[en] Some of the difficulties encountered during the construction of the approach jetty at the Madras Atomic Power Project, Kalpakkam are reported. The practices found desirable for getting good results in designing mixes, mixing and placement of good quality concrete are discussed. (M.G.B.)

[en] In this paper we report the rapid synthesis of Se-Te based chalcogenide glasses through microwave irradiation without the help of metal powders. Mixtures of chalcogens can be made to couple to microwaves when at least one constituent of the mixture has a relatively higher electrical conductivity. Also, this constituent has to be in powder form. The glasses thus prepared have been characterized by thermal analysis and x-ray analysis, and it has been confirmed that the T_g values of our samples are comparable to the already reported T_g values for samples prepared by conventional methods. Thus, this type of rapid synthesis may replace the prolonged conventional procedures for synthesis of these glasses

[en] Purpose: The Integral Quality Monitor (IQM), developed by iRT Systems GmbH (Koblenz, Germany) is a large-area, linac-mounted ion chamber used to monitor photon fluence during patient treatment. Our previous work evaluated the change of the ion chamber’s response to deviations from static 1×1 cm2 and 10×10 cm2 photon beams and other characteristics integral to use in external beam detection. The aim of this work is to simulate two external beam radiation delivery errors, quantify the detection of simulated errors and evaluate the reduction in patient harm resulting from detection. Methods: Two well documented radiation oncology delivery errors were selected for simulation. The first error was recreated by modifying a wedged whole breast treatment, removing the physical wedge and calculating the planned dose with Pinnacle TPS (Philips Radiation Oncology Systems, Fitchburg, WI). The second error was recreated by modifying a static-gantry IMRT pharyngeal tonsil plan to be delivered in 3 unmodulated fractions. A radiation oncologist evaluated the dose for simulated errors and predicted morbidity and mortality commiserate with the original reported toxicity, indicating that reported errors were approximately simulated. The ion chamber signal of unmodified treatments was compared to the simulated error signal and evaluated in Pinnacle TPS again with radiation oncologist prediction of simulated patient harm. Results: Previous work established that transmission detector system measurements are stable within 0.5% standard deviation (SD). Errors causing signal change greater than 20 SD (10%) were considered detected. The whole breast and pharyngeal tonsil IMRT simulated error increased signal by 215% and 969%, respectively, indicating error detection after the first fraction and IMRT segment, respectively. Conclusion: The transmission detector system demonstrated utility in detecting clinically significant errors and reducing patient toxicity/harm in simulated external beam delivery. Future work will evaluate detection of other smaller magnitude delivery errors.

[en] Purpose: A new transmission detector, Delta4 Discover, developed by Scandidos (Uppsala, Sweden) was evaluated for external photon beam verification and quality assurance. The device is an array of 4040 diodes designed to be mounted on the linac accessory tray to measure photon field shape, position and fluence during patient treatment. Interfractional measurements are compared to a baseline measurement made during delivery quality assurance. The aim of this work is to evaluate the stability of the device and its effect on the shape and magnitude of the treatment beam. Methods: Beam profiles, percent depth dose, and beam attenuation was measured for 6, 10, and 15 MV photon beams with and without the device in place for 1×1 and 30×30 cm2 fields. Changes in profile and percent depth dose was quantified to evaluate the need to recommission the treatment beam, or account for the device with a tray factor. The stability of the radiation measurements was evaluated by measuring the deviation of each diode measurement during repeated prostate VMAT treatment delivery. Results: Photon beam profiles changed by < 1.25% in the nonpenumbra regions of the 30×30 cm2 beam. Percent depth dose curves show a 5–7% increased dose at depths < 2.5cm, but agreed within 1% at depths > 2.5cm. This indicates increased skin dose, similar to the use of a physical beam wedge. The device attenuated 6, 10, and 15 MV photon beams by 1.71±0.02%, 1.36±0.03%, and 1.17±0.03%, respectively. The diode array reproduced dosimetric measurements within 0.5% standard deviation for repeated prostate VMAT measurement. Conclusion: The device demonstrated stabile radiation measurements, while not changing the treatment beam shape in a clinically significantly manner. Use of this device can be accounted for with a tray factor, as opposed to recommissioning the treatment beam.

[en] Purpose: We aim to evaluate a new commercial dose mimicking inverse-planning application that was designed to provide cross-platform treatment planning, for its dosimetric quality and efficiency. The clinical benefit of this application allows patients treated on O-shaped linac to receive an equivalent plan on conventional L-shaped linac as needed for workflow or machine downtime. Methods: The dose mimicking optimization process seeks to create a similar DVH of an O-shaped linac-based plans with an alternative treatment technique (IMRT or VMAT), by maintaining target conformity, and penalizing dose falloff outside the target. Ten head and neck (HN) helical delivery plans, including simple and complex cases were selected for re-planning with the dose mimicking application. All plans were generated for a 6 MV beam model, using 7-field/ 9-field IMRT and VMAT techniques. PTV coverage (D1, D99 and homogeneity index [HI]), and OARs avoidance (Dmean / Dmax) were compared. Results: The resulting dose mimicked HN plans achieved acceptable PTV coverage for HI (VMAT 7.0±2.3, 7-fld 7.3±2.4, and 9-fld 7.0±2.4), D99 (98.0%±0.7%, 97.8%±0.7%, and 98.0%±0.7%), as well as D1 (106.4%±2.1%, 106.5%±2.2%, and 106.4%±2.1%), respectively. The OAR dose discrepancy varied: brainstem (2% to 4%), cord (3% to 6%), esophagus (−4% to −8%), larynx (−4% to 2%), and parotid (4% to 14%). Mimicked plans would typically be needed for 1–5 fractions of a treatment course, and we estimate <1% variance would be introduced in target coverage while maintaining comparable low dose to OARs. All mimicked plans were approved by independent physician and passed patient specific QA within our established tolerance. Conclusion: Dose mimicked plans provide a practical alternative for responding to clinical workflow issues, and provide reliability for patient treatment. The quality of dose mimicking for HN patients highly depends on the delivery technique, field numbers and angles, as well as user selection of structures.

[en] In nuclear network calculations especially the p-nucleus ⁹²Mo is frequently underproduced. Since experimental data of the photodisintegration of ⁹²Mo so far do not exist, it was necessary to measure the reaction yields with the photoactivation method using the brems-strahlung facility ELBE at FZ Dresden-Rossendorf. Also the reaction ¹⁰⁰Mo(γ,n) could be tested while irradiating Mo samples of natural composition. The photon fluence was measured with nuclear resonance fluorescence (NRF) of strong and well-known transitions in ¹¹B. As a normalization standard the photoactivation reaction ¹⁹⁷Au(γ,n) was used. For the 65 s half-life of ^91mMo a fast pneumatic delivery was used. The photoactivation yields of the (γ,p) and (γ,n) reactions are compared to yield integrals of the bremsstrahlung spectral shape folded with the cross sections derived from Hauser-Feshbach nuclear model calculations using the TALYS program and cross sections from earlier experiments.

[en] Purpose: Clinical workflow and machine down time occasionally require patients to be temporarily treated on a system other than the initial treatment machine. A new commercial dose mimicking application provides automated cross-platform treatment planning to expedite this clinical flexibility. The aim of this work is to evaluate the feasibility of automatic plan creation and establish a robust clinical workflow for prostate and pelvis patients. Methods: Five prostate and five pelvis patients treated with helical plans were selected for re-planning with the dose mimicking application, covering both simple and complex scenarios. Two-arc VMAT and 7- and 9-field IMRT plans were generated for each case, with the objective function of achieving similar dose volume histogram from the initial helical plans. Dosimetric comparisons include target volumes and organs at risk (OARs) (rectum, bladder, small bowel, femoral heads, etc.). Dose mimicked plans were evaluated by a radiation oncologist, and patient-specific QAs were performed to validate delivery. Results: Overall plan generation and transfer required around 30 minutes of dosimetrist’s time once the dose-mimicking protocol is setup for each site. The resulting VMAT and 7- and 9-field IMRT plans achieved equivalent PTV coverage and homogeneity (D99/DRx = 97.3%, 97.2%, 97.2% and HI = 6.0, 5.8, and 5.9, respectively), compared to helical plans (97.6% and 4.6). The OAR dose discrepancies were up to 6% in rectum Dmean, but generally lower in bladder, femoral heads, bowel and penile bulb. In the context of 1–5 fractions, the radiation oncologist evaluated the dosimetric changes as not clinically significant. All delivery QAs achieved >90% pass with a 3%/3mm gamma criteria. Conclusion: The automated dose-mimicking workflow offers a strategy to avoid missing treatment fractions due to machine down time with non-clinically significant changes in dosimetry. Future work will further optimize dose mimicking plans and investigate other cross-platform treatment delivery options.

[en] The cure kinetics of a composite solid propellant premix based on ammonium perchlorate, hydroxyl-terminated polybutadiene (HTPB) and diisocyanate system was investigated using a rheometer. The cross-linking kinetics of HTPB resin in the presence of tolylene diisocyanate in a propellant was studied under isothermal conditions in the temperature range of 60–70 °C by rheometry. The kinetic parameters of the curing reaction were calculated from the rheological measurements. These parameters were derived by a multiple regression analysis using a classical phenomenological model expanded by an empirically derived diffusion factor. The obtained kinetic parameters were used to generate a master equation capable of predicting the reaction profile at any given temperature. Excellent match between observed and predicted cure profiles in the entire temperature range validated the adequacy of the model.

[en] The neutron deficient p-nuclei are shielded from the s- or r-process by stable isotopes. P-nuclei are likely to be formed in high temperature cosmic scenarios like exploding supernovae by photodisintegration reactions on heavy r- or s- seed nuclei. The lack of experimental information on energy-dependent cross sections especially for (γ,p) and (γ,α) reactions reduces the applicability of nucleosynthesis models. Using intense bremsstrahlung produced at the superconducting electron linear accelerator ELBE at Forschungszentrum Dresden-Rossendorf we investigated (γ,n), (γ,p) and (γ,α) reactions for the medium-mass p-nuclei ⁹²Mo and ¹⁴⁴Sm, as well as (γ,n) reactions for ¹⁰⁰Mo and ¹⁵⁴Sm by photo-activation. The lowest photoactivation yields have been measured in an underground laboratory. The photodisintegration of ¹⁹⁷Au serves as a benchmark and it is compared to data measured previously with the positron annihilation technique.

[en] Purpose: A novel scatter imaging modality is developed and its feasibility for image-guided radiation therapy (IGRT) during stereotactic body radiation therapy (SBRT) for lung cancer patients is assessed using analytic and Monte Carlo models as well as experimental testing. Methods: During treatment, incident radiation interacts and scatters from within the patient. The presented methodology forms an image of patient anatomy from the scattered radiation for real-time localization of the treatment target. A radiographic flat panel-based pinhole camera provides spatial information regarding the origin of detected scattered radiation. An analytical model is developed, which provides a mathematical formalism for describing the scatter imaging system. Experimental scatter images are acquired by irradiating an object using a Varian TrueBeam accelerator. The differentiation between tissue types is investigated by imaging simple objects of known compositions (water, lung, and cortical bone equivalent). A lung tumor phantom, simulating materials and geometry encountered during lung SBRT treatments, is fabricated and imaged to investigate image quality for various quantities of delivered radiation. Monte Carlo N-Particle (MCNP) code is used for validation and testing by simulating scatter image formation using the experimental pinhole camera setup. Results: Analytical calculations, MCNP simulations, and experimental results when imaging the water, lung, and cortical bone equivalent objects show close agreement, thus validating the proposed models and demonstrating that scatter imaging differentiates these materials well. Lung tumor phantom images have sufficient contrast-to-noise ratio (CNR) to clearly distinguish tumor from surrounding lung tissue. CNR=4.1 and CNR=29.1 for 10MU and 5000MU images (equivalent to 0.5 and 250 second images), respectively. Conclusion: Lung SBRT provides favorable treatment outcomes, but depends on accurate target localization. A comprehensive approach, employing multiple simulation techniques and experiments, is taken to demonstrate the feasibility of a novel scatter imaging modality for the necessary real-time image guidance