Radiochromic film is a useful tool for beam quality assurance, but accurate response assessment of the film is still a problem. In this study, the response uncertainties of HDV2 film were investigated using a flatbed ...Radiochromic film is a useful tool for beam quality assurance, but accurate response assessment of the film is still a problem. In this study, the response uncertainties of HDV2 film were investigated using a flatbed scanner from both the scanning settings and interscan variability. Scanning settings are fixed conditions for scanning, including scanning resolution and focus setting.In this study, multipeak distributions of pixel values were found under some dots-per-inch values, which should be avoided, and the optimal setting of 2000 dpi without this problem was selected. By changing the focus setting, the relative standard deviation of pixel values was reduced by 36–50%. The influence of the interscan variability induced by three factors was investigated, including the outside illumination intensity, film homogeneity, and operating temperature. Scanning the film before and after irradiation at the same position was recommended. Moreover, the suitable operating temperature range for the scanner was found to be 15–24 °C, which results in stable film responses. Regarding the studied factors, correction methods and strategies were proposed, and the accurate response assessment of HDV2 film was realized. Finally, a standard operating procedure for response assessment of films was introduced. It can help other researchers study more scanners, films, and particle types.展开更多
Purpose: To assess the possibility of using a public calibration function for radiochromic film dosimetry in dose QA of highly conformal treatment plans. Methods: EBT3 film calibration strips (3.5 × 20 cm2 from l...Purpose: To assess the possibility of using a public calibration function for radiochromic film dosimetry in dose QA of highly conformal treatment plans. Methods: EBT3 film calibration strips (3.5 × 20 cm2 from lots A101212 and A011713) were exposed on a Varian Trilogy at a facility to a 10 × 10 cm2 open field at doses of 80, 160, 320 cGy using 6MV photons. Together with a strip of unexposed film from the same lot, the exposed films were digitized in a single scan using different Epson 10,000 XL scanners at two different facilities. The dose-response data for each color-channel from each facility were generated using the same calibration function X(D) = a + b/(D - c), where X(D) is the response at dose D and a, b and c are the coefficients. Different batches of EBT3 film were exposed to a VMAT beam. These films, plus two reference strips exposed to doses of zero and 160 cGy, were digitized on the scanners at the two facilities. Using the multi-channel dosimetry method and One-scan protocol (Med Phys, 39: 6339-6349, 2012) the recorded doses on the VMAT films were calculated and the results were compared with the VMAT plan using a Gamma index of 3%/3 mm. Results: The passing rates obtained for dose maps calculated for all combinations of VMAT images and calibration functions were nearly unchanged, using the One-scan protocol. Also, in all cases a passing rate of >99% was obtained for Gamma index of 3%/3 mm. On the other hand, if the One-scan protocol was not employed, the dose maps for VMAT images and calibration functions from different scanners showed poor correlation with the treatment plan. This is probably due to the scan-to-scan variability. Conclusions: The authors have found that it is feasible to use a public calibration function for a given radiochromic film lot using the same methodology, One-scan protocol, for patient-specific QA.展开更多
A two-dimensional dose detector for ion beam is required in many high energy density physics experiments.As a solid detector,the GAFChromic film offers a good spatial resolution and dosimetric accuracy.For an absolute...A two-dimensional dose detector for ion beam is required in many high energy density physics experiments.As a solid detector,the GAFChromic film offers a good spatial resolution and dosimetric accuracy.For an absolute dose measurement,the relative effectiveness,which represents the darkening efficiency of the film to a radiation source,needs to be taken into consideration.In this contribution,the dose-response of HD-V2 to argon ions is presented for the first time.The calibration was taken over the dose range of 65 Gy-660 Gy with 8-keV argon ions.The response of net optical density is from 0.01 to 0.05.Triple-color dose-response functions are derived.The relative effectiveness for the argon ion beams is about 5%,much lower than that of protons and carbon ions.To explain this effect,the inactivation probability based on track theory of ion bombardment is proposed.Furthermore,a theoretical prediction of the relative effectiveness for single ion is presented,showing the dependence of the darkening efficiency on the atomic number and the incident energy of ions.展开更多
Accurate dose measurement tools are needed to evaluate the radiation dose delivered to patients by using modern and sophisticated radiation therapy techniques. However, the adequate tools which enable us to directly m...Accurate dose measurement tools are needed to evaluate the radiation dose delivered to patients by using modern and sophisticated radiation therapy techniques. However, the adequate tools which enable us to directly measure the dose distributions in threedimensional(3D) space are not commonly available. One such 3D dose measurement device is the polymerbased dosimeter, which changes the material property in response to radiation. These are available in the gel form as polymer gel dosimeter(PGD) and ferrous gel dosimeter(FGD) and in the solid form as solid plastic dosimeter(SPD). Those are made of a continuous uniform medium which polymerizes upon irradiation. Hence, the intrinsic spatial resolution of those dosimeters is very high, and it is only limited by the method by which one converts the dose information recorded by the medium to the absorbed dose. The current standard methods of the dose quantification are magnetic resonance imaging, optical computed tomography, and X-ray computed tomography. In particular, magnetic resonance imaging is well established as a method for obtaining clinically relevant dosimetric data by PGD and FGD. Despite the likely possibility of doing 3D dosimetry by PGD, FGD or SPD, the tools are still lacking wider usages for clinical applications. In this review article, we summarize the current status of PGD, FGD, and SPD and discuss the issue faced by these for wider acceptance in radiation oncology clinic and propose some directions for future development.展开更多
In this work, a method to reduce increase in optical density (OD) caused by multiple scanning in radiochromic film dosimetry in combination with a flatbed scanner is presented. Gafchromic EBT3 films are scanned with E...In this work, a method to reduce increase in optical density (OD) caused by multiple scanning in radiochromic film dosimetry in combination with a flatbed scanner is presented. Gafchromic EBT3 films are scanned with Epson Pro 1680 Expression scanner and time intervals of 15 minutes and 30 minutes are observed between consecutive scans to reduce the increase in temperature of the scanner. The maximum variations in OD after consecutive scans are calculated and compared to the values obtained for scans without interruption. For film irradiated to 3 Gy, a time interval of 15 minutes between two successive scans leads to a reduction of the OD increase of 56.2% compared to when films are scanned without interruption. Reductions of OD increase of 86.72% and 78.72% respectively for film irradiated to 1 Gy and 2 Gy are obtained when a time interval of 30 minutes is left between two successive scans. These results show that when time intervals are observed between consecutive scans, the increase in OD has significantly reduced. However, the method has the drawback of increasing the time needed to perform radiochromic film dosimetry.展开更多
Purpose: During computed tomography (CT) helical scanning mode the patient surface dose distribution is assumed to be non-uniform, therefore point dose measurement methods may lead to imprecise estimation of the radia...Purpose: During computed tomography (CT) helical scanning mode the patient surface dose distribution is assumed to be non-uniform, therefore point dose measurement methods may lead to imprecise estimation of the radiation dose received by the patient skin in particular. We have used XRQA2 films as in-vivo dosimeters to measure the entrance skin dose during sinus exams. Methods: The films were placed under the patient head rest in order to sample the entrance surface dose in-vivo. We have performed in-vivo film irradiation on 23 patients in this study to verify the clinical suitability of the method and were found adequate. Results: The measured average ESD in the sinus exam was 11.7 ± 1.0 mGy, the PSD was 15.7 ± 1.7 mGy and the CTDI(vol) was 13.3 ± 0.1 mGy. The ratio of ESD/CTDI(vol) and PSD/CTDI(vol) was 0.88 and 1.18 respectively. The results indicate that the scanner registered CTDI(vol) underestimates the PSD and in the same time it overestimates the ESD by 18% and 13.6% respectively. Conclusion: The observed differences between the ESD, PSD and CTDI(vol) although seem small for the radiation dose range measured during CT of the sinus [13.2 - 13.4] mGy, but important for the medical physicist to know, since monitoring of patients’ doses from CT examinations is becoming more mandatory. The use of radiochromic film as in-vivo dosimeter does not interfere with the clinical radiological exam and does not produce any image artifacts. The method can be used to study other CT examinations specially the ones with large beam width, high pitch factor and high dose exams. The method allows measurement of the peak skin dose, examination of the CT dose profile and the 2D dose distribution in the XZ plan.展开更多
Purpose: To evaluate the measured dose distributions using radiochromic EBT2 films for small fields in iPlan (BrainLab) commissioning. Methods: Radiochromic EBT2 films were irradiated with 6 MV photons on a Varian Tri...Purpose: To evaluate the measured dose distributions using radiochromic EBT2 films for small fields in iPlan (BrainLab) commissioning. Methods: Radiochromic EBT2 films were irradiated with 6 MV photons on a Varian Trilogy linac using polystyrene phantoms. The measurements included dose profiles and depth doses for field sizes of 1 × 1, 2 × 2, 3 × 3, 4 × 4, and 10 × 10 cm2 etc. The dose profile measurements were taken at the depth of 5 cm. The calibration films were irradiated at dmax(1.4 cm) for doses up to 6 Gy. Films were scanned using an Epson 10,000 XL flatbed scanner with 72 dpi resolution. Pixel values were converted to doses using the established calibration-curve. The 2D dose distributions were generated from the film data analysis. In-house software was utilized to compare the measured doses from films with the treatment planning data. In addition, selected patients’ SRS fields were also measured with the EBT2 films for comparison with iPlan. An EDGETM detector was also used to check the centralaxis doses for the SRS patients’ measurements. Results and Discussion: The measured planar dose distributions achieved more than 98% and 95% passing rates with a set of 2%/2 mm dose and DTA criteria for all square fields and all patient treatment fields (2), respectively. Agreement with measurement data with the EDGETM detector at the central axis (±1%) was found with the plan data. This is the first report for SRS small photon-field measurement using the latest radiochromic film, EBT2. The results shown in this work indicate that the use of EBT2 film provides accurate dosimetry measure-ments for small photon beams. The measurements show excellent agreement with the iPlan TP commissioning data. Conclusions: The patient-specific EBT2 film QA for iPlan SRS patients showed good results. The EBT2 films could potentially be a useful dosimeter in verification of commissioning as well as patient-specific QA for SRS cases.展开更多
Background and Aim: Irradiation methods such as double scattering method and spot scanning method have been used in proton beam treatment devices. In the scattering method, a ridge filter or a range modulation wheel i...Background and Aim: Irradiation methods such as double scattering method and spot scanning method have been used in proton beam treatment devices. In the scattering method, a ridge filter or a range modulation wheel is used to create a spread-out Bragg peak, but the distribution at the patient position may change due to positional deviation of the incident beam. Therefore, assessment of the incident position of the beam is very important even in the scattering method. To investigate the width and distribution of the proton beam before entering the RMW, a radiochromic film was installed at the outlet of the transport pipe and the entrance of the profile-monitoring detector. Methods: In this study, the distributions of the beam at the exit of the transport pipe and the entrance of the monitor detector were measured using films. The beam width was measured from the full width at half maximum of the profile obtained from the distribution. Measurements were conducted every month for 10 months. Results: Beams of widths ranging from 1.82 to 2.30 mm in the horizontal direction and 4.25 to 5.33 mm in the vertical direction were outputted from the exit of the transport pipe. Beams of widths ranging from 2.16 to 2.67 mm in the horizontal direction and 4.06 to 5.31 mm in the vertical direction were outputted from the entrance of the monitor detector. The maximum width fluctuation for 10 months was 0.55 mm in the horizontal direction and 1.26 mm in the vertical direction at the entrance of the monitor detector. Conclusions: The distribution was obtained before the proton beam was scattered by the scatterer, and then we propose a method to periodically measure and monitor the changes in the beam distributions every month.展开更多
Radiochromic film with a dye incorporated into the radiation sensitive layer [Gafchromic EBT2, Ashland, Inc.] may be digitized by a color transparency scanner, digitally processed, and calibrated so that a digital ima...Radiochromic film with a dye incorporated into the radiation sensitive layer [Gafchromic EBT2, Ashland, Inc.] may be digitized by a color transparency scanner, digitally processed, and calibrated so that a digital image in units of radiation absorbed dose is obtained. A transformation from raw scanner values to dose values was developed based upon a principal component analysis of the optical densities of the red, green and blue channels of the color image of a dose of 0.942 Gy delivered by a Sr-90/Y-90 disk-shaped source. In the order of increasing eigenvalue, the three eigenimages of the principal component analysis contained, by visual inspection, 1) mainly noise;2) mainly a pattern of irregular streaks;and 3) most of the expected dose information along with some of the same background streaking that predominated in the second eigenimage. The combination of the second and third eigenimages that minimized the background streaking was converted into a transformation of the red, green and blue channels’ optical densities and applied to films with a range of doses from 0 to 63.7 Gy. The curve of dose vs. processed optical density was fit by a two-phase association curve. This processing was applied to a film exposed from its edge by a different Y-90 source in a configuration that was modeled by Monte Carlo simulation. The depth-dose curves of the measurement and simulation agree closely, suggesting that this approach is a valid method of processing EBT2 radiochromic film into maps of radiation absorbed dose.展开更多
Purpose: The aim of this study was to develop a method for the direct measurement of electron beam width and distribution at the scattering foil on the carrousel in a medical linear accelerator gantry head, which diff...Purpose: The aim of this study was to develop a method for the direct measurement of electron beam width and distribution at the scattering foil on the carrousel in a medical linear accelerator gantry head, which differs from an existing indirect method for measuring the focal spot size using a camera or metallic slit located outside the gantry head. Methods: The electron beam emitted by the linear accelerator was used to irradiate radiochromic film mounted on the scattering foil on the carrousel, which was not used for clinical treatment. The electron beam width at the scattering foil position was then evaluated using the full width at half maximum of the Gaussian distribution approximated from each one dimensional distribution of the irradiated radiochromic film. Results: The electron beam width at the scattering foil position was found to be 3.1 to 6.4 mm in the crossline direction and 2.8 to 5.5 mm in the inline direction with electron energy of 4 to 16 MeV. The two-dimensional distribution of the electron beam was therefore elliptical or distorted in shape, not circular. Conclusions: Direct measurement of the electron beam width at the scattering foil in the carrousel of a medical linear accelerator is possible, though the use of lower sensitivity film in addition to indirect methods is expected to bring about better results. However, as this method does not allow for direct measurement of the incident angle of the accelerated electron beam, further improvements and refinements are still needed.展开更多
Purpose: To study and compare the dose response curves of the new GafChromic EBT3 film for megavoltage and kilovoltage x-ray beams, with different spatial resolutions. Methods: EBT3 films (lot#A101711-02) were exposed...Purpose: To study and compare the dose response curves of the new GafChromic EBT3 film for megavoltage and kilovoltage x-ray beams, with different spatial resolutions. Methods: EBT3 films (lot#A101711-02) were exposed to each x-ray beam (6 MV, 15 MV, and 50 kV) at 7 dose values (50-3200 cGy). Each film piece was scanned three consecutive times in the center of Epson 10000XL flatbed scanner in 48-bit color at two separate spatial resolutions of 75 and 300 dpi. The data were analyzed using ImageJ and, for each scanned image, a region of interest (ROI) of 2 × 2 cm2 at the field center was selected to obtain the mean pixel value with its standard deviation in the ROI. For each energy, dose value and spatial resolution, the average net optical density (netOD) and its associated uncertainty were determined. The Student’s t-test was performed to evaluate the statistical differences between the net OD/dose values of the three energy modalities, with different color channels and spatial resolutions. Results and Discussion: The dose response curves for the three energy modalities were compared in three color channels. Weak energy dependence was found. For doses above 100 cGy, no statistical differences were observed between 6 and 15 MV beams, regardless of spatial resolution and color channel. However, statistical differences were observed between 50 kV and the megavoltage beams. The degree of energy dependence (from MV to 50 kV) was found to be a function of color channel, dose level, and spatial resolution. Conclusions: The dose response curves for GafChromic EBT3 films were found to be weakly dependent on the energy of the photon beams from 6 MV to 15 MV. For very low energy photon (e.g. 50 kV), variation of more than 11% due to the energy-dependence is observed, depending on the absorbed dose, spatial resolution and color channel used.展开更多
基金supported by the National Natural Science Foundation of China(No.11805100)the Natural Science Foundation of Jiangsu Province(No.BK20180415)+3 种基金the National Key Research and Development Program(No.2016YFE0103600)the National Key Research and Development Program(No.2017YFC0107700)the Foundation of Graduate Innovation Center in NUAA(No.kfjj20180614)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Radiochromic film is a useful tool for beam quality assurance, but accurate response assessment of the film is still a problem. In this study, the response uncertainties of HDV2 film were investigated using a flatbed scanner from both the scanning settings and interscan variability. Scanning settings are fixed conditions for scanning, including scanning resolution and focus setting.In this study, multipeak distributions of pixel values were found under some dots-per-inch values, which should be avoided, and the optimal setting of 2000 dpi without this problem was selected. By changing the focus setting, the relative standard deviation of pixel values was reduced by 36–50%. The influence of the interscan variability induced by three factors was investigated, including the outside illumination intensity, film homogeneity, and operating temperature. Scanning the film before and after irradiation at the same position was recommended. Moreover, the suitable operating temperature range for the scanner was found to be 15–24 °C, which results in stable film responses. Regarding the studied factors, correction methods and strategies were proposed, and the accurate response assessment of HDV2 film was realized. Finally, a standard operating procedure for response assessment of films was introduced. It can help other researchers study more scanners, films, and particle types.
文摘Purpose: To assess the possibility of using a public calibration function for radiochromic film dosimetry in dose QA of highly conformal treatment plans. Methods: EBT3 film calibration strips (3.5 × 20 cm2 from lots A101212 and A011713) were exposed on a Varian Trilogy at a facility to a 10 × 10 cm2 open field at doses of 80, 160, 320 cGy using 6MV photons. Together with a strip of unexposed film from the same lot, the exposed films were digitized in a single scan using different Epson 10,000 XL scanners at two different facilities. The dose-response data for each color-channel from each facility were generated using the same calibration function X(D) = a + b/(D - c), where X(D) is the response at dose D and a, b and c are the coefficients. Different batches of EBT3 film were exposed to a VMAT beam. These films, plus two reference strips exposed to doses of zero and 160 cGy, were digitized on the scanners at the two facilities. Using the multi-channel dosimetry method and One-scan protocol (Med Phys, 39: 6339-6349, 2012) the recorded doses on the VMAT films were calculated and the results were compared with the VMAT plan using a Gamma index of 3%/3 mm. Results: The passing rates obtained for dose maps calculated for all combinations of VMAT images and calibration functions were nearly unchanged, using the One-scan protocol. Also, in all cases a passing rate of >99% was obtained for Gamma index of 3%/3 mm. On the other hand, if the One-scan protocol was not employed, the dose maps for VMAT images and calibration functions from different scanners showed poor correlation with the treatment plan. This is probably due to the scan-to-scan variability. Conclusions: The authors have found that it is feasible to use a public calibration function for a given radiochromic film lot using the same methodology, One-scan protocol, for patient-specific QA.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.U1930107 and 11827807)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grants Nos.XDA25030100,XDA25010000,and XDB16010200).
文摘A two-dimensional dose detector for ion beam is required in many high energy density physics experiments.As a solid detector,the GAFChromic film offers a good spatial resolution and dosimetric accuracy.For an absolute dose measurement,the relative effectiveness,which represents the darkening efficiency of the film to a radiation source,needs to be taken into consideration.In this contribution,the dose-response of HD-V2 to argon ions is presented for the first time.The calibration was taken over the dose range of 65 Gy-660 Gy with 8-keV argon ions.The response of net optical density is from 0.01 to 0.05.Triple-color dose-response functions are derived.The relative effectiveness for the argon ion beams is about 5%,much lower than that of protons and carbon ions.To explain this effect,the inactivation probability based on track theory of ion bombardment is proposed.Furthermore,a theoretical prediction of the relative effectiveness for single ion is presented,showing the dependence of the darkening efficiency on the atomic number and the incident energy of ions.
文摘Accurate dose measurement tools are needed to evaluate the radiation dose delivered to patients by using modern and sophisticated radiation therapy techniques. However, the adequate tools which enable us to directly measure the dose distributions in threedimensional(3D) space are not commonly available. One such 3D dose measurement device is the polymerbased dosimeter, which changes the material property in response to radiation. These are available in the gel form as polymer gel dosimeter(PGD) and ferrous gel dosimeter(FGD) and in the solid form as solid plastic dosimeter(SPD). Those are made of a continuous uniform medium which polymerizes upon irradiation. Hence, the intrinsic spatial resolution of those dosimeters is very high, and it is only limited by the method by which one converts the dose information recorded by the medium to the absorbed dose. The current standard methods of the dose quantification are magnetic resonance imaging, optical computed tomography, and X-ray computed tomography. In particular, magnetic resonance imaging is well established as a method for obtaining clinically relevant dosimetric data by PGD and FGD. Despite the likely possibility of doing 3D dosimetry by PGD, FGD or SPD, the tools are still lacking wider usages for clinical applications. In this review article, we summarize the current status of PGD, FGD, and SPD and discuss the issue faced by these for wider acceptance in radiation oncology clinic and propose some directions for future development.
文摘In this work, a method to reduce increase in optical density (OD) caused by multiple scanning in radiochromic film dosimetry in combination with a flatbed scanner is presented. Gafchromic EBT3 films are scanned with Epson Pro 1680 Expression scanner and time intervals of 15 minutes and 30 minutes are observed between consecutive scans to reduce the increase in temperature of the scanner. The maximum variations in OD after consecutive scans are calculated and compared to the values obtained for scans without interruption. For film irradiated to 3 Gy, a time interval of 15 minutes between two successive scans leads to a reduction of the OD increase of 56.2% compared to when films are scanned without interruption. Reductions of OD increase of 86.72% and 78.72% respectively for film irradiated to 1 Gy and 2 Gy are obtained when a time interval of 30 minutes is left between two successive scans. These results show that when time intervals are observed between consecutive scans, the increase in OD has significantly reduced. However, the method has the drawback of increasing the time needed to perform radiochromic film dosimetry.
文摘Purpose: During computed tomography (CT) helical scanning mode the patient surface dose distribution is assumed to be non-uniform, therefore point dose measurement methods may lead to imprecise estimation of the radiation dose received by the patient skin in particular. We have used XRQA2 films as in-vivo dosimeters to measure the entrance skin dose during sinus exams. Methods: The films were placed under the patient head rest in order to sample the entrance surface dose in-vivo. We have performed in-vivo film irradiation on 23 patients in this study to verify the clinical suitability of the method and were found adequate. Results: The measured average ESD in the sinus exam was 11.7 ± 1.0 mGy, the PSD was 15.7 ± 1.7 mGy and the CTDI(vol) was 13.3 ± 0.1 mGy. The ratio of ESD/CTDI(vol) and PSD/CTDI(vol) was 0.88 and 1.18 respectively. The results indicate that the scanner registered CTDI(vol) underestimates the PSD and in the same time it overestimates the ESD by 18% and 13.6% respectively. Conclusion: The observed differences between the ESD, PSD and CTDI(vol) although seem small for the radiation dose range measured during CT of the sinus [13.2 - 13.4] mGy, but important for the medical physicist to know, since monitoring of patients’ doses from CT examinations is becoming more mandatory. The use of radiochromic film as in-vivo dosimeter does not interfere with the clinical radiological exam and does not produce any image artifacts. The method can be used to study other CT examinations specially the ones with large beam width, high pitch factor and high dose exams. The method allows measurement of the peak skin dose, examination of the CT dose profile and the 2D dose distribution in the XZ plan.
文摘Purpose: To evaluate the measured dose distributions using radiochromic EBT2 films for small fields in iPlan (BrainLab) commissioning. Methods: Radiochromic EBT2 films were irradiated with 6 MV photons on a Varian Trilogy linac using polystyrene phantoms. The measurements included dose profiles and depth doses for field sizes of 1 × 1, 2 × 2, 3 × 3, 4 × 4, and 10 × 10 cm2 etc. The dose profile measurements were taken at the depth of 5 cm. The calibration films were irradiated at dmax(1.4 cm) for doses up to 6 Gy. Films were scanned using an Epson 10,000 XL flatbed scanner with 72 dpi resolution. Pixel values were converted to doses using the established calibration-curve. The 2D dose distributions were generated from the film data analysis. In-house software was utilized to compare the measured doses from films with the treatment planning data. In addition, selected patients’ SRS fields were also measured with the EBT2 films for comparison with iPlan. An EDGETM detector was also used to check the centralaxis doses for the SRS patients’ measurements. Results and Discussion: The measured planar dose distributions achieved more than 98% and 95% passing rates with a set of 2%/2 mm dose and DTA criteria for all square fields and all patient treatment fields (2), respectively. Agreement with measurement data with the EDGETM detector at the central axis (±1%) was found with the plan data. This is the first report for SRS small photon-field measurement using the latest radiochromic film, EBT2. The results shown in this work indicate that the use of EBT2 film provides accurate dosimetry measure-ments for small photon beams. The measurements show excellent agreement with the iPlan TP commissioning data. Conclusions: The patient-specific EBT2 film QA for iPlan SRS patients showed good results. The EBT2 films could potentially be a useful dosimeter in verification of commissioning as well as patient-specific QA for SRS cases.
文摘Background and Aim: Irradiation methods such as double scattering method and spot scanning method have been used in proton beam treatment devices. In the scattering method, a ridge filter or a range modulation wheel is used to create a spread-out Bragg peak, but the distribution at the patient position may change due to positional deviation of the incident beam. Therefore, assessment of the incident position of the beam is very important even in the scattering method. To investigate the width and distribution of the proton beam before entering the RMW, a radiochromic film was installed at the outlet of the transport pipe and the entrance of the profile-monitoring detector. Methods: In this study, the distributions of the beam at the exit of the transport pipe and the entrance of the monitor detector were measured using films. The beam width was measured from the full width at half maximum of the profile obtained from the distribution. Measurements were conducted every month for 10 months. Results: Beams of widths ranging from 1.82 to 2.30 mm in the horizontal direction and 4.25 to 5.33 mm in the vertical direction were outputted from the exit of the transport pipe. Beams of widths ranging from 2.16 to 2.67 mm in the horizontal direction and 4.06 to 5.31 mm in the vertical direction were outputted from the entrance of the monitor detector. The maximum width fluctuation for 10 months was 0.55 mm in the horizontal direction and 1.26 mm in the vertical direction at the entrance of the monitor detector. Conclusions: The distribution was obtained before the proton beam was scattered by the scatterer, and then we propose a method to periodically measure and monitor the changes in the beam distributions every month.
文摘Radiochromic film with a dye incorporated into the radiation sensitive layer [Gafchromic EBT2, Ashland, Inc.] may be digitized by a color transparency scanner, digitally processed, and calibrated so that a digital image in units of radiation absorbed dose is obtained. A transformation from raw scanner values to dose values was developed based upon a principal component analysis of the optical densities of the red, green and blue channels of the color image of a dose of 0.942 Gy delivered by a Sr-90/Y-90 disk-shaped source. In the order of increasing eigenvalue, the three eigenimages of the principal component analysis contained, by visual inspection, 1) mainly noise;2) mainly a pattern of irregular streaks;and 3) most of the expected dose information along with some of the same background streaking that predominated in the second eigenimage. The combination of the second and third eigenimages that minimized the background streaking was converted into a transformation of the red, green and blue channels’ optical densities and applied to films with a range of doses from 0 to 63.7 Gy. The curve of dose vs. processed optical density was fit by a two-phase association curve. This processing was applied to a film exposed from its edge by a different Y-90 source in a configuration that was modeled by Monte Carlo simulation. The depth-dose curves of the measurement and simulation agree closely, suggesting that this approach is a valid method of processing EBT2 radiochromic film into maps of radiation absorbed dose.
文摘Purpose: The aim of this study was to develop a method for the direct measurement of electron beam width and distribution at the scattering foil on the carrousel in a medical linear accelerator gantry head, which differs from an existing indirect method for measuring the focal spot size using a camera or metallic slit located outside the gantry head. Methods: The electron beam emitted by the linear accelerator was used to irradiate radiochromic film mounted on the scattering foil on the carrousel, which was not used for clinical treatment. The electron beam width at the scattering foil position was then evaluated using the full width at half maximum of the Gaussian distribution approximated from each one dimensional distribution of the irradiated radiochromic film. Results: The electron beam width at the scattering foil position was found to be 3.1 to 6.4 mm in the crossline direction and 2.8 to 5.5 mm in the inline direction with electron energy of 4 to 16 MeV. The two-dimensional distribution of the electron beam was therefore elliptical or distorted in shape, not circular. Conclusions: Direct measurement of the electron beam width at the scattering foil in the carrousel of a medical linear accelerator is possible, though the use of lower sensitivity film in addition to indirect methods is expected to bring about better results. However, as this method does not allow for direct measurement of the incident angle of the accelerated electron beam, further improvements and refinements are still needed.
文摘Purpose: To study and compare the dose response curves of the new GafChromic EBT3 film for megavoltage and kilovoltage x-ray beams, with different spatial resolutions. Methods: EBT3 films (lot#A101711-02) were exposed to each x-ray beam (6 MV, 15 MV, and 50 kV) at 7 dose values (50-3200 cGy). Each film piece was scanned three consecutive times in the center of Epson 10000XL flatbed scanner in 48-bit color at two separate spatial resolutions of 75 and 300 dpi. The data were analyzed using ImageJ and, for each scanned image, a region of interest (ROI) of 2 × 2 cm2 at the field center was selected to obtain the mean pixel value with its standard deviation in the ROI. For each energy, dose value and spatial resolution, the average net optical density (netOD) and its associated uncertainty were determined. The Student’s t-test was performed to evaluate the statistical differences between the net OD/dose values of the three energy modalities, with different color channels and spatial resolutions. Results and Discussion: The dose response curves for the three energy modalities were compared in three color channels. Weak energy dependence was found. For doses above 100 cGy, no statistical differences were observed between 6 and 15 MV beams, regardless of spatial resolution and color channel. However, statistical differences were observed between 50 kV and the megavoltage beams. The degree of energy dependence (from MV to 50 kV) was found to be a function of color channel, dose level, and spatial resolution. Conclusions: The dose response curves for GafChromic EBT3 films were found to be weakly dependent on the energy of the photon beams from 6 MV to 15 MV. For very low energy photon (e.g. 50 kV), variation of more than 11% due to the energy-dependence is observed, depending on the absorbed dose, spatial resolution and color channel used.
