Thread by @SprakerMDPhD

As promised, here is a #tweetorial on spatially-fractionated radiotherapy aka Lattice aka GRID.

If you missed the #CTOS2019 talk by @Notorious_RBE, this one is for you!

Spatial fractionation aims to intentionally deliver heterogeneous dose: alternating “hot” and “cold” areas with a differential of 30-100% Rx.

Thats right: you want 30% cold spots in tumor. (👇 #MedPhys reaction).

It seems crazy, but it is associated with excellent response and limited toxicity. Per reports. That are retrospective.

Dramatic response in rads refractory sarcoma: link.springer.com/article/10.100…

Case series of 71 palliative patients: ncbi.nlm.nih.gov/pubmed/1052442…

The idea is that the hot spots induce substantial immune-related bystander effects for cell kill while majority of the field is kept to low dose (and thus limited toxicity).

Peep this excellent review by Billena and Khan: ncbi.nlm.nih.gov/pubmed/30684666

On terminology, generally:

GRID = 2D planned (dose “spears”)

LATTICE = 3D planned, including IMRT or VMAT (dose “spheres”)

Last year, I went to the @theNCI and @the_RSS GRID/LATTICE workshop and decided we needed this @WashURadOnc. I was sick and tired of treating big #sarcomas with wimpy non-ablative therapy.

SBRT is not safe for big tumors.

Ugh.

But what about Lattice?!

So I gathered a team #MedPhys and #Dosimetrist and we got to work. I declared a standard 20 Gy/5 Fx to be the “cold” whole tumor dose (30%), which made the hot spots 66.7 Gy (100%). We had our Rx, so got to planning. Dose constraints per AAPM 5 fx SBRT.

GRID routinely broke OARs so we landed on LATTICE via VMAT. After months of experimentation with Lattice structure, we landed on this arrangement with 1.5 cm spheres that are 4.5 cm apart and 1.5 cm from OTVs.

Close to other pub’d techniques: bit.ly/33ZsOi9

The LITE SABR (credit: @Notorious_RBE) is planned using non-coplanar arcs and tx on a Truebeam. Test plans on 12 patients with tumors all over the body successfully met all constraints. MU ratios reasonable (3-4), and *ALL* plans passed SBRT-like QA using EPID and ion chambers.

@Notorious_RBE Spatial frac is hypothesized to be especially immunogenic. In one study, substantial increases in blood TNFa were seen with GRID. We can’t be the LITE SABR dream team without a biologist, so I reached out to @aadel_chaudhuri lab for help on correlatives.

Here is what’s coming:

Our first clinical trial, LITE SABR M1, is enrolling now! It is testing the safety of LITE SABR in any patient who needs palliative radiation. Primary outcome is CTCAE and correlatives will evaluate PBMCs and cytokines before, during, and after RT. More: clinicaltrials.gov/ct2/show/NCT04…

Our second clinical trial, LITE SABR for #chondrosarcoma, will evaluate the treatment for pts with unresectable or oligometastatic disease. Correlatives will evaluate tumor tissue and blood for immune response. Not yet open. More: clinicaltrials.gov/ct2/show/NCT04…

.@Notorious_RBE is currently writing up our dosimetry results from the modeling study, and Lattice SBRT #MedPhys James Kavanaugh is writing up our detailed QA process and results.

I'm so excited our team can join the small group of GRID/LATTICE believers that are exploring this exciting technique.

Hope to see you all in April! therss.org/UploadedDocs/2…