Patients treated by Model-C gamma knife with APS are less exposed to non-therapeutic irradiation.

OBJECTIVE

The aim of this study was to compare the defocused (non-therapeutic) irradiation between the Model-C gamma knife with the automatic positioning system (APS) and with the non-APS mode.

METHODS

41 males and 59 females (mean age: 54 years) had the following pathologies: 38 benign tumors, 43 malignant tumors, 16 vascular lesions, and 3 trigeminal neuralgias. These included 192 lesions (mean volume: 4.8 mL), 61 (32%) of them were located deeply. The radiation treatment time needed and the choice of helmets and shots for each lesion were analyzed. The inter-group difference is analyzed using the one-way ANOVA method.

RESULTS

The APS mode could be applied alone in 79 patients or was always possible in nearly 95% of patients with benign lesions. APS-treatment failed in three patients due to unexpected collisions, and the other 18 harbored some advanced peripheral metastatic lesions. The non-APS mode required 47% more defocused time than the pure APS mode (1.1 vs. 0.75 minutes, p<0.01) before starting the next shot. Patients treated by the APS mode are exposed to a 70% less (p<0.05) unplanned, defocused irradiation dose than those by the non-APS mode. Although there is a tendency in the APS group to use fewer helmets but more shots per lesion for achieving an optimal dosimetry, there was no difference in the averaged defocused time per patient.

CONCLUSIONS

The APS system makes GK radiosurgery run more smoothly, rapidly, comfortable and safer than ever. It improves the design of more conformal dose plans, especially for benign lesions, and the patients will also be exposed to less unnecessary radiation doses.