Automated algorithm for CBCT-based dose calculations of prostate radiotherapy with bilateral hip prostheses

ABSTRACTOBJECTIVE:Cone beam CT (CBCT) images contain more scatter than a conventional CT image and therefore provide inaccurate Hounsfield units (HUs). Consequently, CBCT images cannot be used directly for radiotherapy dose calculation. The aim of this study is to enable dose calculations to be performed with the use of CBCT images taken during radiotherapy and evaluate the necessity of replanning.METHODS:A patient with prostate cancer with bilateral metallic prosthetic hip replacements was imaged using both CT and CBCT. The multilevel threshold (MLT) algorithm was used to categorize pixel values in the CBCT images into segments of homogeneous HU. The variation in HU with position in the CBCT images was taken into consideration. This segmentation method relies on the operator dividing the CBCT data into a set of volumes where the variation in the relationship between pixel values and HUs is small. An automated MLT algorithm was developed to reduce the operator time associated with the process. An intensity-modulated radiation therapy plan was generated from CT images of the patient. The plan was then copied to the segmented CBCT (sCBCT) data sets with identical settings, and the doses were recalculated and compared.RESULTS:Gamma evaluation showed that the percentage of points in the rectum with γ < 1 (3%/3 mm) were 98.7% and 97.7% in the sCBCT using MLT and the automated MLT algorithms, respectively. Compared with the planning CT (pCT) plan, the MLT algorithm showed −0.46% dose difference with 8 h operator time while the automated MLT algorithm showed −1.3%, which are both considered to be clinically acceptable, when using collapsed cone algorithm.CONCLUSION:The segmentation of CBCT images using the method in this study can be used for dose calculation. For a patient with prostate cancer with bilateral hip prostheses and the associated issues with CT imaging, the MLT algorithms achieved a sufficient dose calculation accuracy that is clinically acceptable. The automated MLT algorithm reduced the operator time associated with implementing the MLT algorithm to achieve clinically acceptable accuracy. This saved time makes the automated MLT algorithm superior and easier to implement in the clinical setting.ADVANCES IN KNOWLEDGE:The MLT algorithm has been extended to the complex example of a patient with bilateral hip prostheses, which with the introduction of automation is feasible for use in adaptive radiotherapy, as an alternative to obtaining a new pCT and reoutlining the structures

Dosimetric feasibility of magnetic resonance (MR)-based dose calculation of prostate radiotherapy using multilevel threshold algorithm

Objective: The development of magnetic resonance (MR) imaging systems has been extended for the entire radiotherapy process. However, MR images provide voxel values that are not directly related to electron densities (ED), thus MR images cannot be used directly for dose calculation. The aim of this study is to investigate the feasibility of dose calculations to be performed on MR images and evaluate the necessity of re-planning.Methods: A prostate cancer patient was imaged using both MR and CT. The multilevel threshold algorithm (MLT) was used categorise to voxel values in the MR images in into three segments (air, water and bone) with homogeneous Hounsfield units (HU). An intensity modulated radiation therapy (IMRT) plan was generated from CT images of the patient. The plan was then copied to the segmented MR data sets and the doses were recalculated using pencil beam, and collapsed cone (CC) algorithms and Monte Carlo (MC) modelling.Results: Gamma evaluation showed that the percentage of points in regions of interest with γ < 1 (3%/3 mm) were more than 94% in the segmented MR. Compared with the planning CT (pCT) plan, the segmented MR plan resulted in a dose difference of –0.3%, 0.8% and –1.3% when using PB, CC and MC algorithms, respectively.Conclusion: The segmentation and conversion of MR images into HUs data using the MLT algorithm, used in this feasibility study, can be used for dose calculation. This method can be used as a dosimetric assessment tool and can be easily implemented into the clinic

Nitrogen deficiency in barley (<i>Hordeum vulgare)</i> seedlings induces molecular and metabolic adjustments that trigger aphid resistance

Agricultural N2O pollution resulting from the use of synthetic fertilisers represents a significant contribution to anthropogenic greenhouse gas emissions, providing a rationale for reduced use of nitrogen fertilisers. Nitrogen limitation results in extensive systems rebalancing that remodels metabolism and defence processes. To analyse the regulation underpinning these responses, barley (Horedeum vulgare) seedlings were grown for seven days under nitrogen-deficient conditions until net photosynthesis was 50% lower than in nitrogen-replete controls. Although shoot growth was decreased there was no evidence for the induction of oxidative stress despite lower total concentrations of nitrogen containing antioxidants. Nitrogen deficient barley leaves were rich in amino acids, sugars and tricarboxylic acid cycle intermediates. In contrast to N-replete leaves one day old nymphs of the green peach aphid (Myzus persicae) failed to reach adulthood when transferred to N-deficient barley leaves. Transcripts encoding cell, sugar and nutrient signalling, protein degradation and secondary metabolism were over-represented in nitrogen-deficient leaves while those associated with hormone metabolism were similar under both nutrient regimes with the exception of mRNAs encoding proteins involved in auxin metabolism and responses. Significant similarities were observed between the N-limited barley leaf transcriptome and that of aphid infested Arabidopsis leaves. These findings not only highlight significant similarities between biotic and abiotic stress signalling cascades but also identify potential targets for increasing aphid resistance with implications for the development of sustainable agriculture

The Future of Work, Digital Labor, and Business Legitimacy

The increasing trend of Internet technology platforms and its offerings of digital labor have revolutionized the world of work. Companies that compete in this so-called gig economy are breaking away from traditional work arrangements and using a business model that challenges current employment and labor laws. While gig economy employers boast the benefit of work flexibility, their workers face compromised fairness in regard to compensation, working conditions, and career development. This chapter discusses how the gig economy redefines the future of work, by focusing on the current state of gig workers, and then explores opportunities for ways in which the gig economy can mutually benefit the employers and its workers