Trends in low temperature and non-thermal technologies for the degradation of persistent organic pollutants.

The daunting effects of persistent organic pollutants on humans, animals, and the environment cannot be overemphasized. Their fate, persistence, long-range transport, and bioavailability have made them an environmental stressor of concern which has attracted the interest of the research community. Concerted efforts have been made by relevant organizations utilizing legislative laws to ban their production and get rid of them completely for the sake of public health. However, they have remained refractive in different compartments of the environment. Their bioavailability is majorly a function of different anthropogenic activities. Landfilling and incineration are among the earliest classical means of environmental remediation of waste; however, they are not sustainable due to the seepage of contaminants in landfills, the release of toxic gases into the atmosphere and energy requirements during incineration. Other advanced waste destruction technologies have been explored for the degradation of these recalcitrant pollutants; although, some are efficient, but are limited by high amounts of energy consumption, the use of organic solvents and hazardous chemicals, high capital and operational cost, and lack of public trust. Thus, this study has systematically reviewed different contaminant degradation technologies, their efficiency, and feasibility. Finally, based on techno-economic feasibility, non-invasiveness, efficiency, and environmental friendliness; radiation technology can be considered a viable alternative for the environmental remediation of contaminants in all environmental matrices at bench-, pilot-, and industrial-scale.

Evaluation of RADIANCE Monte Carlo algorithm for treatment planning in electron based Intraoperative Radiotherapy (IOERT).

PURPOSE: To perform experimental as well as independent Monte Carlo (MC) evaluation of the MC algorithm implemented in RADIANCE version 4.0.8, a dedicated treatment planning system (TPS) for 3D electron dose calculations in intraoperative radiation therapy (IOERT). METHODS AND MATERIALS: The MOBETRON 2000 (IntraOp Medical Corporation, Sunnyvale, CA) IOERT accelerator was employed. PDD and profiles for five cylindrical plastic applicators with 50-90 mm diameter and 0°, 30° beveling were measured in a water phantom, at nominal energies of 6, 9 and 12 MeV. Additional PDD measurements were performed for all the energies without applicator. MC modeling of the MOBETRON was performed with the user code BEAMnrc and egs_chamber of the MC simulation toolkit EGSnrc. The generated phase space files of the two 0°-bevel applicators (50 mm, 80 mm) and three energies in both RADIANCE and BEAMnrc, were used to determine PDD and profiles in various set-ups of virtual water phantoms with air and bone inhomogeneities. 3D dose distributions were also calculated in image data sets of an anthropomorphic tissue-equivalent pelvis phantom. Image acquisitions were realized with a CT scanner (Philips Big Bore CT, Netherlands). Gamma analysis was applied to quantify the deviations of the RADIANCE calculations to the measurements and EGSnrc calculations. Gamma criteria normalized to the global maximum were investigated between 2%, 2 mm and 3%, 3 mm. RESULTS: RADIANCE MC calculations satisfied the gamma criteria of 3%, 3 mm with a tolerance limit of 85% passing rate compared to in- water phantom measurements, except for the dose profiles of the 30° beveled applicators. Mismatches lay in surface doses, in umbra regions and in the beveled end of the 30° applicators. A very good agreement to the EGSnrc calculations in heterogeneous media was observed. Deviations were more pronounced for the larger applicator diameter and higher electron energy. In 3D dose comparisons in the anthropomorphic phantom, gamma passing rates were higher than 96 % for both simulated applicators. CONCLUSIONS: RADIANCE MC algorithm agrees within 3%, 3 mm criteria with in-water phantom measurements and EGSnrc MC dose distributions in heterogeneous media for 0°-bevel applicators. The user should be aware of missing scattering components and the 30° beveled applicators should be used with attention.

Monte Carlo calculated beam quality correction factors for high energy electron beams.

PURPOSE: As the dosimetry protocol TRS 398 is being revised and the ICRU report 90 provides new recommendations for density correction as well as the mean ionization energies of water and graphite, updated beam quality correction factors kQ are calculated for reference dosimetry in electron beams and for independent validation of previously determined values. METHODS: Monte Carlo simulations have been performed using EGSnrc to calculate the absorbed dose to water and the dose to the active volumes of ionization chambers SNC600c, SNC125c and SNC350p (all Sun Nuclear, A Mirion Medical Company, Melbourne, FL). Realistic clinical electron beam spectra were used to cover the entire energy range of therapeutic electron accelerators. The Monte Carlo simulations were validated by measurements on a clinical linear accelerator. With regards to the cylindrical chambers, the simulations were performed according to the setup recommendations of TRS 398 and AAPM TG 51, i.e. with and without consideration of a reference point shift by rcav/2. RESULTS: kQ values as a function of the respective beam quality specifier R50 were fitted by recommended equations for electron beam dosimetry in the range of 5 MeV to 18 MeV. The fitting curves to the calculated values showed a root mean square deviation between 0.0016 and 0.0024. CONCLUSION: Electron beam quality correction factors kQ were calculated by Monte Carlo simulations for the cylindrical ionization chambers SNC600c and SNC125c as well as the plane parallel ionization chamber SNC350p to provide updated data for the TRS 398 and TG 51 dosimetry protocols.

Clinical feasibility of combining intraoperative electron radiation therapy with minimally invasive surgery: a potential for electron-FLASH clinical development

Background Local cancer therapy by combining real-time surgical exploration and resection with delivery of a single dose of high-energy electron irradiation entails a very precise and effective local therapeutic approach. Integrating the benefits from minimally invasive surgical techniques with the very precise delivery of intraoperative electron irradiation results in an efficient combined modality therapy. Methods Patients with locally advanced disease, who are candidates for laparoscopic and/or thoracoscopic surgery, received an integrated multimodal management. Preoperative treatment included induction chemotherapy and/or chemoradiation, followed by laparoscopic surgery and intraoperative electron radiation therapy. Results In a period of 5 consecutive years, 125 rectal cancer patients were treated, of which 35% underwent a laparoscopic approach. We found no differences in cancer outcomes and tolerance between the open and laparoscopic groups. Two esophageal cancer patients were treated with IOeRT during thoracoscopic resection, with the resection specimens showing intense downstaging effects. Two oligo-recurrent prostatic cancer patients (isolated nodal progression) had a robotic-assisted surgical resection and post-lymphadenectomy electron boost on the vascular and lateral pelvic wall. Conclusions Minimally invasive and robotic-assisted surgery is feasible to combine with intraoperative electron radiation therapy and offers a new model explored with electron-FLASH beams (AU)

A Highly Versatile X-ray and Electron Beam Diamond Dosimeter for Radiation Therapy and Protection.

Radiotherapy is now recognized as a pillar in the fight against cancer. Two different types are currently used in clinical practice: (1) external beam radiotherapy, using high-energy X-rays or electron beams, both in the MeV-range, and (2) intraoperative radiotherapy, using low-energy X-rays (up to 50 keV) and MeV-range electron beams. Versatile detectors able to measure the radiation dose independently from the radiation nature and energy are therefore extremely appealing to medical physicists. In this work, a dosimeter based on a high-quality single-crystal synthetic diamond sample was designed, fabricated and characterized under low-energy X-rays, as well as under high-energy pulsed X-rays and electron beams, demonstrating excellent linearity with radiation dose and dose-rate. Detector sensitivity was measured to be 0.299 ± 0.002 µC/Gy under 6 MeV X-ray photons, and 0.298 ± 0.004 µC/Gy under 6 MeV electrons, highlighting that the response of the diamond dosimeter is independent of the radiation nature. Moreover, in the case of low-energy X-rays, an extremely low limit of detection (23 nGy/s) was evaluated, pointing out the suitability of the device to radiation protection dosimetry.

Clinical feasibility of combining intraoperative electron radiation therapy with minimally invasive surgery: a potential for electron-FLASH clinical development.

BACKGROUND: Local cancer therapy by combining real-time surgical exploration and resection with delivery of a single dose of high-energy electron irradiation entails a very precise and effective local therapeutic approach. Integrating the benefits from minimally invasive surgical techniques with the very precise delivery of intraoperative electron irradiation results in an efficient combined modality therapy. METHODS: Patients with locally advanced disease, who are candidates for laparoscopic and/or thoracoscopic surgery, received an integrated multimodal management. Preoperative treatment included induction chemotherapy and/or chemoradiation, followed by laparoscopic surgery and intraoperative electron radiation therapy. RESULTS: In a period of 5 consecutive years, 125 rectal cancer patients were treated, of which 35% underwent a laparoscopic approach. We found no differences in cancer outcomes and tolerance between the open and laparoscopic groups. Two esophageal cancer patients were treated with IOeRT during thoracoscopic resection, with the resection specimens showing intense downstaging effects. Two oligo-recurrent prostatic cancer patients (isolated nodal progression) had a robotic-assisted surgical resection and post-lymphadenectomy electron boost on the vascular and lateral pelvic wall. CONCLUSIONS: Minimally invasive and robotic-assisted surgery is feasible to combine with intraoperative electron radiation therapy and offers a new model explored with electron-FLASH beams.

FLASH radiotherapy treatment planning and models for electron beams.

The FLASH effect designates normal tissue sparing at ultra-high dose rate (UHDR, >40 Gy/s) compared to conventional dose rate (∼0.1 Gy/s) irradiation while maintaining tumour control and has the potential to improve the therapeutic ratio of radiotherapy (RT). UHDR high-energy electron (HEE, 4-20 MeV) beams are currently a mainstay for investigating the clinical potential of FLASH RT for superficial tumours. In the future very-high energy electron (VHEE, 50-250 MeV) UHDR beams may be used to treat deep-seated tumours. UHDR HEE treatment planning focused at its initial stage on accurate dosimetric modelling of converted and dedicated UHDR electron RT devices for the clinical transfer of FLASH RT. VHEE treatment planning demonstrated promising dosimetric performance compared to clinical photon RT techniques in silico and was used to evaluate and optimise the design of novel VHEE RT devices. Multiple metrics and models have been proposed for a quantitative description of the FLASH effect in treatment planning, but an improved experimental characterization and understanding of the FLASH effect is needed to allow for an accurate and validated modelling of the effect in treatment planning. The importance of treatment planning for electron FLASH RT will augment as the field moves forward to treat more complex clinical indications and target sites. In this review, TPS developments in HEE and VHEE are presented considering beam models, characteristics, and future FLASH applications.

Nontarget and Out-of-Field Doses from Electron Beam Radiotherapy.

In clinical radiotherapy, the most important aspects are the dose distribution in the target volume and healthy organs, including out-of-field doses in the body. Compared to photon beam radiation, dose distribution in electron beam radiotherapy has received much less attention, mainly due to the limited range of electrons in tissues. However, given the growing use of electron intraoperative radiotherapy and FLASH, further study is needed. Therefore, in this study, we determined out-of-field doses from an electron beam in a phantom model using two dosimetric detectors (diode E and cylindrical Farmer-type ionizing chamber) for electron energies of 6 MeV, 9 MeV and 12 MeV. We found a clear decrease in out-of-field doses as the distance from the field edge and depth increased. The out-of-field doses measured with the diode E were lower than those measured with the Farmer-type ionization chamber at each depth and for each electron energy level. The out-of-field doses increased when higher energy megavoltage electron beams were used (except for 9 MeV). The out-of-field doses at shallow depths (1 or 2 cm) declined rapidly up to a distance of 3 cm from the field edge. This study provides valuable data on the deposition of radiation energy from electron beams outside the irradiation field.

Adding customized electron energy beams to TrueBeam linear accelerators.

PURPOSE: To better meet clinical needs and facilitate optimal treatment planning, we added two new electron energy beams (7 and 11 MeV) to two Varian TrueBeam linacs. METHODS: We worked with the vendor to create two additional customized electron energies without hardware modifications. For each beam, we set the bending magnet current and then optimized other beam-specific parameters to achieve depths of 50% ionization (I50 ) of 2.9 cm for 7 MeV and 4.2 cm for the 11 MeV beam with the 15 × 15 cm2 cone at 100 cm source-to-surface distance (SSD) by using an ionization chamber profiler (ICP) with a double-wedge (DW) phantom. Beams were steered and balanced to optimize symmetry with the ICP. After all parameters were set, full commissioning was done including measuring beam profiles, percent depth doses (PDDs), output factors (OFs) at standard, and extended SSDs. Measured data were compared between the two linacs and against the values calculated by our RayStation treatment planning system (TPS) following Medical Physics Practice Guideline 5.a (MPPG 5.a) guidelines. RESULTS: The I50 values initially determined with the ICP/DW agreed with those from a PDD-scanned in-water phantom within 0.2 mm for the 7 and 11 MeV on both linacs. Comparison of the beam characteristics from the two linacs indicated that flatness and symmetry agreed within 0.4%, and point-by-point differences in PDD were within 0.01% ± 0.3% for the 7 MeV and 0.01% ± 0.3% for the 11 MeV. The OF ratios between the two linacs were 1.000 ± 0.007 for the 7 MeV and 1.004 ± 0.007 for the 11 MeV. Agreement between TPS-calculated outputs and measurements were -0.1% ± 1.0% for the 7 MeV and 0.2% ± 0.8% for the 11 MeV. All other parameters met the MPPG 5.a's 3%/3-mm criteria. CONCLUSION: We were able to add two new beam energies with no hardware modifications. Tuning of the new beams was facilitated by the ICP/DW system allowing us to have the procedures done in a few hours and achieve highly consistent results across two linacs. PACS numbers: 87.55.Qr, 87.56.Fc.

Generation of ozone during irradiation using medical linear accelerators: an experimental study.

BACKGROUND: Some patients have noted a foul odor during radiation therapy sessions, but the cause of the odor remains unknown. Since we suspected that this phenomenon is due to ozone generated by ionizing radiation, this experimental study measured ozone concentrations in the treatment room and in a coiled polyvinyl chloride (PVC) tube placed within the radiation field. METHODS: We measured ozone concentrations using an ultraviolet absorption method and an ozone monitor. A PVC tube (inner diameter 7 mm, outer diameter 10 mm) was used to mimic the environment of the nasal cavity. The tube (790 cm) was coiled and set between two 4-cm-thick (for X-rays) or 2-cm-thick (for electron beams) water-equivalent solid phantoms. The sampling tube of the ozone monitor was inserted into the PVC tube, and the joint was sealed to prevent environmental air contamination. To measure ozone concentrations in the atmosphere, the sampling tube supplied with the unit was used. A linac was used on a full-sized treatment field (40 cm × 40 cm at a source-to-axis distance of 100 cm). The effect of an electron beam on ozone concentrations was also evaluated with a full-sized treatment field (40 cm × 40 cm at a source-to-surface distance of 100 cm). RESULTS: Ozone levels in the treatment room were undetectable before the start of daily treatment but reached 0.008 parts per million (ppm) or more at 1 h after the start of treatment. Concentrations then remained nearly constant at 0.010-0.015 ppm throughout the day. The maximum ozone concentration in the PVC tube was only 0.006 ppm, even when it was irradiated at 2400 monitor units/min. Depending on the X-ray dose rate, the concentration increased to a maximum of 0.010 ppm with oxygen flowing into the other end of the tube at 1.5 L/min. Ozone concentrations in the PVC tube did not differ significantly between X-ray and electron-beam irradiation. CONCLUSIONS: Only traces of ozone were found in the PVC tube that was used to mimic the nasal passages during radiation, these concentrations were too low for human perception. However, ozone concentrations did reach potentially detectable levels in the treatment room.

Planning and delivery of intensity modulated bolus electron conformal therapy.

PURPOSE: Bolus electron conformal therapy (BECT) is a clinically useful, well-documented, and available technology. The addition of intensity modulation (IM) to BECT reduces volumes of high dose and dose spread in the planning target volume (PTV). This paper demonstrates new techniques for a process that should be suitable for planning and delivering IM-BECT using passive radiotherapy intensity modulation for electrons (PRIME) devices. METHODS: The IM-BECT planning and delivery process is an addition to the BECT process that includes intensity modulator design, fabrication, and quality assurance. The intensity modulator (PRIME device) is a hexagonal matrix of small island blocks (tungsten pins of varying diameter) placed inside the patient beam-defining collimator (cutout). Its design process determines a desirable intensity-modulated electron beam during the planning process, then determines the island block configuration to deliver that intensity distribution (segmentation). The intensity modulator is fabricated and quality assurance performed at the factory (.decimal, LLC, Sanford, FL). Clinical quality assurance consists of measuring a fluence distribution in a plane perpendicular to the beam in a water or water-equivalent phantom. This IM-BECT process is described and demonstrated for two sites, postmastectomy chest wall and temple. Dose plans, intensity distributions, fabricated intensity modulators, and quality assurance results are presented. RESULTS: IM-BECT plans showed improved D90-10 over BECT plans, 6.4% versus 7.3% and 8.4% versus 11.0% for the postmastectomy chest wall and temple, respectively. Their intensity modulators utilized 61 (single diameter) and 246 (five diameters) tungsten pins, respectively. Dose comparisons for clinical quality assurance showed that for doses greater than 10%, measured agreed with calculated dose within 3% or 0.3 cm distance-to-agreement (DTA) for 99.9% and 100% of points, respectively. CONCLUSION: These results demonstrated the feasibility of translating IM-BECT to the clinic using the techniques presented for treatment planning, intensity modulator design and fabrication, and quality assurance processes.

Stopping-power ratios for electron beams used in total skin electron therapy.

PURPOSE: The electron beams for total skin electron therapy (TSET) are often degraded by a scatter plate in addition to extended distances. For electron dosimetry, both the AAPM TG-51 and IAEA TRS-398 recommend the use of two formulas developed by Burns et al [Med. Phys. 23, 489-501 (1996)] to estimate the water-to-air stopping-power ratios (SPRs). Both formulas are based on a fit to SPRs calculated for standard electron beams. This study aims to find: (1) if the formulas are applicable to beams used in TSET and (2) the impact of the ICRU report 90 recommendations on the SPRs for these beams. METHODS: The EGSnrc Monte Carlo code system is used to generate 6 MeV high dose rate total skin electron (HDTSe) beams used in TSET. The simulated beams are used to calculate dose distributions and SPRs as a function of depth in a water phantom. The fitted SPRs using the empirical formulas are compared with MC-calculated SPRs. RESULTS: The electron beam quality specifier, the depth in water at which the absorbed dose falls to 50% of its maximum value, R50 , decreases approximately 1 mm for each additional 100-cm extended distance ranging from 2.24 cm at SSD = 100 to 1.72 cm at SSD = 700 cm. For beams passing through a scatter plate, R50 is 1.76 cm (1.14) at SSD = 300 and 1.48 cm (0.85 cm) at SSD = 600 cm with an Acrylic plate thickness of 3 mm (9 mm), respectively. The discrepancy between fitted and MC-calculated SPRs at dref as a function of R50 is <0.8%, and in many cases <0.4%. The difference between fitted and MC-calculated SPRs as a function of depth and R50 is within 1% at depths <0.8R50 for beams with R50  ≥ 1.14 cm. The ICRU-90 recommendations decrease SPRs by 0.3%-0.4% compared to the use of data recommended in ICRU-37. CONCLUSION: The formulas used by the major protocols are accurate enough for clinical beams used in TSET and the error caused using the formulas is <1% to estimate SPRs as a function of depth and R50 for depths <0.8R50 for beams used in TSET with R50  ≥ 1.14 cm. The impact of the ICRU-90 recommendations shows a decrease of SPRs by a fraction of a percent for beams used in TSET.

Angular dynamics of small nanoparticles induced by non-vortex electron beams.

In this work, we present a theoretical study of the angular dynamics of small nanoparticles induced by fast non-vortex electron beams. General expressions for the torque and the angular momentum transferred from an electron to an arbitrary-but small-nanoparticle are obtained using a full-retarded classical electrodynamics approach, within the small particle limit. We applied this methodology to study a particular case of interest: the angular dynamics of spherical nanoparticles with homogeneous and isotropic electromagnetic responses. We analytically calculate the total angular momentum transferred from a swift electron to such nanoparticles, finding that it is electric in nature and it is always in a direction determined by the electron trajectory relative to the center of the nanoparticle. We realize that it is possible to represent the angular momentum transferred as the product of two functions: the extinction cross-section of the nanoparticle and a function that only contains information about the swift electron. We present numerical results for the total angular momentum transferred from a swift electron to an aluminum and a gold nanoparticle. We also present an analysis of the temporal behavior of the torque and the electric dipole moment induced within the nanoparticle by the swift electron. We compare the angular momentum transfer calculated in this work with a previously reported case of vortex beams, finding that, for both aluminum and gold nanoparticles, our results are two orders of magnitude smaller. Finally, we consider a particular case of a frictionless gold spherical nanoparticle of radius a=5nm, obtaining that it can spin with an angular frequency up to 29.3Hz.

Low-energy electron beam sterilization of solid alginate and chitosan, and their polyelectrolyte complexes.

Polysaccharidic scaffolds hold great hope in regenerative medicine, however their sterilization still remains challenging since conventional methods are deleterious. Recently, electron beams (EB) have raised interest as emerging sterilization techniques. In this context, the aim of this work was to study the impact of EB irradiations on polysaccharidic macroporous scaffolds. The effects of continuous and pulsed low energy EB were examined on polysaccharidic or on polyelectrolyte complexes (PEC) scaffolds by SEC-MALLS, FTIR and EPR. Then the scaffolds' physicochemical properties: swelling, architecture and compressive modulus were investigated. Finally, sterility and in vitro biocompatibility of irradiated scaffolds were evaluated to validate the effectiveness of our approach. Continuous beam irradiations appear less deleterious on alginate and chitosan chains, but the use of a pulsed beam limits the time of irradiation and better preserve the architecture of PEC scaffolds. This work paves the way for low energy EB tailor-made sterilization of sensitive porous scaffolds.

Shielding effect of a lead apron on the peripheral radiation dose outside the applicator of electron beams from an Elekta linear accelerator.

PURPOSE: To evaluate the shielding effect of lead aprons (LAs) on peripheral radiation doses outside the applicator of electron beams from a linear accelerator. METHODS: Out-of-field radiation doses of 4-, 6-, 8-, 10-, 12-, and 15-MeV electron beams from an Elekta Synergy linear accelerator (linac) were measured by thermoluminescence dosimeters (TLD) at different depths (0, 0.5, 1.0, and 2.0 cm) and distances from the applicator edge (0-58 cm) in a water-equivalent slab phantom with a different number of layers of LA shielding (0-5 layers). Measurements were performed by 6 × 6, 10 × 10, 14 × 14, and 20 × 20-cm2 applicators at a gantry and collimator angle of 0°. The out-of-field radiation dose profiles were normalized to the maximum dose of every energy and measuring depth. RESULTS: The out-of-field radiation doses (beyond 3 cm away from the field edge) decreased with an increase in the number of LA layers and distance away from the central beam axis (CAX). After shielding with the LA, the out-of-field doses decreased by up to approximately 99% compared with the no shielding group. For 4-MeV electron beams, there was a peak at 24.5 cm from the CAX, which weakened with an increasing number of LA layers. CONCLUSION: The shielding effect of the LA varied for a different number of LA layers as well as different depths and distances away from the CAX. Four LA layers were sufficient for shielding out-of-field doses of 4-15-MeV electron beams.

Nonlinear Interactions between Free Electrons and Nanographenes.

Free electrons act as a source of highly confined, spectrally broad optical fields that are widely used to map photonic modes with nanometer/millielectronvolt space/energy resolution through currently available electron energy-loss and cathodoluminescence spectroscopies. These techniques are understood as probes of the linear optical response, while nonlinear dynamics has escaped observation with similar degree of spatial detail, despite the strong enhancement of the electron evanescent field with decreasing electron energy. Here, we show that the field accompanying low-energy electrons can trigger anharmonic response in strongly nonlinear materials. Specifically, through realistic quantum-mechanical simulations, we find that the interaction between ≲100 eV electrons and plasmons in graphene nanostructures gives rise to substantial optical nonlinearities that are discernible as saturation and spectral shifts in the plasmonic features revealed in the cathodoluminescence emission and electron energy-loss spectra. Our results support the use of low-energy electron-beam spectroscopies for the exploration of nonlinear optical processes in nanostructures.

A modified formalism for electron beam reference dosimetry to improve the accuracy of linac output calibration.

PURPOSE: To present and demonstrate the accuracy of a modified formalism for electron beam reference dosimetry using updated Monte Carlo calculated beam quality conversion factors. METHODS: The proposed, simplified formalism allows the use of cylindrical ionization chambers in all electron beams (even those with low beam energies) and does not require a measured gradient correction factor. Data from a previous publication are used for beam quality conversion factors. The formalism is tested and compared to the present formalism in the AAPM TG-51 protocol with measurements made in Elekta Precise electron beams with energies between 4 MeV and 22 MeV and with fields shaped with a 10 × 10 cm2 clinical applicator as well as a 20 × 20 cm2 clinical applicator for the 18 MeV and 22 MeV beams. A set of six ionization chambers are used for measurements (two cylindical reference-class chambers, two scanning-type chambers and two parallel-plate chambers). Dose per monitor unit is derived using the data and formalism provided in the TG-51 protocol and with the proposed formalism and data and compared to that obtained using ionization chambers calibrated directly against primary standards for absorbed dose in electron beams. RESULTS: The standard deviation of results using different chambers when TG-51 is followed strictly is on the order of 0.4% when parallel-plate chambers are cross-calibrated against cylindrical chambers. However, if parallel-plate chambers are directly calibrated in a cobalt-60 beam, the difference between results for these chambers is up to 2.2%. Using the proposed formalism and either directly calibrated or cross-calibrated parallel-plate chambers gives a standard deviation using different chambers of 0.4%. The difference between results that use TG-51 and the primary standard measurements are on the order of 0.6% with a maximum difference in the 4 MeV beam of 2.8%. Comparing the results obtained with the proposed formalism and the primary standard measurements are on the order of 0.4% with a maximum difference of 1.0% in the 4 MeV beam. CONCLUSIONS: The proposed formalism and the use of updated data for beam quality conversion factors improves the consistency of results obtained with different chamber types and improves the accuracy of reference dosimetry measurements. Moreover, it is simpler than the present formalism and will be straightforward to implement clinically.

Reduced Number of Lymphocytes by X-ray Irradiation: A Problem in a Combination Therapy Trial that Elicits the Abscopal Effect in Preclinical Studies Using Electron Beam Irradiation.

In preclinical studies with model animals, intravenous administration of a derivative of chemokine CCL3, named eMIP, after local electron-beam irradiation, not only enhanced tumor growth inhibition at a target site but also induced tumor killing beyond the treated site (a phenomenon known as the abscopal effect). eMIP works with alarmins such as high mobility group box 1 (HMGB1) and heat shock protein 70 (HSP70) released from overexpressed tumor cells by irradiation. These alarmins at the irradiated tumor bed trap injected eMIP and, by forming complexes with eMIP, play a key role to recruit and activate tumor inhibitory natural killer (NK) cells and CD4+ and CD8+ T cells. Tumor type-specific secretion of gamma interferon from splenocytes was also demonstrated, which may also activate NK cells. During Phase 1 clinical studies using X-rays, however, no apparent abscopal effect was observed. Instead, we saw frequent reduction in numbers of lymphocytes in the peripheral blood of irradiated patients. The reduced number of lymphocytes recovered poorly once depleted, in contrast to neutrophils, and persisted for months after the treatment. This might have affected outcome after combination treatment of irradiation and eMIP. To enhance host defense mechanisms during and after photon-beam (X-ray) radiotherapy of a deep-seated tumor, it seems essential to keep lymphocytes undamaged by eliminating reactive oxygen species that are formed in the peripheral blood during irradiation.

Monte Carlo Simulation on the Imaging Contrast Enhancement in Nanoparticle-enhanced Radiotherapy.

This study focused on the imaging in radiotherapy by finding the relationship between the imaging contrast ratio and appropriate gold, iodine, iron oxide, silver, and platinum nanoparticle concentrations; the relationship between the imaging contrast ratio and different beam energies for the different nanoparticle concentrations; the relationship between the contrast ratio and various beam energies for gold nanoparticles; and the relationship between the contrast ratio and different thicknesses of the incident layer of the phantom including variety of gold nanoparticles (GNPs) concentration. Monte Carlo simulation was used to model the gold, iodine, iron oxide, silver, and platinum nanoparticle concentration which were infused within a heterogeneous phantom (50 cm × 50 cm × 10.5 cm) choosing different concentrations (3, 7, 18, 30, and 40 mg), and beams (100, 120, 130, and 140 kVp) correspondingly that were delivered into the phantom. The results showed obvious connection between the high concentration and having a high imaging contrast ratio, low energy and a high contrast ratio, small thickness, and a high contrast ratio. The superior nanoparticle obtained was GNP, the better concentration was 40 mg, the better beam energy was 100 kVp, and the better thickness was 0.5 cm. It is concluded that our study successfully proved that medical imaging contrast could be improved by increasing the contrast ratio using GNP as the finest choice to accomplish this improvement considering a high concentration, low beam energy, and a small thickness.

Evaluation of prototype of improved electron collimation system for Elekta linear accelerators.

PURPOSE: This study evaluated a new electron collimation system design for Elekta 6-20 MeV beams, which should reduce applicator weights by 25%-30%. Such reductions, as great as 3.9 kg for the largest applicator, should result in considerably easier handling by members of the radiotherapy team. METHODS: Prototype 10 × 10 and 20 × 20-cm2 applicators, used to measure weight, in-field flatness, and out-of-field leakage dose, were constructed according to the previously published design with two minor modifications: (a) rather than tungsten, lead was used for trimmer material; and (b) continuous trimmer outer-edge bevel was approximated by three steps. Because of lead plate softness, a 0.32-cm aluminum plate replaced the equivalent lead thickness on the trimmer's downstream surface for structural support. Models of all applicators (6 × 6-25 × 25 cm2 ) with these modifications were inserted into a Monte Carlo (MC) model for dose calculations using 7, 13, and 20 MeV beams. Planar dose distributions were measured and calculated at 1- and 2-cm water depths to evaluate in-field beam flatness and out-of-field leakage dose. RESULTS: Prototype 10 × 10 and 20 × 20-cm2 applicator measurements agreed with calculated weights, in-field flatness, and out-of-field leakage doses for 7, 13, and 20 MeV beams. Also, MC dose calculations showed that all applicators (6 × 6-25 × 25 cm2 ) and 7, 13, and 20 MeV beams met our stringent in-field flatness specifications (±3% major axes; ±4% diagonals) and IEC out-of-field leakage dose specifications. CONCLUSIONS: Our results validated the new electron collimating system design for Elekta 6-20 MeV electron beams, which could serve as basis for a new clinical electron collimating system with significantly reduced applicator weights.