- Email: [email protected]
1104 poster INFLUENCE OF THE PHANTOM COMPOSITION ON PERIPHERAL NEUTRON ORGAN EQUIVALENT DOSE EVALUATION
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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D OSE MEASUREMENT: BASIC
1106 poster MEASUREMENTS AND UNCERTAINTIES VALUES FOR DOSE POLARIZATION AND RECOMBINATION CORRECTION FACTORS L. Alejo Luque1 , R. Rodríguez Romero1 , P. Castro Tejero1 , J. M. Fandiño Lareo2 H. U. P UERTA DE H IERRO M AJADAHONDA, Department of Medical Physics and Radiation Safety, Majadahonda, Spain 2 C ENTRO O NCOLÓGICO DE G ALICIA, Department of Medical Physics and Radiation Safety, A Coruña, Spain 1
Conclusions: The original NORMA phantom is a good first approximation for neutron organ dose assessment, although more precise results require the usage of phantoms having composition closer to tissue. Acknowledgements: The authors are indebted to the University Law (LOU) contract between the University of Seville and the Andalusian Health Service (SAS) and especially to the Spanish Nuclear Security Council (CSN). We want to give thanks to J. P. Cano (workshop physics faculty university of Seville), Mariano A. (carpentry) and Alejandro (Matadero del Sur) for the construction and cession of the pork for the phantoms. References: 1. F G et al. (2010), Phys. Med. Biol. 55 10251039. 2. F Shez-Doblado et al. (2009), WC 2009, IFMBE Proccedings 25/I, Berlin: Springer, 259-261. 3. C. Domingo et al. (2009), Radiation Measurements, 44, 1073-1076 4. B.R.L. Siebert and H. Schuhmacher (1995), Radiat, Prot. Dosim., 58, 177-183.
Purpose: Measurements and uncertainties values for dose polarization and recombination correction factors (kpol, ks) for different cylindrical and planeparallel ionization chambers are discussed. These values are obtained using photons and electrons beams of various nominal energies generated by Varian Clinac 21EX linear accelerators and TomoTherapy Hi-Art II, in order to study the behavior of these uncertainties and factors, and analyze trends. Materials: Applying IAEA TRS-398 protocol, kpol and ks values were obtained for different chambers and energies: four PTW 30013 Farmer in 6MV, 15MV and 18 MeV, two PTW 31010 Semiflex, two PTW 31016 PinPoint 3D in 6MV and 15MV, two Exradin A1SL in 6MV, two Roos 34001 and a Markus 34045 in 6MeV, 9MeV, 12MeV, 15MeV and 18MeV electron beams. Except Exradin chambers, whose factors were obtained in TomoTherapy Hi-Art II 6 MV beam, a Varian CLINAC 21EX linear accelerator was used. Since dose calibrations are corrected by recombination effect but not polarity, kpol uncertainty had to be estimated considering its maximum values reported in calibration certificates. Type A and B uncertainties were calculated with a K=2 coverage factor. Results: No significant variations with energy were found for polarity correction values, excluding PinPoint 3D chambers (that increase with photon energy) and Markus (that decrease with electron energy), although their uncertainties are comparatively higher. Also, Markus chamber shows higher kpol values and uncertainties than those obtained for Roos chambers (< 1,001). Excluding Farmer and Semiflex chambers, saturation factor values have no energy dependence. In 18 MeV, Farmer chambers values were greater than 1,007. Markus values were lower (< 1.003) than Roos chamber values (> 1,007). Polarity uncertainties are subestimated due to kpol true value is unknown.
1105 poster IS REFERENCE CHAMBER CALIBRATION IN MV PHOTON BEAMS NECESARRY FOR ABSOLUTE DOSE DETERMINATION? A. Vestergaard1 , H. S. Rønde2 , M. Berg2 , L. H. Præstegaard1 1 A ARHUS U NIVERSITY H OSPITAL, Department of Medical Physics, Aarhus C, Denmark 2 V EJLE H OSPITAL, Department of Medical Physics, Vejle, Denmark
Purpose: To compare the two methods of absolute dose determination suggested in IAEA Technical Reports Series No 398 (TRS 398): 1) Reference chamber calibration in MV photon beams and 2) Reference chamber calibration in 60 Co combined with correction for the radiation quality of the user beam (kQ factor). Materials: The investigation evaluates six cylindrical ionization chambers of the type FC65-G (IBA Dosimetry, Schwarzenbruck, Germany) with calibration factors measured in 60 Co. Three different radiation therapy beams: 6MV SRS (stereotactic radio surgery mode), 6MV and 15MV were used. The corresponding Tissue Phantom Ratios (TPR20,10) of the beams are 0.660, 0.667 and 0.761. In addition, one of the ionization chambers has been calibrated in MV photon beams from 4 to 18 MV at the NPL (National Physics Laboratory, Teddington, Middlesex, UK). Below this chamber is referred to as the reference chamber. All other chambers were cross calibrated with the reference chamber using a solid water phantom (Gammex 457, Gamma Med, North Jackson, Ohio) with chamber inserts. During the cross calibration, the two chambers were interchanged and a mean of the two measurements is used for the cross calibration. All charge measurements were corrected for recombination. The kQ factor for each chamber and beam quality was calculated on the basis of the cross calibration. In addition, the mean kQ value for all chambers for each TPR20,10 was calculated and compared to the corresponding kQ factor tabulated in TRS 398. Results: The mean kQ factors are 0.988 (SD: 0.002), 0.988 (SD: 0.002) and 0.968 (SD: 0.002) for 6MV SRS, 6MV and 15MV beams, respectively. The ratios of mean kQ factors relative to the values in TRS 398 are 0.992, 0.992 and 0.987 for the 6MV SRS, 6MV and 15MV beams, respectively. Conclusions: The measured kQ factors are up to 1.3 % lower than the tabulated kQ factors in TRS 398. As a consequence absolute dose determination measurement using 60 Co calibration and kQ factors from TRS398 is up to 1.3% too high. This corresponds to the delivery of a too low dose to the patients.
Conclusions: An homogeneous behavior for each chamber type can be observed: similar factor and uncertainty values. It seems that a generic polarization and recombination factors can be achieved. Further studies are required. Also, it should be notice that polarity uncertainties grow as ion chamber volume decreases. 1107 poster PARAMETRIC FORMULATION FOR IORT UM CALCULATION E. Cabello Murillo1 , M. A. De la Casa de Julian1 , F. Clemente Gutierrez1 , J. García Ruiz-Zorrilla1 , R. Díaz Fuentes1 , A. Ferrando Sanchez1 , J. Castro Novais1 1 H OSPITAL U NIVERSITARIO 12 DE OCTUBRE, Madrid, Spain Purpose: Intraoperative radiotherapy (IORT) is a direct technique of electron irradiation on surgical bed. UM calculation for IORT requires a fast answer, and we need a quick and simple calculation method (we must manage a great amount of data) and easy to implement. In this paper, we show a simple parametric method to obtain UM for this technique. Materials: A Primus Linac (Siemens), with several IORT cones whose diameters are 3, 4, 5 6, 7 , 8, 9 y 10 cm, and are beveled at 0, 15, 30 y 45, provided by MCP Iberia. We set the Linac apertures to 13x13 field size. Definitions of clinical and geometrical cone axes are referred in the literature. The Relative measurements were performed using a semiconductor detector: PDD along clinical and geometrical axis, y dose profile perpendicular to clinical axis at 90%, 100% and 50% dose (normalized at maximum clinical pdd). In order to characterize dose for each pair cone-bevel degree, a Markus (PTW) ionization chamber was used, at the depth of the geometrical axis maximum, and at source-surface distance (SSD) from 100 cm to 110 cm (we have assumed that maximum depth does not depend on SSD).
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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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D OSE MEASUREMENT: BASIC
1106 poster MEASUREMENTS AND UNCERTAINTIES VALUES FOR DOSE POLARIZATION AND RECOMBINATION CORRECTION FACTORS L. Alejo Luque1 , R. Rodríguez Romero1 , P. Castro Tejero1 , J. M. Fandiño Lareo2 H. U. P UERTA DE H IERRO M AJADAHONDA, Department of Medical Physics and Radiation Safety, Majadahonda, Spain 2 C ENTRO O NCOLÓGICO DE G ALICIA, Department of Medical Physics and Radiation Safety, A Coruña, Spain 1
Conclusions: The original NORMA phantom is a good first approximation for neutron organ dose assessment, although more precise results require the usage of phantoms having composition closer to tissue. Acknowledgements: The authors are indebted to the University Law (LOU) contract between the University of Seville and the Andalusian Health Service (SAS) and especially to the Spanish Nuclear Security Council (CSN). We want to give thanks to J. P. Cano (workshop physics faculty university of Seville), Mariano A. (carpentry) and Alejandro (Matadero del Sur) for the construction and cession of the pork for the phantoms. References: 1. F G et al. (2010), Phys. Med. Biol. 55 10251039. 2. F Shez-Doblado et al. (2009), WC 2009, IFMBE Proccedings 25/I, Berlin: Springer, 259-261. 3. C. Domingo et al. (2009), Radiation Measurements, 44, 1073-1076 4. B.R.L. Siebert and H. Schuhmacher (1995), Radiat, Prot. Dosim., 58, 177-183.
Purpose: Measurements and uncertainties values for dose polarization and recombination correction factors (kpol, ks) for different cylindrical and planeparallel ionization chambers are discussed. These values are obtained using photons and electrons beams of various nominal energies generated by Varian Clinac 21EX linear accelerators and TomoTherapy Hi-Art II, in order to study the behavior of these uncertainties and factors, and analyze trends. Materials: Applying IAEA TRS-398 protocol, kpol and ks values were obtained for different chambers and energies: four PTW 30013 Farmer in 6MV, 15MV and 18 MeV, two PTW 31010 Semiflex, two PTW 31016 PinPoint 3D in 6MV and 15MV, two Exradin A1SL in 6MV, two Roos 34001 and a Markus 34045 in 6MeV, 9MeV, 12MeV, 15MeV and 18MeV electron beams. Except Exradin chambers, whose factors were obtained in TomoTherapy Hi-Art II 6 MV beam, a Varian CLINAC 21EX linear accelerator was used. Since dose calibrations are corrected by recombination effect but not polarity, kpol uncertainty had to be estimated considering its maximum values reported in calibration certificates. Type A and B uncertainties were calculated with a K=2 coverage factor. Results: No significant variations with energy were found for polarity correction values, excluding PinPoint 3D chambers (that increase with photon energy) and Markus (that decrease with electron energy), although their uncertainties are comparatively higher. Also, Markus chamber shows higher kpol values and uncertainties than those obtained for Roos chambers (< 1,001). Excluding Farmer and Semiflex chambers, saturation factor values have no energy dependence. In 18 MeV, Farmer chambers values were greater than 1,007. Markus values were lower (< 1.003) than Roos chamber values (> 1,007). Polarity uncertainties are subestimated due to kpol true value is unknown.
1105 poster IS REFERENCE CHAMBER CALIBRATION IN MV PHOTON BEAMS NECESARRY FOR ABSOLUTE DOSE DETERMINATION? A. Vestergaard1 , H. S. Rønde2 , M. Berg2 , L. H. Præstegaard1 1 A ARHUS U NIVERSITY H OSPITAL, Department of Medical Physics, Aarhus C, Denmark 2 V EJLE H OSPITAL, Department of Medical Physics, Vejle, Denmark
Purpose: To compare the two methods of absolute dose determination suggested in IAEA Technical Reports Series No 398 (TRS 398): 1) Reference chamber calibration in MV photon beams and 2) Reference chamber calibration in 60 Co combined with correction for the radiation quality of the user beam (kQ factor). Materials: The investigation evaluates six cylindrical ionization chambers of the type FC65-G (IBA Dosimetry, Schwarzenbruck, Germany) with calibration factors measured in 60 Co. Three different radiation therapy beams: 6MV SRS (stereotactic radio surgery mode), 6MV and 15MV were used. The corresponding Tissue Phantom Ratios (TPR20,10) of the beams are 0.660, 0.667 and 0.761. In addition, one of the ionization chambers has been calibrated in MV photon beams from 4 to 18 MV at the NPL (National Physics Laboratory, Teddington, Middlesex, UK). Below this chamber is referred to as the reference chamber. All other chambers were cross calibrated with the reference chamber using a solid water phantom (Gammex 457, Gamma Med, North Jackson, Ohio) with chamber inserts. During the cross calibration, the two chambers were interchanged and a mean of the two measurements is used for the cross calibration. All charge measurements were corrected for recombination. The kQ factor for each chamber and beam quality was calculated on the basis of the cross calibration. In addition, the mean kQ value for all chambers for each TPR20,10 was calculated and compared to the corresponding kQ factor tabulated in TRS 398. Results: The mean kQ factors are 0.988 (SD: 0.002), 0.988 (SD: 0.002) and 0.968 (SD: 0.002) for 6MV SRS, 6MV and 15MV beams, respectively. The ratios of mean kQ factors relative to the values in TRS 398 are 0.992, 0.992 and 0.987 for the 6MV SRS, 6MV and 15MV beams, respectively. Conclusions: The measured kQ factors are up to 1.3 % lower than the tabulated kQ factors in TRS 398. As a consequence absolute dose determination measurement using 60 Co calibration and kQ factors from TRS398 is up to 1.3% too high. This corresponds to the delivery of a too low dose to the patients.
Conclusions: An homogeneous behavior for each chamber type can be observed: similar factor and uncertainty values. It seems that a generic polarization and recombination factors can be achieved. Further studies are required. Also, it should be notice that polarity uncertainties grow as ion chamber volume decreases. 1107 poster PARAMETRIC FORMULATION FOR IORT UM CALCULATION E. Cabello Murillo1 , M. A. De la Casa de Julian1 , F. Clemente Gutierrez1 , J. García Ruiz-Zorrilla1 , R. Díaz Fuentes1 , A. Ferrando Sanchez1 , J. Castro Novais1 1 H OSPITAL U NIVERSITARIO 12 DE OCTUBRE, Madrid, Spain Purpose: Intraoperative radiotherapy (IORT) is a direct technique of electron irradiation on surgical bed. UM calculation for IORT requires a fast answer, and we need a quick and simple calculation method (we must manage a great amount of data) and easy to implement. In this paper, we show a simple parametric method to obtain UM for this technique. Materials: A Primus Linac (Siemens), with several IORT cones whose diameters are 3, 4, 5 6, 7 , 8, 9 y 10 cm, and are beveled at 0, 15, 30 y 45, provided by MCP Iberia. We set the Linac apertures to 13x13 field size. Definitions of clinical and geometrical cone axes are referred in the literature. The Relative measurements were performed using a semiconductor detector: PDD along clinical and geometrical axis, y dose profile perpendicular to clinical axis at 90%, 100% and 50% dose (normalized at maximum clinical pdd). In order to characterize dose for each pair cone-bevel degree, a Markus (PTW) ionization chamber was used, at the depth of the geometrical axis maximum, and at source-surface distance (SSD) from 100 cm to 110 cm (we have assumed that maximum depth does not depend on SSD).