Program Information
Online Inter-Beam Replanning Based On Real-Time Dose Reconstruction
CP Kamerling*, MF Fast, P Ziegenhein, S Nill, U Oelfke, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK
Presentations
TH-CD-202-12 (Thursday, August 4, 2016) 10:00 AM - 12:00 PM Room: 202
Purpose:
This work provides a proof-of-concept study for online replanning during treatment delivery for step-and-shoot prostate SBRT, based on real-time dose reconstruction. Online replanning is expected to improve the trade-off between target coverage and organ-at-risk dose in the presence of intra-fractional motion.
Methods:
We have implemented an online replanning workflow on top of our previously reported real-time dose reconstruction software which connects to an Elekta research linac. The treatment planning system DynaPlan was extended to (1) re-optimize and sequence treatment plans (in clockwise beam order) before each beam, based on actual delivered dose, in a timeframe limited by the gantry rotation between subsequent beams, and (2) send the respective segments to the delivery control software DynaTrack which starts/continues treatment immediately.
To investigate the impact of a reduced safety margin, we have created and delivered (on a linac emulator) a conventional CTV+5/3mm (I) and a reduced CTV+1mm margin (II) treatment plan for a prostate patient. We have assessed CTV coverage with and without inter-beam replanning, all exposed to a gradual target shift of 0-5mm in posterior and inferior direction from start until the end of delivery.
Results:
For the reconstructed conventional plan (I), D98 for CTV was 100% of D98 of the planned dose. For the reconstructed margin-reduced plan (II), D98 for CTV was 95% of the planned D98 without replanning, but could be recovered to 99% by replanning for each beam. Plan (II) with replanning resulted in a decrease for bladder V90% by 88% and an increase to rectum V90% by 9% compared to the conventional plan (I). Dose calculation/accumulation was performed in <15ms per MLC aperture, replanning in <15s per beam.
Conclusion:
We have shown that online inter-beam replanning is technically feasible and potentially allows for a margin reduction. Future investigation considering motion-robust replanning optimization parameters is in progress.
Funding Support, Disclosures, and Conflict of Interest: We acknowledge support of the MLC research from Elekta AB. This work is supported by Cancer Research UK under Programme C33589/A19908. Research at ICR is also supported by Cancer Research UK under Programme C33589/A19727 and NHS funding to the NIHR Biomedical Research Centre at RMH and ICR.
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