Room: Exhibit Hall | Forum 4
Purpose: The GammaPod (Xcision Medical System), a novel breast-specific stereotactic radiotherapy device developed at the University of Maryland, has recently completed its first clinical trial and was granted 510k FDA clearance. The GammaPod dynamically dose-paints the target by rotating 36 non-overlapping Co-60 beams while the patient is translated continuously in three longitudinal axes during delivery. From simulation to treatment, the patientâ€™s breast is immobilized using mild negative pressure (150 mmHg) through a device-specific dual cup system with stereotactic fiducials. The cup is secured to both the simulation and treatment tables, functioning as a stereotactic frame. The objective of this study is review the results of the first 17 patientsâ€™ PSQA and independent dose calculations used to validate the new technique.
Methods: In the course of clinically implementing Gamma Pod (2016-2017), we developed a patient quality assurance system comprising of point dose ion chamber and film based measurements along with an independent dose calculation algorithm. Measurements are performed using two phantoms: an acrylic phantom, and the patientâ€™s specific breast cups filled with water. For the acrylic phantom, a QA plan recalculated in the phantom is compared to film and ion chamber measurements. For the water-based measurements, the plan is delivered to the patient-specific breast cup filled with water and compared to ion chamber measurements.
Results: For water-based measurements, the mean difference between measured and planned dose or independent calculation was -1.1% Â± 1.0 and 8.9% Â± 1.8%, respectively. For the acrylic phantom measurements, the mean difference between measured and planned dose or independent calculation was -1.3% Â± 0.5% and 4.9% Â± 1.6%, respectively. The film mean gamma pass rate (2mm/3%) was 97.9% Â± 1.9%.
Conclusion: PSQA for both water and acrylic based measurements have shown that the GammaPod system is able to accurately calculate and deliver the dose to a patient.