Longitudinal studies of lactate MR spectroscopic imaging (MRSI) and dynamic contrast-enhanced MR imaging (DCE-MRI) were performed at 4.7 T in two prostate tumor models grown in rats, the Dunning R3327-AT (AT) and Dunning H (H), to determine the potential of lactate and the perfusion/permeability parameter Akep as markers of tumor aggressiveness. Subcutaneous AT (n = 12) and H (n = 6) tumors were studied at different volumes between 100 and 2900 mm3 (Groups 1 to 5). Lactate concentration was determined from Selective Multiple Quantum Coherence (Sel-MQC) MRSI using phantom substitution method. Tumor enhancement after administration of Gd-DTPA was analyzed using the Brix-Hoffmann model and the Akep parameter was used as a measure of tumor perfusion/permeability. Lactate was not detected in the smallest AT tumors (Group 1; 100–270 mm3). In larger AT tumors, lactate concentration increased from 2.8 ± 1.0 mM (Group 2; 290–700 mm3) to 8.4 ± 2.9 mM (Group 3; 1000–1340 mm3), 8.2 ± 2.2 mM (Group 4; 1380–1750 mm3), and then decreased to 5.0 ± 1.7 mM (Group 5; 1900–2500 mm3) and was consistently higher in the tumor core than in the rim. Lactate was not detected in any of the Dunning H tumors. The mean tumor Akep values decreased with increasing volume in both tumor types, but were significantly higher in H tumors. In AT tumors, the Akep values were significantly higher in the rim than in the core. Histological hypoxic and necrotic fractions in AT tumors increased with volume from 0% in Group 1 to about 20% and 30%, respectively, in Group 5. Minimal amounts of hypoxia and necrosis were found in H tumors of all sizes. Thus the presence of lactate and heterogeneous perfusion/permeability are signatures of aggressive, metabolically deprived Dunning R3327-AT tumor, but not the slow-growing Dunning H tumor.
Purpose: Accurate image registration in patients with Head and Neck (HN) cancer is critical for assessment of treatment response, and must be rigorously validated. To evaluate deformable image registration (DIR) with our previously developed DIR techniques on HN PET‐CT scans, we incorporated distance discordance metric (DDM), a novel method for quantification of local registration uncertainty, as well as traditional quantitative and qualitative measurements. Methods: For each CT image series, six landmark (LM) points relevant for patients with HN cancer were placed, including the inferior‐most extent of the styloid processes, the lateral‐and inferior‐most aspects of the hyoid bone, and the superior central face of the sternum. These points were used either to assist or assess registration.Inter‐patient HN CT image registration for 10 patients was performed using standard intensity‐based B‐Spline and LM‐assisted B‐Spline DIR techniques. Intra‐patient DIR of the same patients was performed using pre‐and post‐radiation therapy image sets of the same patient.DDM metrics were obtained for inter‐patient DIR results and compared to traditional qualitative and quantitative methods including whole image mean square error (MSE), relative landmark distances between scans, and visual judgment by physicians. Results: Registration results were improved with the addition of landmarks on bony structures relevant to HN cancer. While MSE only provides a general estimate of the overall image registration error, the novel DDM metric shows the registration uncertainties for each pixel on the fixed image, allowing for localization of error. Based on DDM, DIR uncertainty was significantly reduced (>50% in region of interest) by LM‐assisted DIR techniques on inter‐patient registration. Relative LM distance was reduced as well for both intra‐and inter‐patient DIR (<1mm). Conclusion: Evaluation of DIR results with novel and traditional methods demonstrates the LM‐assisted DIR approach achieves better registration results on both inter‐and intra‐patient DIR.
6007 Background: We wish to assess on a preliminary basis whether pretreatment DCE-MRI predicts response to chemoradiation in HNSCC. Methods: Tumor perfusion was assessed in 14 patients (median age, 56y; 13 M, 1 F; squamous cell cancer 13, poorly differentiated carcinoma 1; base of tongue 6; tonsil 6; larynx 1; nasopharynx 1) with nodal metastases (size >1 cc for DCE-MRI; N1, 3; N2a, 2; N2b, 4; N2c, 4; N3, 1; Stage III, 3; Stage IVa, 10; Stage IVb, 1) prior to platin-based concurrent chemoradiation therapy. Data were acquired on a 1.5 Tesla clinical scanner with a standard MRI protocol using a clinical contrast agent (Gd-DTPA). The two compartment model analysis measured the rate constants of the contrast agent transfer between the lesion and plasma compartments (kep) and elimination by the plasma (kel). Each patient was assigned a single MR imaging parameter of uptake slope and compartmental model (Akep) on the basis of the histogram analysis of all individually fit tumor voxels. Histogram analysis calculated the amplitude (a), width (s), and median (μ) of the distribution from the fitting procedure. Overall response was determined approximately 2–5 months post treatment. Results: DCE-MRI data showed a rapid rise in the time intensity curves for viable appearing tumor, whereas muscle showed minimal signal enhancement. The mean Akep value was higher for complete responders (CR/near CR, n = 7) than for incomplete responders (ICR, n = 7; 3 partial response, 4 no response) (12.29/min±4.09 vs 7.11/min±2.51 [P = 0.04]. The preliminary histogram analysis for the slope showed that the width and median were able to differentiate between CR and ICR, P=0.039 and P=0.013 respectively, while amplitude was not significant (P=0.150). Conclusions: These preliminary data suggest that DCE-MRI may prove to be a useful predictor of response in HNSCC patients, and thus may enhance prognostication, patient selection, and treatment outcomes. No significant financial relationships to disclose.
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