Quality Control in Radiation Therapy, A New Concept: Dosimetry Check Wendel Dean Renner Math Resolutions, LLC FDA Cleared April 27, 2001 US Patent 6,853,702 http://www.MathResolutions.com

Radiation Therapy Needs Feedback The quality control procedure should tell you if there is a mistake. Diligence in hunting for a mistake is a weak quality control system. Without feedback, how do you know there has been no mistake? This project evolved from an initial consideration of how to quality control compensating filters that are to be used to accomplish IMRT. It soon became apparent that the same solution can be applied to just about any form of radiation therapy. The current method probably most universally used for the quality control of a treatment plan is to have someone review the plan and sign off on it. With that procedure it depends upon the diligence of the person to find a mistake. But without some feedback based upon an actual measurement a mistake could be missed. Further, there could be other mistakes in the execution of the plan involving the devices placed into the collimator. For example, wedges, compensators, or blocks could be wrong. Maybe the wrong file was downloaded to the accelerator multi-leaf system. A QA system that depends upon a measurement can tell you if something is wrong, and can also provide proof that the dosimetry and setup was right. http://www.MathResolutions.com

The New Method: Dosimetry Check Take a calibrated picture of each treatment field. Download the treatment plan (Dicom RT or RTOG format). Recompute the dose using individual measured field fluence of each beam. Compare the dose to the plan dose. See references: WD Renner, et. al., "A dose delivery verification method for conventional and intensity-modulated radiation therapy using measured field fluence distributions", Medical Physics, Vol. 30 No. 11, Nov. 2003, pages 2996-3005. WD Renner, K Norton, "A method for deconvolution of integrated electronic portal images to obtain incident fluence for dose reconstruction", JACMP, Vol. 6, No. 4, Fall 2005, pp. 22-39. WD Renner, "3D Dose Reconstruction to Insure Correct External Beam Treatment of Patients", Medical Dosimetry, Fall 2007, Vol. 32, No. 3, pages 157-165. http://www.MathResolutions.com

Use an Available Electronic Device to Take a Calibrated Picture of Each Field as Used for Treatment Use the Amorphous Silicon Flat-panel Electronic Portal Imaging Device (EPID) on the Varian, Elekta, or Siemens Accelerator in Integration Mode. Use the MapCheck diode array. Use an ion chamber array such as the PTW729 or MatriXX. Using an EPID is most efficient. Works with Varian, Elekta, and Siemens EPIDs. http://www.MathResolutions.com

Use X-ray Film to Take a Calibrated Picture of Each Field as Used for Treatment Film at 100cm on couch or in blocking tray. Use 1 to 3 mm of copper on top of x-ray film. Can use step wedge or dosimeter to calibrate. Can rescale the curve. The beam should be set up as for treatment. 1 percent accuracy is achievable for confidence. Presently you can use the new Kodak EDR2 film in ready pack but we also want to consider using some sort of electronic device instead of film. With film, put the film at 100 cm on top of the couch. Use solid water for bolus. We want to measure the x-ray fluence, not contamination electrons. You must use a consistent setup. Since the film is covered by uniform THIN material, the variation in film speed over the area of the field is not an issue as it would be if you were measuring a percent depth dose. We do not want a phantom under the film. We need an accuracy to 1 percent to have confidence in the result. We have found that 1 to 3 mm of copper works best for shielding the film from contamination electrons. You can adjust the film response curve with an ion or diode measurement, or rescale the calibration curve from a single 10x10 cm field test exposure. http://www.MathResolutions.com

Calibrate to “Relative” Monitor Units A Unit for Fluence RMU is an intensity fluence of the x-ray radiation. Examples of relative monitor units: 100 mu for a 10x10 field is 100 relative monitor units. 100 mu for a 40x40 field with scatter collimator factor of 1.05 is 105 relative monitor units. 100 mu for a 20x20 field with a wedge factor of 0.5 and scatter collimator factor of 1.02 is 51.0 relative monitor units. We had to invent a new unit which we are calling “relative monitor units” for a unit for fluence. Just run the calibration film using 10x10 field. Do the same when calibrating an ion chamber or diode. [read the examples on the slide] http://www.MathResolutions.com

Beam 4 of Seven Field Head and Neck Case to be Shown An IMRT case obviously. http://www.MathResolutions.com

Compute the Dose Download the plan in Dicom RT or RTOG format. Need CT scans, beam positions, 3D dose matrix, outlined regions of interest. Otherwise need the CT scan files and must position the beams to the same isocenter and angles. Must associate each field with the measured field picture. Next we compute the dose distribution to the patient based on the field fluence measured for each field. We need the CT scans used for the plan. To do a dose comparison we would like to have the plan’s dose. This information can be downloaded in Dicom RT or RTOG format. Other wise you will have to relocate isocenter for each beam and type in the couch, gantry, and collimator angles. When you create a second beam, it will start with the same isocenter as the prior. This should not take much time. If you did not download the skin contour we have software that will automatically generate the same. You must then associate each beam with the measured field for that beam. An issue here is also having a positive lock on the orientation of the measured field as regards to collimator angle. The field is to be in beam’s eye view coordinates at your zero or nominal collimator angle. http://www.MathResolutions.com

Show plan dose and recomputed dose together. Dose Comparison Tools Then you can just compute the dose distribution in any 2d plane or a dose cloud in a 3d room perspective view. The dose will be shown in centi-Gray. If you downloaded the 3d dose matrix from the plan, you can show both together with the plan dose in one color and Dosimetry Check in another color. Shown is a comparison for a seven field head and neck case. DC is 6609 cGy at cal point, plan was 6543, 1.0% difference. Show plan dose and recomputed dose together. http://www.MathResolutions.com

Transverse Plane http://www.MathResolutions.com Distance between isodose curves does not necessarily reflect a large difference in dose. The gradient between could be very small over a large distance. http://www.MathResolutions.com

Dose Comparison Tools: Gamma Method Which is why the gamma method was invented. See the reference in Medical Physics by Daniel Low, et. al., Vol 25(5) May 1998, pp. 656-661, "A technique for the quantitative evaluation of dose distributions." 3% - 3 mm criteria. Red tinted area is >= criteria. http://www.MathResolutions.com

Gamma Method: Sagittal Plane See the up coming 1D profile plot. Dose difference is all in low dose areas or buildup area. 3% - 3 mm criteria. But note all outside of target. http://www.MathResolutions.com

Dose Comparison Tools: Compare profile through patient. Notice disagreement is in low dose area. Not typical. Cases usually agree all the way across. Line of plot is shown on CT sagittal segment. http://www.MathResolutions.com

Gamma Volume Histogram Gives a single number to evaluate the plan. 92.7% of the body volume at 20% of the dose or more has a gamma value <= 1.0 http://www.MathResolutions.com

3D Gamma Surface: 3%-3mm http://www.MathResolutions.com Can show where it is. http://www.MathResolutions.com

Dose Comparison Tools Another option with a downloaded 3d dose matrix is to show the dose difference. Certain values can be tinted. Shown is a 196 centiGray dose difference (for sum of all fractions out of 6543 cGy). Show dose difference between plan and recomputed plan, here 196 cG out of 6543 (3%) is tinted red. But we are not considering distance. http://www.MathResolutions.com

Dose Comparison Tools Show dose difference in 3D perspective room view. Red region is an overdose difference. Cyan shows under dose difference. A dose difference can also be shown in a 3d room perspective view, with one color to show higher dose and another to show lower. This is to show you where the dose is different. http://www.MathResolutions.com

Dose Difference Volume Histogram Lastly, you can generate a dose difference volume histogram. Larger doses are shown in red, smaller in cyan. These tools will provide you a means to quickly document the status of the plan check. It is also useful to compare the maximum dose and dose at specific points. For the body volume selected here. http://www.MathResolutions.com

What Does It Take? Fifteen minutes (or treatment time) to do a dry run without the patient. Convert EPID images to fluence, a few minutes. Download plan, a few minutes. Run our program “Dosimetry Check,” print dose distribution, compare dose. Probably 30 to 45 minutes. Someone needs to look at the results and approve the treatment. So what does it take to perform this check? If you cannot download the plan in RTOG format, you must locate the beams. These time estimates are for after the use of this procedure is routine. http://www.MathResolutions.com

What Do You Get? Dose shown on patient anatomy in 2D and 3D. Dose computed dependent upon the measured field fluence. A check on everything in the beam. Confidence that the dosimetry and delivery is correct. Showing the dose on the same anatomy is not an abstract comparison. Remember, our purpose is not to QA the planning system or the accelerator, but to QA a particular patient plan as delivered. http://www.MathResolutions.com

What You Don’t Get: Does not say anything about whether the fields are on the patient correctly. Probably insensitive to using the wrong energy. As regards patient positioning, besides port films, we could expand upon this technology by employing calibrated TV or digital cameras in the treatment room to verify the patient’s position. We would compare the skin contour in different views. http://www.MathResolutions.com

Why? Above all else, do no harm. http://www.MathResolutions.com In conclusion this technology will provide proof that can go into the patient’s chart that the dosimetry and devices used in the beam were correct. You can view these slides and some further discussion and examples of the QA method at our web site. http://www.MathResolutions.com

Two Kinds of Errors: Systematic errors (in your procedures, data, etc.). Random errors (in executing the procedures). http://www.MathResolutions.com

Systematic Errors Can be found by testing your procedures. Irradiating a phantom and measuring the dose constitutes a feedback system. Without this feedback, you could miss a problem. http://www.MathResolutions.com

Random Errors Without feedback you will never know for sure that the treatment was correct for each patient. http://www.MathResolutions.com

Overdose The patient reaction will tell you too late! http://www.MathResolutions.com

Under Dose Might never be noticed. Results in lost opportunity to effectively treat the cancer. http://www.MathResolutions.com

Do we really know the extent of mistakes that occur in radiation therapy? http://www.MathResolutions.com

Effective Quality Assurance We want to maximize feedback. We want to maximize the amount of information that is measured in the treatment room. We want to minimize the amount of information we use that is NOT measured in the room. http://www.MathResolutions.com

Monitor Unit Check Redundancy is good. But there is no feedback. http://www.MathResolutions.com

Present Methods with Feedback Diode surface measurement at one point on each field to be compared to computed dose. Irradiate a cylindrical or square phantom using the plan, recompute the plan to same phantom to compare. http://www.MathResolutions.com

Diode Surface Measurement This is a simple QA procedure, yet a surprising number of centers do not do it. But this only checks the dose at one point. Wedge could still be in wrong direction. Compensator or IMRT could be wrong. Blocks and/or field shape could be wrong (should also pick up from film review, but some redundancy would be good). Dose distribution could still be wrong. http://www.MathResolutions.com

Phantom Quality controls how the beams add up. Maximizes the information measured in room. Can only show dose where measured in the phantom. Comparison of dose is somewhat abstract in relation to the patient. Assumption that dose in patient will be right might not hold. Does not tell you if beams are on the patient correctly. http://www.MathResolutions.com

Our new method: Dosimetry Check Shows the dose on the patient anatomy. Evaluation of dose is not abstract. Can handle arc therapy (but we presently don’t have a device to measure a field that changes shape during gantry rotation). Can show dose in any plane or 3D dose cloud. Same limitation of only checking dosimetry. Easy and fast to do. http://www.MathResolutions.com

Dosimetry Check Adds a Powerful Tool for Quality Control May replace some less effective procedures. May compliment others. http://www.MathResolutions.com

Math Resolutions, LLC, is offering software to accomplish the new method. FDA 510(k) K010225. Software, manuals,and information available at our website: http://MathResolutions.com. U.S. Patent 6,853,702 on this process. http://www.MathResolutions.com

Measuring the field with X-Ray film One could use a device instead of film. Optimally the field should be measured during treatment. That would require a device that the patient could be treated through. Film must be digitized. We would like to use a device instead of film if dosimetry can be done with the device. Ideally, we would like to measure the field during treatment. That would require a device that we can treat the patient through. With film we need a film digitizer. http://www.MathResolutions.com

Use 1 to 3 mm Copper for X-ray Film We have found that using 1 to 3 mm of copper to shield for contamination electrons gives accurate results. 1 mm for 6 MV, 3 for 18 MV Testing is done by using the measured fluence to compute dose profiles at depth that can be compared to measured profiles. http://www.MathResolutions.com

Film to Use Use V film up to 125 mu. Use EDR2 film if over 125 mu. Consider the effective mu for IMRT. Limits depend upon film digitizer. Range depends upon the distance you use. How dark you can go with V film depends upon the film scanner. Vidar should go to a density of 3.00. We have run curves up to 150 mu at a density of 2.89. http://www.MathResolutions.com

Kodak EDR2 Film in Ready Pack We are here showing H&D curve with the density as the independent variable along the horizontal axis because that is the way the curve will be used, to map density to monitor units. Note that a density of 3.0 occurs at 650 mu at 100 cm for a 10x10 cm field size. This should include most field prescriptions. Our software also has the capability to scale the dose given the monitor units used to shoot the film and the monitor units intended for the field. Curve crosses the density of 3.0 at 650 monitor units at 100cm. http://www.MathResolutions.com

Film crosses density of 3.00 at 200 mu at 100 cm Kodak Therapy V Film Film crosses density of 3.00 at 200 mu at 100 cm http://www.MathResolutions.com

Calibration Procedures for X-Ray Film Include ion chamber or diode in bolus stack. Or use a step wedge. Run curve to calibrate the step wedge once. Thereafter use the step wedge with each case. Or consider rescaling the calibration curve from a single test exposure. The goal is accuracy to 1 percent for measuring relative mu We need to correct for the variation in film processing if using film. There are two ways we can do this. One is to make a direct measurement for some spot on the film with an ion chamber or diode. We will have to know where the measurement was made so that we can later identify the spot on the image of the field with the mouse so that the field can be normalized to the measured dose at that point. Or we must first calibrate a step wedge, and then run a film taken of the step wedge with each case. Another option is to make a single exposure of a the calibration field size (10x10 cm). Suppose the exposure was 50 mu, but due to film processing the calibration curve reports 52 mu. The curve can then be rescaled by multiplying the result by the ratio 50/52. Our software provides support for any of the above methods. http://www.MathResolutions.com

Example IMRT Case computed from films http://www.MathResolutions.com

Sagittal, IMRT http://www.MathResolutions.com

Coronal, IMRT http://www.MathResolutions.com