Phase I Trial of SPECT-Guided Liver-Directed Radiotherapy for Patients with Low Functional Liver Volume.

BACKGROUND: Traditional constraints specify that 700 cc of liver should be spared a hepatotoxic dose when delivering liver-directed radiotherapy to reduce the risk of inducing liver failure. We investigated the role of single photon emission computed tomography (SPECT) to identify and preferentially avoid functional liver during liver-directed radiation treatment planning in patients with preserved liver function but limited functional liver volume after receiving prior hepatotoxic chemotherapy or surgical resection. METHODS: This phase I trial with a 3 + 3 design evaluated the safety of liver-directed radiotherapy using escalating functional liver radiation dose constraints in patients with liver metastases. Dose limiting toxicities (DLTs) were assessed 6-8 weeks and 6 months after completing radiotherapy. RESULTS: All twelve patients had colorectal liver metastases and received prior hepatotoxic chemotherapy. Eight patients underwent prior liver resection. Median computed tomography (CT) anatomical non-tumor liver volume was 1,584 cc (range 764-2,699 cc). Median SPECT functional liver volume was 1,117 cc (range 570-1,928cc). Median non-target CT and SPECT liver volumes below the volumetric dose constraint were 997 cc (range 544-1,576 cc) and 684 cc (range 429-1,244 cc), respectively. The prescription dose was 67.5-75 Gy in 15 fractions or 75-100 Gy in 25 fractions. No DLTs were observed during follow-up. One-year in-field control was 57%. One-year overall survival was 73%. CONCLUSION: Liver-directed radiotherapy can be safely delivered to high doses when incorporating functional SPECT into the radiation treatment planning process which may enable sparing of lower volumes of liver than traditionally accepted in patients with preserved liver function. TRIAL REGISTRATION: NCT02626312.

Automated Contouring of Contrast and Noncontrast Computed Tomography Liver Images With Fully Convolutional Networks.

PURPOSE: The deformable nature of the liver can make focal treatment challenging and is not adequately addressed with simple rigid registration techniques. More advanced registration techniques can take deformations into account (eg, biomechanical modeling) but require segmentations of the whole liver for each scan, which is a time-intensive process. We hypothesize that fully convolutional networks can be used to rapidly and accurately autosegment the liver, removing the temporal bottleneck for biomechanical modeling. METHODS AND MATERIALS: Manual liver segmentations on computed tomography scans from 183 patients treated at our institution and 30 scans from the Medical Image Computing & Computer Assisted Intervention challenges were collected for this study. Three architectures were investigated for rapid automated segmentation of the liver (VGG-16, DeepLabv3 +, and a 3-dimensional UNet). Fifty-six cases were set aside as a final test set for quantitative model evaluation. Accuracy of the autosegmentations was assessed using Dice similarity coefficient and mean surface distance. Qualitative evaluation was also performed by 3 radiation oncologists on 50 independent cases with previously clinically treated liver contours. RESULTS: The mean (minimum-maximum) mean surface distance for the test groups with the final model, DeepLabv3 +, were as follows: µContrast(N = 17): 0.99 mm (0.47-2.2), µNon_Contrast(N = 19)l: 1.12 mm (0.41-2.87), and µMiccai(N = 30)t: 1.48 mm (0.82-3.96). The qualitative evaluation showed that 30 of 50 autosegmentations (60%) were preferred to manual contours (majority voting) in a blinded comparison, and 48 of 50 autosegmentations (96%) were deemed clinically acceptable by at least 1 reviewing physician. CONCLUSIONS: The autosegmentations were preferred compared with manually defined contours in the majority of cases. The ability to rapidly segment the liver with high accuracy achieved in this investigation has the potential to enable the efficient integration of biomechanical model-based registration into a clinical workflow.

An open-label, single-arm pilot study of EUS-guided brachytherapy with phosphorus-32 microparticles in combination with gemcitabine +/- nab-paclitaxel in unresectable locally advanced pancreatic cancer (OncoPaC-1): Technical details and study protocol.

Current treatment options for patients with unresectable locally advanced pancreatic cancer (LAPC) include chemotherapy alone or followed by chemoradiation or stereotactic body radiotherapy. However, the prognosis for these patients remains poor, with a median overall survival <12 months. Therefore, novel treatment options are needed. Currently, there is no brachytherapy device approved for pancreatic cancer treatment. Hereby, we present the protocol of a prospective, multicenter, interventional, open-label, single-arm pilot study (OncoPac-1, Clinicaltrial.gov-NCT03076216) aiming to determine the safety and efficacy of Phosphorus-32 when implanted directly into pancreatic tumors using EUS guidance, for patients with unresectable LAPC undergoing chemotherapy (gemcitabine ± nab-paclitaxel).

A personalized, Monte Carlo-based method for internal dosimetric evaluation of radiopharmaceuticals in children.

PURPOSE: Herein, we introduce a methodology for estimating the absorbed dose in organs at risk that is based on specified clinically derived radiopharmaceutical biodistributions and personalized anatomical characteristics. METHODS: To evaluate the proposed methodology, we used realistic Monte Carlo (MC) simulations and computational pediatric models to calculate a parameter called in this work the "specific absorbed dose rate" (SADR). The SADR is a unique quantitative metric in that it is specific to a particular organ. It is defined as the absorbed dose rate in an organ when the biodistribution of radioactivity over the whole body is considered. Initially, we applied a validation procedure that calculated specific absorbed fractions (SAFs) from mono-energetic photon sources in the range of 10 keV-2 MeV and compared them with previously published data. We calculated the SADRs for five different radiopharmaceuticals (99m Tc-MDP, 123 I-mIBG, 131 I-MIBG, 131 I-NaI, and 153 Sm-EDTMP) based on their biodistributions at four or five different times; the biodistributions were derived from the clinical scintigraphic data of pediatric patients. We used six models representing male and female patients aged 5, 8, and 14 yr to investigate the absorbed dose variability due to anatomical variations. The GATE Monte Carlo toolkit was used to calculate absorbed doses per organ. Finally, we compared the SADR methodology to that of OLINDA/EXM 1.1 using rescaled masses according to the studied models. Four target organs were considered for calculating the absorbed doses. RESULTS: The ratios of SAFs calculated with GATE simulations to those based on previously published data were between 0.9 and 2.2 when the liver was used as a source organ. Subsequently, we used GATE to calculate a dataset of SADRs for the six pediatric models. The SADRs for pediatric models whose total body weights ranged from 20 to 40 kg varied up to approximately 90%, whereas those for models of similar body masses varied less than 15%. Finally, we found absorbed dose discrepancies of approximately 10-150% between the SADR methodology and OLINDA for two different radiopharmaceuticals. Absorbed doses from SADRs and from individualized S-values in the same pediatric model differed approximately 1-50%. CONCLUSIONS: Because pediatric radiopharmaceutical dosimetric estimates demonstrate large variation due to the patient's anatomical characteristics, personalized data should be considered. Using our SADR method in a larger population of phantoms and for a variety of radiopharmaceuticals could enhance the personalization of dosimetry in pediatric nuclear medicine. The proposed methodology provides the advantage of creating time-dependent organ dose rate curves.

Updated Results of Rituximab Pre- and Post-BEAM with or without 90Yttrium Ibritumomab Tiuxetan during Autologous Transplant for Diffuse Large B-cell Lymphoma.

Purpose: We evaluated the effect on long-term survival of adding rituximab (R) to BEAM (carmustine, etoposide, cytarabine, and melphalan) conditioning with or without yttrium-90 ibritumomab tiuxetan (90YIT) in patients with relapsed diffuse large B-cell lymphoma (DLBCL) undergoing autologous stem cell transplant (ASCT).Experimental design: Patients were enrolled on three consecutive phase II clinical trials. Patients received two doses of rituximab (375 and 1,000 mg/m2) during mobilization of stem cells, followed by 1,000 mg/m2 on days +1 and +8 after ASCT with R-BEAM or 90YIT-R-BEAM (90YIT dose of 0.4 mCi/kg) conditioning.Results: One hundred thirteen patients were enrolled, with 73 receiving R-BEAM and 40 receiving 90YIT-R-BEAM. All patients had a prior exposure to rituximab. The median follow-up intervals for survivors were 11.8, 8.1, and 4.2 years in the three trials, respectively. The 5-year disease-free survival (DFS) rates were 62% for R-BEAM and 65% for 90YIT-R-BEAM (P = 0.82). The 5-year overall survival rates were 73% and 77%, respectively (P = 0.65). In patients with de novo DLBCL, survival outcomes of the germinal center/activated b-cell histologic subtypes were similar with 5-year OS rates (P = 0.52) and DFS rates (P = 0.64), irrespective of their time of relapse (<1 vs. >1 year) after initial induction chemotherapy (P = 0.97).Conclusions: Administering ASCT with rituximab during stem cell collection and immediately after transplantation induces long-term disease remission and abolishes the negative prognostic impact of cell-of-origin in patients with relapsed DLBCL. The addition of 90YIT does not confer a further survival benefit. Clin Cancer Res; 24(10); 2304-11. ©2018 AACR.

AAPM medical physics practice guideline 6.a.: Performance characteristics of radiation dose index monitoring systems.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education and professional practice of medical physics. The AAPM has more than 8,000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines: •Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. •Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

Qualitative and quantitative comparison of gated blood pool single photon emission computed tomography using low-energy high-resolution and SMARTZOOM collimation.

OBJECTIVE: The aim of this study was to assess the feasibility of IQ-SPECT gated blood pool (MUGA) under conditions of decreased scan time (ST). PATIENTS AND METHODS: Ten patients underwent routine 26-min, two-view planar, followed by LEHR and IQ-SPECT MUGA, on a Siemens dual-head Symbia scanner. Six 'back and forth' 4-min SPECT scans were summed into 4-, 8-, 12-, 16-, 20-, and 24-min equivalent scans, and reconstructed iteratively (IQ-SPECT and LEHR) and with FBP (LEHR). Uniformity, contrast, and wall motion were scored on a five-point scale. Linear regressions of left ventricular (LV) ejection fraction (EF) were performed between FBP, Flash 3D, and IQ-SPECT versus planar and Flash 3D and IQ-SPECT versus FBP. Agreement tables between Flash 3D and IQ-SPECT versus FBP LV EF were generated using a normal versus cardiotoxicity threshold of 50%. RESULTS: IQ-SPECT had the best scores for all STs, and 4, 8, and 16 min IQ-SPECT were judged to be similar to 24-min LEHR FBP, Flash 3D, and planar, respectively. The average LV EF correlation coefficients were 0.69, 0.71, and 0.63 between IQ-SPECT, Flash 3D, and FBP versus planar, respectively; 0.70 between IQ-SPECT and FBP; and 0.88 between Flash 3D and FBP, and all were statistically significant (P<0.05), except for 16-min FBP LEHR versus planar. Agreement tables showed diagnostic equivalence of IQ-SPECT, Flash 3D, and FBP. CONCLUSION: These preliminary results suggest that IQ-SPECT is equivalent to LEHR Flash 3D and FBP for MUGA SPECT, and better at reduced ST. A larger patient population study is necessary for a more definitive assessment.

Evaluation of a deterministic grid-based Boltzmann solver (GBBS) for voxel-level absorbed dose calculations in nuclear medicine.

To evaluate the 3D Grid-based Boltzmann Solver (GBBS) code ATTILA (®) for coupled electron and photon transport in the nuclear medicine energy regime for electron (beta, Auger and internal conversion electrons) and photon (gamma, x-ray) sources. Codes rewritten based on ATTILA are used clinically for both high-energy photon teletherapy and (192)Ir sealed source brachytherapy; little information exists for using the GBBS to calculate voxel-level absorbed doses in nuclear medicine. We compared DOSXYZnrc Monte Carlo (MC) with published voxel-S-values to establish MC as truth. GBBS was investigated for mono-energetic 1.0, 0.1, and 0.01 MeV electron and photon sources as well as (131)I and (90)Y radionuclides. We investigated convergence of GBBS by analyzing different meshes ([Formula: see text]), energy group structures ([Formula: see text]) for each radionuclide component, angular quadrature orders ([Formula: see text], and scattering order expansions ([Formula: see text]-[Formula: see text]); higher indices imply finer discretization. We compared GBBS to MC in (1) voxel-S-value geometry for soft tissue, lung, and bone, and (2) a source at the interface between combinations of lung, soft tissue, and bone. Excluding Auger and conversion electrons, MC agreed within ≈5% of published source voxel absorbed doses. For the finest discretization, most GBBS absorbed doses in the source voxel changed by less than 1% compared to the next finest discretization along each phase space variable indicating sufficient convergence. For the finest discretization, agreement with MC in the source voxel ranged from -3% to -20% with larger differences at lower energies (-3% for 1 MeV electron in lung to -20% for 0.01 MeV photon in bone); similar agreement was found for the interface geometries. Differences between GBBS and MC in the source voxel for (90)Y and (131)I were -6%. The GBBS ATTILA was benchmarked against MC in the nuclear medicine regime. GBBS can be a viable alternative to MC for voxel-level absorbed doses in nuclear medicine. However, reconciliation of the differences between GBBS and MC at lower energies requires further investigation of energy deposition cross-sections.

Skeletal Tumor Burden on Baseline 18F-Fluoride PET/CT Predicts Bone Marrow Failure After 223Ra Therapy.

PURPOSE: Determine if skeletal tumor burden on 18F-fluoride PET/CT (fluoride PET/CT) predicts the risk of bone marrow failure (BMF) after 223Ra dichloride therapy (223Ra). METHODS: Forty-one metastatic prostate cancer patients (43-89 years old; mean, 71 ± 9 years.) underwent fluoride PET/CT prior to 223Ra. Bone marrow failure was the primary end point and was defined as (1) development of hematologic toxicity (World Health Organization grade 3 or 4) associated with no recovery after 6 weeks or (2) death due to BMF after the last 223Ra dose. Bone marrow failure was correlated to fluoride PET/CT skeletal tumor burden (TLF10 [total lesion on fluoride PET/CT with SUVmax of 10 or greater]), use of chemotherapy, serum hemoglobin concentration, serum ALP, and serum prostate-specific antigen. RESULTS: The number of 223Ra cycles ranged from 2 to 6 (mean, 5). Of the 41 patients, 16 developed BMF (G3 = 12; G4 = 4). A significantly increased risk of developing BMF was observed in patients with TLF10 of 12,000 or greater (hazard ratio [HR], 11.09; P < 0.0001), hemoglobin of less than 10 g/dL (HR, 7.35; P = 0.0002), and AP > 146 UI/L (HR, 4.52; P = 0.0100). Neither concomitant (HR, 0.91; P = 0.88) nor subsequent use of chemotherapy (HR, 0.14; P = 0.84) increased the risk of BMF, nor was prostate-specific antigen greater than 10 µg/L (HR, 0.90; P = 0.86). Moreover, in a multivariable analysis, TLF10 was the only independent predictor of BMF (HR, 6.66; P = 0.0237). CONCLUSIONS: 223Ra was beneficial and reduced the risk of death even in patients with a high skeletal tumor burden. Fluoride PET/CT is able to determine which patients will benefit from 223Ra and which will develop BMF.

Correction Techniques in Emission Tomography.

Correction Techniques in Emission Tomography., Dawood M., Jiang X., Schäfers K., CRC Press, Taylor & Francis Group, Boca Raton, FL, 2012. 287 pp. Price: $119.95. ISBN: 9781439812983 (hardcover). © 2013 Doody's Review Service. Doody's Review Service.

Nonmyeloablative allogeneic transplantation with or without 90yttrium ibritumomab tiuxetan is potentially curative for relapsed follicular lymphoma: 12-year results.

In 2008, we reported favorable 5-year outcomes of nonmyeloablative allogeneic stem cell transplantation after fludarabine, cyclophosphamide, rituximab (FCR) conditioning for relapsed and chemosensitive follicular lymphoma. However, innovative strategies were still needed to treat patients with chemorefractory disease. We therefore subsequently performed a trial in which (90)Y-ibritumomab tiuxetan (0.4 mCi/kg) was added to the fludarabine, cyclophosphamide conditioning regimen ((90)YFC). Here, we report updated results of the FCR trial and outcomes after (90)YFC. For the FCR group (N = 47), since the last update, one patient developed recurrent disease. With a median follow-up of 107 months (range, 72-142 months), the 11-year overall survival and progression-free survival rates were 78%, and 72%, respectively. For the (90)YFC group (N = 26), more patients had chemorefractory disease than did those in the FCR group (38% and 0%, P < .001). With a median follow-up of 33 months (range,17-94 months), the 3-year progression-free survival rates for patients with chemorefractory and chemosensitive disease were 80% and 87%, respectively (P = .7). The low frequency of relapse observed after a long follow-up interval of 9 years in the FCR group suggests that these patients are cured of their disease. The addition of (90)Y to the conditioning regimen appears to be effective in patients with chemorefractory disease. This trial was registered at www.clinicaltrials.gov as NCT00048737.

A preclinical investigation of the saturation and dosimetry of 153Sm-DOTMP as a bone-seeking radiopharmaceutical.

INTRODUCTION: The therapeutic potential of the bone-seeking radiopharmaceutical 153Sm-labeled 1,4,7,10-tetraazacyclododecanetetramethylenephosphonic acid (153Sm-DOTMP) was assessed by measuring its dosage-dependent skeletal uptake at two chelant-to-metal ratios and its source organ residence times at a chelant-to-metal ratio of 1.5:1. A similar agent, 153Sm-labeled ethylenediaminetetramethylenephosphonic acid (153Sm-EDTMP), has been reported to exhibit dosage-limiting skeletal saturation. METHODS: Sm-DOTMP was prepared with tracer activity of 153Sm and sufficient stable, unenriched Sm to simulate different activities. Cohorts of seven 280-g Sprague-Dawley rats were administered the equivalent of 296, 592, 888, 1184 and 1480 MBq (8, 16, 24, 32 and 40 mCi) at a fixed chelant-to-metal ratio of 1.5:1 and euthanized 3 h after administration. Cohorts of three 128-g Sprague-Dawley rats were administered equivalent dosages of 10.4, 592 and 888 (0.28, 16 and 32 mCi) at a fixed chelant-to-metal ratio of 270:1 and euthanized 2 h after administration. A simulated activity of 1480 MBq (40 mCi) at a chelant-to-metal ratio of 1.5:1 was administered to cohorts of seven rats that were euthanized at 2, 4, 24 or 48 h postadministration. The heart, lungs, liver, spleen, kidneys, small intestine, large intestine, urinary bladder, muscle and a femur were excised, weighed and counted. The data were analyzed to determine skeletal uptake and source organ residence times. RESULTS: No statistically significant skeletal saturation was observed up to human-equivalent dosages of 370 GBq (10 Ci) at a chelant-to-metal ratio of 1.5:1, but the skeletal uptake dropped by 40% over the range of dosages at a chelant-to-metal ratio of 270:1. At a chelant-to-metal ratio of 1.5:1, the preferred ratio, the skeletal uptake fraction in rats was 0.408 (95% confidence interval 0.396-0.419) with an effective half-life of 47.3 h (95% confidence interval 42.3-53.7; the physical half-life of 153Sm is 46.3 h). Extrapolating to an adult human model, 52.9 GBq (1.43 Ci) of 153Sm-DOTMP would deliver 40 Gy to the red marrow. CONCLUSION: 153Sm-DOTMP has dosimetry equivalent to that of 153Sm-EDTMP at low dosages, yet with no skeletal saturation at higher administered activities.

Hybrid Modality Fusion of Planar Scintigrams and CT Topograms to Localize Sentinel Lymph Nodes in Breast Lymphoscintigraphy: Technical Description and Phantom Studies.

Lymphoscintigraphy is a nuclear medicine procedure that is used to detect sentinel lymph nodes (SLNs). This project sought to investigate fusion of planar scintigrams with CT topograms as a means of improving the anatomic reference for the SLN localization. Heretofore, the most common lymphoscintigraphy localization method has been backlighting with a (57)Co sheet source. Currently, the most precise method of localization through hybrid SPECT/CT increases the patient absorbed dose by a factor of 34 to 585 (depending on the specific CT technique factors) over the conventional (57)Co backlighting. The new approach described herein also uses a SPECT/CT scanner, which provides mechanically aligned planar scintigram and CT topogram data sets, but only increases the dose by a factor of two over that from (57)Co backlighting. Planar nuclear medicine image fusion with CT topograms has been proven feasible and offers a clinically suitable compromise between improved anatomic details and minimally increased radiation dose.

Acquisition parameters for oncologic imaging with a new SPECT/multislice CT scanner.

INTRODUCTION: Single photon emission computed tomography/computed tomography (SPECT/CT) delivers in a single imaging modality the functional-metabolic information from the SPECT image, combined with the detailed anatomical information from a diagnostic quality CT scanner. METHOD: In this review, we provide the details for the acquisition, processing, and display of the SPECT, as well as the CT, and the fused SPECT/CT images, with one of the newest devices that combines a dual-headed gamma camera with a multislice CT scanner. Also, we go over the performance characteristics, including the planning and installation requirements for this type of scanners. In addition, we describe what are the current and feasible near-future applications of this new and exciting hybrid imaging modality. DISCUSSION: The ability to combine an optimized state-of-the-art SPECT image, with resolutions down to 5 mm, with a diagnostic quality CT image-using slices as thin as 1.25 mm-provides a diagnostic advantage that potentially can deliver a more convenient and faster diagnosis, with clinical implications in a significant percentage of patients. This imaging technique has been investigated in a wide range of studies for the oncologic patient, including but not limited to bone scintigraphy, (111)In-pentetreotide scintigraphy, lymphoscintigraphy, (67)Ga and labeled leukocyte infection imaging, (131)I-metaiodobenzylguanidine, parathyroid scintigraphy, (131)I diagnostic scintigraphy, and (111)In ProstaScint, and for planning of radionuclide therapy. CONCLUSION: Therefore, this evolving and exciting imaging modality will continue to grow and define its place as an integral part of the evaluation of the cancer patient.

Effect of voxel size and computation method on Tc-99m MAA SPECT/CT-based dose estimation for Y-90 microsphere therapy.

The use of selective internal radiation therapy for treatment of hepatocellular carcinoma and liver metastases using Y-90 labeled microspheres has become an effective and widely used treatment regimen. However, dosimetric evaluations of this treatment are still primitive as uniform distribution models based only on injected activity are often used. This investigation attempts to quantify the effectiveness of several sophisticated patient-specific techniques which utilize the source distribution of Tc-99m MAA simulation studies to perform voxelized dosimetric computations. Among these techniques are complete Monte-Carlo radiation transport computation in patient-specific CT-based voxel phantoms, local energy deposition in patient specific phantoms and kernel transport techniques in water. Each technique was evaluated using three different phantom voxel dimensions and SPECT reconstruction matrix sizes. Dose evaluation results using all methods were compared to the exact solution, obtained using fully 3-D Monte-Carlo simulations with source distribution based not on SPECT data, but on the injected activity and exact boundaries of the anthropomorphic phantom used in the study. The results of this study show that at large voxel sizes and using SPECT reconstructions with a small matrix size (64 x 64), Monte-Carlo and local deposition methods are nearly equivalent. However, using a large SPECT reconstruction matrix (256 x 256) the local deposition method is significantly more accurate than full 3-D Monte-Carlo transport, and with a negligible computational burden.

A novel method to evaluate gamma camera rotational uniformity and sensitivity variation.

An alternative to the conventional method of performing the AAPM Report 52 rotational uniformity and sensitivity test has been developed. In contrast to the conventional method in which a Co-57 sheet source is fastened to the collimator, this new point-source method acquires the images intrinsically using a Tc-99m point source placed near the isocenter of gantry rotation. As with the conventional method, the point-source method acquires 5 x 10(6) count flood images at four distinct gantry positions to calculate the maximum sensitivity variation (MSV)--a quantitative metric of rotational uniformity and sensitivity variation. The point-source method incorporates corrections for the decay of Tc-99m between acquisitions, the curvature in the image intensity due to variation in photon flux across the detector from a near-field source, and the source-to-detector distance variations between views. The raw point-source images were fitted with an analytic function in order to compute curvature- and distance-corrected images prior to analysis. Five independent MSV measurements were performed using both conventional and point-source methods on a single detector of a dual-headed SPECT system to estimate the precision of each method. The precision of the point-source method was further investigated by performing ten independent measurements of MSV on six different detectors. Correlation between the MSV calculated by the two methods was investigated by performing the test on nine different detectors using both methods. Different levels of sensitivity variations were also simulated on four detectors to generate 40 additional paired points for correlation analysis. The effect of the total image counts on the MSV estimated with the new method was evaluated by acquiring image sequences with 5 x 10(6), 10 x 10(6), and 20 x 10(6) count images. The MSV calculated using the conventional and point-source methods exhibited a high degree of correlation and consistency with equivalence. The precision of the point-source method (0.145%) is lower than the conventional method (0.04%) but sufficient to test MSV. No statistically significant dependence of MSV with the point-source method on the total image counts over a range of (5-20) x 10(6) counts was observed. Curvature correction of the images prior to the generation of difference images renders images more conducive to qualitative inspection for structured, nonrandom patterns. The advantages of the new methodology are that multiple detectors of a gamma camera can be evaluated simultaneously which substantially reduces the time required for MSV testing and the reduced risk of accidental damage to the collimators and patient proximity detection system from having to mount a sheet source on each of the detectors.

Estimation of yttrium-90 Zevalin tumor-absorbed dose in ocular adnexal lymphoma using quantitative indium-111 Zevalin radionuclide imaging.

OBJECTIVE: The purpose of this investigation was to estimate radiation-absorbed dose in orbital tumors from yttrium-90 ibritumomab tiuxetan (Zevalin) radioimmunotherapy of ocular adnexal lymphoma. METHODS: Three patients participating in a prospective research protocol involving treatment of ocular adnexal lymphoma with yttrium-90 Zevalin consented to quantitative radionuclide imaging to estimate tumor radiation-absorbed doses. Each patient received 185 MBq of indium-111 Zevalin, followed by serial planar whole-body scanning, to derive an activity versus time curve for the tumor. Single photon emission computed tomography (SPECT) and computed tomography (CT) imaging, including a calibration source, were performed at 24 h on a SPECT/CT scanner, to obtain a SPECT estimate of the radioactivity (in megabequerels) in the tumor and correct the planar curve, as well as estimate the tumor mass (M) from CT. The curve was then converted to that for yttrium-90 at the prescribed activity, and absorbed dose estimated from the area under the curve multiplied by the Medical Internal Radiation Dose S value (Gy per MBq-h) for a sphere of mass M. RESULTS: A right orbital tumor in one patient was visualized in both the planar and SPECT/CT images, with an estimated absorbed dose of 3.57 Gy. Tumor uptake in the other two patients was not visualized. CONCLUSION: The radiation dose to the orbit and ocular structures during radioimmunotherapy of ocular adnexal lymphoma is well below the threshold for significant radiation-induced ocular toxicity and about 10 times lower than that delivered during external beam radiotherapy.

Radiation dosimetry and biodistribution of (99m)Tc-ethylene dicysteine-deoxyglucose in patients with non-small-cell lung cancer.

PURPOSE: To assess the radiation dosimetry and biodistribution of (99m)Tc-labeled ethylene dicysteine deoxyglucose ((99m)Tc-EC-DG) in patients with non-small-cell lung cancer (NSCLC). METHODS: Serial whole-body scans were acquired 0, 2, 4, 6 and 24 h after injection of (99m)Tc-EC-DG (925 MBq) in seven NSCLC patients. Radiation dosimetry, blood clearance and SPECT imaging of the primary tumor were assessed. RESULTS: The critical organ was the bladder wall, with average radiation absorbed dose over all seven patients of 2.47x10(-2) mGy/MBq. The average effective dose equivalent and effective dose were 6.20x10(-3) mSv/MBq (6.89 mSv/1,110 MBq) and 5.90x10(-3) mSv/MBq (6.54 mSv/1,110 MBq), respectively. The primary tumor was visualized with SPECT in six patients. On final pathology, one patient had a granuloma, which did not enhance with (99m)Tc-EC-DG. CONCLUSION: (99m)Tc-EC-DG has acceptable dosimetric and biodistribution properties as a diagnostic tumor-imaging agent. Future studies are planned to evaluate its diagnostic potential.

Optimal (57)Co flood source activity and acquisition time for lymphoscintigraphy localization images.

UNLABELLED: We evaluated different (57)Co flood source activities and acquisition times to obtain an optimal localization image for breast lymphoscintigraphy that would adequately outline the body and allow detection of nodes seen on the emission scan while minimizing unnecessary radiation exposure to the patient. METHODS: An anthropomorphic thorax breast phantom representing an average-size patient was used to simulate nodes on a breast lymphoscintigraphy scan. The activities in the nodes at the time of acquisition ranged from 37 to 185 kBq (1-5 microCi). Four experiments were performed, consisting of 10-min emission and 3-min localization images. Anterior, posterior, and right and left lateral views of the thorax phantom were acquired, using each of 5 different (57)Co flood sources with activities ranging from 37 to 269 MBq (1.0-7.26 mCi). Ten 1-min localization images for each source were acquired and compared for quality. Three-minute localization images for 2 phantom thicknesses of 10 and 20 cm were acquired to determine the contrast-to-noise ratio for each (57)Co source. The total exposure was measured using an ion chamber survey meter. RESULTS: All sources allowed visualization of the lymphatic nodes in acquisitions as short as 3 min. Images using the 126-MBq (3.41-mCi) source demonstrated an adequate body outline along with visualization of all nodes seen on the emission image. The 37-MBq (1.0-mCi) source did not provide sufficient definition of the body outline, whereas the hotter sources decreased node visualization by increasing the background around the nodes at the same time that they increased the patient exposure. Node activity of 37 kBq (1 microCi) became undetectable on the anterior localization images yet was still visible on the lateral image because of greater attenuation of (57)Co photons. The estimated dose rate from the (57)Co sheet sources was 0.641 microSv/MBq/h. CONCLUSION: Acquiring a 3-min localization scan using a 126-MBq (3.41-mCi) source provided the best combination of clear-body outline and visualization of all nodes seen on the emission image. The estimated dose to the patient from the 126-MBq (3.41-mCi) sheet source was very low (8.7 microSv for unilateral and 13.1 microSv for bilateral). Node detectability decreased in localization images acquired using (57)Co sources of higher activity. This effect would be more pronounced in lymphoscintigrams of thin patients compared with those of patients of average thickness.