Abstract
PurposeThe GammaPod is a dedicated prone breast stereotactic radiosurgery (SRS) machine composed of 25 cobalt‐60 sources which rotate around the breast to create highly conformal dose distributions for boosts, partial‐breast irradiation, or neo‐adjuvant SRS. We describe the development and validation of a patient‐specific quality assurance (PSQA) system for the GammaPod.MethodsWe present two PSQA methods: measurement based and calculation based PSQA. The measurements are performed with a combination of absolute and relative dose measurements. Absolute dosimetry is performed in a single point using a 0.053‐cc pinpoint ionization chamber in the center of a polymethylmethacrylate (PMMA) breast phantom and a water‐filled breast cup. Relative dose distributions are verified with EBT3 film in the PMMA phantom. The calculation‐based method verifies point doses with a novel semi‐empirical independent‐calculation software.ResultsThe average (± standard deviation) breast and target sizes were 1263 ± 335.3 cc and 66.9 ± 29.9 cc, respectively. All ion chamber measurements performed in water and the PMMA phantom agreed with the treatment planning system (TPS) within 2.7%, with average (max) difference of –1.3% (−1.9%) and −1.3% (−2.7%), respectively. Relative dose distributions measured by film showed an average gamma pass rate of 97.0 ± 3.2 when using a 3%/1 mm criteria. The lowest gamma analysis pass rate was 90.0%. The independent calculation software had average agreements (max) with the patient and QA plan calculation of 0.2% (2.2%) and −0.1% (2.0%), respectively.ConclusionWe successfully implemented the first GammaPod PSQA program. These results show that the GammaPod can be used to calculate and deliver the predicted dose precisely and accurately. For routine PSQA performed prior to treatments, the independent calculation is recommended as it verifies the accuracy of the planned dose without increasing the risk of losing vacuum due to prolonged waiting times.
Highlights
The GammaPod (Xcision Medical Systems, LLC; Columbia, MD) is a novel breast‐specific stereotactic radiotherapy device developed at the University of Maryland that has recently received 510(k) clearance from the U.S Food and Drug Administration (FDA).[1]
We developed patient‐specific quality assurance (PSQA) tests to verify planned dose distributions in the initial 15‐patient study
These patients presented with a range of breast and tumor sizes, averaging 1263 ± 335.3 cc and 66.9 ± 29.9 cc, respectively
Summary
The GammaPod (Xcision Medical Systems, LLC; Columbia, MD) is a novel breast‐specific stereotactic radiotherapy device developed at the University of Maryland that has recently received 510(k) clearance from the U.S Food and Drug Administration (FDA).[1] Operating to the long‐established Gamma Knife, the GammaPod’s 25 nonoverlapping cobalt‐60 (60Co) sources dynamically paint dose to a breast lesion by rotating the beams around a small target while the couch translates continuously in three axes during beam delivery. The patient’s breast is immobilized using mild negative pressure through a device‐specific dual‐cup system with stereotactic fiducials. A novel treatment planning system (TPS) optimizes planned dose distributions by varying the collimator size (15 and 25 mm), isocenter position, and beam‐on time for each specific isocenter position. Details of the GammaPod and the GammaPod TPS can be found in a previously published reports.[1,2,3]
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