LII:Radiation Oncology/Physics/ICRU

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International Commission of Radiation Units and Measurements (ICRU)

ICRU Reports

The International Commission on Radiation Units and Measurements (ICRU), since its inception in 1925, has had as its principal objective the development of internationally acceptable recommendations regarding:

Quantities and units of radiation and radioactivity,
Procedures suitable for the measurement and application of these quantities in clinical radiology and radiobiology,
Physical data needed in the application of these procedures, the use of which tends to assure uniformity in reporting.

The Commission also considers and makes similar types of recommendations for the radiation protection field. In this connection, its work is carried out in close cooperation with the International Commission on Radiological Protection (ICRP)

ICRU 29 (1978) - "Dose Specification for Reporting External Beam Therapy with Photons and Electrons"
- Superseded by ICRU 50 (see below)

ICRU 38 (1985) - "Dose and Volume Specification for Reporting Intracavitary Therapy in Gynecology"
- Definitions of concepts:
  - LDR is dose rates between 0.4 and 2 Gy/h and HDR is > 12 Gy/h
  - Target Volume: tissues that are to be irradiated to a specified dose
  - Treatment Volume: volume enclosed by a relevant isodose surface selected by the radiation oncologist; encompasses at least the target volume
  - Reference Volume: volume enclosed by the reference isodose surface (based on agreed reference dose level)
  - Irradiated Volume: volume which receives an absorbed dose considered significant in relation to tissue tolerance; may be a percentage of reference dose
- Recommendations for reporting:
  - Due to steep dose gradient, maximum / minimum / mean absorbed dose irrelevant (ICRU 29)
  - Description of technique used in terms of sources, simulation of linear sources, and applicator
  - Reporting in terms of three complementary approaches: total reference air kerma, reference volume, and absorbed dose at reference points leading to calculation of dose distribution
  - Total reference air kerma: kerma rate to air, in air, at a reference distance of 1 meter, corrected for air attenuation and scattering. Expressed in μGy/h
  - Reference volume:
    - For LDR, should use absorbed dose level of 60 Gy; for HDR an equivalent (according to treating radiation oncologist) dose should be specified
    - Described by three parameters: height (dimension along intrauterine source), width (perpendicular to height in frontal plane), thickness (perpendicular to height in sagittal plane)
  - Absorbed dose at reference points:
    - Definitions apply when calculated from two perpendicular radiographs (AP/lateral)
    - Bladder reference point: Foley catheter is inserted; balloon filled with 7 cm³ radio-opaque fluid. Catheter is pulled downward to bring the balloon against urethra. On lateral radiograph, reference point is on an anterio-posterior line drawn through the center of the balloon, at the posterior surface of the balloon. On AP radiograph, the reference point is at the center of the balloon
    - Rectal reference point: Visualize posterior vaginal wall with intravaginal mould or by opacification of the vaginal cavity with radio-opaque gauze used for packing. On lateral radiograph, a separate anterior-posterior line is drawn from the lower end of the intrauterine source (or the middle of the intravaginal source). Reference point is on this line, 5 mm behind posterior vaginal wall. On AP radiograph, the reference point is at the lower end of the intrauterine source (or the middle of the intravaginal source)
    - Bony structures reference points: On a lateral radiograph, a diagonal line is drawn from S1/S2 to top of symphysis. A line is drawn from a midpoint on this line upward to middle of anterior aspect of L4. The corresponding point on an AP radiograph serves as the top of the lymphatic trapezoid. The right and left lateral points 2 cm from midline provide the R PARA and L PARA dose to low para-aortic area. Inferior base of the trapezoid is at the midpoint of the S1/S2 - symphysis line. The right and left later points 6 cm from midline provide the R EXT and L EXT dose to right and left mid-external iliac lymph nodes. The midpoint line connecting the two points (R PARA and R EXT or L PARA and L EXT) is used for estimating R COM and L COM dose to right and left common iliac lymph nodes
    - Pelvic wall reference point: On lateral radiograph, the highest points of the right and left acetabulum in the cranio-caudal direction are joined, and the midpoint is the lateral projection of the pelvic wall. On AP radiograph, the pelvic wall point (RPW or LPW) is the intersection of two lines. A horizontal line tangential to the highest point of the acetabulum and a vertical line tangential to the inner aspect of the acetabulum
  - Duration of treatment should be reported; there is insufficient evidence fo radiobiological considerations

ICRU 50 (1993) - "Prescribing, Recording, and Reporting Photon Beam Therapy"
- Supersedes and updates Report 29
- Aim of Therapy: Should be defined as radical, palliative, or non-malignant
- Volumes are defined:
  - Gross Tumor Volume (GTV): Gross palpable or visible/demonstrable extent and location of malignant growth
  - Clinical Target Volume (CTV): Anatomical concept. Tissue volume that contains a GTV and/or subclinical microscopic malignant disease, which has to be eliminated. This volume has to be treated adequately in order to achieve the aim of therapy: cure or palliation. The CTV is an anatomical-clinical concept, that has to be defined before a choice of treatment modality and technique is made
  - Planning Target Volume (PTV): Geometrical concept. Defined to select appropriate beam sizes and beam arrangements, taking into consideration the net effect of all the possible geometrical variations and inaccuracies in order to ensure that the prescribed dose is actually absorbed in the CTV. Its size and shape depend on the CTV but also on the treatment technique used, to compensate for the effects of organ and patient movement, and inaccuracies in beam and patient setup
  - Treated Volume: Volume enclosed by an isodose surface (e.g. 95% isodose), selected and specified by radiation oncologist as being appropriate to achieve the purpose of treatment. Ideally, Treated Volume would be identical to PTV, but may also be considerably larger than PTV
  - Irradiated Volume: Tissue volume which receives a dose that is considered significant in relation to normal tissue tolerance. Dose should be expressed either in absolute values or relative to the specified dose to the PTV
  - Organs at Risk: Normal tissues whose radiation sensitivity may significantly influence treatment planning and/or prescribed dose
- Recommendations for Reporting Dose
  - ICRU Reference Point:
    - Dose at the point should be clinically relevant and representative of the dose throughout PTV
    - The point should be easy to define in a clear and unambiguous way
    - The point should be selected where the dose can be accurately determined (physical accuracy)
    - The point should be selected in a region where there is no steep dose gradient
    - ICRU Reference point should be located at the center of the PTV and when possible at the intersection of the beam axes
    - The dose at the ICRU Reference Point is the ICRU Reference Dose
  - Dose at/near center of PTV, maximum dose to PTV, and minimum dose to PTV should always be reported
  - Maximum Dose: Highest dose in PTV. A volume is considered clinically meaningful if its minimum diameter exceeds 15 mm; however, if it occurs in a small organ (e.g. the eye, optic nerve, larynx), a dimension smaller than 15 mm has to be considered
  - Minimum Dose: Lowest dose in PTV. In contrast to Maximum Dose, no volume limit is recommended.
  - Hot Spots: Volume outside the PTV which receives dose larger than 100% of the specified PTV dose. In general considered significant only if minimum diameter exceeds 15 mm; however, if it occurs in a small organ (e.g. the eye, optic nerve, larynx), a dimension smaller than 15 mm has to be considered
  - Levels of Dose Evaluation for Reporting:
    - Basic: Only dose at ICRU Reference Point and its variation along a central beam axis is available
    - Advanced: Dose distribution can be computed for plane(s)
    - Developmental: Dose distribution can be computed for volume(s)

ICRU 58 (1997) - interstitial brachytherapy
- “Dose and Volume Specification for Reporting Interstitial Therapy (1998)”
- • Definition of terms and concepts
  - Temporary and permanent implants
  - Source specification
  - Description Of source patterns
  - TRAK ( Total reference AIR Kerma)
  - Volumes and planes
  - Description of dose distribution :
    - Mean central dose, Minimum target Dose, High dose volume, Low dose volume
  - Time Dose factors
    - Temporary implant = Prescribed dose / initial dose rate
- • Definition of quantities
  - Absorbed dose
  - The Kerma
  - The activity
  - The air Kerma Rate Constant
  - Relationship Between the quantities
  - Reference Air Kerma Rate
- • Recommendations for recording ad reporting
  - Parameters to be recorded and reported
  - Priority
- • Practical applications
  - Temporary implants
  - Permanent implant
  - Single stationary source line
  - Moving sources
  - Surface applicators
ICRU 62 (1999) - "Prescribing, Recording and Reporting Photon Beam Therapy (Supplement to ICRU Report 50)"
- Report
- No change to definition of GTV and CTV, since they are oncologic concepts independent of any technical development
- Global concept and definition of PTV is not changed, but definition is supplemented
  - Internal Margin (IM): Variations in size, shape, and position of the CTV relative to anatomic reference points; e.g., filling of bladder, movements of respiration. The internal variations are physiological ones, and result in change in site, size, and shape of the CTV
  - Internal Target Volume (ITV): Volume encompassing the CTV and IM. (ITV = CTV + IM)
  - Set-up Margin (SM): Uncertainties in patient positioning and alignment of therapeutic beams during treatment planning, and through all treatment sessions. The uncertainties may vary with selection of beam geometries, and may depend on variations in patient positioning, mechanical uncertainties of the equipment (e.g. sagging of gantry, collimators, or couch), dosimetric uncertainties, transfer setup errors from CT simulator to treatment unit, and human factors. These may vary from center to center, and from machine to machine
  - Planning Target Volume: PTV = CTV + IM + SM. The penumbra of the beam(s) is not considered when delineating the PTV. However, when selecting beam sizes, the width of the penumbra has to be taken into account and the beam size adjusted accordingly
  - Dose variation between +7% and -5% is generally accepted
- Treated Volume: Volume enclosed by an isodose surface (e.g. 95%). The relative value of the isodose that was selected to define the Treated Volume in relation to the dose at the ICRU Reference Point should be stated when reporting, or can be expressed in absolute values
- Conformity Index (CI): Treated Volume / PTV; it is implied that Treated Volume completely encompasses the PTV
- Organs at Risk Volumes:
  - Organs at Risk (OAR): Normal tissues whose radiation sensitivity may significantly influence treatment planning and/or prescribed dose. For the moment, is may be useful to state if OAR is serial, parallel, or mixed serial-parallel
  - Planning Organ at Risk Volume (PRV): Analogous to PTV for OAR. PRV = OAR + IM + SM

ICRU LIST OF REPORTS

- 1. ICRU 1*
- Discussion on International Units and Standards for X-ray Work
- Brit. J. Radiol. Vol.23, 64-101 (1927)
- 2. ICRU 2*
- International X-Rays Unit of Intensity
- Brit. J. Radiol.(new series) Vol.1, 360-365 (1928)
- 3. ICRU 3*
- Report of Committee on Standardization of X-ray Measurements
- Radiology Vol.22, 289-294 (1934)
- 4. ICRU 4*
- Recommendations of the International Committee for Radiological Units
- Radiology Vol.23, 580-581 (1934)
- 5. ICRU 5*
- Recommendations of the International Committee for Radiological Units
- Radiology Vol.29, 634 -636 (1937)
- 6. ICRU 6*
- Recommendations of the International Commission on Radiological Protection and of the International Commission on Radiological **Units (NBS 47) (1951)
- 7. ICRU 7*
- Recommendations of the International Commission for Radiological Units
- Radiology Vol.62, 106-109 (1954)
- 8. ICRU 8*
- Report of the International Commission on Radiological Units and Measurements (ICRU)1956 (NBS 62) (1957)
- 9. ICRU 9*
- Report of the International Commission on Radiological Units and Measurements (ICRU)1959 (NBS 78) (1961)
- 10. ICRU 10a*
- Radiation Quantities and Units (NBS 84) (1962)
- 11. ICRU 10b
- Physical Aspects of Irradiation (NBS 85) (1964)
- 12. ICRU 10c
- Radioactivty (NBS 86) (1963)
- 13. ICRU 10d*
- Clinical Dosimetry (NBS 87) (1963)
- 14. ICRU 10e*
- Radiobiological Dosimetry (NBS 88) (1963)
- 15. ICRU 10f
- Methods of Evaluating Radiological Equipment and Materials (NBS 86) (1963)
- 16. ICRU 11*
- Radiation Quantities and Units (1968)
- 17. ICRU 12
- Certification of Standardized Radioactive Sources (1968)
- 18. ICRU 13
- Neutron Fluence, Neutron Spectra and Kerma (1969)
- 19. ICRU 14
- Radiation Dosimetry: X Rays and Gamma Rays with Maximum Photon Energies between 0.6 and 50 MeV (1969)
- 20. ICRU 15
- Cameras for Image Intesifier Fluorography (1969)
- 21. ICRU 16
- Linear Energy Transfer (1970)
- 22. ICRU 17
- Radiation Dosimetry: X Rays Generated at Potentials of 5 to 150 kV (1970)
- 23. ICRU 18
- Specification of High Activity Gamma-Ray sources (1970)
- 24. ICRU 19*
- Radiation Quantities and Units (1971)
- 25. ICRU 19S*
- Dose Equivalent [supplement to ICRU Report 19] (1973)
- 26. ICRU 20
- Radiation Protection Instrumentation and Its Application (1971)
- 27. ICRU 21
- Radiation Dosimetry: Electrons with Initial Energies Between 1 and 50 MeV (1972)
- 28. ICRU 22
- Measurement of Low-Level Radioactivity (1972)
- 29. ICRU 23
- Measurement of Absorbed Dose in a Phantom Irradiated by a Single Beams of X or Gamma Rays (1973)
- 30. ICRU 24
- Determination of Absorbed Dose in a Patient Irradiated by Beams of X or Gamma Rays in Radiotherapy Procedures (1976)
- 31. ICRU 25
- Conceptual Basis for the Determination of Dose Equivalent (1976)
- 32. ICRU 26
- Neutron Dosimetry for Biology Medicine (1977)
- 33. ICRU 27
- An International Neutron Dosimetry Intercomparison (1978)
- 34. ICRU 28
- Basic Aspects of High Energy Particle Interaction and Radiation Dosimetry (1978)
- 35. ICRU 29
- Dose Specification for Reporting External Beam Therapy with Photons and Electrons (1978)
- 36. ICRU 30
- Quantitiatve Concepts and dosimetry in Radiobioloby (1979)
- 37. ICRU 31
- Average Energy Required to Produce an Ion Pair (1979)
- 38. ICRU 32
- Methods Assessment of Absorbed Dose in Clinical Use of Radionuclide (1979)
- 39. ICRU 33
- Radiation Quantities and Units (1980)
- 40. ICRU 34
- The Dosimetery of Pulsed Radiation (1982)
- 41. ICRU 35
- Radiation Dosimetry: Electron Beams with Energies between 1 and 50 MeV (1984)
- 42. ICRU 36
- Microdosimetry (1983)
- 43. ICRU 37
- Stopping Powers for Electrons and Positrons (1984)
- 44. ICRU 38
- Dose and Volume Specification for Reporting Intracavitary Therapy in Gynecology (1985)
- 45. ICRU 39
- Determination of Dose Equivalents Resulting from External Radiation Sources [ -- Part I ] (1985)**
- 46. ICRU 40
- The Quality Factor in Radiation Protection (1986)
- 47. ICRU 41
- Modulation Transfer Function of Screen-Film systems (1986)
- 48. ICRU 42
- Use of Computers in External Beam Radiotherapy Procedures with High-Energy Photons and Electrons (1987)
- 49. ICRU 43
- Determination of Dose Equivalents from External Radiation Sources—Part II (1988)
- 50. ICRU 44
- Tissue Substitutes in Radiation Dosimetry and Measurement (1989)
- 51. ICRU 45
- Clinical Neutron Dosimetry Part 1: Determination of Absorbed Dose in a Patient Treated by External Beams of Fast Neutrons (1989)
- 52. ICRU 46
- Photon, Electron, Proton and Neutron Interaction Data for Body Tissues (1992)
- 53. ICRU 47
- Measurement of Dose Equivalents from External Photon and Electron Radiations (1992)
- 54. ICRU 48
- Phantoms and Computational Models in Therapy, Diagnosis and Protection (1992)
- 55. ICRU 49
- Stopping Powers and Ranges for Protons and Alpha Particles (1993)
- 56. ICRU 50
- Prescribing, Recording, and Reporting Photon Beam Therapy (1993)
- 57. ICRU 51
- Quantities and Units in Radiation Protection Dosimetry (1993)
- 58. ICRU 52
- Particle Counting in Radioactivity Measurements (1994)
- 59. ICRU 53
- Gamma-Ray Spectrometry in the Environment (1995)
- 60. ICRU 54
- Medical Imaging - The Assessment of Image Quality (1996)
- 61. ICRU 55
- Secondary Electron Spectra from Charged Particle Interactions (1996)
- 62. ICRU 56
- Dosimetry of External Beta Rays for Radiation Protection (1997)
- 63. ICRU 57
- Conversion Coefficients for Use in Radiological Protection Against External Radiation (1998)
- 64. ICRU 58
- Dose and Volume Specification for Reporting Interstitial Therapy (1998)
- 65. ICRU 59
- Clinical Proton Dosimetry Part I. - Beam Production, Beam Delivery and Measurement of Absorbed Dose (1998)
- 66. ICRU 60
- Fundamental Quantities and Units for Ionizing Radiation (1998)
- 67. ICRU 61
- Tissue Substitutes, Phantoms and Computational Modeling in Clinical Ultrasound (1998)
- 68. ICRU 62
- Prescribing, Recording and Reporting Photon Beam Therapy (Supplement to ICRU Report 50) (1999)
- 69. ICRU 63
- Nuclear Data for Neutron and Proton Radiotherapy and for Radiation Protection (2000)
- 70. ICRU Report 64: Dosimetry of High-Energy Photon Beams Based on Standards of Absorbed Dose to Water
- 71. ICRU Report 65, Quantities, Units and Terms in Radioecology
- 72. ICRU Report 66: Determination of Operational Dose Equivalent Quantities for Neutrons
- 73. Absorbed-dose specification in nuclear medicine, ICRU Report 67
- 74. ICRU Report 68, Retrospective Assessment of Exposure to Ionising Radiation
- 75. Report 69 : Direct determination of body content of Radionuclides
- 76. Report 70 (2003) Image Quality in Chest Radiography
- 77. . ICRU Report 72 (2004) Dosimetry of Beta Rays and Low-Energy Photons for Brachytherapy with Sealed Source
- 78. Report 73 (2005) on Stopping of Ions Heavier than Helium
- 79. Report 74 (2005) on Patient Dosimetry of X Rays used in Medical Imaging
- 80. Report 75 : Sampling of radionuclides in the environment
- 81. Report 76 (2006) Measurement Quality Assurance for Ionizing Radiation Dosimetry
- 82. Report 77 (2007) Elastic Scattering of Electrons and Positrons
- 83. Report 78 : Prescribing, Recording and Reporting Proton beam therapy
- 84. Report 79 : Receiver Operating characteristic (ROC) analysis of medical imaging
- 85. Report 80: Dosimetry systems for use in Radiation processing