Pancreas Cancer Patient with Vagus Nerve Stimulator Successfully Treated Off-Label on a 0.35T MR-Linac
Abstract
Purpose
Adaptive MR-guided Stereotactic Body Radiation Therapy (MRg-SBRT) is an effective treatment for malignant pancreatic lesions. However, its implementation may be hindered by the presence of implants with scanning conditions interdicting body coil transmission in the thorax. We investigated a case of pancreatic MRg-SBRT at a 0.35T MR-Linac which violated the implanted neurostimulator conditions.
Methods
A 50-year-old male patient with renal carcinoma metastasis in the pancreatic head presented for adaptive MRg-SBRT. The patient reported having an implanted AspireHC LivaNova vagus nerve stimulator (VNS) in his chest wall which was off and no longer used. The pancreas lay in the scanning exclusion zone for RF transmission using the body coil. Surgical device removal would risk vocal cord paralysis and was deemed unwarranted. A risk-benefit analysis allowed MRg-SBRT at a ViewRay 0.35T MR-Linac as sole treatment option for this patient. He underwent 6 imaging sessions (1 simulation, 5 treatment fractions of 10Gy each). The patient and MR safety parameters were monitored throughout imaging and treatment.
Results
Treatment simulation was uneventful. During the first treatment fraction, the patient experienced nerve stimulation leading to coughing. The VNS was determined to have been on and was turned off for the subsequent treatment fractions, during which no adverse effects were observed. In every session, pilot and breath-hold set-up sequences were completed in 15s or 25s each. The average duration of the cine tumor tracking sequence over all fractions was 17±7 min and exceeded the 15min manufacturer restriction for 2 out of 5 fractions. The MR-Linac functioned at Normal Operating Mode for SAR (0.45 W/kg), but at first level for rate of change of magnetic field dB/dt (59.7 T/s).
Conclusion
Pancreatic adaptive MRg-SBRT with a VNS turned off was completed with no adverse effects, suggesting that these implants may be safely scanned off-label on a 0.35T MR-Linac.