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EP-1513: CyberKnife robotic radiotherapy delivery quality assurance using CrystalBall 3D Dosimetry System
S811 ESTRO 36 _______________________________________________________________________________________________
The new IBA Dolphin (IBA Dosimetry, Germany) is a dose transmission detector (DTD) mounted onto the gantry for online treatment verification as well. Aim of this study is to compare the results of the Dolphin/Compass with the traditional 3D dosimetry phantom Delta 4 (Scandidos, Sweden) for lung stereotactic body radiation therapy treatmentsand to mesure the detector attenuation for online dose verification. Material and Methods At first the two systems were compared in terms of ability of error detection of leaf position. A box treatment was measured three times with introduction of a shift of one leaf bank in steps from 0 to 2 mm and the analysis of gamma index or DVHs was carry out. Afterward ten patients with lung cancer, treated by sbrt, were included in the study. All treatment plans were simultaneuslyverified with the Dolphin and the Delta 4.The treatment plans were generated by Monaco system (ver.5.0, Elekta AB, Sweden). Dolphin with the Compass software (v. 4.0) permits the 3D dose distribution reconstruction on a patient CT and the Compass itself is a model-based dose computation, with a collapsed cone dose engine; the beam model of the Compass was validated and accepted. For the quantitative analysis parameters of dose–volume based indices for PTV (V80%, D98%, mean dose, D2% and Gamma index 2%-2mm ) and OARs doses (Dmax and dose at the threshold volume according to AAPM TG101) were evaluated for Compass calculation and DTD reconstruction. At the same time gamma index (2%-2mm) was calculated based on Delta 4 measurements. The detector attenuation was estimated in a clinical context comparing the median dose inside the Delta 4 detector with and without the Dolphin mounted. Results Error detection ability : the fig. 1 shows the variation between difference % of mean dose in a Roi limited to the irradiation beams for DTD versus leaf position shift and the % of points with gamma index > 1 for Delta 4. Quantitative analysis: table 1 shows the results of the comparison between Dolphin/Compass and Delta 4 phantom. The PTV average gamma was 0.64±0.12; the mean percentage differences of V80%, D98%, mean dose and D2% were inferior to 3%. The difference in Gy for OARs were under or equal to 1 Gy, except for D(4cc) of trachea (1.15 Gy). The maximum difference was found for rib Dmax (4.4 Gy). The mean % of point with gamma < 1 for Delta 4 was 83.2±0.06; one patient was considered failed with 72% of points with g<1 in Delta 4. Detector attenuation : a value of 10.5±0.5 % was found. Table 1. Comparison between Compass computed and reconstructed doses
*Dmax defined at 0.035 cc
fig 1 shift leaf detectability Conclusion The DTD system seems to be more sensitive than 3D detector for error detection ability. The Dolphin/Compass system is a useful tool to perform QA patients in a SBRT context offering more clinical evaluable informations than 3D phantoms only. For the online dosimetry, the methodology proposed led to an attenuation correction factor not negligible but constant . EP-1513 CyberKnife robotic radiotherapy delivery quality assurance using CrystalBall 3D Dosimetry System M.A. Al Kafi1, A. Al Moussa1, M.J. Maryanski2, B. Moftah1 1 King Faisal Specialist Hospital and Research Centre, Biomedical Physics, Riyadh 11211, Saudi Arabia 2 MGS Research- Inc., d.b.a. 3D Dosimetry, Madison- CT, USA Purpose or Objective Stereotactic radiosurgery/radiotherapy (SRS) and stereotactic body radiotherapy (SBRT) deliver high dose to the tumor accurately and precisely. With hypo-
S812 ESTRO 36 _______________________________________________________________________________________________
fractionation, even small relative errors can lead to serious complications to the normal tissue or recurrences of the tumor. So delivery quality assurance (DQA) in SRS/SBRT is very critical and poses unique challenges due to extremely high dose gradients and lack of electronic equilibrium. For this reason, dose rate independent dosimeters with precise, high spatial resolution and 3D capabilities are essential as reported by the Council on Ionizing Radiation Measurements and Standards (CIRMS). Material and Methods The new CrystalBall system (3D Dosimetry, Madison, CT, USA) is designed for DQA with sub-millimeter spatial resolution in 3D. The system is composed of a fast laser CT scanner (OCTOPUS, MGS Research, Inc, Madison, CT) and reusable tissue-equivalent radiochromic polymer gel sphere-mounted on a special QA phantom. Gold fiducial markers are affixed in different locations of the phantom for image guidance with fiducial tracking for CyberKnife (CK) robotic SRS/SBRT system (Accuray, Sunnyvale, CA). The CT images of the CrystalBall gel phantom were transferred to the CK Multiplan treatment planning system. A DQA plan was generated by superimposing a patient plan onto the gel phantom CT data set. The DQA plan was then sent for CK irradiation. The CrystalBall’s VOLQA software registers the plan DICOM CT dataset with the laser CT of the irradiated gel, creates OD/cm to dose calibration curve and then compares the CrystalBall irradiation measurements with the Multiplan’s DQA plan. It generates QA reports that feature overlays of isodoses in 2D and 3D, profiles, DVHs, voxel statistics, and pass/fail metrics for dose difference and distance-to-agreement according to gamma index criteria. In this study, we performed DQA for four CK patients who received treatment for brain metastasis, spine metastasis and trigeminal neuralgia as recommended by AAPM TG-135. For each patient, the DQA was done three times. Results Figures 1 and 2 show the CrystalBall phantom setup with OD/cm to dose auto-calibration, 2D and 3D overlay of isodoses for a patient, respectively.
Table 1 shows results of the study for gamma evaluation passing averages for the DQA of the four patients. For all patients studied, we found a passing rate of more than 96% with gamma index criteria of 2 % dose difference and 2
mm distance-to-agreement. For 3 % and 3 mm criteria, the passing rate is found to be above 99%.
Conclusion Our DQA results suggest that the newly developed CrystalBall QA phantom system for robotic radiosurgery can be ideal tool for 3D dose verification with isotropic sub-millimeter spatial resolution and film-equivalent accuracy. This 3D tool can offer unique advantage over other existing 2D tools and techniques in terms of highresolution DQA necessary for radiotherapy with minimal additional physics resources. Electronic Poster: Physics track: Radiation protection, secondary tumour induction and low dose (incl. imaging) EP-1514 Planar kV imaging dose reduction study for Varian iX and TrueBeam linacs E. Gershkevitsh1, D. Zolotuhhin1 1 North-Estonian Regional Hospital Cancer Center Radiotherapy, Radiotherapy, Tallinn, Estonia Purpose or Objective IGRT has become an indispensable tool in modern radiotherapy with kV imaging used in many departments due to superior image quality and lower dose when compared to MV imaging. Since, the frequency of kV images continues to increase (intrafractional imaging, etc.) the reduction of additional dose assumes high priority. Many departments use manufacturer supplied protocols for imaging which are not always optimised between image quality and radiation dose (ALARA). Material and Methods Whole body phantom PBU-50 (Kyoto Kagaku ltd., Japan) for imaging in radiology has been imaged on Varian iX OBI 1.5 and TrueBeam 2.5 accelerators (Varian Medical Systems, USA). Manufacturer’s default protocols were adapted by modifying kV and mAs values when imaging different anatomical regions of the phantom (head, thorax, abdomen, pelvis, extremities). Images with different settings were independently reviewed by two persons and their suitability for IGRT set-up correction protocols were evaluated. The suitable images with the lowest mAs were then selected. The entrance surface dose (ESD) for manufacturer’s default protocols and modified protocols were measured with RTI Black Piranha (RTI Group, Sweden) and compared. Image quality was also measured with kVQC phantom (Standard Imaging, USA) for different protocols. The modified protocols have been applied for clinical work. Results The default manufacturer’s protocols on TrueBeam linac yielded 9.4 times lower ESD than on iX linac (range 2.524.8). For most cases it was possible to reduced the ESD on average by a factor of 3 (range 0.9-8.5) on iX linac by optimising imaging protocols. Further ESD reduction was also possible for TrueBeam linac.
The new IBA Dolphin (IBA Dosimetry, Germany) is a dose transmission detector (DTD) mounted onto the gantry for online treatment verification as well. Aim of this study is to compare the results of the Dolphin/Compass with the traditional 3D dosimetry phantom Delta 4 (Scandidos, Sweden) for lung stereotactic body radiation therapy treatmentsand to mesure the detector attenuation for online dose verification. Material and Methods At first the two systems were compared in terms of ability of error detection of leaf position. A box treatment was measured three times with introduction of a shift of one leaf bank in steps from 0 to 2 mm and the analysis of gamma index or DVHs was carry out. Afterward ten patients with lung cancer, treated by sbrt, were included in the study. All treatment plans were simultaneuslyverified with the Dolphin and the Delta 4.The treatment plans were generated by Monaco system (ver.5.0, Elekta AB, Sweden). Dolphin with the Compass software (v. 4.0) permits the 3D dose distribution reconstruction on a patient CT and the Compass itself is a model-based dose computation, with a collapsed cone dose engine; the beam model of the Compass was validated and accepted. For the quantitative analysis parameters of dose–volume based indices for PTV (V80%, D98%, mean dose, D2% and Gamma index 2%-2mm ) and OARs doses (Dmax and dose at the threshold volume according to AAPM TG101) were evaluated for Compass calculation and DTD reconstruction. At the same time gamma index (2%-2mm) was calculated based on Delta 4 measurements. The detector attenuation was estimated in a clinical context comparing the median dose inside the Delta 4 detector with and without the Dolphin mounted. Results Error detection ability : the fig. 1 shows the variation between difference % of mean dose in a Roi limited to the irradiation beams for DTD versus leaf position shift and the % of points with gamma index > 1 for Delta 4. Quantitative analysis: table 1 shows the results of the comparison between Dolphin/Compass and Delta 4 phantom. The PTV average gamma was 0.64±0.12; the mean percentage differences of V80%, D98%, mean dose and D2% were inferior to 3%. The difference in Gy for OARs were under or equal to 1 Gy, except for D(4cc) of trachea (1.15 Gy). The maximum difference was found for rib Dmax (4.4 Gy). The mean % of point with gamma < 1 for Delta 4 was 83.2±0.06; one patient was considered failed with 72% of points with g<1 in Delta 4. Detector attenuation : a value of 10.5±0.5 % was found. Table 1. Comparison between Compass computed and reconstructed doses
*Dmax defined at 0.035 cc
fig 1 shift leaf detectability Conclusion The DTD system seems to be more sensitive than 3D detector for error detection ability. The Dolphin/Compass system is a useful tool to perform QA patients in a SBRT context offering more clinical evaluable informations than 3D phantoms only. For the online dosimetry, the methodology proposed led to an attenuation correction factor not negligible but constant . EP-1513 CyberKnife robotic radiotherapy delivery quality assurance using CrystalBall 3D Dosimetry System M.A. Al Kafi1, A. Al Moussa1, M.J. Maryanski2, B. Moftah1 1 King Faisal Specialist Hospital and Research Centre, Biomedical Physics, Riyadh 11211, Saudi Arabia 2 MGS Research- Inc., d.b.a. 3D Dosimetry, Madison- CT, USA Purpose or Objective Stereotactic radiosurgery/radiotherapy (SRS) and stereotactic body radiotherapy (SBRT) deliver high dose to the tumor accurately and precisely. With hypo-
S812 ESTRO 36 _______________________________________________________________________________________________
fractionation, even small relative errors can lead to serious complications to the normal tissue or recurrences of the tumor. So delivery quality assurance (DQA) in SRS/SBRT is very critical and poses unique challenges due to extremely high dose gradients and lack of electronic equilibrium. For this reason, dose rate independent dosimeters with precise, high spatial resolution and 3D capabilities are essential as reported by the Council on Ionizing Radiation Measurements and Standards (CIRMS). Material and Methods The new CrystalBall system (3D Dosimetry, Madison, CT, USA) is designed for DQA with sub-millimeter spatial resolution in 3D. The system is composed of a fast laser CT scanner (OCTOPUS, MGS Research, Inc, Madison, CT) and reusable tissue-equivalent radiochromic polymer gel sphere-mounted on a special QA phantom. Gold fiducial markers are affixed in different locations of the phantom for image guidance with fiducial tracking for CyberKnife (CK) robotic SRS/SBRT system (Accuray, Sunnyvale, CA). The CT images of the CrystalBall gel phantom were transferred to the CK Multiplan treatment planning system. A DQA plan was generated by superimposing a patient plan onto the gel phantom CT data set. The DQA plan was then sent for CK irradiation. The CrystalBall’s VOLQA software registers the plan DICOM CT dataset with the laser CT of the irradiated gel, creates OD/cm to dose calibration curve and then compares the CrystalBall irradiation measurements with the Multiplan’s DQA plan. It generates QA reports that feature overlays of isodoses in 2D and 3D, profiles, DVHs, voxel statistics, and pass/fail metrics for dose difference and distance-to-agreement according to gamma index criteria. In this study, we performed DQA for four CK patients who received treatment for brain metastasis, spine metastasis and trigeminal neuralgia as recommended by AAPM TG-135. For each patient, the DQA was done three times. Results Figures 1 and 2 show the CrystalBall phantom setup with OD/cm to dose auto-calibration, 2D and 3D overlay of isodoses for a patient, respectively.
Table 1 shows results of the study for gamma evaluation passing averages for the DQA of the four patients. For all patients studied, we found a passing rate of more than 96% with gamma index criteria of 2 % dose difference and 2
mm distance-to-agreement. For 3 % and 3 mm criteria, the passing rate is found to be above 99%.
Conclusion Our DQA results suggest that the newly developed CrystalBall QA phantom system for robotic radiosurgery can be ideal tool for 3D dose verification with isotropic sub-millimeter spatial resolution and film-equivalent accuracy. This 3D tool can offer unique advantage over other existing 2D tools and techniques in terms of highresolution DQA necessary for radiotherapy with minimal additional physics resources. Electronic Poster: Physics track: Radiation protection, secondary tumour induction and low dose (incl. imaging) EP-1514 Planar kV imaging dose reduction study for Varian iX and TrueBeam linacs E. Gershkevitsh1, D. Zolotuhhin1 1 North-Estonian Regional Hospital Cancer Center Radiotherapy, Radiotherapy, Tallinn, Estonia Purpose or Objective IGRT has become an indispensable tool in modern radiotherapy with kV imaging used in many departments due to superior image quality and lower dose when compared to MV imaging. Since, the frequency of kV images continues to increase (intrafractional imaging, etc.) the reduction of additional dose assumes high priority. Many departments use manufacturer supplied protocols for imaging which are not always optimised between image quality and radiation dose (ALARA). Material and Methods Whole body phantom PBU-50 (Kyoto Kagaku ltd., Japan) for imaging in radiology has been imaged on Varian iX OBI 1.5 and TrueBeam 2.5 accelerators (Varian Medical Systems, USA). Manufacturer’s default protocols were adapted by modifying kV and mAs values when imaging different anatomical regions of the phantom (head, thorax, abdomen, pelvis, extremities). Images with different settings were independently reviewed by two persons and their suitability for IGRT set-up correction protocols were evaluated. The suitable images with the lowest mAs were then selected. The entrance surface dose (ESD) for manufacturer’s default protocols and modified protocols were measured with RTI Black Piranha (RTI Group, Sweden) and compared. Image quality was also measured with kVQC phantom (Standard Imaging, USA) for different protocols. The modified protocols have been applied for clinical work. Results The default manufacturer’s protocols on TrueBeam linac yielded 9.4 times lower ESD than on iX linac (range 2.524.8). For most cases it was possible to reduced the ESD on average by a factor of 3 (range 0.9-8.5) on iX linac by optimising imaging protocols. Further ESD reduction was also possible for TrueBeam linac.