Clinical Evaluation of real-time, patient-centric QA using the Delta 4 Discover Karl H Rasmussen, Ph.D.. khrasmussen@uthscsa.edu Nema Bassiri bassirin@livemail.uthscsa.edu Division of Medical Physics Cancer Therapy & Research Center at UT Health San Antonio San Antonio, TX 78229
Disclaimer ScandiDos paid for my flight and hotel room in order for me to come out and give this presentation
Transmission Detectors Not a new concept 1D, plane of diodes Provide plenty of useful information Verification of machine related errors Dose output drifts, MLC errors, angular position deviations, etc. Increase patient specific safety Monitor patient specific plans Detector deviations on a fraction by fraction based Could provide fluence information *Venkataraman S. Phys Med Biol. 54(10). 2009
Current IMRT QA Approach Calculated Dose Measurement Gamma Index Analysis Instant Pass or Fail All detectors analyzed with same criteria Only a one time verification measurement Patient dosimetric impact not quantified Impact on PTVs? OARs? Unknown. AAPM TG 218 Tolerance Levels and Methodologies for IMRT Verification QA
Current ScandiDos QA Flexibility Express Measure alone MLC position Gantry & collimator angle Combine with Delta 4 Synthesis Dose Anatomy + =
Goal: Real-time, Patient-centric QA Image guided RT Delta 4 Discover Accurate entrance dose measurement Utilize current available information during treatment Using general CT data or fraction specific CBCT data Reconstruction of delivered dose in patient imageset Entrance fluenceas a more pure signal should be easier to produce accurate results
Discover Specifications 4040 diodes 19.5 x 25 cm 2 1mm Ф in beam direction Stated Accuracy Output: 1.5% MLC: 1mm Stated Attenuation: ~1% 2.0mm 19.5 cm 25 cm *Courtesy of ScandiDos
Discover Specifications Slim profile Wi-Fi 802.11n 10 kg with battery > 6 hours Non-Permanent mounting Slides out of way for field light viewing *Courtesy of ScandiDos
Interface Discover Software Interface
Analysis Tools From Fraction to Control Point to per beam analysis Dose distribution Dose deviation DTA Gamma Index (Dose & MLC) Dose profile analysis 3D dose distribution DVH Total delivered dose *Courtesy of ScandiDos
Discover Analysis Tools.
UT Health Evaluation Characterization Attenuation Beam changes Dose output detectability Temporal detection stability Open field VMAT 3D
Attenuation Varian Clinac 6 MV Various FS Ion chamber measurements at various depths Attenuation (6MV) 1.5cm 10cm 3x3 1.47% 1.80% 5x5 1.72% 1.71% 10x10 1.61% 1.57% 20x20 1.53% 1.62% 30x30 1.31% 1.39% Avg. 1.53% 1.62%
PDD 100% 90% 80% 70% 60% 5x5 Open 5x5 Discover 10x10 Open 10x10 Discover 20x20 Open PDD 50% 40% 20x20 Discover 30% 20% 10% 0% 0 25 50 75 100 125 150 175 200 225 250 275 300 Depth [mm]
Beam Parameters PDD(10) Open Discover Abs. Diff. 3x3 69.1% 68.8% 0.3% 5x5 63.0% 63.0% 0.0% 10x10 66.3% 66.3% 0.0% 20x20 69.1% 69.0% 0.1% 30x30 70.0% 69.9% 0.1% Avg 67.5% 67.4% 0.1%
Profile Measurements 110,0% 100,0% 90,0% 80,0% 70,0% 60,0% 50,0% 40,0% 30,0% 20,0% d-15mm Open d-15mm Discover d-100mm Open d-100mm Discover d-200mm Open d-200mm Discover 10,0% 0,0% -160-140 -120-100 -80-60 -40-20 0 20 40 60 80 100 120 140 160 Distance [mm]
Penumbra 80,0% 70,0% d-15mm Open d-15mm Discover d-100mm Open 60,0% d-100mm Discover d-200mm Open d-200mm Discover 50,0% 40,0% 30,0% 20,0% 90 110 130 Distance [mm]
Repeatability - Output 10 x 10 cm 2 Field Trial Median Dose [%] Gamma Index Avg. Gamma 1 0.1 98.7 0.28 2 0.2 98.6 0.28 3 0.0 98.9 0.28 4 0.0 99.1 0.28 5 0.0 98.9 0.28 Avg. 0.1 98.8 0.28 STD 0.1 0.2 0.00 VMAT -Single Arc Trial Median Dose [%] Gamma Index Avg. Gamma 1-0.7 99.3 0.38 2-0.7 98.6 0.40 3-0.7 99.3 0.38 4-0.6 99.1 0.40 5-0.6 99.3 0.38 Avg. -0.7 99.1 0.39 STD 0.1 0.3 0.01
Clinical Prostate Plans 3 weeks 3D <0.2% Variation IMRT <0.9% Variation VMAT <0.6% Variation
Physical Parameter Monitoring Linear Gantry speed example
MLC Analysis Detects individual leaf field edges vs predicted values Simple 3D field
MLC Analysis MLC leaf deviation based on edge data Fixed gantry IMRT field
Therapist view
Therapist view Dose Gamma-Index, Anatomy, MLC, SSD, Gantry, Collimator
Example MLC View
Final Thoughts Goal was to determine the baseline characteristics of the device Discover system shows minimal perturbation of 6MV beam with a 1.5% attenuation System output stability was measured at 0.1%
Final Thoughts MLC tracking features and analysis tools have great potential for independently tracking MLC positions with direct comparison to predicted TPS values Installation does not appear to require a full recommisioning for a non-fff 6X beam, however at a minimum new PDDs and output factors should be reacquired with profile checks over the full clinical range of values
Thank you! Questions?