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1103 poster DOSE MEASUREMENTS IN DOSE-ENHANCED RADIATION THERAPY
D OSE MEASUREMENT: BASIC
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films have a 97-μm thick protective polyester coating only on one side of the 7-μm thick active layer making them suitable for measurements of low energy electrons. The HD-810 films were calibrated in 100, 150, and 200 kV x-ray beams using a PTW 30013 chamber and doses ranging from 0.5 to 70 Gy. Prior the actual dose enhancement measurements, (1x1) cm2 films were soaked in iodine solutions with 0, 40, 80, 160 and 320 mgI/mL for 10 minutes. The films were then placed on a 10 cm thick solid water slab and covered with a 1 cm thick solid water slab for build-up. The films were irradiated to what would be a 2 Gy dose with no iodine using 100, 150, and 200 kV beams. The films were washed with water and dried out after irradiation, read out in a flatbed scanner and converted to absorbed dose using the corresponding calibration curves. Results: The calibration curves for the three voltages are shown in Fig 1a. The film dose response decreases with decreasing photon beam energy. The difference between 200 kV and 100 kV for optical density (OD) of 0.08 is 28%. The difference between 200 and 150 kV for the same OD is 19 %. HD-810 films are highly energy dependent at low photon beam energies. The ratio of dose with iodine to the dose without iodine, the dose enhancement factor (DEF), is plotted as a function of iodine concentration and tube voltage in Fig 1b. As expected, based on the mean energies of the studied beams (53, 71, and 86 keV for the 200, 150, and 100 kV beams, respectively) and the K-edge of iodine (34 keV), the DEF decreases with decreasing tube voltage. The maximum measured DEF of 10.6 for 320 mgI/mL is to the first approximation only 50% of the actual macroscopic DEF. This is due to the fact that the dose enhancement from the polyester coated side could not be measured due to the short range of photoelectrons. Conclusions: A methodology for dose enhancement measurements with HD-810 Gafchromic films has been developed and tested with iodine contrast agent. Additional measurements with tungsten and gold nanoparticles will be taken. 1104 poster INFLUENCE OF THE PHANTOM COMPOSITION ON PERIPHERAL NEUTRON ORGAN EQUIVALENT DOSE EVALUATION C. Domingo1 , K. Amgarou1 , M. J. Garcia-Fuste1 , R. Barquero2 , M. R.
Conclusions: Biodistribution of [201 Tl](III)-DTPA-HIgG demonstrated significant inflammated tissue uptake and low muscle and blood uptake, allowing for imaging of inflammated tissues.
1103 poster DOSE MEASUREMENTS IN DOSE-ENHANCED RADIATION THERAPY E. Graves1 , M. Bazalova1 , G. Nelson2 , N. Ackerman2 1 S TANFORD C ANCER C ENTER, Stanford, USA 2 S TANFORD U NIVERSITY S CHOOL OF M EDICINE, Department of Radiation Oncology, Stanford, USA Purpose: To experimentally evaluate dose enhancement for iodine contrast agent and tungsten and gold nanoparticles irradiated with three kilovoltage photon beams using HD-810 Gafchromic films. Materials: Measurements of dose in dose-enhanced radiation therapy (DERT) are challenging due to the short ranges (20-100 μm) of photoelectrons released by kilovoltage beams in high-Z materials. These electrons typically do not reach the active volume of common dosimeters. In this study, dose enhancement was measured with HD-810 Gafchromic films (ISP, Wayne, NJ). Unlike the laminated EBT and EBT2 Gafchromic films, HD-810
Expósito3 , J. A. Terrón4 , X. L. González Soto5 , F. Gomez5 , F. SanchezDoblado3 4 1 U NIVERSITAT AUTÒNOMA DE B ARCELONA, Department of Physics, Cerdanyola, Spain 2 H OSPITAL U NIVERSITARIO DE VALLADOLID, Valladolid, Spain 3 U NIVERSIDAD S EVILLA - FACULDAD M EDICINA, Sevilla, Spain 4 H OSPITAL U NIVERSITARIO V IRGEN M ACARENA, Sevilla, Spain 5 U NIVERSIDADE DE S ANTIAGO DE C OMPOSTELA, Santiago de Compostela, Spain Purpose: Peripheral dose in radiotherapy could represent an important issue in the decision of the treatment strategy. The NEUTOR project has the goal of estimating peripheral doses from the readings of a new online digital neutron detector [1] placed inside the treatment room. Measurements with passive dosemeters are performed at 16 places of an anthropomorphic phantom (NORMA) to correlate organ equivalent doses with the electronic device measurement [2]. The original NORMA phantom was built in polyethylene, which is almost tissue equivalent for electron and photon transport, and the lungs were simulated by low density wood. Nevertheless, questions may arise about the behaviour of neutrons in polyethylene due the lack of O and, specially, N, which has a relevant cross section for neutron interaction. Materials: A complete abdominal treatment was delivered into four identical shape phantoms, made on different materials: i) the original polyethylene NORMA, ii) a Nylon phantom (with higher N content than tissue) with air cavities to simulate lungs, iii) a polyethylene phantom with thousands of small urea filled cavities (with N content equivalent to tissue), and iv) a phantom with wooden boxes filled with real mammalian tissues, organs, blood or bones, using pork meat. CT scans of the phantoms and posterior photon dose distribution by Pinacle treatment planning system were obtained. CR-39 detectors were employed in the 16 locations prepared inside each phantom, which were processed and read in the standard way [3]. Results: Neutron fluence is calculated from the readings of the CR-39 detectors, using the adequate calibration coefficient. The quality factor weighted kerma factors for each phantom material is then used to convert to (organ) equivalent dose at each measurement location. Figure 1 shows these factors for polyethylene and ICRU tissue [4]. Although the big differences in these coefficients, equivalent dose results for the different phantoms lie in the same order of magnitude
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films have a 97-μm thick protective polyester coating only on one side of the 7-μm thick active layer making them suitable for measurements of low energy electrons. The HD-810 films were calibrated in 100, 150, and 200 kV x-ray beams using a PTW 30013 chamber and doses ranging from 0.5 to 70 Gy. Prior the actual dose enhancement measurements, (1x1) cm2 films were soaked in iodine solutions with 0, 40, 80, 160 and 320 mgI/mL for 10 minutes. The films were then placed on a 10 cm thick solid water slab and covered with a 1 cm thick solid water slab for build-up. The films were irradiated to what would be a 2 Gy dose with no iodine using 100, 150, and 200 kV beams. The films were washed with water and dried out after irradiation, read out in a flatbed scanner and converted to absorbed dose using the corresponding calibration curves. Results: The calibration curves for the three voltages are shown in Fig 1a. The film dose response decreases with decreasing photon beam energy. The difference between 200 kV and 100 kV for optical density (OD) of 0.08 is 28%. The difference between 200 and 150 kV for the same OD is 19 %. HD-810 films are highly energy dependent at low photon beam energies. The ratio of dose with iodine to the dose without iodine, the dose enhancement factor (DEF), is plotted as a function of iodine concentration and tube voltage in Fig 1b. As expected, based on the mean energies of the studied beams (53, 71, and 86 keV for the 200, 150, and 100 kV beams, respectively) and the K-edge of iodine (34 keV), the DEF decreases with decreasing tube voltage. The maximum measured DEF of 10.6 for 320 mgI/mL is to the first approximation only 50% of the actual macroscopic DEF. This is due to the fact that the dose enhancement from the polyester coated side could not be measured due to the short range of photoelectrons. Conclusions: A methodology for dose enhancement measurements with HD-810 Gafchromic films has been developed and tested with iodine contrast agent. Additional measurements with tungsten and gold nanoparticles will be taken. 1104 poster INFLUENCE OF THE PHANTOM COMPOSITION ON PERIPHERAL NEUTRON ORGAN EQUIVALENT DOSE EVALUATION C. Domingo1 , K. Amgarou1 , M. J. Garcia-Fuste1 , R. Barquero2 , M. R.
Conclusions: Biodistribution of [201 Tl](III)-DTPA-HIgG demonstrated significant inflammated tissue uptake and low muscle and blood uptake, allowing for imaging of inflammated tissues.
1103 poster DOSE MEASUREMENTS IN DOSE-ENHANCED RADIATION THERAPY E. Graves1 , M. Bazalova1 , G. Nelson2 , N. Ackerman2 1 S TANFORD C ANCER C ENTER, Stanford, USA 2 S TANFORD U NIVERSITY S CHOOL OF M EDICINE, Department of Radiation Oncology, Stanford, USA Purpose: To experimentally evaluate dose enhancement for iodine contrast agent and tungsten and gold nanoparticles irradiated with three kilovoltage photon beams using HD-810 Gafchromic films. Materials: Measurements of dose in dose-enhanced radiation therapy (DERT) are challenging due to the short ranges (20-100 μm) of photoelectrons released by kilovoltage beams in high-Z materials. These electrons typically do not reach the active volume of common dosimeters. In this study, dose enhancement was measured with HD-810 Gafchromic films (ISP, Wayne, NJ). Unlike the laminated EBT and EBT2 Gafchromic films, HD-810
Expósito3 , J. A. Terrón4 , X. L. González Soto5 , F. Gomez5 , F. SanchezDoblado3 4 1 U NIVERSITAT AUTÒNOMA DE B ARCELONA, Department of Physics, Cerdanyola, Spain 2 H OSPITAL U NIVERSITARIO DE VALLADOLID, Valladolid, Spain 3 U NIVERSIDAD S EVILLA - FACULDAD M EDICINA, Sevilla, Spain 4 H OSPITAL U NIVERSITARIO V IRGEN M ACARENA, Sevilla, Spain 5 U NIVERSIDADE DE S ANTIAGO DE C OMPOSTELA, Santiago de Compostela, Spain Purpose: Peripheral dose in radiotherapy could represent an important issue in the decision of the treatment strategy. The NEUTOR project has the goal of estimating peripheral doses from the readings of a new online digital neutron detector [1] placed inside the treatment room. Measurements with passive dosemeters are performed at 16 places of an anthropomorphic phantom (NORMA) to correlate organ equivalent doses with the electronic device measurement [2]. The original NORMA phantom was built in polyethylene, which is almost tissue equivalent for electron and photon transport, and the lungs were simulated by low density wood. Nevertheless, questions may arise about the behaviour of neutrons in polyethylene due the lack of O and, specially, N, which has a relevant cross section for neutron interaction. Materials: A complete abdominal treatment was delivered into four identical shape phantoms, made on different materials: i) the original polyethylene NORMA, ii) a Nylon phantom (with higher N content than tissue) with air cavities to simulate lungs, iii) a polyethylene phantom with thousands of small urea filled cavities (with N content equivalent to tissue), and iv) a phantom with wooden boxes filled with real mammalian tissues, organs, blood or bones, using pork meat. CT scans of the phantoms and posterior photon dose distribution by Pinacle treatment planning system were obtained. CR-39 detectors were employed in the 16 locations prepared inside each phantom, which were processed and read in the standard way [3]. Results: Neutron fluence is calculated from the readings of the CR-39 detectors, using the adequate calibration coefficient. The quality factor weighted kerma factors for each phantom material is then used to convert to (organ) equivalent dose at each measurement location. Figure 1 shows these factors for polyethylene and ICRU tissue [4]. Although the big differences in these coefficients, equivalent dose results for the different phantoms lie in the same order of magnitude