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EP-1503: The effect of tandem-ovoid applicator on the dose distribution in GYN brachytherapy using Ir-192
S806 ESTRO 36 _______________________________________________________________________________________________
Material and Methods Brass bolus (Radiation Products Design Inc) with a nominal thickness of 1.5mm was used on a tissue equivalent slab phantom (RMI solid water). It was used as single layer and folded over in 2 or 4 layers. Radiochromic film (EBT3) was used to assess surface dose and dose variation on the phantom for a 6 MV and 18MV photon beams (Varian 21iX). Surface dose was measured with and without the brass bolus which was placed on top of the film. A photo of the brass is shown in Figure 1 (a) alongside a 50 mm section of steel ruler. A film calibration curve was derived by exposing samples from the same sheet to various known doses under reference conditions. Film was scanned 12 hours post exposure and manually analysed using ImageJ and MS Excel software. Results Surface dose measured using film in the absence of bolus was 20 % of dose at d-max for a 6 MV beam in a 10 cm x 10 cm jaw-defined square field. Surface dose with a single layer of the brass bolus increased to an average of 57 % of dose at d-max (1.5cm). The mesh-like structure of the brass resulted in a dose enhancement pattern which was non-uniform across the film, as shown for a 1 cm x 1 cm square region in Figure 1 (b), which shows the peaks and troughs resulting from the mesh. The maximum dose (peaks) was 62 % and the minimum (troughs) was 53 % of dose at d-max under reference conditions. Increasing the number of layers of bolus increased the surface dose.
EP-1503 The effect of tandem-ovoid applicator on the dose distribution in GYN brachytherapy using Ir-192 M.H. Sadeghi1, A. Mehdizadeh1, M. Tafi1, R. Faghihi1, S. Sina2, A.S. Meigooni3, A. Shabestani Monfared4 1 Shiraz University, nuclear engineerning department, Shiraz, Iran Islamic Republic of 2 Shiraz University, Radiation Research Center, Shiraz, Iran Islamic Republic of 3 Comprehensive cancer center of Nevada, Las VegasNevada, USA 4 Babol University of Medical Sciences, Babol, Iran Islamic Republic of Purpose or Objective The dosimetry procedures by simple superposition accounts only for the source shield, and does not take in to account the attenuation of photons by the applicators. The purpose of this investigation is estimation of the effects the tandem ovoid applicator on the dose distribution inside the phantom by MCNP5 Monte Carlo simulations. Material and Methods In this study, the superposition method is used for obtaining the dose distribution in the phantom for a typical GYN brachytherapy. Then the sources are simulated inside the tandem ovoid applicator, and the dose at points A, B, bladder and rectum was compared with the results of supper position. The exact dwell positions, and times of the source, and positions of the dosimetry points were determined from images of a patient. The MCNP5 Monte Carlo code was used for simulation of the phantoms, applicators, and the sources. Results The results of this study showed no significant differences between the results of superposition method, and the MC simulations for different dosimetry points. The difference in all important dosimetry points were found to be less than 4%. The maximum dose differences were found at the tip of the detectors. Conclusion According to the results, the superposition method, adding the dose of each source obtained by the TG-43 algorithm, can estimate the dose to point A, B, bladder,and rectum points with good accuracy.
EP-1504 Monte Carlo modeling of non-isocentric proton pencil beam scanning treatments A. Elia1,2, L. Grevillot1, A. Carlino1,3, T. Böhlen1, H. Fuchs1,4,5, M. Stock1, D. Sarrut2 1 EBG MedAustron GmbH, Medical Department, A-2700 Wiener Neustadt, Austria 2 CREATIS- Université de Lyon- CNRS UMR5220- Inserm U1044- INSA-Lyon- Université Lyon 1, Centre Léon Bérard, 69007 Lyon, France 3 University of Palermo, Department of Physics and Chemistry, 90128 Palermo, Italy 4 Medical University of Vienna / AKH, Department of Radiation Oncology, Vienna, Austria 5 Medical University of Vienna, Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria Conclusion Brass bolus may be used for surface dose enhancement in external beam radiotherapy with megavoltage photons. The surface dose increased from 20 % to 57 % of dose at dmax for a 10 cm x 10 cm 6 MV field. The non-uniform surface dose distribution should have minimal clinical impact for multi-fraction radiotherapy regimes where multiple layers and the random orientation of brass links relative to skin surface will vary with daily setup.
Purpose or Objective Monte Carlo (MC) calculation is the gold standard to support dose calculation analytically performed by Treatment Planning Systems (TPS). This work is built upon a preliminary beam model of a fixed beam line based mainly on measurements performed at isocenter. For nonisocentric treatments, accurate description of beam spot size for reduced air-gaps is of paramount importance for accurate treatment planning. This work extends the
Material and Methods Brass bolus (Radiation Products Design Inc) with a nominal thickness of 1.5mm was used on a tissue equivalent slab phantom (RMI solid water). It was used as single layer and folded over in 2 or 4 layers. Radiochromic film (EBT3) was used to assess surface dose and dose variation on the phantom for a 6 MV and 18MV photon beams (Varian 21iX). Surface dose was measured with and without the brass bolus which was placed on top of the film. A photo of the brass is shown in Figure 1 (a) alongside a 50 mm section of steel ruler. A film calibration curve was derived by exposing samples from the same sheet to various known doses under reference conditions. Film was scanned 12 hours post exposure and manually analysed using ImageJ and MS Excel software. Results Surface dose measured using film in the absence of bolus was 20 % of dose at d-max for a 6 MV beam in a 10 cm x 10 cm jaw-defined square field. Surface dose with a single layer of the brass bolus increased to an average of 57 % of dose at d-max (1.5cm). The mesh-like structure of the brass resulted in a dose enhancement pattern which was non-uniform across the film, as shown for a 1 cm x 1 cm square region in Figure 1 (b), which shows the peaks and troughs resulting from the mesh. The maximum dose (peaks) was 62 % and the minimum (troughs) was 53 % of dose at d-max under reference conditions. Increasing the number of layers of bolus increased the surface dose.
EP-1503 The effect of tandem-ovoid applicator on the dose distribution in GYN brachytherapy using Ir-192 M.H. Sadeghi1, A. Mehdizadeh1, M. Tafi1, R. Faghihi1, S. Sina2, A.S. Meigooni3, A. Shabestani Monfared4 1 Shiraz University, nuclear engineerning department, Shiraz, Iran Islamic Republic of 2 Shiraz University, Radiation Research Center, Shiraz, Iran Islamic Republic of 3 Comprehensive cancer center of Nevada, Las VegasNevada, USA 4 Babol University of Medical Sciences, Babol, Iran Islamic Republic of Purpose or Objective The dosimetry procedures by simple superposition accounts only for the source shield, and does not take in to account the attenuation of photons by the applicators. The purpose of this investigation is estimation of the effects the tandem ovoid applicator on the dose distribution inside the phantom by MCNP5 Monte Carlo simulations. Material and Methods In this study, the superposition method is used for obtaining the dose distribution in the phantom for a typical GYN brachytherapy. Then the sources are simulated inside the tandem ovoid applicator, and the dose at points A, B, bladder and rectum was compared with the results of supper position. The exact dwell positions, and times of the source, and positions of the dosimetry points were determined from images of a patient. The MCNP5 Monte Carlo code was used for simulation of the phantoms, applicators, and the sources. Results The results of this study showed no significant differences between the results of superposition method, and the MC simulations for different dosimetry points. The difference in all important dosimetry points were found to be less than 4%. The maximum dose differences were found at the tip of the detectors. Conclusion According to the results, the superposition method, adding the dose of each source obtained by the TG-43 algorithm, can estimate the dose to point A, B, bladder,and rectum points with good accuracy.
EP-1504 Monte Carlo modeling of non-isocentric proton pencil beam scanning treatments A. Elia1,2, L. Grevillot1, A. Carlino1,3, T. Böhlen1, H. Fuchs1,4,5, M. Stock1, D. Sarrut2 1 EBG MedAustron GmbH, Medical Department, A-2700 Wiener Neustadt, Austria 2 CREATIS- Université de Lyon- CNRS UMR5220- Inserm U1044- INSA-Lyon- Université Lyon 1, Centre Léon Bérard, 69007 Lyon, France 3 University of Palermo, Department of Physics and Chemistry, 90128 Palermo, Italy 4 Medical University of Vienna / AKH, Department of Radiation Oncology, Vienna, Austria 5 Medical University of Vienna, Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria Conclusion Brass bolus may be used for surface dose enhancement in external beam radiotherapy with megavoltage photons. The surface dose increased from 20 % to 57 % of dose at dmax for a 10 cm x 10 cm 6 MV field. The non-uniform surface dose distribution should have minimal clinical impact for multi-fraction radiotherapy regimes where multiple layers and the random orientation of brass links relative to skin surface will vary with daily setup.
Purpose or Objective Monte Carlo (MC) calculation is the gold standard to support dose calculation analytically performed by Treatment Planning Systems (TPS). This work is built upon a preliminary beam model of a fixed beam line based mainly on measurements performed at isocenter. For nonisocentric treatments, accurate description of beam spot size for reduced air-gaps is of paramount importance for accurate treatment planning. This work extends the