M P W Intven1, S R de Mol van Otterloo2, S Mook3, P A H Doornaert4, E N de Groot-van Breugel5, G G Sikkes6, M E Willemsen-Bosman7, H M van Zijp8, R H N Tijssen9. 1. Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: M.Intven@umcutrecht.nl. 2. Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: s.r.demolvanotterloo-2@umcutrecht.nl. 3. Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: S.Mook-2@umcutrecht.nl. 4. Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: P.A.H.Doornaert@umcutrecht.nl. 5. Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: E.vanBreugel@umcutrecht.nl. 6. Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: G.G.Sikkes@umcutrecht.nl. 7. Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: mbosman2@umcutrecht.nl. 8. Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: h.m.vanzijp-2@umcutrecht.nl. 9. Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands; Department of Radiation Oncology, Catharina Hospital, Eindhoven, The Netherlands. Electronic address: rob.tijssen@catharinaziekenhuis.nl.
Abstract
BACKGROUND AND PURPOSE: Daily online adaptation of the clinical target volume (CTV) using MR-guided radiotherapy enables margin reduction of the planning target volume (PTV). This study describes the implementation and initial experience of MR-guided radiotherapy on the 1.5T MR-linac and evaluates treatment time, patient compliance, and target coverage, including an initial assessment of margin reduction. MATERIALS AND METHODS: Patients were treated on a 1.5T MR-linac (7MV, FFF). At each fraction a 3D T2 weighted (T2w) MR-sequence was acquired on which the CTV was adapted after a deformable registration of the contours from the pre-planning CT scan. Based on the new contours a full online replanning was done after which a new 3D T2w MR-sequence was acquired for position verification. A 5 field Intensity Modulated Radiotherapy (IMRT) plan was delivered. RESULTS: Forty-three patients with rectal cancer were treated with 25 Gy in 5 fractions of which 18 with reduced margins. In total, 204 of 215 fractions were delivered on the MR-linac all of which obtained a clinically acceptable treatment plan. Median in-room time per fraction was 48 min (interquartile range 8). No fractions were canceled or interrupted because of patient intolerance. CTV coverage after margin reduction was good on all post-treatment scans but one due to passing gas. CONCLUSION: MR-guided radiotherapy using daily full online recontouring and replanning on a 1.5T MR-linac for rectal cancer is feasible and currently takes about 48 min per fraction.
BACKGROUND AND PURPOSE: Daily online adaptation of the clinical target volume (CTV) using MR-guided radiotherapy enables margin reduction of the planning target volume (PTV). This study describes the implementation and initial experience of MR-guided radiotherapy on the 1.5T MR-linac and evaluates treatment time, patient compliance, and target coverage, including an initial assessment of margin reduction. MATERIALS AND METHODS:Patients were treated on a 1.5T MR-linac (7MV, FFF). At each fraction a 3D T2 weighted (T2w) MR-sequence was acquired on which the CTV was adapted after a deformable registration of the contours from the pre-planning CT scan. Based on the new contours a full online replanning was done after which a new 3D T2w MR-sequence was acquired for position verification. A 5 field Intensity Modulated Radiotherapy (IMRT) plan was delivered. RESULTS: Forty-three patients with rectal cancer were treated with 25 Gy in 5 fractions of which 18 with reduced margins. In total, 204 of 215 fractions were delivered on the MR-linac all of which obtained a clinically acceptable treatment plan. Median in-room time per fraction was 48 min (interquartile range 8). No fractions were canceled or interrupted because of patient intolerance. CTV coverage after margin reduction was good on all post-treatment scans but one due to passing gas. CONCLUSION: MR-guided radiotherapy using daily full online recontouring and replanning on a 1.5T MR-linac for rectal cancer is feasible and currently takes about 48 min per fraction.
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