The Role of Radiation Induced Injury on Lung Cancer

Meeting report: the 66th annual meeting of the Japanese Radiation Research Society in Tokyo, Japan, 6-8 November 2023

The 66th Annual Meeting of the Japanese Radiation Research Society took place in Tokyo, Japan, from 6 to 8 November 2023. The meeting covered a wide range of radiation research topics, including basic mechanisms involved in radiation effects, translational research, and epidemiology. Some sessions were jointly organized with the International Commission on Radiological Protection (ICRP). Here, we report on some plenary and keynote talks presented at the meeting.

Using cryoprobes of different sizes combined with cone-beam computed tomography-derived augmented fluoroscopy and endobronchial ultrasound to diagnose peripheral pulmonary lesions: a propensity-matched study

BACKGROUND

Endobronchial ultrasound (EBUS) and cone-beam computed tomography-derived augmented fluoroscopy (CBCT-AF) are utilized for the diagnosis of peripheral pulmonary lesions (PPLs). Combining them with transbronchial cryobiopsy (TBC) can provide sufficient tissue for genetic analysis. However, cryoprobes of different sizes have varying degrees of flexibility, which can affect their ability to access the target bronchus and potentially impact the accuracy. The aim of this study was to compare the diagnostic efficacy of cryoprobes of varying sizes in CBCT-AF and EBUS for the diagnosis of PPLs.

METHODS

Patients who underwent endobronchial ultrasound-guided transbronchial biopsy (EBUS-TBB) and TBC combined with CBCT-AF for PPLs diagnosis between January 2021 and May 2022 were included. Propensity score matching and competing-risks regression were utilized for data analysis. Primary outcome was the diagnostic accuracy of TBC.

RESULTS

A total of 284 patients underwent TBC, with 172 using a 1.7-mm cryoprobe (1.7 group) and 112 using a 1.1-mm cryoprobe (1.1 group). Finally, we included 99 paired patients following propensity score matching. The diagnostic accuracy of TBC was higher in the 1.1 group (80.8% vs. 69.7%, P = 0.050), with a similar rate of complications. Subgroup analysis also revealed that the 1.1 group had better accuracy when PPLs were located in the upper lobe (85.2% vs. 66.1%, P = 0.020), when PPLs were smaller than 20 mm (78.8% vs. 48.8%, P = 0.008), and when intra-procedural CBCT was needed to be used (79.5% vs. 42.3%, P = 0.001). TBC obtained larger specimens than TBB in both groups. There is still a trend of larger sample size obtained in the 1.7 group, but there is no statistically different between our two study groups (40.8 mm2 vs. 22.0 mm2, P = 0.283).

CONCLUSIONS

The combination of TBC with CBCT-AF and EBUS is effective in diagnosing PPLs, and a thin cryoprobe is preferred when the PPLs located in difficult areas.

How the Science of Radiation Biology Can Help Reduce the Crippling Fear of Low-level Radiation

ABSTRACT

The fear of radiation has been present almost since the discovery of radiation, but has intensified since the "dawn of the atomic age" over 75 y ago. This fear has often served as an impediment to the safe and beneficial uses of radiation and radioactive material. The underlying causes of such fear are varied, can be complex, and are often not associated with any scientific knowledge or understanding. The authors believe that a clear understanding of the current scientific knowledge and understanding of the effects of radiation exposure may be useful in helping to allay some of the fear of radiation. This manuscript attempts to (1) address several scientific questions that we believe have contributed to the fear of radiation, (2) review the data derived from research that can be used to address these questions, and (3) summarize how the results of such scientific research can be used to help address the fear of low-dose and low-dose-rate radiation. Several examples of how fear of radiation has affected public perception of radiological events are discussed, as well as a brief history of the etiology of radiation fear. Actions needed to reduce the public fear of radiation and help fulfill the full societal benefits of radiation and radioactive materials are suggested.

Radiation dose rate effects: what is new and what is needed?

Despite decades of research to understand the biological effects of ionising radiation, there is still much uncertainty over the role of dose rate. Motivated by a virtual workshop on the "Effects of spatial and temporal variation in dose delivery" organised in November 2020 by the Multidisciplinary Low Dose Initiative (MELODI), here, we review studies to date exploring dose rate effects, highlighting significant findings, recent advances and to provide perspective and recommendations for requirements and direction of future work. A comprehensive range of studies is considered, including molecular, cellular, animal, and human studies, with a focus on low linear-energy-transfer radiation exposure. Limits and advantages of each type of study are discussed, and a focus is made on future research needs.

McIntyre Powder and its potential contributions to cardiovascular disease risk: A literature review through the McIntyre Powder historical lens

McIntyre Powder (MP) is a fine aluminum powder that was developed to prevent silicosis in gold and uranium mine workers in Ontario, Canada, and was administered to miners there from 1943 to 1979. Mine workers were exposed to high concentrations (35.6 mg/m³) of MP for approximately 10 min before every work shift. Contemporary physical and chemical characterizations of this powder have revealed that 12% of the powder is in the ultrafine particle size‐range (nanoparticles); and the remaining 88%, in the fine particulate size range (below 2.5 µm in diameter). The confluence of ultrafine particulate (UFP) composition and high airborne concentration of MP would be expected to overwhelm the defense mechanisms of the lung and increase the lung dust burden of the mine worker exposed to respirable dust in the mine. Published studies revealing associations between air pollution particulates and increased risk for cardiovascular disease (CVD) shown a dose–response relationship with ambient PM_2.5 and UFP and suggest that miners exposed to MP may also be at increased risk of CVD. The historical perspective of the use of MP in northern Ontario hard‐rock mines and its potential implications for CVD in exposed mine workers are discussed.

Rapid on-site cytologic evaluation by pulmonologist improved diagnostic accuracy of endobronchial ultrasound-guided transbronchial biopsy

BACKGROUND/PURPOSE

Rapid on-site cytologic evaluation (ROSE) has been shown to improve the diagnostic accuracy of endobronchial ultrasound-guided transbronchial biopsy (EBUS-TBB). However, ROSE by a cytopathologist or cytotechnologist is not always available during the procedure. The purposes of this study were to verify that a pulmonologist, after receiving training in cytology, could accurately assess an EBUS-TBB specimen on-site, and to evaluate the contribution of ROSE to EBUS-TBB.

METHODS

A retrospective chart review of patients who underwent EBUS-TBB for diagnosis of peripheral pulmonary lesions (PPLs) from January 2014 to June 2017 was performed. PPLs without a malignant diagnosis were excluded. The ROSE result determined by a pulmonologist was compared to the formal imprint cytologic report and pathologic report. The diagnostic accuracy of EBUS-TBB was also compared between those with and without ROSE.

RESULTS

Two hundred ninety-three patients who underwent 336 EBUS-TBB procedures for PPL diagnosis and were found to have proven malignancy were enrolled. Eighty-six procedures were performed with ROSE. With the formal imprint cytologic diagnosis as the standard, ROSE had 96.9% sensitivity, 68.2% specificity, 89.9% positive predictive value (PPV), 88.2% negative predictive value (NPV), and 89.5% diagnostic accuracy. With the formal pathologic result as the standard, ROSE had 88.2% sensitivity, 80% specificity, 97.1% PPV, 47.1% NPV, and 87.2% diagnostic accuracy, respectively. The diagnostic accuracy was significantly higher when ROSE was performed during EBUS-TBB (88.4% vs 68.0%, P < 0.001).

CONCLUSION

A trained pulmonologist can interpret adequately cytologic smears on-site and effectively improve the accuracy of EBUS-TBB in the diagnosis of PPLs.

A Nontarget Mechanism to Explain Carcinogenesis Following α-Irradiation

This commentary highlights the published data on the metabolic processes that lead to the development of cancer following intakes of asbestos and chemical agents. Following exposure to both, the key initiating event is cell injury leading to cell death that may further lead to inflammation, fibrosis, and cancer. Since α-particle transits also kill cells, it is suggested that cell death and inflammation will also trigger carcinogenesis within tissues irradiated by these particles. Such an explanation would be consistent with the inflammation and fibrosis seen in tumor-bearing tissues irradiated by radon-222, radium-226, thorium-232, plutonium-239, and other α-emitting radionuclides. It would also provide an explanation for dose-related changes in latency and in the similar dose-responses for the same tissue in differently sized species.

A Critical Assessment of the Linear No-Threshold Hypothesis: Its Validity and Applicability for Use in Risk Assessment and Radiation Protection

The Society of Nuclear Medicine and Molecular Imaging convened a task group to examine the evidence for the risk of carcinogenesis from low-dose radiation exposure and to assess evidence in the scientific literature related to the overall validity of the linear no-threshold (LNT) hypothesis and its applicability for use in risk assessment and radiation protection. In the low-dose and dose-rate region, the group concluded that the LNT hypothesis is invalid as it is not supported by the available scientific evidence and, instead, is actually refuted by published epidemiology and radiation biology. The task group concluded that the evidence does not support the use of LNT either for risk assessment or radiation protection in the low-dose and dose-rate region.

Modeling Cell Reactions to Ionizing Radiation: From a Lesion to a Cancer

This article focuses on the analytic modeling of responses of cells in the body to ionizing radiation. The related mechanisms are consecutively taken into account and discussed. A model of the dose- and time-dependent adaptive response is considered for 2 exposure categories: acute and protracted. In case of the latter exposure, we demonstrate that the response plateaus are expected under the modelling assumptions made. The expected total number of cancer cells as a function of time turns out to be perfectly described by the Gompertz function. The transition from a collection of cancer cells into a tumor is discussed at length. Special emphasis is put on the fact that characterizing the growth of a tumor (ie, the increasing mass and volume), the use of differential equations cannot properly capture the key dynamics-formation of the tumor must exhibit properties of the phase transition, including self-organization and even self-organized criticality. As an example, a manageable percolation-type phase transition approach is used to address this problem. Nevertheless, general theory of tumor emergence is difficult to work out mathematically because experimental observations are limited to the relatively large tumors. Hence, determination of the conditions around the critical point is uncertain.

The impact of dose rate on the linear no threshold hypothesis

The goal of this manuscript is to define the role of dose rate and dose protraction on the induction of biological changes at all levels of biological organization. Both total dose and the time frame over which it is delivered are important as the body has great capacity to repair all types of biological damage. The importance of dose rate has been recognized almost from the time that radiation was discovered and has been included in radiation standards as a Dose, Dose Rate, Effectiveness Factor (DDREF) and a Dose Rate Effectiveness Factor (DREF). This manuscript will evaluate the role of dose rate at the molecular, cellular, tissue, experimental animals and humans to demonstrate that dose rate is an important variable in estimating radiation cancer risk and other biological effects. The impact of low-dose rates on the Linear-No-Threshold Hypothesis (LNTH) will be reviewed since if the LNTH is not valid it is not possible to calculate a single value for a DDREF or DREF. Finally, extensive human experience is briefly reviewed to show that the radiation risks are not underestimated and that radiation at environmental levels has limited impact on total human cancer risk.

The influence of changing dose rate patterns from inhaled beta-gamma emitting radionuclide on lung cancer

Purpose:

Dose and dose rate are both appropriate for estimating risk from internally deposited radioactive materials. We investigated the role of dose rate on lung cancer induction in Beagle dogs following a single inhalation of strontium-90 (⁹⁰Sr), cerium-144 (¹⁴⁴Ce), yttrium-91 (⁹¹Y), or yttrium-90 (⁹⁰Y). As retention of the radionuclide is dependent on biological clearance and physical half-life a representative quantity to describe this complex changing dose rate is needed.

Materials and methods:

Data were obtained from Beagle dog experiments from the Inhalation Toxicology Research Institute. The authors selected the dose rate at the effective half-life of each radionuclide (DR_ef).

Results:

Dogs exposed to DRef (1–100 Gy/day) died within the first year after exposure from acute lung disease. Dogs exposed at lower DRef (0.1–10 Gy/day) died of lung cancer. As DR_ef decreased further (<0.1 Gy/day ⁹⁰Sr, <0.5 Gy/day ¹⁴⁴Ce, <0.9 Gy/day ⁹¹Y, <8 Gy/day ⁹⁰Y), survival and lung cancer frequency were not significantly different from control dogs.

Conclusion:

Radiation exposures resulting from inhalation of beta-gamma emitting radionuclides that decay at different rates based on their effective half-life, leading to different rates of decrease in dose rate and cumulative dose, is less effective in causing cancer than acute low linear energy transfer exposures of the lung.