Tissue-to-air ratio (TAR) is a term used in radiotherapy treatment planning to help calculate absorbed dose to water in conditions other than those directly measured.
Definition
The TAR at a point in a water phantom irradiated by a photon beam is taken to be the ratio of the total absorbed dose at that point to the absorbed dose at the same point in a minimal-scatter phantom with just-sufficient build-up.[1][2]
Tissue-air ratio is defined as the ratio of the dose to water at a given depth to the dose in air measured with a buildup cap:
where D(f,z) is the dose at a given depth z and distance focus-detector f; and D(f,0) is the dose in air (z=0).
- TAR increases with increasing beam energy because higher energy radiation is more penetrating
- TAR decreases with depth because of attenuation
- TAR increases with field size due to increased scatter contribution
Measurements for each are taken using an ion chamber for identical source to detector distances and field sizes.[3]
See also
References
- ^ Johns H. E. and Cunningham J. R. (1983). The Physics of Radiology. Charles C. Thomas Publ.
- ^ Hendee W., Ibbott G. and Hendee E. (2005). Radiation Therapy Physics. Wiley-Liss Publ. ISBN 0-471-39493-9.
- ^ Faiz M. Khan. (2010) "The Physics of Radiation Therapy " Lippencott, Wilkins and Williams Publ.
Radiation oncology |
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Specific therapies | Teletherapy1 | |
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Brachytherapy2 |
- Prostate
- Plaque radiotherapy (125I)
- Selective internal radiation therapy / SIR-Spheres / TheraSphere (90Y)
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Unsealed source radiotherapy3 |
- Iobenguane (131I)
- 90Y
- Lexidronam (153Sm)
- 89Sr
- Radioimmunotherapy
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Other |
- Intraoperative radiation therapy
- Tomotherapy
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Conditions |
- Radiation burn
- Radiation proctitis
- Radiation-induced lung injury
- Bystander effect
- Abscopal effect
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Features and equipment |
- BEAMnrc
- Bolus
- Bragg peak
- D50
- Dose profile
- Dose verification system
- Dose-volume histogram
- Dosimetry
- Isocenter
- Mobetron
- Monitor unit
- Multileaf collimator
- Nanoimpellers
- Neutron generator
- Oxygen enhancement ratio
- Pencil
- Pencil-beam scanning
- Percentage depth dose curve
- Radiation oncologist
- Radiation therapist
- Radiation treatment planning
- Radiopharmacology
- (TAR)
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- 1 Also known as external-beam radiotherapy.
- 2 Also known as sealed-source radiation therapy.
- 3 Also known as systemic radioisotope therapy.
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