COMPARISON OF CONVENTIONAL AND VIRTUAL SIMULATION FOR RADIATION TREATMENT PLANNING OF MALIGNANT-LYMPHOMA

Purpose: The exact coverage of the lymph nodes and optimal shielding o f the organs at risk are necessary for patients with Hodgkin's disease or malignant lymphoma to guarantee a high cure rate and a low rate of late effects for normal tissue. The purpose of this study was to comp are conventional simulation and blocking with virtual simulation in te rms of coverage of the target volume and shielding of the organs at ri sk in this highly curative patient group. Patients and Methods: In 10 patients diagnosed with Hodgkin's disease and 5 patients with a Non-Ho dgkin lymphoma radiation treatment planning for a mantle field or para -aortic field with inclusion of the spleen was performed in a conventi onal manner and with virtual simulation. With conventional technique, irradiation portals were defined during fluoroscopy and shielding of t he organs at risk was drawn onto the simulation films, based on the in formation from previous X-ray films, CT or MRI scans. For virtual simu lation, contouring of the target volumes and organs at risk (e. g. the kidneys) and the definition of the irradiation portals were performed with the AcQSim((R)) software package on a VoxelQ((R)) workstation (P icker Inc.) This was done in a beam's eye view environment on a curren tly driven CT scan in the treatment position. Both irradiation portals were compared in terms of coverage of the target volume and shielding of the organs at risk. Results: Planning of a mantle field in the con ventional way resulted in an incomplete coverage of the right hilus in 4/15 cases and of the left in 1/15 cases, respectively. The spleen an d the spleen hilus were not covered completely in 5/15 and 6/15 cases, respectively. The left kidney was adequately shielded in only two thi rds (10/15) of the conventionally planned fields. The planning time re quired for virtual simulation was reduced for the patient, but was inc reased for the physician because of the more time consuming contouring procedure compared to conventional simulation. Conclusions: Virtual s imulation based on CT scans for radiation treatment planning of malign ant lymphoma gives more information about soft tissue structures than conventional treatment planning. Therefore, it allows a more precise c overage of the target volumes and better shielding of the organs at ri sk. However, the time required for the whole procedure is increased. T his is justified because of the often highly curative intention when t reating this group of patients.