Does Intensity Modulation Improve Healthy Tissue Sparing in Stereotactic Radiosurgery of Complex Arteriovenous Malformations?

This planning study evaluates the potential of intensity modulated treatment fields and inverse planning techniques in stereotactic radiosurgery to reduce healthy tissue dose. Twenty patients previously treated with stereotactic radiosurgery for arteriovenous malformation (AVM) were replanned with each of 4 techniques: circular non-coplanar arcs, dynamic arcs, static conformal fields, and intensity modulated radiosurgery (IMRS). Patients were selected having a maximum AVM dimension at least 20 mm, or volume greater than 10 cm3. Target volumes ranged from 2.12 cm3 to 13.87 cm3 with a median of 6.03 cm3. Resulting dose distributions show a statistically significant improvement in target conformality between circular arcs and all other techniques (p ≤ 0.001), between conformal and both dynamic arcs and IMRS (p ≤ 0.03) and with no difference between dynamic arcs and IMRS. However, for AVMs of volume greater than 5.5 cm3, IMRS gives better conformality than dynamic arcs (p = 0.04). IMRS showed consistently lower dose inhomogeneity compared to both dynamic arcs and conformal fields (p < 0.001). At low dose levels, the dynamic arc technique irradiates less healthy tissue than the other techniques (p ≤ 0.001). Both dynamic arcs and IMRS provide increased ability to conform to the AVM, with IMRS showing greater ability to control dose at the periphery.