Total Number Of Segments Research Articles

SU‐FF‐T‐127: Clinical Feasibility of Jaw‐Only IMRT Plan for Prostate Cancer

Purpose: To investigate the feasibility of inverse IMRT plans generated with jaw only, compared to IMRT plans with multi‐leaf collimator (MLC) for patients with the prostate cancer. Method and Materials: For five patients, two different planning techniques were used to generate inverse IMRT plans. One was the aperture‐based IMRT planning using MLC (MLC plans) and the other used jaw only (JO plans), available in a commercial planning system. The conventional 7 beams were employed. The planning goal was to deliver 72 Gy to > 95% of the PTV while keeping 10% of the rectum and 15% of the bladder receiving < 60 Gy and mean dose of the bulb < 30 Gy. For the JO plans, four different numbers of apertures/beam (3, 4, 5, and 6) were tested, compared to the MLC plans set to 3 apertures/beam. All plans (one MLC and four JO plans) for each patient were analyzed using conformal index (COIN), defined endpoint doses to the sensitive structures, total number of segments, and total delivered monitor unit. For each patient, planning dose constraints were kept the same for MLC and JO plans. Results: The COIN values for JO plans were generally increased as the number of apertures/beam increased, up to the same value as the MLC plans. The number of total segments for the JO plans was gradually increased (21, 27, 34, 40) as the number of apertures/beam increased (3, 4, 5, 6), compared to 21 segments for the MLC plans. However, the delivered MU values and doses to sensitive structures were patient‐specific and independent of the number of apertures/beam in JO plans. Conclusion: For centers without MLC collimator, it is possible to deliver inverse planned IMRT plans using jaws only for patients with prostate cancer. Conflict of Interest: Research sponsored by Prowess Inc.

Outcome of Local Bone Versus Autogenous Iliac Crest Bone Graft in the Instrumented Posterolateral Fusion of the Lumbar Spine

Retrospective, comparative study of clinical and radiologic outcome with independent, blinded observer. To compare the clinical and radiologic outcome of instrumented posterolateral lumbar fusion using local bone versus autogenous iliac crest bone graft (ICBG). There is no published report of outcome of posterolateral spinal fusion using local bone alone for degenerative disorders of the lumbar spine. Seventy-six cases (male 26, female 50) of spinal stenosis, operated during 1996 and 1997 by the senior author, were reviewed. All the cases had decompression and posterior spinal fusion with pedicle screw instrumentation. Forty cases had only local bone graft obtained from decompression, morselized in a bone mill, and 36 cases had autogenous ICBG. Mean age was 60 years (range, 27-83 years). Fusion was performed at one level in 51 (67%), two levels in 16 (21%), three levels in 5 (7%), and four or more levels in 4 cases (5%). Minimum follow-up was 2-years (mean, 28 years; range, 24-72 months). An independent, blinded radiologist rated plain radiographs as fused, indeterminate, or nonunion. There was no difference in age, sex, and diagnosis between the two groups. Overall fusion rate was higher in the ICBG group (75%, 27 of 36) compared with the local bone group (65%, 26 of 40) but not significantly different (P = 0.391). Analyzed separately according to the number of fusion levels, the local bone group achieved similar fusion rate ( approximately 80%) in single-level fusion but a much smaller fusion rate in multilevel fusion (20% vs. 66%, P = 0.029) compared with the ICBG group. Mean improvement in the Oswestry Disability Inventory was 36% in the local bone group and 32% in the ICBG group. There was no significant difference in overall clinical outcome between the two groups. There was no correlation between fusion status and clinical outcome. Blood loss and hospital stay were significantly less in the local bone group; however, blood losswas more significantly related to the sum total number of segments undergoing decompression and fusion. Use of local bone graft alone achieved a similar fusion rate in single-level fusion but a much smaller fusion rate in multilevel fusion compared with the ICBG group. Local bone graft alone achieved a similar clinical outcome but less morbidity irrespective of number of fusion level.

Continuous Positive Airway Pressure Breathing Increases the Spread of Sensory Blockade After Low-Thoracic Epidural Injection of Lidocaine

Factors affecting the distribution of sensory blockade after epidural injection of local anesthetics remain incompletely clarified. To evaluate if increasing intrathoracic pressure affects the spread of thoracic epidural anesthesia, we randomized 20 patients who received an epidural catheter at the T7-8 or T8-9 intervertebral space into 2 groups. The control group (n = 10) received an epidural test dose of 4 mL lidocaine 2% during spontaneous breathing at ambient pressure. The continuous positive airway pressure (n = 10) group received the same epidural test dose but during spontaneous respiration with 7.5 cm H2O continuous positive airway pressure. The groups were comparable with respect to demographic variables. Fifteen minutes after the conclusion of the epidural injection, the sensory block ranged from from T4 [median, interquartile range 2.75 segments] to T11 (interquartile range 3.5 segments) in the control group and from T5 (interquartile range 2.25 segments) to L2 (IQR 2.25 segments) in the continuous positive airway pressure group (P = 0.005 for the caudal border). The total number of segments blocked was 7 (median, interquartile range 2.25) in the control group and 11 (interquartile range 3.5) in the continuous positive airway pressure group (P = 0.004). The number of segments blocked caudad to the injection site was 3 (median, interquartile range 3.5) in the control group and 6 (interquartile range 2.25) in the continuous positive airway pressure group (P = 0.005). We conclude that continuous positive airway pressure increases the spread of sensory blockade in thoracic epidural anesthesia, primarily by a more caudad extension of sensory blockade.

Activated barrier crossing of macromolecules at a submicron-size entropic trap

We study the thermally activated barrier crossing by long chain molecules, initially confined to one side of an entropic trap. The entropic barrier is assumed to be of Kramers type. The barrier width is considered to be larger than the chain. The latter is in turn assumed to be long enough, so that a continuum description of the chain is applicable throughout the space. The barrier crossing rate is calculated using multidimensional Kramers theory and the functional integral method. For chains having the same total number of segments, the activation energy itself remains constant. However, the preexponential factor depends on the structure of the polymer. Polymers with the same molecular weight but having longer arms can effect larger fluctuations, thereby increasing its chance to cross the barrier. This leads to an almost exponential increase of the rate prefactor with the radius of gyration. The difference in the barrier crossing rates could be effectively exploited for the separation of molecules having architectural differences, for example, DNA of same length but different degrees of supercoiling. This is illustrated by considering star polymers. The Rouse-Ham model is used to analyze the mechanism of the barrier crossing. We show how the rate expression of the Arrhenius type is affected by the long arms of the star chain.

Elongated beamlets: a simple technique for segment and MU reduction for sMLC IMRT delivery on accelerators utilizing 5 mm leaf widths

The focus of this work is to demonstrate the effects of using an elongated beamlet to achieve similar dose conformity as achieved with a square beamlet while reducing the number of segments and subsequent MU required. A series of 10 patients were planned for IMRT delivery to the prostate using minimum beamlet sizes of 5 × 5 mm2 (default scheme), 10 × 5 mm2 with the short axis parallel to the prostate–rectum interface (scheme 1), and 10 × 5 mm2 with the short axis perpendicular to the prostate–rectum interface (scheme 2). All other parameters between plans were left unchanged. Plans were appropriately normalized and evaluated for R65, R40, conformity index, total number of segments and MU. All plans were generated using the Corvus inverse planning system. The average number of segments in this study decreased by approximately 49% for both schemes 1 and 2. The subsequent number of MU required decreased by approximately 34.6%. The resultant modified modulation scaling factor (MSFmod) decreased by approximately 34.3%. Additionally, we found that each isodose distribution using scheme 2 would still meet our clinical acceptance criteria with no visible degradation in the dose distribution as compared with the default scheme. In conclusion, we have demonstrated that it is possible to achieve similar results as those obtained using a 5 × 5 mm2 beamlet with respect to target coverage and critical structure sparing by using strategically oriented elongated beamlets. This technique directly translates to a decreased MSFmod allowing for decreased leakage dose to the patient, a decreased risk of exceeding secondary shielding limits in pre-existing vaults, and shorter treatment times.

Cine MR Imaging of Myocardial Contractile Impairment in Patients with Hypertrophic Cardiomyopathy Attributable to Asp175Asn Mutation in the α-Tropomyosin Gene

To prospectively investigate the relationship between myocardial contractile impairment and left ventricular (LV) hypertrophy measured at cardiac magnetic resonance (MR) imaging in patients with hypertrophic cardiomyopathy (HCM) caused by the substitution of aspartic acid 175 with asparagine (ie, Asp175Asn mutation) in the alpha-tropomyosin gene (TPM1). The study protocol was approved by the hospital ethics committee, and all subjects gave written informed consent. LV mass, maximal LV wall thickness, and myocardial fractional thickening during systole were measured at cine MR imaging in 24 subjects (11 male, 13 female; mean age, 42 years; age range, 17-68 years) with the Asp175Asn mutation in TPM1 and in 17 healthy volunteers (eight men, nine women; mean age, 38 years; age range, 23-60 years). The proportion of hypokinetic LV segments was calculated as the number of LV segments with fractional thickening of less than 30% divided by the total number of segments measured. Anthropometric and biochemical correlates of LV hypertrophy were determined. Univariate and multiple linear regression analyses were used to investigate the association of the proportion of hypokinetic segments and other correlates of LV hypertrophy with LV mass and maximal wall thickness. The proportion of hypokinetic segments was higher in patients with HCM than in control subjects (37% +/- 20 [standard deviation] vs 12% +/- 12, P < .001). In stepwise multiple regression analysis, the proportion of hypokinetic segments accounted for 42% (P < .001); the LV end-diastolic volume, for 24% (P = .003); and male sex, for 10% (P = .014) of the variability in LV mass in patients with HCM. The proportion of hypokinetic LV segments, which accounted for 48% of the variability in LV maximal wall thickness (P < .001), was the only variable significantly associated with maximal wall thickness. The extent of myocardial contractile impairment is strongly and independently related to LV mass and maximal wall thickness in patients with HCM attributable to the Asp175Asn mutation in TPM1.

SU‐FF‐T‐96: Improvement in IMRT Delivery for Head and Neck Patients Using Simplified IMRT Plans and Enhanced IMRT Delivery System

Purpose: To demonstrate the feasibility of simplified IMRT plans and improved delivery times without significantly degraded plan quality. Method and Materials: Five patients with nasopharynx tumors were selected for evaluation. The plan quality was assessed based on tumor coverage, multiple defined endpoints for sensitive structures, plan dose conformality and homogeneity index. The treatment plans were generated using direct machine parameter based optimization in a commercial treatment planning system. The numbers of beam angles varied from 7‐9. For each plan, the average total numbers of segments were gradually reduced from 98, 63, 48, to 24, while maintaining the planning dose constraints and number of beam angles. Treatment times are based on the latest IMRT delivery option (console 9) installed on a Siemens LINAC. Results: Improvements are two‐fold: (1) reduction of segments and (2) technical changes within the delivery system. All plans achieved the same tumor coverage, delivering &gt;95% of tumor volumes to 70Gy (GTV), 59.4Gy (CTV), and 54Gy (elective CTV) simultaneously. As the number of segments decreased from 98 to 24, the average maximum doses to the brainstem changed from 50,8, 50.4, 51.3, to 55.1 Gy and from 41.9, 42.2, 41.5 to 42.3 Gy to the spinal cord while the average mean parotid doses were 27.0, 26.7, 26.7, and 28.5Gy. As the total number of segments decreased, the average plan conformal indices were 0.63, 0.61, 0.65, and 0.46, and the average dose homogeneity indices were 89%, 87%, 88%, and 84%. Optimized communication within the LINAC control system reduced the inter‐segment delay from six to two seconds. Conclusion: For patients with nasopharyngeal tumors treated with IMRT, 50 segments might be sufficient to achieve clinical requirements. With the latest IMRT delivery system, the treatment time excluding patient setup can be reduced to 6‐8 minutes. Conflict of Interest: Research supported by Siemens.

TU‐C‐T‐6C‐03: Simplifying IMRT Plans Through Efficient Segmentation

Purpose: To analyze the various methods for creating efficient leaf sequences for an IMRT plan, subject to MLC constraints. Method and Materials: An IMRT treatment plan can be simplified at several stages. Careful beam placement can lead to simpler intensity maps. The choice of the dose optimization engine, as well as the spatial and intensity resolution can also affect map complexity. To further reduce the total number of segments and monitor units, an optimal leaf sequence must be used. This reduction is accomplished by a combination of segment extractions and sweeps. The algorithms involve the determination of MLC shape and MUs. Some algorithms use predefined MUs according to a sequence (e.g. Power of two, Half‐Maximum, Triangular numbers), while others optimize the MU selection by evaluating the complexity of the difference between the intensity map and the segment being considered. The selection of the MLC shape can also be achieved through a predetermined geometric process (e.g. largest area, largest area with maximum intensity, leftmost segment, graph theory) or by minimizing the complexity of the difference map. In this step, the machine constraints and the desire to reduce the tongue and groove effect are considered, as they can dramatically increase the number of segments and MUs. Once the leaf sequences have been generated, an examination of the plan may reveal degradation in the DVHs, and appropriate leaf‐sequence modifications can help restore the plan quality. Results: Plans with beams that have minimal critical structure involvement and modulate with more leaves yield less segments and MUs. Optimizers that use gradient methods rather than simulated annealing tend to reduce modulation scaling factors by a factor of 2 to 3. A map resolution of 10 to 15 intensity levels and a leaf spacing of 6 mm produce a reasonably efficient plan without sacrificing its quality, provided that the leaf sequence is optimized by minimizing the difference map complexity. The collision constraint increases the number of segments and MUs by about 20%, and various levels of tongue and groove correction provide an additional increase of about 20 to 30%. Post processing can remove low weight segments, and leaf positions can be adjusted to eliminate hot and cold spots. Conclusion: In order to simplify an IMRT plan, one must take advantage of all the options that affect the leaf sequencing process, including beam placement, map resolution, segmentation algorithm choice and post‐processing.Educational Objectives:1. To understand the importance of beam selection and set‐up prior to plan optimization.2. To know the impact of map resolution set‐up on complexity and the achievement of clinical goals.3. To know the limitations and strengths of the various algorithms for leaf sequencing and how to choose the appropriate one.4. To become familiar with the post‐processing of leaf sequences.

Usefulness of low-dose dobutamine stress echocardiography for the evaluation of spontaneous recovery of stunned myocardium in patients with acute right ventricular infarction

Right ventricular (RV) infarction (RVI) is usually associated with severe RV global dysfunction representing predominantly stunned myocardium that may respond favorably to reperfusion. We assessed the efficacy of low-dose dobutamine stress echocardiography (DSE), performed early in the course of a reperfused RVI, to predict the recovery of RV systolic and diastolic function in 3 months, documenting the recovery of stunned myocardium. In all, 27 patients with acute, successfully thrombolyzed RVI comprised the study population. All patients underwent standard echocardiography at baseline and 3 months later for evaluation of RV systolic and diastolic function. At day 5 DSE was performed for evaluation of RV contractile reserve. Of the total number of segments analyzed, 69% were detected as stunned. At baseline, RV systolic and diastolic indices were seriously impaired showing significant improvement at follow-up. RV wall-motion score index during DSE was positively correlated with the same index at follow-up. DSE is a safe and precise modality to predict recovery of stunned myocardium in the setting of RVI.

Internodal sodium channels ensure active processes under myelin manifesting in depolarizing afterpotentials

The current opinion about processes in myelinated axon is that action potential saltatorially propagates between nodes of Ranvier and passively charges internodal axolemma thus causing depolarizing afterpotentials (DAP). Demyelination blocks the conduction that gives additional argument in favor of hypothesis that internode is not able to be activated by the existing internodal sodium channels. The results of our modeling study shows that, when periaxonal space is sufficiently narrow, saltatorial action potential is able to activate internodes. Low density of internodal sodium channels is sufficient to generate active internodal waves that slowly propagate from nodes towards corresponding midinternodes where they collide. The periaxonal width that stops internodal wave propagation (about 400 nm) is significantly larger than the highest value of the physiological range for this parameter (30 nm). Internodal activation is directly manifested as transmembrane internodal potential or as a full-sized action potential in periaxonal space where it can hardly be detected, and only as a small deflection in intracellular space. However, changes in the periaxonal potential cause transmyelin currents that lead to significant DAP. The shape and amplitude of DAP depends on myelin parameters and densities of internodal channels. Several technical parameters affect the results of calculations. Internodal spatial segmentation has to be sufficiently fine (at most 20 μm) for the model to be able to simulate internodal activation. We employ 338 internodal segments as compared with up to 21 used in previous models. Ionic accumulation together with related diffusive and electrical processes alter the calculated DAP amplitude. Inclusion of these processes in calculations demands such increase in the total number of segments that the numerical methods used up to now become unapplicable. To overcome the problem, an iterative implicit approach is proposed. It reduces a matrix of general type in multi-cable models to tridiagonal one and accelerates calculations considerably.

Chest Compression Rates During Cardiopulmonary Resuscitation Are Suboptimal

Recent data highlight a vital link between well-performed cardiopulmonary resuscitation (CPR) and survival after cardiac arrest; however, the quality of CPR as actually performed by trained healthcare providers is largely unknown. We sought to measure in-hospital chest compression rates and to determine compliance with published international guidelines. We developed and validated a handheld recording device to measure chest compression rate as a surrogate for CPR quality. A prospective observational study of adult cardiac arrests was performed at 3 hospitals from April 2002 to October 2003. Resuscitations were witnessed by trained observers using a customized personal digital assistant programmed to store the exact time of each chest compression, allowing offline calculation of compression rates at serial time points. In 97 arrests, data from 813 minutes during which chest compressions were delivered were analyzed in 30-second time segments. In 36.9% of the total number of segments, compression rates were <80 compressions per minute (cpm), and 21.7% had rates <70 cpm. Higher chest compression rates were significantly correlated with initial return of spontaneous circulation (mean chest compression rates for initial survivors and nonsurvivors, 90+/-17 and 79+/-18 cpm, respectively; P=0.0033). In-hospital chest compression rates were below published resuscitation recommendations, and suboptimal compression rates in our study correlated with poor return of spontaneous circulation. CPR quality is likely a critical determinant of survival after cardiac arrest, suggesting the need for routine measurement, monitoring, and feedback systems during actual resuscitation.

Magnetic resonance T1 gradient-echo imaging in hepatolithiasis

We examined the role of magnetic resonance T1-weighted gradient-echo (MRT1-GE) imaging in hepatolithiasis. MRT1-GE, precontrast computed tomography (CT), and magnetic resonance cholangiopancreatography (MRCP) of 10 patients with hepatolithiasis were compared for their diagnostic accuracies in the detection and localization of intrahepatic calculi. The diagnosis of hepatolithiasis was confirmed by surgery. For localization of the stone, we divided the bile ducts into six areas: right and left hepatic ducts and bile ducts of the lateral, medial, right anterior, and right posterior segments of the liver. Chemical analysis of the stones was performed in eight patients. The total number of segments proved by surgery to contain stones was 18. Although not significantly different, the sensitivity of MRT1-GE was 77.8% (14 of 18 segments), higher than that of MRCP (66.7%, 12 of 18 segments) and that of CT (50%, nine of 18 segments). The sensitivity of magnetic resonance imaging (MRCP + MRT1) was significantly higher than that of CT (p < 0.01). Multiple logistic regression analysis showed that the result of surgery was significantly affected only by the result of magnetic resonance imaging. On MRT1-GE, all the depicted stones appeared as high-intensity signal areas within the low-intensity bile duct irrespective of their chemical composition. MRT1-GE imaging provides complementary information concerning hepatolithiasis.

Properties of Star‐Branched Polymer Chains Near a Surface

AbstractWe considered two model systems of star‐branched polymers near an impenetrable surface. The model chains were constructed on a simple cubic lattice. Each star polymer consisted of f = 3 arms of equal length and the total number of segments was up to 799. The excluded volume effect was included into these models only and therefore the system was studied at good solvent conditions. In the first model system polymer chain was terminally attached with one arm to the surface. The grafted arm could slide along the surface. In the second system the star‐branched chain was adsorbed on the surface and the strength of adsorption was were varied. The simulations were performed using the dynamic Monte Carlo method with local changes of chain conformations. The internal and local structures of a polymer layer were determined. The lateral diffusion and internal mobility of star‐branched chains were studied as a function of strength of adsorption and the chain length. The lateral diffusion and internal mobility of star‐branched chains were studied as a function of strength of adsorption and the chain length. It was shown that the behavior of grafted and weakly adsorbed chains was similar to that of a free three‐dimensional polymer, while the strongly adsorbed chains behave as a two‐dimensional system.

Deformation analyses of the integrated hydro-bulge forming of a spheroidal vessel from different preform types

The integral hydro-bulging technology employed in manufacturing spheroidal vessels has shown its visible benefits of lower cost and easy processing performance in engineering applications. Further potential for more extensive use in industry makes a formability study on the details of the technology more important such study involving the option of preform type and the shape lay-out for each associated segment. Different preform types have an impact on the level of the maximum deformation and the corresponding deformation properties in the performance of the subsequent integral hydro-bulging process. The total number of segments and the shape of the segments are likewise highly important factors. Relying on a simple analytical method, the expansion ratio parameter, the basic formability related to a prepared preform is discussed. The purpose is to determine a fitting preform type for a specified engineering application in a commercially processing performance.

Segmental IMRT for oropharyngeal cancer in a clinical setting

Background and purpose: To develop a segmental intensity-modulated radiotherapy (IMRT) technique for the treatment of oropharyngeal cancer. Patients and methods: Eight patients previously treated for oropharyngeal cancer were replanned with segmental IMRT. The dose distribution was optimized using beam geometries consisting of 3, 5, 7 and 9 equiangular beams. The optimization procedure resulted in a theoretical fluence for each beam. In order to vary the number of segments, the optimized fluence was divided into four different equidistant levels. The final dose distribution was calculated using clinically deliverable segments obtained from optimized fluence. Results: For our segmental IMRT technique the dose homogeneity within the target volumes improved when the total number of segments increased and reached a saturation level at approximately 150 segments. Seven beams were sufficient to achieve the saturation level for dose homogeneity. The mean dose to the parotid glands depended on the beam geometry and tumor location and did not depend on the number of segments. On average the mean dose to the contralateral parotid gland was 35.7 Gy (27.1–39.9 Gy) for all seven beam plans. Conclusions: Seven beams are sufficient to achieve an acceptable dose homogeneity within the target volumes and significant parotid sparing. These results will be used to introduce IMRT in routine clinical practice.

Myocardial contractile reserve by dobutamine stress echocardiography predicts improvement in ejection fraction with beta-blockade in patients with heart failure: the Beta-Blocker Evaluation of Survival Trial (BEST).

beta-Blockers improve survival and reduce hospitalization in chronic heart failure (CHF) by biologically improving left ventricular ejection fraction (LVEF). However, a good predictor of improvement with this therapy has not been identified. This substudy of BEST examined whether myocardial contractile reserve, as determined by dobutamine stress echocardiography, predicts improvement in LVEF. Seventy-nine patients with class III/IV CHF underwent dobutamine stress echocardiography before treatment with bucindolol (n=41) or placebo (n=38). Regional wall motion score index (WMSI) was calculated as the sum of the scores in each segment divided by the total number of segments visualized. WMSI was compared with change in LVEF after 3 months of therapy as determined by gated radionuclide scan. Change in WMSI correlated inversely with change in LVEF after 3 months of bucindolol (r=-0.72, P<0.0001) and was the most significant multivariate predictor of change in LVEF (P=0.0002). Patients with contractile reserve had demographics similar to those of patients without contractile reserve, including RVEF, LVEF, systolic blood pressure, and CHF duration. However, patients without contractile reserve had higher baseline plasma norepinephrine levels (687+/-333 versus 420+/-246 pg/mL, P<0.05) and greater decrease in plasma norepinephrine in response to bucindolol (-249+/-171 versus -35+/-277 pg/mL, P<0.05). This study suggests a direct relationship between contractile reserve and improvement in LVEF with beta-blocker therapy in patients with advanced CHF. Patients without contractile reserve have higher resting adrenergic drive, as reflected by plasma norepinephrine, and may experience greater sympatholytic effects from bucindolol.

Genetic algorithm based deliverable segments optimization for static intensity-modulated radiotherapy

The static delivery technique (also called step-and-shoot technique) has been widely used in intensity-modulated radiotherapy (IMRT) because of the simple delivery and easy quality assurance. Conventional static IMRT consists of two steps: first to calculate the intensity-modulated beam profiles using an inverse planning algorithm, and then to translate these profiles into a series of uniform segments using a leaf-sequencing tool. In order to simplify the procedure and shorten the treatment time of the static mode, an efficient technique, called genetic algorithm based deliverable segments optimization (GADSO), is developed in our work, which combines these two steps into one. Taking the pre-defined beams and the total number of segments per treatment as input, the number of segments for each beam, the segment shapes and weights are determined automatically. A group of interim modulated beam profiles quickly calculated using a conjugate gradient (CG) method are used to determine the segment number for each beam and to initialize segment shapes. A modified genetic algorithm based on a two-dimensional binary coding scheme is used to optimize the segment shapes, and a CG method is used to optimize the segment weights. The physical characters of a multileaf collimator, such as the leaves interdigitation limitation and leaves maximum over-travel distance, are incorporated into the optimization. The algorithm is applied to some examples and the results demonstrate that GADSO is able to produce highly conformal dose distributions using 20–30 deliverable segments per treatment within a clinically acceptable computation time.

On Source-Based Route Computation for Quickest Paths under Dynamic Bandwidth Constraints

Routing in the newer generation of network transmission methods may be performed at various levels of the IP stack such as datagram, TCP stream, and application levels. It is important in the use of these methods to compute the routes that minimize the end-to-end delays for the specific routing mechanism. We formulate an abstract network path computation problem, the dynamic quickest path problem, to encompass a number of message forwarding mechanisms including circuit switching, Internet Protocol, and their variations. This problem deals with the transmission of a message from a source to a destination with the minimum end-to-end delay over a network with propagation delays and dynamic bandwidth constraints on the links. The available bandwidth for each link is specified as a piecewise constant function. We present for each message forwarding mechanism or mode an algorithm to compute a path with the minimum end-to-end delay for a given message size. Our algorithms with suitable network restrictions have polynomial time complexity in the size of the network and total number of segments in the bandwidth list.

Thin-section CT of severe acute respiratory syndrome: evaluation of 73 patients exposed to or with the disease.

To retrospectively analyze the thin-section computed tomographic (CT) features in patients with severe acute respiratory syndrome (SARS) at the authors' institution. From March 11, 2003, to April 2, 2003, 74 patients with symptoms and signs suggestive of SARS underwent CT of the thorax; all underwent thin-section CT except for one patient who underwent conventional CT. Group 1 (n = 23) patients had symptoms of SARS in keeping with criteria from the Centers for Disease Control and Prevention and a positive chest radiograph. Group 2 (n = 17) patients had a high clinical suspicion of SARS but a normal radiograph. Group 3 (n = 34) patients had minor symptoms and a normal chest radiograph. The thin-section CT images were analyzed for ground-glass opacification or consolidation, lesion size in each lung segment, peripheral or central location, interstitial thickening, and other abnormalities. Thin-section CT scans were abnormal only for patients in groups 1 and 2. The patient with only conventional CT scans was in group 3; scans for group 3 patients were normal. Affected segments were predominantly in the lower lobes (91 of 149 affected segments). Common findings included ground-glass opacification, sometimes with consolidation, and interlobular septal and intralobular interstitial thickening. The size of each lesion and the total number of segments involved were smaller in group 2 patients. A majority of patients in group 1 (14 of 23) had mixed central and peripheral lesions. In group 2, however, peripheral lesions were more common (10 of 17). In both groups, a purely central lesion was uncommon (one of 23 in group 1 and two of 17 in group 2). Common thin-section CT features of SARS are ground-glass opacification and lower lobe and peripheral distribution.

Fluenzmodulierte Strahlentherapie mit in die Optimierung integrierter Segmentierung

On the basis of two clinical cases, we present fluence-modulated radiotherapy with a sequencer integrated into the optimization of our treatment-planning software HYPERION. In each case, we achieved simple relations for the dependence of the total number of segments on the complexity of the sequencing, as well as for the dependence of the dose-distribution quality on the number of segments. For both clinical cases, it was possible to obtain treatment plans that complied with the clinical demands on dose distribution and number of segments. Also, compared to the widespread concept of equidistant steps, our method of sequencing with fluence steps of variable size led to a significant reduction of the number of segments, while maintaining the quality of the dose distribution. Our findings substantiate the value of the integration of the sequencer into the optimization for the clinical efficiency of IMRT.