A water calorimeter for on-site absorbed dose to water calibrations in (60)Co and MV-photon beams including MRI incorporated treatment equipment.

In reference dosimetry the aim is to establish the absorbed dose to water, D w, under reference conditions. However, existing dosimetry protocols are not always applicable for rapidly emerging new treatment modalities. For primary standard dosimetry laboratories it is generally not feasible to acquire such modalities. Therefore it is strongly desired that D w measurements with primary standards can be performed on-site in clinical beams for the new treatment modalities in order to characterize and calibrate detectors. To serve this need, VSL has developed a new transportable water calorimeter serving as a primary D w standard for (60)Co and MV-photons including MRI incorporated treatment equipment. Special attention was paid to its operation in different beam geometries and beam modalities including the application in magnetic fields. The new calorimeter was validated in the VSL (60)Co beam and on-site in clinical MV-photon beams. Excellent agreement of 0.1% was achieved with previous (60)Co field calibrations, i.e. well within the uncertainty of the previous calorimeter, and with measurements performed in horizontal and vertical MV-photon beams. k Q factors, determined for two PTW 30013 ionization chambers, agreed very well with available literature data. The relative combined standard uncertainty (k = 1) for D w measurements in (60)Co and MV-photons is 0.37%. Calibrations are carried out with a standard uncertainty of 0.42% and k Q -factors are determined with a relative standard uncertainty of 0.40%.

Recommendations on detectors and quality control procedures for brachytherapy beta sources.

BACKGROUND AND PURPOSE: It is estimated that one third of the institutes applying clinical beta sources does not perform independent dosimetry. The Netherlands commission on radiation dosimetry (NCS) recently published recommended quality control procedures and detectors for the dosimetry of beta sources. The main issues of NCS Report 14 are summarized here. MATERIALS AND METHODS: A dosimetry survey was performed among 23 institutes in The Netherlands and Belgium. Well ionization chambers, a plastic scintillator, plane-parallel ionization chamber, diode and radiochromic film were used for determination of source strength (dose rate at reference distance) and uniformity of intravascular and ophthalmic sources. The source strength of multiple sources of each type was measured and compared with the source strength specified by the manufacturer. RESULTS: The standard deviation of the difference between measured and specified source strength was mostly about 3%, but varied between 0.8 and 15.8% depending on factors such as source type, detector, phantom and manufacturers calibration. The average non-uniformity was about 7% for intravascular sources and 20% for ophthalmic sources. It is estimated that the total relative standard uncertainty can be kept below +/-4% (1 sigma) with all detectors tested. Maximum deviations in source strength of 10% and a non-uniformity below 10% (intravascular) and 30% (ophthalmic) are recommended. CONCLUSIONS: Dosimetric and non-dosimetric quality control procedures on beta sources are recommended. They enable standardized measurements, including the determination of relative source strength and non-uniformity. Absolute calibrations depend on the future introduction of primary standards for clinical beta sources.

Quality control of brachytherapy equipment in the Netherlands and Belgium: current practice and minimum requirements.

BACKGROUND AND PURPOSE: Brachytherapy is applied in 39 radiotherapy institutions in The Netherlands and Belgium. Each institution has its own quality control (QC) programme to ensure safe and accurate dose delivery to the patient. The main goal of this work is to gain insight into the current practice of QC of brachytherapy in The Netherlands and Belgium and to reduce possible variations in test frequencies and tolerances by formulating a set of minimum QC-requirements. MATERIALS AND METHODS: An extensive questionnaire about QC of brachytherapy was distributed to and completed by the 39 radiotherapy institutions. A separate smaller questionnaire was sent to nine institutions performing intracoronary brachytherapy. The questions were related to safety systems, physical irradiation parameters and total time spent on QC. The results of the questionnaires were compared with recommendations given in international brachytherapy QC reports. RESULTS: The answers to the questionnaires showed large variations in test frequencies and test methods. Furthermore, large variations in time spent on QC exist, which is mainly due to differences in QC-philosophy and differences in the available resources. CONCLUSIONS: Based on the results of the questionnaires and the comparison with the international recommendations, a set of minimum requirements for QC of brachytherapy has been formulated. These guidelines will be implemented in the radiotherapy institutions in The Netherlands and Belgium.