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
Radiochromic film for spot-scanning QA provides high spatial resolution and efficiency gains from one-shot irradiation for multiple depths. However, calibration can be a tedious procedure which may limit widespread us...Radiochromic film for spot-scanning QA provides high spatial resolution and efficiency gains from one-shot irradiation for multiple depths. However, calibration can be a tedious procedure which may limit widespread use. Moreover, since there may be an energy dependence, which manifests as a depth dependence, this may require additional measurements for each patient. We present a one-scan protocol to simplify the procedure. A calibration using an EBT3 film, exposed by a 6-level step-wedge plan on a Proteus®PLUS proton system (IBA, Belgium), was performed at depths of 18, 20, 24 cm using Plastic Water®(CIRS, Norfolk, VA). The calibration doses ranged from 65 - 250 cGy (RBE) (relative biological effectiveness) for proton energies of 170 - 200 MeV. A clinical prostate + nodes plan was used for validation. The planar doses at selected depths were measured with EBT3 films and analyzed using one-scan protocol (one-scan digitization of QA film and at least one film exposed to a known dose). The gamma passing rates, dose-difference maps, and profiles of 2D planar doses measured with EBT3 film and IBA MatriXX-PT, versus the RayStation TPS calculations were analyzed and compared. The EBT3 film measurement results matched well with the TPS calculation data with an average passing rate of ~95% for 2%/2 mm and slightly lower passing rates were obtained from an ion chamber array detector. We were able to demonstrate that the use of a proton step-wedge provided clinically acceptable results and minimized variations between film-scanner orientation, inter-scan, and scanning conditions. Furthermore, for relative dosimetry (calibration is not done at the time of experiment), it could be derived from no more than two films exposed to known doses (one could be zero) for rescaling the master calibration curve at each depth. The sensitivity of the calibration to depth variations has been explored. One-scan protocol results appear to be comparable to that of the ion chamber array detector. The use of a proton step-wedge for calibration of EBT3 film potentially increases efficiency in patient-specific QA of proton beams.展开更多
目的比较Compass系统与EBT3胶片的验证计划在同一层面的Gamma通过率。方法选择2020年4月至2021年2月于复旦大学附属中山医院厦门医院接受放射治疗的8例不同肿瘤类型患者在治疗计划系统(TPS)中的放射治疗计划,并以7 cm厚度的固体水作为模...目的比较Compass系统与EBT3胶片的验证计划在同一层面的Gamma通过率。方法选择2020年4月至2021年2月于复旦大学附属中山医院厦门医院接受放射治疗的8例不同肿瘤类型患者在治疗计划系统(TPS)中的放射治疗计划,并以7 cm厚度的固体水作为模体,制定相应的验证计划,导出验证计划的中心点层面,保存并将其命名为TPS_2D;将Compass系统探测器(Dolphin)和EBT3胶片分别在Elekta直线加速器上执行放射治疗计划,再将Dolphin测量数据回传到Compass系统,最终通过软件重建,计算得到验证计划在CT图像上的三维剂量分布,将中心点冠状层面的验证计划文件导出并命名为Compass_2D,经直线加速器照射后的EBT3胶片经过扫描仪处理后,亦能获得与Compass_2D相同层面的验证计划文件,导出并将其命名为EBT3_2D;在RIT113软件中对TPS_2D、Compass_2D和EBT3_2D进行两两比较,在标准3%/3 mm、阈值10%的条件下,得到Compass_2D VS TPS_2D、EBT3_2D VS TPS_2D和Compass_2D VS EBT3_2D的Gamma通过率。结果8例患者Compass_2D VS TPS_2D、EBT3_2D VS TPS_2D、Compass_2D VS EBT3_2D的Gamma通过率均>90%;在Compass_2D VS TPS_2D的验证结果中,仅鼻咽癌的Gamma通过率均<95%;在EBT3_2D VS TPS_2D的验证结果中,小细胞肺癌和乳腺癌的Gamma通过率均<95%;在Compass_2D VS EBT3_2D的验证结果中,小细胞肺癌、乳腺癌和鼻咽癌的Gamma通过率均<95%。结论Compass系统在中心点冠状位层面的验证结果可以真实地反映TPS计划设计与执行的一致性,为Compass系统三维验证结果增加了可信度。展开更多
This work investigated the absorbed dose to water rate under reference conditions in a Cyberknife VSI system using radiochromic films EBT3 and MD-V3 and three ionization chambers: an Exradin A12 and two FC65P Welh&...This work investigated the absorbed dose to water rate under reference conditions in a Cyberknife VSI system using radiochromic films EBT3 and MD-V3 and three ionization chambers: an Exradin A12 and two FC65P Welhöfer Scanditronix with different serial numbers. The correction factor,, was studied using a Varian iX linac and the Cyberknife system. The measurements in the Varian iX were performed in a 10 × 10 cm2 field, 10 cm depth in liquid water at 90 cm and 70 cm SSD and in a 5.4 × 5.4 cm2 field, 10 cm depth at 70 cm SSD to simulate the Cyberknife conditions. In the Cyberknife system, measurements were performed using ionization chambers and both film types at 70 cm SSD and 10 cm depth in its 6 cm diameter reference field. The results indicate that ?is independent of the dosimeters and the evaluation methods. Maximum differences of 0.22% - 0.55% (combined uncertainties of 1.22% - 1.98%, k = 1) are obtained on ?using Varian iX, whereas discrepancies of 2.08% - 2.09% (combined uncertainties of 1.87% - 2.13%, k = 1) are observed using the Cyberknife system. Given the agreement between detectors and the combined standard uncertainties, the data from Varian iX could be considered the most accurate and consequently a weighted average factor of 0.902 ± 0.006 could be used for the Cyberknife VSI system reference field. Within measurement uncertainties, the absorbed dose rate measured in the Cyberknife VSI system reference field was found to be independent of the dosimeters used. These results suggest that the absorbed dose measured at a point within a given field size should be the same, regardless the dosimeter used, if their dosimetric characteristics are well known. This highlighted the importance of performing dosimetry by controlling all parameters that could affect the dosimeter response. One can conclude that radiochromic film dosimetry can be considered as an appropriate alternative for measuring absorbed dose to water rate.展开更多
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.
文摘Radiochromic film for spot-scanning QA provides high spatial resolution and efficiency gains from one-shot irradiation for multiple depths. However, calibration can be a tedious procedure which may limit widespread use. Moreover, since there may be an energy dependence, which manifests as a depth dependence, this may require additional measurements for each patient. We present a one-scan protocol to simplify the procedure. A calibration using an EBT3 film, exposed by a 6-level step-wedge plan on a Proteus®PLUS proton system (IBA, Belgium), was performed at depths of 18, 20, 24 cm using Plastic Water®(CIRS, Norfolk, VA). The calibration doses ranged from 65 - 250 cGy (RBE) (relative biological effectiveness) for proton energies of 170 - 200 MeV. A clinical prostate + nodes plan was used for validation. The planar doses at selected depths were measured with EBT3 films and analyzed using one-scan protocol (one-scan digitization of QA film and at least one film exposed to a known dose). The gamma passing rates, dose-difference maps, and profiles of 2D planar doses measured with EBT3 film and IBA MatriXX-PT, versus the RayStation TPS calculations were analyzed and compared. The EBT3 film measurement results matched well with the TPS calculation data with an average passing rate of ~95% for 2%/2 mm and slightly lower passing rates were obtained from an ion chamber array detector. We were able to demonstrate that the use of a proton step-wedge provided clinically acceptable results and minimized variations between film-scanner orientation, inter-scan, and scanning conditions. Furthermore, for relative dosimetry (calibration is not done at the time of experiment), it could be derived from no more than two films exposed to known doses (one could be zero) for rescaling the master calibration curve at each depth. The sensitivity of the calibration to depth variations has been explored. One-scan protocol results appear to be comparable to that of the ion chamber array detector. The use of a proton step-wedge for calibration of EBT3 film potentially increases efficiency in patient-specific QA of proton beams.
文摘目的比较Compass系统与EBT3胶片的验证计划在同一层面的Gamma通过率。方法选择2020年4月至2021年2月于复旦大学附属中山医院厦门医院接受放射治疗的8例不同肿瘤类型患者在治疗计划系统(TPS)中的放射治疗计划,并以7 cm厚度的固体水作为模体,制定相应的验证计划,导出验证计划的中心点层面,保存并将其命名为TPS_2D;将Compass系统探测器(Dolphin)和EBT3胶片分别在Elekta直线加速器上执行放射治疗计划,再将Dolphin测量数据回传到Compass系统,最终通过软件重建,计算得到验证计划在CT图像上的三维剂量分布,将中心点冠状层面的验证计划文件导出并命名为Compass_2D,经直线加速器照射后的EBT3胶片经过扫描仪处理后,亦能获得与Compass_2D相同层面的验证计划文件,导出并将其命名为EBT3_2D;在RIT113软件中对TPS_2D、Compass_2D和EBT3_2D进行两两比较,在标准3%/3 mm、阈值10%的条件下,得到Compass_2D VS TPS_2D、EBT3_2D VS TPS_2D和Compass_2D VS EBT3_2D的Gamma通过率。结果8例患者Compass_2D VS TPS_2D、EBT3_2D VS TPS_2D、Compass_2D VS EBT3_2D的Gamma通过率均>90%;在Compass_2D VS TPS_2D的验证结果中,仅鼻咽癌的Gamma通过率均<95%;在EBT3_2D VS TPS_2D的验证结果中,小细胞肺癌和乳腺癌的Gamma通过率均<95%;在Compass_2D VS EBT3_2D的验证结果中,小细胞肺癌、乳腺癌和鼻咽癌的Gamma通过率均<95%。结论Compass系统在中心点冠状位层面的验证结果可以真实地反映TPS计划设计与执行的一致性,为Compass系统三维验证结果增加了可信度。
文摘This work investigated the absorbed dose to water rate under reference conditions in a Cyberknife VSI system using radiochromic films EBT3 and MD-V3 and three ionization chambers: an Exradin A12 and two FC65P Welhöfer Scanditronix with different serial numbers. The correction factor,, was studied using a Varian iX linac and the Cyberknife system. The measurements in the Varian iX were performed in a 10 × 10 cm2 field, 10 cm depth in liquid water at 90 cm and 70 cm SSD and in a 5.4 × 5.4 cm2 field, 10 cm depth at 70 cm SSD to simulate the Cyberknife conditions. In the Cyberknife system, measurements were performed using ionization chambers and both film types at 70 cm SSD and 10 cm depth in its 6 cm diameter reference field. The results indicate that ?is independent of the dosimeters and the evaluation methods. Maximum differences of 0.22% - 0.55% (combined uncertainties of 1.22% - 1.98%, k = 1) are obtained on ?using Varian iX, whereas discrepancies of 2.08% - 2.09% (combined uncertainties of 1.87% - 2.13%, k = 1) are observed using the Cyberknife system. Given the agreement between detectors and the combined standard uncertainties, the data from Varian iX could be considered the most accurate and consequently a weighted average factor of 0.902 ± 0.006 could be used for the Cyberknife VSI system reference field. Within measurement uncertainties, the absorbed dose rate measured in the Cyberknife VSI system reference field was found to be independent of the dosimeters used. These results suggest that the absorbed dose measured at a point within a given field size should be the same, regardless the dosimeter used, if their dosimetric characteristics are well known. This highlighted the importance of performing dosimetry by controlling all parameters that could affect the dosimeter response. One can conclude that radiochromic film dosimetry can be considered as an appropriate alternative for measuring absorbed dose to water rate.
