Chamber Film Research Articles

SU-E-T-197: Normoxic Polymer Gel Dosimetry for Intensity Modulated Radiation Therapy

Purpose: To evaluate a tissue equivalent normoxic polymergeldosimeter as a tool for 3‐dimensional dosequality assurance for intensity modulated radiation therapy(IMRT) by measuring the dosecharacteristics of therapeuticradiation by Magnetic Resonance Imaging(MRI). Methods: Polymergel under normoxic conditions was synthesized using gelatin, methyacrylic acid (MAA), hydroquinone (HQ) and tetrakis hydroxymethyl phosphonium chloride (THPC), and polymergeldosimeter was fabricated by placing it into each phantom for the appropriate experiments. Co‐60 gamma‐rays and a 6 MV photon beam were used for the dose reaction experiments. The dose range was 0∼20 Gy. The dosecharacteristics of the polymergeldosimeter were compared with those of the ion chamber and Gafchromic EBT2 film using 3.0T MRI. Results: The linear correlation coefficient was r2=0.970, r2=0.999 and r2=0.972 for the polymergeldosimeter,ion chamber and film, respectively. The percentage depth dose at a depth of 50 mm was 85.8% and 84.6% for the polymergeldosimeter and ion chamber, respectively. The flatness and symmetry of the geldosimeter on the cross‐plane were 3.80% and 3.58%, respectively. After applying the geldosimeter to IMRT, the dosages measured in the 100% dose domain of therapeutic planning for the axial, sagittal and coronal planes were 96.2%, 103.0% and 100%, respectively. Conclusions: The results show a relatively high level of precision in the high dose range in IMRT, which is important in clinic sites. The possibility of this as a 3‐dimensional dosequality assurance tool of a polymergeldosimeter was confirmed This work was supported by National Research Foundation of Korea Grant funded by the Korean Government.

SU-GG-T-395: Monitor Unit Calculation for Electron Arc Therapy Using Monte Carlo Simulations

Purpose: This study reported a monitor unit (MU) calculation method for electron arc therapy. This MU calculation was carried out using Monte Carlo simulation and verified by measurement. Methods and Materials: The 9 MeV phase space electron beam (2.6 × 21 cm2) attached to the block tray holder of a Varian 21 EX linac was generated using the EGSnrc‐based BEAMnrc code, and was verified by dosimetric measurements using ionization chamber and radiographic film. The relative output factor (ROF), source‐to‐surface (SSD) offset and dwell factor (DF), required in the MU calculation, were determined using measurement and Monte Carlo simulation. Solid water rectangular and cylindrical phantom made of polystyrene were used in the measurements. Results: Deviations of ROF, SSD offset and DF between measured and Monte Carlo results were 1.2%, 0.18% and 1.5% respectively. Our results show that the DF decreased with an increase of the treatment arc angle (α), and such decrease of DF was more significant in the α range of 0 – 60 deg than 60 – 120 deg. Comparing the DF determined using the rectangular and cylindrical phantom through measurement and Monte Carlo simulation, we found that the DF determined by the rectangular agreed well with that by the cylindrical phantom within ±1.2%. It shows that a simple setup of solid water rectangular phantom was sufficient to replace the cylindrical phantom to determine the DF associated with the electron arc. Conclusions:Monte Carlo simulation was proved to be an alternative way to determine the MU for electron arc therapy. Since Monte Carlo simulation can generate pre‐calculated database of ROF, SSD offset and DF for the MU calculation with a reduction of human effort and linac beam‐on time, it is suggested to integrate Monte Carlo simulation into the commissioning of electron arc therapy.

SU-GG-T-50: Evaluating Source Constancy from the Xoft Electronic Brachytherapy System

Purpose: The Xoft Axxent 50 kVp electronic brachytherapy source is currently used to treat a variety of clinical sites including endometrial carcinoma (single‐channel HDR cylinder), accelerated partial breast irradiation (single‐channel HDR balloon), and surface lesions (external cone applicator). Unlike conventional linac‐based dosimetrycontrol systems, the 50 kVp x‐ray source is not monitored during treatment, raising the question of source output stability as a function of absolute dose rate and the spatial constancy of the x‐ray emission. This study evaluates the constancy of the Xoft Axxent 50 kVp electronic brachytherapy source using a pinpoint ion chamber and EBT2 GafChromic film. Materials and Methods: A 0.015 cm3 pinpoint ion chamber was used to verify the constancy of source output during pre‐treatment quality assurance checks using a lucite phantom. The phantom is designed to accept a single channel Xoft applicator and a chamber verification plug. A standard treatment plan was developed to verify source output from a single 50 second dwell position. EBT2 GafChromic film was also used to verify the spatial constancy of a coronal dose plane anterior to the source channel. Results: A total of 37 independent quality assurance measurements were performed using 7 different Xoft sources. The mean pinpoint chamber reading was 10.34 nC with a relative standard error of 2.5%. The ratio of the maximum and minimum chamber reading versus the mean was 1.06 and 0.96, respectively. In comparison, the Xoft on‐board well chamber measures a relative standard error of <1% for the pre‐treatment air‐kerma strength. Conclusions: The output from the Xoft electronic brachytherapy source was monitored using a pinpoint ion chamber during pre‐treatment quality assurance checks. The relative standard error of 37 independent ion chamber readings was 2.5% indicating a relatively stable output across multiple x‐ray tubes in a clinical setting. Research sponsored by the Xoft Corporation.

Sci-Fri AM(2): Brachy-02: Realizing Absorbed Dose Directly for HDR Ir-192 Brachytherapy: Water Calorimetry and comparison to Ion Chamber, Gafchromic Film, and TG-43

A new standard based on direct measurement of absolute absorbed dose to water in HDR 192 Ir brachytherapy using water calorimetry is discussed. The calorimetry results are compared with the results from the in‐water measurement of absorbed dose using ionization chamber and EBT Gafchromic film reference dosimetry, as well as TG‐43. The water calorimetry measurements were performed using a spring‐loaded catheter holder system that mounts onto a parallel‐plate calorimetric vessel. The COMSOL MULTIPHYSICS™ software was used to perform the numerical heat‐transport calculations. The calorimetric measurements were performed with three different 192 Ir sources with nominal S k ranging from 31600–36940 U (i.e. 7.6–9.2 Ci activity) over a one‐year period. A source‐to‐detector separation d src ‐ det ranging between 51–67 mm, and an irradiation time ranging between 200–300 s were used. Based on water calorimetry, an average dose rate to water of 361±11 μGy/(h.U) at d src ‐ det =55 mm was measured. Chamber reference dosimetry resulted in a dose rate measurement of 366±9 μGy/(h.U), while EBT Gafchromic film reference dosimetry resulted in 368±11 μGy/(h.U). From TG‐43 protocol, we obtain a value of 364±15 μGy/(h.U), a 0.8% difference from water calorimetry. All Results agree well to within uncertainty. Our work paves the way to successful primary absorbed dose determination for 192 Ir using calorimetric techniques.

Practical uses of liquid methane in rocket engine applications

Liquid methane has been considered an attractive rocket propellant for several decades. However, most rocket engine development efforts in the last 30 years have focused on using more traditional fuels such as hydrogen, kerosene, and earth storables, without any serious development or application of methane to propulsion systems. This paper presents a summary of recent 870 lbf thrust LOX / LCH 4 (liquid oxygen/liquid methane) engine test results and recent LOX / LCH 4 torch igniter testing. Multiple test series were conducted using both radiation cooled and ablative chamber hardware. This engine testing yielded measured minimum C * efficiencies of 97% using non-optimized engine hardware, with expectations that better than 99% efficiency can readily be achieved with minor hardware optimization. The combustion process was shown to be stable in all tests and the operating transition from poor quality methane (two-phase fluid) at startup to liquid–liquid, sub-cooled, steady state operation was demonstrated. Engine test results showed chamber wall compatibility with high propellant mixture ratios and excellent boundary layer performance of methane as a chamber film coolant. The Aerojet work on methane propulsion and energy applications is also briefly summarized.

Poster - Thurs Eve-19: IGRT QA for helical tomotherapy

Helical tomotherapy (HT) with daily imaging using mega-voltage computed tomography for 3D image guided radiotherapy (IGRT). We present two techniques developed in our department to verify the integrity of the HT IGRT process. A phantom was constructed of two equally sized (5×10×10cm3 ) polystyrene blocks stacked on top of each other, each piece having a hole capable of receiving a small volume ionization chamber. A piece of Radiochromic film fits neatly in between the blocks. The phantom was CT scanned and the CT slices were transferred to the HT treatment planning system (TPS). The first procedure is used daily to test the image registration aspects of the IGRT process, and involves setting the phantom on the tomotherapy treatment unit table in an arbitrary position, imaging it, and performing image registration to determine what displacements are necessary to return the phantom to the planned position. A variation of this test is to place the phantom at a position incurring known displacements and ensuring the registration recognizes the shifts. The second procedure verifies the entire IGRT procedure, and includes the first procedure and the delivery of a treatment plan. An inverse plan is created to deliver simultaneously 2 and 3 Gy to 2 pre-defined targets. The treatment plan can be setup as a QA plan in the TPS software, allowing for a detailed comparison of ion chamber measurements and film dosimetry to the planned dose distribution. We have found that these QA procedures adequately test the IGRT capabilities of our HT unit.

SU-GG-T-193: Measurement of Penumbra Using a 2D Ionization Chamber Array

Purpose: Measurement of penumbras associated with jaws and MLCs are problematic in a clinical setting. Typically penumbra are measured by scanning a field profile with a scanning ion chamber, diode or with film. Each measurement modality has a associated with it different difficulties; ion chambers and diodes have a spatial resolution problems, films over respond to low energy photons in the penumbra and umbra regions. These problems affect the results of measurements in the penumbra regions, ion chamber and diode measurements convolve the resolution of the detector with the penumbra function, while film overestimates the values in the low dose regions of the penumbra and umbra. This work reports the results of using a 2D ionization array ((MatriXX, Scanditronic‐Wellhofer) to measure penumbra regions. Method and Materials: The 2D ionization array consists of 1020 separate ionization chambers. The array is arranged in a 32 × 32 chamber grid with the four corner chambers missing. Each chamber is 7.6 mm on center with an active volume of 0.03 cm3. Results from this group have been report previously using this array for IMRT measurements. In this work the penumbra is measured by placing a rotated jaw edge within the area of the array and using a blind deconvolution to determine the spatial response of the detectors and the shape of the penumbra simultaneously. Results: Results of penumbra reconstruction for various field sizes and depths are reported. These results are compared to ion chamber scanning methods and film. Conclusion: Use of the 2D array to measure penumbra widths show good agreement with ion chamber scanning measurements and do not suffer from over response of film measurements in the low dose regions. An average spatial response of the detectors is also determine simultaneously by this procedure.

WE-A-AUD C-01: IMRT Commissioning: A Multi-Center Evaluation of a Standardized Test Protocol

There is evidence that IMRT treatments may not always be as accurate as practitioners believe. In 2006, the Radiological Physics Center (RPC) reported that of the 155 institutions that had irradiated a head and neck phantom as part of an IMRT credentialing process, 54 (35%) had failed to meet accuracy criteria of 7% for dose in a low gradient region and/or 4 mm distance to agreement in a high gradient region. This experience strongly suggests that some clinics have not adequately commissioned their planning and delivery systems for IMRT. By “commissioning”, we mean beam modeling in the treatment planning system and initial verification by phantom studies that treatments can be planned, prepared, and delivered with sufficient accuracy. Task Group 119 of the American Association of Physicists in Medicine (AAPM) has developed a specific set of tests for IMRT commissioning that are representative of common clinical treatments and pose a range of optimization problems requiring simple to complex modulation patterns. The tests include mock prostate, head and neck, and peri‐spinal geometries. Members of the group have planned and delivered the treatments using their local planning and delivery systems, and then assessed the resulting doses using broadly available dosimetry tools following a specified protocol. Measurements included ion chamber point doses and film dosimetry on selected planes for all fields irradiating the phantom. Institutions also evaluated dose distributions produced by individual fields using detector arrays, film, or EPID. Eight institutions have reported their results with nine different combinations of planning systems and accelerators. All have passed the RPC IMRT phantom test. The summary of the preliminary data shows: One institution identified the need to improve the beam modeling using these tests for better agreement between planned and delivered doses for IMRT. The presentation will illustrate (1) that the percent of points passing the gamma criteria is highly dependent on the details of the implementation of the test and (2) that testing the individual fields with a gamma test can be insensitive to problems and is not sufficient for commissioning. (3) The tolerance limits based on Dose‐difference distribution, distance‐to‐agreement (DTA), and a numerical gamma index for IMRT QA are often not adequate because all these methodologies do not account for space‐specific dose uncertainty information. (4) beam modeling affects the plan and delivered dose agreement. Educational Objectives: 1. To describe the uncertainties in IMRT planning and delivery‐describe the impact of spatial and dosimetric uncertainties on the IMRTdose distribution. 2. Obtain examples of commissioning results for standardized IMRT studies that can be used for comparison with a clinic's IMRT system. 3. See how these standardized tests can be downloaded or created for local testing purposes. 4. See examples of how the gamma criterion can vary depending on details of its implementation. 5. See examples of limitation of gamma criterion testing for identifying problems with individual IMRT fields.

WE-D-224C-09: Dosimetric Evaluation of Proton Field Matching by a Robotic Patient Positioner

Purpose: The objective of this study is to evaluate the accuracy from a dosimetry point of view with which proton field matching can be accomplished. Method and Materials: This proton therapy center currently treats patients with a nominal 208 MeV proton beam in a single Fixed Horizontal Beam Line (FHBL) room that employs a double passive beam spreading system with a fixed range modulator. The FHBL room takes advantage of a novel robotic patient positioner system (PPS) providing 6 degrees of freedom with a specified accuracy of 300 microns when transiting up to a 200 kg payload. To investigate field matching doses three methods are used: calculations from a treatment planning system, film dosimetry measurements and scans using a miniature ionization chamber. The field delivery for this study consists of four proton fields matched by the robotic PPS. The measurements are performed in a solid water phantom for the film and a water phantom for the ionization chamber scans Results: The planned dose delivery for the central field is normalized to 100%. The average relative dose values in the field junctions are 128%, 135% and 130% for the ionization chamber scans, film dosimetry and treatment planning calculation, respectively. In this case this was thought to be clinically acceptable as the volume lay entirely within the target. Conclusion:Proton therapy is suitable for treating volumes of relatively large area and shallow depth. In this way the ranged property of the protons can spare underlying structures. The sharp proton penumbra and precision of a robotic patient positioner simplifies field matching. Further study is underway with a half beam block to investigate the range of junction doses that can be expected under a variety of field matching conditions.

Tin foil as bolus material for therapeutic electron beams from the Varian Clinac 2100C/D

Tin foils of sub-millimetre thickness have been investigated as bolus material for therapeutic electron beams from the Varian Clinac 2100C/D linear accelerator. Measurements with ionisation chamber and radiographic film in Plastic Water or water were performed under tin foil bolus to determine surface dose, therapeutic ranges, output factor correction, penumbra and dose outside the field edge. Appropriate thicknesses of tin foil for 90% dose at the surface were found to be approximately 0.3 mm for 6 MeV, and 0.4 mm for 9 MeV and 12 MeV. Enhanced therapeutic interval with tin foil bolus over water-equivalent bolus has previously been reported, but was found not to be evident for 12 MeV and for a small (4 x 4 cm2) 9 MeV field. The penumbra width of fields with tin foil and water-equivalent bolus were found to be within 2 mm, while the doses at 1 cm outside the field edge were within 1.5% of peak dose. Output factor corrections for fields with tin foil were measured as within 2% of unity. Air gaps between the tin foil and phantom surface up to 5 mm were observed to have minimal effect on output correction factor, relative surface dose, and therapeutic range.

Comparison of dose calculation algorithms with Monte Carlo methods for photon arcs.

The objective of this study is to seek an accurate and efficient method to calculate the dose distribution of a photon arc. The algorithms tested include Monte Carlo, pencil beam kernel (PK), and collapsed cone convolution (CCC). For the Monte Carlo dose calculation, EGS4/DOSXYZ was used. The SRCXYZ source code associated with the DOSXYZ was modified so that the gantry angle of a photon beam would be sampled uniformly within the arc range about an isocenter to simulate a photon arc. Specifically, photon beams (6/18 MV, 4 x 4 and 10 x 10 cm2) described by a phase space file generated by BEAM (MCPHS), or by two point sources with different photon energy spectra (MCDIV) were used. These methods were used to calculate three-dimensional (3-D) distributions in a PMMA phantom, a cylindrical water phantom, and a phantom with lung inhomogeneity. A commercial treatment planning system was also used to calculate dose distributions in these phantoms using equivalent tissue air ratio (ETAR), PK and CCC algorithms for inhomogeneity corrections. Dose distributions for a photon arc in these phantoms were measured using a RK ion chamber and radiographic films. For homogeneous phantoms, the measured results agreed well (approximately 2% error) with predictions by the Monte Carlo simulations (MCPHS and MCDIV) and the treatment planning system for the 180 degrees and 360 degrees photon arcs. For the dose distribution in the phantom with lung inhomogeneity with a 90 degrees photon arc, the Monte Carlo calculations agreed with the measurements within 2%, while the treatment planning system using ETAR, PK and CCC underestimated or overestimated the dose inside the lung inhomogeneity from 6% to 12%.

Evaluation of the Shielding Design of the Fuel Handling and Storage System in the Prototype FBR Monju

Shielding performance tests of the fuel handling and storage system were carried out at Monju in October 1993. The performance of the shielding of the fresh fuel storage rack against neutron and gamma radiation from fresh fuel assemblies, that of the invessel fuel transfer machine (IVTM) and the ex-vessel fuel transfer machine (EVTM) against neutron and secondary gamma-rays generated in the shielding or structural materials from the neutron source assembly (252Cf), were assessed. Dose rates were measured using rem-counters and solid-state track-detectors (SSTDs) for neutrons and ionization chamber survey-meters and film dosimeters for gamma-rays. This paper presents an outline of the measurement methods, and results, the design requirements and the design margins, which were evaluated by comparing the measurements with the calculations based on FBR shielding analysis methods.

Thermoluminescence Properties of Novel Thin Clear Fused Quartz Dosemeters

The thermoluminescence properties of novel thin (100 μm) dosemeters of clear fused quartz (CFQ) have been investigated as part of a progranime to optimise the measurement of the spatial beta dose distribution around hot particles and to provide benchmark measurements for the parallel validation of Monte Carlo code calculations. Using the isothermal annealing method seven TL peaks (P1-P7) have been identified for CFQ in the temperature range 122-310°C. The isothermal method has been used to determine the energy depth E and frequency factor s for peaks P2, P3 and P4. The heating rates method has been used to determine the values of E and s for peaks P1 and P6. The results have been compared with'those of computerised glow curve deconvolution. There were large disparities between the results of different methods. These are probably due to artefacts in the methods related to the large number of overlapping peaks. The reproducibility of individual CFQ on the basis of TL integration up to 400°C is good (±5%). On the other hand, the individual sensitivity is different among all the dosemeters (40) from the same batch and the difference in the TL signals sometimes reaches a factor of 5. An analysis of the TL dose response in terms of low and high temperature regions (PL, 50-150°C; P H , 250-350°C) showed a linear response up to ∼60 Gy for PL and a slightly sub-linear response up to only -2 Gy for PH. The sensitivity of CFQ has been found to be -15% of that of LiF TLD 100 and the minimum detectable dose (2σ above background) is ∼580 μGy. The TL response of CFQ was found to be sensitive to natural light exposure. The TL yield was reduced to typically 20% of is original value after only 10 h exposure to natural light at room temperature. After this period of time both peak P1 and peak P2 have been completely removed. Samples kept shielded from light suffered only a 12% decrease of total TL intensity after 48 h at room temperature, A feasibility study has been carried out successfully using CFQ to measure directly the dose distribution around a test 60 Co hot particle source using an imaging photon detector (IPD) technique. CFQ/IPD measurements have a much greater sensitivity than extrapolation chamber and radiochromic dye film techniques, which have previously been used for this application.

Factorial Cumulant Moments and Short Range Correlation in P-P Collisions at 400 GeV/c

The pseudorapidity distribution of charged particles produced in p-p collisions at 400 GeV/c was measured by using the Lexan bubble chamber films offered by the CERN NA27 collaboration. The scaled factorial cumulant moments have been calculated. The results show that the second order cumulants have positive values, while the cumulants of higher order are consistent with zero except for the case with nch ⩾ 4 events, where the third-order cumulants have small positive values beyond the statistical uncertainties. From Monte Carlo events with the same single particle spectrum and no correlations, we observed that for broad mixed-multiplicity distributions, a significant part of K2 is coming from the single-particle fluctuation due to the fluctuation multiplicity.

The early history of the HPD

The initial stages of the development of a system for the rapid measurement of bubble chamber photographs are described. At first called the IEP-X and then IEP-Y, the device which came to be known as the HPD was adopted by several groups both in Europe and the USA. Based on a mechanically generated flying spot, it was the first machine to use this technique for bubble chamber film measurement. Operated in the “road guidance” mode, it provided considerable measurement capacity combined with excellent precision and very acceptable bubble density measurements.

Dosimetry of Planar and Punctiform Beta Sources Using an Automated Extrapolation Chamber and Radiochromic Dye Films

Dosimetry of Planar and Punctiform Beta Sources Using an Automated Extrapolation Chamber and Radiochromic Dye Films

Dosimetry of Planar and Punctiform Beta Sources Using an Automated Extrapolation Chamber and Radiochromic Dye Films

Dosimetry of Planar and Punctiform Beta Sources Using an Automated Extrapolation Chamber and Radiochromic Dye Films

An automatic device for counting a large number of tracks in CR39

In order to perform an indoor survey of internal exposure to radon and its short life daughters using track etching passive detectors, it is necessary to analyze a large amount of information without spending a lot of time and manual work. For this purpose, the possibility of utilizing PEPR (Precision Encoding and Pattern Recognition) normally used in the digitization of low energy particle tracks recorded on Bubble Chamber film has been studied. A special subroutine has been set up for a PDP 11/45 Computer to guide PEPR in studying the tracks of α-particles in CR39.

An on-line system for the analysis of track chamber film

The Inter-University Institute for High Energies in Brussels is involved in experiments based on the analysis of film from several track chambers: the “big” and “little” European Bubble Chambers (BEBC and LEBC) and the UA5 streamer chamber. In order to scan and measure these difficult pictures in optimal conditions, a rather versatile device which we originally called “BEBC table” was designed in the laboratory, offering a high-precision track-ball driven X− Y stage, optical projection with dual magnification, and various operator controls. A PDP-11/40 running RSX-11 M provides real-time support for five of these devices. A link between the PDP-11 and a DEC system 10 allows the geometrical reconstruction of the events to be performed on-line, with feedback to the BEBC table operator.

Track and bubble density measurement with KAMA-II

The second KAMA system (KAMA-II) is controlled by an on-line mini-computer. Simple and reliable algorithms for track measurement and bubble density measurement with KAMA-II have been developed. Results of measurements for events having associated V 0's and kinks from 3.0 and 4.0 GeV/c p p KEK 1 m hydrogen bubble chamber film are discussed.