In this study, we evaluate and compare single isocenter multiple target VMAT (SIMT) and Conformal Arc Informed VMAT (CAVMAT) radiosurgery's sensitivity to uncertainties in dosimetric leaf gap (DLG) and treatment delivery. CAVMAT is a novel planning technique that uses multiple target conformal arcs as the starting point for limited inverse VMAT optimization.Methods: All VMAT and CAVMAT plans were recalculated with DLG values of 0.4, 0.8, and 1.2 mm. DLG effect on V 6Gy [cc], V 12Gy [cc], and V 16Gy [cc], and target dose was evaluated. Plans were delivered to a Delta 4 (ScandiDos, Madison, WI) phantom and gamma analysis performed with varying criteria. Log file analysis was performed to evaluate MLC positional error. Sixteen targets were delivered to a SRS Map-CHECK (Sun Nuclear Corp., Melbourne, FL) to evaluate VMAT and CAVMAT's dose difference (DD) as a function of DLG.Results: VMAT's average maximum and minimum target dose sensitivity to DLG was 9.08 AE3.50%/mm and 9.50 AE 3.30%/mm, compared to 3.20 AE 1.60%/mm and 4.72 AE 1.60%/mm for CAVMAT. For VMAT, V 6Gy [cc], V 12Gy [cc], and V 16Gy [cc] sensitivity was 35.83 AE 9.50%/mm, 34.12 AE 6.60%/mm, and 39.23 AE 8.40%/mm. In comparison, CAVMAT's sensitivity was 23.19 AE 4.50%/mm, 22.45 AE 4.40%/mm, and 24.88 AE 4.90%/mm, respectively. Upon delivery to the Delta 4 , CAVMAT offered superior dose agreement compared to VMAT. For a 1%/1 mm gamma analysis, VMAT and CAVMAT had a passing rate of 94.53 AE 4.40% and 99.28 AE 1.70%, respectively. CAVMAT was more robust to DLG variation, with the SRS MapCHECK plans yielding an absolute average DD sensitivity of 2.99 AE 1.30%/mm compared to 5.07 AE 1.10%/mm for VMAT. Log files demonstrated minimal differences in MLC positional error for both techniques.Conclusions: CAVMAT remains robust to delivery uncertainties while offering a target dose sensitivity to DLG less than half that of VMAT, and 65% of that of VMAT for V 6Gy [cc], V 12Gy [cc], and V 16Gy [cc]. The superior dose agreement and reduced
Brain metastases are a common complication for patients diagnosed with cancer. As stereotactic radiosurgery (SRS) becomes a more prevalent treatment option for patients with many brain metastases, further research is required to better characterize the ability of SRS to treat large numbers of metastases (≥4) and the impact on normal brain tissue and, ultimately, neurocognition and quality of life (QOL). This study serves first as an evaluation of the feasibility of hippocampal avoidance for SRS patients, specifically receiving single-isocenter multitarget treatments (SIMT) planned with volumetric modulated arc therapy (VMAT). Second, this study analyzes the effects of standard-definition (SD) multileaf collimators (MLCs) (5 mm width) on plan quality and hippocampal avoidance.The 40 patients enrolled in this Institutional Review Board (IRB)-approved study had between four and 10 brain metastases and were treated with SIMT using VMAT. From the initial 40 patients, eight hippocampi across seven patients had hippocampal doses exceeding the maximum biologically effective dose (BED) constraint given by RTOG 0933. With the addition of upper constraints in the optimization objectives and one arc angle adjustment in one patient plan, four out of seven patient plans were able to meet the maximum hippocampal BED constraint, avoiding five out of eight total hippocampi at risk. High-definition (HD) MLCs allowed for an average decrease of 29% ± 23% (p = 0.007) in the maximum BED delivered to all eight hippocampi at risk.The ability to meet dose constraints depended on the distance between the hippocampus and the nearest planning target volume (PTV). Meeting the maximum hippocampal BED constraint in re-optimized plans was equally likely with the use of SD-MLCs (five out of eight hippocampi at risk were avoided) but resulted in increased dose to normal tissue volumes (23.67% ± 16.3% increase in V50%[cc] of normal brain tissue, i.e., brain volume subtracted by the total PTV) when compared to the HD-MLC re-optimized plans. Comparing the effects of SD-MLCs on plans not optimized for hippocampal avoidance resulted in increases of 48.2% ± 32.2% (p = 0.0056), 31.5% ± 16.3% (p = 0.024), and 16.7% ± 8.5% (p = 0.022) in V20%[cc], V50% [cc], and V75%[cc], respectively, compared to the use of HD-MLCs. The conformity index changed significantly neither when plans were optimized for hippocampal avoidance nor when SD-MLC leaves were used for treatment. In plans not optimized for hippocampal avoidance, mean hippocampal dose increased with the use of SD-MLCs by 38.0% ± 37.5% (p = 0.01). However, the use of SD-MLCs did not result in an increased number of hippocampi at risk.
This work evaluates two different detector technologies in terms of their performance in making fast, low-signal diffraction measurements. The first detector is a large-area mammography detector that uses a complementary metal-oxide semiconductor (CMOS) crystal, and the second is a cadmium-telluride photon-counting detector. By measuring the diffraction spectra for a diverse range of materials and with acquisition times ranging from 10 seconds and 0.1 seconds, we show how each detector performs as signal-to-noise ratios decrease and counting statistics become less significant. As a result, we show that the photon counting detector slightly better preserves the long-time average signal in short acquisition times in comparison to the CMOS detector when diffraction signals display sharp/narrow features, but that the detectors performed similarly for materials with much broader diffraction signals, like those associated with soft tissue and biological specimen. This leads us to conclude that the photon-counting detector is slightly higher-performing for our purposes.
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