real-time absorbed 4D-dose calculation for carbon ion therapy
MO-0879
Abstract
real-time absorbed 4D-dose calculation for carbon ion therapy
Authors: Cosimo Galeone1,2,3, Timo Steinsberger1, Marco Donetti4, Felix Mas Milian2,5,6, Athena Paz1, Anna Vignati2,5, Lennart Volz1, Marco Durante1,7, Simona Giordanengo2,5, Christian Graeff1,3
1GSI, Biophysics, Darmstadt, Germany; 2University of Torino, Physics, Torino, Italy; 3Technical University of Darmstadt, Electrical Engineering and Information Technology, Darmstadt, Germany; 4Fondazione CNAO, Medical physics, Pavia, Italy; 5National Institute of Nuclear Physics, Division of Torino, Torino, Italy; 6Universidade Estadual de Santa Cruz, Department of Exact and Technological Sciences , Ilheus, Brazil; 7Technical University of Darmstadt, Condensed Matter Physics, Darmstadt, Germany
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Purpose or Objective
The estimation of dose errors is a key part of online adaptive particle therapy. Interplay distorts dose distributions leading to non-ideal tumor coverage and higher dose to healthy tissues.
Fast forward dose calculation (FDC) is mandatory to verify the efficacy of motion mitigation strategies during treatment. We propose and validate in silico a system to reconstruct the planned and delivered absorbed 4D dose in real-time, i.e. within the spill pauses (<5 s) present during the carbon ion therapy delivery.
Material and Methods
The algorithm used for the FDC, was based on the existing RIDOS dose calculation tool, implemented on Graphic Processing Units (GPUs).
For real-time delivered dose calculation, the fast FDC was interfaced with the research version of the CNAO Dose Delivery System (DDS) at GSI through a TCP/IP connection, providing measured and planned spot properties (MU, beam position, and motion phase) during the delivery. The algorithm evaluates the cumulative delivered and prescribed dose distributions within the inter-spill pause and performs a gamma-index comparison. The results are updated on a graphical user interface (Fig. 1).
Figure 1: (1) and (2) are the cumulative planned and delivered doses in XY plane. (3) and (4) are the cumulative planned and delivered doses on YZ plane. (5) and (6) present the gamma-index and the dose difference contribution in XY. (7) shows the passing rate of the spills.
The system has been tested in silico on a virtual XCAT 4DCT, with a simulated data stream from the DDS for dose reconstruction. For verification of advanced motion mitigation strategies, we designed RIDOS to be compatible with the recently developed MultiPhase 4D delivery (MP4D).
Results
The framework successfully achieved the FDC in less than 3 s, i.e., it would enable a delivered dose update during the spill pause. The overall computation time required per spot was ~ 2 ms, where ~ 6 µs were attributed to raytracing for computing water equivalent depths, the dose calculation took ~ 1.7 ms. The dose warping to the reference motion phase was done once per spill and took ~ 300 µs. The processing time of gamma-index comparison between the cumulative planned and delivered dose after the spill was of about 0.2 seconds. Both, the real-time calculated planned and delivered doses, were also validated against a research TPS (TRiP98) log-file based dose reconstruction (Fig. 2), showing good agreement with gamma-index passing rate (3mm/3%) > 98%.
Figure 2: Example of TRiP and RIDOS dose distributions in XY.
Conclusion
We demonstrated the feasibility of a real-time dose calculation with clinically acceptable precision.
The next step will involve experimental tests with carbon and proton beams at the CNAO facility, as well as consideration of more patient data, with variable motion and motion mitigation strategy. In the future, this framework will open the door for possible real-time adaptive particle therapy workflows.
Project funded by the Horizon 2020 program, grant agreement N. 955956 (RAPTOR).