Olga Hamming-Vrieze1, Simon R van Kranen2, Wilma D Heemsbergen2, Charlotte A H Lange3, Michiel W M van den Brekel4, Marcel Verheij2, Coen R N Rasch5, Jan Jakob Sonke2. 1. Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands. Electronic address: o.vrieze@nki.nl. 2. Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands. 3. Department of Radiology, The Netherlands Cancer Institute, Amsterdam, The Netherlands. 4. Department of Head and Neck Surgery, The Netherlands Cancer Institute, Amsterdam, The Netherlands. 5. Department of Radiotherapy, Academic Medical Centre, Amsterdam, The Netherlands.
Abstract
BACKGROUND AND PURPOSE: Adaptive field size reduction based on gross tumor volume (GTV) shrinkage imposes risk on coverage. Fiducial markers were used as surrogate for behavior of tissue surrounding the GTV edge to assess this risk by evaluating if GTVs during treatment are dissolving or actually shrinking. MATERIALS AND METHODS: Eight patients with oropharyngeal tumors treated with chemo-radiation were included. Before treatment, fiducial markers (0.035×0.2cm2, n=40) were implanted at the edge of the primary tumor. All patients underwent planning-CT, daily cone beam CT (CBCT) and MRIs (pre-treatment, weeks 3 and 6). Marker displacement on CBCT was compared to local GTV surface displacement on MRIs. Additionally, marker displacement relative to the GTV surfaces during treatment was measured. RESULTS: GTV surface displacement derived from MRI was larger than derived from fiducial markers (average difference: 0.1cm in week 3). During treatment, the distance between markers and GTV surface on MRI in week 3 increased in 33%>0.3cm and in 10%>0.5cm. The MRI-GTV shrank faster than the surrounding tissue represented by the markers, i.e. adapting to GTV shrinkage may cause under-dosage of microscopic disease. CONCLUSIONS: We showed that adapting to primary tumor GTV shrinkage on MRI mid-treatment is potentially not safe since at least part of the GTV is likely to be dissolving. Adjustment to clear anatomical boundaries, however, may be done safely.
BACKGROUND AND PURPOSE: Adaptive field size reduction based on gross tumor volume (GTV) shrinkage imposes risk on coverage. Fiducial markers were used as surrogate for behavior of tissue surrounding the GTV edge to assess this risk by evaluating if GTVs during treatment are dissolving or actually shrinking. MATERIALS AND METHODS: Eight patients with oropharyngeal tumors treated with chemo-radiation were included. Before treatment, fiducial markers (0.035×0.2cm2, n=40) were implanted at the edge of the primary tumor. All patients underwent planning-CT, daily cone beam CT (CBCT) and MRIs (pre-treatment, weeks 3 and 6). Marker displacement on CBCT was compared to local GTV surface displacement on MRIs. Additionally, marker displacement relative to the GTV surfaces during treatment was measured. RESULTS: GTV surface displacement derived from MRI was larger than derived from fiducial markers (average difference: 0.1cm in week 3). During treatment, the distance between markers and GTV surface on MRI in week 3 increased in 33%>0.3cm and in 10%>0.5cm. The MRI-GTV shrank faster than the surrounding tissue represented by the markers, i.e. adapting to GTV shrinkage may cause under-dosage of microscopic disease. CONCLUSIONS: We showed that adapting to primary tumor GTV shrinkage on MRI mid-treatment is potentially not safe since at least part of the GTV is likely to be dissolving. Adjustment to clear anatomical boundaries, however, may be done safely.
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Authors: Houda Bahig; Ying Yuan; Abdallah S R Mohamed; Kristy K Brock; Sweet Ping Ng; Jihong Wang; Yao Ding; Kate Hutcheson; Molly McCulloch; Peter A Balter; Stephen Y Lai; Abrahim Al-Mamgani; Jan-Jakob Sonke; Uulke A van der Heide; Christopher Nutting; X Allen Li; Jared Robbins; Mussadiq Awan; Irene Karam; Katherine Newbold; Kevin Harrington; Uwe Oelfke; Shreerang Bhide; Marielle E P Philippens; Chris H J Terhaard; Andrew J McPartlin; Pierre Blanchard; Adam S Garden; David I Rosenthal; Gary B Gunn; Jack Phan; Guillaume Cazoulat; Michalis Aristophanous; Kelli K McSpadden; John A Garcia; Cornelis A T van den Berg; Cornelis P J Raaijmakers; Linda Kerkmeijer; Patricia Doornaert; Sanne Blinde; Steven J Frank; Clifton D Fuller Journal: Clin Transl Radiat Oncol Date: 2018-08-24