Eight affected person remedies with 51 targets have been deliberate with numerous margins utilizing Elements Multiple Brain Mets SRS remedy planning software program.
Forty-eight plans with 0 mm, 1 mm and a couple of mm margins have been created, together with plans with variable margins, the place targets greater than 6 cm away from the isocenter have been deliberate with bigger margins. The dosimetric affect of the margins have been analyzed with V5Gy, V8Gy, V10Gy, V12Gy values.
12 extra affected person movement knowledge have been analyzed to find out each the affect of the repositioning threshold and the distributions of the affected person translational and rotational actions.
Results proven that the V5Gy, V8Gy, V10Gy, V12Gy volumes virtually doubled when margins change from 0 to 1 mm and tripled when change from 0 to 2 mm.
With variable margins, the aggregated outcomes are identical as outcomes from plans utilizing the decrease of two margins, since solely 12.2% of the targets have been greater than 6 cm away from the isocenter. With 0.5 mm re-positioning threshold, 57.4% of the time the sufferers are repositioned.
Decreasing the brink to 0.25 mm leads to 91.7% repositioning price, as a result of limitations of the fusion algorithm and precise affected person movement.
The ninetieth percentile of translational actions in all instructions is 0.7 mm, whereas the ninetieth percentile of rotational actions in all instructions is 0.6 levels. Median translations and rotations are 0.2 mm and 0.2 levels, respectively.
Authors concluded that they’ve switched modus operandi from 2 to 1 mm PTV margins, with an eventual objective of utilizing 0.5 and 1.0 mm variable margins when an automatic margin task technique turns into accessible. The 0.5 mm and 0.5 levels repositioning thresholds are higher with small residual affected person actions.
Source: Medindia
