CT beam dosimetric characterization procedure for personalized dosimetry

Personalized dosimetry in computed tomography (CT) can be realized by a full Monte Carlo (MC) simulation of the scan procedure. Essential input data needed for the simulation are appropriate CT x-ray source models and a model of the patient's body which is based on the CT image. The purpose of this work is to develop comprehensive procedures for the determination of CT x-ray source models and their verification by comparison of calculated and measured dose distributions in physical phantoms. Mobile equipment together with customized software was developed and used for non-invasive determination of equivalent source models of CT scanners under clinical conditions. Standard and physical anthropomorphic CT dose phantoms equipped with real-time CT dose probes at five representative positions were scanned. The accumulated dose was measured during the scan at the five positions. ImpactMC, an MC-based CT dose software program, was used to simulate the scan. The necessary inputs were obtained from the scan parameters, from the equivalent source models and from the material-segmented CT images of the phantoms. 3D dose distributions in the phantoms were simulated and the dose values calculated at the five positions inside the phantom were compared to measured dose values. Initial results were obtained by means of a General Electric Optima CT 660 and a Toshiba (Canon) Aquilion ONE. In general, the measured and calculated dose values were within relative uncertainties that had been estimated to be less than 10%. The procedures developed were found to be viable and rapid. The procedures are applicable to any scanner type under clinical conditions without making use of the service mode with stationary x-ray tube position. Results show that the procedures are well suited for determining and verifying the equivalent source models needed for personalized CT dosimetry based on post-scan MC calculations.Peer reviewe

Gastric cancer and Helicobacter pylori: a combined analysis of 12 case control studies nested within prospective cohorts

BACKGROUND: The magnitude of the association between Helicobacter pylori and incidence of gastric cancer is unclear. H pylori infection and the circulating antibody response can be lost with development of cancer; thus retrospective studies are subject to bias resulting from classifi- cation of cases as H pylori negative when they were infected in the past. AIMS: To combine data from all case control studies nested within prospective cohorts to assess more reliably the relative risk of gastric cancer associated with H pylori infection.To investigate variation in relative risk by age, sex, cancer type and subsite, and interval between blood sampling and cancer diagnosis. METHODS: Studies were eligible if blood samples for H pylori serology were collected before diagnosis of gastric cancer in cases. Identified published studies and two unpublished studies were included. Individual subject data were obtained for each. Matched odds ratios (ORs) and 95% confidence intervals (95% CI) were calculated for the association between H pylori and gastric cancer. RESULTS: Twelve studies with 1228 gastric cancer cases were considered. The association with H pylori was restricted to noncardia cancers (OR 3.0; 95% CI 2.3–3.8) and was stronger when blood samples for H pylori serology were collected 10+ years before cancer diagnosis (5.9; 3.4–10.3). H pylori infection was not associated with an altered overall risk of cardia cancer (1.0; 0.7–1.4). CONCLUSIONS: These results suggest that 5.9 is the best estimate of the relative risk of non-cardia cancer associated with H pylori infection and that H pylori does not increase the risk of cardia cancer. They also support the idea that when H pylori status is assessed close to cancer diagnosis, the magnitude of the non-cardia association may be underestimated

Calibration of dosemeters used in mammography with different X ray qualities: Euromet Project No. 526

The effect of different X ray radiation qualities on the calibration of mammographic dosemeters was investigated within the framework of a EUROMET (European Collaboration in Measurement Standards) project. The calibration coefficients for two ionization chambers and two semiconductor detectors were established in 13 dosimetry calibration laboratories for radiation qualities used in mammography. They were compared with coefficients for other radiation qualities, including those defined in ISO 4037-1, with first half value layers in the mammographic range. The results indicate that the choice of the radiation quality is not crucial for instruments with a small energy dependence of the response. However, the radiation quality has to be chosen carefully if instruments with a marked dependence of their response to the radiation energy are calibrate

Centralized repeated resectability assessment of patients with colorectalliver metastases during first-line treatment : prospective study

Y Background: Metastasectomy is probably underused in metastatic colorectal cancer. The aim of this study was to investigate the effect of centralized repeated assessment on resectability rate of liver metastases. Methods: The prospective RAXO study was a nationwide study in Finland. Patients with treatable metastatic colorectal cancer at any site were eligible. This planned substudy included patients with baseline liver metastases between 2012 and 2018. Resectability was reassessed by the multidisciplinary team at Helsinki tertiary referral centre upfront and twice during first-line systemic therapy. Outcomes were resectability rates, management changes, and survival. Results: Of 812 patients included, 301 (37.1 per cent) had liver-only metastases. Of these, tumours were categorized as upfront resectable in 161 (53.5 per cent), and became amenable to surgery during systemic treatment in 63 (20.9 per cent). Some 207 patients (68.7 per cent) eventually underwent liver resection or ablation. At baseline, a discrepancy in resectability between central and local judgement was noted for 102 patients (33.9 per cent). Median disease-free survival (DFS) after first resection was 20 months and overall survival (OS) 79 months. Median OS after diagnosis of metastatic colorectal cancer was 80, 32, and 21 months in R0-1 resection, R2/ablation, and non-resected groups, and 5-year OS rates were 68, 37, and 9 per cent, respectively. Liver and extrahepatic metastases were present in 511 patients. Of these, tumours in 72 patients (14.1 per cent) were categorized as upfront resectable, and 53 patients (10.4 per cent) became eligible for surgery. Eventually 110 patients (21.5 per cent) underwent liver resection or ablation. At baseline, a discrepancy between local and central resectability was noted for 116 patients (22.7 per cent). Median DFS from first resection was 7 months and median OS 55 months. Median OS after diagnosis of metastatic colorectal cancer was 79, 42, and 17 months in R0-1 resection, R2/ablation, and non-resected groups, with 5-year OS rates of 65, 39, and 2 per cent, respectively. Conclusion: Repeated centralized resectability assessment in patients with colorectal liver metastases improved resection and survival rates.Peer reviewe

Laajemmin ja varhaisemmin ; Korkea-asteen opiskelijavalintauudistus ja muutokset valmennuskursseille osallistumisessa

Tässä artikkelissa tutkimme korkeakouluopiskelijoiden ja lukio-opiskelijoiden valmennuskursseille osallistumista. Tarkastelemme etenkin opiskelijavalintauudistuksen aikana tapahtuneita koulutusalakohtaisia muutoksia valmennuskursseille osallistumisessa ja niin sanotun abivalmennuksen roolia. Hyödynnämme tutkimuksessa korkeakouluopiskelijoilta kerättyjä Eurostudent VII ja VIII -kyselyaineistoja sekä Uusvalu (Opiskelijavalinnan uudistus lukion ja lukiolaisten silmin) -tutkimushankkeessa kerättyjä kyselyaineistoja. Tutkimuksen tulokset osoittavat, että valmennuskurssien käyttö on yleistynyt viimeisen vuosikymmenen mittaan toteutetun korkea-asteen opiskelijavalintauudistuksen toimeenpanon aikana sekä yliopisto- että ammattikorkeakouluopiskelijoiden keskuudessa. Valmennuskursseille osallistuminen on yleistynyt etenkin niillä hakualoilla, joilla se on ollut aikaisemmin suhteellisen vähäistä. Valmennuskursseille osallistuneet korkeakouluopiskelijat jakautuvat entistä voimakkaammin perhetaustan mukaisesti siten, että valmennuksen käyttö on yhä selkeämmin aiempaa yleisempää hyvin toimeentulevien ja korkeasti koulutettujen vanhempien lapsilla. Korkeakouluopiskelijat eivät ole vielä laajamittaisesti käyttäneet ylioppilaskirjoituksiin suuntautuvaa abivalmennusta, mutta sen käyttö on huomattavasti yleisempää lukiolaisten keskuudessa. Ylioppilastodistuksen arvosanoja painottava korkea-asteen opiskelijavalinta näyttää vahvistavan ylioppilaskirjoitusten roolia lukio-opinnoissa

BCI for physiological text annotation

IUI'17Peer reviewe