Pelvic PET/MR attenuation correction in the image space using deep learning

IntroductionThe five-class Dixon-based PET/MR attenuation correction (AC) model, which adds bone information to the four-class model by registering major bones from a bone atlas, has been shown to be error-prone. In this study, we introduce a novel method of accounting for bone in pelvic PET/MR AC by directly predicting the errors in the PET image space caused by the lack of bone in four-class Dixon-based attenuation correction.MethodsA convolutional neural network was trained to predict the four-class AC error map relative to CT-based attenuation correction. Dixon MR images and the four-class attenuation correction µ-map were used as input to the models. CT and PET/MR examinations for 22 patients ([18F]FDG) were used for training and validation, and 17 patients were used for testing (6 [18F]PSMA-1007 and 11 [68Ga]Ga-PSMA-11). A quantitative analysis of PSMA uptake using voxel- and lesion-based error metrics was used to assess performance.ResultsIn the voxel-based analysis, the proposed model reduced the median root mean squared percentage error from 12.1% and 8.6% for the four- and five-class Dixon-based AC methods, respectively, to 6.2%. The median absolute percentage error in the maximum standardized uptake value (SUVmax) in bone lesions improved from 20.0% and 7.0% for four- and five-class Dixon-based AC methods to 3.8%.ConclusionThe proposed method reduces the voxel-based error and SUVmax errors in bone lesions when compared to the four- and five-class Dixon-based AC models

Strålingsindusert radikaldannelse i énkrystaller av l-asparagin monohydrat ved 295 K. : Et EPR-, ENDOR-, EIE- og DFT-studium

Strålingsinduserte skader hos levende organismer antas i første rekke å skyldes skader på arvemolekeylet DNA. DNA er under mesteparten av cellesyklus kveilet sammen med histonene i cellekjernen. DNA-histon-kompleksene, nukleosomene, stabiliseres av hydrogenbindinger mellom aminosyrene i histonene og sukker-fosfattrådene og basene i DNA. Den store kontaktflaten mellom DNA og aminosyrene sannsynligjør at aminosyrene kan modifisere strålingsresponsen til DNA ved at skader som oppstår kan forflytte seg mellom molekylene og fikseres et annet sted enn opprinnelsespunktet. I denne sammenhengen er blant annet aminosyren l-asparagin interessant da dens sidekjede inngår i hydrogenbindingene til DNA i nukleosomene. Énkrystaller av l-asparagin monohydrat er røntgenbestrålt ved 295 K og studert med EPR-spektroskopi og avledede teknikker som ENDOR og EIE, som alle er velegnet til studier av radikaler. I tillegg er teoretiske kvantekjemiske beregninger utført med DFT (Density Functional Theory). Til dette ble et cluster av molekyler benyttet for å på best mulig måte modellere bindingsforholdene i krystallstrukturen. Tre radikaler er observert og forsøkt identifisert. De eksperimentelle resultatene tyder på at også andre radikaler er tilstede etter romtemperaturbestråling. Radikal A er foreslått dannet ved netto hydrogenabstraksjon fra et av karbonatomene i sidekjeden i aminosyren. Radikal B ser også ut til å dannes ved netto hydrogenabstraksjon, men i dette tilfellet fra det sentrale karbonatomet i l-asparaginmolekylet. Strukturen til Radikal C er noe mer usikker, men er foreslått å være et dekarboksyleringsradikal. De foreslåtte strukturene for Radikal A, B og C støtter resultater fra tidligere studier av l-asparagin monohydrat, og disse sammen med den foreslåtte strukturen for Radikal B, viser at l-asparagin ikke overraskende har mange fellestrekk med andre aminosyrer når det gjelder strålingsrespons. Radikal B er for øvrig ikke identifisert tidligere. Det foreslås at nye lavtemperaturstudier av l-asparagin monohydrat gjennomføres for å støtte opp om foreslåtte reaksjonsveier fra primærradikaler til romtemperaturradikaler. Sammen med resultatene fra det foreliggende arbeidet vil slike studier være nødvendig for å kunne forstå hvilken rolle l-asparagin spiller for radikaldannelse i bestrålte nukleosomer

Assessment of pulmonary 18 F-FDG-PET uptake and cytokine profiles in non-small cell lung cancer patients treated with radiotherapy and erlotinib

Purpose: To investigate effects of radiotherapy (RT) and erlotinib on pulmonary glucose uptake using 2-deoxy-2-(18F)fluoro-D-glucose (18F-FDG) positron emission tomography (PET) during and after treatment of non-small cell lung cancer (NSCLC) and to identify associations between serum cytokine levels and lung glucose uptake. Material and methods: Twenty-seven patients with advanced NSCLC, receiving RT alone or concomitant RT and erlotinib therapy, were examined by 18F-FDG PET before, during, and after treatment. A total of 57 18F-FDG PET scans were analyzed. Pulmonary 18F-FDG uptake and radiotherapy dose mapping were used to acquire dose-response curves for each patient, where subsequent linear regression gave a glucose uptake level in the un-irradiated parts of the lungs (SUV0) and a response slope (ΔSUV). Serum cytokine levels at corresponding time points were assessed using a multiplex bioassay. Correlations between the most robust cytokines and lung 18F-FDG dose response parameters were further investigated. Results: From the dose response analysis, SUV0 at post-therapy was significantly higher (P < 0.001) than at mid- and pre-therapy (45% and 58%, respectively) for the group receiving RT + erlotinib. Also, SUV0 at post-therapy was higher for patients receiving RT + erlotinib compared to RT alone (42%; P < 0.001). No differences in ΔSUV were seen with treatments or time. SUV0 was positively associated (r = 0.47, P = 0.01) with serum levels of the chemokine C–C motif ligand 21 (CCL21) for patients receiving RT + erlotinib. Conclusions: Concomitant RT and erlotinib causes an elevation in pulmonary 18F-FDG uptake post treatment compared to RT alone. Pulmonary glucose uptake is associated with an upregulation of a chemokine (CCL21) involved in inflammatory reactions

A new method to assess pulmonary changes using (18)F-fluoro-2-deoxyglucose positron emission tomography for lung cancer patients following radiotherapy

BACKGROUND: (18)F-fluoro-2-deoxyglucose positron emission tomography ((18)F-FDG-PET) may be used for assessing radiation induced alterations in the lung. However, there is a need to further develop methodologies to improve quantification. Using computed tomography (CT), a local structure method has been shown to be superior to conventional CT-based analysis. Here, we investigate whether the local structure method based on (18)F-FDG-PET improves radiotherapy (RT) dose-response quantification for lung cancer patients. MATERIAL AND METHODS: Sixteen patients with lung cancer undergoing fractionated RT were examined by (18)F-FDG-PET/CT at three sessions (pre, mid, post) and the lung was delineated in the planning CT images. The RT dose matrix was co-registered with the PET images. For each PET image series, mean (μ) and standard deviation (σ) maps were calculated based on cubes in the lung (3 × 3 × 3 voxels), where the spread in pre-therapy μ and σ was characterized by a covariance ellipse in a sub-volume of 3 × 3 × 3 cubes. Mahalanobis distance was used to measure the distance of individual cube values to the origin of the ellipse and to further form local structure 'S' maps. The structural difference maps (ΔS) and mean difference maps (Δμ) were calculated by subtracting pre-therapy maps from maps at mid- and post-therapy. Corresponding maps based on CT images were also generated. RESULTS: ΔS identified new areas of interest in the lung compared to conventional Δμ maps. ΔS for PET and CT gave a significantly elevated lung signal compared to a control group during and post-RT (p < .05). Dose-response analyses by linear regression showed that ΔS between pre- and post-therapy for (18)F-FDG-PET was the only parameter significantly associated with local lung dose (p = .04). CONCLUSIONS: The new method using local structures on (18)F-FDG-PET provides a clearer uptake dose-response compared to conventional analysis and CT-based approaches and may be valuable in future studies addressing lung toxicity

Positron emission tomography guided dose painting by numbers of lung cancer: Alanine dosimetry in an anthropomorphic phantom

Background and purpose: Dose painting by numbers (DPBN) require a high degree of dose modulation to fulfill the image-based voxel wise dose prescription. The aim of this study was to assess the dosimetric accuracy of 18F-fluoro-2-deoxy-glucose positron emission tomography(18F-FDG-PET)-based DPBN in an anthropomorphic lung phantom using alanine dosimetry. Materials and methods: A linear dose prescription based on 18F-FDG-PET image intensities within the gross tumor volume (GTV) of a lung cancer patient was employed. One DPBN scheme with low dose modulation (Scheme A; minimum/maximum fraction dose to the GTV 2.92/4.26 Gy) and one with a high modulation (Scheme B; 2.81/4.52 Gy) were generated. The plans were transferred to a computed tomograpy (CT) scan of a thorax phantom based on CT images of the patient. Using volumetric modulated arc therapy (VMAT), DPBN was delivered to the phantom with embedded alanine dosimeters. A plan was also delivered to an intentionally misaligned phantom. Absorbed doses at various points in the phantom were measured by alanine dosimetry. Results: A pointwise comparison between GTV doses from prescription, treatment plan calculation and VMAT delivery showed high correspondence, with a mean and maximum dose difference of <0.1 Gy and 0.3 Gy, respectively. No difference was found in dosimetric accuracy between scheme A and B. The misalignment caused deviations up to 1 Gy between prescription and delivery. Conclusion: DPBN can be delivered with high accuracy, showing that the treatment may be applied correctly from a dosimetric perspective. Still, misalignment may cause considerable dosimetric erros, indicating the need for patient immobilization and monitoring

Positron emission tomography guided dose painting by numbers of lung cancer:Alanine dosimetry in an anthropomorphic phantom

BACKGROUND AND PURPOSE: Dose painting by numbers (DPBN) require a high degree of dose modulation to fulfill the image-based voxel wise dose prescription. The aim of this study was to assess the dosimetric accuracy of (18)F-fluoro-2-deoxy-glucose positron emission tomography((18)F-FDG-PET)-based DPBN in an anthropomorphic lung phantom using alanine dosimetry. MATERIALS AND METHODS: A linear dose prescription based on (18)F-FDG-PET image intensities within the gross tumor volume (GTV) of a lung cancer patient was employed. One DPBN scheme with low dose modulation (Scheme A; minimum/maximum fraction dose to the GTV 2.92/4.26 Gy) and one with a high modulation (Scheme B; 2.81/4.52 Gy) were generated. The plans were transferred to a computed tomograpy (CT) scan of a thorax phantom based on CT images of the patient. Using volumetric modulated arc therapy (VMAT), DPBN was delivered to the phantom with embedded alanine dosimeters. A plan was also delivered to an intentionally misaligned phantom. Absorbed doses at various points in the phantom were measured by alanine dosimetry. RESULTS: A pointwise comparison between GTV doses from prescription, treatment plan calculation and VMAT delivery showed high correspondence, with a mean and maximum dose difference of <0.1 Gy and 0.3 Gy, respectively. No difference was found in dosimetric accuracy between scheme A and B. The misalignment caused deviations up to 1 Gy between prescription and delivery. CONCLUSION: DPBN can be delivered with high accuracy, showing that the treatment may be applied correctly from a dosimetric perspective. Still, misalignment may cause considerable dosimetric erros, indicating the need for patient immobilization and monitoring

A new method to assess pulmonary changes using ¹⁸F-fluoro-2-deoxyglucose positron emission tomography for lung cancer patients following radiotherapy

<p><b>Background:</b>¹⁸F-fluoro-2-deoxyglucose positron emission tomography (¹⁸F-FDG-PET) may be used for assessing radiation induced alterations in the lung. However, there is a need to further develop methodologies to improve quantification. Using computed tomography (CT), a local structure method has been shown to be superior to conventional CT-based analysis. Here, we investigate whether the local structure method based on ¹⁸F-FDG-PET improves radiotherapy (RT) dose–response quantification for lung cancer patients.</p> <p><b>Material and methods:</b> Sixteen patients with lung cancer undergoing fractionated RT were examined by ¹⁸F-FDG-PET/CT at three sessions (pre, mid, post) and the lung was delineated in the planning CT images. The RT dose matrix was co-registered with the PET images. For each PET image series, mean (μ) and standard deviation (<i>σ</i>) maps were calculated based on cubes in the lung (3 × 3 × 3 voxels), where the spread in pre-therapy μ and <i>σ</i> was characterized by a covariance ellipse in a sub-volume of 3 × 3 × 3 cubes. Mahalanobis distance was used to measure the distance of individual cube values to the origin of the ellipse and to further form local structure ‘<i>S</i>’ maps. The structural difference maps (Δ<i>S</i>) and mean difference maps (Δμ) were calculated by subtracting pre-therapy maps from maps at mid- and post-therapy. Corresponding maps based on CT images were also generated.</p> <p><b>Results:</b> Δ<i>S</i> identified new areas of interest in the lung compared to conventional Δμ maps. Δ<i>S</i> for PET and CT gave a significantly elevated lung signal compared to a control group during and post-RT (<i>p</i> < .05). Dose–response analyses by linear regression showed that Δ<i>S</i> between pre- and post-therapy for ¹⁸F-FDG-PET was the only parameter significantly associated with local lung dose (<i>p</i> = .04).</p> <p><b>Conclusions:</b> The new method using local structures on ¹⁸F-FDG-PET provides a clearer uptake dose–response compared to conventional analysis and CT-based approaches and may be valuable in future studies addressing lung toxicity.</p