[Practice of virtual simulation at the Saint-André hospital]

Prospective evaluation of a virtual simulation technique.

From September 1993 to February 1997, 343 patients underwent radiation therapy using this technique. Treated sites were mostly: brain (132), rectum (59), lung (43), and prostate (28). A CT-scan was performed on a patient in treatment position. Twenty-five to 70 jointive slices widely encompassed the treated volume. The target volume (CTV according to ICRU 50) and often critical organs were controured, slice by slice, by the radiation oncologist. Beams covering the CTV plus a security margin (PTV) were placed on the "virtual patient". Digital radiographs were reconstructed (DRR) as simulator radiographs for each field. Thus, the good coverage of PTV was assessed. Fields and beam arrangements were further optimized. Definitive isocenter was then placed using a classical simulator. Perfect matching of DRR and actual simulator radiographs had to be obtained.

Nineteen patients presented grade 3, and 1 grade 4 acute radiation effects. With a median follow-up of 18 months, five patients suffered from grade 3, and one from grade 4 complications. Fifty-five patients had tumor recurrence in the treated volume, and 19 had marginal relapse.

In our department, virtual simulation has become a routine technique of treatment planning for deep-seated tumors. This technique remains time-consuming for radiation oncologists: about 2 hours. But it stimulates reflexion on anatomy, tumor extension pathways, target volumes; and is becoming an excellent pedagogical tool.