QA LINAC Daily, Monthly, Annual

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1 QA LINAC Daily, Monthly, Annual Jack Yang, Ph.D., DABR Institute for Advanced Radiation Oncology Barnabas Health Long Branch, NJ New Technologies in Modern Radiotherapy, Chulabhorn Research Institute, Bangkok, Thailand, August 22-25, 2012

2 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

3 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

4 Linac QA Components: Dosimetric accuracy Mechanical Accuracy Safety Frequency: Daily Monthly Annually

5 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

6 Periodic QA of Linear Accelerator (TG-40) Frequency Procedure Tolerence (±) Daily X-ray & electron output constancy 3% Localization lasers 2 mm Safety interlocks (door) functional Monthly X-ray & Electron output constancy 2% Light/radiation field coincidence 2 mm X-ray flatness and symmetry 2% Electron flatness and symmetry 2% X-ray energy 2% in depth dose (2% in ionization ratio) Electron energy 2 mm in R 80 (2 mm in R p ) Optical distance indicator 2 mm Field size indicators 2 mm Gantry angle indicator 1 Collimator angle indicator 1 Cross-hair centering 1 mm Annually Full calibration 2% Isocenter shift 2 mm Collimator rotation 2 mm diameter Gantry rotation 2 mm diameter Couch rotation 2 mm diameter Couch vertical travel 2 mm Tabletop sag 2 mm

7 Radiation Isocenter Checks Collimator» 2 mm diameter circle Treatment table» 2 mm diameter circle Gantry» 2 mm diameter circle

8 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!!

9 Misadministration Definition in US For Stereotactic radiosurgery/radiotherapy (<= 3 fractions) No written directive Wrong patient Wrong site Total dose error exceeds 10%

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.

11 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

12 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

13 MLC QA TG 50 (2001) - Update

14 EPID QA TG 58 (2001) - Update

15 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.

16 TG-142 Daily Procedure Tolerance (non- IMRT 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) Door closing safety Audiovisual monitor(s) Stereotactic interlocks (lockout) NA NA Radiation area monitor (if used) Beam on indicator

17 TG-142 Daily (Continued) Procedure Tolerance (non- IMRT 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) Door closing safety Audiovisual monitor(s) Stereotactic interlocks (lockout) NA NA Radiation area monitor (if used) Beam on indicator

18 TG-142: Monthly Procedure Tolerance (non- IMRT machines) Tolerance (IMRT machines) Tolerance Stereotactic machines Dosimetry X-ray output constancy Electron output constancy 2% Backup monitor chamber constancy Typical dose rate 2 output constancy NA 2% (@ IMRT dose rate) 2% (@ stereo dose rate, MU) Photon beam profile constancy Electron beam profile constancy 1% Electron beam energy constancy 2%/2mm

19 TG Monthly (Continued) Procedure Tolerance (non-imrt machines) Tolerance (IMRT machines) Tolerance Stereotactic 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 2 mm/ 1 deg 1 mm/ 0.5 deg Wedge placement accuracy 2mm Latching of wedges, blocking tray5 5 Localizing lasers ±2 mm ±1 mm <±1 mm Respiratory gating Beam output constancy 2% Phase, Amplitude beam control In room respiratory monitoring system Gating interlock

20 TG Monthly (Continued) Procedure Tolerance (non-imrt machines) Tolerance (IMRT machines) Tolerance Stereotactic machines

21 TG-142: Annual Dosimetry Procedure Tolerance (non- IMRT machines) Tolerance (IMRT machines) 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 ±1% SRS Arc rotation mode (range: 0.5 to 10 MU/deg ) X-ray/electron output calibration (TG-51) 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) X-ray beam quality (PDD 10, TMR ) Electron beam quality (R 50 ) Transmission factor constancy for all treatment accessories Physical wedge transmission factor constancy NA NA ±1%(absolute) 2% for field size < 4x4 cm 2, 1% 4x4 cm 2 ±2% from baseline ±1% from baseline ±1mm ±1% from baseline ±2% Tolerance Stereotactic machines 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)

22 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 Electron output constancy vs gantry angle 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 Tolerance (non-imrt machines) ±2% 5MU Tolerance (IMRT machines) ±5% (2-4 MU), ±2% 5MU ±2% 5MU ±2% from baseline ±1% from baseline ±1% from baseline ±1% from baseline ±1% from baseline Tolerance Stereotactic machines ±5% (2-4), ±2% 5MU 1% (TBI) or 1mm PDD shift (TSET) from baseline 2% from baseline 2% from baseline

23 TG-142 Annual (Continued) Procedure Tolerance (non- IMRT machines) Tolerance (IMRT machines) Tolerance Stereotactic machines Mechanical Collimator rotation isocenter Gantry rotation isocenter Couch rotation isocenter Electron applicator interlocks Coincidence of radiation and mechanical isocenter Table top sag ±2mm from baseline ±1 mm from baseline ±1 mm from baseline ±1 mm from baseline ±2mm from baseline 2mm from baseline ±1mm from baseline Table Angle 1 degree Table travel maximum range movement in all directions ±2mm Stereotactic accessories, lockouts, etc NA Safety Follow manufacturers test procedures Respiratory gating Beam energy constancy 2% Temporal accuracy of Phase/Amplitude Gate-on 100 ms of expected Calibration of surrogate for respiratory phase/amplitude 100 ms of expected Interlock testing

24 Wedge Verification (Not Physical) Dynamic-incl. EDW (Varian), Virtual (Siemens), Universal (Elekta) Wedge quality assurance Frequency Daily Monthly Annual Procedure Morning Check-out run for 1 angle Wedge factor for all energies Check of wedge angle for 60, full field & spot check for intermediate angle, field size * Recommendation to check 45º if angles other than 60º are used. Tolerance Dynamic Universal Virtual C.A. Axis 45º or 60 WF (within 2%)* C.A. Axis 45º or 60 WF (within 2%)* 5% from unity, otherwise 2% Check of Off-center 80% field 10cm to be within 2%

25 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 Monthly Setting vs. radiation field for two patterns (non-imrt) Backup diaphragm settings (Elekta only) Travel speed (IMRT) Leaf position accuracy (IMRT) 2mm 2mm Loss of leaf speed > 0.5 cm/sec 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)

26 MLC - Annual Test MLC Transmission (Average of leaf and interleaf transmission), All Energies ±0.5% from baseline Leaf position repeatability ±1.0 mm MLC spoke shot Coincidence of Light Field and X-ray Field (All energies) Arc dynamic leaf-speed test Arc dynamic interlock trip test Arc dynamic typical plan test Segmental IMRT (Step and Shoot) Test Moving window imrt (4 cardinal gantry angles) 1.0 mm radius ±2.0 mm <0.35 cm Max Error RMS, 95% of error counts <0.35 cm (Varian) Leaf position interlock occurs (Varian) <0.35 cm Max Error RMS, 95% of error counts <0.35 cm (Varian) <0.35 cm Max Error RMS, 95% of error counts <0.35 cm (Varian) <0.35 cm Max Error RMS, 95% of error counts <0.35 cm (Varian)

27 Imaging Equipment Test - Daily Procedure Non-SRS/SBRT Applications Tolerances SRS/SBRT Applications Tolerances MV imaging (EPID) Daily Collision interlocks Spatial linearity1 (x and y) (single gantry angle) Imaging & Treatment coordinate coincidence (single gantry angle) < 2 mm 1 mm < 2 mm 1 mm Positioning/repositioning < 2 mm 1 mm KV imaging 2 Collision interlocks Imaging & treatment coordinate coincidence < 2 mm 1 mm Positioning/repositioning < 2 mm 1 mm Cone-beam CT (kv & MV) Collision interlocks Positioning/repositioning < 2 mm 1 mm

28 Imaging Equipment Test - Monthly Procedure Non-SRS/SBRT Applications Tolerances SRS/SBRT Applications Tolerances MV imaging (EPID) Imaging & treatment coordinate coincidence (4 Cardinal angles) < 2 mm 1 mm Scaling3 < 2 mm < 2 mm Spatial resolution Baseline 4 Baseline Contrast Baseline Baseline Uniformity and noise Baseline Baseline kv imaging 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 Spatial resolution Baseline Baseline Contrast Baseline Baseline Uniformity and noise Baseline Baseline Cone-beam CT (kv & MV) Imaging & treatment coordinate coincidence < 1.5 mm 1 mm Geometric distortion < 2 mm 1 mm Spatial resolution Baseline Baseline Contrast Baseline Baseline HU constancy Baseline Baseline Uniformity and noise Baseline Baseline Spatial linearity (x and y) (single gantry angle) < 1 mm 1 mm

29 Imaging Equipment Test - Annual MV imaging (EPID) Procedure Non-SRS/SBRT Applications Tolerances SRS/SBRT Applications Tolerances Full range of travel SDD ±5 mm ±5 mm Imaging dose5 Baseline Baseline Beam quality / energy Baseline Baseline kv imaging Beam quality / energy Baseline Baseline Imaging dose Baseline Baseline Cone-beam CT (kv & MV) Imaging dose Baseline Baseline

30 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.