Zeitschriften und Ausgaben

Volumen 28 (2022): Heft 3 (September 2022)

Volumen 28 (2022): Heft 2 (June 2022)

Volumen 28 (2022): Heft 1 (March 2022)

Volumen 27 (2021): Heft 4 (December 2021)

Volumen 27 (2021): Heft 3 (September 2021)

Volumen 27 (2021): Heft 2 (June 2021)

Volumen 27 (2021): Heft 1 (March 2021)

Volumen 26 (2020): Heft 4 (December 2020)

Volumen 26 (2020): Heft 3 (September 2020)

Volumen 26 (2020): Heft 2 (June 2020)

Volumen 26 (2020): Heft 1 (March 2020)

Volumen 25 (2019): Heft 4 (December 2019)

Volumen 25 (2019): Heft 3 (September 2019)

Volumen 25 (2019): Heft 2 (June 2019)

Volumen 25 (2019): Heft 1 (March 2019)

Volumen 24 (2018): Heft 4 (December 2018)

Volumen 24 (2018): Heft 3 (September 2018)

Volumen 24 (2018): Heft 2 (June 2018)

Volumen 24 (2018): Heft 1 (March 2018)

Volumen 23 (2017): Heft 4 (December 2017)

Volumen 23 (2017): Heft 3 (September 2017)

Volumen 23 (2017): Heft 2 (June 2017)

Volumen 23 (2017): Heft 1 (March 2017)

Volumen 22 (2016): Heft 4 (December 2016)

Volumen 22 (2016): Heft 3 (September 2016)

Volumen 22 (2016): Heft 2 (June 2016)

Volumen 22 (2016): Heft 1 (March 2016)

Volumen 21 (2015): Heft 1 (December 2015)

Volumen 20 (2014): Heft 1 (March 2014)

Volumen 19 (2013): Heft 2 (December 2013)

Volumen 19 (2013): Heft 1 (March 2013)

Volumen 18 (2012): Heft 2 (June 2012)

Volumen 18 (2012): Heft 1 (March 2012)

Volumen 17 (2011): Heft 4 (December 2011)

Volumen 17 (2011): Heft 3 (September 2011)

Volumen 17 (2011): Heft 2 (June 2011)

Volumen 17 (2011): Heft 1 (March 2011)

Volumen 16 (2010): Heft 2 (June 2010)

Volumen 16 (2010): Heft 1 (March 2010)

Volumen 15 (2009): Heft 4 (December 2009)

Volumen 15 (2009): Heft 3 (September 2009)

Volumen 15 (2009): Heft 2 (June 2009)

Volumen 15 (2009): Heft 1 (March 2009)

Volumen 14 (2008): Heft 4 (December 2008)

Volumen 14 (2008): Heft 3 (September 2008)

Volumen 14 (2008): Heft 2 (June 2008)

Volumen 14 (2008): Heft 1 (March 2008)

Volumen 13 (2007): Heft 4 (December 2007)

Volumen 13 (2007): Heft 3 (September 2007)

Volumen 13 (2007): Heft 2 (June 2007)

Volumen 13 (2007): Heft 1 (March 2007)

Zeitschriftendaten
Format
Zeitschrift
eISSN
1898-0309
Erstveröffentlichung
30 Dec 2008
Erscheinungsweise
4 Hefte pro Jahr
Sprachen
Englisch

Suche

Volumen 24 (2018): Heft 4 (December 2018)

Zeitschriftendaten
Format
Zeitschrift
eISSN
1898-0309
Erstveröffentlichung
30 Dec 2008
Erscheinungsweise
4 Hefte pro Jahr
Sprachen
Englisch

Suche

7 Artikel
Uneingeschränkter Zugang

A review on the dosimetrical and radiobiological prediction of radiation-induced hypothyroidism in radiation therapy of head-and-neck cancer, breast cancer, and Hodgkin’s lymphoma survivors

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 137 - 148

Zusammenfassung

Abstract

A review on the radiobiological modeling of radiation-induced hypothyroidism after radiation therapy of head-and-neck cancers, breast cancer, and Hodgkin’s lymphoma is presented. The current review is based on data relating to dose-volume constrains and normal tissue complication probability (NTCP) as a function of either radiobiological or (pre)treatment-clinical parameters. Also, these data were explored in order to provide more helpful criteria for radiobiological optimization of treatment plans involving thyroid gland as a critical normal organ.

Schlüsselwörter

  • radiation therapy
  • hypothyroidism
  • head-and-neck cancer
  • breast cancer
  • Hodgkin’s lymphoma
  • NTCP modelling
  • QUANTEC
Uneingeschränkter Zugang

Developing of predictive models for pneumonitis with forward variable selection and LASSO logistic model for breast cancer patients treated with 3D-CRT

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 149 - 156

Zusammenfassung

Abstract

Purpose: To develop a multiple logistic regression model as normal tissue complication probability model by least absolute shrinkage and selection operator (LASSO) technique in breast cancer patients treated with three-dimensional conformal radiation therapy (3D-CRT), we focused on the changes of pulmonary function tests to achieve the optimal predictive parameters for the occurrence of symptomatic radiation pneumonitis (SRP).

Materials and methods: Dosimetric and spirometry data of 60 breast cancer patients were analyzed. Pulmonary function tests were done before RT, after completion of RT, 3, and 6 months after RT. Multiple logistic regression model was used to obtain the effective predictive parameters. Forward selection method was applied in NTCP model to determine the effective risk factors from obtained different parameters.

Results: Symptomatic radiation pneumonitis was observed in five patients. Significant changes in pulmonary parameters have been observed at six months after RT. The parameters of mean lung dose (MLD), bridge separation (BS), mean irradiated lung volume (ILVmean), and the percentage of the ipsilateral lung volume that received dose of 20 Gy (IV20) introduced as risk factors using the LASSO technique for SRP in a multiple normal tissue complication probability model in breast cancer patients treated with 3D-CRT. The BS, central lung distance (CLD) and ILV in tangential field have obtained as 23.5 (20.9-26.0) cm, 2.4 (1.5-3.3) cm, and 12.4 (10.6-14.3) % of lung volume in radiation field in patients without pulmonary complication, respectively.

Conclusion: The results showed that if BS, CLD, and ILV are more than 23 cm, 2 cm, and 12%, respectively, so incidence of SRP in the patients will be considerable. Our multiple NTCP LASSO model for breast cancer patients treated with 3D-CRT showed that in order to have minimum probability of SRP occurrence, parameters of BS, IV20, ILV and especially MLD would be kept in minimum levels. Considering dose-volume histogram, the mean lung dose factor is most important parameter which minimizing it in treatment planning, minimizes the probability of SRP and consequently improves the quality of life in breast cancer patients.

Schlüsselwörter

  • radiation therapy
  • radiobiological model
  • breast cancer
  • pneumonitis
Uneingeschränkter Zugang

Optimization of double layered beam shaping assembly using genetic algorithm

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 157 - 164

Zusammenfassung

Abstract

The genetic algorithm method is a new method used to obtain radiation beams that meet the IAEA requirements. This method is used in optimization of configurations and compositions of materials that compose double layered Beam Shaping Assembly (BSA). The double layered BSA is modeled as having two layers of material for each of the components, which are the moderator, reflector, collimator, and filter. Up to 21st generation, the optimization results in four (4) individuals having the capacity to generate the most optimum radiation beams. The best configuration, producing the most optimum radiation beams, is attained by using combinations of materials, that is by combining Al with either one of CaF2 and PbF2for moderator; combining Pb material with either Ni or Pb for reflector; combining Ni and either FeC or C for collimator, and FeC+LiF and Cd for fast and thermal neutron filter. The parameters of radiation resulted from the four configurations of double layer BSA adequately satisfy the standard of the IAEA.

Schlüsselwörter

  • optimization
  • double layered BSA
  • genetic algorithm
  • radiation beams
  • IAEA
Uneingeschränkter Zugang

Gantry angle classification with a fluence map in intensity-modulated radiotherapy for prostate cases using machine learning

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 165 - 169

Zusammenfassung

Abstract

We investigated the gantry-angle classifier performance with a fluence map using three machine-learning algorithms, and compared it with human performance. Eighty prostate cases were investigated using a seven-field-intensity modulated radiotherapy treatment (IMRT) plan with beam angles of 0°, 50°, 100°, 155°, 205°, 260°, and 310°. The k-nearest neighbor (k-NN), logistic regression (LR), and support vector machine (SVM) algorithms were used. In the observer test, three radiotherapists assessed the gantry angle classification in a blind manner. The precision and recall rates were calculated for the machine learning and observer test. The average precision rate of the k-NN and LR algorithms were 94.8% and 97.9%, respectively. The average recall rate of the k-NN and LR algorithms were 94.3% and 97.9%, respectively. The SVM had 100% precision and recall rates. The gantry angles of 0°, 155°, and 205° had an accuracy of 100% in all algorithms. In the observer test, average precision and recall rates were 82.6% and 82.6%, respectively. All observers could easily classify the gantry angles of 0°, 155°, and 205° with a high degree of accuracy. Misclassifications occurred in gantry angles of 50°, 100°, 260°, and 310°. Machine learning could better classify gantry angles for prostate IMRT than human beings. In particular, the SVM algorithm had a perfect classification of 100%.

Schlüsselwörter

  • classification
  • machine learning
  • fluence map
  • IMRT
Uneingeschränkter Zugang

Implementation of compensator-based intensity modulated radiotherapy with a conventional telecobalt machine using missing tissue approach

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 171 - 179

Zusammenfassung

Abstract

Objectives: The present study aimed to generate intensity-modulated beams with compensators for a conventional telecobalt machine, based on dose distributions generated with a treatment planning system (TPS) performing forward planning, and cannot directly simulate a compensator.

Materials and Methods: The following materials were selected for compensator construction: Brass, Copper and Perspex (PMMA). Boluses with varying thicknesses across the surface of a tissue-equivalent phantom were used to achieve beam intensity modulations during treatment planning with the TPS. Beam data measured for specific treatment parameters in a full scatter water phantom with a 0.125 cc cylindrical ionization chamber, with a particular compensator material in the path of beams from the telecobalt machine, and that without the compensator but the heights of water above the detector adjusted to get the same detector readings as before, were used to develop and propose a semi-empirical equation for converting a bolus thickness to compensator material thickness, such that any point within the phantom would receive the planned dose. Once the dimensions of a compensator had been determined, the compensator was constructed using the cubic pile method. The treatment plans generated with the TPS were replicated on the telecobalt machine with a bolus within each beam represented with its corresponding compensator mounted on the accessory holder of the telecobalt machine.

Results: Dose distributions measured in the tissue-equivalent phantom with calibrated Gafchromic EBT2 films for compensators constructed based on the proposed approach, were comparable to those of the TPS with deviation less than or equal to ± 3% (mean of 2.29 ± 0.61%) of the measured doses, with resultant confidence limit value of 3.21. Conclusion: The use of the proposed approach for clinical application is recommended, and could facilitate the generation of intensity-modulated beams with limited resources using the missing tissue approach rendering encouraging results.

Schlüsselwörter

  • telecobalt machine
  • bolus
  • compensator
  • Gafchromic film
  • intensity modulated
Uneingeschränkter Zugang

Can Gafchromic EBT3 films effectively characterize small fields of 6 MV unflattened photon beams of Cyberknife system?

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 181 - 187

Zusammenfassung

Abstract

Shielded silicon diodes are commonly employed in commissioning of Cyberknife 6 MV photon beams. This study aims to measure output factors, off centered ratio (OCR), percentage depth dose (PDD) of 6 MV photons using shielded and unshielded diodes and to compare with Gafchromic EBT3 film measurements to investigate whether EBT3 could effectively characterize small 6 MV photon beams. Output factors, OCR and PDD were measured with shielded and unshielded silicon detectors in a radiation field analyzer system at reference condition. Water equivalent solid phantom were used while irradiating EBT3 films. From multiuser data, diodes underestimated output factor by 3% for collimator fields ≤ 10 mm, while EBT3 underestimated the output factor by 3.9% for 5 mm collimator. 1D Gamma analysis of OCR between diode and film, results in gamma ≤ 1 for all measured points with 1 mm distance to agreement (DTA) and 1% relative dose difference (DD). Dose at surface is overestimated with diodes compared to EBT3. PDD results were within 2% relative dose values between diode and EBT3 except for 5 mm collimator. Except for small collimator fields of up to 10 mm, results of output factor, OCR, PDD of all detectors used in this study exhibited similar results. Relative dose measurements with Gafchromic EBT3 in this work show that EBT3 films can be used effectively as an independent tool to verify commissioning beam data of small fields only after careful verification of methodology for any systematic errors with appropriate readout procedure.

Schlüsselwörter

  • diode detectors
  • GafChromic EBT3
  • small fields
  • output factor
  • off centered ratio
  • percentage depth dose
Uneingeschränkter Zugang

Ultraviolet ray irradiation duration for the pre-exposure of Gafchromic EBT2

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 189 - 193

Zusammenfassung

Abstract

The strength and density change of the ultraviolet (UV) ray of Gafchromic EBT2 were investigated. Previous studies suggested that UV-A rays can be substituted for the x-ray double-exposure technique to correct Gafchromic EBT2’s non-uniformity error. In this study, we aimed to determine the appropriate strength of UV-A rays for irradiating an active layer that would correct the non-uniformity error of Gafchromic EBT2.

UV-A rays with a wavelength of 375 nm were used to irradiate Gafchromic EBT2 in various durations, and the resulting density change was investigated. To correct Gafchromic EBT2’s non-uniformity error, a pre-irradiation with a UV-A lamp was conducted at a distance of 72 cm for 30 min. To determine the most appropriate irradiation duration, a UV light-emitting diode generating UV-A of 375 nm was used to irradiate the Gafchromic EBT2 film with varying durations of 1, 2, 3, 4, 5, 10, 15, 20, 25, and 30 min at a distance of 5.3 cm. A 12.7 diameter region of interest was set by the irradiation area, and a histogram of pixel values was created. The condition options were decided based on two important requirements: 1) no zero values of the mode and seconds exist, and 2) the 1/10 value of the mode intersects both histogram sleeves.

In the case of Gafchromic EBT2, the irradiation strength was 85.43 mJ/cm2 for one minute in which the pixel value of mean ± SD was 255.34 ± 213.29. The irradiation duration of 4 min was the border duration of the above two conditions. When a UV ray of 375 nm wavelength is used to irradiate Gafchromic EBT2 as a substitute for x-ray exposure, the 4-min pre-irradiation duration (341.74 mJ/cm2) is demonstrably sufficient.

Schlüsselwörter

  • ultraviolet rays
  • non-uniformity
  • Gafchromic film
  • radiation measurement
  • computed tomography
7 Artikel
Uneingeschränkter Zugang

A review on the dosimetrical and radiobiological prediction of radiation-induced hypothyroidism in radiation therapy of head-and-neck cancer, breast cancer, and Hodgkin’s lymphoma survivors

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 137 - 148

Zusammenfassung

Abstract

A review on the radiobiological modeling of radiation-induced hypothyroidism after radiation therapy of head-and-neck cancers, breast cancer, and Hodgkin’s lymphoma is presented. The current review is based on data relating to dose-volume constrains and normal tissue complication probability (NTCP) as a function of either radiobiological or (pre)treatment-clinical parameters. Also, these data were explored in order to provide more helpful criteria for radiobiological optimization of treatment plans involving thyroid gland as a critical normal organ.

Schlüsselwörter

  • radiation therapy
  • hypothyroidism
  • head-and-neck cancer
  • breast cancer
  • Hodgkin’s lymphoma
  • NTCP modelling
  • QUANTEC
Uneingeschränkter Zugang

Developing of predictive models for pneumonitis with forward variable selection and LASSO logistic model for breast cancer patients treated with 3D-CRT

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 149 - 156

Zusammenfassung

Abstract

Purpose: To develop a multiple logistic regression model as normal tissue complication probability model by least absolute shrinkage and selection operator (LASSO) technique in breast cancer patients treated with three-dimensional conformal radiation therapy (3D-CRT), we focused on the changes of pulmonary function tests to achieve the optimal predictive parameters for the occurrence of symptomatic radiation pneumonitis (SRP).

Materials and methods: Dosimetric and spirometry data of 60 breast cancer patients were analyzed. Pulmonary function tests were done before RT, after completion of RT, 3, and 6 months after RT. Multiple logistic regression model was used to obtain the effective predictive parameters. Forward selection method was applied in NTCP model to determine the effective risk factors from obtained different parameters.

Results: Symptomatic radiation pneumonitis was observed in five patients. Significant changes in pulmonary parameters have been observed at six months after RT. The parameters of mean lung dose (MLD), bridge separation (BS), mean irradiated lung volume (ILVmean), and the percentage of the ipsilateral lung volume that received dose of 20 Gy (IV20) introduced as risk factors using the LASSO technique for SRP in a multiple normal tissue complication probability model in breast cancer patients treated with 3D-CRT. The BS, central lung distance (CLD) and ILV in tangential field have obtained as 23.5 (20.9-26.0) cm, 2.4 (1.5-3.3) cm, and 12.4 (10.6-14.3) % of lung volume in radiation field in patients without pulmonary complication, respectively.

Conclusion: The results showed that if BS, CLD, and ILV are more than 23 cm, 2 cm, and 12%, respectively, so incidence of SRP in the patients will be considerable. Our multiple NTCP LASSO model for breast cancer patients treated with 3D-CRT showed that in order to have minimum probability of SRP occurrence, parameters of BS, IV20, ILV and especially MLD would be kept in minimum levels. Considering dose-volume histogram, the mean lung dose factor is most important parameter which minimizing it in treatment planning, minimizes the probability of SRP and consequently improves the quality of life in breast cancer patients.

Schlüsselwörter

  • radiation therapy
  • radiobiological model
  • breast cancer
  • pneumonitis
Uneingeschränkter Zugang

Optimization of double layered beam shaping assembly using genetic algorithm

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 157 - 164

Zusammenfassung

Abstract

The genetic algorithm method is a new method used to obtain radiation beams that meet the IAEA requirements. This method is used in optimization of configurations and compositions of materials that compose double layered Beam Shaping Assembly (BSA). The double layered BSA is modeled as having two layers of material for each of the components, which are the moderator, reflector, collimator, and filter. Up to 21st generation, the optimization results in four (4) individuals having the capacity to generate the most optimum radiation beams. The best configuration, producing the most optimum radiation beams, is attained by using combinations of materials, that is by combining Al with either one of CaF2 and PbF2for moderator; combining Pb material with either Ni or Pb for reflector; combining Ni and either FeC or C for collimator, and FeC+LiF and Cd for fast and thermal neutron filter. The parameters of radiation resulted from the four configurations of double layer BSA adequately satisfy the standard of the IAEA.

Schlüsselwörter

  • optimization
  • double layered BSA
  • genetic algorithm
  • radiation beams
  • IAEA
Uneingeschränkter Zugang

Gantry angle classification with a fluence map in intensity-modulated radiotherapy for prostate cases using machine learning

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 165 - 169

Zusammenfassung

Abstract

We investigated the gantry-angle classifier performance with a fluence map using three machine-learning algorithms, and compared it with human performance. Eighty prostate cases were investigated using a seven-field-intensity modulated radiotherapy treatment (IMRT) plan with beam angles of 0°, 50°, 100°, 155°, 205°, 260°, and 310°. The k-nearest neighbor (k-NN), logistic regression (LR), and support vector machine (SVM) algorithms were used. In the observer test, three radiotherapists assessed the gantry angle classification in a blind manner. The precision and recall rates were calculated for the machine learning and observer test. The average precision rate of the k-NN and LR algorithms were 94.8% and 97.9%, respectively. The average recall rate of the k-NN and LR algorithms were 94.3% and 97.9%, respectively. The SVM had 100% precision and recall rates. The gantry angles of 0°, 155°, and 205° had an accuracy of 100% in all algorithms. In the observer test, average precision and recall rates were 82.6% and 82.6%, respectively. All observers could easily classify the gantry angles of 0°, 155°, and 205° with a high degree of accuracy. Misclassifications occurred in gantry angles of 50°, 100°, 260°, and 310°. Machine learning could better classify gantry angles for prostate IMRT than human beings. In particular, the SVM algorithm had a perfect classification of 100%.

Schlüsselwörter

  • classification
  • machine learning
  • fluence map
  • IMRT
Uneingeschränkter Zugang

Implementation of compensator-based intensity modulated radiotherapy with a conventional telecobalt machine using missing tissue approach

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 171 - 179

Zusammenfassung

Abstract

Objectives: The present study aimed to generate intensity-modulated beams with compensators for a conventional telecobalt machine, based on dose distributions generated with a treatment planning system (TPS) performing forward planning, and cannot directly simulate a compensator.

Materials and Methods: The following materials were selected for compensator construction: Brass, Copper and Perspex (PMMA). Boluses with varying thicknesses across the surface of a tissue-equivalent phantom were used to achieve beam intensity modulations during treatment planning with the TPS. Beam data measured for specific treatment parameters in a full scatter water phantom with a 0.125 cc cylindrical ionization chamber, with a particular compensator material in the path of beams from the telecobalt machine, and that without the compensator but the heights of water above the detector adjusted to get the same detector readings as before, were used to develop and propose a semi-empirical equation for converting a bolus thickness to compensator material thickness, such that any point within the phantom would receive the planned dose. Once the dimensions of a compensator had been determined, the compensator was constructed using the cubic pile method. The treatment plans generated with the TPS were replicated on the telecobalt machine with a bolus within each beam represented with its corresponding compensator mounted on the accessory holder of the telecobalt machine.

Results: Dose distributions measured in the tissue-equivalent phantom with calibrated Gafchromic EBT2 films for compensators constructed based on the proposed approach, were comparable to those of the TPS with deviation less than or equal to ± 3% (mean of 2.29 ± 0.61%) of the measured doses, with resultant confidence limit value of 3.21. Conclusion: The use of the proposed approach for clinical application is recommended, and could facilitate the generation of intensity-modulated beams with limited resources using the missing tissue approach rendering encouraging results.

Schlüsselwörter

  • telecobalt machine
  • bolus
  • compensator
  • Gafchromic film
  • intensity modulated
Uneingeschränkter Zugang

Can Gafchromic EBT3 films effectively characterize small fields of 6 MV unflattened photon beams of Cyberknife system?

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 181 - 187

Zusammenfassung

Abstract

Shielded silicon diodes are commonly employed in commissioning of Cyberknife 6 MV photon beams. This study aims to measure output factors, off centered ratio (OCR), percentage depth dose (PDD) of 6 MV photons using shielded and unshielded diodes and to compare with Gafchromic EBT3 film measurements to investigate whether EBT3 could effectively characterize small 6 MV photon beams. Output factors, OCR and PDD were measured with shielded and unshielded silicon detectors in a radiation field analyzer system at reference condition. Water equivalent solid phantom were used while irradiating EBT3 films. From multiuser data, diodes underestimated output factor by 3% for collimator fields ≤ 10 mm, while EBT3 underestimated the output factor by 3.9% for 5 mm collimator. 1D Gamma analysis of OCR between diode and film, results in gamma ≤ 1 for all measured points with 1 mm distance to agreement (DTA) and 1% relative dose difference (DD). Dose at surface is overestimated with diodes compared to EBT3. PDD results were within 2% relative dose values between diode and EBT3 except for 5 mm collimator. Except for small collimator fields of up to 10 mm, results of output factor, OCR, PDD of all detectors used in this study exhibited similar results. Relative dose measurements with Gafchromic EBT3 in this work show that EBT3 films can be used effectively as an independent tool to verify commissioning beam data of small fields only after careful verification of methodology for any systematic errors with appropriate readout procedure.

Schlüsselwörter

  • diode detectors
  • GafChromic EBT3
  • small fields
  • output factor
  • off centered ratio
  • percentage depth dose
Uneingeschränkter Zugang

Ultraviolet ray irradiation duration for the pre-exposure of Gafchromic EBT2

Online veröffentlicht: 24 Dec 2018
Seitenbereich: 189 - 193

Zusammenfassung

Abstract

The strength and density change of the ultraviolet (UV) ray of Gafchromic EBT2 were investigated. Previous studies suggested that UV-A rays can be substituted for the x-ray double-exposure technique to correct Gafchromic EBT2’s non-uniformity error. In this study, we aimed to determine the appropriate strength of UV-A rays for irradiating an active layer that would correct the non-uniformity error of Gafchromic EBT2.

UV-A rays with a wavelength of 375 nm were used to irradiate Gafchromic EBT2 in various durations, and the resulting density change was investigated. To correct Gafchromic EBT2’s non-uniformity error, a pre-irradiation with a UV-A lamp was conducted at a distance of 72 cm for 30 min. To determine the most appropriate irradiation duration, a UV light-emitting diode generating UV-A of 375 nm was used to irradiate the Gafchromic EBT2 film with varying durations of 1, 2, 3, 4, 5, 10, 15, 20, 25, and 30 min at a distance of 5.3 cm. A 12.7 diameter region of interest was set by the irradiation area, and a histogram of pixel values was created. The condition options were decided based on two important requirements: 1) no zero values of the mode and seconds exist, and 2) the 1/10 value of the mode intersects both histogram sleeves.

In the case of Gafchromic EBT2, the irradiation strength was 85.43 mJ/cm2 for one minute in which the pixel value of mean ± SD was 255.34 ± 213.29. The irradiation duration of 4 min was the border duration of the above two conditions. When a UV ray of 375 nm wavelength is used to irradiate Gafchromic EBT2 as a substitute for x-ray exposure, the 4-min pre-irradiation duration (341.74 mJ/cm2) is demonstrably sufficient.

Schlüsselwörter

  • ultraviolet rays
  • non-uniformity
  • Gafchromic film
  • radiation measurement
  • computed tomography

Planen Sie Ihre Fernkonferenz mit Scienceendo