MRI appearance of Treated lesions: 

external beam: early response to external beam irradiation, case 2 after external beam, but regrowth after external beam here , another case two months after external beam here. Lung cancer brain mets two months after external beam here and here and at 4 months here. Small brain met after two months here and another case here.

Rectal cancer brain met at 3 and 5 months post radiation here. lung cancer at 4 months here. More sensitive cancers may respond quite well to external beam, such as small cell (go here).

radiosurgery: small mets may be almost gone by 3 weeks. response after 3 weeks and same case after 4 months, gamma knife mets after two months here and here  another case at 4 months here. Lung cancer large met after 4 weeks here. Lung cancer lesion after 10 months here, another lung cancer case at 19 months here.

Breast mets at two and three month here and here. . Breast cancer single met at 2 months here. Another breast case at two months here. Ovary cancer mets at two months here and here. Another large cystic met (ovary) 6 months after gamma knife here. A classic problem with brain mets is the development of new lesions (see here)

radionecrosis: It is important to try to distinguish between recurrent cancer and simply dead tumor (necrosis) typical picture here or here or here or here or here and read the section on side effects here and here . A PET scan may be helpful in distinguishing recurrent tumor (hot or hypermetabolic on PET, see here) from radionecrosis (cold on PET). Another case of radionecrosis that was cold on PET (see here and here).


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