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Bragg Peak Flattening Filter for Dose Delivery Utilizing Energy Stacking region (Fujitaka, Takayanagi, Fujimoto, Fujii, 1' G. Warrell Terunuma 3101 ; Weber, Kraft 2765).
Abstract Previous ripple filters have either used multiple Proton beam radiotherapy is attractive for cancer treatment because of the unusually sharp Bragg simply consisted of single sheets of material wit peak exhibited by proton beams. However, many beam energies are needed to cover the entire thicknesses (Fujitaka, Takayanagi, Fujimoto, Fr volume of the tumor, increasing the sensitivity of the treatment to target motion. It is therefore Terunuma 3 JO I ; Weber, Kraft 2767). The goal ' desirable to have a flattening filter that necessitates fewer beam energies to cover the target by single-layer flattening filter, consisting of an ak spreading out the Bragg peak. A prototype aluminum grid flattening filter was designed, proton Bragg peak in a clinically useful way. Tl manufactured, and tested at the Indiana University Cyclotron Facility (IUCF). It has been found the Indiana University Cyclotron Facility (IUCI feasible to use such a filter to treat the patient with fewer beam energies. However, further work is necessary to generate a sufficiently uniform dose for clinical purposes. Materials and Methods
Introduction Aluminum, an easily machined material with a 1 filter in order to minimize the lateral scattering'
obert Wilson initially proposed proton radiotherapy for cancer treatment in his seminal for manufacturing the flattening filter had a thic 1946 paper, Radiological Use of Fast Protons (Wilson 487). Since then, twenty-six clinical first step in designing the prototype flattening fi R find the proper weighting factor, defined as the proton therapy facilities have been built worldwide, and nearly as many are planned to be built (Kraft 1083). Although the infrastructure for proton therapy is far more expensive than photon of empty space in it, as seen by the unmodulate1 or electron therapy, the unusually sharp Bragg peak of protons makes them very attractive for with and without being passed through the alurr cancer therapy. The short Bragg peak means that at energies typically used for clinical purposes, energies: 6 cm in water and 8 cm in water. (As t most of the beam energy is deposited in the last few millimeters of travel. This makes precision material is directly proportional to its energy, p1 targeting of the tumor possible, but also necessitates a large number of beam energies to provide a in water.) As shown in Figure 1, the data were t uniform dose in depth over the target region. Moreover, the small irradiated region sensitizes the phantom. This apparatus was used to find the d< treatment to target motion. A single proton energy may be split up by means of a propeller and the beam passed through the aluminum plat modulator (Koehler, Schneider, and Sisterson 438) or a series of binary in-beam degraders to pull back the maximum penetration range in carefully weighted energy steps (Farr, Mascia, Hsi, Allgower, Jesseph, Schreuder, Wolanski, Nichiporov, Anferov 4845). In order to cover the entire lateral area of the tumor, beams may be spread transversely either by passing the beam through thin lead foils or by utilizing a wobbling magnet to scan the beam across the target area. The latter method is used by the beam nozzles at the Midwest Proton Radiotherapy Institute (MPRI) (Anferov 3560).
A possible alternative to traditional methods of beam spreading is to use a Bragg peak flattening filter, also known as a ripple filter, to split up the proton beam. Flattening filters typically consist of multiple sheets, each containing alternating regions ofmater!al and empty space. As the beam passes through varying thicknesses of material, it is split into multiple beams. The number of beams depends on the number of layers in the ripple filter. As the beams reach the target, they add together to produce a dose profile with a flattened Bragg peak. The result is that a single beam irradiates a large portion of the tumor, and fewer beams are needed to cover the entire targeted
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Delivery Utilizing Energy Stacking region (Fujitaka, Takayanagi, Fujimoto, Fujii, Nishiuchi, Ebina, Okazaki, Hiramoto, Sakae, :ell Terunuma 310 I; Weber, Kraft 2765).
1ct Previous ripple filters have either use? multiple layers of material with slits cut into them, or have ·eatment because of the unusually sharp Bragg simply consisted of single sheets of material with grooves cut into them of depth-varying beam energies are needed to cover the entire thicknesses (Fujitaka, Takayanagi, Fujimoto, Fujii, Nishiuchi, Ebina, Okazaki, Hiramoto, Sakae, the treatment to target motion. It is therefore Terunuma 3101 ; Weber, Kraft 2767). The goal of this project was to determine if a much simpler :s fewer beam energies to cover the target by single-layer fl attening filter, consisting of an aluminum grid, could be used at MPRI to flatten the 1minum grid flattening filter was designed, proton Bragg peak in a clinically useful way. The filter was designed, manufactured, and tested at Cyclotron Facility (IUCF). It has been found the Indiana University Cyclotron Facility (IUCF). fewer beam energies. However, further work is clinical purposes. Materials and Methods
Aluminum, an easily machined material with a relatively low density, was chosen for the fl attening filter in order to minimize the lateral scattering effects of the protons. The aluminum sheet chosen •therapy for cancer treatment in his seminal for manufacturing the flattening filter had a thickness of0.063 inches (approximately 1.6 mm). The is (Wilson 487). Since then, twenty-six clinical first step in designing the prototype flattening filter was to do computer simulations of it in order to ·ldwide, and nearly as many are planned to be find the proper weighting factor, defined as the ratio of the area of material in the filter to the area oton therapy is far more expensive than photon of empty space in it, as seen by the unmodulated proton beam. To do this, data on the proton beam Jf protons makes them very attractive for with and without being passed through the aluminum sheet were taken at two clinically significant nergies typically used for clinical purposes, energies: 6 cm in water and 8 cm in water. (As the penetration depth of a proton in a uniform nillimeters of travel. This makes precision material is directly proportional to its energy, proton energies are typically measured in centimeters a large number of beam energies to provide a in water.) As shown in Figure 1, the data were taken by means of an ionization chamber in a water rer, the small irradiated region sensitizes the phantom. This apparatus was used to find the dose versus depth profile of the unmodulated beam ay be split up by means of a propeller and the beam passed through the aluminum plate. r a series of binary in-beam degraders to pull ighted energy steps (Farr, Mascia, Hsi, , Anferov 4845). In order to cover the entire ·ersely either by passing the beam through thin b.e beam across the target area. The latter 'roton Radiotherapy Institute (MPRI)
spreading is to use a Bragg peak flattening ton beam. Flattening filters typically consist s of material and empty space. As the beam plit into multiple beams. The number of beams 's the beams reach the target, they add agg peak. The result is that a single beam ns are needed to cover the entire targeted
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Figure 1. The upper image shows the proton Once the dose-versus-depth data of the beam hi beam nozzle and the water phantom used to Microsoft Office Excel to obtain a preliminary • find the dose-versus-depth data for the water equivalent thickness of the aluminum pl ai modulated and unmodulated proton beams, travel through water to undergo the same energ and later to test the completed flattening filter. The lower image is a schematic of the determined. Using these data, Excel was used t< gantry beam nozzle. The beam is spread out defined as the area of aluminum in the plate div laterally by the wobbling magnet, on the far weighting factor, the spreadsheet predicted that left, and passed through the range modulator, a series of binary in-beam energy degraders. least 80% of the maximum dose would be depo The X and Y jaws were formerly used to energies. The spreadsheet also predicted that th• shape the beam in the X-Y plane (under the some ripple, while the 8 cm in water beam wou convention that the beam travels along the Z axis), but their function has been replaced by simulation suggested that at the chosen weighti1 the aperture, placed on the nozzle for of the flattened 6 cm in water Bragg peak woul< treatments. The prototype flattening filter flattened 8 cm in water peak would have a sligh was affixed between the wobbling magnet and the range modulator, in order to provide sufficient distance between the filter and the target for scattering effects to conceal the grid structure of the flattening filter.
The proton beam used at MPRI is accelerated by a cyclotron to a fixed extraction energy of208 mega-electron volts (MeV), and sent to one of three treatment rooms. Two of the treatment rooms contain 90-ton beam gantries that rotate the beam nozzle around the patient to obtain nearly 4p geometry around the tumor. The patient is secured to a carbon-fiber treatment couch attached to a large robotic arm, which moves so that the tumor is at the isocenter of the beam nozzle. Control of the beam energy (and therefore the penetration depth) is accomplished by energy degrading range 6 modulators in each treatment room and built into each of the beam nozzles. In the case of patient ~ Deplh, tm treatments, a beam aperture and compensator specifically designed for each patient are placed on A more accurate value for the proper weighting the end of the beam nozzle to confine the dose to the treatment area. No aperture or compensator Bragg Peak Width (BPW) and LAMINATE for was used to find the dose versus depth for this project. The beam was passed horizontally through dose-versus-depth data for a Bragg peak and sp the water hantom. points. It adjusts the cubics to fit the remaining Figure 2. The dose-versus-depth by LaMPRI. LaMPRI uses this file to plan a sp profiles for the proton beam at 6 cm in water and 8 cm in water profile with an mso approximately the width of - OJ . ~ penetration depth, with and without The program modulates the beam by simulating .! modulation by the aluminum plate. ~ 0.6 was simulated by replacing one of the degrader The taller peaks are of the ~ unmodulated beam, and the shorter the filter. The weighting factor was found by di ~' 04 ones resulted from the beam passed calculated should go through the degrader by tt ~ through t.he aluminum. The effect of The optimal weighting factors obtained by LalV 01 the aluminum plate was to both shift With the spreadsheet's value for the weighting the Bragg peaks to a lower penetration and to decrease the depth profiles of both the 6 cm in water flattem intensity of the beam. peak would have a negative slope, as shown in Depth, cm 'j
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Once the dose-versus-depth data of the beam had been taken (Figure 2), they were imported into Microsoft Office Excel to obtain a preliminary estimate for the appropriate weighting factor. The water equivalent thickness of the aluminum plate, defined as the distance the beam would have to travel through water to undergo the s_ame energy shift as that produced by the plate, was determined. Using these data, Excel was used to estimate the desired weighting factor of the filter, defined as the area of aluminum in the plate divided by the area of empty space. With the proper weighting factor, the spreadsheet predicted that the mso (length of the path in water at which at least 80% of the maximum dose would be deposited) would more than double for both beam energies. The spreadsheet also predicted that the peak of the 6 cm in water beam would exhibit some ripple, while the 8 cm in water beam would have a more rounded peak. Finally, the simulation suggested that at the chosen weighting factor the peak of the dose-versus-depth profile of the flattened 6 cm in water Bragg peak would have a slight positive slope, while that of the flattened 8 cm in water peak would have a slightly negative slope (Figure 3).
Figure 3. The dose-versus-depth profiles for the simulated optimized ~ l flattened Bragg peaks, for the 6 cm 08 in water and 8 cm in water beam i energies, obtained by Excel. The j yclotron to a fixed extraction energy of208 !06 graph demonstrates the double-peak treatment rooms. Two of the treatment rooms . structure for the 6 cm in water i flattened Bragg peak. It also 1zzle around the patient to obtain nearly 4p E04 ~ suggests that the peak of the 6 cm in >a carbon-fiber treatment couch attached to a water dose profile has a slight 01 ~t the isocenter of the beam nozzle. Control of positive slope, while the 8 cm in water dose profile has a slightly 1) is accomplished by energy degrading range negative slope. :h of the beam nozzles. In the case of patient 5 Depth. cm 6 cally designed for each patient are placed on : treatment area. No aperture or compensator A more accurate value for the proper weighting factor was found with the FORTRAN programs :t. The beam was passed horizontally through Bragg Peak Width (BPW) and LAMINATE for MPRI (LaMPRI) (Gottschalk). BPW takes the dose-versus-depth data for a Bragg peak and splices together several cubics to fit a handful of the points. It adjusts the cubics to fit the remaining points and outputs a parameter file that can be read Figure 2. The dose-versus-depth profiles for the proton beam at 6 cm by LaMPRI. LaMPRI uses this file to plan a spread-out Bragg peak (SOBP) dose-versus-depth in water and 8 cm in water profile with an mso approximately the width of the simulated flattened Bragg peaks (Gottschalk). penetration depth, with and without The program modulates the beam by simulating the effect of beam degraders. The flattening filter modulation by the aluminum plate. was simulated by replacing one of the degraders with an aluminum plate of the same thickness as The taller peaks are of the unmodulated beam, and the shorter the filter. The weighting factor was found by dividing the amount of beam that the program ones resulted from the beam passed calculated should go through the degrader by the amount it calculated should be left unmodulated. through the aluminum. The effect of The optimal weighting factors obtained by LaMPRI were slightly less than those yielded by Excel. the aluminum plate was to both shift the Bragg peaks to a lower With the spreadsheet's value for the weighting factor, LaMPRI predicted that the dose-versus penetration and to decrease the depth profiles of both the 6 cm in water flattened Bragg peak and the 8 cm in water flattened Bragg intensity of the beam. peak would have a negative slope, as shown in Figure 4. Like the spreadsheet, LaMPRI predicted
65 PHYSICS that the peak of the dose-versus-depth profile of the 6 cm in water beam passed through the fl attening filter would display a ripple effect, while very little ripple would appear in the peak of the 8 cm in water flattened Bragg peak.
Figure 4. The normalized dose-versus-depth profiles for the simulated optimized flattened Bragg peaks, for the 6 cm in water and 8 cm in water energies, obtained by LaMPRI. Like the results from Excel, the 6 cm in water peak is predicted to have a double peak structure, while the 8 cm in Once the flattening filter had been manufacture water peak is rounded. With programs used to find the weighting factor was the weighting factor from proton beam with penetration ranges of 6 cm in Excel, both profiles exhibit a negative slope over the and ion chamber apparatus that had been used t flattened peak. the flattened beams as a function of depth. The laterally in the beam to verify that the period of scattering to mask its structure in the target. No At first, the programs FitScan Dose Delivery (FitDD) and LAMINATE, also published by the water phantom was found. Gottschalk, were used to determine the weighting factor. It was found that LAMINATE was unable to return accurate results for an SOBP with an m9o of less than approximately 1.5 cm. The calculated weighting factor would be far too small, and the dose-versus-depth profile would not be Ii uniform. The program would return an error message if an attempt was made to obtain an m9o of less than 1 cm, whereas the experimentally determined m9o' s of the flattened Bragg peaks were less ~ 0.8 than 0.5 cm. Because of these limitations, LaMPRI was used for the project instead. - ~ ~ ~ 0.6 The ripple filter was manufactured from a sheet of aluminum 1.6 mm thick, with slits cut through it .§ ~ via electrical discharge machining (EDM), as seen in Figure 5. The slits were each 3 mm wide, and ~ ~ 0.4 separated by 1.5 mm of aluminum to obtain a 50% weighting factor. This gave the grid pattern a z~ period of 4.5 mm, considered sufficiently small to allow multiple scattering of the protons travelling through the filter to prevent the structure of the grid from being projected into the target. Initially, the filter was planned to have 2 mm wide slits separated by 1 mm of aluminum, but the period of the grid pattern had to be increased as a result of excessive vibration observed during the cutting process, which was feared to prevent accurate cutting of the slits to the required tolerance of De pth, cm ± 0.002 inches (approximately 0.05 mm).
Once the results of the programs had been fou peaks, the next step was to use the flattened Br beam degraders in the MPRI gantry beam noz2 with the ripple filter required eight energy step by flattened Bragg peaks lacked a uniform dos1
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: 6 cm in water beam passed through the Figure 5. The completed flattening filter, very little ripple would appear in the peak of the with the grooves cut by electrical discharge machining. The two grooves near the top of the filter, as viewed in this image, are the result of the attempt to Figure 4. The normalized machine the filter with slits 2 mm wide. dose-versus-depth profiles for The filter was completed with slits 3 mm the simulated optimized wide. The manufacture of the filter flattened Bragg peaks, for the 6 proceeded without any further problems, cm in water and 8 cm in water except for the aluminum plate slipping at energies, obtained by LaMPRI. one point, evidenced by the discontinuity Like the results from Excel, the in the pattern near the top. 6 cm in water peak is predicted to have a double peak structure, while the 8 cm in Once the flattening filter had been manufactured, its performance as well as the accuracy of the water peak is rounded. With programs used to find the weighting factor was experimentally assessed by using a monoenergetic the weighting factor from Excel, both profiles exhibit a proton beam with penetration ranges of 6 cm in water and 8 cm in water. The same water phantom negative slope over the and ion chamber apparatus that bad been used to obtain the initial data was used to find the dose of flattened peak. the flattened beams as a function of depth. The ion chamber in the water phantom was also moved laterally in the beam to verify that the period of the filter pattern was small enough to allow scattering to mask its structure in the target. No evidence of the grid pattern being projected into 1 ) and LAMINATE, also published by the water phantom was found. :tor. It was found that LAMINATE was unable 1f less than approximately 1.5 cm. The nd the dose-versus-depth profile would not be Figure 6. Experimentally I +------~-- determined dose-versus-depth ! if an attempt was made to obtain an m9o of profiles for the 6 cm in water and ~d m9o 's of the flattened Bragg peaks were less 8 cm in water flattened Bragg ~ 0.8 +-- vas used for the project instead. peaks, obtained by passing the ·! proton beam through the prototype ripple filter into a water uminum 1.6 mm thick, with slits cut through it 1 06 ~ phantom. The qualitative features . ~ Figure 5. The slits were each 3 mm wide, and 1l" of the profiles as predicted by ~ 0.4 eighting factor. This gave the grid pattern a LaMPRI were experimentally z~ realized, demonstrating the ow multiple scattering of the protons applicability of the program to the O.l -- fthe grid from being projected into the target. project. The irregularities in the its separated by I mm of aluminum, but the profiles at low depths are the result of fluctuations in beam ult of excessive vibration observed during the intensity. cutting of the slits to the required tolerance of Depth, cm
Once the results of the programs had been found to be accurate in simulating the flattened Bragg peaks, the next step was to use the flattened Bragg peak to generate a 4 cm wide SOBP, using the beam degraders in the MPRI gantry beam nozzles. According to LaMPRI, the SOBP generated with the ripple filter required eight energy steps instead of fourteen. However, the SOBP generated by flattened Bragg peaks lacked a uniform dose profile. According to LaMPRI documentation, an
67 PHYSICS optimal SOBP generated from pristine Bragg peaks may be obtained ifthe distance between peaks is approximately the same as the width of a Bragg peaks at 80% of the maximum (mso) (Preston, Koehler). It was found that decreasing the width of the 8 cm in water flattened Bragg peak by 0.3 mm would significantly decrease the amount of ripple in the final SOBP, although changing it by other amounts would make the ripple worse. It was also found that changes of the weighting factor of less than 10% hardly affected the shape of the SOBP. o•o- --+--+-- -r--1--- o~- · --+--+--+--+~ Figure 7. Graphs of simulated relative dose versus depth in the target for the SOBPs generated without (top) and with (bottom) the flattening filter, as obtained by LaMPRI. Without the flattening filter, 14 energies are Figure 8. Experimentally determined predicted to be needed to long SOBP obtained with the flatteni1 generate an SOBP with a smooth profile is due to an incorrect paramett dose profile in depth. With the is a fair amount of experimental error simulated flattening filter, only 8 profile than the amount predicted by l beam energies are needed to cover the 4 cm dimension of the tumor in the Z-axis, but there is a Results very significant amount ofripple over the dose profile. Given that adjusting the thickness of the By finding the shift in the Bragg peaks for the ( simulated filter dose not passed through the aluminum plate, the water e eliminate the ripple, it is believed plate was found to be 0.35 cm. It was estimated that the irregular dose profile is due to a software limitation on the flattened 6 cm in water beam would have ar the part ofLaMPRI. least 80% of the maximum dose would be depo beam would have an mso of0.65 cm. This was Finally, the prototype ripple filter was used to try to experimentally generate a 4-cm SOBP. The of the unmodified beams from 0.25 and 0.30 er dose-versus depth profile was obtained by means of a multi-layer ion chamber, consisting of a stack of thin, uniform ion chambers. Because the SOBP was generated with multiple beam energies, use The results from LaMPRI suggested that the op of the water phantom would have taken an excessive amount of time to obtain the dose-versus slightly smaller than Excel's estimate of 50%, r depth profile of the SOBP. However, the multi-layer ion chamber also introduced a fairly beam and 47.3% for the 8 cm in water beam. Tl significant amount of experimental error. justify manufacturing the filter with a 50% weii
According to the multi-layer ion chamber, use c in the dose-versus-depth profile; however, som amount of ripple observed experimentally is le ~
Discussion
Although the preliminary simulations from Exe prototype ripple filter would have a slightly pm
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Hlll -- 1y be obtained ifthe distance between peaks I I 0-'1 100 • I •"I 0.90 I ff'
According to the multi-layer ion chamber, use of the flattening filter decreases the amount of ripple in the dose-versus-depth profile; however, some ripple can still be detected in the profile. The amount of ripple observed experimentally is less than what LaMPRI predicted.
Discussion
Although the preliminary simulations from Excel suggested that the flattened Bragg peak of the prototype ripple filter would have a slightly positive slope, BPW and LaMPRI predicted the
69 PHYSICS opposite. The data taken from the completed flattening filter showed a slight negative slope. The 2009, Dr. Andrew Bacher and Dr. John Carini l results from the Microsoft Excel spreadsheet were obtained by adding the water phantom data from Foundation for funding it. the tests on the aluminum plate, while BPW and LaMPRI used a series of polynomial curves to find the optimal weighting factor. It therefore seems reasonable that the simulated dose profiles would be different for the two methods. Works Cited
Anferov, V. Scan Pattern Optimization for Unil According to LaMPRI, a smooth dose profile cannot be generated; although making one appears (2009) 3560-3567. Print. possible if the filter is of exactly the correct thickness. Because the dose profile of the experimental SOBP is smoother than that predicted by LaMPRI, the failure of LaMPRJ to achieve a uniform Farr, J., Mascia, A. , Hsi, W., Allgower, C., Jess dose profile is more likely due to a software limitation than a design flaw in the ripple filter. More Nichiporov, D., Anferov, V. Clinical research is necessary to detern1ine the best thickness of the flattening filter for the 8 cm in water Uniform Scanning System with Dose proton beam and whether a filter optimized for one particular energy (e.g., 8 cm in water) could be 4954. Print.
used for other relevant energies. However, because a sufficiently thin degrader shifts different beam Fujitaka, S. , Takayanagi, T., Fujimoto, R., Fuji energies by almost the same depth, regardless of the impingent energy, such a flattening filter Hiramoto, K., Sakae, T., Terunuma, ~ would most likely be useful for other energies (Preston, Koehler). Proton Uniform Scattering. Physics ii Print. Conclusion Gottschalk, B. Passive Beam Spreading in Prot
A single-layer ripple filter of the aluminum grid design can be used to decrease the number of Koehler, A. , Schneider, R., Sisterson, J., "Ran!! proton beams necessary to irradiate a given target volume by a factor of two. If the period of the Jnstrum. Methods 131 (1975) 437--4t grid pattern is less than 10% of the filter-to-target distance for this particular filter, the scattering Kraft, G. Medical Application of Accelerators i effects of the protons in the aluminum effectively conceal the grid structure in the target. Because School Fifth Advanced Accelerator F the sharpness of the proton Bragg peak is dependent on the initial energy, the flattened Bragg peak generated by the prototype flattening filter exhibits more ripple for the 6 cm in water proton beam Larsson, B. Radiological Properties of High-Er than the 8 cm in water proton beam. Supplement. 7 (1967) 304-311. Print
Preston, W., Koehler, A. The Effects of Scatter According to the LaMPRI simulation, the prototype single-layer aluminum flattening filter could not be used to generate a smooth SOBP, but this result appears to be due to a software limitation. Tsunemoto, H., Morita, S., Ishikawa, T., Furuk Experimental tests of the prototype flattening filter show less ripple than predicted in the Kitigawa, T., lnada, T. Proton Therai simulations. This strongly suggests that the design can be perfected to permit an SOBP smooth S-243. Print.
enough for clinical purposes. As the shift in maximum depth of the proton beam is far more Weber, U., Kraft, G. Design and Construction dependent on the water-equivalent thickness of the filter than the impingent energy, a flattening Distribution in Conformal Particle T filter optimized for a given energy would be useful for other energies as well. A Bragg peak 2765 - 2775. Print. flattening filter can therefore reduce the risk of proton radiotherapy treatments. Wilson, R. Radiological Use of Fast Protons. }
Acknowledgments George is a senior Majoring in Physics The author wishes to thank Dr. Vladimir Anferov for acting as the advisor for this project in the Research Experience for Undergraduate Research Experience for Undergraduates (REU) program held at IU Bloomington in the summer of
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5 filter showed a slight negative slope. The 2009, Dr. Andrew Bacher and Dr. John Carini for hosting the program, and the National Science ained by adding the water phantom data from Foundation for funding it. PRJ used a series of polynomial curves to :asonable that the simulated dose profiles Works Cited
Anferov, V. Scan Pattern Optimization for Uniform Proton Beam Scattering. Medical Physics 36 >e generated; although making one appears (2009) 3560-3567. Print. Because the dose profile of the experimental : failure ofLaMPRJ to achieve a uniform Farr, J., Mascia, A. , Hsi, W. , Allgower, C. , Jesseph, F. , Schreuder, A., Wolanski, M., than a design flaw in the ripple filter. More Nichiporov, D., Anferov, V. Clinical Characterization ofa Proton Beam Continuous fthe flattening filter for the 8 cm in water Uniform Scanning System with Dose Layer Stacking. Medical Physics 35 (2008) 4845- rticular energy (e.g., 8 cm in water) could be 4954. Print. ufficiently thin degrader shifts different beam Fujitaka, S., Takayanagi, T., Fujimoto, R., Fujii, Y. , Nishiuchi, H., Ebina, F., Okazaki, T. , npingent energy, such a flattening filter Hiramoto, K. , Sakae, T. , Terunuma, T. Reduction of the Number of Stacking Layers in i, Koehler). Proton Uniform Scattering. Physics in Medicine and Biology 54 (2009) 3101-3111. Print.
Gottschalk, B. Passive Beam Spreading in Proton Radiation Therapy. (2004) Print. i can be used to decrease the number of Koehler, A., Schneider, R., Sisterson, J., "Range Modulators for Protons and Heavy Ions," Nucl. 1me by a factor of two. If the period of the lnstrum. Methods 131 (1975) 437--440. Print. mce for this particular filter, the scattering Kraft, G. Medical Application of Accelerators in Tumor Therapy. Fifth CERN Accelerator :eal the grid structure in the target. Because n the initial energy, the flattened Bragg peak School Fifth Advanced Accelerator Physics Course. 2 ( 1993) 1083-1096. Print. •re ripple for the 6 cm in water proton beam Larsson, B. Radiological Properties of High-Energy Protons. Radiation Research Supplement. 7 (1967) 304-311. Print.
Preston, W., Koehler, A. The Effects of Scattering on Small Proton Beams. (1968) Print. ngle-layer aluminum flattening filter could : appears to be due to a software limitation. Tsunemoto, H. , Morita, S., Ishikawa, T. , Furukawa, S. , Kawachi, K. , Kanai, T., Ohara, H. , ow less ripple than predicted in the Kitigawa, T., Inada, T. Proton Therapy in Japan. Radiation Research 104 (1985) S-235 - be perfected to permit an SOBP smooth S-243. Print. depth of the proton beam is far more Weber, U. , Kraft, G. Design and Construction of a Ripple Filter for a Smoothed Depth Dose er than the impingent energy, a flattening Distribution in Conformal Particle Therapy. Physics in Medicine and Biology 44 (1999) other energies as well. A Bragg peak 2765 - 2775. Print. radiotherapy treatments. Wilson, R. Radiological Use of Fast Protons. Radiology 47 (1946) 487-491. Print.
George is a senior Majoring in Physics. He has worked on this project as part of the cting as the advisor for this project in the Research Experience for Undergraduates (REU) with Dr. Anferov at IU Bloomington. 1m held at ru Bloomington in the summer of
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