Like it hot.

Dose homogeneity marks a watershed in stereotactic radiosurgery (SRS). Gamma Knifers are accustomed to relatively high (inhomogeneous) max doses within the target. But as SRS moved to linear accelerators, LINACers just haven’t been able to let go of the concept of a homogeneous dose distribution. We know that, even on a LINAC, dose falloff for SRS targets is steepest with hotter max doses. But how is tumor control effected? This report describes a LINAC-SRS experience where targets were prescribed 7.7 Gy x 3 fractions with max doses of only 107% for the first few years. Later, targets were prescribed 7.7 Gy x 3, but to the 70% isodose line, meaning the hotspots were much higher. The latter (inhomogeneous) treatments resulted in significantly better tumor control at one year (78 → 93%). Radionecrosis events were few but still significantly lower in the inhomogeneous group. TBL: Higher SRS hot spots may not only improve dose fall-off outside the target but also improve tumor control within it. | Lucia, Radiother Oncol 2018