Organ Tolerance


* Liver
* Lung
* Kidney
* Spinal cord
* Rectum
* CNS & Brain

Estimation of Risk

General Considerations

Normal tissue tolerance has been of interest to radiation oncologists for decades - in fact since we learnt that a patient's life or function could be eradicated by a sufficient amount of poorly placed radiation. Since it has always been unethical to experiment on patients by deliberately inflicting harm, our data is derived from routine treatment mishaps. Obviously the detail provided is as good as our ability to plan, predict and quantitate delivered dose.

Probably the major piece of literature relevant to NTCP is a list published some time ago that provided a wide coverage of organs and attempted to specify a dose tolerance or safe dose level. The TD5/5 is the tolerance dose that results in 5% of cases within a 5 year period, and the TD50/5 is the tolerance dose that results in 50% of cases within a 5 year period. I could not find the original reference from 1991 in PDF format unfortunately. The choice of 5% is somewhat arbitrary, but has not seen any major discussion, so I also assume that it is a reasonable level of detriment. Of course a 50% level is far too high unless there is a certainty of horrendous cancer problems.

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