The Experts below are selected from a list of 6825 Experts worldwide ranked by ideXlab platform

Clive Baldock - One of the best experts on this subject based on the ideXlab platform.

  • An investigation of dose changes for therapeutic kilovoltage x-ray beams with underlying Lead Shielding
    Medical physics, 2007
    Co-Authors: Robin Hill, Brendan Healy, Lois C Holloway, Clive Baldock
    Abstract:

    Kilovoltage x-ray beams are used to treat cancer on or close to the skin surface. Many clinical cases use high atomic number materials as Shielding to reduce dose to underlying healthy tissues. In this work, we have investigated the effect on both the surface dose and depth doses in a water phantom with Lead Shielding at depth in the phantom. The EGSnrc Monte Carlo code was used to simulate the water phantom and to calculate the surface doses and depth doses using primary x-ray beam spectra derived from an analytical model. The x-ray beams were in the energy range of 75-135 kVp with field sizes of 2, 5 and 8 cm diameter. The Lead sheet was located beneath the water surface at depths ranging from 0.5-7.5 cm. The surface dose decreased as the Lead was positioned closer to the water surface and as the field size was increased. The variation in surface dose as a function of x-ray beam energy was only small but the maximum reduction occurred for the 100 kVp x-ray beam. For the 8 cm diameter field with the Lead at 1 cm depth and using the 100 kVp x-ray beam, the surface dose was reduced tomore » 0.898 of the surface dose in the water phantom only. Measured surface dose changes, using a Farmer-type ionization chamber, agreed with the Monte Carlo calculated doses. Calculated depth doses in water with a Lead sheet positioned below the surface showed that the dose fall-off increased as the Lead was positioned closer to the water surface as compared to the depth dose in the water phantom only. Monte Carlo calculations of the total x-ray beam spectrum at the water surface showed that the total fluence decreased due to a reduction in backscatter from within the water and very little backscatter from the Lead. The mean energy of the x-ray spectrum varied less than 1 keV, with the Lead at 1 cm beneath the water phantom surface. As the Monte Carlo calculations showed good agreement with the measured results, this method can be used to verify surface dose changes in clinical situations where measurements are difficult. The clinical impact of the use of Lead must be considered in the dose prescription for patients being treated with kilovoltage x-ray beams.« less

  • SU-FF-T-181: An Investigation of Surface Dose Changes for Therapeutic Kilovoltage X-Ray Beams with Underlying Lead Shielding
    Medical Physics, 2005
    Co-Authors: Robin Hill, Brendan Healy, Lois C Holloway, Clive Baldock
    Abstract:

    Purpose: The effect on surface dose from underlying Lead Shielding in water was investigated for therapeutic kilovoltage x‐ray beams by experimental and Monte Carlo methods.Method and Materials: A Farmer type ionisation chamber was used to measure the surface dose in a water phantom for x‐ray beams with energies from 75 to 135 kVp. A 5 mm thick Lead sheet was positioned at various depths below the surface. The surface dose ratio was calculated by comparison with the surface dose with no Lead sheet present. A Monte Carlo model of the x‐ray beam and the phantom was generated using the EGSnrcMP code (V4.2). The initial energy spectrum was determined using an empirical method and verified by calculation of depth dose data. The dose was scored in a 1 mm thick slab at the phantom surface. The change in surface dose was calculated as a function of depth to the Lead and compared to measured data. Results: The reduction in surface dose was a function of x‐ray beam energy, beam area and the depth of water to the Lead. As the depth of water to the Lead sheet decreased, there was a reduction in the surface dose. With the 8 cm diameter applicator and 1 cm depth of water to the Lead, the surface dose ratio was 0.918 for the 75 kVp x‐ray beam and 0.890 for the 100 kVp x‐ray beam. For the smaller applicators, there was less reduction in the surface dose ratios. Surface dose ratios calculated by the EGSnrcMP code were in good agreement with measured data, with a maximum deviation of 1.2%. Conclusion: The surface dose for kilovoltage x‐ray beams is reduced when Lead is underlying in the phantom. The Monte Carlo results indicate the model is sufficiently accurate to predict changes in the surface dose.

Robin Hill - One of the best experts on this subject based on the ideXlab platform.

  • An investigation of dose changes for therapeutic kilovoltage x-ray beams with underlying Lead Shielding
    Medical physics, 2007
    Co-Authors: Robin Hill, Brendan Healy, Lois C Holloway, Clive Baldock
    Abstract:

    Kilovoltage x-ray beams are used to treat cancer on or close to the skin surface. Many clinical cases use high atomic number materials as Shielding to reduce dose to underlying healthy tissues. In this work, we have investigated the effect on both the surface dose and depth doses in a water phantom with Lead Shielding at depth in the phantom. The EGSnrc Monte Carlo code was used to simulate the water phantom and to calculate the surface doses and depth doses using primary x-ray beam spectra derived from an analytical model. The x-ray beams were in the energy range of 75-135 kVp with field sizes of 2, 5 and 8 cm diameter. The Lead sheet was located beneath the water surface at depths ranging from 0.5-7.5 cm. The surface dose decreased as the Lead was positioned closer to the water surface and as the field size was increased. The variation in surface dose as a function of x-ray beam energy was only small but the maximum reduction occurred for the 100 kVp x-ray beam. For the 8 cm diameter field with the Lead at 1 cm depth and using the 100 kVp x-ray beam, the surface dose was reduced tomore » 0.898 of the surface dose in the water phantom only. Measured surface dose changes, using a Farmer-type ionization chamber, agreed with the Monte Carlo calculated doses. Calculated depth doses in water with a Lead sheet positioned below the surface showed that the dose fall-off increased as the Lead was positioned closer to the water surface as compared to the depth dose in the water phantom only. Monte Carlo calculations of the total x-ray beam spectrum at the water surface showed that the total fluence decreased due to a reduction in backscatter from within the water and very little backscatter from the Lead. The mean energy of the x-ray spectrum varied less than 1 keV, with the Lead at 1 cm beneath the water phantom surface. As the Monte Carlo calculations showed good agreement with the measured results, this method can be used to verify surface dose changes in clinical situations where measurements are difficult. The clinical impact of the use of Lead must be considered in the dose prescription for patients being treated with kilovoltage x-ray beams.« less

  • SU-FF-T-181: An Investigation of Surface Dose Changes for Therapeutic Kilovoltage X-Ray Beams with Underlying Lead Shielding
    Medical Physics, 2005
    Co-Authors: Robin Hill, Brendan Healy, Lois C Holloway, Clive Baldock
    Abstract:

    Purpose: The effect on surface dose from underlying Lead Shielding in water was investigated for therapeutic kilovoltage x‐ray beams by experimental and Monte Carlo methods.Method and Materials: A Farmer type ionisation chamber was used to measure the surface dose in a water phantom for x‐ray beams with energies from 75 to 135 kVp. A 5 mm thick Lead sheet was positioned at various depths below the surface. The surface dose ratio was calculated by comparison with the surface dose with no Lead sheet present. A Monte Carlo model of the x‐ray beam and the phantom was generated using the EGSnrcMP code (V4.2). The initial energy spectrum was determined using an empirical method and verified by calculation of depth dose data. The dose was scored in a 1 mm thick slab at the phantom surface. The change in surface dose was calculated as a function of depth to the Lead and compared to measured data. Results: The reduction in surface dose was a function of x‐ray beam energy, beam area and the depth of water to the Lead. As the depth of water to the Lead sheet decreased, there was a reduction in the surface dose. With the 8 cm diameter applicator and 1 cm depth of water to the Lead, the surface dose ratio was 0.918 for the 75 kVp x‐ray beam and 0.890 for the 100 kVp x‐ray beam. For the smaller applicators, there was less reduction in the surface dose ratios. Surface dose ratios calculated by the EGSnrcMP code were in good agreement with measured data, with a maximum deviation of 1.2%. Conclusion: The surface dose for kilovoltage x‐ray beams is reduced when Lead is underlying in the phantom. The Monte Carlo results indicate the model is sufficiently accurate to predict changes in the surface dose.

Brendan Healy - One of the best experts on this subject based on the ideXlab platform.

  • An investigation of dose changes for therapeutic kilovoltage x-ray beams with underlying Lead Shielding
    Medical physics, 2007
    Co-Authors: Robin Hill, Brendan Healy, Lois C Holloway, Clive Baldock
    Abstract:

    Kilovoltage x-ray beams are used to treat cancer on or close to the skin surface. Many clinical cases use high atomic number materials as Shielding to reduce dose to underlying healthy tissues. In this work, we have investigated the effect on both the surface dose and depth doses in a water phantom with Lead Shielding at depth in the phantom. The EGSnrc Monte Carlo code was used to simulate the water phantom and to calculate the surface doses and depth doses using primary x-ray beam spectra derived from an analytical model. The x-ray beams were in the energy range of 75-135 kVp with field sizes of 2, 5 and 8 cm diameter. The Lead sheet was located beneath the water surface at depths ranging from 0.5-7.5 cm. The surface dose decreased as the Lead was positioned closer to the water surface and as the field size was increased. The variation in surface dose as a function of x-ray beam energy was only small but the maximum reduction occurred for the 100 kVp x-ray beam. For the 8 cm diameter field with the Lead at 1 cm depth and using the 100 kVp x-ray beam, the surface dose was reduced tomore » 0.898 of the surface dose in the water phantom only. Measured surface dose changes, using a Farmer-type ionization chamber, agreed with the Monte Carlo calculated doses. Calculated depth doses in water with a Lead sheet positioned below the surface showed that the dose fall-off increased as the Lead was positioned closer to the water surface as compared to the depth dose in the water phantom only. Monte Carlo calculations of the total x-ray beam spectrum at the water surface showed that the total fluence decreased due to a reduction in backscatter from within the water and very little backscatter from the Lead. The mean energy of the x-ray spectrum varied less than 1 keV, with the Lead at 1 cm beneath the water phantom surface. As the Monte Carlo calculations showed good agreement with the measured results, this method can be used to verify surface dose changes in clinical situations where measurements are difficult. The clinical impact of the use of Lead must be considered in the dose prescription for patients being treated with kilovoltage x-ray beams.« less

  • SU-FF-T-181: An Investigation of Surface Dose Changes for Therapeutic Kilovoltage X-Ray Beams with Underlying Lead Shielding
    Medical Physics, 2005
    Co-Authors: Robin Hill, Brendan Healy, Lois C Holloway, Clive Baldock
    Abstract:

    Purpose: The effect on surface dose from underlying Lead Shielding in water was investigated for therapeutic kilovoltage x‐ray beams by experimental and Monte Carlo methods.Method and Materials: A Farmer type ionisation chamber was used to measure the surface dose in a water phantom for x‐ray beams with energies from 75 to 135 kVp. A 5 mm thick Lead sheet was positioned at various depths below the surface. The surface dose ratio was calculated by comparison with the surface dose with no Lead sheet present. A Monte Carlo model of the x‐ray beam and the phantom was generated using the EGSnrcMP code (V4.2). The initial energy spectrum was determined using an empirical method and verified by calculation of depth dose data. The dose was scored in a 1 mm thick slab at the phantom surface. The change in surface dose was calculated as a function of depth to the Lead and compared to measured data. Results: The reduction in surface dose was a function of x‐ray beam energy, beam area and the depth of water to the Lead. As the depth of water to the Lead sheet decreased, there was a reduction in the surface dose. With the 8 cm diameter applicator and 1 cm depth of water to the Lead, the surface dose ratio was 0.918 for the 75 kVp x‐ray beam and 0.890 for the 100 kVp x‐ray beam. For the smaller applicators, there was less reduction in the surface dose ratios. Surface dose ratios calculated by the EGSnrcMP code were in good agreement with measured data, with a maximum deviation of 1.2%. Conclusion: The surface dose for kilovoltage x‐ray beams is reduced when Lead is underlying in the phantom. The Monte Carlo results indicate the model is sufficiently accurate to predict changes in the surface dose.

Lois C Holloway - One of the best experts on this subject based on the ideXlab platform.

  • An investigation of dose changes for therapeutic kilovoltage x-ray beams with underlying Lead Shielding
    Medical physics, 2007
    Co-Authors: Robin Hill, Brendan Healy, Lois C Holloway, Clive Baldock
    Abstract:

    Kilovoltage x-ray beams are used to treat cancer on or close to the skin surface. Many clinical cases use high atomic number materials as Shielding to reduce dose to underlying healthy tissues. In this work, we have investigated the effect on both the surface dose and depth doses in a water phantom with Lead Shielding at depth in the phantom. The EGSnrc Monte Carlo code was used to simulate the water phantom and to calculate the surface doses and depth doses using primary x-ray beam spectra derived from an analytical model. The x-ray beams were in the energy range of 75-135 kVp with field sizes of 2, 5 and 8 cm diameter. The Lead sheet was located beneath the water surface at depths ranging from 0.5-7.5 cm. The surface dose decreased as the Lead was positioned closer to the water surface and as the field size was increased. The variation in surface dose as a function of x-ray beam energy was only small but the maximum reduction occurred for the 100 kVp x-ray beam. For the 8 cm diameter field with the Lead at 1 cm depth and using the 100 kVp x-ray beam, the surface dose was reduced tomore » 0.898 of the surface dose in the water phantom only. Measured surface dose changes, using a Farmer-type ionization chamber, agreed with the Monte Carlo calculated doses. Calculated depth doses in water with a Lead sheet positioned below the surface showed that the dose fall-off increased as the Lead was positioned closer to the water surface as compared to the depth dose in the water phantom only. Monte Carlo calculations of the total x-ray beam spectrum at the water surface showed that the total fluence decreased due to a reduction in backscatter from within the water and very little backscatter from the Lead. The mean energy of the x-ray spectrum varied less than 1 keV, with the Lead at 1 cm beneath the water phantom surface. As the Monte Carlo calculations showed good agreement with the measured results, this method can be used to verify surface dose changes in clinical situations where measurements are difficult. The clinical impact of the use of Lead must be considered in the dose prescription for patients being treated with kilovoltage x-ray beams.« less

  • SU-FF-T-181: An Investigation of Surface Dose Changes for Therapeutic Kilovoltage X-Ray Beams with Underlying Lead Shielding
    Medical Physics, 2005
    Co-Authors: Robin Hill, Brendan Healy, Lois C Holloway, Clive Baldock
    Abstract:

    Purpose: The effect on surface dose from underlying Lead Shielding in water was investigated for therapeutic kilovoltage x‐ray beams by experimental and Monte Carlo methods.Method and Materials: A Farmer type ionisation chamber was used to measure the surface dose in a water phantom for x‐ray beams with energies from 75 to 135 kVp. A 5 mm thick Lead sheet was positioned at various depths below the surface. The surface dose ratio was calculated by comparison with the surface dose with no Lead sheet present. A Monte Carlo model of the x‐ray beam and the phantom was generated using the EGSnrcMP code (V4.2). The initial energy spectrum was determined using an empirical method and verified by calculation of depth dose data. The dose was scored in a 1 mm thick slab at the phantom surface. The change in surface dose was calculated as a function of depth to the Lead and compared to measured data. Results: The reduction in surface dose was a function of x‐ray beam energy, beam area and the depth of water to the Lead. As the depth of water to the Lead sheet decreased, there was a reduction in the surface dose. With the 8 cm diameter applicator and 1 cm depth of water to the Lead, the surface dose ratio was 0.918 for the 75 kVp x‐ray beam and 0.890 for the 100 kVp x‐ray beam. For the smaller applicators, there was less reduction in the surface dose ratios. Surface dose ratios calculated by the EGSnrcMP code were in good agreement with measured data, with a maximum deviation of 1.2%. Conclusion: The surface dose for kilovoltage x‐ray beams is reduced when Lead is underlying in the phantom. The Monte Carlo results indicate the model is sufficiently accurate to predict changes in the surface dose.

Paul W. Read - One of the best experts on this subject based on the ideXlab platform.

  • Use of megavoltage computed tomography with image registration for high-dose rate treatment planning of an oral tongue cancer using a custom oral mold applicator with embedded Lead Shielding.
    Brachytherapy, 2011
    Co-Authors: Bruce Libby, Ke Sheng, Robert Mclawhorn, Alyson Mcintosh, Ray Van Ausdal, Andrew B. Martof, Paul W. Read
    Abstract:

    Abstract Purpose A patient with a lateral oral tongue cancer was treated with high–dose rate brachytherapy using an oral applicator with embedded Lead Shielding making conventional simulation, using either kilovoltage computed tomography or radiographs, impossible because of scatter artifact. Methods and materials Treatment simulation was accomplished using megavoltage computed tomography (MVCT) simulation on a helical tomotherapy unit. Because of difficulty in visualization of the catheters on the patient MVCT images, Velocity AI image registration software (Velocity Medical Solutions, Atlanta, GA) was used to register an MVCT of the applicator itself with the patient MVCT simulation. The treatment plan was manually optimized to prescribe 4 Gy/fraction to the gross tumor volume. Results The patient tolerated the treatment well, with no evidence of disease 6 months after treatment. Thermoluminescent dosimeter measurements showed that the Shielding reduced the dose by up to 90%, depending on the location of the thermoluminescent dosimeter. While the patient was treated using dose distributions calculated in a homogeneous medium (Task Group-43), an approximation of the true dose distributions was retrospectively calculated using Acuros (Varian Medical Systems Inc., Palo Alto, CA), which accounts for heterogeneities in the patient. Discussion Use of the MVCT with image registration allowed treatment planning in the presence of Lead Shielding. Dose–volume histograms showed that recalculation of the dose using heterogeneity correction did not affect the dose to the gross tumor volume, but that the dose to normal structures (maxilla and mandible) was reduced by the Lead Shielding. Conclusion The use of MVCT and image registration allows for optimized planning in the presence of Shielding, which would not be possible with conventional kilovoltage computed tomography.

  • SU‐GG‐T‐45: Use of MVCT with Image Registration for Planning HDR Treatments Using a Custom Oral Applicator with Lead Shielding
    Medical Physics, 2010
    Co-Authors: Bruce Libby, Ke Sheng, Robert Mclawhorn, Alyson Mcintosh, Andrew B. Martof, R. Van Ausdal, Paul W. Read
    Abstract:

    Purpose:Treatment planning for HDR brachytherapy can be difficult in cases in which it is necessary to create custom applicators that incorporate Shielding for the protection of normal structures. This can be overcome by the use of MVCT, which reduces artifacts in the image set. Method and Materials: A custom oral applicator was created by a dentist for the treatment of a superficial recurrence of an oral tongue cancer. The applicator contained two interstitial catheters placed one cm. apart, along with approximately 2.1 mm of Lead sheeting to shield the maxilla, mandible, and supporting structures. At time of simulation, the applicator was placed in the patient's mouth, with dummy strands inside the catheters, and an MVCT was performed on the Tomotherapy® system. Another MVCT was performed of just the applicator with dummy strands. The MVCT images were transferred to the Velocity ®system for image registration. The catheters were visualized on the scan of the applicator, and then the contours were transferred to the full MVCT set. The MVCT and contour DICOM sets were transferred to BrachyVision for HDR planning. Dwell times were manually optimized to cover the target volume, with a prescription of 32 Gy in 8 BID fractions. Results: Due to the Lead Shielding, 3DCT treatment planning would have been difficult without the use of MVCT. TLDs placed inside the applicator's tooth cavities for a test run showed that the Lead shield reduced the dose by 65–75%, depending on the location of the TLD.Conclusion: The use of MVCT along with image registration software allows visualization of HDR applicators in the presence of Shielding or other high‐Z materials. This work can be extended to the use of MVCT for planning treatments with standard applicators, such as T&O, which may not be kVCT compatible.