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We aim to evaluate the basic characteristics of SRS MapCHECK (SRSMC) for CyberKnife (CK) and establish a dose verification system using SRSMC for the tumor-tracking irradiation for CK. The field size and angular dependence of SRSMC were evaluated for basic characterization. The output factors (OPFs) and absolute doses measured by SRSMC were compared with those measured using microDiamond and microchamber detectors and those calculated by the treatment planning system (TPS). The angular dependence was evaluated by comparing the SRSMC with a microchamber. The tumor-tracking dose verification system consists of SRSMC and a moving platform. The doses measured using SRSMC were compared with the doses measured using a microchamber and radiochromic film. The OPFs and absolute doses of SRSMC were within ±3.0% error for almost all field sizes, and the angular dependence was within ±2.0% for all incidence angles. The absolute dose errors between SRSMC and TPS tended to increase when the field size was smaller than 10 mm. The absolute doses of the tumor-tracking irradiation measured using SRSMC and those measured using a microchamber agreed within 1.0%, and the gamma pass rates of SRSMC in comparison with those of the radiochromic film were greater than 95%. The basic characteristics of SRSMC for CK presented acceptable results for clinical use. The results of the tumor-tracking dose verification system realized using SRSMC were equivalent to those of conventional methods, and this system is expected to contribute toward improving the efficiency of quality control in many facilities.
We aim to evaluate the basic characteristics of SRS MapCHECK (SRSMC) for CyberKnife (CK) and establish a dose verification system using SRSMC for the tumor-tracking irradiation for CK. The field size and angular dependence of SRSMC were evaluated for basic characterization. The output factors (OPFs) and absolute doses measured by SRSMC were compared with those measured using microDiamond and microchamber detectors and those calculated by the treatment planning system (TPS). The angular dependence was evaluated by comparing the SRSMC with a microchamber. The tumor-tracking dose verification system consists of SRSMC and a moving platform. The doses measured using SRSMC were compared with the doses measured using a microchamber and radiochromic film. The OPFs and absolute doses of SRSMC were within ±3.0% error for almost all field sizes, and the angular dependence was within ±2.0% for all incidence angles. The absolute dose errors between SRSMC and TPS tended to increase when the field size was smaller than 10 mm. The absolute doses of the tumor-tracking irradiation measured using SRSMC and those measured using a microchamber agreed within 1.0%, and the gamma pass rates of SRSMC in comparison with those of the radiochromic film were greater than 95%. The basic characteristics of SRSMC for CK presented acceptable results for clinical use. The results of the tumor-tracking dose verification system realized using SRSMC were equivalent to those of conventional methods, and this system is expected to contribute toward improving the efficiency of quality control in many facilities.
Recently, there has been increased interest worldwide in the use of conventional linear accelerator (linac)-based systems for delivery of stereotactic radiosurgery/radiotherapy (SRS/SRT) contrasting with historical delivery in specialised clinics with dedicated equipment. In order to gain an understanding and define the current status of SRS/SRT delivery in Australia and New Zealand (ANZ) we conducted surveys and provided a single-day workshop. Prior to the workshop ANZ medical physicists were invited to complete two surveys: a departmental survey regarding SRS/SRT practises and equipment; and an individual survey regarding opinions on current and future SRS/SRT practices. At the workshop conclusion, attendees completed a second opinion-based survey. Workshop discussion and survey data were utilised to identify areas of consensus, and areas where a community consensus was unclear. The workshop was held on the 8th Sept 2020 virtually due to pandemic-related travel restrictions and was attended by 238 radiation oncology medical physicists from 39 departments. The departmental survey received 32 responses; a further 89 and 142 responses were received to the pre-workshop and post-workshop surveys respectively. Workshop discussion indicated a consensus that for a department to offer an SRS/SRT service, a minimum case load should be considered depending on availability of training, peer-review, resources and equipment. It was suggested this service may be limited to brain metastases only, with less common indications reserved for departments with comprehensive SRS/SRT programs. Whilst most centres showed consensus with treatment delivery techniques and image guidance, opinions varied on the minimum target diameter and treatment margin that should be applied.
Purpose: To determine optimal values for parameters of manual normal tissue objectives (mNTO) in non-coplanar RapidArc (RA) SRS plans and compare them with HyperArc (HA) plans Methods and Materials: Eighteen patients with single solitary brain metastases, receiving 21 Gy prescriptions, were retrospectively enrolled. Non-coplanar RapidArc plans (RA-mNTO) were generated using mNTO for a range of dose fall-off values (0.1–5.0 mm− 1) and end dose values (50%, 25%, 10%). Additionally, HyperArc plans were generated using SRS NTO (HA-sNTO) and manual NTO (HA-mNTO), with optimal parameters derived from RA-mNTO plans. Plans were created using TrueBeam 6 MV-FFF and Eclipse 16.1 TPS. Plans were evaluated using parameters: Paddick Conformity Index (CI), Gradient Index (GI), Homogeneity Index (HI), Brain-GTV (18Gy, 15Gy & 12Gy), MU, and delivery accuracy. Plan comparisons utilized an integrated scoring approach and Wilcoxon signed-rank test. Results: The optimal RA-mNTO plan, with 0.5 mm− 1 dose fall-off and 25% end-dose values, significantly surpassed HA plans (p < 0.05) in CI, GI, and HI values (0.92 ± 0.02, 2.99 ± 0.15, 0.32 ± 0.05 vs. 0.91 ± 0.03, 3.40 ± 0.18, 0.39 ± 0.04 for HA-sNTO, and 0.91 ± 0.03, 3.16 ± 0.23, 0.40 ± 0.05 for HA-mNTO). Furthermore, RA-mNTO significantly (p < 0.05) reduced brain doses at V18Gy (0.90 ± 0.40), V15Gy (1.85 ± 0.77), and V12Gy (3.27 ± 1.35) compared to HA-sNTO (1.16 ± 0.51, 2.37 ± 1.01, 4.07 ± 1.72) and HA-mNTO (1.05 ± 0.44, 2.12 ± 0.86, 3.62 ± 1.45). Moreover, RA-mNTO showed significantly (p < 0.05) lower MUs (8302 ± 934) compared to HA (9556 ± 1005) and HA-mNTO (9327 ± 390), and higher gamma pass rates (99.8 ± 0.35) than HA-sNTO (98.9 ± 0.61) and HA-mNTO (99.1 ± 0.47). Conclusion: Non-coplanar RA plans with optimal mNTO settings outperformed both HA-sNTO and HA-mNTO plans for all studied dosimetric parameters.
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