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Abstract
We examined the dose of radiation received during diagnosis of lung cancer as this may add to the risk of a second primary cancer. Patients undergoing surgery (n=40) or (chemo)radiotherapy (n=40) received comparable doses (28.6 and 25.8 mSv, respectively), significantly higher than that for supportive care (n=40; 15.1 mSv). The effective dose of radiation received was higher for early stage disease than for those with metastatic disease. The mean lifetime attributable risk of malignancy for those receiving treatment with curative intent in our cohort was 0.059%, and lung-specific risk 0.019%.
- Lung Cancer
- Imaging/CT MRI etc
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Introduction
During work-up of patients with (suspected) lung cancer for treatment with curative intent, healthy tissues are exposed to ionising radiation. This may add to the risk of a future second primary cancer and is particularly pertinent to the growing number of younger long-term survivors. At present, the total radiation dose received by patients during diagnostic work-up is not monitored or restricted, and there remains a paucity of literature on the subject.
Given recent changes in investigation algorithms used in lung cancer1 and the importance of understanding the risks associated with ionising radiation, we sought to evaluate diagnostic radiation exposure in a cohort of patients investigated through the Papworth and Addenbrooke’s Thoracic Oncology Service.
Methods
The cumulative radiation dose received by patients undergoing investigation for treatment with curative intent for primary lung cancer at Papworth and Addenbrooke's Hospitals between December 2012 and March 2014 was calculated. Retrospective data were gathered from electronic reporting systems including patient demographics, stage and type of cancer, and participation in clinical studies involving ionising radiation (see online supplementary tables S1–S4). Information on all radiological investigations involving ionising radiation between the first targeted investigation and the start of definitive treatment was gathered. Similar data for a group of patients (n=40) undergoing best supportive care (BSC) were also collected. If data on individual studies were not available, an estimate derived from local diagnostic reference levels was used. The total effective radiation dose was calculated for each patient, and percentage lifetime attributable risk (LAR) estimated using conversion coefficients in HPA-CRCE-028 and HPA-CRCE-012, NRPB-W67 and ICRP106.2–5
supplementary data
Comparisons between groups were made using Student's t-test, with a value of p<0.05 considered significant.
Results
The mean cumulative dose of radiation received by 80 patients undergoing investigation for treatment with curative intent (surgery or radical (chemo)radiotherapy) was 27.6 mSv±0.9 (table 1). Patients in the surgical and (chemo)radiotherapy groups received comparable doses—surgery 28.6 mSv, (chemo)radiotherapy 25.8 mSv; p=0.89 (table 1 and figure 1). This was significantly higher than those who received BSC (n=40; 15.1 mSv±1.4; p<0.05). When stratified by the stage of disease (figure 2), the effective dose of radiation received was higher for early stage disease than for those with metastatic disease (μ=26.9 mSv for stage I, 24.6 mSv for stage II, 22.3 mSv for stage III and 14.4 mSv for stage IV). As might be expected, there was a correlation between body mass and effective dose (see online supplementary figure 1; r=0.44, p<0.05), but no significant correlation with patient age (see online supplementary figure 2; r=0.058, p=0.52). For patients undergoing treatment with curative intent, the median number (range) of investigations undertaken was CT staging 1 (0–4); CT head 1 (0–2); CT-guided biopsy 1 (0–3) and positron emission tomography (PET)-CT 1 (0–2) (see online supplementary table S5).
Effective dose of radiation received/mSv
Effective radiation dose (mSv) received by patients during diagnostic work-up stratified by surgical, (chemo)radiotherapy (CRT) and best supportive care (BSC) groups.
Effective radiation dose (mSv) received by patients during diagnostic work-up stratified by stage of disease.
The mean LAR of malignancy for those receiving treatment with curative intent was 0.059%, that is, 5.9 in 10 000 long-term survivors would be expected to develop a second primary cancer as a direct consequence of diagnostic imaging investigations. The lung-specific risk was 0.019% (table 2).
Lifetime added risk of malignancy/%
Discussion
Despite lung cancer being one of the most common cancers globally, there is a paucity of information on the usual radiation dose patients receive during diagnostic work-up. We have shown that the mean cumulative dose of radiation received by patients undergoing investigation for treatment with curative intent (surgery, radical (chemo)radiotherapy) is around 28 mSv substantially lower than that identified by Stiles et al 6 who found that in 94 patients, the 3-year median estimated dose was 84.0 mSv and that the highest dose occurred in the preoperative year. In any one year, 66% of their patients received more than 50 mSV, while 19% received over 100 mSv. Only one of our 80 patients exceeded 50 mSv. Our finding that the radiation dose received by those who ultimately received treatment with curative intent was significantly higher than the dose received for those treated with BSC is not unexpected. This is because those being assessed for treatment with curative intent underwent additional investigations including PET-CT and CT head, and some patients being assessed for surgical resection required coronary angiography and/or quantitative ventilation/perfusion scintigraphy. The overall reduction in radiation dose compared with the work by Stiles et al 6 is most likely due to improvements in radiation technology over the last decade, which allows equivalent imaging at lower radiation doses.
Although we have estimated the associated LAR of malignancy, this value remains difficult to interpret with regard to setting ‘limits’ of acceptability. Typically, LAR values are calculated in healthy subjects, but the effect of radiation exposure in a high-risk tobacco-exposed population may be greater. A number of factors should be considered. Age at presentation may be significant. For patients presenting over age 70, the risk of developing a second primary cancer as a result of previous radiation exposure is likely to be considerably lower than the risk conferred by previous/current cigarette smoking. However, for younger patients being treated with curative intent, thought should be given to LAR given that they will likely have longer life expectancy.
In conclusion, newer algorithms for investigating patients with suspected lung cancer, combined with improvements in imaging technology, have reduced the average radiation dose in patients receiving definitive treatment to 28 mSv. Although this is considerably lower than previous reports, it is still associated with a quantifiable mean LAR of malignancy of 0.059% in our patient cohort.
Footnotes
Contributors The original project was conceived by ERC. All authors developed the methodology. RA and KT collected data which were analysed by RA, RCR and ERC. RCR produced the first draft of the manuscript which was reviewed and approved by all.
Funding RCR is part-funded by the Cambridge Biomedical Research Centre and Cancer Research UK Cambridge Centre.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.