2013.5.9 Global Harmonization Group meeting ICCR2013 @ Melbourne Activity report from JCOG physics group 1 Hokkaido University, Graduate School of Medicine, 2 National Cancer Center, Center for Cancer Control and Information Services, 3 National Cancer Center East, Proton Center, 4 Chiba Cancer Center, Radiation Oncology, 5 Hirosaki University, Graduate School of Medicine, 6 Juntendo University, Graduate School of Medicine
Current activities of JCOG physics WG JCOG0403/0702 (Stereotactic Lung cancer therapy) Evaluation of calculation in inhomogeneous regions(dr. Nishio) JCOG1015 (Head & Neck IMRT) Independent QA program for IMRT (Dr. Minemura) Other activities Development of new dose distribution analysis method (Dr. Ishikawa) Development of Linac QC tools (Dr. Narita) IMRT postal dosimetry audit using glass dosimeter (Dr. Tohyama)
Evaluation of calculation in inhomogeneous regions Prior to the clinical study, the accuracy of dose calculation in radiation treatment planning system was surveyed in participating institutions, and differences in the irradiated dose among the institutions were investigated. We developed a water tank-type lung phantom appropriate for verification of the exposure dose of lung stereotactic body radiotherapy. Using this water tank-type lung phantom, the dose calculated in radiation treatment planning system and measured dose using an air-filled ionization chamber and dosimetric film were compared in a visiting survey of 7 institutions participating in the clinical study.
Evaluation of calculation in inhomogeneous regions Water tank phantom For chambers Plan#1 Plan#2 For glass dosimeters Plan#3 For films
Evaluation of calculation in inhomogeneous regions Physical length / Water-equivalent length verification Plots for each institute adequately concentrated within standard value from phantom design. Material Density (g/cm 3 ) Water 1 PMMA 1.16 Cork 0.309
Evaluation of calculation in inhomogeneous regions Individuals Total Individuals Total Individuals Total For total dose, the measurements are agreed with the planning within 3%.
Evaluation of calculation in inhomogeneous regions Film-based verification for 2D dose distribution were also performed, and confirmed that the distributions are adequately matched with calculation. We are now trying to perform quantitative analysis for 3-dimentional film dosimetry (e.g. D95 for PTV).
Independent Quality Assurance Program for IMRT We have provided program to assure of the quality for IMRT The IMRT treatment plan was drafted by each institution to satisfy the following optimization conditions. D95 prescription (PTV) : 2Gy PTV maximum dose : Dmax (PTV) < 110 % Organs at risk (OAR) : Dmax (OAR) < 60 % The absolute dose was executed with the ionization chamber for C1 and C2 in PTV. The dose distributions in axial, coronal and sagittal planes calculated compared with the dose measured using the gafchromic film.
Independent Quality Assurance Program for IMRT We have provided on-site visit IMRT program for 10 institutions participating in clinical trial. The differences in dose measured with dose calculated at C1 and C2 center points were within ±3%. In the results of dose distribution measured using the films, the differences for the position gap were within ±2mm.
New criteria for dose distribution analysis Gamma index is effective for analyzing complex of absolute (relative) dosimetric and positional errors, however, the dimensions are different. The most important thing in IMRT-QA is to judge whether the difference between measurement and calculation is less than the tolerances (dosimetric and positional) or not. As a new criteria, we develop a Gradient method which uses a dose gradient map to convert positional error in dosimetric dimension.
New pass/fail criteria taking dose gradient into account Pass/Fail Criteria Positional tolerance Small Gradient Large Gradient D meas D calc D Dosimetric tolerance acceptable D x x Dose gradient acceptable ΔD/Δx Dosimetric error 6 6 6 4 4 4 2 2 2 D x x error D error Positional error Z Axis Z Axis Z Axis 0-2 -4 0-2 -4 0-2 -4-6 -6-6 -4-2 0 2 4 6-6 -6-4 -2 0 X Axis 2 4 6 0 X Axis -6-4 -2 2 4 6 X Axis 3D dose distribution calculated by TPS Z Axis 6 4 2 0-2 -4-6 -6-4 -2 0 2 4 6 3D Dose gradient at each position can be calculated from 3 continuous dose planes. X Axis
Development of film analysis software for gradient method
Inter-institutional comparison using a dummy plan Targets TPS Phantom Software Analysis :9 institutes participating JCOG1015 and additional 4 institutes (Total: 13 institutes) :Eclipse, Pinnacle and Acuros XB :In-house verification phantom :Simple IMRT Analysis (Triangle Products) :Gamma and Gradient scores are calculated 6 6 4 4 2 2 Z axis [cm] 0-2 Z axis [cm] 0-2 -4-4 -6-6 Verification Phantom -6-4 -2 0 2 4 6 X Axis [cm] Film -6-4 -2 0 2 4 6 X Axis [cm] Gradient
Pass/Fail criteria including measurement uncertainty D meas D calc D acceptable Dosimetric Tolerance D x x acceptable Positional Tolerance D meas_ error Measurement Uncertainty Measurement uncertainty is estimated when making an OD-dose conversion table (k=2) If dosimetric and positional error is smaller than tolerance, the pass rate should be 100% with 95% confidence level. If pass rate is lower than 99%, something might be wrong!!
Gradient score map (Relative 3%, 1mm) Gradient 3%,1mm (Relative) A B C D E F G H I J K L A B C D E F G H I J K L Ave JCOG >10% 100% 100% 98.7% 100% 100% 100% 99.5% 99.9% 99.5% 99.8% 99.5% 99.8% 99.7% 99.9% 50~90% 100% 100% 100% 100% 100% 100% 99.6% 99.9% 99.9% 99.9% 99.8% 99.9% 99.9% 99.9% >90% 100% 100% 100% 99.9% 100% 100% 99.3% 99.9% 99.9% 100% 100% 100% 99.9% 99.9% >99% <95%
Gamma score map (Relative 3%, 1mm) Gamma 3%,1mm (Relative) A B C D E F G H I K L J A B C D E F G H I J K L Ave JCOG >10% 84.4% 94.1% 77.8% 80.0% 91.1% 71.3% 83.2% 96.0% 86.2% 80.9% 72.1% 88.4% 83.8% 86.0% 50~90% 77.1% 97.7% 86.6% 88.8% 90.3% 76.1% 81.1% 96.3% 88.4% 88.4% 88.4% 88.4% 87.3% 87.0% >90% 98.0% 99.9% 99.6% 100% 94.5% 99.9% 95.1% 99.8% 99.5% 85.7% 89.5% 99.8% 96.8% 98.4% >90% <80%
IMRT postal dosimetry audit using glass dosimeter In Japan, postal dosimetry audit using radiophoto-luminescence glass dosimeter (RGD) has been carried out for the reference condition and the wedged field. We are trying to implement the comprehensive postal dosimetry audit system using RGD for IMRT. The IMRT phantom was scanned at each institutions, planning and irradiation with various IMRT technique (static IMRT: 6, dynamic IMRT: 6 and VMAT: 2) were performed. Contents No. of field PTV: D 95% PTV: D max OAR: D max Global max Constraints 4 to 9 or VMAT 200 cgy 220 cgy 120 cgy In PTV
IMRT postal dosimetry audit using glass dosimeter The calculated combined relative standard uncertainty (k=1) of dose measurement for IMRT beam with RGDs was 2.5%. In the PTV, the mean of dose difference between measured and calculated was less than 2.5 % (from -2.2 % to 1.0 %) over 14 IMRT beams. Point dose at the OAR were agreed within 10 cgy (from -6.9 to 4.0 cgy). The means of position errors of AP and RL direction were -0.6 mm (from - 1.5 to -0.1 mm) and 0.7 mm (from -0.3 mm to 2.3 mm), respectively. AP LR