𝗕𝗶𝗼𝗹𝗼𝗴𝗶𝗰 𝗨𝗻𝗱𝗲𝗿𝗽𝗶𝗻𝗻𝗶𝗻𝗴𝘀 𝗼𝗳 𝗦𝗶𝗱𝗲 𝗘𝗳𝗳𝗲𝗰𝘁𝘀 𝗼𝗳 𝗥𝗮𝗱𝗶𝗮𝘁𝗶𝗼𝗻 Radiobiologic models developed with the use of characteristics such as mitotic capacity, tissue hierarchy, and differentiation state can predict responses in normal tissue at the levels of the cell, tissue, and organ. For example, the interaction of the dose and volume of radiation with the risk of effects in normal tissue is tissue- or organ-specific and dependent on the organization of the smallest functional subunits (e.g., nephrons, neurons, or alveoli) within the tissue. For some organs in which the functional subunits are organized in parallel (e.g., nephrons in the kidney), approximately a third of the total volume of the organ must be spared from receiving a relatively low threshold dose to maintain functional organ viability. The remaining two thirds of the organ constitutes a functional reserve. In contrast, when functional subunits are arranged in series (e.g., spinal cord neurons), even a focal injury threatens organ function (e.g., spinal cord myelopathy). Tissues with parallel organization generally have a higher tolerance for radiation than tissues with serial organization. Ablative treatments such as stereotactic ablative radiotherapy are more likely to have an acceptable safety profile when applied in and around tissues with parallel organization or in tissues capable of compensatory hyperplasia after injury than in serially functioning tissues (seen in figure). Learn more in the Review Article “Effects of Radiotherapy in Normal Tissue” by @DeborahCitrin, MD, and Robert D. Timmerman, MD (@BobTimmermanMD), from the National Cancer Institute and @UTSWMedCenter: nejm.org/doi/full/10.1056/NE…

Hmmm those are quite high pneumonitis numbers. Curious that steroids during RT would be effective like that? @DeborahCitrin