Abstract
BackgroundPancreatic ductal adenocarcinoma has dismal prognosis. Most patients receive radiation therapy (RT), which is complicated by respiration induced organ motion in upper abdomen. The purpose of this study is to report our early clinical experience in a novel self-gated k-space sorted four-dimensional magnetic resonance imaging (4D-MRI) with slab-selective (SS) excitation to highlight tumor infiltrating blood vessels for pancreatic RT.MethodsTen consecutive patients with borderline resectable or locally advanced pancreatic cancer were recruited to the study. Non-contrast 4D-MRI with and without slab-selective excitation and 4D-CT with delay contrast were performed on all patients. Vessel-tissue CNR were calculated for aorta and critical vessels (superior mesenteric artery or superior mesenteric vein) encompassed by tumor. Respiratory motion trajectories for tumor, as well as involved vessels were analyzed on SS-4D-MRI. Intra-class cross correlation (ICC) between tumor volume and involved vessels were calculated.ResultsAmong all 4D imaging modalities evaluated, SS-4D-MRI sampling trajectory results in images with highest vessel-tissue CNR comparing to non-slab-selective 4D-MRI and 4D-CT for all patients studied. Average (±standard deviation) CNR for involved vessels are 13.1 ± 8.4 and 3.2 ± 2.7 for SS-4D-MRI and 4D-CT, respectively. The ICC factors comparing tumor and involved vessels motion trajectories are 0.93 ± 0.10, 0.65 ± 0.31 and 0.77 ± 0.23 for superior-inferior, anterior-posterior and medial-lateral directions respectively.ConclusionsA novel 4D-MRI sequence based on 3D-radial sampling and slab-selective excitation has been assessed for pancreatic cancer patients. The non-contrast 4D-MRI images showed significantly better contrast to noise ratio for the vessels that limit tumor resectability compared to 4D-CT with delayed contrast. The sequence has great potential in accurately defining both the tumor and boost volume margins for pancreas RT with simultaneous integrated boost.
Highlights
Pancreatic ductal adenocarcinoma (PDA) has the worst outcome of any solid tumor [1]
There are significant technical challenges associated with accurately escalating radiation dose to the vessel/tumor interface due to substantial internal organ motion in the upper abdominal region. [7,8,9,10] Stereotactic body radiation therapy (SBRT) with simultaneous integrated boost (SIB) to tumor/vessel interface is further complicated by the fact that the motion of the cancerous tissue surrounding the tumor infiltrating vessels may be different from center of the pancreas tumor [11]
SS-4D-magnetic resonance imaging (MRI) was successfully implemented on 10 pancreatic cancer patients
Summary
Pancreatic ductal adenocarcinoma (PDA) has the worst outcome of any solid tumor [1]. Whereas surgical resection remains the mainstay therapy, 80% of patients with non-metastatic disease have unresectable tumors that are unlikely to be down-staged after standard chemo-radiation therapy, due to the geometric relationship of the primary tumor to the surrounding vasculature [2]. Radiation therapy (RT) with simultaneous integrated boost (SIB) to cancerous tissue surrounding tumor infiltrating vasculature has the potential to sterilize tumor around the vessels that have precluded resectability [5, 6]. There are significant technical challenges associated with accurately escalating (boosting) radiation dose to the vessel/tumor interface due to substantial internal organ motion in the upper abdominal region. [12, 13] The problem is further compounded by poor CT soft tissue contrast and 4D-CT stitching artifacts [14] For these reasons, 4D-CT with delayed intravenous and oral contrasts often has limited value to evaluate soft tissue and blood vessel respiratory motion. The purpose of this study is to report our early clinical experience in a novel self-gated k-space sorted four-dimensional magnetic resonance imaging (4D-MRI) with slab-selective (SS) excitation to highlight tumor infiltrating blood vessels for pancreatic RT
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