Using Dosimetry Check for IMRT QA

With Eclipse and Varian EPID

 

By D. Jay Freedman, Kevin Norton

Edited by Wendel Dean Renner

 

Sept 20, 2006

 

Introduction. 1

1.Exporting the plan from Eclipse (or Somavision) to the Dosimetry Check computer 1

2.Creating the QA plan. 2

3.Preparing the QA plan for Dosimetry Check imaging. 2

4.Acquiring and exporting images for Dosimetry Check. 3

5.Bringing CT slices, treatment plans, and dose matrices into Dosimetry Check. 4

6.Bring the EPID images into Dosimetry Check. 5

7.Performing the IMRT QA in Dosimetry Check. 6

8.Reference Points. 8

 

 

 

Introduction

Ideally, IMRT QA is performed using the same plan and R&V parameters that will be used during the patient treatment. This includes measuring or recording dose using the same linear accelerator geometries that the patient will experience. Unfortunately, Varis does not allow this but we are able to deliver and record radiation dose under the same geometry dictated by the plan. The one exception is the couch angle, which has no affect on the outcome here.

 

Dosimetry Check works by converting each beamís 2D image information (film or EPID images) to a calibrated fluence, which is then projected onto the patientís CT dataset. In this way the dose that the linac delivers is reconstructed on the same CT dataset as the original plan and the planned and reconstructed doses are compared.Plan comparison includes isodoses, point doses, dose differences, 3D surface doses, gamma analysis, and DVH analysis.

 

 

1.Exporting the plan from Eclipse (or Somavision) to the Dosimetry Check computer

a.      In Field Setup, make the approved plan active

b.      In the File dropdown menu chose Export/Wizard

c.      Under Export Objects select Plan, then Next

d.      Under Plan Export Details select Include Structures, Include Images, Planning Fields, Total Plan Dose and Absolute Values; then Next.Note: Dosimetry Check reconstructs the dose for a single fraction.Consider downloading the dose for a single fraction.

e.      If the DVH Export Details window opens, click on Clear and Next.

f.        In the Filter Selection window, select the DICOM export filter created for this purpose, then Next. (To map to the computer that runs Dosimetry Check if on the same network, select the drive and then type in the path.)

g.      When the File Export Filter opens, select Change for All Objects.

h.      The Save As location should be (drive-letter):\MathResolutions\Images.d\Smith, where Smith is a patient name.If not, navigate to that location.If necessary, create the patient folder using the patientís last name.If itís a boost plan, use a convention such as place a 2 at the end of the name (Smith2).Double-click on the folder to ensure that it appears in the Save As line near the bottom of the window.Then click Open.

i.        Select all the objects in the File Export Filter and click on Finish.

 

 

2.Creating the QA plan

a.       If not done, from Eclipse (or Somavision), push the plan to Treatment in the usual manner.

b.      Create a new QA course and name it QA A1-5, for example.

c.       Copy the plan from the treatment course (probably 01) to the new QA course and make it active.Name it QA A1-5, the same as the new course.Remove any Setup Fields that may be present.Save All.

d.      Create a new reference point called DC Calc located at the isocenter or the RadCalc point.Make it primary.Remove (do not delete) the old reference point(s) using the reference point organizer.Save All.

e.       Push the QA plan to Treatment in the usual fashion.

 

From here on all Varis/Vision work may be done on any Varis workstation.

 

 

3.Preparing the QA plan for Dosimetry Check imaging.

a.      Open the QA plan in RT chart and select the Parameters tab.

b.      Complete the table lat, long, and vert cells for each field using

Vrt = 100.0, Lng = 17.0 for 21EX and Trilogy or Lng = 42.0 for 21CD; and Lat = 100.0.Save All.Note:these settings are to avoid a collision.

c.      To create the calibration fields required by DC (10x10 cm), copy each treatment field in succession, and then paste it back into the same QA plan as a treatment field without reference image.If there are split fields, only one calibration field is needed for each gantry angle.The quickest way to edit each cal field is to right click on it and select properties.

d.      Make the ID of each copied field cal1, for example, referenced to its original treatment field (A1). Leave the Name blank.

e.      Enter 100 MU.

f.        Under Geometry, change the field sizes for each calibration field to 10x10, symmetric.Even if the field size is 10.0, re-enter the value of 10.0 to force the field size to be symmetric.Change all cal field couch angles to 180.Click OK to close properties.

g.      For each Calibration field, click on the MLC icon in the lower left window and delete it.

h.      Save All.

i.        While still in the Parameters window you may re-order the beams using the Order button near the top right of the window. It is necessary to acquire each cal beam with itís associated treatment beam while at that gantry angle. So, for example, cal1 should be next to A1 in the beam order list. Save All. If you forget to order the beams here it may also be done at the 4D Treatment Console.

j.        Change to the Reference Points tab.IGNORE THE EMPTY YELLOW CELLS.Set the fractionation (at the top of the page) to 1 fraction.Save All.

k.      On the Scheduling Tab, schedule 1 session.Activate it.

l.        Click the Show Sequence Image Scheduling Check box.

m.    Highlight all the empty cells just under the Active cell.Right click in one of them and select IMRT QA.This automatically tags each beam to acquire an integrated image at the 4D Treatment Console.Save All.

n.      Return to the Parameters tab, select the Parameters drop down menu and select Validate Plan.Fix any problems that emerge.Save All.

o.      Open Time Planner and schedule an IMRT QA session for the desired day.

 

 

4.Acquiring and exporting images for Dosimetry Check

a.      QA images are all acquired at the same gantry and collimator settings as the treatment fields.Each gantry angle also requires a 10x10 calibration image.(This depends upon the physical stability of the EPID as to whether you need to find the central axis at each gantry angle.)

b.      In the treatment room extend the EPID using the P1 button.Then raise it to its maximum vertical setting.In each motion allow sufficient time for the image to ďfindĒ its final position.Note that the imager may need to be offset to capture large asymmetric fields.

c.      Open the patient in 4D Console and re-order (if necessary) the beams so that each cal beam is treated just before or after its treatment beam (you should go to each gantry angle only once).Treat all fields.The portal images will be automatically saved.Note also that the beam name is included in the image files names.This is important for Dosimetry Check to automatically sort images to the corresponding treatment beam.

d.      After the last field is treated, close the patient in 4D Console (there is no billing at this time), and open the patient in Vision Task Review.Approve each QA portal image and save all.

e.      Change to the Patient Viewing Task.

f.        In the Selection tab check Treatment Fields and Portal Images.Uncheck Ref. Images.

g.      In the Fast Track Context window choose the treatment fields containing the images just acquired.

h.      In the Available Images window choose the images desired and move to the gallery.

i.        Click on Apply and move to the 2D Viewing tab.

j.        Make sure you have all the needed images in the gallery at the bottom.Select all images, then click on the File/Export/Wizard dropdown menu.

k.      Select Image, Next.

l.        Select Gallery Selection, Include Structures, Next.

m.    Select the DICOM export filter created for this purpose, Next.

n.      Select Change for All Objects and choose the patientís file folder on the Dosimetry Check computer (for example, c:\MathResolutions\Images.d\Smith), Open.

o.      Manually choose all the files that appear and click on Finish, then OK.

 

At this point, all files/images required to perform the QA analysis should reside on the DC computer in (c:\MathResolutions\Images.d\PatientFolder).

 

 

5.Bringing CT slices, treatment plans, and dose matrices into Dosimetry Check

Dosimetry Check (DC) consists of three programs, shortcuts for which are on the DC computer desktop.ReadDicomCheck translates the Eclipse plan, structures and dose into DCís patient directory.ReadVarianEPID converts the EPID images to fluence and normalizes to the mu for the 10x10.Dosimetry Check does the rest:calculates 3D dose from the fluence, compares Eclipse dose to reconstructed dose, gamma analysis, and so on.

 

ReadDicomCheck is used first since this is where the patient is entered into the database.Then run ReadVarinEPID to convert the field images.Just remember that the first time you use Dosimetry Check you must specify which structure is the skin (Body) and which RED curve to use to convert CT number to density.

 

Note: When exiting any DC programs please use the Exit button at the top left of the window.An abnormal exit will leave a lock file on the patient directory which you would have to delete.

 

    1. Open ReadDicomCheck.exe
    2. Click on Patient/New and fill in the form and click OK.
    3. If you wish to add additional demographic information, choose the appropriate menu button.Otherwise, click on Return.
    4. Click on Stacked Image Sets/New
    5. Enter a name for the image set in the popup window and click on OK (choose a descriptive name such as A1-5 pelvis, or A6-10 cd).Click on OK in the new popup window.
    6. Navigate to the folder containing the CT images.Select All the CT images in the folder and click OK.You can put CT* for the filter and hit Select All instead of clicking on all the image file names.
    7. Confirm the patient name is correct by clicking on it in the popup window and click on OK.
    8. The program will calculate orthogonal scout views and post the images.Click on OK in the popup.
    9. Click on Return.
    10. Click on Stacked Image Sets\Read In Dicom RT Structures and navigate to the correct location.
    11. Select the structure set file.It will begin with RS. and will probably be at the bottom of the list.Click OK.
    12. Click on Plan/Read Beams.The file selection window will open again.If necessary, navigate to the right place.Beams are in the file beginning with RP.Select the file and click on OK.
    13. If a popup appears instructing you to select an accelerator, click on OK, then on the menu bar click on Select an Accelerator.Then choose the correct unit (for example t VarianStd for all 6 MV beams and GeneralAccel for 10 MV and 18 MV.This depends upon the machine data you have set up to use).
    14. Click on Plan/Read Dose.Select the dose file.It begins with RD., and click on OK.
    15. Exit the application.

 

 

6.Bring the EPID images into Dosimetry Check

a.      Open ReadVarianEPID.exe

b.      Click on Select Accelerator (for example select VarianStd for all 6 MV beams and GeneralAccel for 10 MV and 18 MV.Use the accelerator you have set up).

c.      Click on Select Energy

d.      Click on Continue

e.      Click on Patient/Select and choose your patient.Click on OK

f.        Click on Convert Images.Navigate to where the EPID images were stored (c:\MathResolutions\Images.d\PatientFolder).

g.      Select all of the fluence images (Click on each image file Ė no need to use the Shift or Ctrl keys).You DO NOT need to select the calibration images.Click on OK.

h.      Dismiss the calibration curve graph if it pops up.

i.        The Convert to MU screen will open.You do not need to select a calibration curve since each beam image will be calibrated with its corresponding calibration image.Leave the calibration curve blank.[To stop the calibration curve from being selected, erase the file EPIDcalFile in data.d/acc_name/Xnn.You donít want to use the calibration curve by accident if you forget to type in the mu below for a 10x10 reference field.]But, you do need to select the appropriate Deconvolution Kernel.

j.        A separate calibration image must be brought in for each fluence image at each gantry angle unless your EPID does not drift relative to the c.a. upon gantry rotation.For each field in turn, click on the Center/Calibration button beneath the field name.Alternately, you could use a single 10x10 to calibrate all the images IF the EPID does not move significantly with gantry rotation.In that case use the Center All/Cal. All button and type in the mu in the provided text field at the bottom of the popup.

k.      Choose the 10x10 calibration image and click on OK.A new screen showing the cal beam image opens.

l.        Click on the button in the upper right corner of the frame with the image.The image will fill the window and the button will turn yellow.

m.    If you want to enlarge the image, place the cursor on the center of the field and push the middle mouse button (scroll wheel) once or twice.(The right mouse button zooms back out).

n.      Using the controls in the LocateField window, adjust the position so it accurately aligns the image to the projected field size.Usually there is no need to alter the field size.Then click on dismiss.The box surrounding the image will turn green.Repeat j through n for each image if calibrating each image separately.

o.      When the last Calibration image is centered, return to the ConvertToMU window and enter the calibration image exposure MUs for each field (probably 100MUs).You can change the label for each image if you want, or its output file name.Click on Convert to RMU in the lower left of the window.NOTE:if you forget to enter MU in one of the fields, the calibration curve will be used instead if one is showing, otherwise you will get an error message.

p.      A screen will open showing all fluence maps converted to dose.You are done with this program.

q.      Click on Return on the toolbar and then Exit.

 

 

7.Performing the IMRT QA in Dosimetry Check

1.      Open Dosimetry Check.exe

2.      Click on Patient/Select and choose your patient.Click on OK.

3.      First time do c - i:click on Stacked Image Sets/Select.Choose your image set and click on OK.All the CTs will populate a new screen.

4.      This is a good time to enlarge the main application window to fill the screen by clicking on the box icon in the upper right of the window.

5.      Click on Stacked Image Sets/Options

6.      Click on Skin.If the structure named alongside the Select Skin Volume button on the toolbar does not represent the patientís skin surface, click on the button to select the correct structure.

7.      Click on Return, then select the Density button on the toolbar.

8.      Click on Select Curve.Dismiss whatever shows up in the little popup and select the CT number to density curve to use.Click on OK and OK again when the graph appears.

9.      On the toolbar, click on Return twice to return to the main toolbar.

10.  Click on Applications pulldown to Dosimetry Check.

11.  Click on Plan/Retrieve Plan.Select the desired plan and click OK.Another new screen will be created and be populated by the beam images you imported above using ReadVarianEPID and the plan toolbar is pushed.If you have not used ReadVarianEPID yet, the window will still be created but the sub-windows will be empty.This is normal.After you execute ReadVarianEPID these beam images will show up the next time you re-open the plan IF the image files created above contain the name of the beam.If not, you will have to manually select the converted field dose files that belong to each beam.Selecting more than one image for a beam will cause the two to be added together.Once assigned, the program does not look again unless you manually reselect images for a beam.

12.  Optional:select each field in turn by clicking on its image, click on the Restrict Area button in the tool bar.

13.  Then use the RestrictField controls to approximately center the box around the fluence and enlarge the box to allow a generous margin.You can also drag a box with the left mouse to accomplish the same.The goal here is to reduce calculation time later by not forcing the program to calculate over the entire black field, but on the other hand you must provide sufficient margins to allow for faint signals around the edges of the visible fluence maps.Margins of about 3 to 4 cm should be sufficient.

14.  In the little reddish-pink text window at the top of the screen on the plan toolbar enter the number of fractions planned if the downloaded dose was for more than one fraction.

15.  Select Display pull down and go down to Make Screen Centered on Isocenter.Then select one of the beams.This opens yet another new screen showing transverse, coronal, sagittal, and 3D perspective room view of the anatomy (ROIís).

16.  Click on the Evaluate pull down and select Compare 2D Dose.

17.  In the popup window, choose a dose value of interest, say, the prescription dose.Select a screen on the Main window which displays the desired orthogonal views and select a frame (the current frame is outlined in red).Click on Display in Current Frame.

18.  Note that you can change the colors of the respective isodose lines, line width, and make either one dotted.You can turn on and off the display of the hot spot, and turn on and off reconstructed dose, the plan dose (foreign), and dose difference with their respective toggle buttons.

19.  After the calculations are done, the current frame may be enlarged and the image zoomed to check results.Add or change isodose and difference values as desired.

20.  To print the results, enlarge the desired frame to full screen and click left mouse inside the frame.Then press the Print Screen key on the keyboard.A Print Image window will open.In the pink text area at the top, enter any appropriate legendary information such as dose values, color values, dose difference values.

21.  Click on the Print button at the bottom of the window.You may also save the images from this popup.The print job will appear using Gsview as a printer review.Look for the Gsview opening up.Send to the print from Gsview

22.  Then Dismiss the print window when done.

23.  It may be useful to compute the difference volume histogram.This takes a while and may be skipped.It is available under the Evaluate button.

24.  Click Evaluate/Compare with Gamma Method.This will trigger computing all the beam for the full 3D matrix which may take a few minutes.

25.  Leave the distance at 0.3cm and the difference at 3%.Enter a dose value, such as the prescribed dose or dose to isocenter, for the normalization value.Choose a unique color for the Gamma curve (default is red) and turn the tint on.Start with a gamma value of 1.0, then click on Display in Current Frame.The calculation takes a few minutes.

26.  If the plan is good, there will be little red tinted areas for a gamma value of 1.0 and mostly will be outside of the target area.Try other, lower values, if nothing shows up.Print a representative plot.

27.  Gamma values may be calculated and printed for the other orthogonal views as well.

28.  Compute a gamma volume histogram.Selecting the body outline will give the percent of points, hence volume, with values <= a gamma value of 1.0 and is a useful single number statistic.

 

 

8.Reference Points

Points are specified in Eclipse in the Dicom coordinate system:Z axis towards the patientís head, Y axis down.Dosimetry Check uses the IEC system, Y toward the patientís head, Z axis up.To enter a point relative to isocenter, subtract the Eclipse isocenter coordinates from the Eclipse reference point.†† Enter the result relative to isocenter.†† Eclipse X as X, Eclipse Z as Y, and Eclipse ĖY as Z.All bets are off for a prone or feet first patient orientation, check your results.