Скачать презентацию Quality Control in Radiation Therapy A New Concept

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Quality Control in Radiation Therapy, A New Concept: Dosimetry Check Math Resolutions, LLC www. Dosimetry. Check. com FDA Cleared April 27, 2001 http: //www. Math. Resolutions. com US Patents 6, 853, 702, 8, 351, 572, 8, 605, 857 1

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? http: //www. Math. Resolutions. com 2

The New Method: Dosimetry Check • Take a calibrated picture of each treatment field using EPID, arrays, or film. • Download the treatment plan (Dicom RT). • Recompute the dose using the individually measured field fluence of each beam (pencil beam or convolution/superposition). • Compare the dose to the plan dose. http: //www. Math. Resolutions. com 3

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 Map. Check diode array. • Use an ion chamber array such as the PTW 729 or Matri. XX. • Can use film. http: //www. Math. Resolutions. com 4

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 10 x 10 field is 100 relative monitor units. • 100 mu for a 40 x 40 field with scatter collimator factor of 1. 05 is 105 relative monitor units. • 100 mu for a 20 x 20 field with a wedge factor of 0. 5 and scatter collimator factor of 1. 02 is 51. 0 relative monitor units. http: //www. Math. Resolutions. com 5

Beam 4 of Seven Field Head and Neck Case to be Shown http: //www. Math. Resolutions. com 6

Compute the Dose • Download the plan in Dicom format. Need CT scans, beam positions, 3 D 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. http: //www. Math. Resolutions. com 7

Dose Comparison Tools Show plan dose and recomputed dose together. http: //www. Math. Resolutions. com 8

Transverse Plane http: //www. Math. Resolutions. com 9

Dose Comparison Tools: Gamma Method 3% - 3 mm criteria. Red tinted area is >= criteria. http: //www. Math. Resolutions. com 10

Gamma Method: Sagittal Plane 3% - 3 mm criteria. But note all outside of target. http: //www. Math. Resolutions. com 11

Dose Comparison Tools: Compare profile through patient. http: //www. Math. Resolutions. com 12

Gamma Volume Histogram 92. 7% of the body volume at 20% of the dose or more has a gamma value <= 1. 0 http: //www. Math. Resolutions. com 13

3 D Gamma Surface: 3%-3 mm http: //www. Math. Resolutions. com 14

Dose Comparison Tools Show dose difference between plan and recomputed plan, here 196 c. G out of 6543 (3%) is tinted red. But we are not considering distance. http: //www. Math. Resolutions. com 15

Dose Comparison Tools • Show dose difference in 3 D perspective room view. • Red region is an overdose difference. • Cyan shows under dose difference. http: //www. Math. Resolutions. com 16

Dose Difference Volume Histogram For the body volume selected here. http: //www. Math. Resolutions. com 17

What Does It Take? • • • Download and import the plan. Treatment time to do a dry run without the patient. OR Take images during treatment for transit dosimetry. Automated mode available to convert EPID images to fluence and generate a report. • OR • Run the program “Dosimetry Check, ” compare dose and generate a custom report. • Someone needs to look at the results and approve the treatment. http: //www. Math. Resolutions. com 18

Transit Dosimetry • Images are back traced through the patient CT scan set to produce the in air fluence before the patient. • Deconvolution of EPID image takes into account scatter of patient to EPID. • Dose is then computed same as for pretreatment images. http: //www. Math. Resolutions. com 19

What Do You Get? • Dose shown on patient anatomy in 2 D and 3 D. • Dose computed dependent upon the measured field fluence. • A check on everything in the beam. • Confidence that the dosimetry and delivery is correct. http: //www. Math. Resolutions. com 20

What You Don’t Get: • Does not say anything about whether the fields are in fact on the patient correctly. • Probably insensitive to using the wrong energy (pre-treatment). http: //www. Math. Resolutions. com 21

Why? • Above all else, do no harm. http: //www. Math. Resolutions. com 22

Two Kinds of Errors: • Systematic errors (in your procedures, data, etc. ). • Random errors (in executing the procedures). http: //www. Math. Resolutions. com 23

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. Math. Resolutions. com 24

Random Errors • Without feedback you will never know for sure that the treatment was correct for each patient. http: //www. Math. Resolutions. com 25

Overdose • The patient reaction will tell you too late! http: //www. Math. Resolutions. com 26

Under Dose • Might never be noticed. • Results in lost opportunity to effectively treat the cancer. http: //www. Math. Resolutions. com 27

Do we really know the extent of mistakes that occur in radiation therapy? http: //www. Math. Resolutions. com 28

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. Math. Resolutions. com 29

Monitor Unit Check • Redundancy is good. • But there is no feedback. http: //www. Math. Resolutions. com 30

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. Math. Resolutions. com 31

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. Math. Resolutions. com 32

Phantom • Shows 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 if right in phantom might not hold (such a case was encountered). • Does not tell you if beams are on the patient correctly. http: //www. Math. Resolutions. com 33

Our new method: Dosimetry Check • • • Shows the dose on the patient anatomy. Evaluation of dose is not abstract. Can handle arc therapy with EPID in cine mode. Can show dose in any plane or 3 D dose cloud. Same limitation of only checking dosimetry. Easy and fast to do. http: //www. Math. Resolutions. com 34

Dosimetry Check Adds a Powerful Tool for Quality Control • May replace some less effective procedures. • May compliment others. http: //www. Math. Resolutions. com 35

Math Resolutions, LLC, is offering software to accomplish the new method. • FDA 510(k) K 010225, K 101503, K 132605, K 162577 • Software, manuals, and information available at our website: • www. Dosmetry. Check. com • www. Math. Resolutions. com. http: //www. Math. Resolutions. com 36