TG-148 overview. Introduction. System Overview. System Overview. QA for Helical Tomotherapy: Report of the AAPM Task Group 148. Conflict of Interest:

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1 QA or Helical Tomotherapy: Report o the AAPM Tas Group 148 Members: Conlict o Interest: r. John Balog owns TomoTherapy stoc. Katja Langen (Co-chair) Nio Papaniolaou (Co-chair) Walter Grant Richard Crilly Murty Goddu Chengyu Shi avid Followill Chester Ramsey John Balog Gustavo Olivera r. Gustavo Olivera is an employee o TomoTherapy Inc. and has a inancial interest in TomoTherapy, Inc. Introduction TG-148 provides QA guidelines speciic or helical tomotherapy. Adapt guidelines rom current TG reports where appropriate (e.g. output constancy test). Generate technology speciic guidelines or QA aspects that are not covered elsewhere (e.g. speciic mechanical alignment tests). TG-148 overview Introductory chapters. eine TomoTherapy speciic terminology. Cover unique aspects o technology and clinical implementation. Provide QA guidelines or treatment delivery, imaging, and treatment planning system. Recommendations on what to test. Provide examples o how to test. Provide summary o QA aspects according to requency. System Overview System Overview Front view Lateral view Gantry continuously rotates while patient is translated through beam plane rom: W. Kalender, Computed Tomography: Fundamentals, System Technology, Image Quality, Applications 1

2 System Overview binary MLC System Overview binary MLC System Overview Front view - QA o mechanical alignments - QA o beam parameters - QA o mechanical alignments - QA o beam parameters - Alignment o Linac in y-direction against y-jaw sweep y-jaw in y-direction, measure output 2

3 - Alignment o Linac in x-direction against MLC measure Tongue & Groove proile, loo or symmetry - Alignment o Linac beam divergence perpendicular to plane o rotation Mechanical alignment QA For treatment - 3 commissioned ield sizes in y-direction: 1, 2.5, and 5 cm Treatment ield centering: test that all ields have common center Mechanical alignment QA MLC centering and twist: test that MLC is centered and parallel to plane o rotation 0 Irradiate ilm positioned at iso Swing gantry to 180 Close central leas Film Iso Mechanical alignment QA MLC centering and twist: test that MLC is centered and parallel to plane o rotation Two outer areas should be parallel- no twist Central area should be centered between outer areas-no oset - QA o mechanical alignments - QA o beam parameters 3

4 Fan Beam X-direction Beam parameter QA no lattening ilter X-direction beam proile: Monthly: consistency 400 mm 10, 25, or 50 mm Y-direction Annual: agreement with model TG-142 tolerance Beam parameter QA Beam parameter QA Longitudinal beam proile: Percentage epth ose: Monthly: consistency Annual: agreement with model 1% FWHM tolerance Monthly: consistency Annual: agreement with model TG-142 tolerance Beam parameter QA Monitor output using static and/or rotational procedures: Beam parameter QA Monitor rotational output variation monthly aily (within 3%) Monthly (with calibrated IC) within 2 % Fixed gantry No MLC action Rotating gantry MLC action e.g. phantombased treatment plan Tolerance 2% 4

5 - QA o mechanical alignments - QA o beam parameters Synchronicity (quarterly) Gantry angle: Consistency and accuracy during tx Couch speed: Uniormity Couch translation per gantry rotation: Synchronicity Example tests are detailed in Fenwic et al. (PMB, 49, ) - QA o mechanical alignments - QA o beam parameters Miscellaneous (monthly) Interrupted procedure = Uninterrupted procedure (tolerance 3% in delivered dose) Couch travel: actual distance = digital readout (tolerance 1 mm) Misc. couch aspects (level, sag, travel perpendicular to treatment plane) Lasers: Stationary (green) Movable (red) Miscellaneous Lasers: Miscellaneous aily: Red=Green at initialization Monthly: Red laser movement=planned movement Annual (green): Virtual iso to treatment plane = 70 cm x and z location cross in center o imaging plane 5

6 - QA o mechanical alignments - QA o beam parameters Calibration TG-51 equivalent static beam calibration: Problem: Q values in TG-51 are a unction o 100 cm SS or 10 by 10 cm ield >> not achievable on Tomo (85 cm SS, max ield length 5 cm) >> IAEA/AAPM joint committee proposed noncompliant beam calibration ormalism (Alonso et al., Med Phys, 35, , 2008) Calibration Allow two calibration routes: Machine-speciic reerence ield: (static delivery) Plan class speciic reerence ield: pcsr (rotational delivery) Calibration-machine speciic reerence ield () Tomo-: 5 cm by 10 cm SS = w,q Q M N,w,Q 0, re Q,Q (Alonso et al., Med Phys, 35, , 2008) Calibration-machine speciic reerence ield () Tomo-: 5 cm by 10 cm SS = w,q Q M N,w,Q 0, re Q,Q Calibration-machine speciic reerence ield () Tomo-: 5 cm by 10 cm SS = w,q Q M N,w,Q 0, re Q,Q Corrected reading in -ield Chamber calibration actor 6

7 Calibration-machine speciic reerence ield () Tomo-: 5 cm by 10 cm SS = w,q Q M N,w,Q 0, re Q,Q Calibration-machine speciic reerence ield () Tomo-: 5 cm by 10 cm SS = w,q Q M N,w,Q 0, re Q,Q Q under standard conditions Correction or IC response rom (hypothetical) standard to ield Calibration-determine Q,Q0 Measure Q in ield, convert to Q Q = Q Q Q Example: Calibration-determine Q,Q0 Example: Q = Q Q = Q= Q Q= Thomas et al., Med Phys, 32, , 2005 Small correction Calibration-machine speciic reerence ield () Tomo-: 5 cm by 10 cm SS = w,q Q M N,w,Q 0, re Q,Q Calibration-plan-class speciic reerence ield (pcsr) pcsr: as close as possible to a inal clinical delivery scheme, but delivers a homogeneous absorbed dose to an extended geometrically simple target volume pscr w,q pscr = pcsr Q pcsr M N,W,Q o Q,Q o, re Q,Q pcsr, Q pcsr, Q Monte Carlo Calculations by Jerai = (Jerai et al., Med Phys, 32, 570-7, 2005) (uane et al., Med Phys, 33, 2093, 2006) uane (experimental) = For 2.5 and 5 cm ield 7

8 Calibration-plan-class speciic reerence ield (pcsr) pcsr: as close as possible to a inal clinical delivery scheme, but delivers a homogeneous absorbed dose to an extended geometrically simple target volume Calibration O the two calibration routes, the calibration via pcsr-ield (rotational delivery) is the relevant route or tomotherapy. pscr w,q pscr = pcsr Q pcsr M N,W,Q o Q,Q o, re Q,Q pcsr, Q pcsr, Q (Alonso et al., Med Phys, 35, , 2008) = 1 For 2.5 and 5 cm ields Imaging QA - Spatial/Geometry Tests - Image Quality Tests - MVCT osimetry Spatial/Geometry Tests - MVCT Image Reconstruction Accuracy (Annual) Image nown object, chec dimension, orientation, and location Tolerance: within 1 MVCT pixel Spatial/Geometry Tests - Image Registration tests (Annual) Use phantom with high contrast object: position with respect to external lasers or use nown oset Tolerance: within 1 MV/V pixel (larger pixel is limiting) aily imaging Test -Test imaging, registration, alignment chain 1) Scan 2 ) Register -compare to nown osets 3) Align -test automatic couch setup Tolerance: Consistency within 2 mm 8

9 Phantom-based end-to-end test - osimetric end-to-end test o registration accuracy (Annual) Phantom based end-to-end test, image, register, treat Analyze spatial accuracy o dose distribution in phantom using ilm dosimetry Accounts or registration, dose calculation, and delivery accuracy Image Quality (monthly) - Noise - Uniormity - Spatial resolution - CT-number - MVCT ose Noise Standard deviation o HU in uniorm phantom Uniormity In uniorm phantom, central and peripheral ROI: Typical noise level: HU central region HU in peripheral region Tolerance: less than 25 HU dierence Spatial resolution Resolution o high contrast object: CT number Important i MVCT is used or dose calculations Monitor HU or water, lung, bone equivalent material Tolerance: 1.6 mm object should be resolved Tolerance: less than 30 HU or water less than 50 HU or lung/bone 9

10 MVCT dosimetry Monthly MVCT QA Multiple slice average dose (MSA) measurement: Test Consistency Scan phantom with IC inserted In cheese phantom: 1-3 cgy or Normal scan HU Noise Uniormity Spatial resolution ose On monthly basis: less than 30 % variation can be done with 1 MVCT scan Treatment Planning QA Geometric validation tests osimetric validation test TPS- Geometric test (annual) Test CT data import- dimensions, orientation, text Test integrity o imported structure set -volume and dimension TPS- osimetric tests (annual) Generate phantom-based plans test with IC measurements Generate plans or on- and o-axis targets Generate plans or each commissioned ield size TPS- Patient Plan QA (QA) Recalculate plan in phantom geometry: Expectation: 90% o measurements pass 3%/3mm test Example: Cheese phantom, IC and Film Tolerance: 3%/3 mm 10

11 Frequency: aily, monthly, quarterly, annual Example: System Maintenance Provide guidance o what to test ater wor on: Magnetron/SSM Linac/Target Y-Jaw MCL Where is TG-148 now? - Initial submission to TPC in March - Received TPC reviews in late April - Re-submission to TPC in July 11