Integrating cine EPID, dynamic delivery, and the off-axis Winston-Lutz test to enhance quality control in multiple brain metastasis stereotactic radiotherapy.

PURPOSE: Stereotactic radiotherapy (SRT) has transformed cancer treatment, especially for brain metastases. Ensuring accurate SRT delivery is crucial, with the Winston-Lutz test being an important quality control tool. Off-axis Winston-Lutz (OAWL) tests are designed for accuracy assessment, but most are limited to fixed angles and hampered by local-field shifts caused by suboptimal Multi-Leaf Collimator (MLC) positioning. This study introduces a new OAWL approach for quality control in multi-brain-metastasis SRT. Utilizing cine Electronic Portal Imaging Device (EPID) images, it can be used with dynamic conformal arc (DCA) therapy. However, dynamic OAWL (DOAWL) is prone to more local-field shifts due to dynamic MLC movements. A two-step DOAWL is proposed: step 1 calculates local-field shifts using dynamic MLC movements in the beam-eye view data from the Treatment Planning System (TPS), while step 2 processes cine EPID images with an OAWL algorithm to isolate true deviations. METHODS: Validation involved an anthropomorphic head phantom with metallic ball-bearings, Varian TrueBeam STx accelerator delivering six coplanar/non-coplanar DCA beams, cine EPID, and ImageJ's OAWL analysis algorithm. RESULTS: Inherent local-field shifts ranged from 0.11 to 0.49 mm; corrected mean/max EPID-measured displacement was 0.34/1.03 mm. Few points exceeded 0.75/1.0-mm thresholds. CONCLUSIONS: This two-step DOAWL test merges cine-EPID acquisitions, DCA, OAWL, and advanced analysis and offers effective quality control for multi-brain-metastasis SRT. Its routine implementation may also improve physicist knowledge of the treatment precision of their machines.

Personalization of 99mTc-sestamibi activity in SPECT/CT myocardial perfusion imaging with the cardiofocal SmartZoom® collimator.

BACKGROUND: Patient radioprotection in myocardial perfusion imaging (MPI)-SPECT is important but difficult to optimize. The aim of this study was to adjust injected activity according to patient size-weight or BMI-by using a cardiofocal collimator camera. METHODS: The correlation equation between size and observed counts in image was determined in patients who underwent stress Tc-99m-sestamibi MPI-SPECT/CT with a cardiofocal collimator-equipped conventional Anger SPECT/CT system. Image quality analyses by seven nuclear physicians were conducted to determine the minimum patient size-independent observed count threshold that yielded sufficient image quality for perfusion-defect diagnosis. These data generated an equation that can be used to calculate personalized activity for patients according to their size. RESULTS: Analysis of consecutive patients (n = 294) showed that weight correlated with observed counts better than body mass index. The correlation equation was used to generate the equation that expressed the relationship between observed counts, patient weight, and injected activity. Image quality analysis with 50 images yielded an observed count threshold of 22,000 counts. Using this threshold means that the injected activity in patients with < 100 kg would be reduced (e.g., by 67% in 45-kg patients). Patients who are heavier than 100 kg would also benefit from the use of the threshold because although the injected activity would be higher (up to 78% for 150-kg patients), good image quality would be obtained. CONCLUSIONS: This study provided a method for determining the optimal injected activity according to patient weight without compromising the image quality of conventional Anger SPECT/CT systems equipped with a cardiofocal collimator. Personalized injected activities for each patient weight ranging from 45 to 150 kg were generated, to standardize the resulting image quality independently of patient attenuation. This approach improves patient/staff radioprotection because it reduces the injected activity for < 100-kg patients (the majority of patients).

Evaluation of the ability of the Brainlab Elements Cranial Distortion Correction algorithm to correct clinically relevant MRI distortions for cranial SRT.

PURPOSE: Cranial stereotactic radiotherapy (SRT) requires highly accurate lesion delineation. However, MRI can have significant inherent geometric distortions. We investigated how well the Elements Cranial Distortion Correction algorithm of Brainlab (Munich, Germany) corrects the distortions in MR image-sets of a phantom and patients. METHODS: A non-distorted reference computed tomography image-set of a CIRS Model 603-GS (CIRS, Norfolk, VA, USA) phantom was acquired. Three-dimensional T1-weighted images were acquired with five MRI scanners and reconstructed with vendor-derived distortion correction. Some were reconstructed without correction to generate heavily distorted image-sets. All MR image-sets were corrected with the Brainlab algorithm relative to the computed tomography acquisition. CIRS Distortion Check software measured the distortion in each image-set. For all uncorrected and corrected image-sets, the control points that exceeded the 0.5-mm clinically relevant distortion threshold and the distortion maximum, mean, and standard deviation were recorded. Empirical cumulative distribution functions (eCDF) were plotted. Intraclass correlation coefficient (ICC) was calculated. The algorithm was evaluated with 10 brain metastases using Dice similarity coefficients (DSC). RESULTS: The algorithm significantly reduced mean and standard deviation distortion in all image-sets. It reduced the maximum distortion in the heavily distorted image-sets from 2.072 to 1.059 mm and the control points with > 0.5-mm distortion fell from 50.2% to 4.0%. Before and especially after correction, the eCDFs of the four repeats were visually similar. ICC was 0.812 (excellent-good agreement). The algorithm increased the DSCs for all patients and image-sets. CONCLUSION: The Brainlab algorithm significantly and reproducibly ameliorated MRI distortion, even with heavily distorted images. Thus, it increases the accuracy of cranial SRT lesion delineation. After further testing, this tool may be suitable for SRT of small lesions.

Technical Note: A 3D-printed phantom for radiochromic film evaluation of moving lung tumor SBRT without dose convolution.

PURPOSE: A common dosimetric quality assurance (QA) method in stereotactic body radiation therapy (SBRT) of lung tumors is to use lung phantoms with radiochromic film. However, in most phantoms, the film moves with the tumor, leading to the blurring effect. This technical note presents the QA performance of a novel phantom in which the film is fixed; this phantom can be used for both patient-specific QA and end-to-end testing. METHODS: Lung tumor motion was simulated with the CIRS Model 008A phantom. A lung-equivalent insert that consisted of a fixed radiochromic film around which a 2-cm tumor moved in the inferior/superior direction (i.e., mimicking respiration-induced tumor motion) was generated by 3D printing. Two common SBRT plans [dynamic conformal arc (DCA) and volumetric-modulated arc therapy (VMAT)] were calculated on the average intensity projection (AIP) image set in Varian Eclipse using the dose calculation algorithm Acuros XB. The plans were delivered by a Varian TrueBeam STx accelerator using 6-MV flattening filter-free energy. EBT3 films were used for treatment-dose verification. The measured and planned dose distributions were compared by using the local gamma index at 3% and 2 mm. RESULTS: Mean gamma pass rates of film and planned dose distributions were all ≥95%. DCA and VMAT plans did not differ in gamma pass rates. Planned and measured dose distributions agreed well, as did planned and measured gamma maps. CONCLUSIONS: With this new insert, measured and planned dose distributions were very similar, which supports the current view in the field that dose calculations on AIP image sets account sufficiently for tumor motion during treatment. The phantom also performed well despite challenging breathing parameters (large tumor amplitude and slow breathing rate) and the application of a complex treatment technique (VMAT). This phantom could facilitate clinical and end-to-end film-based dosimetric QA for lung SBRT. TAXONOMY: Twenty-seven TH- Radiation dose measurement devices. Eleven Phantoms for dosimetric measurement.