Comparison of conventional and virtual simulation for radiation treatment planning of malignant lymphoma.

ABSTRACT

PURPOSE: The exact coverage of the lymph nodes and optimal shielding of 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 compare conventional simulation and blocking with virtual simulation in terms of coverage of the target volume and shielding of the organs at risk in this highly curative patient group. PATIENTS AND METHODS: In 10 patients diagnosed with Hodgkin's disease and 5 patients with a Non-Hodgkin lymphoma radiation treatment planning for a mantle field or para-aortic field with inclusion of the spleen was performed in a conventional manner and with virtual simulation. With conventional technique, irradiation portals were defined during fluoroscopy and shielding of the organs at risk was drawn onto the simulation films, based on the information from previous X-ray films, CT or MRI scans. For virtual simulation, 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 software package on a VoxelQ workstation (Picker Inc.) This was done in a beam's eye view environment on a currently 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 conventional 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 and the spleen hilus were not covered completely in 5/15 and 6/15 cases, respectively. The left kidney was adequately shielded in only two thirds (10/15) of the conventionally planned fields. The planning time required for virtual simulation was reduced for the patient, but was increased for the physician because of the more time consuming contouring procedure compared to conventional simulation. CONCLUSIONS: Virtual simulation based on CT scans for radiation treatment planning of malignant lymphoma gives more information about soft tissue structures than conventional treatment planning. Therefore, it allows a more precise coverage of the target volumes and better shielding of the organs at risk. However, the time required for the whole procedure is increased. This is justified because of the often highly curative intention when treating this group of patients.