Aman Anand

Fabrication of oxidation-resistant metal wire network-based transparent electrodes by a spray-roll coating process

Roll and spray coating methods have been employed for the fabrication of highly oxidation resistant transparent and conducting electrodes (TCEs) by a simple solution process using crackle lithography technique. We have spray-coated a crackle paint-based precursor to produce highly interconnected crackle network on PET roll mounted on a roll coater with web speed of 0.6 m/min. Ag TCE with a transmittance of 78% and sheet resistance of ∼20 Ω/□ was derived by spraying Ag precursor ink over the crackle template followed by lift-off and annealing under ambient conditions. The Ag wire mesh was stable toward bending and sonication tests but prone to oxidation in air. When electrolessly coated with Pd, its robustness toward harsh oxidation conditions was enhanced. A low-cost transparent electrode has also been realized by using only small amounts of Ag as seed layer and growing Cu wire mesh by electroless method. Thus, made Ag/Cu meshes are found to be highly stable for more than a year even under ambient atmosphere.

Scanning proton beam therapy reduces normal tissue exposure in pelvic radiotherapy for anal cancer

An inter-comparison planning study between photon beam therapy (IMRT) and scanning proton beam therapy (SPBT) for squamous cell carcinoma of the anus (SCCA) is presented. SPBT plans offer significant reduction (>50%, P=0.008) in doses to small bowel, and bone marrow thereby offering the potential to reduce bowel and hemotoxicities.

LET dependence of the response of EBT2 films in proton dosimetry modeled as a bimolecular chemical reaction

The dose response for films exposed to clinical x-ray beams is not linear and a calibration curve based on absorbed dose can be used to account for this effect. However for proton dosimetry the dose response of films exhibits an additional dependence because of the variation of the linear energy transfer (LET) as the protons penetrate matter. In the present study, we hypothesized that the dose response for EBT2 films can be mathematically described as a bimolecular chemical reaction. Furthermore, we have shown that the LET effect can be incorporated in the dose-response curve. A set of EBT2 films was exposed to pristine 161.6 MeV proton beams. The films were exposed to doses ranging from 0.93 to 14.82 Gy at a depth of 2 cm in water. The procedure was repeated with one film exposed to a lower energy beam (85.6 MeV). We also computed the LET and dose to water in the sensitive layer of the films with a validated Monte Carlo system, taking into account the film construction (polyester, adhesive and sensitive layers). The bimolecular model was able to accurately fit the experimental data with a correlation factor of 0.9998, and the LET correction factor was determined and incorporated into the dose-response function. We also concluded that the film orientation is important when determining the LET correction factor because of the asymmetric construction of the film.

Proton beam therapy for locally advanced lung cancer: A review.

Protons interact with human tissue differently than do photons and these differences can be exploited in an attempt to improve the care of lung cancer patients. This review examines proton beam therapy (PBT) as a component of a combined modality program for locally advanced lung cancers. It was specifically written for the non-radiation oncologist who desires greater understanding of this newer treatment modality. This review describes and compares photon (X-ray) radiotherapy (XRT) to PBT. The physical differences of these beams are described and the clinical literature is reviewed. Protons can be used to create treatment plans delivering significantly lower doses of radiation to the adjacent organs at risk (lungs, esophagus, and bone marrow) than photons. Clinically, PBT combined with chemotherapy has resulted in low rates of toxicity compared to XRT. Early results suggest a possible improvement in survival. The clinical results of proton therapy in lung cancer patients reveal relatively low rates of toxicity and possible survival benefits. One randomized study is being performed and another is planned to clarify the clinical differences in patient outcome for PBT compared to XRT. Along with the development of better systemic therapy, newer forms of radiotherapy such as PBT should positively impact the care of lung cancer patients. This review provides the reader with the current status of this new technology in treating locally advanced lung cancer.

Hydrogel Nanosensors for Colorimetric Detection and Dosimetry in Proton Beam Radiotherapy

Proton beam therapy (PBT) is a state-of-the-art radiotherapy treatment approach that uses focused proton beams for tumor ablation. A key advantage of this approach over conventional photon radiotherapy (XRT) is the unique dose deposition characteristic of protons, which results in superior healthy tissue sparing. This results in fewer unwanted side effects and improved outcomes for patients. Currently available dosimeters are intrinsic, complex, and expensive and are not routinely used to determine the dose delivered to the tumor. Here, we report a hydrogel-based plasmonic nanosensor for detecting clinical doses used in conventional and hyperfractionated proton beam radiotherapy. In this nanosensor, gold ions, encapsulated in a hydrogel, are reduced to gold nanoparticles following irradiation with proton beams. Formation of gold nanoparticles renders a color change to the originally colorless hydrogel. The intensity of the color can be used to calibrate the hydrogel nanosensor in order to quantify different radiation doses employed during proton treatment. The potential of this nanosensor for clinical translation was demonstrated using an anthropomorphic phantom mimicking a clinical radiotherapy session. The simplicity of fabrication, detection range in the fractionated radiotherapy regime, and ease of detection with translational potential makes this a first-in-kind plasmonic colorimetric nanosensor for applications in clinical proton beam therapy.

Tissue Expanders and Proton Beam Radiotherapy: What You Need to Know

Summary: Proton beam radiotherapy (PBR) has gained acceptance for the treatment of breast cancer because of unique beam characteristics that allow superior dose distributions with optimal dose to the target and limited collateral damage to adjacent normal tissue, especially to the heart and lungs. To determine the compatibility of breast tissue expanders (TEs) with PBR, we evaluated the structural and dosimetric properties of 2 ex vivo models: 1 model with internal struts and another model without an internal structure. Although the struts appeared to have minimal impact, we found that the metal TE port alters PBR dynamics, which may increase proton beam range uncertainty. Therefore, submuscular TE placement may be preferable to subcutaneous TE placement to reduce the interaction of the TE and proton beam. This will reduce range uncertainty and allow for more ideal radiation dose distribution.

Use of a radial projection to reduce the statistical uncertainty of spot lateral profiles generated by Monte Carlo simulation

Abstract Monte Carlo (MC) simulation has been used to generate commissioning data for the beam modeling of treatment planning system (TPS). We have developed a method called radial projection (RP) for postprocessing of MC‐simulation‐generated data. We used the RP method to reduce the statistical uncertainty of the lateral profile of proton pencil beams with axial symmetry. The RP method takes advantage of the axial symmetry of dose distribution to use the mean value of multiple independent scores as the representative score. Using the mean as the representative value rather than any individual score results in substantial reduction in statistical uncertainty. Herein, we present the concept and step‐by‐step implementation of the RP method, as well as show the advantage of the RP method over conventional measurement methods for generating lateral profile. Lateral profiles generated by both methods were compared to demonstrate the uncertainty reduction qualitatively, and standard error comparison was performed to demonstrate the reduction quantitatively. The comparisons showed that statistical uncertainty was reduced substantially by the RP method. Using the RP method to postprocess MC data, the corresponding MC simulation time was reduced by a factor of 10 without quality reduction in the generated result from the MC data. We concluded that the RP method is an effective technique to increase MC simulation efficiency for generating lateral profiles for axially symmetric pencil beams.

Validation of a track-repeating algorithm versus measurements in water for proton scanning beams

Dose distributions calculated with the fast dose calculator (FDC), a track repeating-algorithm for proton therapy, have been validated versus dose measurements in water for scanning proton beams at the University of Texas MD Anderson Cancer Center Proton Therapy Center in Houston. The dose calculated with FDC, at the position of the measured points for depth and lateral profiles, was compared to the measurements with a gamma-index analysis. It was found that 99.9% and 99.5% of the measured points had a gamma-index value smaller than unity for the 3%/3 mm and 2%/2 mm dose/distance agreement criteria, respectively.

SU-C-19A-07: Influence of Immobilization On Plan Robustness in the Treatment of Head and Neck Cancer with IMPT

PURPOSE We evaluated the effect of interposing immobilization devices into the beams path on the robustness of a head and neck plan. METHODS An anthropomorphic head phantom was placed into a preliminary prototype of a specialized head and neck immobilization device for proton beam therapy. The device consists of a hard low density shell, a custom mold insert, and thermoplastic mask to immobilize the patients head in the shell. This device was provided by CIVCO Medical Solutions for the purpose of evaluation of suitability for proton beam therapy. See Figure 1. Two pairs of treatment plans were generated. The first plan in each pair was a reference plan including only the anthropomorphic phantom, and the second plan in each pair included the immobilization device. In all other respects the plans within the pair were identical. RESULTS In the case of the simple plan the degradation of plan robustness was found to be clinically insignificant. In this case, target coverage in the worst case scenario was reduced from 95% of the target volume receiving 96.5% of prescription dose to 95% of the target volume receiving 96.3% of prescription dose by introducing the immobilization device. In the case of the complex plan, target coverage of the boost volume in the worst case scenario was reduced from 95% of the boost target volume receiving 97% of prescription dose to 95% of the boost target volume receiving 83% of prescription dose by introducing the immobilization device. See Figure 2. CONCLUSION Immobilization devices may have a deleterious effect on plan robustness. Evaluation of the preliminary prototype revealed a variable impact on the plan robustness depending of the complexity of the case. Brian Morse is an employee of CIVCO Medical Solutions.

SU-E-T-584: Commissioning of the MC2 Monte Carlo Dose Computation Engine

PURPOSE An automated system, MC2, was developed to convert DICOM proton therapy treatment plans into a sequence MCNPX input files, and submit these to a computing cluster. MC2 converts the results into DICOM format, and any treatment planning system can import the data for comparison vs. conventional dose predictions. This work describes the data and the efforts made to validate the MC2 system against measured dose profiles and how the system was calibrated to predict the correct number of monitor units (MUs) to deliver the prescribed dose. METHODS A set of simulated lateral and longitudinal profiles was compared to data measured for commissioning purposes and during annual quality assurance efforts. Acceptance criteria were relative dose differences smaller than 3% and differences in range (in water) of less than 2 mm. For two out of three double scattering beam lines validation results were already published. Spot checks were performed to assure proper performance. For the small snout, all available measurements were used for validation vs. simulated data. To calibrate the dose per MU, the energy deposition per source proton at the center of the spread out Bragg peaks (SOBPs) was recorded for a set of SOBPs from each option. Subsequently these were then scaled to the results of dose per MU determination based on published methods. The simulations of the doses in the magnetically scanned beam line were also validated vs. measured longitudinal and lateral profiles. The source parameters were fine tuned to achieve maximum agreement with measured data. The dosimetric calibration was performed by scoring energy deposition per proton, and scaling the results to a standard dose measurement of a 10 x 10 x 10 cm3 volume irradiation using 100 MU. RESULTS All simulated data passed the acceptance criteria. CONCLUSION MC2 is fully validated and ready for clinical application.