Delivery Quality Assurance with a High Resolution Liquid Filled Ion Chamber Array for Robotic Radiosurgery

Transcription

1 Adamczyk S, Chan M, Stelljes T, Schmitt D, Skrobala A, Poppinga D, Adamczyk M, Pawalowski B, Hildebrandt G, Poppe B, Blanck O Dr. Oliver Blanck University Clinic Lübeck, Germany Phone: Oliver@Blanck.de Delivery Quality Assurance with a High Resolution Liquid Filled Ion Chamber Array for Robotic Radiosurgery

2 Introduction CyberKnife radiosurgery has a high demand for precise (delivery) quality assurance Film has a great spatial resolution, but its dosimetric accuracy is only around 3% Diode Arrays are generally sparse in resolution and are prone to directional beam orientation We evaluated a 2D liquid filled ion chamber array (Octavius 1000 SRS, PTW, Freiburg, Germany) and present our first experiences regarding sensitivity and usability for the CyberKnife in clinical practice

3 Material and Methods Octavius 1000 SRS (PTV, Freiburg) 977 liquid filled ion chambers MicroLion (PTW) technology Chamber size: 2.3 x 2.3 x 0.5 mm 10 cm x 10 cm field 2.5 mm in central 5 cm x 5 cm field

4 Material and Methods Test 1: Resolution check 1000SRS versus Diamond Test 2: Detection of geometric beam profile positioning Single vertical CyberKnife beam pointed to the central chamber Robot was moved in 0.1 mm steps in all directions Registration of reference to shifted measurements using auto-alignment function in VeriSoft Test 3: Repetition With fiducial plate on 1000SRS delivery AQA beam multiple times Remove fiducial plate, change 1000SRS, separate multiple weeks

5 Material and Methods Test 4: Response changes from beam orientation Isocentrical beam delivery and comparing measurement versus plan calculation beam by beam Test 5: Response to system delivery errors Complex C-shaped dose distribution Deleting beams in a specific region (1%, 1.5%, 2.5% and 3% MU) Comparing results to calculated dose distribution of original non-modified treatment plan Test 6: Usage in clinical routine Initial validation on 20 extracranial and 20 intracranial clinical treatment plans

6 Test 1: Resolution check

7 Test 2: Detection of geometric beam profile positioning Almost perfect agreement Works with collimators >= 10mm Robot offset Autoalignment Difference baseline mm mm mm mm mm mm mm mm mm mm Test 3: Repetition Max displacement: 0.34mm Max dose difference : 0.48% (1 degree warmer in room) Auto align Dose Time X (mm) Y (mm) Dose (Gy) Diff (%) Baseline min min min min Next day min min min min Next day min min min min Screw Screw Screw Random Shift Random Shift Random Shift Mean Min Max

8 3 months later: No change that is a different array by the way 8

9 Test 4: Response changes from beam orientation

10 Test 4: Response changes from beam orientation Calibrated dose difference per CyberKnife Body Path node

11 Test 5: Response to system delivery errors (original, 1mm/2%)

12 Test 5: Response to system delivery errors (1% less MU)

13 Test 5: Response to system delivery errors (1.5% less MU)

14 Test 5: Response to system delivery errors (2.5% less MU)

15 Test 5: Response to system delivery errors (3% less MU)

16 Test 5: Response to system delivery errors (3% less MU, 2mm/2%!!)

17 Test 6: Usage in clinical routine Gamma (2% local pixel dose difference, 1mm distance to agreement) Intracranial passing rates: 96.3% (min 84.5%, max 100%, SD 4.0%) Extracranial passing rates: 89.1% (min 75.9%, max 99.4%, SD 6.3%)

18 Conclusion and Outlook We demonstrated that a high-resolution array of ion chambers (Octavius 1000 SRS) can be a precise dosimetric tool for routine and delivery quality assurance for robotic radiosurgery with beam angles below 85 degree Work in progress Vertical 1000 SRS holder and modifying the fiducial plate -> AQA Detailed analysis of treatment plan beam directions -> DQA Plan to 1000SRS registration with 3D max Gamma search -> E2E Synchrony treatment verification (log files) -> Patient delivery QA Small lesions

19 Patient delivery QA Static vs. Patient motion with additional 1cm drift!! Gamma 0mm/0.5%!!

20 Adamczyk S, Chan M, Stelljes T, Schmitt D, Skrobala A, Poppinga D, Adamczyk M, Pawalowski B, Hildebrandt G, Poppe B, Blanck O Dr. Oliver Blanck University Clinic Lübeck, Germany Phone: Oliver@Blanck.de Thanks to PTW