Clinical Characterization of a Novel Robotic IORT Unit

Abstract

A novel mobile robotically-guided low-energy intra-operative radiation therapy device was characterized for clinical use. The compact system offers flexible positioning with treatment delivery up to 70 kV energy and 10 Gy/min dose rate with radially collimated emission, and underwent characterization for its dosimetric performance, positioning accuracy and overall clinical suitability. The Morpheus system (Empyrean Medical Systems) consists of a miniature electron esource and a partitioned partial-transmission tungsten target capable of producing 50, 60, and 70 kVp x-rays, mounted on a robotic arm and supported by a motorized mobile base. The radially collimated beam is partitioned in six segments with three radial positions per segment for selective emission, target irradiation and tissue sparing. The beam characteristics were assessed with ion chamber and film dosimetry, both in-air and in a water tank. Radiation levels were assessed for safety and shielding requirements. The absolute dose rate at the surface of a 2 cm radius sterilizable treatment balloon is 8 Gy/min for the 70 kV beam using the AAPM TG-61 formalism. The six treatments sectors emit radially in 60 degrees wedges to within +/- 15% of each other, which can be simply corrected for treatment delivery. The dose falls off to 50% of its initial value within 8 mm from the surface of a treatment balloon for a 70 kV beam. The robotic arm enables a free-hand positioning of the X-ray treatment head to within 1 mm. All interlocks and sterility requirements for operation within an operating room environment were found to be satisfactory. Radiation levels require mobile shielding or a shielded room to be within permissible public radiation levels. The clinical characterization shows the new unit provides a stable and flexible beam delivery platform suitable for IORT treatments. The simplified docking and collimated beam emission provides enhanced capabilities for patient treatment.