Howard J. Halpern

Imaging radio frequency electron‐spin‐resonance spectrometer with high resolution and sensitivity for in vivo measurements

We report the development of a novel radio frequency electron‐spin‐resonance spectrometer designed to provide measurements with high molar sensitivity and resolution in vivo. Radio frequency (250 MHz) is chosen to obtain good penetration in animal tissue and large aqueous samples with modest sacrifice of sensitivity. The spectrometer has a lumped component resonator and operates in continuous‐wave mode. The spectrometer is capable of two‐dimensional imaging, and with a modest addition should be capable of three‐dimensional imaging. We demonstrate 3‐mm spatial resolution for DPPH samples. For 10‐ml samples of aqueous nitroxide, we demonstrate sensitivity (normalized to spectral width of 1 G) to 3×10−8‐M concentrations and spectral resolution of 0.1 G. Spectra from nitroxide spin label injected into a live mouse are shown.

Quantitative tumor oxymetric images from 4D electron paramagnetic resonance imaging (EPRI): methodology and comparison with blood oxygen level-dependent (BOLD) MRI.

This work presents a methodology for obtaining quantitative oxygen concentration images in the tumor‐bearing legs of living C3H mice. The method uses high‐resolution electron paramagnetic resonance imaging (EPRI). Enabling aspects of the methodology include the use of injectable, narrow, single‐line triaryl methyl spin probes and an accurate model of overmodulated spectra. Both of these increase the signal‐to‐noise ratio (SNR), resulting in high resolution in space (1 mm)3 and oxygen concentrations (∼3 torr). Thresholding at 15% the maximum spectral amplitude gives leg/tumor shapes that reproduce those in photographs. The EPRI appears to give reasonable oxygen partial pressures, showing hypoxia (∼0–6 torr, 0–103 Pa) in many of the tumor voxels. EPRI was able to detect statistically significant changes in oxygen concentrations in the tumor with administration of carbogen, although the changes were not increased uniformly. As a demonstration of the method, EPRI was compared with nearly concurrent (same anesthesia) T  2* /blood oxygen level‐dependent (BOLD) MRI. There was a good spatial correlation between EPRI and MRI. Homogeneous and heterogeneous T  2* /BOLD MRI correlated well with the quantitative EPRI. This work demonstrates the potential for EPRI to display, at high spatial resolution, quantitative oxygen tension changes in the physiologic response to environmental changes. Magn Reson Med 49:682–691, 2003.

Acute toxicity during external-beam radiotherapy for localized prostate cancer: Comparison of different techniques

PURPOSE The chronic and acute toxicities associated with conventional radiotherapy of localized prostate cancer are well documented. However, the degree and incidence of toxicities with conformal techniques are not known. Studying side effects associated with modern radiotherapeutic techniques is more important now since there has been a general trend to use computerized tomography-based techniques in recent years; beams eye view-based conformal techniques are also becoming more commonplace. It is possible that the local disease control can be improved with the delivery of higher doses than currently used. Conformation of the treatment volume to the target volume may facilitate such dose-escalation. However, prior to such dose-escalation, it is important to know the toxicities associated with such techniques with conventional doses. METHODS AND MATERIALS We have compared week-by-week acute toxicities associated with conventional (Group A, 16 patients), computerized tomography-based, manual (Group B, 57 patients) and beams eye view-based (Group C, 43 patients) techniques during 7 weeks of radiotherapy. Group B and C patients were treated contemporaneously (1988-1990). RESULTS Acute side effects gradually increased from week 1 through weeks 4-5 and generally declined or plateaued after that. The incidence of acute toxicities was significantly less with the beams eye view/based technique than with the other two methods. For instance, the percentages of Grade 2 acute genitourinary toxicities for Groups A, B, and C were as follows: Week 1-0, 0, 0; Week 2-6, 0, 0; Week 3-6, 9, 2; Week 4-12, 14, 9; Week 5-35, 14, 9; Week 6-31, 16, 7; Week 7-33, 8, 8, respectively. The p values associated with differences in acute genitourinary toxicities for Weeks 1-7 using chi-square test were 0.072, 0.627, 0.389, 0.538, 0.123, 0.06, and 0.012; the p values for acute gastrointestinal toxicities were 0.512, 0.09, 0.031, 0.031, 0.003, < 0.0001, and 0.004, respectively. Pairwise comparison (Wilcoxon rank-sum test) showed statistically significant lower acute toxicity in Group C than Group B (e.g., p values, Weeks 1-7 for gastrointestinal toxicity: 0.633, 0.056, 0.010, 0.014, < 0.0001, < 0.0001, and < 0.0001, respectively) in the latter part of the treatment course. No correlation was found between the extent of toxicity and the patient age or the overall treatment time. Also, no correlation was found between the degree of toxicity and the radiation dose and fraction size, within the narrow ranges used (65-70 Gy and 180-200 cGy, respectively). A trend suggesting increased severity of toxicity with increase in the volume of treatment was seen. CONCLUSION The findings in this retrospective study need to be confirmed by other prospective studies.

Late rectal sequelae following definitive radiation therapy for carcinoma of the uterine cervix: A dosimetric analysis☆

PURPOSE This study attempted to correlate patient, treatment, and dosimetric factors with the risk of late rectal sequelae in patients treated with radiation therapy (RT) for cervical carcinoma. METHODS AND MATERIALS A total of 183 patients with cervical carcinoma (67 Stage I, 93 Stage II, and 23 Stage III) treated with definitive RT with a minimum of 2 years follow-up were evaluated. Treatment consisted of external beam pelvic RT (EBRT) followed by intracavitary RT (ICRT) consisting of one or two insertions. Complications were scored and analyzed as a function of 25 patient and treatment factors. Conventional total rectal doses were obtained by adding together the EBRT and ICRT rectal doses. To account for differences in dose rate between the ICRT and EBRT, and variations in EBRT fractionation schemes, biologically equivalent rectal doses (BED) were calculated using a linear quadratic model. In addition, the influence of the varying proportions of EBRT and ICRT rectal doses were evaluated. RESULTS Twenty-eight patients (15.3%) developed late rectal sequelae (13 Grade 1, 3 Grade 2, and 12 Grade 3). Diabetes (p = 0.03), Point A dose (p = 0.04), and conventional EBRT dose (p = 0.03) were the most significant factors on multivariate analysis. Logistic regression analysis demonstrated a low risk (<10%) of late rectal sequelae below conventional and biological rectal doses of 75 Gy and 135 BED, respectively. The percentage of rectal dose delivered by the EBRT significantly influenced the dose-response relationship. A defined threshold percentage above which rectal sequelae were more common was identified over the range of doses evaluated. This threshold was 87% at a total rectal dose of 60 Gy and decreased to 60% at 80 Gy. CONCLUSION Diabetes, Point A, and EBRT doses are the most significant factors associated with the risk of late rectal sequelae in patients treated with RT for cervical carcinoma. The percentage of rectal dose delivered by the EBRT significantly affects the conventional and biological dose-response relationship. This suggests that the volume of rectum irradiated is an important and independent parameter in the development of late rectal sequelae.

Electron paramagnetic resonance oxygen images correlate spatially and quantitatively with Oxylite oxygen measurements.

Tumor oxygenation predicts cancer therapy response and malignant phenotype. This has spawned a number of oxymetries. Comparison of different oxymetries is crucial for the validation and understanding of these techniques. Electron paramagnetic resonance (EPR) imaging is a novel technique for providing quantitative high-resolution images of tumor and tissue oxygenation. This work compares sequences of tumor pO2 values from EPR oxygen images with sequences of oxygen measurements made along a track with an Oxylite oxygen probe. Four-dimensional (three spatial and one spectral) EPR oxygen images used spectroscopic imaging techniques to measure the width of a spectral line in each image voxel from a trityl spin probe (OX063, Amersham Health R&D) in the tissues and tumor of mice after spin probe injection. A simple calibration allows direct, quantitative translation of each line width to an oxygen concentration. These four-dimensional EPR images, obtained in 45 minutes from FSa fibrosarcomas grown in the legs of C3H mice, have a spatial resolution of ∼1 mm and oxygen resolution of ∼3 Torr. The position of the Oxylite track was measured within a 2-mm accuracy using a custom stereotactic positioning device. A total of nine images that involve 17 tracks were obtained. Of these, most showed good correlation between the Oxylite measured pO2 and a track located in the tumor within the uncertainties of the Oxylite localizability. The correlation was good both in terms of spatial distribution pattern and pO2 magnitude. The strong correlation of the two modalities corroborates EPR imaging as a useful tool for the study of tumor oxygenation.

Optimization of radical radiotherapy with beam's eye view techniques for non-small cell lung cancer

The presence of vital and sensitive organs such as the spinal cord, heart, and lungs makes curative radiotherapy of non-small cell lung cancer difficult to implement and necessitates use of oblique portals. Defining the target volumes in oblique portals is very difficult. We now show, for non-small cell lung cancer, how beams eye view-based radiotherapy can be used for accurate delineation of treatment volumes and for avoidance of real or dosimetric geographic misses. Furthermore, the beams eye view-based method enables one to project accurately a 2-dimensional image of 3-dimensional disease extension, especially in oblique fields, thus facilitating the design of accurate customized blocking and avoiding inadvertent blocking of the tumor or unnecessary irradiation of normal tissues. Beams eye view volumetric analysis is helpful for devising a customized treatment plan for each patient. Such customization may minimize local failure, which is one cause of poor results of radiotherapy in this site. Beams eye view-based radiotherapy has the potential of improving local control and hence may improve the survival of patients with non-small-cell lung cancer.

Spin trapping of nitric oxide by ferro-chelates: kinetic and in vivo pharmacokinetic studies

Biologically generated nitric oxide appears to play a pivotal role in the control of a diverse series of physiologic functions. Iron-chelates and low-frequency EPR spectroscopy have been used to verify in vivo production of nitric oxide. The interpretation of in vivo identification of nitric oxide localized at the site of evolution in real time is complicated by the varied kinetics of secretion. The quantitative efficiency of the spectroscopic measurement, so important in understanding the physiology of nitric oxide, remains elusive. The development of a more stable iron-chelate will help better define nitric oxide physiology. In this report, we present data comparing the commonly used ferro-di(N-methyl-D-glucamine-dithiocarbamate) (Fe2+(MGD)2) and the novel chelate ferro-di(N-(dithiocarboxy)sarcosine) (Fe2+(DTCS)2) quantifying the in vitro and in vivo stability of the corresponding spin trapped adducts, NO-Fe(MGD)2 and NO-Fe(DTCS)2. Finally, very low frequency EPR spectroscopy has been used to evaluate the pharmacokinetics of NO-Fe(MGD)2 and NO-Fe(DTCS)2 in mice in real time.

ELECTRON PARAMAGNETIC RESONANCE OXYGEN IMAGE HYPOXIC FRACTION PLUS RADIATION DOSE STRONGLY CORRELATES WITH TUMOR CURE IN FSA FIBROSARCOMAS

PURPOSE Tumor hypoxia has long been known to produce resistance to radiation. In this study, electron paramagnetic resonance (EPR) oxygen imaging was investigated for its power to predict the success of tumor control according to tumor oxygenation level and radiation dose. METHODS AND MATERIALS A total of 34 EPR oxygen images were obtained from the legs of C3H mice bearing 0.5-cm(3) FSa fibrosarcomas under both normal (air breathing) and clamped tumor conditions. Under the same conditions as those during which the images were obtained, the tumors were irradiated to a variety of doses near the FSa dose at which 50% of tumors were cured. Tumor tissue was distinguished from normal tissue using co-registration of the EPR oxygen images with spin-echo magnetic resonance imaging of the tumor and/or stereotactic localization. The tumor voxel statistics in the EPR oxygen image included the mean and median partial pressure of oxygen and the fraction of tumor voxels below the specified partial pressure of oxygen values of 3, 6, and 10 mm Hg. Bivariate logistic regression analysis using the radiation dose and each of the EPR oxygen image statistics to determine which best separated treatment failure from success. RESULTS The measurements of the dose at which 50% of tumors were cured were similar to those found in published data for this syngeneic tumor. Bivariate analysis of 34 tumors demonstrated that tumor cure correlated with dose (p = 0.004) and with a <10 mm Hg hypoxic fraction (p = 0.023). CONCLUSION Our results have shown that, together, radiation dose and EPR image hypoxic fraction separate the population of FSa fibrosarcomas that are cured from those that fail, thus predicting curability.

Selective isotopic labeling of a nitroxide spin label to enhance sensitivity for T2 oxymetry

Abstract The synthesis and application of a novel compound, a variant of a standard spin label which has been used for T2-based oxymetry, is described. The compound is 4-hydro-3carbamoyl-2,2,5,5-tetraperdeuteromethylpyrrolin-1-yloxy-d12 (mHCTPO). It was developed to optimize both the sensitivity of the T2 method to oxygen tension and the spectrometer signal for a given concentration of spin label. The compound is used with a very low frequency (250 MHz) electron paramagnetic resonance spectrometer for in vivo application and for imaging, but has application at X band. The compound provides a convenient spectral feature distinguishing broadening associated with self-interaction from that due to environmental oxygen.

In vivo spin-label murine pharmacodynamics using low-frequency electron paramagnetic resonance imaging

A novel, very-low-frequency electron paramagnetic resonance (EPR) technique is used to image the distribution of several nitroxides with distinct pharmacologic compartment affinities in the abdomens of living mice. Image acquisition is sufficiently rapid to allow a time sequence of the distribution for each compound. The spectra and concentrations of these nitroxides are imaged with the use of spectral-spatial imaging to distinguish a single spatial dimension. Liver and bladder of the mouse anatomy are distinguished by this technique. After an intraperitoneal injection of the spin-label probes, a shift in the distribution of the compounds from the upper abdomen (primarily liver) to the lower abdomen (primarily bladder) is observed. The time dependence of the shift in regional distribution depends on the structural properties of the side chain attached to the spin label. These results indicate that this application of in vivo electron paramagnetic resonance imaging will provide a new method of magnetic resonance imaging for determination of pharmacodynamics in the body of an intact animal.