Showing papers by "Cécile M. Ronckers published in 2014"

Leukemia and brain tumors among children after radiation exposure from CT scans : design and methodological opportunities of the Dutch Pediatric CT Study

Abstract: Computed tomography (CT) scans are indispensable in modern medicine; however, the spectacular rise in global use coupled with relatively high doses of ionizing radiation per examination have raised radiation protection concerns. Children are of particular concern because they are more sensitive to radiation-induced cancer compared with adults and have a long lifespan to express harmful effects which may offset clinical benefits of performing a scan. This paper describes the design and methodology of a nationwide study, the Dutch Pediatric CT Study, regarding risk of leukemia and brain tumors in children after radiation exposure from CT scans. It is a retrospective record-linkage cohort study with an expected number of 100,000 children who received at least one electronically archived CT scan covering the calendar period since the introduction of digital archiving until 2012. Information on all archived CT scans of these children will be obtained, including date of examination, scanned body part and radiologist's report, as well as the machine settings required for organ dose estimation. We will obtain cancer incidence by record linkage with external databases. In this article, we describe several approaches to the collection of data on archived CT scans, the estimation of radiation doses and the assessment of confounding. The proposed approaches provide useful strategies for data collection and confounder assessment for general retrospective record-linkage studies, particular those using hospital databases on radiological procedures for the assessment of exposure to ionizing or non-ionizing radiation.

Fertility studies in female childhood cancer survivors: selecting appropriate comparison groups

Abstract: Little information is available on the use of appropriate comparison groups for studies investigating late effects of childhood cancer. Two comparison groups in a nationwide study on reproductive function and ovarian reserve in female childhood cancer survivors were recruited (The Dutch Childhood Oncology Group Long-Term Effects After Childhood Cancer Cohort Study). Experiences of this process are reported. Two types of comparison groups were used: sisters of participating survivors and controls from the general population. A total of 352 out of 580 (61%) of the participating survivors who had a sister gave permission to invite them for the study. The participation rate of sisters was much higher than control participants from the general population (74% versus 21%, respectively), whereas considerably more effort was involved in recruiting controls from the general population. Participants in this group were significantly older and more highly educated than sister controls (P < 0.001 for both groups). No significant differences were observed between both types of comparison groups in several fertility-related characteristics, suggesting minimal bias owing to selective participation. Researchers setting up a study to investigate late effects among survivors of childhood cancer should carefully consider the advantages and disadvantages of using various types of comparison groups.

The use of equivalent radiation dose in the evaluation of late effects after childhood cancer treatment

Abstract: In epidemiologic research radiation-associated late effects after childhood cancer are usually analyzed without considering fraction dose. According to radiobiological principles, fraction dose is an important determinant of late effects. We aim to provide the rationale for using equivalent dose in 2-Gy fractions (EQD2 α/β ) as the measure of choice rather than total physical dose as prescribed according to the clinical protocol. Between 1966 and 1996, 597 (43.8 %) children in our cohort of 1,362 5-year childhood cancer survivors (CCS) received radiotherapy before the age of 18 years as part of their primary cancer treatment. Detailed information from individual patients’ charts was collected and physical doses were converted into the EQD2 α/β , which includes total dose, fraction dose, and the tissue-specific α/β ratio. The use of EQD2 α/β is illustrated in examples studies describing different analyses using EQD2 α/β and physical dose. Radiotherapy information was obtained for 510 (85.4 %) CCS. Multivariable analyses rendered different risk estimates for total body irradiation in EQD2 α/β -based vs. physical-dose-based models. For other radiotherapy regimens, risk estimates were similar. Using the total physical dose is not adequate for advanced analyses of radiation-associated late effects in CCS. Therefore, it is advised that for future studies the EQD2 α/β is used, because the EQD2 α/β incorporates the fraction dose, and the tissue-specific α/β ratio. Furthermore, it enables comparisons across fractionation regimens and allows for summing doses delivered by various contemporary and future radiation modalities. Risk estimates of radiation-associated side effects expressed in EQD2 α/β provide more precise, clinically relevant information for cancer survivor screening guidelines.