TOTALLY INTEGRATED SIMULATION TECHNIQUE FOR 3-FIELD BREAST TREATMENT USING A CT SIMULATOR

A method was devised to simulate patients with breast cancer in the ac tual treatment position utilizing a diagnostic CT spiral scanner, 3-D Image Workstation for virtual simulation, and a laser coordinate syste m to transfer planning parameters to the patient's skin. It was desire d to produce non-divergent tangential beams through the lung as well a s a matched line for tangential and supraclavicular fields. The patien ts were immobilized in an Alpha Cradle (TM) cast. Radio-opaque markers were placed on the superior, inferior, medial, and lateral margins of the field so as to afford appropriate initial field set-up approximat ions. The patient was scanned. The data set was then transferred to th e workstation where an isocenter was chosen. The patient was marked. V irtual simulation was then performed. This method employed a half beam technique for the posterior edge of the tangential fields. Table rota tion and blocking of the superior margin of the tangential fields were used to produce a vertical edge to match a supraclavicular field. Usi ng a beam's eye view the lateral tangent was matched to the medial exi t. A digitally reconstructed radiograph was created to define the tang ent fields and place the supraclavicular block. Our initial experience with 50 patients verifies that this is a reproducible and accurate te chnique. Time required for immobilization and tangential field simulat ion is approximately 30 minutes. Data is available for 3-D treatment p lanning or 2-D treatment planning on a reconstructed transverse slice angled to match the collimator angle through the patient. Using a CT s imulator for simulation of breast cancer affords accuracy of at least equal magnitude to conventional simulators as determined by beam films and ease of set-up. This technique also affords greater ease in chang ing treatment parameters without having to resimulate the patient. (C) 1996 American Association of Physicists in Medicine.