I understand the first two paragraphs so I left those out.
I suppose what you're saying is that your 3 part regimen should be equivalent to 37.5/15, and therefore adding SRS at the initial treatment would be safe, as salvage 37.5/15 WBRT is generally considered safe after SRS. Thanks for the more in-depth explanation.
I guess my final questions are what is the general time frame for the SRS planning MRI (and subsequent initiation of SRS) after the initial 15Gy? I guess my concern is that you will be seeing some tumor shrinkage and possibly shift of it as the (large volume) edema improves with the 15Gy; the time frame between SRS planning MRI and initiation of SRS treatment then becomes important. Are you fractionating these SRS treatments or going single-fraction?
Is this something you do routinely (or I suppose, uncommonly) or is this more like 1 - 3 cases/year?
I don't mean to give you the nth degree, I'm just genuinely curious about your technique.
My most recent patient, 70yo WF ~6 mos out from chemoRT for NSCLC. Disease-free in chest, body.
12/13/16:
XXXXX came to the hospital today with what appeared to be stroke-like symptoms and a quivering of her right jaw. I had previously noticed a little weakness in her right hand as well. Workup ensued including a CT of the head and MRI of the brain. There looks to be a high left parietal lesion. It’s about 1.5 to 2 cm in size and is ring enhancing and gives off a couple of centimeters of edema but without any significant mass effect in that left parietal region. She is about to be admitted to the hospital and is started on IV Decadron. Right now she is completely mentally alert and is really not having any neurological problems at all. Of course she is recently s/p chemoradiation for a locally advanced lung cancer. She had been s/p neoadjuvant chemotherapy before that. Her disease status appears to be stable at the present time at the very least. As mentioned she’s being admitted here to the hospital and I wanted to see her to get some radiation therapy started to the brain.
Labs/X-rays/Pathology:
FINDINGS:
BRAIN AND VENTRICLES: A 1.2 x 1.3 x 1.5 cm ring-enhancing lesion within the left parietal lobe
demonstrates restricted diffusion with moderate adjacent vasogenic edema compatible with
intra-axial metastasis. No intracranial hemorrhage or mass effect. Ventricles are unremarkable. Diffuse
age-appropriate atrophy. Scattered periventricular and subcortical white matter changes are stable.
Posterior fossa is unremarkable.
ASSESSMENT: Oligometastatic non-small cell lung cancer.
PLAN: Right now I want to start with some fractionated partial brain radiation therapy to bring down the swelling. After a few fractions of this we will come in with stereotactic radiosurgery. The risks, benefits, side effects, logistics and indications were all discussed with her today. We’ll get her treatment started likely tomorrow and simulate today.
12/14 to 12/21, patient received 15 Gy/6 fx using the 12/13 diagnostic MRI to plan. We used a 5-field conformal 3D plan, lesion/edema+1 cm PTV margin. The 50% isovolume was ~400cc's, the brain volume was ~1400cc's.
Due to the holidays, we put off the SRS until a few days later. (Normally I would do it just 1-2 days later.) We got a tx planning MRI on 12/27 and there was about 50% less edema and the lesion was down to ~1.2 cm max diameter. We performed SRS on 12/29, 21 Gy minimal lesional dose @81% line using static beams. Frameless. Actually we used a 2 mm PTV margin and that was the lesion. CTV ~1.1 cc's, PTV ~2.6 cc's, 50% isovolume ~7.6 cc's.
