Model 37-001 Tel-Align™

Precision radiation therapy requires treatment geometry that is accurate and reproducible.  Since machine geometry can easily become misaligned, it should be checked frequently.  The Tel-Align™ permits a quick check of these parameters and facilitates the adjustment of those which require realignment.  It is especially useful in an overall QA program.

The device consists of a rectangular plastic base, 17.5cm x 14cm x 1cm thick, with a removable vertical scale, 18cm high.  The upper surface of the base has lead markers that form a square (10 x 10cm) for visualization on film.  A cross hair in the centre of the square lines up with two additional sets of cross hairs, one on each outer edge of the base.

The Tel-Align™ is easy to use.  the machine field size (10 x 10cm) has been set, the table height is adjusted until the base surface is at the isocenter distance.  The collimator rotation angle is set at 0-degrees.  When positioned properly, the edges of the light field should coincide with the inscribed square.  The field center should intersect the center cross hair and the side lights should agree with the corresponding cross hairs at the edges of the base.

The vertical scale is placed on the base to check the optical distance indicator, or a film can be placed under the base to check the light field versus the radiation field.  By rotating the gantry angle at ±90°, the isocenter variation and optical back pointer are also checked.  If adjustment of the machine geometry is needed, it can be done readily with the Tel-Align™ in place.

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