Target Volume Delineation Using Diffusion-weighted Imaging for MR-guided Radiotherapy: A Case Series of Laryngeal Cancer Validated by Pathology

摘要

In radiotherapy treatment planning, tumor delineation based on diffusion-weighted imaging (DWI) by magnetic resonance imaging (MRI) is a promising technique. MR-only-based target definition becomes important with the?recent development of MRI integrated radiotherapy treatment modalities. In this case series, DWI-based gross tumor volume (GTV) was validated using pathology and compared with a clinical GTV based on computed tomography (CT) imaging and MRI. This case series includes three patients with a laryngeal tumor. Prior to total laryngectomy (TLE), imaging was performed on CT and MRI, including a DWI scan. After TLE, the surgical specimen was processed and cut into 3-mm thick slices. The?tumor was delineated on hematoxylin-eosin (HE) stained sections by a pathologist (tumorsubHE/sub). This pathological imaging, including the tumorsubHE/sub delineation, was three-dimensionally reconstructed and registered to the imaging. The GTV was delineated by a radiation oncologist based on CT and MR imaging (GTVsubclinical/sub) and semi-automatically delineated based on DWI (GTVsubDWI/sub). The microscopic tumor extent outside the GTVsubDWI/sub contour was 3.0 mm, 2.7 mm, and 11.3 mm for cases I, II, and III, respectively. The microscopic tumor extent outside the GTVsubclinical/sub was 7.5 mm, 2.1 mm, and 1.5 mm for cases I, II, and III, respectively. The tumor,?on histology, was covered?by the GTVs for 80%, 74%, and 31% (GTVsubDWI/sub) and 73%, 72%, and 89% (GTVsubclinical/sub) for the three subsequent cases, respectively. The GTVsubDWI/sub resembled the tumorsubHE/sub more than the GTVsubclinical/sub in case I and case II. In case III, GTVsubDWI/sub missed the caudal part of the tumor that was included in the clinical delineation?due to a lack of contrast and the heterogeneous signal intensity of the tumor in DWI. In this case series, we?showed the potential?of?DWI?for MR-guided radiotherapy treatment if a clear contrast is visible. DWI-based GTV delineation might be a fast alternative to manual delineation, which?could speed up the on-table target definition using an MRI-linac system. A larger case series is needed to verify these results.