Initiation of multileaf collimator conformal radiation therapy

Abstract Clinical studies have been initiated in conformal radiotherapy using a computer controlled multileaf collimator. Quantitative dosimetry and treatment planning studies comparing field shaping by lead alloy blocks and the multileaf collimator demonstrate the clinical acceptability of the multileaf collimator. Sixteen patients with tumors in multiple sites have received some part of their treatments with both blocking systems. Studies of dosimetry and field shaping show that the multileaf collimator produces clinically acceptable blocking for most field shapes and disease sites. The 80 – 20% penumbra was characterized for a wide range of shaped beams. For straight edges perpendicular to the leaf travel, the penumbra of measured dose distributions from the multileaf collimator is equal to conventional divergent blocking. When the multileaf collimator leaves approach a contour at an angle, the penumbra increases. At forty-five degrees, the maximum angle of approach, the penumbra is approximately 4 mm wider than that for divergent blocks. Three-dimensional treatment planning demonstrates that equivalent dose distributions can be obtained from the two field shaping systems. The multileaf collimator can be used effectively and efficiently to treat a variety of disease sites. Its optimal utility may be in treating complex fields—five or more shaped coplanar or non-coplanar beams. It is well suited for conformal therapy applications.