A packed building-block compensator (TETRIS-RT) and feasibility for IMRT delivery

A packed building-block compensator (TETRIS-RT) for IMRT (Intensity Modulated Radiation Therapy) delivery has been proposed. The compensator contains two kinds of cubic blocks: x-ray absorbing blocks for intensity modulation and x-ray transparent blocks for packing. The packed blocks are placed inside a rectangular enclosure, and the resulting compensators can be attached to a linac gantry head through a rotatable mount for efficient multiportal IMRT. A fabrication device and a sorting device were also developed. The fabrication device can automatically stack two different types of blocks to produce a compensator while the sorting device can separate each type of the blocks for subsequent fabrication. Preliminary film experiments have shown that an additional leakage dose through the rounded edges of the ten-layered x-ray absorbing blocks was 0.9% of the delivered dose with a total shielded dose ratio of 10% including the peak leakage. It was observed that the proposed compensator may provide a highly modulated dose distribution. This suggests its feasibility for IMRT delivery with a limit of 1cm×1cm spatial resolution at isocenter in the plane perpendicular to the beam, and larger discrete intensity steps of approximately 10% compared to conventional compensators. Advantages of the proposed compensator include that the compensator blocks are reusable and can be utilized to automatically and quickly fabricate a compensator, thereby minimizing human labor.