A method and apparatus for precisely reproducing the position of a vaginal cylinder in relation to a patient to ensure that a planned
radiation dose can be delivered with high precision to the intended treatment target volumes. In order to properly define the treatment volume, a vaginal cylinder with proper
diameter is inserted into the patient's
vagina. This invention addresses two potential errors: one, the incorrect vaginal cylinder position in relation to the
radiation beams, and second, the inconsistent positional correlation between the vaginal cylinder and the patient's body. These two geometric errors will cause dosimetric errors. The present invention provides a method and apparatus for minimizing the
geometric error and dosimetric error associated with conventional
external beam radiation therapy or
radiosurgery used in treating gynecological tumors. First a
treatment plan is carried out to determine the treatment target volume. Second,
treatment delivery is carried out by using an image-guided
system to locate the position of the vaginal cylinder and comparing it relative to the
treatment delivery system coordinate
system and the patient's coordinate system. The displacement in the position of the vaginal cylinder from the
treatment plan is corrected by calculating the
transformation matrix and entering the resulting value into a position adjusting
assembly. The position adjusting
assembly adjusts the vaginal cylinder to exactly reproduce its location relative to the patient's coordinate system. This ensures that the image-guided system locates the precise
radiation delivery position and that the
radiation dose is delivered precisely to the treatment target volume.