Dosimetric properties of a commercial PTW 60019 synthetic diamond detector in small photon fields

Objective To investigate the dosimetric properties of PTW 60019 synthetic diamond detector in small photon beams. Methods A PTW 60019 synthetic diamond detector was tested under 6 and 10 MV photon beams, respectively. Linearity with dose, dose rate dependence and off-axis ratio were measured and compared to those measured by an IBA SFD. Percentage depth doses were measured and compared to those measured by an IBA SFD and a PTW 31010 semiflex chamber. Total scatter factors were measured and compared to those measured by an IBA SFD and a PTW 31016 PinPoint chamber. Results The dose response of a PTW 60019 synthetic diamond detector showed a good linear behavior as a function of dose, with observed deviations below 0.2% over a dose range from 100 to 1 000 MU. The dose rate response was almost independent, with deviations below 0.2% in the dose rate range from 37 to 614 MU/min. For the fields of 20-100 mm in diameter, there were dose differences in percentage depth doses within 1% as compared to an IBA SFD and a PTW 31010 semiflex chamber. For the 10 mm diameter field, the differences were up to 5.8% in the build-up region. Off-axis ratios measurements showed a good agreement among the involved detectors (<1%). The higher differences appeared in the penumbra region. A good agreement was also found in terms of total scatter factor measurements for the related detectors. Conclusions The observed dosimetric properties of the PTW 60019 synthetic diamond detector indicate that it is a suitable candidate for small photon beam dosimetry.     

EPR dosimetry using commercial glasses for high gamma doses.

Commercial transparent and colored (bronze, brown, and green) glasses were studied as possible dosimeters for high gamma doses using electronic paramagnetic resonance (EPR). All EPR spectra showed the characteristic Fe3+ signals, g=4.27 and 2.01. The signal at g=2.01 presented a more useable behavior for the calibration curve. All samples showed their usefulness as high dose dosimeters.     

Application of commercial glasses for high dose measurement using the thermoluminescent technique.

Commercial glasses under this study showed linear thermoluminescence (TL) response in gamma dose range 100 Gy to 10 kGy, glow peaks between 175 and 200 degrees C, fading under dark and room light 2.86-7.36% and 10.42-20.82%, respectively, in 24h and 34.86-70.80% under sunlight in 5h after exposure. The TL glass dosimetric results have been found to be reproducible within +/- 6.0%. Glasses have been observed as thermally unstable and its TL sensitivity reduces after annealing. The TL response of the glasses has been found to reduce by 7.40-51.49% after first annealing of the samples at 400 degrees C for 15 min. The trace element study suggests that presence of impurities has no role in TL sensitivity of glasses rather imperfections and dislocations in the lattice are the major contributor in the formation of TL centers. Commercial glasses can serve as good TL material for gamma irradiator and gamma chamber dosimetry. The various radiation parameters for glass TL dosimetry have been studied in detail and presented.     

Technetium-99m-sulfur colloid. In vitro studies of various commercial kits.

The quality of five commercial 99mTc-sulfur colloid kits was compared. A number of chemical parameters, which characterize the colloids, was used in order to study the influence of variations in the preparation procedures and storage of the final products. The differences between the kits could mainly be referred to the order of addition of the reagents. The quality was generally unaffected by variations in time-intervals during preparation. However, a certain heating time was necessary for optimal labeling. Variations in quantities of acid and buffer were found to influence the particle size as well as the content of unreacted pertechnetate. No deterioration in quality by storage was observed; on the contrary in some cases the content of free activity decreased.     

Dosimetric properties of the Theraview fluoroscopic electronic portal imaging device

Electronic portal imaging devices (EPIDs) can be used for non-imaging applications in radiotherapy such as patient dosimetry. Of the systems available, the fluoroscopic camera-based EPID Theraview (InfiMed Inc.) has not been studied to date, and a review of the dosimetric properties of the system is presented here. In the "single set-up" mode of image acquisition, pixel intensity increases sublinearly with applied dose. The response was dependent on the system's video signal gain and showed a threshold dose to the detector in the range 0.05-0.35 cGy, and pixel saturation at detector doses in the range 1.2-1.6 cGy. Repeated exposures of the EPID were observed to be extremely reproducible (standard deviation 0.5%). The sensitivity of the system showed a linear decline of 0.04% day-1 over a 68-day period, during which time the relative off-axis response within 10 x 10 cm2 field was constant to within a standard deviation of 0.56%. The system shows spatial non-uniformity, which requires correction for application to dose measurements in two-dimensions. Warm-up of the camera control unit required a period of at least 40 min and was associated with an enhancement in pixel intensity of up to 12%. A radiation dose history effect was observed at doses as low as 0.2 Gy. Camera dark current was shown to be negligible at normal accelerator operation. No discernible image distortion was found. Mechanical stability on gantry rotation was also assessed and image displacement of up to 5 mm at the isocentre was observed. It was concluded that the device could be used for dosimetry provided necessary precautions were observed and corrections made.     

Adsorption properties of porous glasses containing alumina towards cesium

Porous glasses (PGs) containing alumina may be applied as specific adsorbents of cesium for analytical purposes. These adsorbents are particularly useful for determination of radiocesium because the radioactivity may be measured directly from the adsorbent bed. Leaching out the soluble phase without prior heating of the raw glass gives the most selective PG.     

Dosimetric evaluation of a computed tomography treatment system.

Pixel-by-pixel correction for tissue inhomogeneities was performed with a CT-interfaced treatment planning system. The CT number for each pixel was converted to a physical density. Comparison of the resulting data with dose measurements in a RANDO phantom shows that pixel calculation overestimates dose by 5--7% at locations adjoining the lung, where loss of scatter is not taken into account by the algorithm. However, the new system does have some advantages over conventional treatment planning systems.     

Dosimetric properties and commissioning of cone-beam CT image beam line with a carbon target

Background and purpose

Accurate patient positioning before radiotherapy is often verified using advanced imaging techniques such as cone-beam computed tomography (CBCT). Even for dedicated imaging beam lines, the applied dose is not necessarily negligible with respect to the treatment dose and should be considered in the treatment plan.

Materials and methods

This study presents measurements of the beam properties of the Siemens kView (Siemens AG, Munich, Germany) image beam line (IBL) and the commissioning in the Philips Pinnacle³ treatment planning system (TPS; Philips, Amsterdam, Netherlands).

Results

The percent depth dose curve reaches its maximum at a depth of 10 mm, with a surface dose of 44?%. The IBL operates in flattening filter-free mode, showing the characteristic dose falloff from the central axis. Stability over several days to months is within less than 2?% dose deviation or 1 mm distance-to-agreement. Modelling of the IBL beam line was performed using the Pinnacle³ automatic modelling routine, with absolute dosimetric verification and film measurements of the fluence distribution.

Conclusion

After commissioning of the IBL beam model, the dose from the imaging IBL CBCT can be calculated. Even if the absolute dose deposited is small, repeated imaging doses may sum up to significant amounts and can shift the position of the dose maximum by several centimetres.     

Dosimetric assessment of nonperfectly abutted fields using asymmetric collimators.

The abutment of adjacent fields has been facilitated through the use of asymmetric collimators. Conceptually, the abutment yields a perfectly uniform dose distribution across the junction, provided the asymmetric jaw is set precisely at the beam central axis. However, the asymmetric jaw has an associated tolerance, which can cause the abutment to be misaligned. This study examined the dose distribution at the junction of nonperfectly abutted fields. The abutment of fields was carried out using an asymmetric collimation of 5 x 10 cm, with an asymmetric jaw positioned at the beam central axis. A film was initially exposed using this field with the collimator set at 90 degrees. The collimator was then rotated 180 degrees and the same film was exposed for the second time to create the field abutment. Positioning the asymmetric jaw with respect to the beam central axis set the amount of gap and overlap between the abutted fields. The dose distribution was measured for asymmetric jaw positioning of -2, -1, 0, + 1, and +2 mm from the beam central axis. In addition, the dose distribution was also computed mathematically by summing the 2 dose profiles with defined gap or overlap. A field mismatch of +/-1 mm would result in a dose nonuniformity of 17%, and a +/-2 mm mismatch would produce a 35% dose nonuniformity.     

Dosimetric characterization of 142Pr glass seeds for brachytherapy.

A glass bead consisted of the beta(-)-emitting (142)Pr is proposed for brachytherapy treatment of prostate cancer. Appropriate radionuclide and seed dimensions were selected and sample seeds were manufactured. For the quantitative dosimetric parameters, two-dimensional dose distributions were calculated using the MCNP5 Monte Carlo code and measured using radiochromic film. The computational results compared well with measurements. Dose at 0.6 cm from the seed center can exceed 130 Gy. The reference dose rate, radial dose function and the anisotropy function were derived.     

Labeling conditions, in vitro properties and biodistributions of various Sn-labeled complexes.

Conditions for preparing Sn-EDTMP, Sn-DTPMP, Sn-TTHMP, Sn-HEDTMP and Sn-DTPA in aqueous solution in open air environments, and their in vitro properties including adsorption on hydroxyapatite (HA) and collagen (I) and binding to bovine serum albumin (BSA) were studied using (117m)Sn and 113Sn as tracers. Biodistributions of SnO2.xH2O.yEDTMP, SnO2.xH2O.yDTPMP, SnO2.xH2O.yTTHMP, SnO2.xH2O.yHEDTMP, SnO2.xH2O.yDTPA in normal mice were also tested. Based on the above experiments, the relationship between in vitro biochemical properties and biodistributions of these SnO2.xH2O.yLigands was investigated. The results show that Sn(IV)-Ligands are prone to hydrolysis into SnO2.xH2O.yLigands in aqueous solutions in open air environments, especially when the ligand is DTPA, when the molar ratio of metal to ligand is higher than 1:200, or when the pH of the solution is higher than 10. The in vitro experiments show that all of the SnO2.xH2O.yLigands bind strongly to BSA, and the binding percentages of SnO2.xH2O.yLigands to BSA are much higher than those of the corresponding Sn(IV)-Ligands. The biodistribution data indicate that all of the SnO2.xH2O.yLigands locate mainly in bone with little uptake in liver. When the binding percentages of SnO2.xH2O.yLigands to BSA are similar, those SnO2.xH2O.yLigands with higher adsorption on HA and collagen (I) undergo lower liver uptake.     

Dosimetric properties of a flattening filter-free 6-MV photon beam: a Monte Carlo study

Purpose The dosimetric features of an unflattened 6-MV photon beam of an Elekta SL-25 linac was calculated by the Monte Carlo (MC) method. Material and methods The head of the Elekta SL-25 linac was simulated using the MCNP4C MC code. The accuracy of the model was evaluated using measured dosimetric features, including depth dose values and dose profiles in a water phantom. The flattening filter was then removed, and beam dosimetric properties were calculated by the MC method and compared with those of the flattened photon beam. Results Our results showed a significant (twofold) increase in the dose rate for all field sizes. Also, the photon beam spectra for an unflattened beam were softer, which led to a steeper reduction in depth doses. The decrease in the out-of-field dose and increase in the contamination electrons and a buildup region dose were the other consequences of removing the flattening filter. Conclusion Our study revealed that, for recent radiotherapy techniques, the use of multileaf collimators for beam shaping removing the flattening filter could offer some advantages, including an increased dose rate and decreased out-of-field dose.     

Dosimetric characteristics with spatial fractionation using electron grid therapy.

Recently, promising clinical results have been shown in the delivery of palliative treatments using megavoltage photon grid therapy. However, the use of megavoltage photon grid therapy is limited in the treatment of bulky superficial lesions where critical radiosensitive anatomical structures are present beyond tumor volumes. As a result, spatially fractionated electron grid therapy was investigated in this project. Dose distributions of 1.4-cm-thick cerrobend grid blocks were experimentally determined for electron beams ranging from 6 to 20 MeV. These blocks were designed and fabricated at out institution to fit into a 20 x 20-cm(2) electron cone of a commercially available linear accelerator. Beam profiles and percentage depth dose (PDD) curves were measured in Solid Water phantom material using radiographic film, LiF TLD, and ionometric techniques. Open-field PDD curves were compared with those of single holes grid with diameters of 1.5, 2.0, 2.5, 3.0, and 3.5 cm to find the optimum diameter. A 2.5-cm hole diameter was found to be the optimal size for all electron energies between 6 and 20 MeV. The results indicate peak-to-valley ratios decrease with depth and the largest ratio is found at Dmax. Also, the TLD measurements show that the dose under the blocked regions of the grid ranged from 9.7% to 39% of the dose beneath the grid holes, depending on the measurement location and beam energy.     

Dosimetric characteristics of 192Ir sources used in interstitial brachytherapy.

Dosimetric quantities of 192Ir seed (5 mm length) and wire (10 mm length) brachytherapy sources have been determined. The quantities were measured based on the protocol introduced by the Radiation Therapy Committee of the American Association of Physicists in Medicine (AAPM) Task Group 43. Quantities such as dose rate constant, (lambda), radial dose function, g(r), and anisotropy function, F(r, theta) were experimentally determined and the geometry function, G(r, theta), was calculated. TLD measurements were made in a polymethyl methacrylate (PMMA) phantom of dimensions 25 cm x 20 cm x 5 cm by means of LiF:Mg,Ti (TLD-100) dosimeters for distances of 1-10 cm for g(r), and the same distances at angles of 0-180 degrees for F(r, theta). Dose rate constant for 192Ir seed and wire were found to be 1.196+/-5 and 1.082+/-5% cGy h(-1) U(-1), respectively (1 U = unit of air Kerma strength = 1 microGy m2 h(-1) = 1 cGy cm2 h(-1)). The obtained results for g(r), G(r, theta) and F(r, theta) are also presented and discussed.     

Dosimetric consequences of interstitial extravasation following i.v. administration of a radiopharmaceutical

The worst case radiation dose to tissue due to inadvertent intravenous injection of a radiopharmaceutical was estimated for the most commonly utilised radioisotopes. The probability of radiation injury induction was examined for the various radionuclides considering the maximal specific activity values encountered in diagnostic practice. A possible approach to the management of incidents involving extravasal activity deposition is discussed.