TR 5 CyberKnife Machine Setup
Technical Reference 5 – CyberKnife Machine Setup This reference document discusses some of the issues related to defining a machine in RadCalc for use with CyberKnife. CyberKnife Cones and Iris 1)
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3) 4) 5) 6)
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On the Machine Information window the Photon Only option should be chosen and the CyberKnife CheckBox must be checked. 80cm should be entered for the machine’s SAD. The machine name should be the actual name from the Accuray planning system. This is typically in the form CK(serial number). On the Photon Energies window, the reference depth will be about 1.5cm and the reference SSD will be 80cm minus the reference depth. The reference equivalent square will be 6cm. The reference dose rate will most likely be 1.000 cGy/MU. If you are entering data for the Cones and Iris treatment modes, then it will be necessary to enter two separate 6MV energies under the same machine name. In order for RadCalc to distinguish between these two energies when it imports a plan, you must specify the Treatment Mode (FIXED or IRIS) on the Photon Energies window. On the Jaw Settings window, the max jaw setting will be 6cm and the jaws will not be asymmetric. The gantry, collimator, and couch angle conventions should be entered appropriately. There will not be any wedge or attenuators to enter. The TPR data for each cone size can be imported using the Import From Spreadsheet method. The equivalent square should correlate to the cone diameter and should not be converted from a diameter to equivalent square value. Generally, this data is already in a spreadsheet format or is in a .txt file that can be open with a spreadsheet program by indicating that the data is comma delimited. If non-SAD dependent output factors are being entered then these values should be entered as follows: The option to use Sc and Sp Factors should be chosen. The Sc factors should be entered on the Sc Factors tab of the Output Factors window as 1.000 for a field size of 0.5cm and a field size of 6.0cm. This way RadCalc will always return a value of 1.000 for the Sc factor. The cone outputs factors should be entered as Sp factors on the Sp Factors tab. If SAD dependent output factors are being entered then these values should be entered as follows: The option to use Scp Factors Only should be chosen. The option to allow Scp factors to be SAD dependent should be checked. The output factors should then be entered in the table. Ideally they would be pasted into the table. The profile data for each cone can be imported from the OAR Data Import window using the Import From Spreadsheet method. Generally, this data is already in a spreadsheet format or is in a .txt file that can be opened with a spreadsheet program by indicating that the data is comma or tab delimited. The field size should correlate to the cone diameter or field size (i.e. for Iris). The measured data may have been obtained SSD or SAD. It is critical that the profile data be entered properly in order to obtain accurate off axis calculation point results. Contact
TR-5 – CyberKnife Machine Setup
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technical support if you have doubts about how to enter this data. If the data was obtained as SAD data, then it will be necessary to import the profile data by specifying 80cm as the SSD value and NOT checking the Fanline data option. After the import is complete, the SSD for each profile will need to be modified appropriately. For example, if the profile depth was 10cm then the SSD will need to be changed to 70cm and if the depth was 20cm then the SSD would need to be 60cm. In order to achieve the best results possible for beam calculations to large off axis distances it will be necessary to massage the profile data in the following manner. The last three values on both sides of every profile should be averaged and then the profile extended to an offset of 20cm. For example, let’s assume we want to extend a 3x3cm profile at a depth of 5cm. If the last three off axis ratio values on the negative side of the profile are (-5.2, 0.011), (-5.1, 0.012), and (-5.0, 0.012) then the average off axis ratio would be (0.011 + 0.012 + 0.012)/3 = (0.01167). This average value can then be added to the profile by adding a new data point and then giving it an offset of -20.0 and an off axis ratio of 0.01167. The same steps would then be performed on the positive side of the profile. This process would need to be repeated for each profile. This will successfully extend the profile data. The last task to perform for the profile data is to add a flat profile with a 40x40cm field size and a depth of Dmax. This is necessary because there is a problem when extrapolating to distances too far off axis. The POCR may extrapolate to a negative value and cause an invalid calculation. To avoid this, a 40x40cm flat profile at a depth of Dmax should be added to the data. This can be done manually by simply going into the OAR Data File Editor and adding a new curve. Once the curve is added, points should be added with the following offsets in centimeters: -20, -19, 10, 0, +10, +19, and +20. The off axis ratio for each offset should be entered as 1.000.
CyberKnife with MLC 1) A model for this machine is available from LifeLine Software, Inc. It is included in the demo machine data located in the SAMPDATA folder within the RadCalc main installation directory. It is recommended that this machine be used. In order to load this machine into RadCalc, simply go to Physics Setup and select the Restore Physics Data option. In the resulting window, browse to where the DEMODATA.zip file is, choose the file, and press the Open button from the Browse window. The data will be extracted and a list of machines will be displayed. Select the “CyberKnife MLC” machine from the list and then press the “Restore Selected” button. This machine will then be added to your database. 2) This machine will have the CyberKnife machine with an MLC defined having all of the proper leaf widths and positions. There will be a single “6 MV” photon energy with a Treatment Mode of “MLC” designated on the Photon Energies tab. The reference conditions will need to be verified along with the leaf transmission, Radiation Light Field Offset values in the X and Y directions. The Y direction refers to the direction perpendicular to the leaf motion.
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3) This machine will have a set of Sp factors defined that correlate to some standard or “golden” machine data values. These values should be verified. The Sc factors should be set to 1.0. 4) A set of standard or “golden” TPR values is also provided but should be validated against any measured values for your clinic. 5) A set of standard or “golden” OAR data is provided for the various field sizes at depths of 1.5cm, 5cm, 10cm, 20cm, and 30cm. The Pencil Beam Modeling tab on the OAR Data File Editor window has preset values for every curve. These can be modified but it is not recommended. Each curve has a Sigma for the source and a sigma for the filter as well as a weighting value for the filter. Basically these values represent the sigmas of two Gaussian curves. The two Gaussian curves are added together according to the weighting factor. For example, if the Filter Weight is 0.10 or 10% then the Gaussian curve defined by the Sigma Source values gets a 90% weight while the Gaussian defined by the Sigma Filter receives a 10% weight. One can think of this as the Source Gaussian representing the primary while the Filter Gaussian represents the scatter. When RadCalc performs a calculation, it determines an incident fluence according to its traditional methods (i.e. a transmission fluence). This fluence is then convolved or blurred by the composite Gaussian and then the MLC scatter summation is performed for the beam. This is slightly different than the typical way the MCI calculation is performed in that the incident fluence is “blurred” prior to the computation. If one desires to see how well the parameters fit the curve, the “Show Computed Curve” and “Use Clarkson” CheckBoxes must be checked. If any of the sigmas are changed or the Filter Weight is changed then boxes will have to be rechecked in order to see the effect on the computed curve. If one desires to change any of the model parameters then the “Save Model Parameters” button must be pressed in or to save the changes. The “Auto Model” button is used to go through every curve and try to set some initial model parameters. This process can take several minutes to complete. Once complete, the model can be evaluated on a curve by curve basis and adjustments made accordingly. As previously stated, it is not recommended that one go through this process.
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2)
3) 4) 5) 6)
7)
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On the Machine Information window the Photon Only option should be chosen and the CyberKnife CheckBox must be checked. 80cm should be entered for the machine’s SAD. The machine name should be the actual name from the Accuray planning system. This is typically in the form CK(serial number). On the Photon Energies window, the reference depth will be about 1.5cm and the reference SSD will be 80cm minus the reference depth. The reference equivalent square will be 6cm. The reference dose rate will most likely be 1.000 cGy/MU. If you are entering data for the Cones and Iris treatment modes, then it will be necessary to enter two separate 6MV energies under the same machine name. In order for RadCalc to distinguish between these two energies when it imports a plan, you must specify the Treatment Mode (FIXED or IRIS) on the Photon Energies window. On the Jaw Settings window, the max jaw setting will be 6cm and the jaws will not be asymmetric. The gantry, collimator, and couch angle conventions should be entered appropriately. There will not be any wedge or attenuators to enter. The TPR data for each cone size can be imported using the Import From Spreadsheet method. The equivalent square should correlate to the cone diameter and should not be converted from a diameter to equivalent square value. Generally, this data is already in a spreadsheet format or is in a .txt file that can be open with a spreadsheet program by indicating that the data is comma delimited. If non-SAD dependent output factors are being entered then these values should be entered as follows: The option to use Sc and Sp Factors should be chosen. The Sc factors should be entered on the Sc Factors tab of the Output Factors window as 1.000 for a field size of 0.5cm and a field size of 6.0cm. This way RadCalc will always return a value of 1.000 for the Sc factor. The cone outputs factors should be entered as Sp factors on the Sp Factors tab. If SAD dependent output factors are being entered then these values should be entered as follows: The option to use Scp Factors Only should be chosen. The option to allow Scp factors to be SAD dependent should be checked. The output factors should then be entered in the table. Ideally they would be pasted into the table. The profile data for each cone can be imported from the OAR Data Import window using the Import From Spreadsheet method. Generally, this data is already in a spreadsheet format or is in a .txt file that can be opened with a spreadsheet program by indicating that the data is comma or tab delimited. The field size should correlate to the cone diameter or field size (i.e. for Iris). The measured data may have been obtained SSD or SAD. It is critical that the profile data be entered properly in order to obtain accurate off axis calculation point results. Contact
TR-5 – CyberKnife Machine Setup
Page 1 of 3
9)
technical support if you have doubts about how to enter this data. If the data was obtained as SAD data, then it will be necessary to import the profile data by specifying 80cm as the SSD value and NOT checking the Fanline data option. After the import is complete, the SSD for each profile will need to be modified appropriately. For example, if the profile depth was 10cm then the SSD will need to be changed to 70cm and if the depth was 20cm then the SSD would need to be 60cm. In order to achieve the best results possible for beam calculations to large off axis distances it will be necessary to massage the profile data in the following manner. The last three values on both sides of every profile should be averaged and then the profile extended to an offset of 20cm. For example, let’s assume we want to extend a 3x3cm profile at a depth of 5cm. If the last three off axis ratio values on the negative side of the profile are (-5.2, 0.011), (-5.1, 0.012), and (-5.0, 0.012) then the average off axis ratio would be (0.011 + 0.012 + 0.012)/3 = (0.01167). This average value can then be added to the profile by adding a new data point and then giving it an offset of -20.0 and an off axis ratio of 0.01167. The same steps would then be performed on the positive side of the profile. This process would need to be repeated for each profile. This will successfully extend the profile data. The last task to perform for the profile data is to add a flat profile with a 40x40cm field size and a depth of Dmax. This is necessary because there is a problem when extrapolating to distances too far off axis. The POCR may extrapolate to a negative value and cause an invalid calculation. To avoid this, a 40x40cm flat profile at a depth of Dmax should be added to the data. This can be done manually by simply going into the OAR Data File Editor and adding a new curve. Once the curve is added, points should be added with the following offsets in centimeters: -20, -19, 10, 0, +10, +19, and +20. The off axis ratio for each offset should be entered as 1.000.
CyberKnife with MLC 1) A model for this machine is available from LifeLine Software, Inc. It is included in the demo machine data located in the SAMPDATA folder within the RadCalc main installation directory. It is recommended that this machine be used. In order to load this machine into RadCalc, simply go to Physics Setup and select the Restore Physics Data option. In the resulting window, browse to where the DEMODATA.zip file is, choose the file, and press the Open button from the Browse window. The data will be extracted and a list of machines will be displayed. Select the “CyberKnife MLC” machine from the list and then press the “Restore Selected” button. This machine will then be added to your database. 2) This machine will have the CyberKnife machine with an MLC defined having all of the proper leaf widths and positions. There will be a single “6 MV” photon energy with a Treatment Mode of “MLC” designated on the Photon Energies tab. The reference conditions will need to be verified along with the leaf transmission, Radiation Light Field Offset values in the X and Y directions. The Y direction refers to the direction perpendicular to the leaf motion.
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3) This machine will have a set of Sp factors defined that correlate to some standard or “golden” machine data values. These values should be verified. The Sc factors should be set to 1.0. 4) A set of standard or “golden” TPR values is also provided but should be validated against any measured values for your clinic. 5) A set of standard or “golden” OAR data is provided for the various field sizes at depths of 1.5cm, 5cm, 10cm, 20cm, and 30cm. The Pencil Beam Modeling tab on the OAR Data File Editor window has preset values for every curve. These can be modified but it is not recommended. Each curve has a Sigma for the source and a sigma for the filter as well as a weighting value for the filter. Basically these values represent the sigmas of two Gaussian curves. The two Gaussian curves are added together according to the weighting factor. For example, if the Filter Weight is 0.10 or 10% then the Gaussian curve defined by the Sigma Source values gets a 90% weight while the Gaussian defined by the Sigma Filter receives a 10% weight. One can think of this as the Source Gaussian representing the primary while the Filter Gaussian represents the scatter. When RadCalc performs a calculation, it determines an incident fluence according to its traditional methods (i.e. a transmission fluence). This fluence is then convolved or blurred by the composite Gaussian and then the MLC scatter summation is performed for the beam. This is slightly different than the typical way the MCI calculation is performed in that the incident fluence is “blurred” prior to the computation. If one desires to see how well the parameters fit the curve, the “Show Computed Curve” and “Use Clarkson” CheckBoxes must be checked. If any of the sigmas are changed or the Filter Weight is changed then boxes will have to be rechecked in order to see the effect on the computed curve. If one desires to change any of the model parameters then the “Save Model Parameters” button must be pressed in or to save the changes. The “Auto Model” button is used to go through every curve and try to set some initial model parameters. This process can take several minutes to complete. Once complete, the model can be evaluated on a curve by curve basis and adjustments made accordingly. As previously stated, it is not recommended that one go through this process.
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