246
TECHNICAL NOTES
Obstruction of the fluoroscopic image is minimized since the only element in the x-ray beam is an 8 X 8 X 0.7-mm mirror mounted in a 5-mm thick perspex plate, which is secured directly over the grid of the image intensifier and covers the entire viewing area. We use a low-power (0.5 mW) helium-neon laser (Spectra Physics Model 155). This is a compact laser with a built-in power supply. It has a beam diameter of 0.88 mm and a divergence of 1.0 milliradians. As presently used, the beam diameter is less than 2 mm at the isocenter of the simulator. A polarizing filter decreases the intensity of the light. The laser assembly is constructed of aluminum and is mounted transversely on the intensifier support arm (Fig. 1). To avoid interference with table motion, it is positioned away from the image intensifier. The laser beam is reflected upward into a turret and subsequently directed toward the image intensifier by a second mirror. The beam is aligned by varying the height and angle of this mirror. The height is kept as low as possible to prevent obstruction of the laser beam by table, patient, or technician. Minimum height is that which allows the beam to pass unobstructed to the chip mirror mounted at the center of the intensifier. To avoid possible misalignment when inserting radiographic cassettes, the angle of the chip mirror is not adjustable; the mirror is fixed in a groove in the perspex plate, and adjustment of the plate by rotation about the central axis permits transverse alignment of the laser beam. A cassette holder is mounted directly over the plate.
October 1979
With the image intensifier in its central position, the laser beam is aligned such that it is collinear with the central axis of the x-ray beam. Recentering of the image intensifier is automatic and is accurate to within ± 0.7 mm in the longitudinal direction. Only longitudinal centering requires great accuracy, since the face of the chip mirror is parallel to the transverse scanning motion. On gantry rotation, the isocentric accuracy of the back pointer is within a sphere 1.0 mm in radius, resulting in a maximum deviation of 1.7 mm at the isocenter. The chip mirror on the image intensifier causes a slight darkening of the fluoroscopic image at the center of the viewing field because the mirror is of higher density than the perspex plate in which it is fixed. The introduction of the perspex plate over the grid of the intensifier has had no noticeable effect on the quality of the fluoroscopic image. The laser backpointer has been in use on our simulator since June 1976. It is reliable and requires infrequent re-alignment. The main advantage of the design described is the ease of use which results in significantly reduced mark-up time. In addition, accuracy may be improved since re-checking of patient positioning has been simplified.
1 From the Ontario Cancer Treatment and Research Foundation, Henderson General Hospital, Hamilton, Ontario, Canada L8V 1C3. Received June 9, 1978; accepted Oct. 2. evm
- - WITHOUT
The Effect of Bone on Dose Distributions Produced by the Fermi National Laboratory Fast-Neutron Beam 1
- - - WITH
Patton H. McGinley, Ph.D. and John R. McLaren, M.D. The dose distortion produced by bone during fast-neutron therapy was studied using a target-to-skln distance of 153 em, with beams 10 X 10 field size at the surface of a phantom. Doses were measured using several muscie-eqelvalent ionIzation chambers in the phantom. ResuUs showed that the dose was reduced by interposing bone-equivalent material between the point In question and the surface of the phantom.
lONE
4.6,m
lONE
100
-
80
Q
60
'" 0
i v
40
::: 20
oL..-..,--r--,-----r-~--r-___.___,_-.-_,_-r--..--,---.-,r---"--r--r~
9876543210123456789
INDEX TERMS:
Bones. Neutrons. Therapeutic radiology, dosimetry
Radiotogy 133:246-248, October 1979
In order to accurately predict the dose received by patients involved in fast-neutron clinical trials, it is desirable to determine the perturbation of dose distributions produced by inhomogeneities, such as lung and bone. This investigation studied the dose distortion produced by bone when patients undergo neutron therapy at the Fermi Accelerator National Laboratory (Fermilab). MATERIAL AND METHODS Several thicknesses of bone were simulated by cylinders of plastic (type B-100) (1) with a diameter of 4.95 cm and lengths of 1, 2.3, and 4.6 cm. This material has a composition similar to that suggested for the skeletal region (marrow as well as mineral bone) of reference man (2). Gary et al. (3) have devel-
T RAN S V E R S l
PO SIT ION
(m
Fig. 1. Transverse dose distribution for 10 X 10-cm beam, 6-cm depth, and target-to-skin distance of 153 em.
oped a liquid which has an elemental composition and density close to that of bone. Liquid bone was employed in this work in order to test the suitability of type B-100 plastic for use in fastneutron fields. The liquid was used to fill cylindrical Lucite containers, each with a wall thickness of 2 mm and external dimensions similar to the plastic. Depth dose measurements were made in a Lucite container 44 cm wide, 38 cm high, and 38 cm in length along the beam axis. The beam entered the container through a thin window of. 3-mm thickness, and muscle-equivalent liquid (4) of 1.065 g/cm 3 density filled the phantom. A Lucite holder was used to position the bone-equivalent cylinders in the phantom (Fig. 1). Ionization chambers (Edgerton, Germershausen, and Grier, Inc., Goleta, CA) were utilized to establish percent depth-dose values with
247
TECHNICAL NOTES
Vol. 133
and without the bone cylinders in the phantom. Measurements were made along the central axis of the beam with both a 0.1 ern" chamber and a 1.0 ern" chamber. The walls of each chamber were constructed of Shonka plastic (type A-150), and a collection voltage of +500 V was employed. Dry air was allowed to flow throt4l the chambers (5 cm 3/min) when ionization measurements were conducted. A remote-control drive was used to position the chambers at points in a horizontal plane at the level of the beam central axis with a reproducibility of approximately ± 1 mm. All measurements were conducted with a neutron beam of 10 X 10-cm size at the front surface of the phantom and a target-to-phantom distance of 153 cm. This neutron beam, which is routinely used for treatment, was produced by bombarding a beryllium target with 66-MeV protons. The neutron energy spectrum generated by this reaction extends from about zero to approximately 65 MeV and has a modal energy of about 20 MeV (5). The ionization measurements were normalized to the same neutron output by use of the Fermilab dose monitor system. Temperatures were measured in the vicinity of the transmission monitor chamber and in the phantom liquid before and after each run; appropriate corrections were applied to the ionization chamber reading. Central-axis ionization measurements were obtained with both the 0.1 and 1.0 crrr' EG & G chambers, and transverse ionization measurements were carried out at depths of 6 and 10 cm. Each run was conducted with and without bone-equivalent cylinders. The cylinders, when used, were positioned at either the front of the phantom or at a depth of 10 cm. RESULTS AND DISCUSSION TABLE I presents central-axis-depth dose values obtained with and without bone-equivalent material. All values have been normalized to 100 % at a depth of 1.9 cm without bone. Based on these values, it can be concluded that bone produces a shielding effect. For example, a dose reduction of 3.5-5.4 % was observed for the 4.6-cm cylinder at various depths. A similar shielding effect has been reported for the fast-neutron beam employed at the Naval Research Laboratory (NRL) for neutron therapy (6) and fission neutrons (7). However, the magnitude of the reduction varied appreciably with distance from the boneequivalent material. For the NRL neutron beam, the dose was reduced by 7% at a distance of 0.7 cm behind a 4.8-cm long cylinder and by 15% at a distance of 8.6 cm. The difference in magnitude between the NRL and Fermilab beams may be attributed to the different neutron energy spectra for these two beams. To illustrate this point, it has been found that 4 cm of bone produces essentially no shielding effect for 15-MeV neutrons generated by the deuterium-tritium reaction (8). Measurements made behind a 2.3-cm cylinder of boneequivalent plastic with its distal end at 10-cm depth yielded dose-reduction values about half as large as those found for points behind the plastic when placed at the surface of the phantom. It was also found that the plastic produced a beam attenuation similar to the liquid. Dose measurements were made in a horizontal plane along a line at right angles to the central axis of the beam at depths of 6 and 10 ern. As shown by Figure 1, the maximum dose perturbation occurred at the central axis, and lower values were found
Technical Notes
TABLE I: CENTRAL-AXIS PERCENT DEPTH DOSE VALUES WITH AND WITHOUT BONE FOR A BEAM OF FAST NEUTRONS
Depth (ern)
Phantom without Bone
1.3 1.5 1.7 1.9 2.0 2.2 2.5 2.7 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0 33.0 35.0
98.8 99.8 99.9 100 99.6 99.1 97.8 97.1 96.3 92.2 87.7 83.1 78.8 74.2 70.2 66.4 58.5 52.4 46.0 40.9 36.0 31.6 28.0 24.8 22.1 19.4 15.9 14.1
lcm B-l00 Bone at Surface
2.3cm B-l00 Bone at Surface
91.1 87.2 82.5 78.1 73.7 69.5 65.2 58.1 51.3 45.5 40.2 35.4 31.3 28.0 24.6 22.1 18.9 15.6 13.7
86.5 82.1 77.3 73.4 69.1 65.0 57.8 50.9 45.4 39.8 35.3 30.8 27.2 24.4 21.1 19.1 15.7 13.9
2.3 cm 4.6cm Bone B-l00 Liquid Bone at Surface at Surface
86.0 81.4 76.9 73.0 68.5 64.7 57.3 50.8 44.8 39.6 34.9 30.7 27.0 24.4 21.2 18.7 15.6 13.5
80.2 76.5 71.9 67.9 63.9 56.6 49.9 44.2 39.1 34.4 30.4 26.9 24.0 21.2 18.4 14.4 13.4
The neutron beam was produced by bombarding a Be target with 66-MeV protons. A field size of 10 X 10 cm and a target-to-phantom distance of 153 cm was employed for these measurements. All values normalized to 100 % at a depth of 1.9 em without bone.
TABLE II: BE:AM FLATNESS, PENUMBRA WIDTH, AND DOSE L~V~L OUTSIDE BEAM WITH AND WITHOUT BON~-EQUIVALENT MATERIAL
Depth (em) 6
Bone Thickness (em)
o 4.6
10
o 4.6
Percent Flatness (%)
Penumbra Width (em)
Percent Dose 10 cm from Center of Field (%)
77 77 76 76
1.1,1.2 1.1, 1.2 1.5. 1.2 1.5, 1.2
5.2.5.1 5.3,5.3 7.1,6.7 7.0,6.9
A lOX 10-cm field size at a tarqet-to-phantom distance of 153 cm was used.
equivalent material in the neutron field. The penumbra width was evaluated by determining the transverse distance required for the beam intensity to decrease from 80 % to 20 % of the central-axis value; the percent flatness represents the percent beam width over which the dose is at least 90 % of the central-axis value. Figure 1 and TABLE II show that bone causes only small changes in beam flatness, penumbra width, and dose levels due to scattered radiation. As a result of this study, it has been established that corrections of 5.5 % or less are required to adjust the dose distributions measured in muscle-equivalent liquid to account for the pres-
for points off the beam axis. TABLE II shows values of the percent
ence of bone. In all cases, the dose was reduced for points lo-
beam flatness and penumbra width with and without bone-
cated behind the bone-muscle interface.
248
TECHNICAL NOTES
ACKNOWLEl:>GWENTS: The authors are indebted to Dr. M. Awschalom and Mr. Duane Voy for their invaluable help with this project.
REFERENCES 1. Wingate CL, Gross W, Failla G: Experimental determination of absorbed dose from x-rays near the interface of soft tissue and other materials. Radiology 79:984-999, Dec 1962 2. International Commission of Radiological Protection Report No. 23. Report of the task group on reference man. Oxford, Pergamon Press, 1975, p 273 3. Garry SM, StansburyPS, PostonJW: MeaslXementof absorbed dose for photon sources distributed uniformly in various organs of a heterogeneous phantom. ORNL-TM-4411, Oak Ridge National Laboratory, 1974 4. Frigerio NA, Coley RF, Sampson MJ: Depth dose determinations. I. Tissue-equivalent liquids for standard man and muscle. Phys Med Bioi 17:792-802, Nov 1972
October 1979
5. Amols HI, Dicello JF, Awschalom M, et al: Physical characterization of neutron beams produced by protons and deuterons of various energies bombarding beryllium and lithium targets of several thicknesses. Fermilab-Pub-76/102-Exp 1184.000, Dec 1976 6. McGinley PH, McLaren JR: Distortion of fast-neutron dose distribution by bone. Med Phys 3: 181-183, May/Jun 1976 7. Sohrabi M: Electrochemical etching amplification of Jow-LET recoil particle tracks in polymers for fast neutron dosimetry. Ph.D. thesis, Georgia Institute of Technology, 1975 8. McGinley PH: Fast-neutron therapy treatment planning. Ph.D. thesis, Georgia Institute of Technology, 1971
1 From the Division of Radiation Therapy, Emory University Clinic, 1365 Clifton Rd., N.E., Atlanta, GA 30322. Received Nov. 14, 1978; revision requested Feb. 8, 1979; accepted March 6. jr
Adaptation of Multiformat Film Holder to Real-Time tlltrasound" Andrew M. Fried, M.D., and Richard C. Huesman A method is described for adaptation of a multiformat film holder to a free-standing real-time imaging unit. No additional electronics are necessary for modification. INDrx TERM:
Ultrasound, instrumentation
Radiology 133:248, October 1979
Virtually all electronically independent real-time imaging devices come equipped with the capability for instant film processmq,? Our experience with multiformat imaging cameras" and film holders" in both ultrasonography and computed tomography led us to examine the feasibility of such a device for the real-time irnaqer." The Nise film holder can be mounted on the oscilloscope camera" as on any other diagnostic device; however, the viewing port is obscured as a result, rendering simultaneous filming and viewing of the oscilloscope image impossible. An additional oscilloscope to allow this would be both cumbersome and costly. We therefore modified the existing unit. By removing the viewing port from the camera and interposing a three-sided opaque plastic extension 7 between the two, the viewing port is raised by an angle of approximately 20.6 0 . The port then clears the slide plate on the film holder while still providing a full view of the oscilloscope screen (Fig. 2). All of our real-time studies are now recorded with a six-on-one format on 20 X 25-cm (8 X 10-in.) radiographic film. Advantages include transmitted-light viewing, ease of handling and storage, and significant reduction in cost.
)
"
\
Fig. 1. The unit demonstrates elevation of the viewing port above the film format to allow simultaneous viewing and filming. The opaque plastic insert (black wedge) is labeled.
'From the Department of Diagnostic Radiology, University of Kentucky Medical Center, Lexington, KY 40506. Received August 18, 1978; accepted and revision requested April 19, 1979; received May 15. 2Polaroid Corporation, 575 Technology Square, Cambridge, MA 02139. 3Dunn Instruments, 52 Colin P. Kelly, Jr. St., San Francisco, CA 94107. "Nise Camera Corp., 20018 State Road, Cerritos, CA 90701. 5Advanced Diagnostic Research Corp. (ADR), 2224 S. Priest Drive, Tempe, AZ 85282. 6Model 197A. Hewlett Packard Corp., 3450 S. Dixie Drive, Dayton, OH 45439. 'Black plexiglass (GM: Acrylic sheet; thickness 0.152 cm 10.060in. j). Cadlo Corp., Dayton, OH 45439. jr
TECHNICAL NOTES
Obstruction of the fluoroscopic image is minimized since the only element in the x-ray beam is an 8 X 8 X 0.7-mm mirror mounted in a 5-mm thick perspex plate, which is secured directly over the grid of the image intensifier and covers the entire viewing area. We use a low-power (0.5 mW) helium-neon laser (Spectra Physics Model 155). This is a compact laser with a built-in power supply. It has a beam diameter of 0.88 mm and a divergence of 1.0 milliradians. As presently used, the beam diameter is less than 2 mm at the isocenter of the simulator. A polarizing filter decreases the intensity of the light. The laser assembly is constructed of aluminum and is mounted transversely on the intensifier support arm (Fig. 1). To avoid interference with table motion, it is positioned away from the image intensifier. The laser beam is reflected upward into a turret and subsequently directed toward the image intensifier by a second mirror. The beam is aligned by varying the height and angle of this mirror. The height is kept as low as possible to prevent obstruction of the laser beam by table, patient, or technician. Minimum height is that which allows the beam to pass unobstructed to the chip mirror mounted at the center of the intensifier. To avoid possible misalignment when inserting radiographic cassettes, the angle of the chip mirror is not adjustable; the mirror is fixed in a groove in the perspex plate, and adjustment of the plate by rotation about the central axis permits transverse alignment of the laser beam. A cassette holder is mounted directly over the plate.
October 1979
With the image intensifier in its central position, the laser beam is aligned such that it is collinear with the central axis of the x-ray beam. Recentering of the image intensifier is automatic and is accurate to within ± 0.7 mm in the longitudinal direction. Only longitudinal centering requires great accuracy, since the face of the chip mirror is parallel to the transverse scanning motion. On gantry rotation, the isocentric accuracy of the back pointer is within a sphere 1.0 mm in radius, resulting in a maximum deviation of 1.7 mm at the isocenter. The chip mirror on the image intensifier causes a slight darkening of the fluoroscopic image at the center of the viewing field because the mirror is of higher density than the perspex plate in which it is fixed. The introduction of the perspex plate over the grid of the intensifier has had no noticeable effect on the quality of the fluoroscopic image. The laser backpointer has been in use on our simulator since June 1976. It is reliable and requires infrequent re-alignment. The main advantage of the design described is the ease of use which results in significantly reduced mark-up time. In addition, accuracy may be improved since re-checking of patient positioning has been simplified.
1 From the Ontario Cancer Treatment and Research Foundation, Henderson General Hospital, Hamilton, Ontario, Canada L8V 1C3. Received June 9, 1978; accepted Oct. 2. evm
- - WITHOUT
The Effect of Bone on Dose Distributions Produced by the Fermi National Laboratory Fast-Neutron Beam 1
- - - WITH
Patton H. McGinley, Ph.D. and John R. McLaren, M.D. The dose distortion produced by bone during fast-neutron therapy was studied using a target-to-skln distance of 153 em, with beams 10 X 10 field size at the surface of a phantom. Doses were measured using several muscie-eqelvalent ionIzation chambers in the phantom. ResuUs showed that the dose was reduced by interposing bone-equivalent material between the point In question and the surface of the phantom.
lONE
4.6,m
lONE
100
-
80
Q
60
'" 0
i v
40
::: 20
oL..-..,--r--,-----r-~--r-___.___,_-.-_,_-r--..--,---.-,r---"--r--r~
9876543210123456789
INDEX TERMS:
Bones. Neutrons. Therapeutic radiology, dosimetry
Radiotogy 133:246-248, October 1979
In order to accurately predict the dose received by patients involved in fast-neutron clinical trials, it is desirable to determine the perturbation of dose distributions produced by inhomogeneities, such as lung and bone. This investigation studied the dose distortion produced by bone when patients undergo neutron therapy at the Fermi Accelerator National Laboratory (Fermilab). MATERIAL AND METHODS Several thicknesses of bone were simulated by cylinders of plastic (type B-100) (1) with a diameter of 4.95 cm and lengths of 1, 2.3, and 4.6 cm. This material has a composition similar to that suggested for the skeletal region (marrow as well as mineral bone) of reference man (2). Gary et al. (3) have devel-
T RAN S V E R S l
PO SIT ION
(m
Fig. 1. Transverse dose distribution for 10 X 10-cm beam, 6-cm depth, and target-to-skin distance of 153 em.
oped a liquid which has an elemental composition and density close to that of bone. Liquid bone was employed in this work in order to test the suitability of type B-100 plastic for use in fastneutron fields. The liquid was used to fill cylindrical Lucite containers, each with a wall thickness of 2 mm and external dimensions similar to the plastic. Depth dose measurements were made in a Lucite container 44 cm wide, 38 cm high, and 38 cm in length along the beam axis. The beam entered the container through a thin window of. 3-mm thickness, and muscle-equivalent liquid (4) of 1.065 g/cm 3 density filled the phantom. A Lucite holder was used to position the bone-equivalent cylinders in the phantom (Fig. 1). Ionization chambers (Edgerton, Germershausen, and Grier, Inc., Goleta, CA) were utilized to establish percent depth-dose values with
247
TECHNICAL NOTES
Vol. 133
and without the bone cylinders in the phantom. Measurements were made along the central axis of the beam with both a 0.1 ern" chamber and a 1.0 ern" chamber. The walls of each chamber were constructed of Shonka plastic (type A-150), and a collection voltage of +500 V was employed. Dry air was allowed to flow throt4l the chambers (5 cm 3/min) when ionization measurements were conducted. A remote-control drive was used to position the chambers at points in a horizontal plane at the level of the beam central axis with a reproducibility of approximately ± 1 mm. All measurements were conducted with a neutron beam of 10 X 10-cm size at the front surface of the phantom and a target-to-phantom distance of 153 cm. This neutron beam, which is routinely used for treatment, was produced by bombarding a beryllium target with 66-MeV protons. The neutron energy spectrum generated by this reaction extends from about zero to approximately 65 MeV and has a modal energy of about 20 MeV (5). The ionization measurements were normalized to the same neutron output by use of the Fermilab dose monitor system. Temperatures were measured in the vicinity of the transmission monitor chamber and in the phantom liquid before and after each run; appropriate corrections were applied to the ionization chamber reading. Central-axis ionization measurements were obtained with both the 0.1 and 1.0 crrr' EG & G chambers, and transverse ionization measurements were carried out at depths of 6 and 10 cm. Each run was conducted with and without bone-equivalent cylinders. The cylinders, when used, were positioned at either the front of the phantom or at a depth of 10 cm. RESULTS AND DISCUSSION TABLE I presents central-axis-depth dose values obtained with and without bone-equivalent material. All values have been normalized to 100 % at a depth of 1.9 cm without bone. Based on these values, it can be concluded that bone produces a shielding effect. For example, a dose reduction of 3.5-5.4 % was observed for the 4.6-cm cylinder at various depths. A similar shielding effect has been reported for the fast-neutron beam employed at the Naval Research Laboratory (NRL) for neutron therapy (6) and fission neutrons (7). However, the magnitude of the reduction varied appreciably with distance from the boneequivalent material. For the NRL neutron beam, the dose was reduced by 7% at a distance of 0.7 cm behind a 4.8-cm long cylinder and by 15% at a distance of 8.6 cm. The difference in magnitude between the NRL and Fermilab beams may be attributed to the different neutron energy spectra for these two beams. To illustrate this point, it has been found that 4 cm of bone produces essentially no shielding effect for 15-MeV neutrons generated by the deuterium-tritium reaction (8). Measurements made behind a 2.3-cm cylinder of boneequivalent plastic with its distal end at 10-cm depth yielded dose-reduction values about half as large as those found for points behind the plastic when placed at the surface of the phantom. It was also found that the plastic produced a beam attenuation similar to the liquid. Dose measurements were made in a horizontal plane along a line at right angles to the central axis of the beam at depths of 6 and 10 ern. As shown by Figure 1, the maximum dose perturbation occurred at the central axis, and lower values were found
Technical Notes
TABLE I: CENTRAL-AXIS PERCENT DEPTH DOSE VALUES WITH AND WITHOUT BONE FOR A BEAM OF FAST NEUTRONS
Depth (ern)
Phantom without Bone
1.3 1.5 1.7 1.9 2.0 2.2 2.5 2.7 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0 33.0 35.0
98.8 99.8 99.9 100 99.6 99.1 97.8 97.1 96.3 92.2 87.7 83.1 78.8 74.2 70.2 66.4 58.5 52.4 46.0 40.9 36.0 31.6 28.0 24.8 22.1 19.4 15.9 14.1
lcm B-l00 Bone at Surface
2.3cm B-l00 Bone at Surface
91.1 87.2 82.5 78.1 73.7 69.5 65.2 58.1 51.3 45.5 40.2 35.4 31.3 28.0 24.6 22.1 18.9 15.6 13.7
86.5 82.1 77.3 73.4 69.1 65.0 57.8 50.9 45.4 39.8 35.3 30.8 27.2 24.4 21.1 19.1 15.7 13.9
2.3 cm 4.6cm Bone B-l00 Liquid Bone at Surface at Surface
86.0 81.4 76.9 73.0 68.5 64.7 57.3 50.8 44.8 39.6 34.9 30.7 27.0 24.4 21.2 18.7 15.6 13.5
80.2 76.5 71.9 67.9 63.9 56.6 49.9 44.2 39.1 34.4 30.4 26.9 24.0 21.2 18.4 14.4 13.4
The neutron beam was produced by bombarding a Be target with 66-MeV protons. A field size of 10 X 10 cm and a target-to-phantom distance of 153 cm was employed for these measurements. All values normalized to 100 % at a depth of 1.9 em without bone.
TABLE II: BE:AM FLATNESS, PENUMBRA WIDTH, AND DOSE L~V~L OUTSIDE BEAM WITH AND WITHOUT BON~-EQUIVALENT MATERIAL
Depth (em) 6
Bone Thickness (em)
o 4.6
10
o 4.6
Percent Flatness (%)
Penumbra Width (em)
Percent Dose 10 cm from Center of Field (%)
77 77 76 76
1.1,1.2 1.1, 1.2 1.5. 1.2 1.5, 1.2
5.2.5.1 5.3,5.3 7.1,6.7 7.0,6.9
A lOX 10-cm field size at a tarqet-to-phantom distance of 153 cm was used.
equivalent material in the neutron field. The penumbra width was evaluated by determining the transverse distance required for the beam intensity to decrease from 80 % to 20 % of the central-axis value; the percent flatness represents the percent beam width over which the dose is at least 90 % of the central-axis value. Figure 1 and TABLE II show that bone causes only small changes in beam flatness, penumbra width, and dose levels due to scattered radiation. As a result of this study, it has been established that corrections of 5.5 % or less are required to adjust the dose distributions measured in muscle-equivalent liquid to account for the pres-
for points off the beam axis. TABLE II shows values of the percent
ence of bone. In all cases, the dose was reduced for points lo-
beam flatness and penumbra width with and without bone-
cated behind the bone-muscle interface.
248
TECHNICAL NOTES
ACKNOWLEl:>GWENTS: The authors are indebted to Dr. M. Awschalom and Mr. Duane Voy for their invaluable help with this project.
REFERENCES 1. Wingate CL, Gross W, Failla G: Experimental determination of absorbed dose from x-rays near the interface of soft tissue and other materials. Radiology 79:984-999, Dec 1962 2. International Commission of Radiological Protection Report No. 23. Report of the task group on reference man. Oxford, Pergamon Press, 1975, p 273 3. Garry SM, StansburyPS, PostonJW: MeaslXementof absorbed dose for photon sources distributed uniformly in various organs of a heterogeneous phantom. ORNL-TM-4411, Oak Ridge National Laboratory, 1974 4. Frigerio NA, Coley RF, Sampson MJ: Depth dose determinations. I. Tissue-equivalent liquids for standard man and muscle. Phys Med Bioi 17:792-802, Nov 1972
October 1979
5. Amols HI, Dicello JF, Awschalom M, et al: Physical characterization of neutron beams produced by protons and deuterons of various energies bombarding beryllium and lithium targets of several thicknesses. Fermilab-Pub-76/102-Exp 1184.000, Dec 1976 6. McGinley PH, McLaren JR: Distortion of fast-neutron dose distribution by bone. Med Phys 3: 181-183, May/Jun 1976 7. Sohrabi M: Electrochemical etching amplification of Jow-LET recoil particle tracks in polymers for fast neutron dosimetry. Ph.D. thesis, Georgia Institute of Technology, 1975 8. McGinley PH: Fast-neutron therapy treatment planning. Ph.D. thesis, Georgia Institute of Technology, 1971
1 From the Division of Radiation Therapy, Emory University Clinic, 1365 Clifton Rd., N.E., Atlanta, GA 30322. Received Nov. 14, 1978; revision requested Feb. 8, 1979; accepted March 6. jr
Adaptation of Multiformat Film Holder to Real-Time tlltrasound" Andrew M. Fried, M.D., and Richard C. Huesman A method is described for adaptation of a multiformat film holder to a free-standing real-time imaging unit. No additional electronics are necessary for modification. INDrx TERM:
Ultrasound, instrumentation
Radiology 133:248, October 1979
Virtually all electronically independent real-time imaging devices come equipped with the capability for instant film processmq,? Our experience with multiformat imaging cameras" and film holders" in both ultrasonography and computed tomography led us to examine the feasibility of such a device for the real-time irnaqer." The Nise film holder can be mounted on the oscilloscope camera" as on any other diagnostic device; however, the viewing port is obscured as a result, rendering simultaneous filming and viewing of the oscilloscope image impossible. An additional oscilloscope to allow this would be both cumbersome and costly. We therefore modified the existing unit. By removing the viewing port from the camera and interposing a three-sided opaque plastic extension 7 between the two, the viewing port is raised by an angle of approximately 20.6 0 . The port then clears the slide plate on the film holder while still providing a full view of the oscilloscope screen (Fig. 2). All of our real-time studies are now recorded with a six-on-one format on 20 X 25-cm (8 X 10-in.) radiographic film. Advantages include transmitted-light viewing, ease of handling and storage, and significant reduction in cost.
)
"
\
Fig. 1. The unit demonstrates elevation of the viewing port above the film format to allow simultaneous viewing and filming. The opaque plastic insert (black wedge) is labeled.
'From the Department of Diagnostic Radiology, University of Kentucky Medical Center, Lexington, KY 40506. Received August 18, 1978; accepted and revision requested April 19, 1979; received May 15. 2Polaroid Corporation, 575 Technology Square, Cambridge, MA 02139. 3Dunn Instruments, 52 Colin P. Kelly, Jr. St., San Francisco, CA 94107. "Nise Camera Corp., 20018 State Road, Cerritos, CA 90701. 5Advanced Diagnostic Research Corp. (ADR), 2224 S. Priest Drive, Tempe, AZ 85282. 6Model 197A. Hewlett Packard Corp., 3450 S. Dixie Drive, Dayton, OH 45439. 'Black plexiglass (GM: Acrylic sheet; thickness 0.152 cm 10.060in. j). Cadlo Corp., Dayton, OH 45439. jr
