Energy Photon Beams Research Articles

Angular Dependence ofϕMeson Production for Different Photon Beam Energies

The dependence ofϕ-meson photoproduction on the polar angle is investigated in the framework of a multisource thermal model. We present a detailed comparison between our results and experimental data of the neutral decay mode in the reactionγp→pϕ(KSKL). The results are in good agreement with the experimental data. It is found that the movement factorbzincreases linearly with the photon beam energies.

Assessment of Photon Propagation through Fatby Monte Carlo Simulation and Experimental Work in Linear Accelerator of Imam Reza Hospital

The aim of radiation therapy is to maximise the dose to the tumour, while minimising the dose to healthy tissue. Monte Carlo (MC) methods are now widely used to model radiotherapy systems for accurate treatment planning and evaluate the accuracy of the dose distributions in a variety of clinical situations involving highly heterogeneous media, such as lung or head and neck treatments. This study aimed to simulate the photon propagation in tissue using MC technique.The MC simulation was written in Fortran 77 program. Moreover, emigration of photons in tissue was determined using MCNP-4C code. The tally F5: P, 9 MeV photons beam as a source and point detector was utilized to calculate the flux of photon at various depths of tissue. Neptun 10 PC linear accelerator of Imam Reza Hospital with 9 MeV photon beam energy was used to determine experimental results.The result of MC methodwas evaluated withthose of MCNP-4C code and experimental result performed by clinical treatment planning system. The result of MC method shows a good consistent with those of MCNP-4C code and experimental result. The results of this research provide a method to characterize the primary radiation energy spectrum produced by a linear accelerator.

Effective Point of Measurement in Cylindrical Ion Chamber for Megavoltage Photon Beams

Introduction For dose measurement in Megavoltage (MV) photon beams with ion chambers, the effect of volume occupied by the air cavity is not negligible. Therefore, the result of measurement should be corrected with a displacement perturbation correction factor (Pdis) or using an effective point of measurement (EPOM). The aim of this study is to calculate the EPOM for cylindrical ion chamber and to evaluate the fixed EPOM that was recommended by standard dosimetry protocols. Materials and Methods Percent depth doses (PDDs) for 6 MV and 18 MV were measured with two types of chambers for different depths and field sizes. The EPOM was calculated using results obtained from measurement data for two types of chambers, comparison of the readings, and using dosimetry, mathematical, and statistical consideration. For displacement correction factor 12∆r'> =0, 12∆r'> = 0.6r and different 12∆r'>, the minimum standard deviations ratio (SDRs) were calculated at several depths and field sizes. Results Maximum level of SDRs was about 0.38% and 0.49% (when assuming variable 12∆r'>) for 6 MV and 18 MV, respectively (which was less than 0.5% and acceptable). This quantity was greater than one (for assuming 12∆r'> = 0.6r) and greater than 2 when there was no shift ( 12∆r'> =0) Conclusion The results show that the recommended shift for cylindrical ion chamber in dosimetry protocols (upstream of 0.6r) is not correct and using a fixed value for the EPOM at all photon beam energies, depths, and field sizes is not suitable for accurate dosimetry.

The effect of radiotherapy beam energy on modern cardiac devices: an in vitro study

Radiotherapy (RT) for malignancies can harm pacemakers (PMs) and implantable cardioverter-defibrillators (ICDs). There is some evidence that, besides cumulative dose, the damaging radiation effects increase with beam energy. The aim of this study was to determine whether modern PMs and ICDs are more sensitive to high-energy than to low-energy photon beams. Two groups of unused PMs and explanted ICDs (five PMs and one ICD in each) were subjected to irradiations in a phantom with 6 and 18 megavolt (MV) photons, respectively. The devices were exposed to radiation at doses of 2 gray (Gy) daily to simulate two clinical scenarios with the PM/ICD in the RT field. A cumulative dose of 150 Gy was given to each device, corresponding to approximately twice the therapeutic dose. In the 6 MV group, one episode of PM malfunction was detected after reaching 150 Gy. In the 18 MV group, a total of 14 episodes of malfunction were detected starting at 30 Gy in all five PMs. No episodes appeared in the ICD, at the respective treatment groups. This corresponded to a hazard ratio of 9.11 [∼95% confidence interval (CI): 1.04-79.69] by Cox regression analysis between the two groups. In a repeated measures logistic regression model comparing the incidence rate of malfunctions, the odds ratio was 18.29 (∼95% CI: 1.52-219.41). Photon beam energy plays a considerable role in inducing implantable cardiac device malfunctions. Low-energy RT may be safer in PM/ICD patients despite relatively high radiation dose to the device.

Evaluation the Effect of Photon Beam Energies on Organ at Risk Doses in Three-Dimensional Conformal Radiation Therapy

As regards, the selection of appropriate energy in radiotherapy tumors that are placed in non-homogen areas is important, so the aim of the present study is evaluating the effect of 6 and 15MV photon beam energies on dose distribution in 3D-CRT for lower esophageal and rectal cancers. 12 patients with lower esophageal cancer and 12 patients with rectal cancer respectively, with the prescription dose of 7000 cGy and 5040 cGy were studied. For treatment of esophagus the three-field technique and for treatment of rectum the four-field technique was used. In the thoracic area, the spinal cord and in the pelvis, the bladder and head of femurs were considered as OARs. For comparing the results, all parameters used for treatment planning except the photon beam energy were kept constant. After performing the treatment planning with two different energies in each region, the received dose rate of spinal cord, bladder and head of femurs as OARs and dose distribution in PTVs were studied. The results of this study showed that the difference between doses received by OARs in 6MV and 15MV therapeutic plans, resulted 5.2, 5.06 and -9.14%, respectively. Also the PTVs received dose difference of esophagus and rectum in the performed therapeutic plans with energy of 6 MV than energy of 15MV is 1.52 and -0.63%, respectively. We found that using of low energy photons in lower esophageal treatment and high energy photons in the rectal treatment provides the better dose coverage. Finally, with such as therapeutic plans the cumulative dose of organs at risk will be reduced.

SU‐E‐T‐378: IMRT Severity Scoring for TG‐100: Do You Really Know?

Purpose: Failure modes and effects analysis (FMEA) as defined in TG‐100 has become a popular concept throughout the radiotherapy community. This risk mitigation technique involves detailed process mapping, analysis, and ranking of potential errors by means of a subjective, ordinal scoring system. This study aims to reduce the subjectivity of FMEA severity scoring for IMRT delivery by providing quantitative values. Methods: First we created an IMRT delivery process map for physics‐applicable processes and identified 11 physical failure modes (FMs). To determine the magnitude of dose delivery errors for several of the physical FMs (i.e., the severity of the FM), FMs were induced and dosimetry measurements were performed on a Varian Clinac accelerator going out of clinical service. Treatment planning studies to simulate remaining FMs are to follow. The quantitative severity scores will be compared to recommended FMEA subjective scores. Results: We identified the following physical FMs to investigate: photon beam energy, symmetry, MLC position, MLC transmission and leakage, MLC rounded‐end and leaf offset, MLC tongue‐and‐groove, CT look‐up table, gantry angle, collimator angle, couch angle and displacement, and MU linearity. Within the PTV of a H&N IMRT phantom, the maximum dose delivery error of 3% absolute dose was seen for 2 mm systematic MLC offsets, 4% for 1.1% increased energy, and 4% for 3.5% symmetry error. Measurements will be compared to computational study results and then used for quantitative severity scoring determination. Conclusion: Current FMEA practice for radiotherapy requires quantitative data in order to make accurate assessments associated with clinical QA programs. This study has shown examples of error magnitudes induced by IMRT physical FMs that can be used to quantitate and rank FMEA severity scoring. Work supported by grants CA10953 and CA81647 (NCI, DHHS).

SU-E-T-536: A Simple Method for Optimal Field Abutment Between Photon and Electron Beams in Mixed Beam Radiation Therapy

Purpose: Significant efforts have been made to develop practical methods for the clinical implementation of advanced mixed beam therapy. One of the problems with the use of multiple adjacent electron radiation fields is the possibility of extreme dose inhomogeneity in the junction region. Because radiation beams are divergent, adjacent fields can overlap at depth and give rise to regions of excessive dose. Overlaps can be avoided by separating the electron fields but this in turn can give rise to areas of reduced dose at shallow depths. Thus the aim of this work is to find the optimal gap for different combined electron and photon beam situations. Method: Monte Carlo simulation was conducted for our Varian treatment head using the MCBEAM code, and the MCSIM code was used for modeling a water phantom to derive the dose distribution. Simulated PDDs and profiles were compared to measurements for photon and electron beams. Then isodose distributions were generated for adjacent fields with different separation gaps for different abutment situations such as photon‐photon, electron‐electron and photon‐electron combinations. Results: Good agreement was achieved between Monte Carlo simulation and measurement for all studied photon and electron beam energies. Separation gaps can be chosen that would Result in a flatter profile at a desired depth. Optimal gaps can be selected that compromise between the cold and hot spots inside the target. Conclusion: The Monte Carlo code used was capable of modeling our photon and electron beams accurately. We addressed a simple method to solve the field abutment problem in combined photon and electron treatments for advance mixed beam radiation therapy.

SU-E-T-290: Results of a 12 Year Survey of Workload for 10 Linear Accelerators at a High-Throughput Comprehensive Cancer Center

Purpose: To report on the workload for 10 different treatment machines in terms of number of patients (pts), monitor units delivered (MUs), dose at isocenter (Gys), use factors (U) and modulation factors (C). Methods: The survey was performed for 10 treatment machines in the years from 2001 to 2012. The machines represented different generations of Varian linear accelerators (6EX, 600C, 2100C, 2100EX, and True Beam) operating at different electron and photon energies (6, 9, 12, 16 and 20 MeV electrons and, 6 and 15MV photons). An IRB approval was acquired to perform this study. Data regarding patient workload, number of monitor units delivered, dose at isocenter, beam energies, gantry angles, and techniques were exported from ARIA treatment management system (Varian Medical Systems) into excel spreadsheets. Data analysis was performed in Matlab (R2011a). Results: The number of patients, dose at isocenter, and number of monitor units delivered per week in 2002 was on average 92±32 pts, 267±34 Gys, and (49.2±10) × 103 MUs respectively. Meanwhile, the average workload in 2012 was 106±38 pts, 326±69 Gys, and (110.7±34) × 103 MUs. The photon beam energies predominantly used were the 6 and 15 MV. The modulation factors for SBRT (CS) and IMRT (CI) were 4.1 and 3.4. Use factor (30° bin angles) varied considerably among different techniques and ranged between 0.06 and 0.35. Conclusion: The workload, in terms of monitor units (MUs), has been steadily increasing over the past decade. However, the patient workload and consequently the dose at isocenter remained relatively constant. This increase can be attributed to the emergence of treatment techniques (SBRT, IMRT) which require more MUs per Gy as compared to more conventional treatment (3DCRT). The findings of this report show that variables are still within the recommendation of NCRP Report 151. youtube to mp3

SU-E-T-116: Dosimetry On Beam Modeling at the Small Field for Stereotactic Radiosurgery

Purpose: Beam modeling performed based on the results of the present study, measuring the amount of radiation from a variety of small field of radiation measurement equipment beam modeling is based on the results of clinical practice, such as stereotactic radiosurgery and radiation therapy planning system applied to the treatment plan of each radiation dose distribution is to compare and analyze. Methods: A RapidArc medical linear accelerator was used with norminal 6 and 15 MV photon beam energies in this study. The small beams were generated that field sizes were 1×1, 2×2, 3×3 cm2 and reference field size was 10×10 cm2 to compare small field. We were generated the beam modeling and performed the automatic modeling with adjusted the mean and standard deviation of energy with the spectrum modeling base on the generated the PDD of the beam model. And, we were the lateral profile modeling by using adjusted each horn factor, effect source size, jaw transmission factor, MLC transmission factor, softening factor. Results: In this study, the edge detector measured a narrower penumbra width than the other detectors for small field sizes. For the 20–80% penumbra, the penumbra width measured with the ion chamber was approximately two times wider than the penumbra measured with the edge detector in all cases. The CC13 measured a penumbra width that was 25% wider for all field sizes. We found that the PDD measured with film had some signal fluctuation at the buildup region(6 MV: 1.5 cm, 15 MV: 2.9 cm) for the smallest field size when compared to the standard ionization chamber. Conclusion: The edge detector showed a greater suitability for small field dosimetry than the other detectors tested. We compared the detectors and evaluated the beam modeling results that as they have relatively large volumes, significant discrepancies could occur during the small field dosimetry.

SU-E-T-510: Mitigation Strategies to Reduce the Relative Extrafocal Dose (RED)

Purpose: Several studies [1,2] indicate that IMRT may lead to peripheral (extrafocal) dose outside the intended treatment‐field. The purpose of this study is to: (a) obtain an accurate assessment of the relationship between the relative extrafocal dose (RED) and beam energy, modulation factor, treatment modality, and Y‐jaw settings in connection with the high‐definition HD120‐leaf MLC from Varian; and (b) identify the most efficient mitigation strategies to reduce RED when significant. Methods: IMRT fields with varying modulation were simulated by using an accurate representation of the TrueBeam linac equipped with HD120‐MLC in Geant4 (v9.4.p02). Dose to water phantom calculations were performed relative to a 10×10cm2 field. RED distributions were normalized to dmax for the 6MV, 6FFF, 10MV, 10FFF and 15MV beams. Inline profiles indicated the spatial location of the RED maximum, while simulations with and without the flattening filter revealed its origin. The effect of reducing the Y‐jaw position was quantified for different incident energies. Results: RED is mainly due to photons scattered by the flattening filter, therefore it is not a concern (∼0.7%) when the filter is removed (i.e. 6FFF and 10FFF). The RED maximum is located 4cm outside the outermost boundary leaf (i.e. 15cm off‐axis for HD120‐MLC). Its magnitude can be reduced below 1% by decreasing the Y‐jaw setting, lowering the photon beam energy, lowering the modulation factor of the plan or by using FFF beams, if available. At 15MV, the RED magnitude was reduced from 2.6% to 0.9% by setting the Y‐jaw limit to 8cm. Conclusion: Methodologies to effectively lower the relative extrafocal dose were identified for various photon beams on a Varian linac with HD120‐MLC, including using FFF modes, choosing lower‐energy beams, limiting the Y‐field size and lowering the modulation.[1]E.E. Klein et al., Med.Phys.33 (2006), 2525‐1531[2]D.S. Sharma et al., B.J.R.79 (2006), 331–335

SU‐E‐T‐257: A Monte Carlo Simulation Study of Photon Beam with Energies 6X, 10X, 6FFF, 10FFF From a TrueBeam Linear Accelerator

Purpose: To compare the quality of Monte Carlo simulation results of photon beams with multiple energies with the corresponding measured beam commissioning data from a Varian TrueBeam accelerator. Methods: IAEA phase space files for photon beam energies 6X, 10X, 6FFF, 10FFF from TrueBeam linear accelerator provided by Varian were implemented as source files in the GEANT4 Monte Carlo code. The simulation geometry consisted of upper and lower tungsten alloy jaws and a cubic water phantom (50 × 50 × 50 cm3). Central axis depth dose curves (PDD) for multiple field sizes (1×1, 2×2, 4×4, 6×6, 10×10, 20×20, 30×30 cm2) and radial and transverse dose profiles for identical field sizes at 5 different depths (Dmax, 5, 10, 20, 30 cm) for all four energies were recorded in the phantom. Each simulation was performed with 2.0E9 incident particles. The results of PDD and profiles from simulations were then compared with the corresponding beam commissioning data collected with a Wellhoffer Blue Phantom using a 0.13cc ion‐chamber and a 0.8 × 0.8 mm2 diode. Results: The GEANT4 simulated PDD curve for photon beam compared favorably well, within ∼2%, against the corresponding measured ion‐chamber PDD for all energies and field sizes. The simulated in‐plane and cross‐plane profiles also compared well, within 2 mm, at the 50% level against the measured profiles for all energies, field sizes and depths. Conclusion: For the commissioning of a linear accelerator, the feasibility of utilizing Monte‐Carlo simulated beam data has been demonstrated in this study. The increase of computer speed and capabilities may Result in the adoption of Monte‐Carlo techniques for future machine commissioning and dose calculations.

Prostate volumetric‐modulated arc therapy: dosimetry and radiobiological model variation between the single‐arc and double‐arc technique

This study investigates the dosimetry and radiobiological model variation when a second photon arc was added to prostate volumetric‐modulated arc therapy (VMAT) using the single‐arc technique. Dosimetry and radiobiological model comparison between the single‐arc and double‐arc prostate VMAT plans were performed on five patients with prostate volumes ranging from 29−68.1 cm3. The prescription dose was 78 Gy/39 fractions and the photon beam energy was 6 MV. Dose‐volume histogram, mean and maximum dose of targets (planning and clinical target volume) and normal tissues (rectum, bladder and femoral heads), dose‐volume criteria in the treatment plan (D99% of PTV; D30%,D50%,V17Gy and V35Gy of rectum and bladder; D5% of femoral heads), and dose profiles along the vertical and horizontal axis crossing the isocenter were determined using the single‐arc and double‐arc VMAT technique. For comparison, the monitor unit based on the RapidArc delivery method, prostate tumor control probability (TCP), and rectal normal tissue complication probability (NTCP) based on the Lyman‐Burman‐Kutcher algorithm were calculated. It was found that though the double‐arc technique required almost double the treatment time than the single‐arc, the double‐arc plan provided a better rectal and bladder dose‐volume criteria by shifting the delivered dose in the patient from the anterior–posterior direction to the lateral. As the femoral head was less radiosensitive than the rectum and bladder, the double‐arc technique resulted in a prostate VMAT plan with better prostate coverage and rectal dose‐volume criteria compared to the single‐arc. The prostate TCP of the double‐arc plan was found slightly increased (0.16%) compared to the single‐arc. Therefore, when the rectal dose‐volume criteria are very difficult to achieve in a single‐arc prostate VMAT plan, it is worthwhile to consider the double‐arc technique.PACS number: 87.55.D‐, 87.55.dk, 87.55.K‐, 87.55.Qr

L’activité du système limbique corrèle avec l’indice de masse corporelle à l’éveil et pendant le sommeil lent

The dosimetry of high-energy photon beams in the treatment of superficial lesions occurring in extremities was examined. Large parallel-opposed fields with different photon beam energies were used. The extremity was immersed in water contained in a commercially available plastic wastebasket. The water bolus serves to even out the surface irregularities of the extremities and to remove the skin sparing effect. A polystyrene block was placed at the floor of the wastebasket to ensure that the extremity was encompassed in the radiation fields. The photon beam energies considered were 4 MV, 6 MV, 10 MV, and 24 MV. The results show that the dose distributions are more homogeneous with higher photon beam energies. The isodose lines are more constricted at mid-plane for low energy photon beams. Higher energy photon beams, 10 MV and up would be preferable for the treatment of superficial lesions of the extremities immersed in water bolus contained in a typical wastebasket size.

Measurement of changes in linear accelerator photon energy through flatness variation using an ion chamber array

To compare the use of flatness versus percent depth dose (PDD) for determining changes in photon beam energy for a megavoltage linear accelerator. Energy changes were accomplished by adjusting the bending magnet current by up to ± 15% in 5% increments away from the value used clinically. Two metrics for flatness, relative flatness in the central 80% of the field (Flat) and average maximum dose along the diagonals normalized by central axis dose (FDN), were measured using a commercially available planner ionization chamber array. PDD was measured in water at depths of 5 and 10 cm in 3 × 3 cm(2) and 10 × 10 cm(2) fields using a cylindrical chamber. PDD was more sensitive to changes in energy when the beam energy was increased than when it was decreased. For the 18-MV beam in particular, PDD was not sensitive to energy reductions below the nominal energy. The value of Flat was found to be more sensitive to decreases in energy than to increases, with little sensitivity to energy increases above the nominal energy for 18-MV beams. FDN was the only metric that was found to be sensitive to both increases and reductions of energy for both the 6- and 18-MV beams. Flatness based metrics were found to be more sensitive to energy changes than PDD, In particular, FDN was found to be the most sensitive metric to energy changes for photon beams of 6 and 18 MV. The ionization chamber array allows this metric to be conveniently measured as part of routine accelerator quality assurance.

EP-1292: Measuring photon beam energy through EPID image analysis of physically wedged fields

EP-1292: Measuring photon beam energy through EPID image analysis of physically wedged fields

Dosimetric impact of monoenergetic photon beams in the small-animal irradiation with inhomogeneities: A Monte Carlo evaluation

This study investigated the variations of the dose and dose distribution in a small-animal irradiation due to the photon beam energy and presence of inhomogeneity. Based on the same mouse computed tomography image set, three Monte Carlo phantoms namely, inhomogeneous, homogeneous and bone-tissue phantoms were used in this study. These phantoms were generated by overriding the relative electron density of no voxel (inhomogeneous), all voxel (homogeneous) and the bone voxel (bone-tissue) to one. 360° photon arcs with beam energies of 50–1250kV were used in mouse irradiations. Doses in the above phantoms were calculated using the EGSnrc-based DOSXYZnrc code through the DOSCTP. It was found that the dose conformity increased with the increase of the photon beam energy from the kV to MV range. For the inhomogeneous mouse phantom, increasing the photon beam energy from 50kV to 1250kV increased about 21 times the dose deposited at the isocenter. For the bone dose enhancement, the mean dose was 1.4 times higher when the bone inhomogeneity was not neglected using the 50kV photon beams in the mouse irradiation. Bone dose enhancement affecting the mean dose in the mouse irradiation can be found in the photon beams with energy range of 50–200kV, and the dose enhancement decreases with an increase of the beam energy. Moreover, the MV photon beam has a higher dose at the isocenter, and a better dose conformity compared to the kV beam.

EBT GAFCHROMICTM film dosimetry in compensator-based intensity modulated radiation therapy

The electron benefit transfer (EBT) GAFCHROMIC films possess a number of features making them appropriate for high-quality dosimetry in intensity-modulated radiation therapy (IMRT). Compensators to deliver IMRT are known to change the beam-energy spectrum as well as to produce scattered photons and to contaminate electrons; therefore, the accuracy and validity of EBT-film dosimetry in compensator-based IMRT should be investigated. Percentage-depth doses and lateral-beam profiles were measured using EBT films in perpendicular orientation with respect to 6 and 18MV photon beam energies for: (1) different thicknesses of cerrobend slab (open, 1.0, 2.0, 4.0, and 6.0cm), field sizes (5×5, 10×10, and 20×20cm2), and measurement depths (Dmax, 5.0 and 10.0cm); and (2) step-wedged compensator in a solid phantom. To verify results, same measurements were implemented using a 0.125cm3 ionization chamber in a water phantom and also in Monte Carlo simulations using the Monte Carlo N-particle radiation transport computer code. The mean energy of photons was increased due to beam hardening in comparison with open fields at both 6 and 18MV energies. For a 20×20cm2 field size of a 6MV photon beam and a 6.0cm thick block, the surface dose decreased by about 12% and percentage-depth doses increased up to 3% at 30.0cm depth, due to the beam-hardening effect induced by the block. In contrast, at 18MV, the surface dose increased by about 8% and depth dose reduced by 3% at 30.0cm depth. The penumbral widths (80% to 20%) increase with block thickness, field size, and beam energy. The EBT film results were in good agreement with the ionization chamber dose profiles and Monte Carlo N-particle radiation transport computer code simulation behind the step-wedged compensator. Also, there was a good agreement between the EBT-film and the treatment-planning results on the anthropomorphic phantom. The EBT films can be accurately used as a 2D dosimeter for dose verification and quality assurance of compensator-based C-IMRT.

Microfocusing of the FERMI@Elettra FEL beam with a K–B active optics system: Spot size predictions by application of the WISE code

FERMI@Elettra, the first seeded EUV-SXR free electron laser (FEL) facility located at Elettra Sincrotrone Trieste has been conceived to provide very short (10–100fs) pulses with ultrahigh peak brightness and wavelengths from 100nm to 4nm. A section fully dedicated to the photon transport and analysis diagnostics, named PADReS, has already been installed and commissioned. Three of the beamlines, EIS-TIMEX, DiProI and LDM, installed after the PADReS section, are in advanced commissioning state and will accept the first users in December 2012. These beam lines employ active X-ray optics in order to focus the FEL beam as well as to perform a controlled beam-shaping at focus.Starting from mirror surface metrology characterization, it is difficult to predict the focal spot shape applying only methods based on geometrical optics such as the ray tracing. Within the geometrical optics approach one cannot take into account the diffraction effect from the optics edges, i.e. the aperture diffraction, and the impact of different surface spatial wavelengths to the spot size degradation. Both these effects are strongly dependent on the photon beam energy and mirror incident angles.We employed a method based on physical optics, which applies the Huygens–Fresnel principle to reflection (on which the WISE code is based). In this work we report the results of the first measurements of the focal spot in the DiProI beamline end-station and compare them to the predictions computed with Shadow code and WISE code, starting from the mirror surface profile characterization.

Effect of photon beam energy, gold nanoparticle size and concentration on the dose enhancement in radiation therapy.

Gold nanoparticles have been used as radiation dose enhancing materials in recent investigations. In the current study, dose enhancement effect of gold nanoparticles on tumor cells was evaluated using Monte Carlo (MC) simulation. We used MCNPX code for MC modeling in the current study. A water phantom and a tumor region with a size of 1×1×1 cm3 loaded with gold nanoparticles were simulated. The macroscopic dose enhancement factor was calculated for gold nanoparticles with sizes of 30, 50, and 100 nm. Also, we simulated different photon beams including mono-energetic beams (50-120 keV), a Cobalt-60 beam, 6 & 18 MV photon beams of a conventional linear accelerator. We found a dose enhancement factor (DEF) of from 1.4 to 3.7 for monoenergetic kilovoltage beams, while the DEFs for megavoltage beams were negligible and less than 3% for all GNP sizes and concentrations. The optimum energy for higher DEF was found to be the 90 keV monoenergetic beam. The effect of GNP size was not considerable, but the GNP concentration had a substantial impact on achieved DEF in GNP-based radiation therapy. The results were in close agreement with some previous studies considering the effect of photon energy and GNP concentration on observed DEF. Application of GNP-based radiation therapy using kilovoltage beams is recommended.

A Real-time Scintillating Fiber Detector to Improve Patient Safety in External Beam Radiation Therapy

The purpose of this study is to improve patient safety in radiation oncology by implementing real time verification of fluence delivered during external beam radiation therapy using a radiation hard scintillating fiber sensor array architecture and real time data acquisition hardware. Radiation oncology patients undergo highly complicated treatment procedures in which delivered dose should be controlled, recorded, and verified for quality and safety. Currently, radiation treatment cumulative dose is measured prior to delivery, which is not sensitive to temporal variations that could occur during imaging or treatment. Therefore, the actual quality and safety of the radiation therapy procedure is unknown and any deviation from the intended dose cannot be identified, thus cannot be corrected. To address this gap in patient safety, we developed scintillating fiber array sensors with real time data acquisition hardware to implement real time fluence verification of photon and electron beams. These on line detectors can operate on a wide range of clinical devices through modification of sensor element geometry and front end electronics operating parameters. This common technological platform provides a simplified method to construct low cost radiation based modality specific dosimeters. As an example, we developed and tested a scintillating fiber array for linac external beam radiation therapy with plastic encapsulated scintillating fibers and photodetectors integrated in a monolithic configuration. This detector has high speed front end amplifiers for real time acquisition and verification of the pulsed linac output during treatment. We determined the detector sensitivity and linearity response with respect to beam intensity and field size for the clinical range of photon beam energies. The scintillating fiber spatial detection sensitivity is 2.3 mV/mm with a statistical error of 0.5 mV. Fiber linearity response with respect to beam intensity and field size was within 2% for all tested beams. The front end amplifiers have a time response of 250 nsec. The fiber dosimeter has a maximum beam attenuation of 2.4% and is used in an online transmission configuration for in vivo treatment delivery accuracy monitoring. The development of this technology addresses the urgent need for in vivo real time quality assurance of external beam therapy to increase patient safety. The developed linear fiber array has high spatial and temporal resolution to provide accurate dose verification, thus providing therapists real time feedback of external beam treatment fluence with minimum beam attenuation to increase patient safety. Configurations for other external beam treatment devices such as tomotherapy machines could be done with little design modification.