TY - JOUR
T1 - Gating has a negligible impact on dose delivered in MRI-guided online adaptive radiotherapy of prostate cancer
AU - Wahlstedt, Isak
AU - Andratschke, Nicolaus
AU - Behrens, Claus P.
AU - Ehrbar, Stefanie
AU - Gabryś, Hubert S.
AU - Schüler, Helena Garcia
AU - Guckenberger, Matthias
AU - Smith, Abraham George
AU - Tanadini-Lang, Stephanie
AU - Tascón-Vidarte, José D.
AU - Vogelius, Ivan R.
AU - van Timmeren, Janita E.
N1 - Publisher Copyright:
© 2022 The Authors
PY - 2022
Y1 - 2022
N2 - Background and purpose: MR-guided radiotherapy (MRgRT) allows real-time beam-gating to compensate for intra-fractional target position variations. This study investigates the dosimetric impact of beam-gating and the impact of PTV margin on prostate coverage for prostate cancer patients treated with online-adaptive MRgRT. Materials and methods: 20 consecutive prostate cancer patients were treated with online-adaptive MRgRT SBRT with 36.25 Gy in 5 fractions (PTV D95% ≥ 95% (N = 5) and PTV D95% ≥ 100% (N = 15)). Sagittal 2D cine MRIs were used for gating on the prostate with a 3 mm expansion as the gating window. We computed motion-compensated dose distributions for (i) all prostate positions during treatment (simulating non-gated treatments) and (ii) for prostate positions within the gating window (gated treatments). To evaluate the impact of PTV margin on prostate coverage, we simulated coverage with smaller margins than clinically applied both for gated and non-gated treatments. Motion-compensated fraction doses were accumulated and dose metrics were compared. Results: We found a negligible dosimetric impact of beam-gating on prostate coverage (median of 0.00 Gy for both D95% and Dmean). For 18/20 patients, prostate coverage (D95% ≥ 100%) would have been ensured with a prostate-to-PTV margin of 3 mm, even without gating. The same was true for all but one fraction. Conclusion: Beam-gating has negligible dosimetric impact in online-adaptive MRgRT of prostate cancer. Accounting for motion, the clinically used prostate-to-PTV margin could potentially be reduced from 5 mm to 3 mm for 18/20 patients.
AB - Background and purpose: MR-guided radiotherapy (MRgRT) allows real-time beam-gating to compensate for intra-fractional target position variations. This study investigates the dosimetric impact of beam-gating and the impact of PTV margin on prostate coverage for prostate cancer patients treated with online-adaptive MRgRT. Materials and methods: 20 consecutive prostate cancer patients were treated with online-adaptive MRgRT SBRT with 36.25 Gy in 5 fractions (PTV D95% ≥ 95% (N = 5) and PTV D95% ≥ 100% (N = 15)). Sagittal 2D cine MRIs were used for gating on the prostate with a 3 mm expansion as the gating window. We computed motion-compensated dose distributions for (i) all prostate positions during treatment (simulating non-gated treatments) and (ii) for prostate positions within the gating window (gated treatments). To evaluate the impact of PTV margin on prostate coverage, we simulated coverage with smaller margins than clinically applied both for gated and non-gated treatments. Motion-compensated fraction doses were accumulated and dose metrics were compared. Results: We found a negligible dosimetric impact of beam-gating on prostate coverage (median of 0.00 Gy for both D95% and Dmean). For 18/20 patients, prostate coverage (D95% ≥ 100%) would have been ensured with a prostate-to-PTV margin of 3 mm, even without gating. The same was true for all but one fraction. Conclusion: Beam-gating has negligible dosimetric impact in online-adaptive MRgRT of prostate cancer. Accounting for motion, the clinically used prostate-to-PTV margin could potentially be reduced from 5 mm to 3 mm for 18/20 patients.
KW - Adaptive radiotherapy
KW - Beam-gating
KW - Deformable image registration
KW - Dose accumulation
KW - Margin assessment
KW - Motion-mitigation
KW - MR-guided radiotherapy
KW - Prostate cancer
KW - Prostate motion
KW - Radiotherapy
UR - http://www.scopus.com/inward/record.url?scp=85128282685&partnerID=8YFLogxK
U2 - 10.1016/j.radonc.2022.03.013
DO - 10.1016/j.radonc.2022.03.013
M3 - Journal article
C2 - 35351536
AN - SCOPUS:85128282685
VL - 170
SP - 205
EP - 212
JO - Radiotherapy & Oncology
JF - Radiotherapy & Oncology
SN - 0167-8140
ER -