- Journal Details
- First Published
- 30 Dec 2008
- Publication timeframe
- 4 times per year
- Open Access
Page range: 63 - 77
The treatment planning system (TPS) has become a key element in the radiotherapy process with the introduction of computer tomography (CT) based 3D conformal treatment planning. Commissioning of a MLC on a TPS either for conformal radiotherapy or intensity modulated radiation therapy (IMRT) requires beam data to be generated on a linear accelerator. Most of the TPS require these beam data to be generated with routine collimator jaws. However some TPS demand the data to be provided for MLC shaped fields. This prompted us to investigate whether beam data with jaws differ than that with MLC and whether the jaw based beam data would suffice for the commissioning of a MLC on a TPS.
Beam data like percentage depth dose (PDD), cross beam profiles and output factors was acquired for jaws and MLC defined square fields for 6, 10 and 23 MV photon beams. Percentage depth dose and cross beam profiles were acquired with a radiation field analyzer RFA-200, CC13-S ion chambers with active volume of 0.13 cm3 and OmniPro-Accept software from Scanditronix-Wellhofer. A Medtec-TG51 water tank with Max-4000 electrometer and 0.6 cc PTW ionization chamber and a mini phantom from Standard Imaging was utilized for output measurements for millennium-120 MLC (Varian Medical Systems) and SRS diode detector (Scanditronix-Wellhofer) of 0.6 mm diameter of active area and 0.3 mm of active volume thickness for micro-MLC (BrainLab).
The difference in PDD in the build-up region for millennium MLC was ±1.0% for 6 MV photons. For 10 MV photons the PDD difference was within ±4.0%. The difference in PDD for 23 MV photons ranged from 0% to 40.0%. PDD difference from build-up depth to about 28 cm was within ±1.0%. Difference in PDD crossed ±1.0% at 30 cm depth for 6 MV photons. The difference in PDD in the build-up region for mMLC was ±8.0% for 6 MV photons. For the smallest field size studied with micro-MLC i.e. 0.6 × 0.6 cm2 difference in PDD was more than ±1.0% in the build-up region and beyond a depth of 8.0 cm. The profiles for jaws and MLC agreed within the umbra region. However in the penumbra region small differences in doses were observed. The collimator scatter factor (Sc), phantom scatter factor (Sp) and output factor values for MLC were different that those for jaws.
The differences in beam characteristics could have implication for intensity modulated radiation therapy and stereotactic radiosurgery in terms of dose in the build up region, exit dose, dose to the planning target volume (PTV) and organ at risk (OAR). Impact of these dosimetric differences between jaw and MLC needs to be further studied in terms of dose volume histograms for PTV and OAR and its further impact on tumor control probability (TCP) and normal tissue complication probability (NTCP).
- beam data
- MLC commissioning
- Open Access
Monte Carlo calculations of epithermal and fast neutron dose in a human head model for Boron Neutron Capture Therapy
Page range: 79 - 85
Boron Neutron Capture Therapy is a very promising form of cancer therapy, consisting in irradiating a stable isotope of boron (10B) concentrated in tumor cells with a low energy neutron beam. This technique makes it possible to destroy tumor cells, leaving healthy tissues practically unaffected. In order to carry out the therapy in the proper way, the proper range of the neutron beam energy has to be chosen.
In this paper we continue the earlier started calculations of the optimum energy range for BNCT, taking into account the absorbed dose from fast neutrons.
- Boron Neutron Capture Therapy
- Open Access
Page range: 87 - 98
This study evaluates the image quality for different radiation doses in full-field digital mammography (FFDM). The potential of dose reductions is evaluated for both, the transition from screen-film mammography (SFM) to FFDM as well as within FFDM due to the optimization of exposure parameters.
Exposures of a 4.5 cm breast phantom rendering different contrasts as well as bar patterns were made using a FFDM system (GE Senographe 2000D). For different kVp and mAs settings as well as different target/filter combinations chosen for the above exposures, average glandular dose (AGD), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and modulation transfer function (MTF) were determined. To benchmark the results, relative change of AGD was evaluated against SNR, CNR and MTF. Eventually, the results were normalized to AGD's rendered by settings typically used in today's clinical routine.
For standard settings (automatic mode), both FFDM and SFM deliver approximately the same AGD of about 2.2 mGy. From that, AGD reduction can be substantial in FFDM if only SNR and high contrast CNR are considered. In this case, reduction of up to 40% can be achieved in a wide kVp range if switching from the standard target/filter combination Mo/Rh to Rh/Rh. However, if low contrast CNR is to remain unchanged, dose reduction is practically impossible. The change of peak voltage and target/filter material had no influence on MTF.
Assuming current CNR requirements as standards, significant dose reduction in FFDM cannot be achieved. Only by compromising low contrast CNR levels AGD of up to 40% can be saved at current standards of SNR and high contrast CNR.
- Conventional mammography
- digital mammography
- dose reduction
- Open Access
IEC/EN standards relating to diagnostic radiology equipment, and testing according to these standards
Page range: 99 - 111
The paper gives an outlook of history, present and future of international (IEC) and European (EN) standards relating to diagnostic radiology equipment. These standards may be safety, quality assurance or performance standards; all of them include testing methods. Elaboration and publication of a new series of safety standards is in progress.
Acceptance and conformance testing activity of the accredited Radiohygiene Department Laboratory of NRIRR according to these standards is reported.
- diagnostic radiology
- quality assurance
- International Electrotechnical Commission
- Open Access
An analysis of calibration coefficients measured in water and in air for Farmer-type cylindrical ionization chambers
Page range: 113 - 121
A comparison of calibration coefficients of Farmer-type cylindrical ionization chambers calibrated in a Co-60 beam according to the IAEA Reports 277 and 398 formalisms.
91 calibration coefficients measured in air and in water.
Calibration coefficients, determined according to the IAEA Report 398, are higher by about 1% than those determined according to the IAEA Report 277, and they depend slightly on the wall material of the chamber.
The introduction of the IAEA dosimetry Report 398 resulted in an increase in the doses delivered to patients by about 1% as compared with the period of application of Report 277. The regression equations may assure increased accuracy in retrospective comparative calculation of doses according to both reports as compared with the correction based on mean percent values.
- ionization chambers