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Session: Space-time Modulation of Treatment [Return to Session]

A Study of Shifting 3D Dose GRID for Adaptive Spatially Fractionated Brain Radiosurgery

L Ma*, H Zhang, E Chang, USC Radiation Oncology, Keck School of Medicine, University of Southern California, Los Angeles, CA


TU-G-BRA-4 (Tuesday, 7/12/2022) 1:45 PM - 2:45 PM [Eastern Time (GMT-4)]

Ballroom A

Purpose: Spatially fractionated GRID therapy has been clinically implemented to debulk large tumors. In this study, we developed a new adaptive grid brain radiosurgery (AGBRS) approach by shifting a 3D dose grid placed inside a target volume over a conventional 3D dose distribution from one fraction to another to enable adaptive spatial fractionation for hypofractionated radiosurgery of large brain tumors.

Methods: AGBRS was developed for hypofractionated Gamma Knife radiosurgery by superimposing a grid of 3D dose spikes inside the target volume via optimizing a series of 4-mm shots placed over the conventional treatment plan for concomitant boosting of target (c.f. Med Phys 2005;32(11)3419-23, PMID:16370428). Once placed, such a 3D dose grid was then systematically shifted from one fraction to another to achieve adaptive spatial fractionation. Applying a generalized linear-quadratic model, voxel-by-voxel spatial dosing variation was accounted to produce a composite equivalent uniform biological effective dose (cEUBED) for the whole target. The cEUBEDs were compared between AGBRS and the conventional treatments without grid boosted spatial fractionation.

Results: AGBRS significantly (p<0.02) increased the mean cEUBED of the target by >30% while maintaining the same target volume coverage and dose conformity as the conventional treatments. The increase in cEUBEDs for the late-responding target (such as α/β=3 Gy) was significantly higher (approximately two-fold) than for early-responding tumors (such as α/β=10 Gy) receiving the same treatment course of 30 Gy in 5 fractions. AGRBS somewhat lowered the dose to the normal brain as well but did not achieve statistical significance (p = 0.10) for the study.

Conclusion: By harnessing unique radiobiological advantages of spatial fractionation, AGBRS significantly improved the current hypofractionated brain radiosurgery of large brain tumors, where the outcome from the conventional treatment tends to be poor. Clinical trials are warranted to validate the benefits of AGBRS as predicted by our study.


Not Applicable / None Entered.


TH- Response Assessment: Modeling: other than machine learning

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