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A Simplified Method of Estimating Integral Dose in Radiotherapeutic Practice

A Simplified Method of Estimating Integral Dose in Radiotherapeutic Practice A Simplified Method of Estimating Integral Dose in Radiotherapeutic Practice 1 R. Kenneth Loeffler , M.D. Excerpt The influence of integral or volume dose upon the response of the patient was recognized empirically shortly after the first use of ionizing radiation for the treatment of human illness. Béclère in 1915 noted that large-field irradiation is less well tolerated than that limited to small areas or volumes (1). Integral dose alone is certainly not sufficient to predict lethality, radiation illness, hematopoietic depression, or local reaction. The tissue irradiated, the size of the subject, and the protection of hematopoietic tissue are among the many variables shown to influence response (2-4). Recognizing these limitations, it is nevertheless likely that a useful correlation between integral dose and patient response for many treatment conditions may be obtained. For such clinical correlation to become routine, there must be a simple and reasonably accurate technic for calculating integral dose with each treatment planning. Mayneord and his associates (5-7) initiated a formal and quantitative approach to the subject, proposing the “gram-roentgen” as a unit of measure and developing several mathematical solutions for the estimation of integral dose. Happey, Smithers, Ellis, and others have contributed to the development of this subject (8-11). These treatises are thorough, but they present computations too laborious for routine use. A simplified formula proposed by Mayneord (12) is given in the sections on integral dose in two frequently used texts on medical physics: those of Glasser, Quimby, Taylor, and Weatherwax (13), and of Johns (14). For this formula, I = 1.44 × A × D 0 × d 1/2 , to be perfectly accurate, the following conditions would be required: ( a ) exponential decrease of dose; ( b ) parallel beam; ( c ) flat isodose surfaces; ( d ) complete absorption. Since all of the these conditions are only approximately realized, correction factors have been proposed to compensate partially for the deviations. The initial portion of the depth-dose curve is not exponential, because of forward scatter and, with multimillion-volt radiation, because of electron build-up. This portion can be estimated separately, and the formula used for the deeper, more exponential region. Mayneord, Quimby, and Johns add another term to the above formula to compensate for the divergence of the beam. Quimby also describes a method to correct for incomplete absorption due to the finite thickness of the patient. Thus, even the simplified formula leads to a series of calculations for each field used. The solution to be proposed here involves no new concepts. The intent rather is to simplify the calculations to the level of routine applicability, without unduly sacrificing accuracy. The energy absorbed from a beam of radiation is equal to the energy of the radiation which enters the body, times the percentage of this which is absorbed within that body. The portion which is absorbed is dependent, in turn, upon the quality of the radiation, and the composition and size of the absorber. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Radiology Radiological Society of North America, Inc.

A Simplified Method of Estimating Integral Dose in Radiotherapeutic Practice

Radiology , Volume 67 (3): 371 – Sep 1, 1956

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References (7)

Publisher
Radiological Society of North America, Inc.
Copyright
Copyright © 1956 by Radiological Society of North America
ISSN
1527-1315
eISSN
0033-8419
DOI
10.1148/67.3.371
pmid
13359716
Publisher site
See Article on Publisher Site

Abstract

A Simplified Method of Estimating Integral Dose in Radiotherapeutic Practice 1 R. Kenneth Loeffler , M.D. Excerpt The influence of integral or volume dose upon the response of the patient was recognized empirically shortly after the first use of ionizing radiation for the treatment of human illness. Béclère in 1915 noted that large-field irradiation is less well tolerated than that limited to small areas or volumes (1). Integral dose alone is certainly not sufficient to predict lethality, radiation illness, hematopoietic depression, or local reaction. The tissue irradiated, the size of the subject, and the protection of hematopoietic tissue are among the many variables shown to influence response (2-4). Recognizing these limitations, it is nevertheless likely that a useful correlation between integral dose and patient response for many treatment conditions may be obtained. For such clinical correlation to become routine, there must be a simple and reasonably accurate technic for calculating integral dose with each treatment planning. Mayneord and his associates (5-7) initiated a formal and quantitative approach to the subject, proposing the “gram-roentgen” as a unit of measure and developing several mathematical solutions for the estimation of integral dose. Happey, Smithers, Ellis, and others have contributed to the development of this subject (8-11). These treatises are thorough, but they present computations too laborious for routine use. A simplified formula proposed by Mayneord (12) is given in the sections on integral dose in two frequently used texts on medical physics: those of Glasser, Quimby, Taylor, and Weatherwax (13), and of Johns (14). For this formula, I = 1.44 × A × D 0 × d 1/2 , to be perfectly accurate, the following conditions would be required: ( a ) exponential decrease of dose; ( b ) parallel beam; ( c ) flat isodose surfaces; ( d ) complete absorption. Since all of the these conditions are only approximately realized, correction factors have been proposed to compensate partially for the deviations. The initial portion of the depth-dose curve is not exponential, because of forward scatter and, with multimillion-volt radiation, because of electron build-up. This portion can be estimated separately, and the formula used for the deeper, more exponential region. Mayneord, Quimby, and Johns add another term to the above formula to compensate for the divergence of the beam. Quimby also describes a method to correct for incomplete absorption due to the finite thickness of the patient. Thus, even the simplified formula leads to a series of calculations for each field used. The solution to be proposed here involves no new concepts. The intent rather is to simplify the calculations to the level of routine applicability, without unduly sacrificing accuracy. The energy absorbed from a beam of radiation is equal to the energy of the radiation which enters the body, times the percentage of this which is absorbed within that body. The portion which is absorbed is dependent, in turn, upon the quality of the radiation, and the composition and size of the absorber.

Journal

RadiologyRadiological Society of North America, Inc.

Published: Sep 1, 1956

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