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Journal Details
Format
Journal
eISSN
1898-0309
First Published
30 Dec 2008
Publication timeframe
4 times per year
Languages
English

Search

Volume 14 (2008): Issue 3 (September 2008)

Journal Details
Format
Journal
eISSN
1898-0309
First Published
30 Dec 2008
Publication timeframe
4 times per year
Languages
English

Search

4 Articles
Open Access

Spectrometric measurements of radioisotope activity in the thyroid

Published Online: 14 Apr 2009
Page range: 123 - 134

Abstract

Spectrometric measurements of radioisotope activity in the thyroid

The results of measurements of iodine 131I and technetium 99mTc uptake in human thyroid, performed with scintillation or semiconductor detectors can exhibit a considerable uncertainty due to the differences in the thyroid position in the patient's neck. Basic physical laws of radiation attenuation and scattering show that the final shape of the registered spectrum should depends on the thyroid position in the neck and on the thickness of the tissue between the thyroid and the detector. The use of the spectrometric measuring method is proposed in this work for determination of the iodine gathering effective depth. The performed studies showed that the measurements results can be used for improving the accuracy of the iodine 131I activity in thyroid measurements and for selection of the group of patients for whom the anatomical position of the thyroid or the spatial distribution of the iodine gathering is much different than the standard one, assumed during the calibration of the counters. The results of the measurements were in agreement with Monte-Carlo calculations of the detector response. The method was used in routine monitoring of occupationally exposed persons, using the thyroid counter. A group of six persons with measurable internal contamination was selected and the measurements were performed on consecutive days, so the results could be registered at decreasing iodine activities in the thyroid. Larger series of measurements were performed at Brodno Regional Hospital in Warsaw, for a group of 95 patients after diagnostic administration of iodine 131I.

Keywords

  • thyroid
  • radioisotope activity
  • spectrometric measurements
Open Access

Entropy as a quality descriptor for the dose distribution — theory and practice for the patient target volume

Published Online: 14 Apr 2009
Page range: 135 - 149

Abstract

Entropy as a quality descriptor for the dose distribution — theory and practice for the patient target volume

The most common and established way to evaluate the quality of a radiotherapy plan is to use the dose-volume histogram (DVH). The evaluation of the DVH, however, is a subjective procedure. This may not be crucial as long as the two plans are significantly different. In the case of several plans obtained with different planning or optimisation strategies the differences are often subtle and therefore a more objective comparison method is desirable. A commonly used approach is based on evaluation of the conformity index, however we show how it can fail for plans of similar quality.

Therefore we propose a new method based on the similarity of DVH to statistical distributions, which can be characterised uniquely by their entropy. The concept is defined separately for target volumes, where it is derived from the Fermi-like distribution, and for organs at risk, where the traditional approach is also considered in its derivation. The artificial illustratory and clinical examples show the properties of the entropy as the quality descriptor and compare it to the conformity index. The examples are focused to the patient target volumes, where the advantage of the concept is more evident.

Keywords

  • plan evaluation
  • IMRT
  • DVH
  • conformity index
Open Access

IMRT versus 3D-CRT for thyroid cancer

Published Online: 14 Apr 2009
Page range: 151 - 162

Abstract

IMRT versus 3D-CRT for thyroid cancer

A 3D-CRT involving a 4-field (5-field, 6-field, etc.) technique (photon and electron beams) and an alternative IMRT 7-field technique with 6 MV photon fields for thyroid cancer were compared. The IMRT allows reduction in the dose to the spinal cord of about 12 Gy and permits better coverage of the target volume with smaller standard deviation (average 4.65% for 3D-CRT as compared with 1.81% for IMRT). The time needed to prepare therapy (TPS, dosimetry, preparing boluses and electron aperture) and the session time are about the same for both techniques.

Keywords

  • thyroid
  • IMRT
  • 3D-CRT
  • Target Conformity Index
  • comparison of treatment plans
Open Access

Assesing multileaf collimator effect on the build-up region using Monte Carlo method

Published Online: 14 Apr 2009
Page range: 163 - 182

Abstract

Assesing multileaf collimator effect on the build-up region using Monte Carlo method

Previous Monte Carlo studies have investigated the multileaf collimator (MLC) contribution to the build-up region for fields in which the MLC leaves were fully blocking the openings defined by the collimation jaws. In the present work, we investigate the same effect but for symmetric and asymmetric MLC defined field sizes (2×2, 4×4, 10×10 and 3×7 cm2). A Varian 2100C/D accelerator with 120-leaf MLC is accurately modeled for a 6MV photon beam using the BEAMnrc/EGSnrc code.

Our results indicate that particles scattered from accelerator head and MLC are responsible for the increase of about 7% on the surface dose when comparing 2×2 and 10×10 cm2 fields. We found that the MLC contribution to the total build-up dose is about 2% for the 2×2 cm2 field and less than 1% for the largest fields.

Keywords

  • surface dose
  • build-up dose
  • MLC
  • IMRT
  • Monte Carlo
4 Articles
Open Access

Spectrometric measurements of radioisotope activity in the thyroid

Published Online: 14 Apr 2009
Page range: 123 - 134

Abstract

Spectrometric measurements of radioisotope activity in the thyroid

The results of measurements of iodine 131I and technetium 99mTc uptake in human thyroid, performed with scintillation or semiconductor detectors can exhibit a considerable uncertainty due to the differences in the thyroid position in the patient's neck. Basic physical laws of radiation attenuation and scattering show that the final shape of the registered spectrum should depends on the thyroid position in the neck and on the thickness of the tissue between the thyroid and the detector. The use of the spectrometric measuring method is proposed in this work for determination of the iodine gathering effective depth. The performed studies showed that the measurements results can be used for improving the accuracy of the iodine 131I activity in thyroid measurements and for selection of the group of patients for whom the anatomical position of the thyroid or the spatial distribution of the iodine gathering is much different than the standard one, assumed during the calibration of the counters. The results of the measurements were in agreement with Monte-Carlo calculations of the detector response. The method was used in routine monitoring of occupationally exposed persons, using the thyroid counter. A group of six persons with measurable internal contamination was selected and the measurements were performed on consecutive days, so the results could be registered at decreasing iodine activities in the thyroid. Larger series of measurements were performed at Brodno Regional Hospital in Warsaw, for a group of 95 patients after diagnostic administration of iodine 131I.

Keywords

  • thyroid
  • radioisotope activity
  • spectrometric measurements
Open Access

Entropy as a quality descriptor for the dose distribution — theory and practice for the patient target volume

Published Online: 14 Apr 2009
Page range: 135 - 149

Abstract

Entropy as a quality descriptor for the dose distribution — theory and practice for the patient target volume

The most common and established way to evaluate the quality of a radiotherapy plan is to use the dose-volume histogram (DVH). The evaluation of the DVH, however, is a subjective procedure. This may not be crucial as long as the two plans are significantly different. In the case of several plans obtained with different planning or optimisation strategies the differences are often subtle and therefore a more objective comparison method is desirable. A commonly used approach is based on evaluation of the conformity index, however we show how it can fail for plans of similar quality.

Therefore we propose a new method based on the similarity of DVH to statistical distributions, which can be characterised uniquely by their entropy. The concept is defined separately for target volumes, where it is derived from the Fermi-like distribution, and for organs at risk, where the traditional approach is also considered in its derivation. The artificial illustratory and clinical examples show the properties of the entropy as the quality descriptor and compare it to the conformity index. The examples are focused to the patient target volumes, where the advantage of the concept is more evident.

Keywords

  • plan evaluation
  • IMRT
  • DVH
  • conformity index
Open Access

IMRT versus 3D-CRT for thyroid cancer

Published Online: 14 Apr 2009
Page range: 151 - 162

Abstract

IMRT versus 3D-CRT for thyroid cancer

A 3D-CRT involving a 4-field (5-field, 6-field, etc.) technique (photon and electron beams) and an alternative IMRT 7-field technique with 6 MV photon fields for thyroid cancer were compared. The IMRT allows reduction in the dose to the spinal cord of about 12 Gy and permits better coverage of the target volume with smaller standard deviation (average 4.65% for 3D-CRT as compared with 1.81% for IMRT). The time needed to prepare therapy (TPS, dosimetry, preparing boluses and electron aperture) and the session time are about the same for both techniques.

Keywords

  • thyroid
  • IMRT
  • 3D-CRT
  • Target Conformity Index
  • comparison of treatment plans
Open Access

Assesing multileaf collimator effect on the build-up region using Monte Carlo method

Published Online: 14 Apr 2009
Page range: 163 - 182

Abstract

Assesing multileaf collimator effect on the build-up region using Monte Carlo method

Previous Monte Carlo studies have investigated the multileaf collimator (MLC) contribution to the build-up region for fields in which the MLC leaves were fully blocking the openings defined by the collimation jaws. In the present work, we investigate the same effect but for symmetric and asymmetric MLC defined field sizes (2×2, 4×4, 10×10 and 3×7 cm2). A Varian 2100C/D accelerator with 120-leaf MLC is accurately modeled for a 6MV photon beam using the BEAMnrc/EGSnrc code.

Our results indicate that particles scattered from accelerator head and MLC are responsible for the increase of about 7% on the surface dose when comparing 2×2 and 10×10 cm2 fields. We found that the MLC contribution to the total build-up dose is about 2% for the 2×2 cm2 field and less than 1% for the largest fields.

Keywords

  • surface dose
  • build-up dose
  • MLC
  • IMRT
  • Monte Carlo

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