[en] Plutonium, because of its self-irradiation by alpha decay, ages by means of lattice damage and helium in-growth. These integrated aging effects result in microstructural and physical property changes. Because these effects would normally require decades to measure, studies are underway to asses the effects of extended aging on the physical properties of plutonium alloys by incorporating roughly 7.5 wt% of highly specific activity isotope ²³⁸Pu into weapons-grade plutonium to accelerate the aging process. This paper presents updated results of self-irradiation effects on enriched and reference alloys measured from immersion density, dilatometry, and mechanical tests. After nearly 90 equivalent years of aging, both the immersion density and dilatometry show that the enriched alloys at 35 deg. C have decreased in density by ∼0.19% and now exhibit a near linear density decrease, without void swelling. Both tensile and compression measurements show that the aging process continues to increase the strength of plutonium alloys. (authors)

[en] Purpose: To estimate the local control and patterns of failure for pediatric patients with low-grade astroglial tumors (LGA) and ependymoma (EP) treated with three-dimensional conformal radiation therapy (CRT) using an anatomically defined clinical target volume (CTV). Methods and Materials: >From an ongoing, prospective Phase II trial initiated in July 1997, 102 pediatric patients with LGA (n=38) and EP (n=64) have been treated with CRT using an anatomically defined CTV extending 1.0 cm beyond the gross tumor volume and a 0.5-cm margin (planning target volume) extending outside of the CTV. The prescribed dose was 54 Gy (LGA) and 59.4 Gy (EP). Results: Patients with EP have been followed for a median of 17 months (range 3-43 months), and six failures have occurred. Patients with LGA have been followed for a median of 17 months (3-44 months), and four failures have occurred. Three-dimensional magnetic resonance (MR) studies performed to document treatment failure were registered with the MR and computed tomography (CT) data used in the treatment planning process. Failure occurred within the CTV for 5 patients with EP, including 3 with concurrent subarachnoid dissemination. One patient with EP developed metastatic disease with no evidence of local failure. Three patients with LGA failed within the CTV and one failed immediately outside of the CTV. Conclusions: Treatment of an anatomically defined CTV, encompassing 1.0 cm of noninvolved brain beyond the margin of resection or neuroimaging-defined tumor, appears to be safe for pediatric patients with LGA and EP based on these preliminary data. Normal tissue sparing through the use of advanced radiation therapy treatment planning and delivery techniques should be beneficial to pediatric patients if the rate and patterns of failure are similar to conventional techniques and toxicity reduction can be objectively documented

[en] We present changes in volume, immersion density, and tensile property observed from accelerated aged plutonium alloys. Accelerated alloys (or spiked alloys) are plutonium alloys enriched with approximately 7.5 weight percent of the faster-decaying ²³⁸Pu to accelerate the aging process by approximately 17 times the rate of un-aged weapons-grade plutonium. After sixty equivalent years of aging on spiked alloys, the dilatometry shows the samples at 35 C have swelled in volume by 0.15 to 0.17 % and now exhibit a near linear volume increase due to helium in-growth. The immersion density of spiked alloys shows decrease in density, similar normalized volumetric changes (expansion) for spiked alloys. Tensile tests show increasing yield and engineering ultimate strength as spiked alloys are aged. (authors)

[en] Purpose: To provide evidence that radiation therapy alone in the form of craniospinal irradiation (CSI) and a boost to the primary site of disease provides effective disease control and limited additional morbidity for patients with CNS germinoma. Methods and Materials: Twelve patients with a median age of 12 years (range 9-16 years) with CNS germinoma were treated with CSI (median 25.6 Gy, range 23.4-32 Gy) and a boost to the primary site of disease (50.4 Gy, range 45-54 Gy) between January 1987 and June 1998. All patients were biopsied prior to radiation therapy and none received chemotherapy. No patients were lost to follow-up and the majority had long-term (> 45 month) pre- and postirradiation endocrine and psychology assessment. Results: All 12 patients are alive and no failures have occurred with a median follow-up of 69 months (range 14-143 months). Preirradiation endocrine deficiencies were present in 6 of 6 suprasellar tumors and 1 of 6 pineal tumors; with follow-up there was no substantial difference between age and gender adjusted pre- and postirradiation stature and weight. With long-term follow-up, there were no significant differences between pre- and postirradiation full-scale, verbal, and performance IQ scores. Conclusions: This study confirms the ability of radiation therapy alone to achieve disease control with a high rate of success in pediatric patients and demonstrates that the treatment toxicity faced by these patients may be less than anticipated. Because these patients present with substantial preexisting morbidity at diagnosis and may be of an age where the potential for radiation-related side effects is relatively small, the superiority of treatment alternatives may be difficult to prove

[en] Purpose: To review our institution's experience in the treatment of craniopharyngioma and assess the merits of initial therapy with limited surgery and irradiation. Methods and Materials: The data of 30 patients (median age 8.6 years) with a diagnosis of craniopharyngioma between April 1984 and September 1997 were reviewed. Their course of treatment, neurologic, endocrine, and cognitive function, and quality of life at last follow-up were compared. Results: Fifteen patients were initially treated with surgery (8 required irradiation after relapse) and 15 with limited surgery and irradiation (2 required additional treatment for tumor progression). Only 1 patient died of tumor progression. The surgery group lost a mean of 9.8 points in full-scale IQ, and the combined-modality group lost only 1.25 points (p<0.063). Patients in the surgery group who had relapses (n=9) lost a mean of 13.1 points (p<0.067). A loss of 10 points was considered clinically significant. The surgery group also had more frequent neurologic, ophthalmic, and endocrine complications. The mean Health Utility Index (a functional quality-of-life index) was higher for the combined-modality group (0.85) than for the surgery group (0.71; p<0.063, one-sided t test). Conclusions: The acute neurologic, cognitive, and endocrine effects of surgery often affect long-term function and quality of life. Our experience suggests that limited surgery and radiotherapy cause lesser or comparable sequelae. Diabetes insipidus was the only endocrine deficiency that differed substantially in frequency between the two groups. Newer radiation planning and delivery techniques may make a combined-modality approach a good initial option for most patients

[en] Flat-panel (FP) based digital radiography systems have recently been introduced as a new and improved digital radiography technology; it is important to evaluate and compare this new technology with currently widely used conventional screen/film (SF) and computed radiography (CR) techniques. In this study, the low-contrast performance of an amorphous silicon/cesium iodide (aSi/CsI)-based flat-panel digital chest radiography system is compared to those of a screen/film and a computed radiography system by measuring their contrast-detail curves. Also studied were the effects of image enhancement in printing the digital images and dependence on kVp and incident exposure. It was found that the FP system demonstrated significantly better low-contrast performance than the SF or CR systems. It was estimated that a dose savings of 70%-90% could be achieved to match the low-contrast performance of the FP images to that of the SF images. This dose saving was also found to increase with the object size. No significant difference was observed in low-contrast performances between the SF and CR systems. The use of clinical enhancement protocols for printing digital images was found to be essential and result in better low-contrast performance. No significant effects were observed for different kVps. From the results of this contrast-detail phantom study, the aSi/CsI-based flat-panel digital chest system should perform better under clinical situations for detection of low-contrast objects such as lung nodules. However, proper processing prior to printing would be essential to realizing this better performance

[en] Purpose: To investigate the influence of histologic grade on progression-free survival (PFS) after irradiation (RT) for pediatric patients with localized ependymoma. Methods and Materials: Fifty patients with localized ependymoma (median age 3.6 years, range 1-18 years at the time of RT) were treated with RT between December 1982 and June 1999. Anaplastic features were identified in 14 of 50 patients. The extent of resection was characterized as gross-total in 36 patients, near-total in 5, and subtotal in 9. The median dose to the primary site was 54 Gy. Of the 50 patients, 23 received pre-RT chemotherapy. Results: Thirty-nine patients were alive at a median follow-up of 46 months (range 21-214) from diagnosis. Thirty-four patients remained progression free at a median follow-up of 35 months (range 13-183) after the initiation of RT. Progression occurred in 16 patients (12 local and 4 local and distant), with a median time to failure of 21.2 months (range 4.6-65.0). The tumor grade significantly influenced the PFS after RT (p<0.0005). The estimated 3-year PFS rate was 28%±14% for patients with anaplastic ependymoma compared with 84% ± 8% for patients with differentiated ependymoma. These results remained significant when corrected for age at diagnosis (<3 years), pre-RT chemotherapy, and extent of resection. Patients who received pre-RT chemotherapy had an inferior 3-year PFS estimate after RT (49±12%) compared with those who did not (84%±10%; p=0.056). Anaplastic ependymoma was found more frequently in the supratentorial brain (p=0.002). Six of 12 patients with supratentorial tumor developed recurrence; recurrence was restricted to patients with anaplastic ependymoma. Conclusion: Tumor grade influences outcome for patients with ependymoma independent of other factors and should be considered in the design and analysis of prospective trials involving pediatric patients treated with RT. Chemotherapy before RT influences the PFS and overall survival after RT. The effect is more pronounced when progression occurs during chemotherapy

[en] Dual energy detector systems are combinations of x-ray detectors, x-ray source spectrum switching, and x-ray filter attenuation that provide two measurements of transmitted flux through the object with different effective spectra. We describe technology independent methods to measure and compare the quantum noise and sensitivity to motion artifacts of these systems. The experimental methods use relatively simple phantoms to measure the parameters in the general mathematical expressions for the noise in the subtracted image. The parameters are used to compute an x-ray energy spectrum quality factor and a subtracted image noise per unit patient dose quality factor. Patient motion causes artifacts in switched spectrum systems, particularly with the heart in chest radiography. We describe a method to measure effective interexposure time using subtracted image data of a uniformly moving object. This parameter measures the sensitivity to patient motion artifacts. We use these methods to compare three examples of systems with different dual energy detector technologies: a passive, 'sandwich' detector with two computed radiography plates separated by a copper filter, an 'active' detector that uses voltage switching with an electro-optical system and computed radiography plates, and a flat-panel, solid state detector with voltage switching

[en] We present dimensional and density changes in an aging plutonium alloy enriched with 7.3 at.% of ²³⁸Pu and reference alloys of various ages. After 45 equivalent years of aging, the enriched alloys at 35 deg. C have swelled in length by 0.048-0.052% and now exhibit a near linear dimensional increase, without void swelling. Based on X-ray diffraction measurements, the lattice expansion by self-irradiation appears to be the primary cause for dimensional changes during the initial 2-3 years of aging. Following the initial transient, the density change is primarily cause by a constant helium in-growth rate as a result of α-particle decay

[en] Crystalline metal (IV) phosphates with variable zirconium-to-titanium molar ratios of general formula (Ti_1-xZr_x)(HPO₄)₂.H₂O have been prepared by precipitation of soluble salts of the metals with phosphoric acid and heating the amorphous solids in 12 M H₃PO₄ in an autoclave. The new materials are structurally characterised by Rietveld analysis of synchrotron X-ray powder diffraction data and pair distribution function (PDF) analysis of high energy synchrotron X-ray total scattering data. A broad range of zirconium-titanium phosphate solid solutions were formed showing isomorphous substitution of titanium by zirconium in the α-titanium phosphate lattice and vice versa for titanium substitution into the α-zirconium phosphate lattice. In both cases the solubility is partial with the coexistence of two substituted phases observed in samples with nominal compositions between the solubility limits. - Graphical abstract: Layered phosphates of general formula (Ti_1-xZr_x)(HPO₄).H₂O have been prepared by the hydrothermal treatment of amorphous gels in phosphoric acid and characterised by Rietveld analysis of high resolution synchrotron X-ray powder diffraction data and pair distribution function analysis of high energy synchrotron X-ray total scattering data.