Marielle Philippens

Correlation of [18F]FMISO autoradiography and pimonodazole immunohistochemistry in human head and neck carcinoma xenografts.

PurposeTumour cell hypoxia is a common feature in solid tumours adversely affecting radiosensitivity and chemosensitivity in head and neck squamous cell carcinomas. Positron emission tomography (PET) using the tracer [18F]fluoromisonidazole ([18F]FMISO) is most frequently used for non-invasive evaluation of hypoxia in human tumours. A series of ten human head and neck xenograft tumour lines was used to validate [18F]FMISO as hypoxia marker at the microregional level.MethodsAutoradiography after injection of [18F]FMISO was compared with immunohistochemical staining for the hypoxic cell marker pimonidazole in the same tumour sections of ten different human head and neck xenograft tumour lines. The methods were compared: first, qualitatively considering the microarchitecture; second, by obtaining a pixel-by-pixel correlation of both markers at the microregional level; third, by measuring the signal intensity of both images; and fourth, by calculating the hypoxic fractions by pimonidazole labelling.ResultsThe pattern of [18F]FMISO signal was dependent on the distribution of hypoxia at the microregional level. The comparison of [18F]FMISO autoradiography and pimonidazole immunohistochemistry by pixel-by-pixel analysis revealed moderate correlations. In five tumour lines, a significant correlation between the mean [18F]FMISO and pimonidazole signal intensity was found (range, r2u2009=u20090.91 to r2u2009=u20090.99). Comparison of the tumour lines with respect to the microregional distribution pattern of hypoxia revealed that the correlation between the mean signal intensities strongly depended on the microarchitecture. Overall, a weak but significant correlation between hypoxic fractions based on pimonidazole labeling and the mean [18F]FMISO signal intensity was observed (r2u2009=u20090.18, pu2009=u20090.02). For the three tumour models with a ribbon-like microregional distribution pattern of hypoxia, the correlation between the hypoxic fraction and the mean [18F]FMISO signal intensity was much stronger and more significant (r2u2009=u20090.73, pu2009<u20090.001) than for the tumours with a more homogenous, patchy, microregional distribution pattern of hypoxia.ConclusionDifferent patterns of [18F]FMISO accumulation dependent on the underlying microregional distribution of hypoxia were found in ten head and neck xenograft tumours. A weak albeit significant correlation was found between the mean [18F]FMISO signal intensity and the hypoxic fraction of the tumours. In larger clinical tumours, [18F]FMISO–PET provides information on the tumour oxygenation status on a global level, facilitating dose painting in radiation treatment planning. However, caution must be taken when studying small tumour subvolumes as accumulation of the tracer depends on the presence of hypoxia and on the tumour microarchitecture.

Diffusion-weighted MR Imaging in Laryngeal and Hypopharyngeal Carcinoma: Association between Apparent Diffusion Coefficient and Histologic Findings

PURPOSEnTo investigate the relationship between the histologic characteristics of head and neck squamous cell carcinoma and apparent diffusion coefficient (ADC) at diffusion-weighted magnetic resonance (MR) imaging.nnnMATERIALS AND METHODSnThe institutional ethics committee approved this study and waived informed consent. In head and neck squamous cell carcinoma, local failure after chemotherapy and/or radiation therapy correlates with pretreatment ADC. However, the histopathologic basis of this correlation remains unclear. In this study, 16 patients with head and neck squamous cell carcinoma were enrolled (median age, 60 years; range, 49-78 years). Before undergoing total laryngectomy, patients underwent 1.5-T diffusion-weighted MR imaging. After resection, whole-mount hematoxylin-eosin-stained sections were registered to the MR images. Cellular density; nuclear, cytoplasmic, and stromal area; and nuclear-cytoplasmic ratio within the tumor were calculated by using image-based segmentation on four consecutive slices. Mean ADC of the corresponding tumor region was calculated. Spearman correlations between ADC and histologic characteristics were calculated.nnnRESULTSnADC was significantly and inversely correlated with cell density (n = 16, r = -0.57, P = .02), nuclear area (n = 12, r = -0.64, P = .03), and nuclear-cytoplasmic ratio (n = 12, r = -0.77, P ≤ .01). ADC was significantly and positively correlated with percentage area of stroma (n = 12, r = 0.69, P = .01). Additionally, the percentage area of stroma was strongly interdependent with the percentage area of nuclei (n = 12, r = -0.97, P ≤ .01).nnnCONCLUSIONnADC was significantly correlated with cellularity, stromal component, and nuclear-cytoplasmic ratio. The positive correlation of ADC and stromal component suggests that the poor prognostic value of high pretreatment ADC might partly be attributed to the tumor-stroma component, a known predictor of local failure.

Comparison of Tumor Volumes Derived from Glucose Metabolic Rate Maps and SUV Maps in Dynamic 18F-FDG PET

Tumor delineation using noninvasive medical imaging modalities is important to determine the target volume in radiation treatment planning and to evaluate treatment response. It is expected that combined use of CT and functional information from 18F-FDG PET will improve tumor delineation. However, until now, tumor delineation using PET has been based on static images of 18F-FDG standardized uptake values (SUVs). 18F-FDG uptake depends not only on tumor physiology but also on blood supply, distribution volume, and competitive uptake processes in other tissues. Moreover, 18F-FDG uptake in tumor tissue and in surrounding healthy tissue depends on the time after injection. Therefore, it is expected that the glucose metabolic rate (MRglu) derived from dynamic PET scans gives a better representation of the tumor activity than does SUV. The aim of this study was to determine tumor volumes in MRglu maps and to compare them with the values from SUV maps. Methods: Twenty-nine lesions in 16 dynamic 18F-FDG PET scans in 13 patients with non–small cell lung carcinoma were analyzed. MRglu values were calculated on a voxel-by-voxel basis using the standard 2-compartment 18F-FDG model with trapping in the linear approximation (Patlak analysis). The blood input function was obtained by arterial sampling. Tumor volumes were determined in SUV maps of the last time frame and in MRglu maps using 3-dimensional isocontours at 50% of the maximum SUV and the maximum MRglu, respectively. Results: Tumor volumes based on SUV contouring ranged from 1.31 to 52.16 cm3, with a median of 8.57 cm3. Volumes based on MRglu ranged from 0.95 to 37.29 cm3, with a median of 3.14 cm3. For all lesions, the MRglu volumes were significantly smaller than the SUV volumes. The percentage differences (defined as 100% × (VMRglu − VSUV)/VSUV, where V is volume) ranged from −12.8% to −84.8%, with a median of −32.8%. Conclusion: Tumor volumes from MRglu maps were significantly smaller than SUV-based volumes. These findings can be of importance for PET-based radiotherapy planning and therapy response monitoring.

Measurements of T1 and T2 relaxation times of colon cancer metastases in rat liver at 7 T

The purpose of this study was to investigate the magnetic resonance imaging (MRI) characteristics of colon cancer metastases in rat liver at 7 T. A dedicated RF microstrip coil of novel design was built in order to increase the signal-to-noise ratio and, in combination with respiratory triggering, to minimize motion artifacts. T1- and T2-weighted MR imaging was performed to follow tumor growth. T1-weighted images provided a good anatomical delineation of the liver structure, while the best contrast between metastases and normal liver tissue was achieved with T2-weighted images.Measurements of T1 and T2 relaxation times were performed with inversion recovery FLASH and Carr–Purcell–Meiboom–Gill and inversion recovery FLASH imaging sequences, respectively, for quantitative MR characterization of metastases. Both the T1 and T2 of the metastases were significantly higher than those of normal liver tissue. Further, an increase in the T1 relaxation time of the metastases was observed with tumor growth. These findings suggest that quantitative in vivo MR characterization provides information on tumor development and possibly response to therapy, though additional studies are needed to elucidate the correlation between the changes in relaxation times and tumor microenvironment.

Bath and Shower Effect in Spinal Cord: The Effect of Time Interval

PURPOSEnTo evaluate the time dependency of the sensitizing effect of a large low-dose field on a small high-dose field in the rat cervical spinal cord.nnnMETHODS AND MATERIALSnIrradiation experiments with a relatively low dose to a large volume (bath, 2 cm, 4 Gy) were combined with high doses to a small volume (shower, 4.7 mm, 26-43 Gy) at intervals of 8 minutes and 3, 12, and 24 hours. Both a functional score defined as motor impairment and a histologic score characterized as white matter necrosis were used as end points.nnnRESULTSnApplication of the 4-Gy bath dose resulted in a significant decrease in 50% isoeffective dose (ED(50)) from 48.7 Gy (small field) to 40.8 Gy. If the interval was extended, the ED(50) increased to 44.4 (3 hours) and 44.8 Gy (12 hours), whereas a 24-hour interval resulted in a significant increase to 51.9 Gy. If the histologic end point was considered, the ED(50) for all dose-response curves decreased slightly with 0.2 to 2.6 Gy without significantly changing the kinetics.nnnCONCLUSIONSnThe bath effect as applied in the bath-and-shower experiment lasted for at least 12 hours and disappeared in the 24-hour interval. This time scale clearly deviates from the repair kinetics in spinal cord derived from low-dose-rate and fractionated irradiations.

Radiation Effects in the Rat Spinal Cord: Evaluation with Apparent Diffusion Coefficient versus T2 at Serial MR Imaging

PURPOSEnTo prospectively determine whether apparent diffusion coefficients (ADCs) are more sensitive to radiation-induced changes in the rat spinal cord than T2 relaxation times.nnnMATERIALS AND METHODSnThe study was approved by the institutional ethical committee on animal welfare. One centimeter of the thoracolumbar spinal cord of six rats was irradiated with 36 Gy. For 3-6 months after irradiation, five 7.0-T magnetic resonance (MR) imaging measurements were performed in each rat until motor impairment developed. Six age-matched rats were examined as controls. Measurements were performed by using diffusion-weighted imaging with five b values and a spin-echo sequence with 20 echoes. ADC and T2 values were calculated, and the spatiotemporal evolution of the radiation-induced lesions was determined semiautomatically. The final MR measurements were compared with the histologic findings.nnnRESULTSnShortly before the neurologic signs appeared, the first radiation effects manifested as well-circumscribed white matter (WM) lesions with a low longitudinal ADC and normal or high T2. WM lesions with high T2 correlated with confluent necrosis at histologic analysis, whereas WM lesions with normal T2 correlated with focal necrosis and demyelination. In the gray matter (GM), lesions with diffusely high T2 were present and were attributed to edema. T2 changes in the GM preceded T2 and ADC changes in the WM.nnnCONCLUSIONnIn the WM, longitudinal ADC was more sensitive for the detection of radiation damage than T2, but in the GM, T2 was more sensitive.

Assessment of Blood Hemodynamics by USPIO-Induced R(1) Changes in MRI of Murine Colon Carcinoma.

The objective of this study is to assess whether ultrasmall superparamagnetic iron oxide (USPIO)-induced changes of the water proton longitudinal relaxation rate (R1) provide a means to assess blood hemodynamics of tumors. Two types of murine colon tumors (C26a and C38) were investigated prior to and following administration of USPIO blood-pool contrast agent with fast R1 measurements. In a subpopulation of mice, R1 was measured following administration of hydralazine, a well-known blood hemodynamic modifier. USPIO-induced R1 increase in C38 tumors (ΔR1xa0=xa00.072xa0±xa00.0081xa0s−1) was significantly larger than in C26a tumors (ΔR1xa0=xa00.032xa0±xa00.0018xa0s−1, Nxa0=xa09, t test, Pxa0<xa00.001). This was in agreement with the immunohistochemical data that showed higher values of relative vascular area (RVA) in C38 tumors than in C26a tumors (RVAxa0=xa00.059xa0±xa00.015 vs. 0.020xa0±xa00.011; Pxa0<xa00.05). Following administration of hydralazine, a decrease in R1 value was observed. This was consistent with the vasoconstriction induced by the steal effect mechanism. In conclusion, R1 changes induced by USPIO are sensitive to tumor vascular morphology and to blood hemodynamics. Thus, R1 measurements following USPIO administration can give novel insight into the effects of blood hemodynamic modifiers, non-invasively and with a high temporal resolution.

Characterization of late radiation effects in the rat thoracolumbar spinal cord by MR imaging using USPIO.

The aim of this study was to detect late radiation effects in the rat spinal cord using MR imaging with ultra-small particles of iron oxide (USPIO) contrast agent to better understand the development of late radiation damage with emphasis on the period preceding neurological signs. Additionally, the role of an inflammatory reaction was assessed by measuring macrophages that internalized USPIO. T2-weighted spin echo MR measurements were performed at 7T in six rats before paresis was expected (130–150 days post-irradiation, early group), and in six paretic rats (150–190 days post-irradiation, late group). Measurements were performed before, directly after and, only in the early group, 40 h after USPIO administration and compared with histology. In the early group, MR images showed focal regions in grey matter (GM) and white matter (WM) with signal intensity reduction after USPIO injection. Larger lesions with contrast enhancement were located in and around edematous GM of three animals of the early group and five of the late group. Forty hours after injection, additional lesions in WM, GM and nerve roots appeared in animals with GM edema. In the late paretic group, MR imaging showed WM necrosis adjacent to areas with large contrast enhancement. In conclusion, detection of early focal lesions was improved by contrast administration. In the animals with extended radiation damage, large hypo-intense regions appeared due to USPIO, which might be attributed to blood spinal cord barrier breakdown, but the involvement of blood-derived iron-loaded macrophages could not be excluded.

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

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 (tumorHE). This pathological imaging, including the tumorHE delineation, was three-dimensionally reconstructed and registered to the imaging. The GTV was delineated by a radiation oncologist based on CT and MR imaging (GTVclinical) and semi-automatically delineated based on DWI (GTVDWI). The microscopic tumor extent outside the GTVDWI 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 GTVclinical 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% (GTVDWI) and 73%, 72%, and 89% (GTVclinical) for the three subsequent cases, respectively. The GTVDWI resembled the tumorHE more than the GTVclinical in case I and case II. In case III, GTVDWI 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.