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TH‐CD‐202‐12: Online Inter‐Beam Replanning Based On Real‐Time Dose Reconstruction
Author(s) -
Kamerling CP,
Fast MF,
Ziegenhein P,
Nill S,
Oelfke U
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4958169
Subject(s) - margin (machine learning) , linear particle accelerator , beam (structure) , medicine , radiation treatment planning , workflow , nuclear medicine , software , computer science , medical physics , radiation therapy , physics , surgery , optics , database , machine learning , programming language
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. 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.