Calibration curves by 60Co with low dose rate are different in terms of dose estimation - a comparative study.

Biological dosimetry aims to estimate individual absorbed doses due ionizing radiation exposure. The dicentric chromosomes are considered the most specific biomarker for dose estimation. This study aimed to compare calibration curves for linear low energy transfer (LET) radiation built from low dose rates and whether they vary in terms of dose estimation. For that we did a search in the literature of all calibration curves produced with low dose rates and we simulated the dose estimation from pre-established dicentric's frequencies. The information on methodologies and cytogenetic results of each study were analyzed. As expected dose rate influence ß coefficients, especially at higher doses. However, we have seen that some doses were not statistically different but they should be, because there is a significant association between the productions of dicentrics and dose rate. This comparative study reinforced the robustness of the dicentric assay and its importance in biological dosimetry. We also emphasized that the dose rate was an important factor in dose estimations. Thus, intercomparison exercises should take into account the dose rates of the participating laboratories, because the dose rates might explain why some results of estimated doses fall outside the recommendations.

LBDNet interlaboratory comparison for the dicentric chromosome assay by digitized image analysis applying weighted robust statistical methods.

PURPOSE: This interlaboratory comparison was conducted to evaluate the performance of the Latin-American Biodosimetry Network (LBDNet) in analyzing digitized images for scoring dicentric chromosomes from in vitro irradiated blood samples. The exercise also assessed the use of weighted robust algorithms to compensate the uneven expertise among the participating laboratories. METHODS: Three sets of coded images obtained through the dicentric chromosome assay from blood samples irradiated at 1.5 Gy (sample A) and 4 Gy (sample B), as well as a non-irradiated whole blood sample (sample C), were shared among LBDNet laboratories. The images were captured using the Metafer4 platform coupled with the AutoCapt module. The laboratories were requested to perform triage scoring, conventional scoring, and dose estimation. The dose estimation was carried out using either their laboratory calibration curve or a common calibration curve. A comparative statistical analysis was conducted using a weighted robust Hampel algorithm and z score to compensate for uneven expertise in dicentric analysis and dose assessment among all laboratories. RESULTS: Out of twelve laboratories, one had unsatisfactory estimated doses at 0 Gy, and two had unsatisfactory estimated doses at 1.5 Gy when using their own calibration curve and triage scoring mode. However, all doses were satisfactory at 4 Gy. Six laboratories had estimated doses within 95% uncertainty limits at 0 Gy, seven at 1.5 Gy, and four at 4 Gy. While the mean dose for sample C was significantly biased using robust algorithms, applying weights to compensate for the laboratory's analysis expertise reduced the bias by half. The bias from delivered doses was only notable for sample C. Using the common calibration curve for dose estimation reduced the standard deviation (s*) estimated by robust methods for all three samples. CONCLUSIONS: The results underscore the significance of performing interlaboratory comparison exercises that involve digitized and electronically transmitted images, even when analyzing non-irradiated samples. In situations where the participating laboratories possess different levels of proficiency, it may prove essential to employ weighted robust algorithms to achieve precise outcomes.

Optimization of ablative dose for thyroid cancer

Esta investigación propone un protocolo de planificación individualizada de dosis ablativas basado en el metabolismo individual del paciente y en la medida de la masa de los remanescientes tiroideanos. Utilizando SPECT, el metabolismo de I-131 fue estudiado en 9 pacientes tiroidectomizados, y la actividad optima para la terapia fue calculada y comparada con la actividad fija establecida de 3.7 GBq (100 mCi), que és en general administrada. Fue observado que 78 por ciento de las pacientes podrian tener recibido actividades reduzidas de 131I (de 0.8-3.2 GBq (20-87 mCi)). Además, 33 por ciento destes pacientes podrian recibir actividades tan bajas que no necesitarian internamiento hospitalar. Visando facilitar los calculos de la actividad terapeutica optima de 131I hacia pacientes individuales, un programa de planificación de dosis simples y rápido fue criado (PlanDose). Este protocolo de cálculo de actividades de 131I específicas para el paciente permite una mejor determinación de la dosis ablativa necesaria en caso de pacientes con carcinoma diferenciado de la tiroide, y és un ejemplo de optimización de la práctica de protección radiologica.

This investigation proposes a protocol for planning of thyroid ablation therapy for individual patients, based on individual patient metabolic data and measured thyroid remnant masses. Using SPECT, I-131 uptake and clearance was studied in 9 patients who had undergone thyroidectomies, and the optimum activity for their therapy was calculated and compared to the established fixed activity of 3.7 GBq (100 mCi), which normally would have been assigned. It was observed that 7 of the patients could have received reduced activities of 131I (from 0.8-3.2 GBq (20-87 mCi)). In addition, 3 patients could have received low enough activities to have been discharged from the hospital. To facilitate the calculations of the optimum therapeutic activity of 131I for individual patients, a computer program was created (PlanDose). This protocol of calculated optimal patient-specific 131I activities allows a better determination of the necessary ablative dose for patients with differentiated carcinoma of the thyroid, and is an important example of optimization of the practice of radiation protection.