Development and validation of a comprehensive patient‐specific quality assurance program for a novel stereotactic radiation delivery system for breast lesions

Abstract

Purpose: The 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. Methods: We 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 calculationbased method verifies point doses with a novel semi-empirical independent-calculation software.Results: The 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. Conclusion:We 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.---

Reproducibility of a novel, vacuum‐assisted immobilization for breast stereotactic radiotherapy

“…The device has been activated clinically at two institutions with four additional sites projected within the next 2 years. [22][23][24][25]28 5 | CONCLUSION…”

“…The current work has verified the appropriateness of margins utilized for setup uncertainty. The device has been activated clinically at two institutions with four additional sites projected within the next 2 years 22‐25,28 …”

“…In parallel, a novel breast‐specific stereotactic radiotherapy (BSRT) device (GammaPod; Xcision Medical Systems, LLC, Columbia, MD) was developed at our academic medical institution. This device employs non‐overlapping, non‐coplanar 60 Co beams that rotate around the breast as the patient, in the prone position, is translated over the apertures employing a dynamic dose‐painting technique 20‐25 . We have recently reported in silico results demonstrating improvements in dose fall‐off and conformity in comparison with traditional APBI techniques (e.g., 3DCRT, intensity‐modulated radiation therapy, etc) 26,27 .…”

“…This device employs nonoverlapping, non-coplanar 60 Co beams that rotate around the breast as the patient, in the prone position, is translated over the apertures employing a dynamic dose-painting technique. [20][21][22][23][24][25] We have recently reported in silico results demonstrating improvements in dose fall-off and conformity in comparison with traditional APBI techniques (e.g., 3DCRT, intensity-modulated radiation therapy, etc). 26,27 The purpose of this study was to establish the setup accuracy for this stereotactic system that allows for a substantial reduction in planning target volume (PTV) for APBI.…”

Technical challenges of linac-based stereotactic ablative body radiotherapy: short review for non-radiation oncologists

“…Notably, SABR to sites of oligoprogression delays the time to further progression, and allows for continuation of systemic therapy that has been mostly effective (in all but the sites of oligoprogression). SABR is also used for recurrent head and neck cancers (13), as a curative treatment option for prostate cancer (14)(15)(16) and unresectable kidney cancers (17,18), and is being investigated as an adjuvant to surgery for early stage breast cancer (19,20) and other indications. Table 1 presents the main indications of SABR in current clinical practice…”