenomena↗
PubMed1993

Influence of cisplatinum on intestinal tolerance to photon and neutron irradiation in mice.

The hypothesis that cisplatinum (c-DDP) interacts with radiation by inhibiting the cellular repair capacities, was tested by comparing the interaction of c-DDP with low-LET (60Co gamma-rays) and high-LET radiation (d(50) + Be neutrons) in mice. The biological endpoint was lethality, 6 days after total body irradiation (early intestinal tolerance). The dose modifying factor was 1.80 +/- 0.25 for c-DDP plus 60Co gamma-rays, and 1.97 +/- 0.3 for c-DDP plus neutrons. As less repairable damage is induced by fast neutrons than by photons, this suggests that, in this system, the interaction between radiation and c-DDP is not explained by repair inhibition but is purely additive.

Animals↗
PubMed1993

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.

Belgium↗
PubMed1993

Is it possible to verify directly a proton-treatment plan using positron emission tomography?

A PET camera is used to visualize the positron activity induced during protonbeam therapy in order to verify directly the proton-treatment plans. The positron emitters created are predominantly the 15O and 11C, whose total activity amounts to 12 MBq after an irradiation with 85 MeV protons, delivering 3 Gy in a volume of approximately 300 cm3. Although this method is a useful verification of patient set-up, care must be taken when deriving dose distributions from activity distributions. Correlation between both quantities is difficult, moreover at the last millimeters of their range, protons will no longer activate tissue. Due to the short half-lives the PET camera must be located close to the treatment facility.

Humans↗
PubMed1993

Radiobiological intercomparison of p(45)+Be and p(65)+Be neutron beams for lung tolerance in mice after single and fractionated irradiation.

The lung tolerance in mice after single and fractionated irradiations with p(45)+Be and p(65)+Be neutrons produced at the isochronous cyclotron "CYCLONE" of Louvain-la-Neuve (Belgium) was studied. Cobalt-60 gamma rays were used for control irradiations. The end point was the dose which was lethal to 50% of the mice by 180 days (LD50/180). On a log-log plot, the slope (+/- SE) of the relationship between total isoeffect dose and fraction number decreases from 0.34 +/- 0.01 for gamma rays to 0.19 +/- 0.01 for p(65)+Be and 0.12 +/- 0.01 for p(45)+Be neutrons. The data have been analyzed using the linear-quadratic (LQ) model. The alpha/beta ratio (+95% confidence interval) increases from 5.3 (4.3-6.4) for gamma rays to 20.7 (16.7-24.9) for p(65)+Be and 37.9 (25.8-65.8) for p(45)+Be. The RBEs of neutrons relative to gamma rays were estimated from the LQ parameters, to 1.15 and 1.19 for a dose of 14 Gy gamma rays and 2.02 and 2.47 for a dose of 2 Gy gamma rays for p(65)+Be and p(45)+Be neutrons, respectively. The neutron RBE of the p(45)+Be relative to the p(65)+Be calculated from the ratio of their respective RBEs relative to gamma rays reaches 1.03 and 1.23 for doses of 14 and 2 Gy gamma-ray equivalent, respectively. These data are compared with other published data on lung tolerance after irradiation with lower-energy neutrons and with data obtained previously in our laboratory on mouse jejunum and Vicia faba.

Animals↗
PubMed1992

[Treatment of retinoblastoma using accelerated protons].

Thanks to the Bragg vertical and the straight course of protons, the physical selectivity of proton beam is greater then that of megavoltage photons. Since January 1991 we treated 3 retinoblastomas with proton beam at the cyclotron of Louvain-la-Neuve. Results are encouraging. The short term outcome seems comparable to phototherapy, but the long term expectancy is better, because of reduced secondary malignancies. Proton beam treatment for selected retinoblastomas seems a good alternative to external radiotherapy.

Child, Preschool↗
PubMed1991

Code of practice for clinical proton dosimetry.

The objective of this document is to make recommendations for the determination of absorbed dose to tissue for clinical proton beams and to achieve uniformity in proton dosimetry. A Code of Practice has been chosen, providing specific guidelines for the choice of the detector and the method of determination of absorbed dose for proton beams only. This Code of Practice is confined specifically to the determination of absorbed dose and is not concerned with the biological effects of proton beams. It is recommended that dosimeters be calibrated by comparison with a calorimeter. If this is not available, a Faraday cup, or alternatively, an ionization chamber, with a 60Co calibration factor should be used. Physical parameters for determining the dose from tissue-equivalent ionization chamber measurements are given together with a worksheet. It is recommended that calibrations be carried out in water at the centre of the spread-out-Bragg-peak and that dose distributions be measured in a water phantom. It is estimated that the error in the calibrations will be less than +/- 5% (1 S.D.) in all cases. Adoption and implementation of this Code of Practice will facilitate the exchange of clinical information.

Cobalt Radioisotopes↗
PubMed1990

Radiobiological intercomparison of two clinical neutron beams using the regeneration of mouse intestinal crypts.

Determination of dose modification factor greatly facilitates the introduction of clinically proven neutron therapy schedules at new installations. We have compared the biological performance of the p(66)+Be neutron facility at Faure, South Africa, with the established p(65)+Be installation at Louvain-la-Neuve, Belgium. Filtration, D gamma/DT, dose rate and HVT 5/15 for the Louvain and Faure beam are: 2 cm, 2.5 cm polyethylene; 3%, 5%; 0.2 Gy/min, 0.4 Gy/min; and 20 cm and 19 cm respectively. Dosimetry was done in A-150 plastic. Irradiation of BALB/C mice was carried on according to the dose accumulation method in a perspex phantom at 5 cm depth and at an SSD of 150 cm at a field size of 28 X 28 cm2. Sections of the jejunum were prepared at each centre and analyzed by both. The RBE of the Faure beam determined at a survival level of 50 crypts ranged from 1.64 to 1.69. The dose modification factor RBE of the Louvain beam given by Beauduin et al. was 1.61 +/- 0.14. The dose modification factor of the Faure beam relative to the Louvain beam is thus 1.03 +/- 0.13 which could be expected from the similarity of the physical characteristics. Independent RBE measurements in a variety of systems also suggest similar biological properties. The depth variation of the RBE was found to be 4% (mouse gut) using 3 cm polyethylene filter over the depth range of 2.5 to 13.5 cm. This is in agreement with microdosimetry measurements using polyethylene filters of various thicknesses and with V79 measurements reported by Slabbert et al.

Animals↗
PubMed1990

A comparison of the gamma component of two high energy neutron therapy beams.

Reciprocal neutron dosimetry intercomparisons have been undertaken between the National Accelerator Centre (NAC), South Africa, and the Université Catholique de Louvain (UCL), Belgium. A comparison of the gamma components measured in the respective therapy beams using the classic twin-detector method formed part of the study. This is important in clinical applications since the biological effects of neutrons and gamma rays are different. The gamma component under various irradiation conditions was derived from pairs of measurements with tissue equivalent ionization chambers and Geiger-Müller counters. The gamma component expressed as a fraction of the gamma dose relative to the total dose agreed within less than 0.01, with the measurements with the NAC Geiger-Müller counters being consistently higher than those with the UCL counter. A re-evaluation of the kU value of the UCL Geiger-Müller counter reduces the differences to less than 0.005 at NAC and less than 0.002 for the measurements at UCL. The results obtained are highly satisfactory in view of the complexity and difficulty of the measurements.

Fast Neutrons↗
PubMed1990

Neutron dosimetry intercomparisons between National Accelerator Centre, Université Catholique de Louvain and Clatterbridge Hospital.

Neutron dosimetry intercomparison studies have been undertaken at three neutron therapy facilities which have similar beam characteristics; viz. National Accelerator Centre, South Africa [p(66 MeV)+Be], Université Catholique de Louvain, Belgium, [p(65 MeV)+Be] and MRC Cyclotron Unit, Clatterbridge Hospital, U. K. [p(62 MeV)+Be]. The procedures followed at all centres were the same: tissue equivalent (TE) ionization chambers were first calibrated in 60Co beams and then exposed under various conditions in the respective neutron therapy beams. Measurements were made with the chambers flushed with TE gas or filled with static air. The neutron beam measurements differed by a maximum of 2.4%, whereas if only one particular type of ionization chamber is considered the spread in values is reduced to +/- 0.5%. The TE gas/air response ratios are consistent with calculated values. The results obtained are highly satisfactory and confirm that the dosimetry procedures adopted by the participating institutes conform to international standards.

Belgium↗