Program Information
4D Measurement-Guided Dose Reconstruction (4D-MGDR) in End-End Quality Assurance (E2E QA) for Assessing Safety Margin in Radiosurgery (SRS) From Clinical Perspectives
M Chan1*, R Leung2 , M Wong3 , V Lee4 , G Law5 , K Lee6 , S Tung7 , O Blanck8 , (1) Tuen Mun Hospital, Hong Kong, Hong Kong (S.A.R), (2) Tuen Mun Hospital, Hong Kong, Hong Kong (S.A.R), (3) Tuen Mun Hospital, Hong Kong, Hong Kong (S.A.R), (4) Tuen Mun Hospital, Hong Kong, Hong Kong (S.A.R), (5) Tuen Mun Hospital, Hong Kong, Hong Kong (S.A.R), (6) Tuen Mun Hospital, Hong Kong, Hong Kong (S.A.R), (7) Tuen Mun Hospital, Hong Kong, Hong Kong (S.A.R), (8) University Clinic Schleswig-Holstein, Kiel, Kiel
Presentations
SU-E-T-5 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:
To assess the plan robustness and safety margin in SRS from 4D-MGDR in E2E QA based on clinical objectives.
Methods:
OCTAVIUS SRS 1000 detector array and 4D phantom (PTW, Freiburg, Germany) were used to measure 5 coplanar SRS plans with 1 and 2 mm planning target volume (PTV). 3 targets were clinical, and 2 were virtual simulated to be 1mm from the brainstem (BS), and between chiasm (CS) and optic nerve (ON). Planning was done on Monaco v5.0 (Elekta, Maryland Heights, MO) to achieve 95-99% PTV and 100% gross tumor volume (GTV) prescription dose coverage. CBCT setup of the 4D phantom by 6D robotic couch was performed as for real patient. 4D-MGDR in patient CT and dosimetric analysis were performed in PTW Verisoft v6.1. The safety margin that achieved 100% GTV coverage was determined, and doses to 2% (D2%) of BS, ON and CS were assessed from E2E QA.
Results:
100% GTV coverage was achieved with 1mm margin for 2 plans and 2mm margin for all plans. 98.3% and 99.4% GTV coverage were found in E2E QA for 1mm PTVs that either had sharp changing contour, or was nearby CS and ON or BS, and had either low planned minimum GTV dose (~101% of the prescribed dose vs.~106%) or compromised PTV coverage (95% vs. 99%). D2% to CS obtained with 4D-MGDR for one virtual target were 18.8Gy for 1mm PTV and 19.2Gy for 2mm PTV, exceeding the planned tolerance of 18Gy/3 fractions for prescription dose of 24Gy.
Conclusion:
1mm margin is generally sufficient for dose planning and machine delivery errors. Irregular GTV with just enough dose coverage to spare critical organs may need 2mm margin at the costs of possible higher organ doses. 4D MGDR in an E2E QA approach can put the treatment plan evaluation in clinical perspectives.
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