Organ doses and cancer risk assessment in patients exposed to high doses from recurrent CT exams

Characterizing imaging radiation risk in a population of 8918 patients with recurrent imaging for a better effective dose

An updated extension of effective dose was recently introduced, namely relative effective dose ( E r ), incorporating age and sex factors. In this study we extended E r application to a population of about 9000 patients who underwent multiple CT imaging exams, and we compared it with other commonly used radiation protection metrics in terms of their correlation with radiation risk. Using Monte Carlo methods, E r , dose-length-product based effective dose ( E DLP ), organ-dose based effective dose ( E OD ), and organ-dose based risk index ( RI ) were calculated for each patient. Each metric's dependency to RI was assessed in terms of its sensitivity and specificity. E r showed the best sensitivity, specificity, and agreement with RI (R2 = 0.97); while E DLP yielded the lowest specificity and, along with E OD , the lowest sensitivity. Compared to other metrics, E r provided a closer representation of patient and group risk also incorporating age and sex factors within the established framework of effective dose.

Evaluation of patient radiation dose and risk of cancer from CT examinations

Computed tomography (CT) examinations have been increasingly requested and become the major sources of patient exposure. The cancer risk from CT scans is contingent upon the amount of absorbed dose of organs. This study aims to determine the organ doses and risk of cancer incidence and mortality from CT examinations at high dose (cumulative effective dose, CED ≥ 100 mSv) in a single day to low dose (CED < 100 mSv) from common CT procedures. Data were gathered from two academic centers of patients aged 15 to 75 years old performed CT examinations during the period of 5 years. CED and organ dose were calculated using Monte Carlo simulation software. Lifetime attributable risk (LAR) was determined following Biological Effects of Ionizing Radiation (BEIR) VII report based on life table and baseline cancer rates of Thai population. At high dose, the highest LAR for breast cancer incidence in young female was 82 per 100,000 exposed patients with breast dose of 148 mGy (CT whole abdomen). The highest LAR for liver cancer incidence in male patient was 72 per 100,000 with liver dose of 133 mGy (multiple CT scans). At low dose, the highest average LAR for breast cancer incidence in young female was 23 per 100,000 while for liver cancer incidence in male patients was 22 per 100,000 (CTA whole aorta). Even though the LAR of cancer incidence and mortality was less than 100 per 100,000, they should not be neglected. The risk of cancer incidence may be increased in later life, particularly in young patients.

Is a one percent occurrence of high-dose patients significant?

Risk-free society is utopian. We come across risks in everyday life, and we use probabilities to get a feel of how risky a situation is. Risk probability numbers of around 1% are comforting, but an intercomparison of numbers among various low risks in popular situations can be enlightening. In this article, we compare risks of complications or death in several surgeries and risks in commercial air travel with risks for patients getting cumulative effective dose (CED) of 100 mSv or more, as the latter is a hot and controversial topic currently. The analysis shows that many common surgeries are a few tens or hundreds of times less risky than the risk from a 100 mSv dose, even though the former often frightens us more. Despite there being a much higher chance of developing cancer from radiation than being involved in a commercial plane accident, there is much less emphasis on patient radiation safety than aviation safety. Further, a look at the system of control on prescription drugs indicates that there is much to learn for policy planning. This analysis may help the International Commission on Radiological Protection (ICRP) in their review of recommendations.

Cumulative Effective Dose During Fluoroscopically Guided Interventions (FGI): Analysis of More Than 5000 FGIs in a Single European Center

BACKGROUND

The number of fluoroscopically guided interventions (FGI) has increased significantly over time. However, little attention has been paid to possible stochastic radiation effects. The aim of this retrospective study was to investigate the number of patients who received cumulative effective doses over 100 mSv during FGI procedures.

MATERIAL AND METHODS

Five thousand five hundred and fifty four classified FGI procedures were included. Radiation dose data, retrieved from an in-house-dose-management system, was analysed. Effective doses and cumulative effective doses (CED) were calculated. Patients who received a CED > 100 mSv were identified. Radiology reports, patient age, imaging and clinical data of these patients were used to identify reasons for CED ≥ 100 mSv.

RESULTS

One Hundred and thirty two (41.1% female) of 3981 patients received a CED > 100 mSy, with a mean CED of 173.5 ± 84.5 mSv. Mean age at first intervention was 66.1 ± 11.7 years. 81 (61.4%) of 132 were older than 64 years, one patient was < 30 years. 110 patients received ≥ 100 mSv within one year (83.4%), through FGIs: EVAR, pelvic/mesenteric interventions (stent or embolization), hepatic interventions (chemoembolization, TIPSS), embolization of cerebral aneurysms or arterio-venous-malformations.

CONCLUSIONS

Substantial CED may occur in a small but not ignorable fraction of patients (~ 3%) undergoing FGIs. Approximately 2/3rd of patients may most likely not encounter radiation-related stochastic effects due to life-threatening diseases and age at first treatment > 65 years but 1/3rd may. Patients undergoing more than one FGI (77%) carry a higher risk of accumulating effective doses > 100 mSv. Remarkably, 23% received a mean CED 162.2 ± 72.3 mSv in a single procedure.

Estimation of the Added Cancer Risk Derived From EVAR and CTA Follow-Up

OBJECTIVE

The aim of this study was to assess the risk of radiation-induced cancer development in patients that have undergone an infrarenal EVAR, stratifying the relative contributions of the procedure and the preoperative and postoperative CTAs.

METHODS AND MATERIALS

The organ-specific absorbed radiation doses from CTA and the EVAR procedure were estimated from the radiation exposures of 95 and 45 male patients, respectively. Lifetime attributable risk (LAR) cancer predictions were calculated for 14 different organs. Life expectancy was assumed from a previous cohort of patients undergoing infra-renal EVAR.

RESULTS

The calculated total excess cancer risk was 0.0046, ie, 1 out of 220 patients will develop a neoplasm after being exposed to the ionizing radiation from the preoperative CTA, the EVAR and annual CTA examinations for 15 years. The procedure and the preoperative CTA contributed with 38% of the total excess risk, while the rest was derived from the follow-up. If the entire CTA based follow-up would have been eliminated, an excess risk of 0.0018 (1/560) would remain.

CONCLUSIONS

1 out of 219 patients who have undergone EVAR of an infra-renal AAA have a lifetime risk of developing cancer secondary to the radiation exposures related to the procedure and the CTAs used preoperatively and during follow-up. This risk derives mostly from the yearly postoperative CTAs, underlining the potential benefits of reducing or replacing their use.

CLINICAL IMPACT

A simulation-based estimation reinforced the potential deleterious effects of the radiation exposure for patients undergoing Endovascular Aneurysm Repair (EVAR) of Abdominal Aortic Aneurysms (AAA) and subsequently followed by yearly Computer Tomography Angiographies (CTAs). The risk could be as high as 1 out 219 patients developing a neoplasm after 15 years. The largest exposure derives from the follow-up CTAs and efforts to minimize their use as well as the intraoperative radiation are greatly needed. The simulation-based estimations done in this study reinforce potential deleterious effects of the radiation exposure for patients undergoing EVAR of AAA. Efforts should be done to minimize the intraoperative radiation and the number of CTAs used during follow-up.

Real-time, acquisition parameter-free voxel-wise patient-specific Monte Carlo dose reconstruction in whole-body CT scanning using deep neural networks

OBJECTIVE

We propose a deep learning-guided approach to generate voxel-based absorbed dose maps from whole-body CT acquisitions.

METHODS

The voxel-wise dose maps corresponding to each source position/angle were calculated using Monte Carlo (MC) simulations considering patient- and scanner-specific characteristics (SP_MC). The dose distribution in a uniform cylinder was computed through MC calculations (SP_uniform). The density map and SP_uniform dose maps were fed into a residual deep neural network (DNN) to predict SP_MC through an image regression task. The whole-body dose maps reconstructed by the DNN and MC were compared in the 11 test cases scanned with two tube voltages through transfer learning with/without tube current modulation (TCM). The voxel-wise and organ-wise dose evaluations, such as mean error (ME, mGy), mean absolute error (MAE, mGy), relative error (RE, %), and relative absolute error (RAE, %), were performed.

RESULTS

The model performance for the 120 kVp and TCM test set in terms of ME, MAE, RE, and RAE voxel-wise parameters was  - 0.0302 ± 0.0244 mGy, 0.0854 ± 0.0279 mGy,  - 1.13 ± 1.41%, and 7.17 ± 0.44%, respectively. The organ-wise errors for 120 kVp and TCM scenario averaged over all segmented organs in terms of ME, MAE, RE, and RAE were  - 0.144 ± 0.342 mGy, and 0.23 ± 0.28 mGy,  - 1.11 ± 2.90%, 2.34 ± 2.03%, respectively.

CONCLUSION

Our proposed deep learning model is able to generate voxel-level dose maps from a whole-body CT scan with reasonable accuracy suitable for organ-level absorbed dose estimation.

CLINICAL RELEVANCE STATEMENT

We proposed a novel method for voxel dose map calculation using deep neural networks. This work is clinically relevant since accurate dose calculation for patients can be carried out within acceptable computational time compared to lengthy Monte Carlo calculations.

KEY POINTS

• We proposed a deep neural network approach as an alternative to Monte Carlo dose calculation. • Our proposed deep learning model is able to generate voxel-level dose maps from a whole-body CT scan with reasonable accuracy, suitable for organ-level dose estimation. • By generating a dose distribution from a single source position, our model can generate accurate and personalized dose maps for a wide range of acquisition parameters.

Rhodamine-Conjugated Anti-Stokes Gold Nanoparticles with Higher ROS Quantum Yield as Theranostic Probe to Arrest Cancer and MDR Bacteria

Photodynamic therapy (PDT) has recently become significant as a clinical modality for cancer therapy and multidrug-resistant (MDR) infections, replacing conventional chemotherapy and radiation therapy protocols. PDT involves the excitation of certain nontoxic molecules called photosensitizers (PS), applying a specific wavelength of light to generate reactive oxygen species (ROS) to treat cancer cells and other pathogens. Rhodamine 6G (R6G) is a well-known laser dye with poor aqueous solubility, and lower sensitivity poses an issue in using PS for PDT. Nanocarrier systems are needed to deliver R6G to cancer targets since PDT requires a higher accumulation of PS. It was found that R6G-conjugated gold nanoparticles (AuNP) have a higher ROS quantum yield of 0.92 compared to 0.3 in an aqueous R6G solution, increasing their potency as PS. Cytotoxicity assessment on A549 cells and antibacterial assay on MDR Pseudomonas aeruginosa collected from a sewage treatment plant are the evidence to support efficient PDT. In addition to their enhanced quantum yields, the decorated particles are effective in generating fluorescent signals that can be used for cellular imaging and real-time optical imaging, and the presence of AuNP is a valuable addition to CT imaging. Furthermore, the fabricated particle exhibits anti-Stokes properties, which makes it suitable for use as a background-free biological imaging agent. As a result, R6G-conjugated AuNP is an effective theranostic agent that prevents the progression of cancer and MDR bacteria, along with contrasting abilities in medical imaging with minimal toxicity observed in in vitro and in vivo assays using zebrafish embryos.

Diagnostic reference level quantities for adult chest and abdomen-pelvis CT examinations: correlation with organ doses

OBJECTIVES

To evaluate correlations between DRL quantities (DRLq) stratified into patient size groups for non-contrast chest and abdomen-pelvis CT examinations in adult patients and the corresponding organ doses.

METHODS

This study presents correlations between DRLq  (CTDI_vol, DLP and SSDE) stratified into patient size ranges and corresponding organ doses shared in four groups: inside, peripheral, distributed and outside. The demographic, technical and dosimetric parameters were used to identify the influence of these quantities in organ doses. A robust statistical method was implemented in order to establish these correlations and its statistical significance.

RESULTS

Median values of the grouped organ doses are presented according to the effective diameter ranges. Organ doses in the regions inside the imaged area are higher than the organ doses in peripheral, distributed and outside regions, excepted to the peripheral doses associated with chest examinations. Different levels of statistical significance between organ doses and the DRLq were presented.

CONCLUSIONS

Correlations between DRLq and target-organ doses associated with clinical practice can support guidance's to the establishment of optimization criteria. SSDE demonstrated to be significant in the evaluation of organ doses is also highlighted. The proposed model allows the design of optimization actions with specific risk-reduction results.

Patient effective dose and radiation biological risk in the chest and abdominopelvic computed tomography

The incidence and mortality (per 100,000) rates in chest CT are highest for the lungs and breasts (incidence: lung = 116, breast = 98.64; mortality: lung = 113.43, breast = 49.72). Abdominopelvic CT scans showed the highest incidence for stomach (79.57), colon (62.86), bladder (48.69), and liver (28.63), respectively. Mortality is highest for the bladder (80.44), stomach (72.43), colon (69.02), and liver (63.78), respectively. This study helps to better understand the concept of radiation dose and the numbers reported as organ dose and effective dose and identify the probability of the stochastic effect.

Patients undergoing multiple 18F-FDG PET/CT exams: Assessment of frequency, dose and disease classification

OBJECTIVE

To analyse the frequency, demographics, primary disease and cumulative effective dose of patients undergoing two or more 18F-FDG PET/CT examinations in a year.

METHODS

In a retrospective study performed at a tertiary-care hospital, patients who underwent ≥2 18F-FDG PET/CT scans in a calendar year were identified for two consecutive years. The CT radiation dose was calculated using dose-length-product and sex-specific conversion factors. The primary malignancy of patients was retrieved from electronic medical records.

RESULTS

10,714 18F-FDG PET/CT exams were performed for 6,831 unique patients in 2 years, yielding an average of 1.6 exams per patient. The maximum number of 18F-FDG PET/CT examinations any patient underwent in a single year was seven. 20.9% patients had ≥2 18F-FDG PET/CT exams in any single year. Thirty nine percent patients in the cohort were below 60 years age. The median dose for 18F-FDG PET/CT examination was 25.1 mSv and maximum value reaching 1.7 to 2.9 times the median value. Cumulative effective dose (CED) was≥100 mSv in 12-13% of the patients. The cumulative dose for both years combined demonstrated the 25th percentile, 50th percentile and 75th percentile as well as the mean to be over 100 mSv, with the 25th percentile being 109 mSv. The dominant primary malignancies contributing to serial 18F-FDG PET/CTs in decreasing frequency were melanoma, non-Hodgkin's lymphoma (NHL), gastrointestinal cancer, breast cancer and Hodgkin's lymphoma.

CONCLUSIONS

A sizeable number of patients undergo≥2 18F-FDG PET/CT exams with one out of every eight patients receiving cumulative dose≥100 mSv and that includes patients with long-life expectancy.

ADVANCES IN KNOWLEDGE

The study found that one of five patients had≥2 18F-FDG PET/CT exams in a calendar year, one of four patients in two years and one of eight patients received cumulative dose≥100 mSv. Top malignancies associated with serial imaging in decreasing order of frequency included melanoma, non-Hodgkin's lymphoma (NHL), gastrointestinal cancer, breast cancer and Hodgkin's lymphoma.