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QA – LINAC Daily, Monthly, Annual Jack Yang, Ph.D., DABR Institute for Advanced Radiation Oncology Barnabas Health Long Branch, NJ 07740 New Technologies in Modern Radiotherapy, Chulabhorn Research Institute, Bangkok, Thailand, August 22-25, 2012 Outlines Definition of treatment delivery quality assurance for LINAC Assure that the 5% final dose discrepancy can be achieved with the site specific QA process Current QA protocols implemented in modern radiation oncology clinics with updated LINAC functionalities Radiation Oncology Error Management Clinical experience has shown that variations of 10% or more in the delivered dose can sharply reduce the probability of local tumor control. ICRU Report 62 recommends that radiotherapy be delivered within 5% of the prescribed dose to ensure adequate tumor control. The global aim is to achieve the desired tumor control while maintaining toxicities to normal tissues to a minimum Are these endpoints achievable with current delivery technology? Fig., Connor et al, IJROBP 1975 Linac QA Components: Dosimetric accuracy Mechanical Accuracy Safety Frequency: Daily Monthly Annually The Early QA report (1994) AAPM TG-40 report Comprehensive QA program QA of EXRT (External Beam Treatment) equipment QA of RTP (Information and IT tools) system Brachytherapy Clinical practice Periodic QA of Linear Accelerator (TG-40) Frequency Daily Monthly Annually Procedure X-ray & electron output constancy Localization lasers Safety interlocks (door) X-ray & Electron output constancy Light/radiation field coincidence X-ray flatness and symmetry Electron flatness and symmetry X-ray energy Electron energy Optical distance indicator Field size indicators Gantry angle indicator Collimator angle indicator Cross-hair centering Full calibration Isocenter shift Collimator rotation Gantry rotation Couch rotation Couch vertical travel Tabletop sag Tolerence (±) 3% 2 mm functional 2% 2 mm 2% 2% 2% in depth dose (2% in ionization ratio) 2 mm in R80 (2 mm in Rp) 2 mm 2 mm 1° 1° 1 mm 2% 2 mm 2 mm diameter 2 mm diameter 2 mm diameter 2 mm 2 mm Radiation Isocenter Checks Collimator » 2 mm diameter circle Treatment table » 2 mm diameter circle Gantry » 2 mm diameter circle Misadministration Definition in US For external beam (>3 fractions) No written directive Wrong patient Wrong site Weekly dose exceeds 30% Total dose exceed 20% Most of the LINACs are inspected and governed by the state government !! Misadministration Definition in US For Stereotactic radiosurgery/radiotherapy (<= 3 fractions) No written directive Wrong patient Wrong site Total dose error exceeds 10% Background of TG 142 Principles - TG-40 was the International Commission on Radiation Units and Measurements (ICRU) recommendation that the dose delivered to the patient be within ±5% of the prescribed dose. The goal of a QA program for linear accelerators is to assure that the machine characteristics do not deviate significantly from their baseline values acquired at the time of acceptance and commissioning. Rationales for Developing TG 142 New Technology since TG 40 MLC, as Asymmetric Jaws, Dynamic & virtual wedges, EPIDs……. Imaging: kV and cone beam, Respiratory gating….. Clinical procedures not emphasized in TG 40 with new modalities such SRS, SBRT, TBI, IMRT…… TG50, TG58, TG76 TG106, TG104, TG100 for various LINAC QAs TG 142 fro Linear Accelerator QAs What This Report Doesn’t cover (some special techniques) Describe the techniques for performing QA tests Accelerator beam data commissioning equipment and procedures – TG-106 QA for TomoTherapy –TG-148 QA for Robotic Radiosurgery – TG-135 QA for Non-Radiographic Radiotherapy Localization & Positioning Systems – TG-147 Does add Specific Recommendations / Supplements the Work of Basic Applications of Multileaf Collimators – TG-50 Clinical use of electronic portal imaging - TG-58 Management of Respiratory Motion– TG-76 Kilovoltage localization in therapy – TG-104 MLC QA TG 50 (2001) - Update EPID QA TG 58 (2001) - Update TG-142 Testing Standards Acceptance Testing Procedure (ATP) Standards Acceptance testing sets the baseline for future dosimetric measurements for beam performance constancy, verifies that the equipment is mechanically functional and operates within certain tolerances from absolute specified values. Tolerances and Action Levels Level 1 – Inspection Action Level 2 – Scheduled Action Level 3 – Immediate Action or Stop Treatment Action or Corrective Action With these 3 action levels, there is an institutional need to specify the thresholds associated with Levels 2 and 3. Level 1 threshold isn’t a critical requirement but can lead to improvements in the QA program. TG-142 Daily Procedure Tolerance (nonIMRT machines) Tolerance (IMRT machines) Tolerance (Stereotactic machines) Dosimetry X-ray output constancy (all energies) Electron output constancy (Weekly, except for machines with unique e- monitoring requiring daily) 3% Mechanical Laser localization 2 mm 1.5 mm 1 mm Distance indicator (ODI)@ iso 2 mm 2 mm 2 mm Collimator size indicator 2 mm 2 mm 1 mm Safety Door interlock (beam off) Functional Door closing safety Functional Audiovisual monitor(s) Functional Stereotactic interlocks (lockout) 1 NA NA Radiation area monitor (if used) Functional Beam on indicator Functional Functional TG-142 Daily (Continued) Procedure Tolerance (nonIMRT machines) Tolerance (IMRT machines) Tolerance (Stereotactic machines) Dosimetry X-ray output constancy (all energies) Electron output constancy (Weekly, except for machines with unique e- monitoring requiring daily) 3% Mechanical Laser localization 2 mm 1.5 mm 1 mm Distance indicator (ODI)@ iso 2 mm 2 mm 2 mm Collimator size indicator 2 mm 2 mm 1 mm Safety Door interlock (beam off) Functional Door closing safety Functional Audiovisual monitor(s) Functional Stereotactic interlocks (lockout) 1 NA NA Radiation area monitor (if used) Functional Beam on indicator Functional Functional TG-142: Monthly Procedure Tolerance (nonIMRT machines) Tolerance (IMRT machines) Tolerance Stereotactic machines Dosimetry X-ray output constancy 2% Electron output constancy Backup monitor chamber constancy Typical dose rate2 output constancy Photon beam profile constancy Electron beam profile constancy Electron beam energy constancy 1 NA 2% (@ IMRT dose rate) 1% 2%/2mm 2% (@ stereo dose rate, MU) TG-142 - Monthly (Continued) Procedure Tolerance (non-IMRT machines) Mechanical Light/radiation field coincidence* 2 mm or 1% on a side Light/radiation field coincidence* (Asymmetric) 1 mm or 1% on a side Distance check device used for lasers/ODI (vs. front pointer) 1mm Gantry/collimator angle indicators (@ cardinal angles) (Digital only) 1.0 deg Accessory trays (i.e. Port film graticle tray) 2 mm Jaw position indicators (Symmetric)3 2 mm Jaw position indicators (Asymmetric)1 1 mm Cross-hair centering (walk-out) 1 mm Treatment couch position indicators4 2 mm/1 deg Wedge placement accuracy Localizing lasers 1 mm/ 0.5 deg Functional5 ±2 mm ±1 mm Respiratory gating Beam output constancy 1 2 mm/ 1 deg Tolerance Stereotactic machines 2mm Latching of wedges, blocking tray5 1 Tolerance (IMRT machines) 2% Phase, Amplitude beam control Functional In room respiratory monitoring system Functional Gating interlock Functional <±1 mm TG-142 - Monthly (Continued) Procedure Tolerance (non-IMRT machines) Tolerance (IMRT machines) Tolerance Stereotactic machines TG-142: Annual Procedure Tolerance (nonIMRT machines) Tolerance (IMRT machines) Tolerance Stereotactic machines Dosimetry X-ray flatness change from baseline 1% X-ray symmetry change from baseline ±1% Electron flatness change from baseline 1% Electron symmetry change from baseline SRS Arc rotation mode (range: 0.5 to 10 MU/deg ) NA NA Monitor units set vs. delivered:1.0 MU or 2% (whichever is greater) Gantry arc set vs. delivered: 1.0 deg or 2% (whichever is greater) X-ray/electron output calibration (TG-51) ±1%(absolute) Spot check of field size dependent output factors for X-ray (2 or more FS) Output factors for electron applicators (spot check of 1 applicator/energy) 2% for field size < 4x4 cm2, 1% ≥4x4 cm2 X-ray beam quality (PDD10, TMR1020) Electron beam quality (R50) Transmission factor constancy for all treatment accessories Physical wedge transmission factor constancy 1 ±1% ±2% from baseline ±1% from baseline ±1mm ±1% from baseline ±2% TG-142 – Annual (Continued) Procedure X-ray monitor unit linearity [output . constancy ] Electron monitor unit linearity [output . constancy ] X-ray output constancy vs dose rate X-ray output constancy vs gantry angle 1 Tolerance (non-IMRT machines) ±2% ≥5MU Tolerance (IMRT machines) ±5% (2-4 MU), ±2% ≥5MU Tolerance Stereotactic machines ±5% (2-4), ±2% ≥5MU ±2% ≥5MU ±2% from baseline ±1% from baseline Electron output constancy vs gantry angle ±1% from baseline Electron and X-ray Off-axis factor constancy vs gantry angle Arc mode (expected MU, degrees) TBI/TSET Mode PDD or TMR and OAF constancy TBI/TSET Output calibration TBI/TSET accessories ±1% from baseline ±1% from baseline Functional 1% (TBI) or 1mm PDD shift (TSET) from baseline 2% from baseline 2% from baseline TG-142 – Annual (Continued) Procedure Tolerance (nonIMRT machines) Mechanical Collimator rotation isocenter Gantry rotation isocenter Couch rotation isocenter Electron applicator interlocks Coincidence of radiation and mechanical isocenter Tolerance (IMRT machines) ±1 mm from baseline ±1 mm from baseline ±1 mm from baseline Functional ±2mm from baseline ±2mm from baseline Table top sag 2mm from baseline Table Angle 1 degree Table travel maximum range movement in all directions Stereotactic accessories, lockouts, etc Safety Follow manufacturers test procedures Respiratory gating Beam energy constancy Temporal accuracy of Phase/Amplitude Gate-on Calibration of surrogate for respiratory phase/amplitude Interlock testing 1 Tolerance Stereotactic machines ±1mm from baseline ±2mm NA Functional Functional 2% 100 ms of expected 100 ms of expected Functional Wedge Verification (Not Physical) Dynamic-incl. EDW (Varian), Virtual (Siemens), Universal (Elekta) Wedge quality assurance Frequency Procedure Tolerance Dynamic Universal Virtual Daily 1 Morning Check-out run for 1 angle Functional Monthly Wedge factor for all energies C.A. Axis 45º or 60° WF (within 2%)* Annual Check of wedge angle for 60°, full field & spot check for intermediate angle, field size Check of Off-center ratios @ 80% field width @ 10cm to be within 2% * Recommendation to check 45º if angles other than 60º are used. C.A. Axis 5% from 45º or 60° unity, WF otherwise (within 2% 2%)* MLC Verification Multi-leaf collimation quality assurance (with differentiation of IMRT vs. non-IMRT machines) Frequency Procedure Tolerance Weekly (IMRT machines) Qualitative test (i.e. matched segments, aka, “picket fence”) Visual inspection for discernable deviations such as an increase in interleaf trransmission Setting vs. radiation field for two patterns (non-IMRT) 2mm Backup diaphragm settings (Elekta only) 2mm Travel speed (IMRT) Loss of leaf speed > 0.5 cm/sec Leaf position accuracy (IMRT) 1mm for leaf positions of an IMRT field for 4 cardinal gantry angles. (Picket fence test may be used, test depends on clinical planning – segment size) Monthly 1 MLC - Annual Test 1 MLC Transmission (Average of leaf and interleaf transmission), All Energies ±0.5% from baseline Leaf position repeatability ±1.0 mm MLC spoke shot ≤1.0 mm radius Coincidence of Light Field and X-ray Field (All energies) ±2.0 mm Arc dynamic leaf-speed test <0.35 cm Max Error RMS, 95% of error counts <0.35 cm (Varian) Arc dynamic interlock trip test Leaf position interlock occurs (Varian) Arc dynamic typical plan test <0.35 cm Max Error RMS, 95% of error counts <0.35 cm (Varian) Segmental IMRT (Step and Shoot) Test <0.35 cm Max Error RMS, 95% of error counts <0.35 cm (Varian) Moving window imrt (4 cardinal gantry angles) <0.35 cm Max Error RMS, 95% of error counts <0.35 cm (Varian) Imaging Equipment Test - Daily Procedure Non-SRS/SBRT Applications Tolerances SRS/SBRT Applications Tolerances Daily MV imaging (EPID) Collision interlocks Functional Functional Spatial linearity1 (x and y) (single gantry angle) < 2 mm ≤ 1 mm Imaging & Treatment coordinate coincidence (single gantry angle) < 2 mm ≤ 1 mm Positioning/repositioning < 2 mm ≤ 1 mm Functional Functional Imaging & treatment coordinate coincidence < 2 mm ≤ 1 mm Positioning/repositioning < 2 mm ≤ 1 mm Functional Functional < 2 mm ≤ 1 mm KV imaging2 Collision interlocks Cone-beam CT (kV & MV) Collision interlocks Positioning/repositioning 1 Imaging Equipment Test - Monthly Procedure Non-SRS/SBRT Applications Tolerances SRS/SBRT Applications Tolerances 1 MV imaging (EPID) Imaging & treatment coordinate coincidence (4 Cardinal angles) < 2 mm ≤ 1 mm Scaling3 < 2 mm < 2 mm Spatial resolution Baseline Contrast Uniformity and noise kV imaging Baseline Baseline Baseline Baseline Imaging & treatment coordinate coincidence (4 Cardinal angles) < 2 mm ≤ 1 mm Scaling < 2 mm ≤ 1 mm Spatial linearity (x and y) (single gantry angle) < 2 mm ≤ 1 mm Baseline Baseline Baseline Baseline Baseline Baseline Imaging & treatment coordinate coincidence < 1.5 mm ≤ 1 mm Geometric distortion Spatial resolution Contrast HU constancy Uniformity and noise < 2 mm Baseline Baseline Baseline Baseline ≤ 1 mm Baseline Baseline Baseline Baseline Spatial linearity (x and y) (single gantry angle) < 1 mm ≤ 1 mm Spatial resolution Contrast Uniformity and noise Cone-beam CT (kV & MV) 1 4 Baseline Imaging Equipment Test - Annual Procedure 1 SRS/SBRT Applications Tolerances MV imaging (EPID) Full range of travel SDD ±5 mm ±5 mm Baseline Baseline Beam quality / energy kV imaging Baseline Baseline Beam quality / energy Imaging dose Cone-beam CT (kV & MV) Baseline Baseline Baseline Baseline Baseline Baseline Imaging dose5 Imaging dose 1 Non-SRS/SBRT Applications Tolerances Conclusions LINAC QA protocols have become extensive through modern LINAC development and implementation. AAPM TG-40 report still function as the base lines. AAPM TG-142 has gradually emerging into modern clinical practice (some of those testing are tedious and maybe not applicable to a busy clinic). However, regulatory agencies still have hard time to follow due to manpower, training and budgeting constraints. Annual report should include but not limited to the following: . (1) Dosimetry, (2) Mechanical, (3) Safety, (4) Imaging, and (5) Special Devices/Procedures.
