وبلاگ جامع علوم پرتو پزشکی و فیزیک پزشکی

پرتو پزشکی, فیزیک پزشکی, ام آر آی MRI ,سی تی اسکن Ct Scan , رادیولوژی, رادیوتراپی, پزشکی هسته ای, مهندسی هسته ای

وبلاگ جامع علوم پرتو پزشکی و فیزیک پزشکی

پرتو پزشکی, فیزیک پزشکی, ام آر آی MRI ,سی تی اسکن Ct Scan , رادیولوژی, رادیوتراپی, پزشکی هسته ای, مهندسی هسته ای

TAR or Tissue Air Ratio

medradiation | پنجشنبه, ۱۹ شهریور ۱۳۹۴، ۰۹:۲۴ ق.ظ

Tissue-Air Ratio


Tissue-air ratio (TAR) was first introduced by Johns  in 1953 and was originally called the “tumor-air ratio.” At that time, this quantity was intended specifically for rotation therapy calculations. In rotation therapy, the radiation source moves in a circle around the axis of rotation, which is usually placed in the tumor. Although the SSD may vary depending on the shape of the surface contour, the source-axis distance remains constant.
Since the percent depth dose depends on the SSD , the SSD correction to the percent depth dose will have to be applied to correct for the varying SSD—a procedure that becomes cumbersome to apply routinely in clinical practice. A simpler quantity—namely TAR—has been defined to remove the SSD dependence. Since the time of its introduction, the concept of TAR has been refined to facilitate calculations not only for rotation therapy, but also for stationary isocentric techniques as well as irregular fields.


Tissue-air ratio may be defined as the ratio of the dose (Dd) at a given point in the phantom to the dose in free space (Dfs) at the same point.


This is illustrated in Figure 2 For a given quality beam, TAR depends on depth d and field size rd at that depth:

Fig 2: Illustration of the definition of tissue-air ratio (TAR). TAR(d,rd) = Dd/Dfs



Physics of Radiation Therapy, The, 5th Edition

Faiz M. Khan PhD

Professor Emeritus

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