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Potential Dosimetric Benefit of PBS-PT and MRI-Guided IMRT Compared to Clinical VMAT Used to Treat Children

F Guerreiro1*, E Seravalli1 , G Janssens1 , J Maduro2 , C Brouwer2 , E Korevaar2 , A Knopf2 , B Raaymakers1 , (1) University Medical Center Utrecht, Utrecht, The Netherlands, (2) University Medical Center Groningen, University of Groningen, Groningen, The Netherlands


(Tuesday, 7/31/2018) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 7

Purpose: Flank irradiation for Wilms' tumor (WT) is currently performed at our institute using cone-beam computed tomography-guided volumetric modulated arc (VMAT_CBCT). With novel techniques such as robust pencil-beam scanning proton therapy (PBS-PT) and MRI-guided intensity modulated radiation therapy (IMRT_MRI), sparing of organs at risk (OAR) and normal tissue (NT) might be achieved. The study purpose was to quantify the dosimetric benefit when using robust PBS-PT and IMRT_MRI compared to the clinically used VMAT_CBCT workflow.

Methods: PBS-PT, IMRT_MRI and VMAT_CBCT treatment plans were calculated for 15 patients (range 1-8 years), with prescription doses ranging between 14.4-25.2Gy. PBS-PT plans were robust optimized on an internal target volume (ITV) accounting for a 5mm patient set-up and 3% range uncertainties. The IMRT_MRI plans were optimized with a 1.5T transverse magnetic field turned-on to realistically model an MRI-linac treatment and using a planning target volume (PTV) margin of 1mm to simulate a best-case scenario. VMAT_CBCT plans were optimized using a PTV margin of 5mm. All treatment plans were evaluated using dose-volume statistics.

Results: For all delivery techniques, the ITV coverage was fulfilled (V95%>99%). Moreover, better sparing of the OAR and NT was achieved with PBS-PT and IMRT_MRI when compared to VMAT_CBCT. Average mean doses for the PBS-PT, IMRT_MRI and VMAT_CBCT plans were 12.4±7.6%, 18.3±8.6%, 27.3±11.3% to the kidneys; 12.3±10.5%, 28.8±13.1%, 36.2±14.1% to the liver; 22.5±32.0%, 31.5±32.7%, 38.8±36.8% to the spleen; 54.9%±25.3%, 67.2±19.6%, 77.3±17.8% to the pancreas and 9.3±1.9%, 17.2±4.3%, 18.6±4.5% to the NT, respectively.

Conclusion: When compared to VMAT_CBCT, PBS-PT and IMRT_MRI treatment plans present equal target coverage while sparing the OAR and NT to a higher extent. However from a dosimetrical point-of-view, the PBS-PT technique is more favorable to treat WT patients than the best-case scenario for IMRT_MRI. In the future, further OAR and NT dose reductions might be foreseen when using MRI-guided PBS-PT.


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