How do you approach SRS reirradiation for brain metastases overlapping previous sites of SRS?

This situation has several variants.

First of all its incidence should be about 5% in most SRS cases.

Second all retreatment decisions should be made following co-registration of current images with treatment images. Easy to be tricked based on scan angle.

Variant 1: Response followed by recurrence matches original tumor location and spread (verified on PET/Delayed MRI images and Perfusion or Mukti voxel MRS)

Answer: Retreat to standard dose if over 1 yr from original RX.

If less than 1 year reduced dose SRS if volume exceeds 2 cc (or hypofractionated SRS with ICON at our center).

If recurrence under 2 cc would repeat full dose SRS

Variant 2: Part of treated tumor persists or recurs (Verify on imaging)

Ans : Treat recurrent area alone to fu...

This is not a common scenario, ie a new brain metastases so adjacent that there is overlap with a previously SRSed lesion. But if I am sure it is separate but beside a previously treated lesion, I would probably do SRS with usual dose. More commonly, there is an increase in size of the previously treated metastasis and the question then is whether this represents necrosis or tumor growth. If they are symptomatic I would try steroids to see if that resolves the issue. Or if systemic therapy can be altered if it is suspected tumor growth. If steroids or systemic therapy don’t work, I would discuss this patient with the neurosurgeon to see if the lesion can be resected. If it is unresectable I would have a discussion with the patient about fra...