Evaluation of improvements in plan quality with Photon Optimizer v16.1 for single brain lesion SRS treatment.

Background: The purpose of this study is to compare the performance of the Photon Optimizer (PO) version 16.1 algorithm with its earlier version PO v13.6 and with Progressive Resolution Optimizer (PRO) version 13.6 algorithms. Materials and methods: 20 patients with single brain lesions treated with the stereotactic radiosurgery (SRS) technique were retrospectively selected for this study. Initially, for all patients volumetric modulated arc therapy (VMAT) SRS plans were generated with the PRO v 13.6 algorithm. Then, all the plans were re-generated with two versions 13.6 and 16.1 of PO algorithm using the same setup and dose-volume optimization objectives as that of PRO with a similar planning approach. The quality of the generated plans was analysed using ICRU 91 plan evaluation parameters and also using dice similarity co-efficient (DSC), centre of mass distance (CMD) between target and prescription isodose line, Monitor units (MU) and brain-gross tumor volume (GTV) 12 Gy volume. Paired Student t-test was used for statistical analysis with 0.05 as a significant value. Results: PO v16.1 improved all the dosimetric parameters studied compared to PO 13.6, the difference is statistically significant for all the parameters (p < 0.05), except for median dose and brain-GTV 12 Gy volume. PO v16.1 also showed statistically significant improvement for all the dosimetric parameters evaluated, except DSC and conformity index (CI), compared to PRO v13.6. Conclusion: The PO v16.1 generated plans are dosimetrically superior to PO v13.6 and PRO v13.6 in terms of target dose coverage and dose gradient with lesser beam modulation and plan complexity for single brain lesion SRS.

Study of dosimetric properties of flattened and unflattened megavoltage x ray beam on high Z implant materials.

PURPOSE: Addition of high Z implants in the treatment vicinity or beam path is unavoidable in certain clinical situation. In this work, we study the properties of radiation interaction parameters such as mass attenuation coefficient (MAC), x ray beam transmission factor (indirect beam attenuation), interface effects like backscatter dose perturbation factor (BSDF) and forward dose perturbation factor (FDPF) for flattened (FF) and unflattened (UF) x ray beams. METHODS: MAC for stainless steel and titanium alloy was measured using CC13 chamber with appropriate buildup in narrow beam geometry. The x ray beam transmission factors were measured for stainless steel and titanium alloy for different field size, off-axis, and depths. Profile analysis was performed using a radiation field analyzer (RFA) as a function of field size and depth to study the influence of phantom scattering and spectral variation in the beam. In addition, interface effects such as BSDF and FDPF were measured with gafchromic films at maximum BSDF peak position calculated using Acuros XB algorithm and with PPC40 chamber measured at exit side of high Z material, respectively. RESULTS: The MAC in both cases decreases with increase in energy for stainless steel (SS) and titanium (Ti) alloy. The MAC increases with the change in x ray beam type from flattened to UF beam because of relatively lower mean energy. The x ray beam transmission factor increases with the increase in energy, field size, and depth owing to increase in penetration power phantom scatter, respectively. The measured BSDF and FDPF were found to be in good agreement with AXB algorithm. CONCLUSION: The dosimetric properties of x ray photon beam were studied comprehensively in the presence of high Z material like stainless steel and titanium alloy using both flattened and UF beams to understand and incorporate the findings of various parameters in clinical condition due to the variation in energy spectrum from FF to UF x ray beam.

Dosimetric Systems in Pre-Treatment QA for Stereotactic Treatments: Correlation Agreements and Target Volume Dependency.

AIM: This study comprehensively investigated pre-treatment quality assurance (QA) for 100 cancer patients undergoing stereotactic treatments (SRS/SRT) using various detectors. METHODS: The study conducted QA for SRS/SRT treatments planned with a 6MV SRS beam at a dose rate of 1,000 MU/min, utilizing Eclipse v13.6 Treatment Planning System (TPS). Point dose measurements employed 0.01cm3 and 0.13cm3 cylindrical ionization chambers, while planar dose verification utilized Gafchromic EBT-XD Film and Portal Imager (aS1000). Plans were categorized by target volume, and a thorough analysis compared point dose agreements, planar dose gamma pass rates, and their correlations with chamber volume mean dose, detector type, and point dose agreement. Additionally, the consistency between different ionization chambers was assessed. RESULTS: Point dose agreement generally improved with increasing target volume, except for volumes over 10cm3 with 0.01cm3 chambers, showing a contrary trend. Significant differences (p<0.05) were observed between TPS and measured doses for both chambers. Gamma pass rate improved with increasing target volume in EBT XD and aS1000 analyses, except for the >10cm3 group in EBT XD. EBT XD demonstrated better agreement with TPS for target volumes up to 10cm3 compared to aS1000, with a statistically significant difference (p<0.05) between the detectors. Strong correlations were found between chamber point dose and chamber volume mean dose agreement, as well as between the two gamma criteria analyses of the same detector type in the planar dose correlation analysis. However, weak correlations were discovered for other analyses. CONCLUSION: This study found weak correlation between different detector types in pre-treatment QA for point dose and planar dose evaluation. However, within a specific detector type, strong correlation was observed for different point dose evaluation methods and gamma criteria. This highlights the importance of cautious interpretation of QA results, particularly for SRS QA, due to the lack of correlation between detector types.

Inflammatory Fabry Cardiomyopathy Demonstrated Using Simultaneous [18F]-FDG PET-CMR.

Using hybridized [18F]-fluorodeoxyglucose positron emission tomography with cardiac magnetic resonance, we identify active myocardial inflammation and demonstrate its relationship with late gadolinium enhancement, in Fabry disease. We demonstrate that late gadolinium enhancement represents, at least in part, active myocardial inflammation and identify an early inflammatory phenotype that may represent a therapeutic window before irreversible tissue injury and adaptation occur. (Level of Difficulty: Intermediate.).

Attenuation correction of myocardial perfusion SPET in patients of normal body mass index.

Soft tissue attenuation artefacts are more likely to occur in patients with high body mass index (BMI) undergoing myocardial perfusion imaging (MPI) and therefore it is routine practice in our department to perform attenuation correction in this group of patients. However, we suspected that attenuation artefacts may also occur in patients with normal BMI. We collected data prospectively on 57 patients with BMI less than 25kg/m(2) who underwent stress-rest MPI single photon emission tomography (SPET) as part of their standard management at our institution. The differences between the attenuation corrected (AC) and non attenuation corrected (NC) images were evaluated by two experienced readers blinded to patient gender and clinical details. Visual improvement in perfusion with attenuation correction was seen in 54.4% of patients with normal BMI and was more common in males (84.2%) than females (39.5%). Discordances between AC and NC were most frequent in the inferior, inferolateral and anteroseptal segments in both males and females and were also seen in the apical and anterior segments in some patients, mainly in females, in keeping with the well-recognized distribution pattern for attenuation artefacts. In conclusion, although a small sample size was used in this study, changes in appearance with attenuation correction likely to represent attenuation artefacts were seen in 54.4% of patients with normal BMI and were two times more common in males than females. These changes were felt to be clinically relevant in that they could lead to a change in the final report and may ultimately affect the diagnosis and clinical management. Thus, attenuation correction could be of value in patients of normal BMI. Further larger studies with correlation with clinical follow-up or invasive coronary angiography are warranted.

18 F-FDG PET/CT Uptake in Acute Pontine Infarct Mimicking Intracranial Metastasis.

ABSTRACT: Infarcts are generally nonviable and are not avid on an 18 F-FDG PET/CT. Here, we discuss a 53-year-old man who presented with chest pain and raised d -dimer. CT pulmonary angiogram was performed to exclude pulmonary embolism, which identified incidental lung nodules. 18 F-FDG PET/CT was performed for the assessment of lung nodules, which showed incidental focal FDG uptake in the pons. This was concluded as an acute infarct on subsequent MR scan. This highlights the importance of not interpreting all focal FDG uptakes as malignant. In rare circumstances, false-positive benign causes should be considered, such as in this rare case of an acute pontine infarct.

Studies on Fundamental Interaction Parameters for Stainless Steel and Titanium Biomaterials Using Flattened and Un-Flattened Megavoltage X-Ray Beams.

Purpose: This work presents the measure of fundamental interaction parameters like mass attenuation coefficient (µ/ρ), mean energy, total atomic (σa) and electronic (σe) cross section, effective atomic number (Zeff), electron density (Nel) and mean free path (mfp) using FF and UF megavoltage x-ray beam for high Z implants. Methods: Narrow beam geometry is used to find out mass attenuation coefficient (µ/ρ) (MAC) which is then used to calculate mean energy (using NIST data), total atomic (σa) and electronic cross section (σe) for different energies. The effective atomic number (Zeff), Electron density (Nel), mean free path (mfp) for both flattened and unflattened x-ray beams for high Z material stainless steel (SS316) and titanium alloy (Grade 5) are studied. Results: The mean energies calculated from NIST data against mass attenuation coefficient were in good agreement with Monte Carlo value. It shows that spectral weighted effective atomic number is independent of megavoltage energies in the Compton region. Effective electron density calculated using Zeff and MAC method is lesser compared to direct method for both high Z materials. The mean free path (mfp) is higher along the central axis than off-axis for flattened beam in comparison to unflattened beam for both of the high Z materials studied because of the variation in energy spectrum for both FF and UF x-ray beams. Conclusion: This study elaborated the fundamental interaction parameters of different energies of flattened and unflattened x-ray beam interactions with high Z materials such as Stainless Steel (SS316) and Titanium (Grade5) relevant in a clinical scenario.

An Assessment of Dosimetric Characteristics of Inline 2.5 Mega Voltage Unflattened Imaging X-Ray Beam.

Purpose: The aim of this work is to study the dosimetric parameters of newly introduced 2.5 MV imaging x-ray beam used as inline imaging to do setup verification of the patient undergoing radiation therapy. As this x-ray beam is in megavoltage range but comprises of a lower energy spectrum. It is essential to study the pros and cons of 2.5 MV imaging x-ray beam for clinical use.Methods: The mean energy was calculated using the NIST XCOM table through MAC. Profile analysis was done using RFA to understand the percentage depth dose, degree of unflatteness, symmetry, penumbra and out of field dose. Dose to skin for the 2.5 MV x-ray beam was analysed for field sizes 10x10 cm2, 20x20 cm2, 30x30 cm2. Leakage measurements for treatment head and at the patient plane were done using IEC 819/98 protocol. Finally, the spatial resolution and contrast were analyzed with and without patient scatter medium. Results: The MAC at 15 cm off-axis was found to be lower than that at the CAX. Similarly, there was a decrease in mean energy from 0.47 MV to 0.37 MV at 15 cm off-axis. The reduction of mean energy towards off-axis is lower than the other high energy MV x-ray beams. The tuned absolute dose of 1 cGy/MU is consistent and within < ±1 %. The relative output factors were found to be in correlation with Co-60. The beam quality of 2.5 MV x-ray beam was found to be 0.4771. The profile parameters like the degree of unflatness of the 2.5 x-ray beam were studied at 85 %, 90 %, 95 % lateral distances, and the penumbra at different depth and field sizes are higher than the 6 MV treatment beam. In addition, out of field dose also drastically increases to a maximum of up to 30 % laterally at 5cm at deeper depths. The skin dose increases from 48.51 % to 88.15 % from 6 MV to 2.5 MV x-ray beam for the field size 10x10 cm2. Also, the skin dose increases from 88.15 % to 91.78 % from the field size 10x10 cm2 to 30x30 cm2. Although the measured leakage radiation for 2.5 MV x-ray beam at the patient plane and other than patient planes are with the tolerance limit, an increase in exposure towards gantry side compared to other areas around treatment head and the patient plane may lead to more skin dose to head and chest while imaging pelvis region. The MLC transmission of 2.5 MV x-ray beam such as inter, intra and edge effect are 0.40 %, 0.37 % and 11% respectively. The spatial resolution of 2.0, 1.25 and 0.9 LP/mm was observed for KV, 2.5MV, and 6 MV x-ray beams. The spatial resolution and contrast of 2.5 MV x-ray beam are superior to 6 MV x-ray beam and inferior to KV x-rays. Conclusions: The 2.5 MV x-ray imaging beam is analysed in view of beam characteristics and radiation safety to understand the above-studied concepts while using this imaging beam in a clinical situation. In future, if 2.5MV x-ray beam is used for treatment purpose with increased dose rate, the above-studied notions can be incorporated prior to implementation.

First case on fluorodeoxyglucose positron emission tomography/computerized tomography of a distant skip metastases to parotid node from esophageal adenocarcinoma.

We are presenting the first case of a gastro-oesophageal junction adenocarcinoma with metastasis only to the intraparotid lymph node simulating Warthin's tumor. A 66-year-old man underwent an esophagogastroduodenoscopy that found circumferential ulcerated esophageal tumor beginning 40 cm from incisors resulting in stricture and two discrete erosions in the proximal third of esophagus. Biopsies from the stricture have demonstrated a poorly differentiated gastric adenocarcinoma. Computerized tomography (CT) confirmed the site of primary without evidence of distant metastasis. Positron emission tomography/CT showed high uptake in the known carcinoma in distal esophagus involving the gastro-oesophageal junction extending into the cardia of the stomach, the maximum standardized uptake value (SUVmax) 7.4. Furthermore, there was a focus of high-grade tracer activity, SUVmax 6.2, in the left intraparotid nodule which was initially thought to represent Warthin's tumor rather than metastasis; there was no evidence to suggest metastases elsewhere. Fine needle aspiration and biopsy from the enlarged intraparotid lymph node revealed that the histology was consistent with a poorly differentiated adenocarcinoma, metastasis from upper gastrointestinal tract.

Assessment of a protocol for routine simultaneous myocardial blood flow measurement and standard myocardial perfusion imaging with rubidium-82 on a high count rate positron emission tomography system.

OBJECTIVES: High count rate positron emission tomography (PET) systems offer the potential for accurate myocardial blood flow (MBF) quantification during first-pass dynamic imaging in conjunction with standard rubidium-82 (Rb-82) PET myocardial perfusion imaging (MPI). We investigate the feasibility of this using a Siemens Biograph mCT. MATERIALS AND METHODS: Current routine clinical PET MPI is performed with 1480 MBq (40 mCi) Rb-82. Dynamic first-pass images from 217 consecutive patients were reviewed for evidence of detector saturation, indicating that count rate limits had been exceeded. Phantom acquisitions in the presence of high count rates were performed to assess the effect of detector saturation on quantitative accuracy. RESULTS: Accurate MBF quantification and perfusion imaging using current protocols was successful in 85% of clinical cases. Detector block saturation was observed in 15% of cases, and phantom acquisitions indicate that saturation may have an adverse effect on quantitative accuracy. Visualization of transit or pooling of Rb-82 in the vessels in the axilla was the most consistent feature when saturation occurred. Reduction of administered activity to 1110 MBq (30 mCi) and subsequent evaluation of 159 patients ensured successful MBF quantification while maintaining good diagnostic quality perfusion imaging in 99% of cases. CONCLUSION: MBF quantification and good-quality standard perfusion imaging can be performed on a high count rate PET system using a single-acquisition protocol. The administered activity requires optimization and we recommend 1110 MBq for PET MPI with a Biograph mCT.