Multifraction radiation response of mouse lung.

Area of Science:

• Radiation oncology
• Radiobiology
• Pulmonary medicine

Background:

• Accurate modeling of normal tissue responses to radiation is crucial for optimizing radiotherapy. Mouse lung pneumonitis is a common endpoint for assessing radiation damage.
• Understanding dose-response relationships for lung tissue informs clinical radiation therapy protocols.

Purpose of the Study:

• To investigate the response of mouse lung to fractionated doses of 60Co gamma-rays.
• To determine the total dose required for 50% mortality (LD50) at varying doses per fraction.
• To evaluate the clinical relevance of lung's response to dose fractionation.

Main Methods:

• Mice were subjected to fractionated 60Co gamma-ray irradiation with doses as low as 115 centiGray (cGy) per fraction.
• Pneumonitis occurring 80-120 days post-irradiation was the primary endpoint.
• Fractionation intervals were primarily 3 hours, with some 12-hour intervals used.
• Total doses for 50% mortality (LD50) were calculated across different dose per fraction regimens.

Main Results:

• The total dose required for LD50 increased continuously as the dose per fraction decreased, even from 160 to 115 cGy.
• The isoeffect curve over the 115-500 cGy dose range indicated substantial dose sparing in the lung.
• Lung demonstrated greater sparing from fractionation compared to rapidly responding normal tissues, similar to slowly responding tissues like the spinal cord.
• A non-linear relationship was observed between the reciprocal of LD50 and dose per fraction.

Conclusions:

• Mouse lung exhibits significant radioresistance to fractionated radiation, behaving like slowly responding tissues.
• The observed non-linearity suggests that linear-quadratic models may not fully capture lung's response, potentially due to incomplete cellular repair within 3-hour intervals.
• Findings have clinical implications for radiotherapy planning, highlighting the lung's capacity for dose sparing through fractionation.