Quality Assurance Implementation at the Roberts Proton Therapy Center. James McDonough 3 August 2013

Transcription

1 Quality Assurance Implementation at the Roberts Proton Therapy Center James McDonough 3 August

2 Roberts Proton Therapy Center Machine configuration and layout 4 gantries, 1 fixed beam line, 1 research room Delivery systems Fixed beam room has a dedicated PBS nozzle 1 gantry currently using DS & US; will be commissioned for PBS 1 gantry currently using PBS; previously treated with US 2 gantries treating with DS; will likely stay that way 5 linacs, 2 CT-Sims, 1 PET-CT-Sim, 1 MRI plus treatment planning & exam rooms in adjacent space on same floor as the proton center (total is approximately 80,000 square feet) The Abramson Cancer Center occupies ~200,000 square feet on the floors above where radiation oncologists see their new consult and follow up patients 2

3 Roberts Proton Therapy Center ~100 patients treated per day (in ~12 hrs) Typical patient mix 30% prostate, prostate bed, prostate whole pelvis 20% GI 15% lung 15% CNS 10% H&N 10% other (sarcoma, Gyn, breast, ) ~15% Pediatric ~10% re-irradiation 3

4 Roberts Proton Therapy Center Staffing ~10 FTE physicists (~25 physicists in department) 3 MMP students help with morning QA ~20 therapists (~55 in whole clinic) 10 treatment planners (includes 2 physicists) ~15 FTE clinical MDs in proton + linac 4

5 Daily Machine QA 1 physicist medical physics students perform QA All rooms: Align MatrixX using x-ray system & check lasers; perform safety checks (door, lights, video/intercom, radiation detector, pause) For DS & US rooms: two beams measure output (constancy 3%), flatness (2%)& symmetry(3%), and range (3 mm) using IBA Faraday detector in the Y-jaw). For PBS rooms: three beams one for range (dose within 20% on falling edge) & two for output (2%), flatness & symmetry (2%), and field size (2 mm). In the room that has a range shifter one of the fields will use that. If all goes well rooms with DS take minutes; the rooms with PBS take minutes and the room with both US&DS takes minutes. 5

6 Weekly/Monthly QA No weekly QA Monthly QA Mechanical tests for gantry, collimator, couch angles X-ray vs proton alignment at 4 gantry & 2 collimator (DS/US) angles, 3 field sizes; x-ray vs compensator alignment (DS/US) DS Range/Modulation (Zebra or water tank), output (PPC05) for 5 fields; US R/M for 4 fields & output for 7 fields PBS test pattern (5 energies, 3 gantry angles), spot spacing (4 fields covering full 34 x 25 cm 2 ), R/M & output for 3 fields Takes 2-3 hours per room Equipment used: PPC05, LynX, MatrixX, Zebra, sometimes Blue Phantom 6

7 Test Pattern 7

8 Annual QA Standard monthly measurements TRS-398 using FC-65 for R15M10 and R25M10 Check Matrix & PPC05 calibrations Star shots for couch, gantry and (for DS/US) collimator PDDs to get range and modulation for 7 beams (DS); 4 beams (US); & 3 beams (PBS) Field size measurements (3 fields) for DS/US ball test for PBS to check alignment of x-ray and proton Dose/MU linearity RPC TLDs 8

9 Patient Specific QA DS Use MatrixX to measure the output of each field at mid-sobp to determine MUs. We compare this to a model based on the MGH model. Also verify compensators using a depth gauge. We use the measurement for the MUs but if it differs from the model by >3% we investigate by running standard fields to see if something has changed. Takes ~15 minutes to prepare the validation plan + ~30 minutes to set up and run the fields. Another physicist enters the MUs as part of the initial check. US Same as DS except we also measure range & modulation with Zebra. Tolerance on range is 2 mm; modulation is 88-92%.Takes an extra 30 minutes. PBS Use MatrixX to measure 3 depths proximal, mid-sobp, and distal. Use gamma analysis (>90% pass 3% & 3 mm) to compare to Eclipse. If mid- SOBP output is 5-10% off we renormalize the plan. If <3% off we do nothing; for 3-5% we evaluate plan to decide whether to normalize. Takes minutes to prepare validation and export planes; another minutes to deliver each field three times; and another 30 minutes for the analysis. 9

10 Unique Implementations MLC (For DS & US) + Very helpful when feathering + Therapists are happy not dealing with apertures - Sometimes causes large air gaps - Limits DS & US field size (24 cm x 18 cm) - Limits PBS field size (34 cm x 25 cm) - Snout cannot translate in PBS mode Range-shifter close to the patient (PBS) Minimum range out of the nozzle is 7.5 cm so a range-shifter is needed but we cannot move our snout. To minimize the spot size we have made several versions of range-shifters mounted on, or built into, the couch. 10

11 Top 3 wish list items 1. Better treatment planning (Eclipse) especially dealing with heterogeneities and range uncertainties tools to make optimization easier (e.g., tapering dose at matched PBS fields) faster PBS optimization 2. Better interface between Aria & IBA We essentially have no R&V system neither side pays any attention to daily, session, or total dose limits We have huge issues with Aria containing the right information about fractions delivered, dose delivered, & even planned dose We still cannot get our imaging into off-line review in a smooth way 3. Faster beam delivery (IBA) better room switching time currently ~35 sec; want ~15 sec better layer switching time (PBS) currently 5-6 seconds; want 2-3 seconds. 4 & 5 - Verification of range in patient & a 3-D dosimeter 11

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