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BACKGROUND The kidneys are the dose-limiting organ in lutetium-177 DOTATATE therapy. Therefore, it is advisable to perform critical organ dosimetry focussed on renal dose in treated patients. A key uncertainty in such dose estimates is the use of standard phantoms to represent the individual patient. The primary aim of this study was to investigate the accuracy of methods for estimating kidney size, and hence absorbed kidney dose, by comparison with individual measurements from computed tomography (CT) imaging. MATERIALS AND METHODS Kidney volume was measured using diagnostic CT images for 57 patients who underwent lutetium-177 DOTATATE therapy. Kidney mass was also estimated in two ways: using the standard adult phantoms, as well as through the application of a weight scaling factor to these phantoms and their organs. Dose calculations were performed for each of the three methods using OLINDA/EXM software. RESULTS Scaling of the phantom by patient weight gave a more accurate result when compared with the CT gold standard than the standard phantom. The dose difference from the CT method had mean values of 1.4% (SD=22.6%) and 8.4% (SD=21.5%) for scaled and unscaled, respectively. Patient weight was not found to be a good predictor of kidney mass in these patients (r of 0.12 from linear regression analysis). CONCLUSION The most accurate method of organ volume estimation would be individual measurements from CT imaging; however, where this is not possible, scaling of organ masses by weight ratio is more accurate than the use of the standard phantom.

The objective of our study was to measure thyroid volumes using semiautomated 3D CT and to compare the 3D CT volumes with volumes measured using 2D ultrasound, 2D CT, and the water displacement method.In 47 patients, 2D ultrasound volumes and 2D CT volumes of the thyroid gland were estimated using the ellipsoid volume formula, and 3D CT volumes were calculated using semiautomated reconstructive techniques. All volume data were compared with thyroid specimen volumes obtained using the water displacement method and were statistically analyzed using the one-way ANOVA, the Pearson correlation coefficient (R), linear regression, and the concordance correlation coefficient (CCC). The processing time of semiautomated 3D CT thyroid volumetry was measured.The paired mean differences ± SD between the three imaging-determined volumes and the specimen volumes were 0.8 ± 3.1 mL for 2D ultrasound, 4.0 ± 4.7 mL for 2D CT, and 0.2 ± 2.5 mL for 3D CT. A significant difference in the mean thyroid volume was found between 2D CT and specimen volumes (p = 0.016) compared with the other pairs (p = 0.937 for 2D ultrasound mean volume vs specimen mean volume, and p = 0.999 for 3D CT mean volume vs specimen mean volume). Between specimen volume and 2D ultrasound volume, specimen volume and 2D CT volume, and specimen volume and 3D CT volume, R values were 0.885, 0.724, and 0.929, respectively, and CCC values were 0.876, 0.598, and 0.925, respectively. The mean processing time of semiautomated 3D CT thyroid volumetry was 7.0 minutes.Thyroid volumes measured using 2D ultrasound or semiautomated 3D CT are substantially close to thyroid specimen volumes measured using the water displacement method. Semiautomated 3D CT thyroid volumetry can provide a more reliable measure of thyroid volume than 2D ultrasound.

Objective To assess the accuracy of a semiautomated 3D volume reconstruction method for organ volume measurement by postmortem MRI. Methods This prospective study was approved by the institutional review board and the infants9 parents gave their consent. Postmortem MRI was performed in 16 infants (1 month to 1 year of age) at 1.5 T within 48 h of their sudden death. Virtual organ volumes were estimated using the Myrian software. Real volumes were recorded at autopsy by water displacement. The agreement between virtual and real volumes was quantified following the Bland and Altman9s method. Results There was a good agreement between virtual and real volumes for brain (mean difference: −0.03% (−13.6 to +7.1)), liver (+8.3% (−9.6 to +26.2)) and lungs (+5.5% (−26.6 to +37.6)). For kidneys, spleen and thymus, the MRI/autopsy volume ratio was close to 1 (kidney: 0.87±0.1; spleen: 0.99±0.17; thymus: 0.94±0.25), but with a less good agreement. For heart, the MRI/real volume ratio was 1.29±0.76, possibly due to the presence of residual blood within the heart. The virtual volumes of adrenal glands were significantly underestimated (p=0.04), possibly due to their very small size during the first year of life. The percentage of interobserver and intraobserver variation was lower or equal to 10%, but for thymus (15.9% and 12.6%, respectively) and adrenal glands (69% and 25.9%). Conclusions Virtual volumetry may provide significant information concerning the macroscopic features of the main organs and help pathologists in sampling organs that are more likely to yield histological findings.

The purpose of this study was to evaluate automated CT volumetry in the assessment of living-donor livers for transplant and to compare this technique with software-aided interactive volumetry and manual volumetry.Hepatic CT scans of 18 consecutively registered prospective liver donors were obtained under a liver transplant protocol. Automated liver volumetry was developed on the basis of 3D active-contour segmentation. To establish reference standard liver volumes, a radiologist manually traced the contour of the liver on each CT slice. We compared the results obtained with automated and interactive volumetry with those obtained with the reference standard for this study, manual volumetry.The average interactive liver volume was 1553 ± 343 cm(3), and the average automated liver volume was 1520 ± 378 cm(3). The average manual volume was 1486 ± 343 cm(3). Both interactive and automated volumetric results had excellent agreement with manual volumetric results (intraclass correlation coefficients, 0.96 and 0.94). The average user time for automated volumetry was 0.57 ± 0.06 min/case, whereas those for interactive and manual volumetry were 27.3 ± 4.6 and 39.4 ± 5.5 min/case, the difference being statistically significant (p0.05).Both interactive and automated volumetry are accurate for measuring liver volume with CT, but automated volumetry is substantially more efficient.

Purpose To calculate the measurement error of the hourly fetal urine production rate (HFUPR) and evaluate the implication of different methods for measuring the HFUPR, i.e. ellipsoid versus sum-of-cylinders method. Methods The calculation was based on sonographic documentation of the increased bladder volumes during the filling phase, the bladder volume measurement error and the number and time points of bladder image capture. Results The probability of a false pathological reading was excluded (0%) with the sum-of-cylinders method for gestational ages of ≥30 weeks. With the ellipsoid method, the risk was higher. The maximum changes which could be exclusively explained by measurement error were four to five times greater with the ellipsoid method compared with the sum-of-cylinders method. Conclusions The present paper illustrates a careful evaluation of the HFUPR measurement error and the implications of using different ultrasound methods for bladder volume estimations. Electronic supplementary material The online version of this article (doi:10.1007/s00404-009-1242-6) contains supplementary material, which is available to authorized users.

The purpose of our study was to evaluate the interobserver variability of transrectal ultrasound for prostate volume measurement according to the prostate volume and the level of observer experience.Endorectal sonography was performed independently by two experienced observers in 101 patients and by one experienced and one less experienced observer in 110 patients; the prostate volume was then measured using the prolate ellipsoid formula. The volume difference between observers was analyzed according to the mean measured prostate volume determined by the observers and according to the level of observer experience.The volume difference was greater in prostates with a mean measured volumeor= 30 mL than in prostates with a mean measured volume30 mL (6.00 vs 1.51 mL in the experienced observers and 6.84 vs 3.99 mL in the experienced and less experienced observers) (p0.05). The frequency of volume differences5 mL was greater in prostates with a mean measured volumeor= 30 mL than in prostates with a mean measured volume30 mL (between the experienced observers, 18% vs 1%; between the experienced and less experienced observers, 54% vs 25%) (p0.01 in both comparisons). The volume difference was greater between the experienced and less experienced observers (5.00 mL) than between the experienced observers (2.96 mL) (p = 0.01). The frequency of volume difference5 mL was greater between the experienced and less experienced observers (35%) than between the experienced observers (7%) (p0.01).Prostate volume measurement by transrectal ultrasound may vary when patients have large prostates or observers have varying levels of experience.

We developed a novel digital tomosynthesis (DTS) reconstruction method using a deformation field map to optimally estimate volumetric information in DTS images. The deformation field map is solved by using prior information, a deformation model, and new projection data. Patients’ previous cone-beam CT (CBCT) or planning CT data are used as the prior information, and the new patient volume to be reconstructed is considered as a deformation of the prior patient volume. The deformation field is solved by minimizing bending energy and maintaining new projection data fidelity using a nonlinear conjugate gradient method. The new patient DTS volume is then obtained by deforming the prior patient CBCT or CT volume according to the solution to the deformation field. This method is novel because it is the first method to combine deformable registration with limited angle image reconstruction. The method was tested in 2D cases using simulated projections of a Shepp–Logan phantom, liver, and head-and-neck patient data. The accuracy of the reconstruction was evaluated by comparing both organ volume and pixel value differences between DTS and CBCT images. In the Shepp–Logan phantom study, the reconstructed pixel signal-to-noise ratio (PSNR) for the 60° DTS image reached 34.3 dB. In the liver patient study, the relative error of the liver volume reconstructed using 60° projections was 3.4%. The reconstructed PSNR for the 60° DTS image reached 23.5 dB. In the head-and-neck patient study, the new method using 60° projections was able to reconstruct the 8.1° rotation of the bony structure with 0.0° error. The reconstructed PSNR for the 60° DTS image reached 24.2 dB. In summary, the new reconstruction method can optimally estimate the volumetric information in DTS images using 60° projections. Preliminary validation of the algorithm showed that it is both technically and clinically feasible for image guidance in radiation therapy.

Circulatory models for interpreting the kinetics of substances in vivo explain the kinetics of the intact body with the concepts of organ kinetics. In this paper, it is first shown that classical organ kinetic analysis is incomplete for metabolized substances, and an appropriate extension is developed. It is then discussed how the concepts of the extended organ kinetic analysis apply to circulatory models. At an organ level, it is shown that two impulse responses are necessary to characterize the organ, one relating influx and outflux, and one relating influx and uptake. The consideration of the inlet-uptake path is of fundamental importance for a correct calculation of the organ volume. It is demonstrated that the total volume is the sum of two components, the first related to the inlet-outlet path, the second to the inlet-uptake path. The first term is computable without assumptions, while the second is model-dependent. Analogous results hold at a total-body level. The relationships between circulatory models and compartmental and non-compartmental analysis are also precisely established. The significance of the non-compartmental estimate of the distribution volume is clarified. The usual strategy of compartmental modeling by which losses are placed in peripheral compartments according to a correspondence between tissues and compartments is shown to be misleading. An example concerning glucose kinetics is given. In conclusion, this paper shows that many of the dominating paradigms of organ and total-body kinetic analysis must be revised.

A Korean adult male computational phantom was constructed based on the current anthropometric and organ volume data of Korean average adult male, and was applied to calculate internal photon dosimetry data. The stylised models of external body, skeleton, and a total of 13 internal organs (brain, gall bladder, heart, kidneys, liver, lungs, pancreas, spleen, stomach, testes, thymus, thyroid and urinary bladder) were redesigned based on the Oak Ridge National Laboratory (ORNL) adult phantom. The height of trunk of the Korean phantom was 8.6% less than that of the ORNL adult phantom, and the volumes of all organs decreased up to 65% (pancreas) except for brain, gall bladder wall and thymus. Specific absorbed fraction (SAF) was calculated using the Korean phantom and Monte Carlo code, and compared with those from the ORNL adult phantom. The SAF of organs in the Korean phantom was overall higher than that from the ORNL adult phantom. This was caused by the smaller organ volume and the shorter inter-organ distance in the Korean phantom. The self SAF was dominantly affected by the difference in organ volume, and the SAF for different source and target organs was more affected by the inter-organ distance than by the organ volume difference. The SAFs of the Korean stylised phantom differ from those of the ORNL phantom by 10-180%. The comparison study of internal dosimetry will be extended to tomographic phantom and electron source in the future.

Objectives: We sought to evaluate the capabilities of different magnetic resonance imaging (MRI)-based methodologies for measuring prostate volume. Materials and Methods: Twenty-four male beagles with benign prostatic hyperplasia were enrolled in a drug trial and imaged at 5 time points. A total of 120 prostate volumes were determined by MRI-based semiautomated segmentation. For planimetric assessment, 8 diameter locations were determined in the axial and coronal plane of the MRI slice with maximum extension of the prostate. Thirteen calculation models based on these diameters were determined by comparison to the reference volume and evaluated during treatment. Results: The segmented MRI prostate volume significantly correlated with post necropsy volume. The best diameter-based model also worked very well for monitoring prostate volume of dogs under treatment. Conclusions: MRI-based segmentation is highly accurate in assessing prostate volume. Diameter-based measurements are closely correlated to the segmented prostate volume and are feasible to monitor therapy.

Purpose: In this study, two commercially available programs were compared for the evaluation of delivered daily dose using cone beam CT (CBCT). Methods: Thirty (n=30) patients previously treated in our clinic (10 prostate, 10 SBRT lung and 10 abdomen) were used in this study. The patients' plans were optimized and calculated using the Pinnacle treatment planning system. The daily CBCT scans were imported into Velocity and RayStation along with the corresponding planning CTs, structure sets and 3D dose distributions for each patient. The organs at risk (OAR) were contoured on each CBCT by the prescribing physician and were included in the evaluation of the daily delivered dose. Each CBCT was registered to the planning CT, once with rigid registration and then again, separately, with deformable registration. After registering each CBCT, the dose distribution from the planning CT was overlaid and the dose volume histograms (DVH) for the OAR and the planning target volumes (PTV) were calculated. Results: For prostate patients, we observed daily volume changes for the OARs. The DVH analysis for those patients showed variation in the sparing of the OARs while PTV coverage remained virtually unchanged using both Velocity and RayStation systems. Similar results were observed for abdominalmore » patients. In contrast, for SBRT lung patients, the DVH for the OARs and target were comparable to those from the initial treatment plan. Differences in organ volume and organ doses were also observed when comparing the daily fractions using deformable and rigid registrations. Conclusion: By using daily CBCT dose reconstruction, we proved PTV coverage for prostate and abdominal targets is adequate. However, there is significant dosimetric change for the OARs. For lung SBRT patients, the delivered daily dose for both PTV and OAR is comparable to the planned dose with no significant differences.« less

Members of one class of organs—including kidney and lung—consist chiefly of repeating units, or subunits, similar in size and shape. Across species, both the number and size of repeating units may increase with increasing organ size. A simple model is proposed, relating the scaling of unit-size and unit-number to that of organ volume. The model makes three structural assumptions, the crucial one, biologically speaking, being that the numerical density of repeating units scales as does organ surface-to-volume ratio. Data were collected from the literature bearing on the number, diameter, total surface area and total volume of such repeating units (i.e., alveoli, air capillaries, renal tubules and glomeruli), for avian and mammalian lung and for mammalian kidney, each as a function of organ size. These data, after log-log transformation, were submitted to standard linear least squares regression analysis. The resultant slopes for nine different regression lines are in good agreement with the model predictions. This finding suggests, surprisingly, that organ scale-up, at least for selected organs, expressed in terms of repeating units, as a function of organ volume, in mammals and birds, and conceivably in other phyla, may be based on a small number of elementary structural principles.

RATIONALE AND OBJECTIVES A radiologist often wishes to measure organ volume or monitor changes in internal lesion volume during treatment. If this can be determined via three-dimensional ultrasound, the relative simplicity of the procedure and the decreased cost and known risks to the patient would make this method an attractive alternative to other modalities. METHODS Three-dimensional ultrasound scans were made of six phantoms: four nonechogenic spheres, one echogenic sphere, and one echogenic, irregularly shaped phantom. A total of 22 volume scans were produced. Volume estimations were made using data from cross-sectional areas and from linear measurements. In all, 193 volume estimations were made. These results were compared with known volumes and with volume estimates from computed tomography scans. RESULTS Three-dimensional ultrasound detected size differences of 10% with 95% certainty. CONCLUSIONS The accuracy and precision of volume estimates via three-dimensional ultrasound is at least as good as those obtained via conventional ultrasound.

Purpose: To determine the impact of the deformation of rectum and bladder on the assessment of dose‐volume constraints for these organs at risk (OARs) in adaptive prostate IMRT. Methods: Five prostate cancer patients treated with both prostate and seminal vesicle as the initial PTV and with prostate only as the boost PTV were selected for this study. All patients received two CT simulations with the first CT scanned for the initial treatment volume followed by a second CT simulation after 45 Gy. All patients were treated to a total dose of 79.2 Gy in 1.8 Gy fractions delivered with seven‐coplanner IMRT beams. MIM‐Adaptive deformation workflow (MIMVista, Cleveland, OH) was used to perform deformation image registration of the two CTimage sets. For evaluation of the accumulative dose delivered to the OARs in presence of organ deformation, MIM‐Dose deformation tool was used to register the deformed dose matrices of two CT sets. The dose‐volume constraints, D25%, calculated for rectum and bladder with and without consideration of organ deformation were compared. Results: Differences in rectal D25% of up to 9.8% (from −9.8% to +2.8%) and in bladder D25% of up to 19.5% (from −19.5% to +9.0%) were observed. The deformation of OARs during IMRT caused the values of D25% for rectum to change from −646 cGy to +173 cGy and for bladder from −831 to +541 cGy from patient to patient. Conclusions: Discrepancies in OAR dose‐volume constraints can be calculated using modern deformable registration tools with and without consideration of organ volume change and deformation and should be carefully considered in the evaluation of OAR complication risks in adaptive prostate IMRT. MIMVista work station which was used to conduct this research was provided by MIM software Inc.

Designing dose distributions that minimize the risk of radiation‐induced normal tissue toxicity is one of the hardest parts of treatment planning. Commonly, many planners use the tolerance guidelines set forth in the famous 1991 ‘Emami paper’. A wealth of more recent information exists but is dispersed over many, diverse publications. Therefore, AAPM and ASTRO funded the QUANTEC (Quantitative Analysis of Normal Tissue Effects in the Clinic) effort, wherein over 60 volunteer physicists and radiation oncologists collaborated in an expert review of the literature from the “3DCRT” era. Consensus dosimetric guidelines for 16 normal organs were published in early 2010 (International Journal of Radiation Oncology, Biology and Physics V76, #3S supplement). For some complications, the QUANTEC recommendations are in general concordance with the Emami guidelines but for others there are notable differences and the mathematical models of normal tissue complication risk built accordingly reveal wide variations among the different studies. The reasons for these differences and what needs to be done to reconcile them with previous and future clinical practice will be discussed for selected disease sites and organs. Course outline: 1. A user's guide to QUANTEC: All the organ‐complication articles have the same format and address the same topics: clinical significance, complication endpoints, organ volume definition, literature review, non‐dosimetric risk factors, mathematical/biological models, special situations, recommended dose‐volume limits, future studies. The difficulties QUANTEC encountered relative to each section are instructive, as they indicate problems in the way outcomes are reported in the literature. These will be described to aid in understanding the limitations of the Quantec reviews and to improve the state of knowledge going forward. [Presenter: Andrew Jackson, MSKCC] 2. What's new since Emami: For some major dose‐limiting complications, the QUANTEC and ‘Emami’ guidelines differ substantially — for others there is general concordance. Examples of each sort will be presented along with suggestions as to clinical application. [Presenter: Larry Marks, MD, UNC] Learning Objectives: 1. Understand the broad goals and methods of the QUANTEC review. 2. Identify several organs where the dose/volume' outcome data presented by QUANTEC is ‘significantly’ different from what was presented by Emami in 1991. 3. Broadly understand the shortcomings of the QUANTEC review and methods and opportunities for acquiring additional and improved information.

Purpose: In an effort to accurately consider historical radiation in treatment planning and outcome analysis for pediatric radiotherapy patients, we investigate the correlations of the volume of the liver and kidneys with age, total body mass, and body height of pediatric patients. Method and Materials: The liver and kidneys were delineated upon CTimages acquired for 48 patients (27 male, 21 female) ranging in age from 0.7 to 19.3 years at the first CT acquisition. For age‐based correlations, statistics were compiled among all images and among only the images acquired pre‐treatment. For the mass‐based and height‐based correlations, total patient body mass and height were obtained from supplemental chart information. Plots of total‐kidney volume versus age were compiled among male and female patients separately. Plots of liver and total‐kidney volume versus body weight and body height were complied from among all patients. Linear fits were applied to each data set, and the standard deviation of the difference between the measurement and the linear fit was compiled. Results: Increased liver and kidney volume with increasing age, body mass, and height are apparent. Excluding post‐treatment image data led to improved linear correlations. Linear fits suggest larger kidney volume at birth for males (99 cm3 vs. 63 cm3 for females), although for both males and females the kidney growth rate is similar (approximately 17 cm3 per year). The ratio of the right‐ to left‐kidney volume was 0.95±0.14. Although there is relatively little variation in body mass among the patient set, greater body mass appears to predict greater organ volume. Conclusions: The correlation of liver and kidney volume with patient age, body mass, and height are apparent for pediatric patients, and can be used to construct organ‐growth models that may be useful in image registration, dose accumulation and radiation‐response assessment for pediatric radiotherapytreatment planning.

Purpose: Whole‐body patient models of various sizes and postures are needed for the assessment of organdoses in CTimaging, internal nuclear medicine and external‐beam radiation treatment procedures. This paper discusses a deformable mesh‐based modeling method to create patient‐specific phantoms that are morphed by changing to 5th‐ to 95th‐percentiles of body height and weight, as well as internal organ volume and masse. Method and Materials: The mesh‐based reference adult male and female phantoms were deformed by mainly two different percentile data: 1) the whole‐body size percentile data which were defined by the anthropometric parameters such as height and weight from the National Health and Nutrition Examination Survey (NHANES). 2) individual internal organ percentile data which were derived by the cumulative pattern analysis based on the International Commission on Radiological Protection (ICRP) 23 and 89 references. These mesh‐based percentile phantoms were converted into the voxel‐based phantoms. The final step is to link the voxel phantom with correct tissue density and elemental composition, so that radiation transport through the human‐body phantom was modeled correctly in a Monte Carlo code. Results: The whole‐body size percentile models have been created by the NHANES anthropometric data and the details of organ percentiles derived from ICRP references. The deformability of the RPI reference adult phantoms has been shown through the demonstration of percentiles‐ and postures‐specific adult models. Conclusion: A next generation deformable patient modeling method has been demonstrated. With the mesh deformation algorithms, the individual organs are able to be deformed to match the volumes and masses with desired organ percentiles. The flexible modeling allows patients to be represented in various sizes and postures for the purpose of Monte Carlodose calculations. This study also identified the need for further research to develop method to run Monte Carlo calculations in mesh geometry directly.

Purpose: phenomenological normal tissue complications probability (NTCP) models use generalized equivalent uniform dose (gEUD) as a summary measure which converts an inhomogeneous dose distribution into an "equivalent" uniform dose. We have investigated adapting gEUD models to brachytherapydose distributions which are characterized by small focal hotspots. We have found that small hotspots dominate the behavior of gEUD measure. As it is unlikely that clinical NTCP values are determined to this extent by small focal hotspots, we have developed an alternative to gEUD‐based dose‐volume histogram reduction for adapting the phenomenological NTCP models to combined external‐beam and brachytherapy treatments. Our revised metric allows for local saturation in biological effectiveness in volume‐limited high‐dose regions. Materials & Methods: Three summary measures were computed on rectal DVHs. The gBEUD is an equivalent of gEUD, but with the physical dose replaced by biologically equivalent dose (BED). The tESD and vESD measures compute ESD index (equivalent uniform dose leading to the same cell survival fraction as the inhomogeneous dose distribution) on high BED portions of rectal DVHs. The tESD measure uses common BED threshold for all DVHs, which becomes an adjustable parameter of the measure. The vESD measure uses common fraction of the rectal volume as an adjustable parameter, and thus computes a BED threshold for each DVH. Properties of the three measures are compared. A database of 9 prostate patients with 7‐field IMRT boost plans and HDR brachytherapy boost plans delivering biologically equivalent D98 doses were used for the study. Results: For 6 of the 9 patients the gBEUD increased by approximately 100% due to doses confined to volumes

Purpose: Digital Tomosynthesis (DTS) is a quasi‐3D imaging technique which reconstructsimages from a limited angle of on‐board projections with significantly lower dose and shorter acquisition time than full cone‐beam CT(CBCT). However, DTS imagesreconstructed by the conventional filtered back projection method have low plane‐to‐plane resolution and can't provide full volumetric information for target localization. In this study, we developed a novel DTS reconstruction method using prior information and a deformation model to recover volumetric information. Method and Materials: A patient's previous CBCT or CT data were used as the prior information, and the new patient volume was considered as a deformation of the prior volume. The deformation fields were solved by minimizing bending energy and maintaining data fidelity. A nonlinear conjugate gradient method was used as the optimizer. The algorithm was tested using simulated projections of a Shepp‐Logan phantom, liver and head‐and‐neck patient data. The accuracy of the reconstruction was evaluated by comparing both pixel value and contour differences between DTS and CBCTimages.Results: In the liver patient study, the systematic and random errors for the live contour reconstructed using a 60‐degree scan angle were 0.5 and 1.6mm, respectively, showing the new organ volume was accurately reconstructed. The pixel signal‐to‐noise ratio (PSNR) for 60‐degree DTS reaches 23.5dB. In the head‐and‐neck patient study, the method using 60‐degree scan was able to reconstruct the 8.1 degree rotation of the bony structure with 0.0 degree error. The PSNR for 60‐degree DTS reaches 24.2dB. Conclusion: A novel reconstruction method was developed to reconstruct DTS images using prior information and a deformation model. Volumetric information was accurately obtained using a 60‐degree scan angle. Preliminary validation of the algorithm showed that it is both technically and clinically feasible for image‐guidance in radiation therapy. Partially supported by Grants from NIH and Varian Medical Systems.

Purpose: In radiotherapytreatment planning, the voxel size plays a role in each step, from the structure contouring, beamlet calculation, treatment optimization to plan analysis. Large voxels may affect the planning accuracy while small voxels will increase computation time significantly. The choice of voxel size is a compromise between planning accuracy and computation speed. This work investigates the effect of voxel size on the accuracy and computational speed of Monte Carlo based treatment planning for IMRT.Method and Materials: Selected patients with various treatment sites were scanned on a CT simulator and the CT data with RT structures were converted to patient geometry files with different voxel sizes for Monte Carlo simulations. Comparisons of the structure volume, beamlet dose distribution, plan optimization, DVHs and dose distributions were made with different voxel sizes. Target and critical structures with small volumes, such as the optical nerves in head and neck cases, were specially considered in the comparison. Results: In Monte Carlo IMRT planning, differences in the open‐field dose calculations prior to the optimization process using different voxel sizes (4 × 4 mm2 and 2 × 2 mm2) were usually small. However, the results from the optimization showed that different voxel sizes could generate different beamlet weights resulting in different treatment plans. The effects could be clinically significant. For the same IMRT plans, the effects of voxel sizes in the dose and DVH calculations vary depending on the treatment sites, anatomy and target/organ volume. Small voxel sizes (1–2mm) are necessary for small structures in and near heterogeneous geometries such as in the head and neck regions. Conclusions: The effect of voxel size on dose calculation and plan optimization can be clinically significant in IMRTtreatment planning. Small voxel (1–2mm) should be used for head and neck cases.

The aim of this study was to develop a new algorithm for volume determination by single photon emission computed tomography (SPECT). Different algorithms were evaluated through phantom studies. The results show that the algorithm combining moment-preserving bilevel thresholding and best-fit Laplacian second derivative edge detection can provide the most accurate measurement of volume. Besides, this method can be utilized in different SPECT systems with no need for further phantom studies. In patient studies, the results of liver volume calculation have indicated that this is a useful technique in clinical medicine.

Liver-spleen ratio, volume and uptake were measured in 20 patients undergoing routine 99Tcm-colloid examinations. Methods using planar views only were compared with results obtained using SPECT techniques and automated slice processing. The results suggest that a reasonable estimate of liver-spleen ratio may be obtained using anterior and posterior planar views only. Estimates of organ volume and absolute uptake were not reliably obtained using planar views only, and SPECT studies are required. The choice of attenuation correction technique for SPECT studies did not affect the results obtained for liver-spleen ratios and volumes, although systematic underestimation of absolute uptake occurred with simpler techniques.

The purpose of this study was to compare different techniques for the estimation of liver volume, and to evaluate errors associated with volume estimation techniques based on linear measurements. Fifteen patients with focal liver lesion underwent spiral CTA for preoperative evaluation. The scan protocol was: collimation 3 mm; rotation time 0.75 s; pitch 2; and reconstruction index 1 mm. Reconstructed images were sent to a workstation running on a NT platform equipped with post-processing software allowing 3D reconstructions. Linear measurements and volume estimation through manual segmentation were obtained with preset window and magnification. Volume was calculated from linear measures using different equations. With equations based on linear measurements the right lobe was overestimated (mean=+53%; mean error=14.7%), the second and third segments were underestimated (mean=-47%; mean error=43.3%) and the total volume was underestimated (mean=-86%; mean error=36%). The volume calculated by summing the areas of all the sections and multiplying the result by the increment was not significantly different from the volume estimated using the manual volumetric segmentation technique. Volume estimation obtained through linear measurements is not reliable to appraise the volume of irregular-shaped solids, even assuming the prevalence of a particular morphology.

Introduction: Organ volumes at postmortem magnetic resonance imaging (PMMR) should reflect autopsy organ weights, and thus brain:liver volume ratios on imaging could be a surrogate for weight volume ratios at autopsy to indicate fetal growth restriction (FGR). This study aims to determine whether imaging-based organ volume ratios can replace autopsy organ weight ratios. Materials and Meth ods: An unselected cohort of perinatal deaths underwent PMMR prior to autopsy. Semiautomated brain and liver volumes were compared to autopsy organ weights and ratios. Ratios were compared using Bland-Altman plots, and intra- and interobserver variability was assessed. Results: A total 49 fetuses (25 male, 51%) at 17–42 weeks gestation were ­assessed. There was a reasonable correlation between autopsy-derived brain:liver weight ratios (AB:LwR) and imaging-derived brain:liver volume ratios (IB:LvR; r = 0.8). The mean difference between AB:LwR and IB:LvR was +0.7 (95% limits of agreement range –1.5 to +2.9). In a small subset where FGR was present, the optimal IB:LvR ≥5.5 gave 83.3% sensitivity and 86.0% specificity for diagnosis. There was acceptable agreement within readers (mean difference in IB:LvRs 0.77 ± 2.21) and between readers –0.36 ± 0.68. Conclusion: IB:LvR provides a surrogate evaluation of AB:LwRs, and may be used as a marker of FGR where autopsy is declined.