Structural shielding design and evaluation for megavoltage x- and gamma-ray radiotherapy facilities : recommendations of the National Council on Radiation Protection and Measurements

256 Pages·2005·2.272 MB·English

by  National Council on Radiation Protection and Measurements

NCRP REPORT No. 151
Structural Shielding
Design and Evaluation for
Megavoltage X- and
Gamma-Ray Radiotherapy
Facilities
Recommendations of the
NATIONAL COUNCIL ON RADIATION
PROTECTION AND MEASUREMENTS
December 31, 2005
NationalCouncilonRadiationProtectionandMeasurements
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LEGAL NOTICE
This Report was prepared by the National Council on Radiation Protection and
Measurements (NCRP). The Council strives to provide accurate, complete and use-
ful information in its documents. However, neither NCRP, the members of NCRP,
other persons contributing to or assisting in the preparation of this Report, nor any
person acting on the behalf of any of these parties: (a) makes any warranty or rep-
resentation, express or implied, with respect to the accuracy, completeness or use-
fulness of the information contained in this Report, or that the use of any
information, method or process disclosed in this Report may not infringe on pri-
vately owned rights; or (b) assumes any liability with respect to the use of, or for
damages resulting from the use of any information, method or process disclosed in
this Report, under the Civil Rights Act of 1964, Section 701 et seq. as amended 42
U.S.C. Section 2000e et seq. (Title VII) or any other statutory or common law theory
governing liability.
Disclaimer
Any mention of commercial products within NCRP publications is for informa-
tion only; it does not imply recommendation or endorsement by NCRP.
Library of Congress Cataloging-in-Publication Data
National Council on Radiation Protection and Measurements.
Structural shielding design and evaluation for megavoltage x- and gamma-ray
radiotherapy facilities:recommendations of the National Council on Radiation
Protection and Measurements.
p.cm.— (NCRP report;no. 151)
“Issued December 2005.”
Includes bibliographical references and index.
ISBN-13: 978-0-929600-87-1
ISBN-10: 0-929600-87-8
1. Radiology, Medical—Equipment and supplies—Safety measures. 2. Shielding
(Radiation) 3. Radiotherapy—Safety measures. 4. Gamma rays—Physiological
effect. 5. Radiology, Medical—Safety measures. I. Title. II. Series.
RA975.5.R3S77 2005
616.07’572--dc22
2006002275
Copyright © NationalCouncilonRadiation
ProtectionandMeasurements2005
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tion may be reproduced in any form or by any means, including photocopying, or
utilized by any information storage and retrieval system without written permission
from the copyright owner, except for brief quotation in critical articles or reviews.
[For detailed information on the availability of NCRP publications see page227.]
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Preface
This Report was developed under the auspices of Program Area
Committee 2 of the National Council on Radiation Protection and
Measurements (NCRP), the Committee that is concerned with
operational radiation safety. The Report addresses the structural
shielding design and evaluation for medical use of megavoltage
xand gamma rays for radiotherapy and supersedes related mate-
rial in NCRP Report No. 49, Structural Shielding Design and Eval-
uation for Medical Use of X Rays and Gamma Rays of Energies Up
to 10 MeV, which was issued in September 1976. The descriptive
information in NCRP Report No. 49 unique to x-ray therapy instal-
lations of less than 500 kV (Section 6.2) and brachytherapy (Sec-
tion 7) is not included in this Report and that information in NCRP
Report No.49 for those categories is still applicable.
This Report was prepared through a joint effort of NCRP Scien-
tific Committee 46-13 on Design of Facilities for Medical Radiation
Therapy and the American Association of Physicists in Medicine
(AAPM). NCRP gratefully acknowledges the support of AAPM for
several of its members to serve on Scientific Committee 46-13 and
the many opportunities that were made available for Scientific
Committee 46-13 to meet at AAPM annual meetings. Serving on
Scientific Committee 46-13 were:
James A. Deye, Chairman
National Cancer Institute
Rockville, Maryland
Vice-Chairmen
James E. Rodgers Raymond K. Wu
Maryland Regional Cancer Care OhioHealth Hospitals
Silver Spring, Maryland Columbus, Ohio
Members
Peter J. Biggs Patton H. McGinley
Massachusetts General Hospital Stone Mountain, Georgia
Boston, Massachusetts
Richard C. McCall
Woodside, California
iii
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iv / PREFACE
Liaisons
Kenneth R. Kase Marc Edwards
Lyncean Technologies, Inc. Radiation Oncology Associates of
Palo Alto, California Kansas City
Overland Park, Kansas
Consultants
Robert O. Gorson Jeffrey H. Kleck
Columbia, South Carolina Attania Corporation
San Jose, California
Nisy E. Ipe
San Carlos, California
NCRP Secretariat
Marvin Rosenstein, Consultant, 2001–2005
Eric E. Kearsley, Staff Scientist/Consultant, 1998–2001
James A. Spahn, Jr., Senior Staff Scientist, 1995–1998
Cindy L. O’Brien, Managing Editor
David A. Schauer, Executive Director
The contents are the sole responsibility of NCRP and do not nec-
essarily represent the official views of the National Cancer Insti-
tute or the National Institutes of Health.
The Council wishes to express its appreciation to the Committee
members, liaisons and consultants for the time and effort devoted
to the preparation of this Report.
Thomas S. Tenforde
President
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Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Quantities and Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Controlled and Uncontrolled Areas. . . . . . . . . . . . . . . . . 4
1.4 Shielding Design Goals and Effective Dose . . . . . . . . . . 5
1.4.1 Controlled Areas . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4.2 Uncontrolled Areas . . . . . . . . . . . . . . . . . . . . . . . 6
1.4.3 Shielding Design Assumptions. . . . . . . . . . . . . . 7
1.4.4 Measurements to Assess Compliance with
the ShieldingDesign Goals. . . . . . . . . . . . . . . . . 8
1.5 Workload. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.6 Use Factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.7 Occupancy Factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.8 Protective Barriers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.9 Basic Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.10 General Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.11 Types of Radiotherapy Installations. . . . . . . . . . . . . . . 14
1.12 Strategic Shielding Planning. . . . . . . . . . . . . . . . . . . . . 15
1.12.1 Planning and Budgeting. . . . . . . . . . . . . . . . . . 16
1.12.2 Programming. . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.12.3 Schematic (Preliminary) Design. . . . . . . . . . . . 17
1.12.4 Design Development . . . . . . . . . . . . . . . . . . . . . 17
1.12.5 Construction Document Preparation . . . . . . . . 17
1.12.6 Construction Inspection . . . . . . . . . . . . . . . . . . 18
1.13 Documentation Requirements. . . . . . . . . . . . . . . . . . . . 18
2. Calculational Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.1 Basic Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2 Primary Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.2.1 Standard Approach . . . . . . . . . . . . . . . . . . . . . . 22
2.2.2 Barrier Widths. . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.2.3 Laminated Barriers. . . . . . . . . . . . . . . . . . . . . . 27
2.3 Secondary Barriers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
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2.4 Doors and Mazes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
2.4.1 Low-Energy Accelerators. . . . . . . . . . . . . . . . . .34
2.4.2 High-Energy Accelerators. . . . . . . . . . . . . . . . .40
2.4.2.1 Photon Dose-Equivalent Calculation
at the Maze Door . . . . . . . . . . . . . . . .40
2.4.2.2 Neutron Dose Equivalent at the
Maze Door. . . . . . . . . . . . . . . . . . . . . .43
2.4.2.2.1 Kersey’s Method. . . . . . . .43
2.4.2.2.2 Modified Kersey’s
Method . . . . . . . . . . . . . . .44
2.4.2.3 Total Dose Equivalent at the
Maze Door. . . . . . . . . . . . . . . . . . . . . .45
2.4.3 Door Shielding . . . . . . . . . . . . . . . . . . . . . . . . . .46
2.4.4 Alternate Maze and Door Designs . . . . . . . . . .46
2.4.5 Direct-Shielded Door . . . . . . . . . . . . . . . . . . . . .47
2.4.5.1 Design Problems with Direct-
Shielded Doors . . . . . . . . . . . . . . . . . .48
2.4.5.2 Neutron Capture Gamma Rays with
Direct-Shielded Doors . . . . . . . . . . . .51
2.4.5.3 Alternative Room Design for
Direct-Shielded Doors . . . . . . . . . . . .51
3. Workload, Use Factor, and Absorbed-Dose Rate
Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52
3.1 Conventional Procedures . . . . . . . . . . . . . . . . . . . . . . . .53
3.1.1 Conventional Workloads . . . . . . . . . . . . . . . . . .53
3.1.2 Conventional Use Factors . . . . . . . . . . . . . . . . .54
3.2 Special Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
3.2.1 Total-Body Irradiation Considerations. . . . . . .55
3.2.2 Intensity Modulated Radiation Therapy
Considerations . . . . . . . . . . . . . . . . . . . . . . . . . .57
3.2.3 Quality Assurance . . . . . . . . . . . . . . . . . . . . . . .58
3.2.4 Dedicated Purpose Machines . . . . . . . . . . . . . .58
3.2.5 Effect of Special Procedures on Shielding
Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
3.2.5.1 Primary-Barrier Calculations . . . . . .59
3.2.5.2 Patient- or Phantom-Scattered-
Radiation Calculations. . . . . . . . . . . .59
3.2.5.3 Leakage-Radiation Shielding
Considerations . . . . . . . . . . . . . . . . . .60
3.2.5.4 Maze Entrance Calculations . . . . . . .60
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3.3 Time Averaged Dose-Equivalent Rates. . . . . . . . . . . . . 61
3.3.1 Weekly Time Averaged Dose-Equivalent
Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.3.2 In-Any-One-Hour Time Averaged
Dose-Equivalent Rate . . . . . . . . . . . . . . . . . . . . 63
4. Structural Details. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.1.1 Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.1.2 Provision for Future Needs. . . . . . . . . . . . . . . . 66
4.1.3 Size of Treatment Room . . . . . . . . . . . . . . . . . . 66
4.1.4 Interlocks and Warning Lights. . . . . . . . . . . . . 67
4.1.5 Control Console . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.2 Barriers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.3 Shielding Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.3.1 Ordinary Concrete. . . . . . . . . . . . . . . . . . . . . . . 69
4.3.2 Heavy Concrete . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.3.3 Lead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.3.4 Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.3.5 Polyethylene and Paraffin. . . . . . . . . . . . . . . . . 71
4.3.6 Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.3.7 Wood. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.3.8 Rebar and Form Ties. . . . . . . . . . . . . . . . . . . . . 72
4.3.8.1 Rebar. . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.3.8.2 Form Ties . . . . . . . . . . . . . . . . . . . . . . 73
4.4 Joints, Concrete Slab Junctions . . . . . . . . . . . . . . . . . . 74
4.5 Access to Radiation Vault . . . . . . . . . . . . . . . . . . . . . . . 76
4.6 Ducts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
4.6.1 Heating, Ventilation and Air-Conditioning,
andHigh-Voltage Ducts . . . . . . . . . . . . . . . . . . 78
4.6.1.1 Rooms with Mazes. . . . . . . . . . . . . . . 78
4.6.1.2 Rooms without Mazes . . . . . . . . . . . . 79
4.6.1.3 Ducts Passing Through the Ceiling . 80
4.6.2 Machine Cables . . . . . . . . . . . . . . . . . . . . . . . . . 81
4.6.3 Water and Electrical Conduits. . . . . . . . . . . . . 81
4.7 Lead-Only Rooms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4.8 Beamstoppers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
5. Special Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.1 Skyshine Radiations. . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.2 Side-Scattered Photon Radiation. . . . . . . . . . . . . . . . . . 88
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5.3 Groundshine Radiation. . . . . . . . . . . . . . . . . . . . . . . . . .89
5.4 Activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90
5.5 Ozone Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91
5.6 Tomotherapy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93
5.7 Robotic Arm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94
5.8 Dedicated Intraoperative-Radiotherapy Units . . . . . . .95
5.9 Cobalt-60 Units. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95
6. Shielding Evaluation (Surveys) . . . . . . . . . . . . . . . . . . . .97
6.1 Construction Inspection . . . . . . . . . . . . . . . . . . . . . . . . .97
6.2 Interlocks, Restrictive Devices, and Radiation
WarningLights and Signs . . . . . . . . . . . . . . . . . . . . . . .98
6.3 Radiation Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99
6.4 Shielding Evaluation Report . . . . . . . . . . . . . . . . . . . .101
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105
7.1 Conventional Treatment Unit with Maze. . . . . . . . . .105
7.1.1 Primary Barrier at Location C . . . . . . . . . . . .105
7.1.2 Time Averaged Dose-Equivalent Rate
Considerations atLocation C . . . . . . . . . . . . .107
7.1.3 Patient-Scattered Radiation
ConsiderationsatLocation C . . . . . . . . . . . . .109
7.1.4 Leakage-Radiation Considerations at
Location C. . . . . . . . . . . . . . . . . . . . . . . . . . . . .111
7.1.5 Leakage- and Patient-Scattered-Radiation
Considerations for Location A. . . . . . . . . . . . .113
7.1.6 Time Averaged Dose-Equivalent Rate
(in-any-one-hour) Considerations for
Location A. . . . . . . . . . . . . . . . . . . . . . . . . . . . .117
7.1.7 Primary Barrier at Location D in the
TreatmentControl Area . . . . . . . . . . . . . . . . .120
7.1.8 Secondary Barrier at Location B. . . . . . . . . . .121
7.1.9 Secondary Barrier at Location E. . . . . . . . . . .124
7.1.10 Leakage and Scattered Radiation at the
MazeDoor. . . . . . . . . . . . . . . . . . . . . . . . . . . . .128
7.1.10.1 Wall-Scattered Radiation
Component, H . . . . . . . . . . . . . . . . .129
S
7.1.10.2 Head-Leakage Wall-Scattered
Radiation Component, H . . . . . . . .129
LS
7.1.10.3 Patient-Scattered Radiation
Component, H . . . . . . . . . . . . . . . . .130
ps
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7.1.10.4 Head-Leakage Radiation Through
Maze Wall, H . . . . . . . . . . . . . . . . . 131
LT
7.1.10.5 Total Dose Equivalent Due to
Scattered and Leakage
Radiations, H . . . . . . . . . . . . . . . . 132
Tot
7.1.10.6 IMRT Modifications. . . . . . . . . . . . . 132
7.1.10.6.1 Head-Leakage
Wall-Scattered-Radiation
Component, H . . . . . . . 132
LS
7.1.10.6.2 Head-Leakage Radiation
Transmitted Through
MazeWall, H . . . . . . . . 132
LT
7.1.11 Neutron Capture Gamma-Ray Dose
Equivalentat theMaze Door . . . . . . . . . . . . . 133
7.1.12 Neutron Dose Equivalent at the Maze Door . 135
7.1.13 Shielding Barrier for the Maze Door . . . . . . . 136
7.1.14 Primary Barrier for Roof Location G . . . . . . . 138
7.1.15 Secondary Barrier for Roof Location H . . . . . 142
7.1.16 Time Averaged Dose-Equivalent Rate for
theSecondaryBarrier at Location H with
Intensity ModulatedRadiation Therapy . . . . 146
7.1.17 Maze Barrier Thickness . . . . . . . . . . . . . . . . . 146
7.2 Robotic Arm Stereotactic-Radiosurgery Room . . . . . . 148
7.2.1 Time Averaged Dose-Equivalent Rate
Considerations forLocation A. . . . . . . . . . . . . 151
7.2.2 Barrier for Location B. . . . . . . . . . . . . . . . . . . 153
7.2.3 Shielding for Location C . . . . . . . . . . . . . . . . . 154
7.2.4 Determination of the Maze Barrier
Thickness(Location D) . . . . . . . . . . . . . . . . . . 155
7.2.5 Shielding at Location E (Roof) . . . . . . . . . . . . 156
Appendix A. Supporting Data (Figures) . . . . . . . . . . . . . . . 158
Appendix B. Supporting Data (Tables) . . . . . . . . . . . . . . . . 160
Appendix C. Neutron Monitoring for Radiotherapy
Facilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
C.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
C.2 Neutron Monitoring Techniques . . . . . . . . . . . . . . . . . 178
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C.2.1 Active Monitoring. . . . . . . . . . . . . . . . . . . . . . .178
C.2.1.1 Rem-Meters. . . . . . . . . . . . . . . . . . . .178
C.2.1.2 Commercial Instruments. . . . . . . . .181
C.2.1.3 Fluence Meters. . . . . . . . . . . . . . . . .184
C.2.1.4 Neutron Spectrometers . . . . . . . . . .185
C.2.2 Passive Monitoring . . . . . . . . . . . . . . . . . . . . .186
C.2.2.1 Activation Detectors. . . . . . . . . . . . .186
C.2.2.2 Solid-State Nuclear Track
Detectors. . . . . . . . . . . . . . . . . . . . . .189
C.2.2.3 Bubble Detectors . . . . . . . . . . . . . . .191
C.2.2.4 Comparison of Various Passive
Monitors . . . . . . . . . . . . . . . . . . . . . .192
C.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .195
Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .198
Symbols and Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .205
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .210
The NCRP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .219
NCRP Publications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .227
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .237
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