Zeitschrift fur medizinische Physik最新文献

{"title":"Sensitivity and specificity of Monte Carlo based independent secondary dose computation for detecting modulation-related dose errors in intensity modulated radiotherapy.","authors":"Matthias Kowatsch,&nbsp;Philipp Szeverinski,&nbsp;Patrick Clemens,&nbsp;Thomas Künzler,&nbsp;Matthias Söhn,&nbsp;Markus Alber","doi":"10.1016/j.zemedi.2023.10.001","DOIUrl":"https://doi.org/10.1016/j.zemedi.2023.10.001","url":null,"abstract":"<p><strong>Background: </strong>The recent availability of Monte Carlo based independent secondary dose calculation (ISDC) for patient-specific quality assurance (QA) of modulated radiotherapy requires the definition of appropriate, more sensitive action levels, since contemporary recommendations were defined for less accurate ISDC dose algorithms.</p><p><strong>Purpose: </strong>The objective is to establish an optimum action level and measure the efficacy of a Monte Carlo ISDC software for pre-treatment QA of intensity modulated radiotherapy treatments.</p><p><strong>Methods: </strong>The treatment planning system and the ISDC were commissioned by their vendors from independent base data sets, replicating a typical real-world scenario. In order to apply Receiver-Operator-Characteristics (ROC), a set of treatment plans for various case classes was created that consisted of 190 clinical treatment plans and 190 manipulated treatment plans with dose errors in the range of 1.5-2.5%. All 380 treatment plans were evaluated with ISDC in the patient geometry. ROC analysis was performed for a number of Gamma (dose-difference/distance-to-agreement) criteria. QA methods were ranked according to Area under the ROC curve (AUC) and optimum action levels were derived via Youden's J statistics.</p><p><strong>Results: </strong>Overall, for original treatment plans, the mean Gamma pass rate (GPR) for Gamma(1%, 1 mm) was close to 90%, although with some variation across case classes. The best QA criterion was Gamma(2%, 1 mm) with GPR > 90% and an AUC of 0.928. Gamma criteria with small distance-to-agreement had consistently higher AUC. GPR of original treatment plans depended on their modulation degree. An action level in terms of Gamma(1%, 1 mm) GPR that decreases with modulation degree was the most efficient criterion with sensitivity = 0.91 and specificity = 0.95, compared with Gamma(3%, 3 mm) GPR > 99%, sensitivity = 0.73 and specificity = 0.91 as a commonly used action level.</p><p><strong>Conclusions: </strong>ISDC with Monte Carlo proves highly efficient to catch errors in the treatment planning process. For a Monte Carlo based TPS, dose-difference criteria of 2% or less, and distance-to-agreement criteria of 1 mm, achieve the largest AUC in ROC analysis.</p>","PeriodicalId":101315,"journal":{"name":"Zeitschrift fur medizinische Physik","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"61567129","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Impact of the maximum ring difference on image quality and noise characteristics of a total-body PET/CT scanner.","authors":"F P Schmidt,&nbsp;J G Mannheim,&nbsp;P M Linder,&nbsp;P Will,&nbsp;L S Kiefer,&nbsp;M Conti,&nbsp;C la Fougère,&nbsp;I Rausch","doi":"10.1016/j.zemedi.2023.09.001","DOIUrl":"https://doi.org/10.1016/j.zemedi.2023.09.001","url":null,"abstract":"<p><p>The sensitivity of a PET system highly depends on the axial acceptance angle or maximum ring difference (MRD), which can be particularly high for total-body scanners due to their larger axial field of views (aFOVs). This study aims to evaluate the impact on image quality (IQ) and noise performance when MRD85 (18°), the current standard for clinical use, is increased to MRD322 (52°) for the Biograph Vision Quadra (Siemens Healthineers).</p><p><strong>Methods: </strong>Studies with a cylindrical phantom covering the 106 cm aFOV and an IEC phantom filled with ¹⁸F, ⁶⁸Ga and ⁸⁹Zr were performed for acquisition times from 60 to 1800 s and activity concentrations from 0.4 to 3 kBq/ml to assess uniformity, contrast recovery coefficients (CRCs) and to characterize noise by coefficient of variation (CV). Spatial resolution was compared for both MRDs by sampling a quadrant of the FOV with a point source. Further IQ, CV, liver SUV_mean and SUV_max were compared for a cohort of 5 patients scanned with [¹⁸F]FDG (3 MBq/kg, 1 h p.i.) from 30 to 300 s.</p><p><strong>Results: </strong>CV was improved by a factor of up to 1.49 and is highest for short acquisition times, peaks at the center field of view and mitigates parabolic in axial direction with no difference to MRD85 beyond the central 80 cm. No substantial differences between the two evaluated MRDs in regards to uniformity, SUV_mean or CRC for the different isotopes were observed. A degradation of the average spatial resolution of 0.9 ± 0.2 mm in the central 40 cm FOV was determined with MRD322. Depending on the acquisition time MRD322 resulted in a decrease of SUV_max between 23.8% (30 s) and 9.0% (300 s).</p><p><strong>Conclusion: </strong>Patient and phantom studies revealed that scan time could be lowered by approximately a factor of two with MRD322 while maintaining similar noise performance. The moderate degradation in spatial resolution for MRD322 is worth to exploit the full potential of the Quadra by either shorten scan times or leverage noise performance in particular for low count scenarios such as ultra-late imaging or dynamic studies with high temporal resolution.</p>","PeriodicalId":101315,"journal":{"name":"Zeitschrift fur medizinische Physik","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49695836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}