The first probe of a FLASH proton beam by PET

The recently observed FLASH effect related to high doses delivered with high rates has the potential to revolutionize radiation cancer therapy if promising results are confirmed and an underlying mechanism understood. Comprehensive measurements are essential to elucidate the phenomenon. We report the first-ever demonstration of measurements of successive in-spill and post-spill emissions of gammas arising from irradiations by a FLASH proton beam. A small positron emission tomography (PET) system was exposed in an ocular beam of the Proton Therapy Center at MD Anderson Cancer Center to view phantoms irradiated by 3.5 × 1010protons with a kinetic energy of 75.8 MeV delivered in 101.5 ms-long spills yielding a dose rate of 164 Gy s-1. Most in-spill events were due to prompt gammas. Reconstructed post-spill tomographic events, recorded for up to 20 min, yielded quantitative imaging and dosimetric information. These findings open a new and novel modality for imaging and monitoring of FLASH proton therapy exploiting in-spill prompt gamma imaging followed by post-spill PET imaging.

The treatment of dispersion terms for solution systems

DFT calculations of reaction mechanisms in solution have always been a hot topic, especially for transition-metal-catalyzed reactions, in which the traditional DFT-D3 method has been extensively employed. The overestimation of the dispersion from the traditional DFT-D3 method leads to a quite low activation free-energy barrier, so it is worth finding a proper way to deal with the dispersion for solution systems. The solvent-solute dispersion is also important for solution systems, and thus it should be calculated together with the solute dispersion. The newly generated solute-solute dispersion energy should be shared equally with the newly formed cavity between two interacting species; therefore, only half of the solute-solute and solvent-solute dispersion terms belong to the solute molecule. The detailed treatment of dispersion correction for solution systems has been fully addressed, and this method has been confirmed with the examples of ligand exchange reactions and catalytic reactions.

Stiffness changes in internal rotation muscles of the shoulder and its influence on hemiplegic shoulder pain

Background

Hemiplegic shoulder pain (HSP) is a common complication in patients with stroke. The pathogenesis of HSP is complex, and muscle hypertonia, especially the hypertonia of internal rotation muscles of the shoulder, may be one of the important causes of shoulder pain. However, the relationship between muscle stiffness and HSP has not been well studied. The purpose of this study is to explore the correlations between the stiffness of internal rotation muscles and clinical symptoms in patients with HSP.

Methods

A total of 20 HSP patients and 20 healthy controls were recruited for this study. The stiffness of internal rotation muscles was quantified using shear wave elastography, and Young's modulus (YM) of the pectoralis major (PM), anterior deltoid (AD), teres major ™, and latissimus dorsi (LD) were measured. Muscle hypertonia and pain intensity were evaluated using the Modified Ashworth Scale (MAS) and Visual Analog Scale (VAS), respectively. The mobility of the shoulder was evaluated using the Neer score. The correlations between muscle stiffness and the clinical scales were analyzed.

Results

YM of internal rotation muscles on the paretic side was higher than that of the control group in the resting and passive stretching positions (P < 0.05). YM of internal rotation muscles on the paretic side during passive stretching was significantly higher than that at rest (P < 0.05). YM of PM, TM, and LD during passive stretching were correlated with MAS (P < 0.05). In addition, the YM of TM during passive stretching was positively correlated with VAS and negatively correlated with the Neer score (P < 0.05).

Conclusion

Increased stiffness of PM, TM, and LD was observed in patients with HSP. The stiffness of TM was associated with pain intensity of the shoulder and shoulder mobility.

Cytokine expression in gingival crevicular fluid around teeth opposing dental implants and 3-unit fixed partial dentures in a cross-sectional study

OBJECTIVE

This study aimed to study the cytokines in gingival crevicular fluid (GCF) of the teeth opposing to dental implants and 3-unit fixed partial dentures (FPDs).

MATERIALS AND METHODS

A total of 74 participants were recruited for this cross-sectional study. Based on the status of lower first molars, the participants were divided into dental implants group and 3-unit FPDs group. Social index and oral hygiene were recorded. Occlusal loading was evaluated with a T-scan. GCF was sampled from the upper first molar and assessed with a commercial cytokine assay kit.

RESULTS

Forty three dental implants patients and 31 3-unit FPDs patients received all of the clinical and laboratory evaluation. The dental implants group had a higher occlusion force distribution on first molars region. IL-10, IL-17, RANK had a higher mean in dental implants group and was associated with occlusion force of first molar. There was a weakly association between IL-10 and dental implants in the binary logistic regression analyses.

CONCLUSIONS

In this study, the teeth opposing implants have a higher level of cytokines in the GCF than teeth opposing to 3-unit FPDs in periodontal healthy participants because of the poor osseoperception of dental implants. IL-10 might reflect a higher occlusion force in dental implants region.

CLINICAL RELEVANCE

This study provided that different tooth restoration methods could influence the periodontal status of the contact teeth.

DFT calculations in solution systems: solvation energy, dispersion energy and entropy

DFT calculations of reaction mechanisms in solution have always been a hot topic, especially for transition-metal-catalyzed reactions. The calculation of solvation energy is performed using either the polarizable continuum model (PCM) or the universal solvation model SMD. The PCM calculation is very sensitive to the choice of atomic radii to form a cavity, where the self-consistent isodensity PCM (SCI-PCM) has been recognized as the best choice and our IDSCRF radii can provide a similar cavity. Moving from a gas-phase case to a solution case, dispersion energy and entropy should be carefully treated. The solvent-solute dispersion is also important in solution systems, and it should be calculated together with the solute dispersion. Only half of the solvent-solute dispersion energy from the PCM calculation belongs to the solute molecules to maintain a thermal equilibrium between a solute molecule and its cavity, similar to the treatment of electrostatic energy. Relative solute dispersion energy should also be shared equally with the newly formed cavity. The entropy change from a gas phase to a liquid phase is quite large, but the modern quantum chemistry programs can only calculate the gas-phase translational entropy based on the idea-gas equation. In this review, we will provide an operable method to calculate the solution translational entropy, which has been coded in our THERMO program.

[Preparation and roles of sliver-loaded viscous hydrogel in healing of full-thickness skin defect wounds with bacterial colonization in mice]

Objective: To prepare the modified hyaluronic acid viscous hydrogel loaded with sliver particles and to explore the roles and mechanism of the hydrogel in healing of full-thickness skin defect wounds with bacterial colonization in mice. Methods: The experimental research method was adopted. Dopamine modified hyaluronic acid (HA-DA) and phenylboric acid modified hyaluronic acid (HA-PBA) were prepared, and their characteristic peaks were detected by Fourier-transform infrared spectroscopy. Different mass of acrylamides was added to HA-DA and HA-PBA to prepare the viscous hydrogel with mass fraction of acrylamide in 10%, 15%, and 20%. The gelation of the viscous hydrogel with mass fraction of acrylamide in 20% was observed in the state of tilt and inversion at 37 ℃, and the storage modulus and loss modulus of the above 3 kinds of viscous hydrogels were detected by rotational rheometer. The sliver-loaded viscous hydrogel was prepared by adding nano silver ions to the viscous hydrogel with mass fraction of acrylamide in 20%. The concentration of silver ions released by sliver-loaded viscous hydrogel was measured by inductively coupled plasma mass spectrometer, and the cumulative release rate of silver ion was calculated (n=5). The mouse fibroblasts L929 were divided into phosphate buffered saline (PBS) group, viscous hydrogel group, and sliver-loaded viscous hydrogel group, which were dealt correspondingly, and the cell survival was detected by cell counting kit 8 method after 1, 2, and 3 d of culture (n=5). Twenty-four male C57BL/6 mice aged 6-8 weeks were selected, and forty-eight full-thickness skin defect wounds were inflicted and inoculated with the mixture of Escherichia coli and Staphylococcus aureus in the back of the mice, with two wounds in each mouse. The wounds were divided into normal saline group, viscous hydrogel group, and sliver-loaded viscous hydrogel group, which were dealt correspondingly, with 16 wounds in each group, and two wounds in each mouse were divided into different groups. On post injury day (PID) 3, 7, 10, and 14, the wound healing was observed and the wound healing rate was calculated. On PID 3, the colony forming units of Escherichia coli and Staphylococcus aureus in wounds were observed and counted. On PID 14, the epithelized epidermal thickness and the optical density of collagen fiber in wounds were observed and analyzed after hematoxylin eosin staining and Masson staining, respectively. On PID 3, 7, and 10, the expressions of tumor necrosis factor α (TNF-α), transforming growth factor β₁ (TGF-β₁), and vascular endothelial growth factor (VEGF) were detected by immunohistochemistry. The number of wounds in each index detecting at each time point was four. Data were statistically analyzed with analysis of variance for factorial design, one-way analysis of variance, and Bonferroni correction. Results: The characteristic peaks of HA-PBA were detected at the wave numbers of 1 369 and 1 425 cm^-1, indicating that phenylboric acid had been successfully grafted on hyaluronic acid, and the characteristic peaks of HA-DA were detected at the wave numbers of 1 516 and 1 431 cm^-1, indicating that dopamine had been successfully grafted on hyaluronic acid. The viscous hydrogel with mass fraction of acrylamide in 20% maintained the stable and no-flow condition of gelation in the state of tilt and inversion at 37 ℃. The storage modulus and loss modulus of the viscous hydrogel increased with the increase of acrylamide content, the storage modulus and loss modulus of the 3 kinds of viscous hydrogels had no obvious changes with the increase of the oscillation frequency or time, and the storage modulus of the 3 kinds of acrylamide hydrogels were greater than the loss modulus. The release of silver ion in the sliver-loaded viscous hydrogel lasted for 7 days, and the cumulative release rate of silver ion was up to 65%. After 1, 2, and 3 d of culture, the cell survival rates in sliver-loaded viscous hydrogel group were significantly lower than those in PBS group and viscous hydrogel group (P<0.05 or P<0.01), while after 1 d of culture, the cell survival rate in viscous hydrogel group was significantly lower than that in PBS group (P<0.01). With extension of time after injury, the wounds of mice in the 3 groups shrank gradually. On PID 3, 7, 10, and 14, the wound healing rates in sliver-loaded viscous hydrogel group were (53.0±3.6)%, (75.3±6.9)%, (93.3±1.2)%, and (96.7±0.8)%, which were significantly higher than (21.8±6.4)%, (53.9±8.2)%, (72.0±7.8)%, and (92.5±0.4)% in normal saline group (P<0.01). On PID 3 and 14, the wound healing rates in sliver-loaded viscous hydrogel group were significantly higher than (43.5±2.4)% and (94.1±1.5)% in viscous hydrogel group (P<0.05). On PID 3 and 10, the wound healing rates in viscous hydrogel group were significantly higher than those in normal saline group (P<0.01). On PID 3, the colony forming units of two bacteria in wound of sliver-loaded viscous hydrogel group were significantly less than those in normal saline group and viscous hydrogel group (P<0.01), while the colony forming units of two bacteria in wound of viscous hydrogel group were significantly less than those in normal saline group (P<0.05). On PID 14, the wounds were basically epithelialized and the epidermis was thicker, with collagen protein content being increased significantly and more orderly arranged collagen in sliver-loaded viscous hydrogel group compared with those in the other 2 groups. On PID 14, the epidermal thickness in wounds of sliver-loaded viscous hydrogel group was significantly increased compared with that in the other two groups (P<0.05), and the optical density of collagen fiber was significantly increased compared with those in normal saline group (P<0.05). On PID 3, the expressions of TGF-β₁ and VEGF in wounds of sliver-loaded viscous hydrogel group were significantly higher than those in normal saline group (P<0.05 or P<0.01), while the expression of VEGF in wounds of viscous hydrogel group was significantly higher than that in normal saline group (P<0.01). On PID 7, the expression of TGF-β₁ in wounds of sliver-loaded viscous hydrogel group was significantly higher than that in the other 2 groups (P<0.01), and the expression of VEGF was significantly higher than that in normal saline group (P<0.01). On PID 10, the expression of TNF-α in wounds of sliver-loaded viscous hydrogel group was significantly lower than that in normal saline group (P<0.05), the expressions of TGF-β₁ and VEGF in wounds of sliver-loaded viscous hydrogel group were significantly higher than those in normal saline group (P<0.05 or P<0.01), and the expression of VEGF in wounds of sliver-loaded viscous hydrogel group was significantly higher than that in viscous hydrogel group (P<0.05). Conclusions: The sliver-loaded viscous hydrogel prepared in this study has good stability and elasticity, which can continuously release silver ions and help to accelerate the healing of full-thickness defect wounds with bacterial colonization in mice. Besides, the sliver-loaded viscous hydrogel has low biological toxicity and can promote re-epithelialization, collagen deposition as well as angiogenesis of wounds, which may be related to the infiltration and regression of inflammatory cells.

Mixed Transcriptome Analysis Revealed the Possible Interaction Mechanisms between Zizania latifolia and Ustilago esculenta Inducing Jiaobai Stem-Gall Formation

The smut fungus Ustilago esculenta infects Zizania latifolia and induces stem expansion to form a unique vegetable named Jiaobai. Although previous studies have demonstrated that hormonal control is essential for triggering stem swelling, the role of hormones synthesized by Z. latifolia and U. esculenta and the underlying molecular mechanism are not yet clear. To study the mechanism that triggers swollen stem formation, we analyzed the gene expression pattern of both interacting organisms during the initial trigger of culm gall formation, at which time the infective hyphae also propagated extensively and penetrated host stem cells. Transcriptional analysis indicated that abundant genes involving fungal pathogenicity and plant resistance were reprogrammed to maintain the subtle balance between the parasite and host. In addition, the expression of genes involved in auxin biosynthesis of U. esculenta obviously decreased during stem swelling, while a large number of genes related to the synthesis, metabolism and signal transduction of hormones of the host plant were stimulated and showed specific expression patterns, particularly, the expression of ZlYUCCA9 (a flavin monooxygenase, the key enzyme in indole-3-acetic acid (IAA) biosynthesis pathway) increased significantly. Simultaneously, the content of IAA increased significantly, while the contents of cytokinin and gibberellin showed the opposite trend. We speculated that auxin produced by the host plant, rather than the fungus, triggers stem swelling. Furthermore, from the differently expressed genes, two candidate Cys2-His2 (C2H2) zinc finger proteins, GME3058_g and GME5963_g, were identified from U. esculenta, which may conduct fungus growth and infection at the initial stage of stem-gall formation.

[Effectiveness evaluation of health belief model-based health education intervention for patients with hypertension in community settings]

Objective: To evaluate the effectiveness of health belief model-based health education intervention in improving blood pressure control of patients with hypertension in community settings. Methods: From September 2016 to September 2017, 400 newly diagnosed patients with hypertension were recruited from 6 community healthcare centers with comparable population size and health services in the Shunyi District of Beijing. All community healthcare centers were randomly assigned to the intervention group (206 patients) and the control group (194 patients). Patients in the intervention group received 3 lectures (20-30 min for each) of health belief model-based health education. Patients in the control group received usual care. The basic characteristics, health beliefs, and health literacy were collected, and blood pressure was measured before and after the intervention, respectively. The difference-in-difference model was used to analyze the change of blood pressure and the influencing factors between two groups before and after the intervention. Results: A total of 134 patients in the intervention group and 129 patients in the control group completed the study. After adjusting for the age, gender, family income, medical insurance, chronic diseases and family history, the score of perceived barriers was increased by 1.65 (P=0.016), and perceived seriousness was decreased by 0.73 (P=0.018). The systolic blood pressure of patients was decreased by 7.37 mmHg (1 mmHg=0.133 kPa, P=0.001) and diastolic blood pressure was decreased by 4.07 mmHg (P=0.014), respectively. The β (95%CI) values were -7.37 (-11.88,-2.86) and -4.07 (-7.30, -0.84). The perceived susceptibility and self-efficacy had a significant influence on the blood pressure of patients (P<0.05). Conclusion: Health belief model-based health education intervention could significantly improve the blood pressure control of patients with hypertension in the community settings.

Crystallization of Lennard-Jones liquids under dynamic compression: Heterogeneous and homogeneous nucleation

We investigate crystallization of Lennard-Jones liquids on substrates under dynamic compression with large-scale molecular dynamics simulations. The substrates examined include single crystals and bicrystals with different crystallographic orientations, and the loading paths include shock and quasi-isentropic loading. Microstructure is characterized with simulated x-ray diffraction and orientation mapping. For shock loading, only heterogeneous nucleation occurs at the simulation scales. Quasi-isentropic loading induces less heating and larger supercooling; as a result, heterogeneous nucleation occurs at low loading strengths, and both heterogeneous and homogeneous nucleation occur at high loading strengths, despite the crystalline substrates. Crystallization depends on the substrate structure (crystal orientation and grain boundary) and loading characteristics. Deformation may induce grain structure change (e.g., reorientation and twinning) of substrates and affect subsequent crystallization. Crystallization rate is anisotropic, inversely proportional to the cosine of the dihedral angle between the substrate plane and a main {111} growth plane.

[Advances in immune checkpoint inhibitors in gastrointestinal cancer]

Currently, immunotherapy is considered as the fourth major modality of cancer treatment except surgery, chemotherapy and radiotherapy. The new therapeutic approach based on immune checkpoint inhibitors is a landmark innovation. Strategies considering checkpoint inhibitors have shown good anti-tumor effect by targeting cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1) or programmed cell death ligand 1 (PD-L1). Moreover, DNA mismatch repair-deficient tumors appear to be potential candidates for these therapies. This review summarizes the discussion and oral presentations in the annual meeting of American Society of Clinical Oncology (ASCO) and ASCO-gastrointestinal cancer (GI) in 2016 and provides an update on immunotherapy in gastrointestinal cancers.

Methylation analysis of CXCR1 in mammary gland tissue of cows with mastitis induced by Staphylococcus aureus

Mastitis is the most important disease in the global dairy industry, and causes large economic losses. Staphylococcus aureus is one of most common pathogens that cause bovine mastitis. CXCR1 has been implicated as a prospective genetic marker for mastitis resistance in dairy cows; CXCR1 expression significantly increases when cows have mastitis. To investigate the mechanisms involved in its increased expression, bisulfite sequencing polymerase chain reaction (PCR) was used to detect the methylation status of CXCR1 CpG island, and quantitative fluorescence PCR was used to detect CXCR1 expression in bovine mammary tissue induced with S. aureus in three Chinese Holstein cows. No CpG island was found for bovine CXCR1 in the upstream 2-kb region, whereas one CpG island that contained 13 CpG sites was found in exon 1 of CXCR1. All of the CpG sites were under hypermethylation from 90 to 100% in the mammary tissues. When the mammary gland mRNA expression of CXCR1 was 12.10-fold higher in infected cow quarters than in uninfected quarters, the methylation levels of the CpG site at position 519 were significantly lower in the infected quarters than in the uninfected quarters. Pearson correlation analysis showed that the methylation level at position 519 was significantly negatively correlated with the CXCR1 mRNA expression level (P < 0.05). These results indicate that the methylation of the CpG site at position 519 may regulate CXCR1 expression in cows with mastitis induced by S. aureus, but further studies are needed to elucidate the mechanisms involved.

Commissioning dose computation models for spot scanning proton beams in water for a commercially available treatment planning system

PURPOSE

To present our method and experience in commissioning dose models in water for spot scanning proton therapy in a commercial treatment planning system (TPS).

METHODS

The input data required by the TPS included in-air transverse profiles and integral depth doses (IDDs). All input data were obtained from Monte Carlo (MC) simulations that had been validated by measurements. MC-generated IDDs were converted to units of Gy mm(2)/MU using the measured IDDs at a depth of 2 cm employing the largest commercially available parallel-plate ionization chamber. The sensitive area of the chamber was insufficient to fully encompass the entire lateral dose deposited at depth by a pencil beam (spot). To correct for the detector size, correction factors as a function of proton energy were defined and determined using MC. The fluence of individual spots was initially modeled as a single Gaussian (SG) function and later as a double Gaussian (DG) function. The DG fluence model was introduced to account for the spot fluence due to contributions of large angle scattering from the devices within the scanning nozzle, especially from the spot profile monitor. To validate the DG fluence model, we compared calculations and measurements, including doses at the center of spread out Bragg peaks (SOBPs) as a function of nominal field size, range, and SOBP width, lateral dose profiles, and depth doses for different widths of SOBP. Dose models were validated extensively with patient treatment field-specific measurements.

RESULTS

We demonstrated that the DG fluence model is necessary for predicting the field size dependence of dose distributions. With this model, the calculated doses at the center of SOBPs as a function of nominal field size, range, and SOBP width, lateral dose profiles and depth doses for rectangular target volumes agreed well with respective measured values. With the DG fluence model for our scanning proton beam line, we successfully treated more than 500 patients from March 2010 through June 2012 with acceptable agreement between TPS calculated and measured dose distributions. However, the current dose model still has limitations in predicting field size dependence of doses at some intermediate depths of proton beams with high energies.

CONCLUSIONS

We have commissioned a DG fluence model for clinical use. It is demonstrated that the DG fluence model is significantly more accurate than the SG fluence model. However, some deficiencies in modeling the low-dose envelope in the current dose algorithm still exist. Further improvements to the current dose algorithm are needed. The method presented here should be useful for commissioning pencil beam dose algorithms in new versions of TPS in the future.

64-Slice spiral CT perfusion combined with vascular imaging of acute ischemic stroke for assessment of infarct core and penumbra

The aim of this study was to determine the value of computed tomography perfusion (CTP) parameters, including cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT) and time-to-peak (TP), in a clinical study of patients with stroke. Additionally, we determined which parameter or combination of parameters are reliable in detecting the presence of an infarct and penumbra. CTP was performed within 24 h of the onset of symptoms in 20 patients with possible stroke. Magnetic resonance imaging (MRI) was performed 3-7 days later and the threshold of the CTP was adjusted according to the results to provide CT images that correlated with the MRI; the MRI results were taken as the gold standard. CBV, CBF and TP contrast agent enhancement were calculated using the CT results. The CTP results were compared with the MRI findings. All CTP parameters were reliable in detecting the penumbra (P<0.001). In these parameters, changes of MTT were the most useful. CTP revealed various changes in CBF, CBV, MTT and TP in ischemic areas. CTP parameters were also reliable in detecting the infarct core (P<0.001). We determined that when detecting the penumbra, all CTP parameters are reliable, and when detecting cerebral ischemia, a combination of parameters should be used.

Fluorescence correlation spectroscopy with patterned photoexcitation for measuring solution diffusion coefficients of robust fluorophores

Patterned fluorescence correlation spectroscopy is developed as a new technique for measuring diffusion coefficients of photostable fluorescent probe molecules. In this method, interference between two intersecting, coherent laser beams creates an excitation fringe pattern from which fluorescence emission is monitored. Spontaneous concentration fluctuations of fluorescent molecules within the excitation volume are detected as excess noise on a fluorescence transient; concentration fluctuations are driven primarily by diffusion of these molecules between interference fringes although contributions from photobleaching and diffusion over the entire pattern dimensions can also be observed. Autocorrelation of the fluorescence transient allows analysis of the temporal characteristics of the fluctuations, which were used to determine solution diffusion coefficients; the method was applied to study the diffusion of Rhodamine 6G (R6G) in water/methanol solutions containing added electrolyte and in pure ethanol. The method can be used to characterize the diffusive transport of fluorescently labeled species, which is an important issue in designing small-volume detection experiments.

Magnetic resonance imaging retinal oximetry: a quantitative physiological biomarker for early diabetic retinopathy?

AIMS

To assess the efficacy of using magnetic resonance imaging measurements of retinal oxygenation response to detect early diabetic retinopathy in patients with Type 2 diabetes.

METHODS

Magnetic resonance imaging was conducted during 100% oxygen inhalation in patients with Type 2 diabetes with either no diabetic retinopathy (n = 12) or mild to moderate background diabetic retinopathy (n = 12), as well as in healthy control subjects (n = 12). Meanwhile, changes in retinal oxygenation response were measured.

RESULTS

In the healthy control group, levels of retinal oxygenation response increased slowly during 100% oxygen inhalation. In contrast, they increased more quickly and attained homeostasis much earlier in the groups with background diabetic retinopathy (at the 20-min time point) and with no diabetic retinopathy (at the 25-min time point) than in the healthy control group (at the 42-min time point). Furthermore, levels of retinal oxygenation response in the group with background diabetic retinopathy increased more than that of the group with no diabetic retinopathy, which in turn increased more than that of the healthy control group. There are statistically significant differences between the group with background diabetic retinopathy and the healthy control group at 6-, 8-, 10-, 15-, 20- and 25-min time points (P < 0.05). According to the normal range of the healthy control group by setting fundus photography results as 'gold standard' in our research, the sensitivity, specificity, positive predictive value, negative predictive value and receiver operating characteristic area for reporting the early indications of utility of diabetic retinopathy were 83.33%, 58.33%, 50%, 87.5% and 0.774, respectively.

CONCLUSIONS

The results indicate that magnetic resonance imaging is a potential screening method and probably a quantitative physiological biomarker to find early diabetic retinopathy in patients with Type 2 diabetes.

Does kV-MV dual-energy computed tomography have an advantage in determining proton stopping power ratios in patients?

Conventional kilovoltage (kV) x-ray-based dual-energy CT (DECT) imaging using two different x-ray energy spectra is sensitive to image noise and beam hardening effects. The purpose of this study was to evaluate the theoretical advantage of the DECT method for determining proton stopping power ratios (SPRs) using a combination of kV and megavoltage (MV) x-ray energies. We investigated three representative x-ray energy pairs: 100 and 140 kVp comprised the kV-kV pair, 100 kVp and 1 MV comprised the kV-MV pair, and two 1 MV x-ray beams-one with and one without external filtration-comprised the MV-MV pair. The SPRs of 34 human tissues were determined using the DECT method with these three x-ray energy pairs. Small perturbations were introduced into the CT numbers and x-ray spectra used for the DECT calculation to simulate the effects of random noise and beam hardening. An error propagation analysis was performed on the DECT calculation algorithm to investigate the propagation of CT number uncertainty to final SPR estimation and to suggest the best x-ray energy combination. We found that the DECT method using each of the three beam pairs achieved similar accuracy in determining the SPRs of human tissues in ideal conditions. However, when CT number uncertainties and artifacts such as imaging noise and beam hardening effects were considered, the kV-MV DECT improved the accuracy of SPR estimation substantially over the kV-kV or MV-MV DECT methods. Furthermore, our error propagation analysis showed that the combination of 100 kVp and 1 MV beams was close to the optimal selection when using the DECT method to determine SPRs. Overall, the kV-MV combination makes the DECT method more robust in resolving the effective atomic numbers for biological tissues than the traditional kV-kV DECT method.

Intensity modulated proton therapy treatment planning using single-field optimization: the impact of monitor unit constraints on plan quality

PURPOSE

To investigate the effect of monitor unit (MU) constraints on the dose distribution created by intensity modulated proton therapy (IMPT) treatment planning using single-field optimization (SFO).

METHODS

Ninety-four energies between 72.5 and 221.8 MeV are available for scanning beam IMPT delivery at our institution. The minimum and maximum MUs for delivering each pencil beam (spot) are 0.005 and 0.04, respectively. These MU constraints are not considered during optimization by the treatment planning system; spots are converted to deliverable MUs during postprocessing. Treatment plans for delivering uniform doses to rectangular volumes with and without MU constraints were generated for different target doses, spot spacings, spread-out Bragg peak (SOBP) widths, and ranges in a homogeneous phantom. Four prostate cancer patients were planned with and without MU constraints using different spot spacings. Rounding errors were analyzed using an in-house software tool.

RESULTS

From the phantom study, the authors have found that both the number of spots that have rounding errors and the magnitude of the distortion of the dose distribution from the ideally optimized distribution increases as the field dose, spot spacing, and range decrease and as the SOBP width increases. From our study of patient plans, it is clear that as the spot spacing decreases the rounding error increases, and the dose coverage of the target volume becomes unacceptable for very small spot spacings.

CONCLUSIONS

Constraints on deliverable MU for each spot could create a significant distortion from the ideally optimized dose distributions for IMPT fields using SFO. To eliminate this problem, the treatment planning system should incorporate the MU constraints in the optimization process and the delivery system should reliably delivery smaller minimum MUs.

Assessment of the accuracy of an MCNPX-based Monte Carlo simulation model for predicting three-dimensional absorbed dose distributions

In recent years, the Monte Carlo method has been used in a large number of research studies in radiation therapy. For applications such as treatment planning, it is essential to validate the dosimetric accuracy of the Monte Carlo simulations in heterogeneous media. The AAPM Report no 105 addresses issues concerning clinical implementation of Monte Carlo based treatment planning for photon and electron beams, however for proton-therapy planning, such guidance is not yet available. Here we present the results of our validation of the Monte Carlo model of the double scattering system used at our Proton Therapy Center in Houston. In this study, we compared Monte Carlo simulated depth doses and lateral profiles to measured data for a magnitude of beam parameters. We varied simulated proton energies and widths of the spread-out Bragg peaks, and compared them to measurements obtained during the commissioning phase of the Proton Therapy Center in Houston. Of 191 simulated data sets, 189 agreed with measured data sets to within 3% of the maximum dose difference and within 3 mm of the maximum range or penumbra size difference. The two simulated data sets that did not agree with the measured data sets were in the distal falloff of the measured dose distribution, where large dose gradients potentially produce large differences on the basis of minute changes in the beam steering. Hence, the Monte Carlo models of medium- and large-size double scattering proton-therapy nozzles were valid for proton beams in the 100 MeV-250 MeV interval.

Measurements of in-air output ratios for a linear accelerator with and without the flattening filter

The in-air output ratio (Sc) for photon beams from linear accelerators describes the change of in-air output as a function of the collimator settings. The physical origin of the Sc is mainly due to the change in scattered radiation that can reach the point of measurement as the geometry of the head changes. The flattening filter (FF) and primary collimator are the major sources of scattered radiation. The change in amount of backscattered radiation from the collimator into the beam-monitoring chamber also contributes to the variation of output. In this work, we measured the Sc and backscatter factors (Sb) into the beam-monitoring chamber for a linear accelerator with and without the FF. We measured the Sc with a Farmer-type chamber in a miniphantom at the depth of 10 g/cm2 for 6- and 18-MV x-ray beams from a Varian Clinac 2100EX linear accelerator. The Sb were measured with a universal pulse counter and a diode array with build-in counting hardware and software. The head scatter component (Sh) was then derived from the relationship Sc= Sh x Sb, where Sb was the linear fit of measured results. Significant differences were observed for Sc with and without the FF. Within the range of experimental uncertainty, the Sb was similar with and without the FF. The variations in Sh differed significantly over the range of field sizes of 3 X 3 to 40 X 40 cm2 with and without the FF; for the 6-MV beam, it was 8% vs 3%, and for the 18-MV beam, 7% vs 1%. By analyzing the contributions of backscatter factor and total in-air output ratios with and without the FF, we directly gained insight into the contributions of different components to the total variations in Sc of a linear accelerator. Sc, Sb, and Sh are basic and useful dosimetric quantities for delivery of intensity-modulated radiation therapy using a linear accelerator operating in a mode without the FF.

Derivation of the distribution of extrafocal radiation for head scatter factor calculation

Head scatter factors for high energy photon beams from linear accelerators can be modeled using a two-source model consisting of focal and extrafocal radiation. The focal radiation can be approximated as a point source, and the distribution of the extrafocal radiation is a two-dimensional (2D) radial symmetric function. Various methods, including analytical, Monte Carlo, and empirical trial functions, have been used to determine the radial symmetric function of extrafocal radiation distribution. This article describes a method for directly determining the extrafocal radiation distribution without assuming any empirical trial function. The extrafocal radiation distribution is determined with measured head scatter factors for rectangular fields defined by the lower jaw (X) fixed at 40 cm and the upper jaw (Y) varying from 3 to 40 cm. The derivatives of the measured head scatter factors, with respect to the Y jaw position projected in the plane of extrafocal radiation, are proportional to the one-dimensional (1D) projection (also called the line spread function) of the extrafocal radiation distribution. Two methods are used to solve the radial function of extrafocal radiation from the 1D projection. The first method uses a 2D filtered backprojection algorithm, originally developed for parallel beam computed tomography reconstruction, to directly derive the radial dependence of the extrafocal radiation distribution. The method has been applied to 6 and 18 MV photon beams from a Siemens linear accelerator and has been tested by comparing measured and calculated head scatter factors for square and rectangular fields. The second method uses a Fourier transform followed by a Fourier-Bessel transform to solve the problem. The distributions of extrafocal radiation derived from these two methods are virtually identical.

Characteristics of sensitometric curves of radiographic films

A new type of radiographic film, EDR (extended dose range) film, has been recently become available for film dosimetry. It is particularly attractive for composite isodose verification of intensity modulated radiation therapy because of its low sensitivity relative to the more common Kodak XV film. For XV film, the relationship between optical density and dose, commonly known as the sensitometric curve, depends linearly on the dose at low densities. Unlike XV film, the sensitometric curve of EDR film irradiated by megavoltage x rays is not linearly dependent on the dose at low densities. In this work, to understand the mechanisms governing the shape of the sensitometric curves, EDR film was studied with kilovoltage x rays, 60Co gamma rays, megavoltage x rays, and electron beams. As a comparison, XV film was also studied with the same beams mentioned above. The model originally developed by Silberstein [J. Opt. Soc. Am. 35, 93-107, 1945)] is used to fit experimental data. It is found that the single hit model can be used to predict the sensitometric curve for XV films irradiated by all beams used in this work and for EDR films exposed to kilovoltage x rays. For EDR film irradiated by 60Co gamma rays, megavoltage x rays, and electron beams, the double hit model is used to fit the sensitometric curves. For doses less than 100 cGy, a systematic difference between measured densities and that predicted by the double hit model is observed. Possible causes of the observed differences are discussed. The results of this work provide a theoretical explanation of the sensitometric behavior of EDR film.

Evaluation of Kodak EDR2 film for dose verification of intensity modulated radiation therapy delivered by a static multileaf collimator

A new type of radiographic film, Kodak EDR2 film, was evaluated for dose verification of intensity modulated radiation therapy (IMRT) delivered by a static multileaf collimator (SMLC). A sensitometric curve of EDR2 film irradiated by a 6 MV x-ray beam was compared with that of Kodak X-OMAT V (XV) film. The effects of field size, depth and dose rate on the sensitometric curve were also studied. It is found that EDR2 film is much less sensitive than XV film. In high-energy x-ray beams, the double hit process is the dominant mechanism that renders the grains on EDR2 films developable. As a result, in the dose range that is commonly used for film dosimetry for IMRT and conventional external beam therapy, the sensitometric curves of EDR2 films cannot be approximated as a linear function, OD = c * D. Within experimental uncertainty, the film sensitivity does not depend on the dose rate (50 vs 300 MU/min) or dose per pulse (from 1.0 x 10(-4) to 4.21 x 10(-4) Gy/pulse). Field sizes and depths (up to field size of 10 x 10 cm2 and depth = 10 cm) have little effect on the sensitometric curves. Percent depth doses (PDDs) for both 6 and 23 MV x rays were measured with both EDR2 and XV films and compared with ion chamber data. Film data are within 2.5% of the ion chamber results. Dose profiles measured with EDR2 film are consistent with those measured with an ion chamber. Examples of measured IMRT isodose distributions versus calculated isodoses are presented. We have used EDR2 films for verification of all IMRT patients treated by SMLC in our clinic. In most cases, with EDR2 film, actual clinical daily fraction doses can be used for verification of composite isodose distributions of SMLC-based IMRT.

Dependence of virtual wedge factor on dose calibration and monitor units

One of the important features of the Siemens Virtual Wedge (VW) is that the VW factor (VWF) is approximately equal to unity for all beams with a total deviation for a given wedge no greater than 0.05, as specified by Siemens. In this note we report the observed dependence of VWF on dose calibration (cGy/MU), monitor units (MU), and beam tuning for a Primus, a linear accelerator with two dose-rate ranges available for VW operation. The VWF is defined as the ratio of doses measured on the beam central axis for the wedge field to the open field; the open field dose is always measured with the nominal high dose-rate beam. When VW operates in the high dose-rate range, the VWF is independent of calibration (cGy/MU). When VW works in the low dose-rate range, the VWF varies linearly with the calibration of the low dose-rate mode. For a linear accelerator that has only one dose-rate range for VW, there is no observable dependence of VWF on the calibration. We also studied the monitor unit dependence of VWF. A discontinuity in VWF was observed at the switching point between the high and low dose-rate ranges. Working with Siemens, we have investigated causes of this discontinuity. As a result of this investigation, the discontinuity in VWF as a function monitor unit is practically removed.

Parkin expression in the adult mouse brain

Mutations in a protein designated Parkin were shown to be involved in the pathogenesis of autosomal recessive juvenile parkinsonism. Nothing is known about its regional and subcellular distribution in the mouse. In order to elucidate the Parkin mRNA and protein distribution in the adult mouse, the mouse cDNA was cloned and polyclonal antisera were generated against the N-terminal part of mouse Parkin. The antibodies were shown to be specific using Western blot analysis, immunostaining of cells transfected with mouse Parkin and pre-absorption tests. The Parkin protein expression profile was studied using immunohistochemistry and Western blot analysis and was compared with that of the mRNA yielded by in situ hybridization and RT-PCR analysis. Parkin protein was widely distributed in all subdivisions of the mouse brain. Low levels were found in the telencephalon and diencephalon, while the brainstem contained a large number of cells heavily expressing Parkin. Ultrastructural analysis and double immunohistochemistry revealed that the majority of Parkin-expressing cells were neurons, while only single glial cells exhibited immunostaining. The protein was distributed nonhomogeneously throughout the entire cytoplasm. A subpopulation of Parkin-immunopositive cells displayed speckled immunodeposits in the nucleus. Dopaminergic cells of the substantia nigra pars compacta exhibited high levels of Parkin mRNA but no Parkin protein, while the striatum contained immunopositive profiles but no mRNA signals. Our data indicate that Parkin is neither restricted to a single functional system nor associated with a particular transmitter system. The speckled nuclear distribution of Parkin immunoreactivity strongly suggests a role for Parkin in gene expression.

Comparison of dosimetric characteristics of Siemens virtual and physical wedges

Dosimetric properties of Virtual Wedge (VW) and physical wedge (PW) in 6 and 23 MV photon beams from a Siemens Primus linear accelerator, including wedge factors, depth doses, dose profiles, peripheral doses and surface doses, are compared. While there is a great difference in absolute values of wedge factors, VW factors (VWFs) and PW factors (PWFs) have a similar trend as a function of field size. PWFs have a stronger depth dependence than VWF due to beam hardening in PW fields. VW dose profiles in the wedge direction, in general, match very well with PW, except in the toe area of large wedge angles with large field sizes. Dose profiles in the nonwedge direction show a significant reduction in PW fields due to off-axis beam softening and oblique filtration. PW fields have significantly higher peripheral doses than open and VW fields. VW fields have similar surface doses as the open fields while PW fields have lower surface doses. Surface doses for both VW and PW increase with field size and slightly with wedge angle. For VW fields with wedge angles 45 degrees and less, the initial gap up to 3 cm is dosimetrically acceptable when compared to dose profiles of PW. VW fields in general use less monitor units than PW fields.

Implementation and verification of virtual wedge in a three-dimensional radiotherapy planning system

Virtual Wedge (VW) is a Siemens treatment modality which generates wedge-shaped dose distributions by moving a collimator jaw from closed to open at a constant speed while varying the dose rate in every 2 mm jaw position. In this work, the implementation and verification of VW in a radiotherapy treatment planning (RTP) system is presented. The VW implementation models the dose delivered by VW using the Siemens monitor units (MU) analytic formalism which determines the number of MU required to generate a wedge-fluence profile at points across the VW beam. For any set of treatment parameters, the VW algorithm generates an "intensity map" that is used to model the modification of fluence emanating from the collimator. The intensity map is calculated as the ratio of MU delivered on an axis point, divided by the monitor units delivered on the central-axis MU(0). The dose calculation is then performed using either the Clarkson or Convolution/ Superposition algorithms. The VW implementation also models the operational constraints for the delivery of VW due to dose rate and jaw speed limits. Dose verifications with measured profiles were performed using both the Clarkson and Convolution/Superposition algorithms for three photon beams; Siemens Primus 6 and 23 MV, and Mevatron MD 15 MV. Agreement within 2% or 2 mm was found between calculated and measured doses, over a large set of test cases, for 15, 30, 45, and 60 degree symmetric and asymmetric VW fields, using the manufacturer's supplied mu and c values for each beam.

Total scatter factors and tissue maximum ratios for small radiosurgery fields: comparison of diode detectors, a parallel-plate ion chamber, and radiographic film

Two p-type diode detectors, a parallel-plate ion chamber, and radiographic film were used to measure total scatter factors and tissue maximum ratios (TMRs) for a stereotactic radiosurgery system with circular fields ranging from 5 to 50 mm in diameter. One diode has a square detection diagonal of 2.3 mm and the other diode has a circular detection diameter of 1 mm. It is found that the two diodes measured essentially the same total scatter factors for all field sizes. Total scatter factors measured by film are within 3% of diode values. Our results also suggest that the parallel-plate ion chamber could underestimate total scatter factors for fields as large as 15 mm in diameter, although it is recommended for field diameters > or = 12.5 mm. The total scatter factors used in our clinic are combined from data measured with the ion chamber and the 2-mm-diam diode. The combined total scatter factors generally agree with published data. While film overestimates TMRs for the smallest fields at large depths because of energy dependence of the film, the measurements with the 1-mm-diam diode agree with published data measured with thermoluminescent dosimeters. It is demonstrated that the accurate measurements of total scatter factors and TMRs for small fields can be obtained by combining results of the commercially available detectors used in this study.

Structural and functional characterization of Kv6.2 a new gamma-subunit of voltage-gated potassium channel

We have cloned and functionally expressed Kv6.2, a new member of the Kv6 subfamily of voltage-gated potassium channel subunits. The human Kv6.2 (KCNF2) gene was mapped at 18q22-18q23. Kv6.2 mRNA is preferentially expressed in rat and human myocard. Rat and human Kv6.2 subunits appear to be unable to form functional Kv channels in a heterologous expression system, but, when coexpressed with Kv2.1 alpha subunits, heteromultimeric Kv channels were formed mediating voltage-activated delayed-rectifier type outward currents. Their kinetics and conductance-voltage relationship were different from those mediated by homomultimeric Kv2.1 channels. Yeast two-hybrid reporter assays indicated that Kv6.2 amino-termini are able to interact specifically with the Kv2.1 amino-terminus. It is proposed that this protein protein interaction underlies Kv2.1/Kv6.2 subunit assembly and the expression of functional heteromultimeric Kv2.1/Kv6.2 channels. The most resiliant feature of the Kv2.1/Kv6.2 channels was their submicromolar sensitivity to the antiarrhythmic drug propafenone. The data suggest that delayed-rectifier type channels containing Kv6.2 subunits may contribute to cardiac action potential repolarization.

Characterization of human Kv4.2 mediating a rapidly-inactivating transient voltage-sensitive K+ current

A human cDNA for the voltage-sensitive potassium channel subunit Kv4.2 has been cloned and functionally characterized. The human Kv4.2 (KCND2) gene was mapped at 7q31-32. Kv4.2 mRNA is prominently expressed in human brain. Relatively high concentrations of Kv4.2 mRNA occurred in mRNA preparations of amygdala, caudate nucleus, cerebellum, hippocampus, substantia nigra, and thalamus. Kv4.2 mRNA was not detected in human heart, kidney, liver, lung, pancreas, and skeletal muscle. The derived Kv4.2 open reading frame consists of 630 amino acids. In comparison to rat Kv4.2, the human Kv4.2 sequence is highly conserved showing amino acid sequence differences at five positions only. The Kv4.2 subunits were expressed heterologously in human embryonic kidney (293) cells and mediated a rapidly inactivating, A-type outward K+ current. The gating kinetics of the Kv4.2-mediated currents were very similar to those of rat Kv4.2-mediated currents. Both the Kv4.2 and Kv4.3 subunits have been implicated in mediating the transient outward K+ current Ito in rodent cardiac myocytes. In contrast we did not detect Kv4.2. but solely Kv4.3 mRNA in human heart RNA preparations. This may suggest that Kv4.2 subunits do not contribute to the rapid transient outward K+ current of atrial and ventricular myocytes in humans.

Geometric and dosimetric analysis of multileaf collimation conformity

BACKGROUND AND PURPOSE

There is concern over the stepped edges of multileaf collimator (MLC) fields for target coverage compared with those of cerrobend. Despite recent reports dispelling this concern, users are still cautious when using MLCs for small fields. Leaf orientation can be a problem if one is required to orient the leaves along an axis not ideal for conformity (such as dynamic or universal wedge cases). In this study we examined the dependence of MLC field conformity on field size and elongation.

MATERIALS AND METHODS

We examined circles of varying diameter and ellipses of varying eccentricity with leaves oriented along the major and minor axes of ellipses. The tests were both geometric, comparing areas of overblocking or underblocking (leaves inside and outside the field), and dosimetric, using radiographic films at depth in the beam's eye view plane.

RESULTS

For the geometric comparison there is a rapid increase in non-conformity, defined as the percentage of overblocking or underblocking area, as the circle diameter decreases. For ellipses, when the leaves move along one axis direction, the conformity does not depend on the diameter of the same axis, but instead improves as the dimension of the axis in the non-leaf motion direction increases. The best conformity is achieved when the maximum number of leaves is used to shape the field. When the dosimetry is analyzed, the predictability of these trends decreases due to the impact of undulations (scatter), leaf inaccuracies and dosimetric uncertainties.

CONCLUSIONS

We recommend that for small round fields MLC should be used with caution and that for ellipses the direction of leaf movement should be aligned with the minor axis whenever possible. Though these experiments are for idealized geometries, the observations can be applied to clinical fields. An MLC with a thinner leaf width could be beneficial for small round fields.

Multiple machine implementation of enhanced dynamic wedge

PURPOSE

After acquiring 4 years of experience with Dynamic Wedge, a software-driven one-dimensional (1D) compensation system, we implemented a new software version called Enhanced Dynamic Wedge (EDW). The EDW allows larger (30 cm) and asymmetric field sizes and additional angles for wedged fields. We implemented this software on four similar dual-energy accelerators that also possess upper and lower physical wedge sets. Our goal was to implement EDW with one common wedge factor (WF) table and one set of treatment-planning files.

METHODS AND MATERIALS

We measured WFs with an ionization chamber and isodose profiles with both film and a diode array. We used a calculation scheme that requires only entry of the wedge angle and fixed jaw value. Filters for computerized treatment planning were configured for each wedge angle. We also examined to what degree the multileaf collimation (MLC) orientation, which is orthogonal to the EDW direction, was compromised for specific treatment sites. As a comparative test, we examined the dosimetric consistency for the 8 sets of physical wedges on the four machines. Finally, we updated our DW quality assurance program for EDW.

RESULTS

The measured EDW WF was common for all four machines to within +/- 1.5% and the calculation scheme held to within 1.5%. The EDW isodoses were consistent among the machines as measured by film and diode array. The treatment-planning filters provided computed isodose profiles that were nearly identical to measured profiles. Regarding MLC orientation, we found that the collimator angle needed for EDW did not compromise isodose distributions, as apparent in measured isodoses and calculated dose-volume histograms. The consistency of the physical wedges did not fare as well. Two of the lower wedge sets had Wfs and profiles different (> 3%) from the other wedge sets.

CONCLUSIONS

We have successfully implemented EDW on four machines using only one WF table and one set of treatment-planning filters. The EDW provides for improved treatment techniques for particular sites due to the large field sizes and additional angles available. Daily treatment efficiency has increased because of the remote capability provided by EDW.

Integrin-mediated short-term memory in Drosophila

Volado is a new memory mutant of Drosophila. The locus encodes two isoforms of a new alpha-integrin, a molecule that dynamically mediates cell adhesion and signal transduction. The Volado gene is expressed preferentially in mushroom body cells, which are neurons known to mediate olfactory learning in insects. Volado proteins are concentrated in the mushroom body neuropil, brain areas that contain mushroom body processes in synaptic contact with other neurons. Volado mutants display impaired olfactory memories within 3 min of training, indicating that the integrin is required for short-term memory processes. Conditional expression of a Volado transgene during adulthood rescues the memory impairment. This rescue of memory is reversible, fading over time along with expression of the transgene. Thus the Volado integrin is essential for the physiological processes underlying memory. We propose a model in which integrins act as dynamic regulators of synapse structure or the signalling events underlying short-term memory formation.

The influence of angular misalignment on fixed-portal intensity modulated radiation therapy

A method has been developed to estimate potential dose errors due to linear accelerator angular setting misalignments of Intensity Modulated Radiation Therapy (IMRT) treatments. A first-order approximation to the dose error at a point is modeled as the dot product of the dose gradient and the shift vector of the point due to the rotational error. The analysis method is applied to a previously published set of optimized fluences for a 50 MV IMRT pelvis irradiation. Three of the published cases exhibiting a wide range of modulation are presented; a rectangular open field, a field optimized for a static multileaf collimator defining the portal outline coupled with a single broad bremsstrahlung profile modulation, and a fully modulated field using a physical modulator. To examine the energy dependence of angle setting errors, the study is repeated using the same fluence distributions, but with a dose-spread kernel appropriate for a 6 MV photon beam. The collimator angle error is set to 2 degree, and the dose error determined with both a centrally located isocenter and an isocenter chosen to model a split-field geometry. The dose error due to a 2 degree gantry setting error is assessed at a plane 10 cm distal to the isocenter. The mathematical form of the dose error due to couch motion is similar to the other two errors, so the dose error resulting from a couch angle missetting is not presented. The magnitude of the errors is largest for the 6 MV beam, while the volume encompassed by the errors is greater for the 50 MV beam. The gantry error yields the largest dose error values, with the 6 MV modulated case presenting dose errors of greater than 40%.

Measurement of a photon penumbra-generating kernel for a convolution-adapted ratio-TAR algorithm for 3D treatment planning

A method has been developed to measure a photon penumbra-generating kernel using dosimetry equipment available in most radiation therapy departments. The kernel is used in a convolution-adapted ratio-TAR algorithm in our three-dimensional treatment planning system. The kernel is assumed to be invariant with respect to off-axis position, axially symmetric, and is divided into short- and long-range components, with a different measurement technique for each. The data required to obtain the short-range component are measured by scanning across a split-field geometry incident on a water phantom. The derivative of the measured profile is proportional to one-dimensional projections across the kernel. Because the kernel is axially symmetric, only one profile measurement is required for each depth. A CT reconstruction technique is used to extract the radial dependence of the kernel from the strip integrals. Electronic noise in the acquisition system yields significant uncertainties in the kernel shape for distances beyond 3 cm. The long-range portion of the kernel is obtained by examining tissue-air ratios (TARs). The derivative of the TAR at the center of a circular field is proportional to the kernel value at the distance corresponding to the radius of the field. The kernel measurement method was tested by comparing measured and calculated square-field profiles at a variety of depths. Agreement was within 1% within the field boundary and 3% outside the field boundary for all depths.

A convolution-adapted ratio-TAR algorithm for 3D photon beam treatment planning

A convolution-adapted ratio of tissue-air ratios (CARTAR) method of dose calculation has been developed at the Mallinckrodt Institute of Radiology. This photon pencil-beam algorithm has been developed and implemented specifically for three-dimensional treatment planning. In a standard ratio of tissue-air ratios (RTAR) algorithm, doses to points in irregular field geometries are not adequately modeled. This is inconsistent with the advent of conformal therapy, the goal of which is to conform the dose distribution to the target volume while sparing neighboring sensitive normal critical structures. This motivated us to develop an algorithm that can model the beam penumbra near irregular field edges, while retaining much of the speed for the original RTAR algorithm. The dose calculation algorithm uses two-dimensional (2D) convolutions, computed by 2D fast Fourier transform, of pencil-beam kernels with a beam transmission array to calculate 2D off-axis profiles at a series of depths. These profiles are used to replace the product of the transmission function and measured square-field boundary factors used in the standard RTAR calculation. The 2D pencil-beam kernels were derived from measured data for each modality using commonly available dosimetry equipment. The CARTAR algorithm is capable of modeling the penumbra near block edges as well as the loss of primary and scattered beam in partially blocked regions. This paper describes the dose calculation algorithm, implementation, and verification.

minibrain: a new protein kinase family involved in postembryonic neurogenesis in Drosophila

The development of the adult central nervous system of Drosophila requires a precise and reproducible pattern of neuroblast proliferation during postembryonic neurogenesis. We show here that mutations in the minibrain (mnb) gene cause an abnormal spacing of neuroblasts in the outer proliferation center (opc) of larval brain, with the implication that mnb opc neuroblasts produce less neuronal progeny than do wild type. As a consequence, the adult mnb brain exhibits a specific and marked size reduction of the optic lobes and central brain hemispheres. The insufficient number of distinct neurons in mnb brains is correlated with specific abnormalities in visual and olfactory behavior. The mnb gene encodes a novel, cell type-specific serine-threonine protein kinase family that is expressed and required in distinct neuroblast proliferation centers during postembryonic neurogenesis. The mnb kinases share extensive sequence similarities with kinases involved in the regulation of cell division.

Frequenin--a novel calcium-binding protein that modulates synaptic efficacy in the Drosophila nervous system

The T(X;Y)V7 rearrangement in Drosophila has originally been recognized as a Shaker-like mutant because of its behavioral and electrophysiological phenotype. The gene whose expression is altered by the V7 rearrangement has been characterized. It encodes a novel Ca(2+)-binding protein named frequenin, which is related to recoverin and visinin. In vitro, the frequenin protein functions like recoverin as a Ca(2+)-sensitive guanylyl cyclase activator. Anti-frequenin antibodies stain the central and peripheral nervous system in Drosophila embryos and in larval and adult tissue sections. Frequenin appears to be particularly enriched in synapses, such as the motor nerve endings at neuromuscular junctions. Neuromuscular junctions of transgenic flies, which overexpress frequenin upon heat shock, exhibit an extraordinarily enhanced, frequency-dependent facilitation of neurotransmitter release, with properties identical to those observed in V7 junctions. We propose that frequenin represents a new element for the Ca(2+)-dependent modulation of synaptic efficacy.

Cloning of the crystalline cell wall protein gene of Bacillus licheniformis NM 105

A protein with a tetragonal pattern, defined as RS protein, was found on the wall surface of an alkaline phosphatase secretion-deficient mutant (NM 105) of Bacillus licheniformis 749/C. The protein was present on the wall surface of the exponential-growth-phase cells, but at the stationary growth phase it was overproduced and hypersecreted. This protein was precipitated to homogeneity from the culture fluid by 80% ammonium sulfate saturation and chilled acetone. The molecular mass of the protein was 98 kilodaltons, and it had a single subunit in a sodium dodecyl sulfate gel. Specific anti-RS antibody was generated in rabbits and used to immunolabel the RS protein on the cells at different growth phases. In early-exponential-growth-phase cells, the outside surface of the wall, the cytoplasm, and the inside surface of the cytoplasmic membrane were labeled. In stationary-growth-phase cells, the cytoplasm was poorly labeled, but the labeling on the outside surface of the wall was high. AB. licheniformis NM 105 gene library was made by using the lambda phage EMBL3. The RS protein expression from this gene library was detected by a modified autoradiographic procedure. One of the amplified RS protein-positive plaques (4213-1) containing recombinant DNA was chosen, and the restriction map of this DNA was prepared. The RS protein expressed in Escherichia coli NM 539 infected with 4213-1 recombinant phage had a lower molecular mass than the purified authentic RS protein. The 4.5-kilobase-pair (kbp) SalI-EcoRI fragment of the recombinant DNA was cloned in the shuttle plasmid pMK4 to construct pMK462, which was expressed in B. subtilis MI112 and produced the RS protein identical in molecular mass to the purified authentic RS protein. The RS protein expression was also demonstrated in cryosections of transformed E. coli and B. subtilis cells by immunoelectron microscopy. The 1.2-kbp SalI-HindIII and 1.8-kbp HindIII-HindIII recombinant DNA restriction enzyme fragments, respectively, from the right of the restriction map produced anti-RS antibody cross-reacting proteins. The expression of the 1.2-kbp SalI-HindIII DNA fragment cloned in pUC8 could be induced with isopropyl-beta-D-thiogalactopyranoside. The 1.8-kbp DNA restriction fragment hybridized with both the chromosomal DNA of strain NM 105 and the recombinant phage 4213-1 DNA. The RS gene expression was finally demonstrated in transformed E. coli 539 cells by in situ hybridization of frozen thin sections with the 1.8-kbp HindIII biotin-dATP probe and immunolabeling these with anti-biotin immunoglobulin G and protein A-gold.