Quantitative assessment of provability of radiation-related cancers considering unavoidable existence of unadjusted risk factors

The 2021 Bo Lindell Lecture: Inclusive, accountable, transparent: the direction we should take for the benefit of present and future generations

The International Commission on Radiological Protection (ICRP) is recognised as the de-facto world authority in the field of radiological protection. The ICRP Recommendations have been used as a basis for regulations and policy in almost every country, and with the current review and revision of the System of Radiological Protection, it will continue to make significant contributions in radiation safety for patients, workers, the public, and the environment. In a society undergoing significant change, it is necessary to give careful thought to which groups will be perceived as authoritative organisations by the constituents of the future. The ideal form of an authoritative organisation in the new society of the future is to continue to show how it came to make such recommendations, how it reflected the opinions of interested parties in the process, and how it discloses its records with as much transparency as possible. The question now is what we must do to ensure that decision-making advances in a way that not only makes sense to the present generation, but will be easily consumed by future generations. The path that ICRP is taking to formulate the next set of General Recommendations is doing just that, in line with the key procedural values of INCLUSIVE, ACCOUNTABLE, AND TRANSPARENT.

Benefits of Low-Dose CT Scan of Head for Patients With Intracranial Hemorrhage

Objectives:

For patients with intracranial hemorrhage (ICH), routine follow-up computed tomography (CT) scans are typically required to monitor the progression of intracranial pathology. Remarkable levels of radiation exposure are accumulated during repeated CT scan. However, the effects and associated risks have still remained elusive. This study presented an effective approach to quantify organ-specific radiation dose of repeated CT scans of head for patients with ICH. We also indicated whether a low-dose CT scan may reduce radiation exposure and keep the image quality highly acceptable for diagnosis.

Methods:

Herein, 72 patients with a history of ICH were recruited. The patients were divided into 4 groups and underwent CT scan of head with different tube current–time products (250, 200, 150, and 100 mAs). Two experienced radiologists visually rated scores of quality of images according to objective image noise, sharpness, diagnostic acceptability, and artifacts due to physiological noise on the same workstation. Organ-/tissue-specific radiation doses were analyzed using Radimetrics.

Results:

In conventional CT scan group, signal to noise ratio (SNR) and contrast to noise ratio (CNR) of ICH images were significantly higher than those in normal brain structures. Reducing the tube current–time product may decrease the image quality. However, the predilection sites for ICH could be clearly identified. The SNR and CNR in the predilection sites for ICH were notably higher than other areas. The brain, eye lenses, and salivary glands received the highest radiation dose. Reducing tube current–time product from 250 to 100 mA can significantly reduce the radiation dose.

Discussion:

We demonstrated that low-dose CT scan of head can still provide reasonable images for diagnosing ICH. The radiation dose can be reduced to ∼45% of the conventional CT scan group.

Case Study of the Minimum Provable Risk Considering the Variation in Background Risk: Effect of Residual Risk on Epidemiological Studies and a Comparative Assessment of Fatal Disease Risk Due to Radiation Exposure

In order to prove a small increment in a risk of concern in an epidemiological study, a large sample of a population is generally required. Since the background risk of an end point of interest, such as cancer mortality, is affected by various factors, such as lifestyle (diet, smoking, etc.), adjustment for such factors is necessary. However, it is impossible to inclusively and completely adjust for such factors; therefore, uncertainty in the background risk remains for control and exposed populations, indicating that there is a minimum limit to the lower bound for the provable risk regardless of the sample size. In this case study, we developed and discussed the minimum provable risk considering the uncertainty in background risk for hypothetical populations by referring to recent Japanese statistical information to grasp the extent of the minimum provable risk. Risk of fatal diseases due to radiation exposure, which has recently been the focus of radiological protection, was also examined by comparative assessment of the minimum provable risk for cancer and circulatory diseases. It was estimated that the minimum provable risk for circulatory disease mortality was much greater than that for cancer mortality, approximately five to seven times larger; circulatory disease mortality is more difficult to prove as a radiation risk than cancer mortality under the conditions used in this case study.

Examining the association of body mass index and the depth of epidural space, radiation dose exposure and fluoroscopic screening time during transforaminal nerve block injection: a retrospective cohort study

OBJECTIVE

The primary objective of this study was to examine the association between body mass index (BMI) and the depth of tissue overlying the epidural space. Secondary objectives examined the association between BMI and (1) radiation dose exposure and (2) fluoroscopic screening time during transforaminal nerve block (TFNB) injections.

METHODOLOGY

This is a retrospective cohort study including patients aged ≥ 16 years who underwent unilateral single-level TFNB in a single centre over a 28-month period, by a single spinal orthopaedic surgeon. Demographic data, BMI (kg/m²), fluoroscopic screening time (seconds) and radiation dose exposure (centi-gray per square centimetre squared (cGy-cm²)) were recorded. Exposure of interest: BMI.

PRIMARY OUTCOME

depth of epidural space.

SECONDARY OUTCOMES

(1) radiation dose exposure, (2) fluoroscopic screening time. Descriptive statistics for study participants' demographics are presented. Spearman's rank (r) coefficient and linear regression analysis was performed examining the association between BMI and the outcome measures.

RESULTS

A total of 362 patients met inclusion criteria; n = 45 patients were excluded due to incomplete data, final analysis included 317 patients. Mean age was 62.6 years (IQR 53-74). Male:female ratio was 37.9% (n = 120):62.1%(n = 197). Mean BMI was 26.9 kg/m² (IQR 24.4-28.9 kg/m²). Following adjustment for age, gender and spinal comorbidities there is a statistically significant association between BMI and the depth of tissue overlying the epidural space (adjusted coefficient 2.41, (95% CI (2.14, 2.68), p < 0.001)). We also found a significant association between BMI and both secondary outcomes, radiation dose exposure (adjusted coefficient 1.45, (95% CI (0.84, 2.06), p < 0.001)) and fluoroscopic screening time (adjusted coefficient 0.11, (95% CI (0.02, 0.20), p = 0.02)).

CONCLUSION

This study has demonstrated a significant association between increasing BMI and increased depth of the epidural space. Furthermore, significant associations between increasing BMI, radiation dose exposure and fluoroscopy screening time have been identified. BMI may represent a modifiable risk factor with a view to decreasing patient exposure to medical ionised radiation.

Current situations and discussions in Japan in relation to the new occupational equivalent dose limit for the lens of the eye

Since the International Commission on Radiological Protection recommended reducing the occupational equivalent dose limit for the lens of the eye in 2011, there have been extensive discussions in various countries. This paper reviews the current situation in radiation protection of the ocular lens and the discussions on the potential impact of the new lens dose limit in Japan. Topics include historical changes to the lens dose limit, the current situation with occupational lens exposures (e.g., in medical workers, nuclear workers, and Fukushima nuclear power plant workers) and measurements, and the current status of biological studies and epidemiological studies on radiation cataracts. Our focus is on the situation in Japan, but we believe such information sharing will be useful in many other countries.

Selective Shielding of Bone Marrow: An Approach to Protecting Humans from External Gamma Radiation

The current feasibility of protecting emergency responders through bone marrow selective shielding is highlighted in the recent OECD/NEA report on severe accident management. Until recently, there was no effective personal protection from externally penetrating gamma radiation. In Chernobyl, first-responders wore makeshift lead sheeting, whereas in Fukushima protective equipment from gamma radiation was not available. Older protective solutions that use thin layers of shielding over large body surfaces are ineffective for energetic gamma radiation. Acute exposures may result in Acute Radiation Syndrome where the survival-limiting factor up to 10 Gy uniform, homogeneous exposure is irreversible bone marrow damage. Protracted, lower exposures may result in malignancies of which bone marrow is especially susceptible, being compounded by leukemia's short latency time. This highlights the importance of shielding bone marrow for preventing both deterministic and stochastic effects. Due to the extraordinary regenerative potential of hematopoietic stem cells, to effectively prevent the deterministic effects of bone marrow exposure, it is sufficient to protect only a small fraction of this tissue. This biological principle allows for a new class of equipment providing unprecedented attenuation of radiation to select marrow-rich regions, deferring the hematopoietic sub-syndrome of Acute Radiation Syndrome to much higher doses. As approximately half of the body's active bone marrow resides within the pelvis region, shielding this area holds great promise for preventing the deterministic effects of bone marrow exposure and concomitantly reducing stochastic effects. The efficacy of a device that selectively shields this region and other radiosensitive organs in the abdominal area is shown here.