Effect of intrafraction adaptation on PTV margins for MRI guided online adaptive radiotherapy for rectal cancer.

Autor: Kensen CM; Department of Radiation Oncology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX, Amsterdam, The Netherlands., Janssen TM; Department of Radiation Oncology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX, Amsterdam, The Netherlands., Betgen A; Department of Radiation Oncology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX, Amsterdam, The Netherlands., Wiersema L; Department of Radiation Oncology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX, Amsterdam, The Netherlands., Peters FP; Department of Radiation Oncology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX, Amsterdam, The Netherlands., Remeijer P; Department of Radiation Oncology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX, Amsterdam, The Netherlands., Marijnen CAM; Department of Radiation Oncology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX, Amsterdam, The Netherlands., van der Heide UA; Department of Radiation Oncology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX, Amsterdam, The Netherlands. u.vd.heide@nki.nl.
Jazyk: angličtina
Zdroj: Radiation oncology (London, England) [Radiat Oncol] 2022 Jun 21; Vol. 17 (1), pp. 110. Date of Electronic Publication: 2022 Jun 21.
DOI: 10.1186/s13014-022-02079-2
Abstrakt: Purpose: To determine PTV margins for intrafraction motion in MRI-guided online adaptive radiotherapy for rectal cancer and the potential benefit of performing a 2nd adaptation prior to irradiation.
Methods: Thirty patients with rectal cancer received radiotherapy on a 1.5 T MR-Linac. On T2-weighted images for adaptation (MRI adapt ), verification prior to (MRI ver ) and after irradiation (MRI post ) of 5 treatment fractions per patient, the primary tumor GTV (GTV prim ) and mesorectum CTV (CTV meso ) were delineated. The structures on MRI adapt were expanded to corresponding PTVs. We determined the required expansion margins such that on average over 5 fractions, 98% of CTV meso and 95% of GTV prim on MRI post was covered in 90% of the patients. Furthermore, we studied the benefit of an additional adaptation, just prior to irradiation, by evaluating the coverage between the structures on MRI ver and MRI post. A threshold to assess the need for a secondary adaptation was determined by considering the overlap between MRI adapt and MRI ver. RESULTS: PTV margins for intrafraction motion without 2nd adaptation were 6.4 mm in the anterior direction and 4.0 mm in all other directions for CTV meso and 5.0 mm isotropically for GTV prim . A 2nd adaptation, applied for all fractions where the motion between MRI adapt and MRI ver exceeded 1 mm (36% of the fractions) would result in a reduction of the PTV meso margin to 3.2 mm/2.0 mm. For PTV prim a margin reduction to 3.5 mm is feasible when a 2nd adaptation is performed in fractions where the motion exceeded 4 mm (17% of the fractions).
Conclusion: We studied the potential benefit of intrafraction motion monitoring and a 2nd adaptation to reduce PTV margins in online adaptive MRIgRT in rectal cancer. Performing 2nd adaptations immediately after online replanning when motion exceeded 1 mm and 4 mm for CTV meso and GTV prim respectively, could result in a 30-50% margin reduction with limited reduction of dose to the bowel.
(© 2022. The Author(s).)
Databáze: MEDLINE
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