CT surveillance for type 1 autoimmune pancreatitis: cumulative radiation dose and diagnostic performance for disease relapse Journal: European Radiology. 2024 Nov. DOI: 10.1007/s00330-024-11161-0 Type 1 autoimmune pancreatitis is a pancreatic manifestation of immunoglobulin G4 (IgG4)-related disease. Despite initial remission following corticosteroid treatment (CST), relapses are common, with a recurrence rate of up to 33%. The 2022 Japanese consensus guidelines recommended that maintenance treatment should be continued for around 3 years even if the initial treatment achieved clinical complete remission, and continuous follow-up should be continued even after 3 years. Hence, once a clinical diagnosis of AIP is established, patients will inevitably undergo multiple radiological follow-ups. Particularly, CT and MRI are crucial for monitoring disease progression and recurrence. This retrospective study examines the cumulative radiation dose from CT during the follow-up of patients with type 1 AIP and evaluates the diagnostic performance of CT and MRI in detecting disease relapse. The authors evaluated 827 CT scans of 119 patients diagnosed with type AIP (72.5% males, average age 58.6 ± 10.5 years). The median follow-up duration for these patients was approximately 2.3 years (21 days to 9.2 years). The average cumulative radiation dose per patient was 51.2 ± 44.0 mSv, with a median dose of 37.5 mSv. This cumulative dose is notable, as it exceeds the annual dose limit recommended by international guidelines, particularly for patients undergoing long-term imaging follow-up. In fact, 11.3% of patients exceeded 100 mSv during follow-up, which raises concerns about the potential long-term risks of radiation exposure, such as cancer and genetic mutations. Among the patients with more than one year of follow-up, 52 patients (approximately 18.8%) had an average annual radiation dose greater than 20 mSv. This is significantly above the International Commission on Radiological Protection (ICRP) recommended limit. The diagnostic performance of CT in detecting AIP relapse was evaluated by comparing the results of follow-up CT scans to clinical and imaging-based diagnoses of relapse. A total of 39 relapses were observed in 37 patients. The sensitivity of CT for detecting AIP relapse was 64.1%, which indicates that CT missed a significant proportion of relapses. However, CT exhibited very high specificity (99.6%) and overall accuracy (97.0%), which suggests that it was very effective in ruling out relapses when the scan did not show any abnormalities. The positive predictive value (PPV) was 92.6%, meaning that when CT showed signs of relapse, it was highly likely to be accurate. The negative predictive value (NPV) was also high (97.3%), indicating that a negative CT scan was reliable in excluding the possibility of relapse. The authors also evaluated the performance of MRI in detecting AIP relapse in a secondary cohort. MRI for AIP relapse demonstrated significantly better sensitivity (90.5%), a slightly higher specificity (99.2%), and a comparable overall accuracy (98.5%). This suggests that MRI may be a preferable method for follow-up in patients with suspected recurrence, especially when initial CT scans are inconclusive. This study highlights several key findings regarding the use of CT in the long-term follow-up of AIP patients. While CT remains a widely used imaging technique for monitoring AIP, particularly due to its broad availability and shorter scan times, the study emphasizes its limitations in terms of sensitivity for detecting relapse. Although the overall accuracy of CT was high, the relatively low sensitivity (64.1%) for detecting AIP recurrence suggests that CT may miss relapses in some patients, particularly those with subtle or early changes. This is a critical concern for a disease like AIP, where relapses are common, and early detection is essential for timely intervention. | The cumulative radiation dose is another major concern raised by this study. Given the high number of follow-up scans that AIP patients typically undergo, the radiation exposure from multiple CT exams can accumulate to significant levels. As noted, some patients in this cohort exceeded 100 mSv, a dose threshold associated with an increased risk of radiation-related side effects, such as cancer. This risk is particularly relevant for younger patients who will undergo long-term surveillance over many years. The findings suggest that alternative imaging modalities, such as MRI, may offer a safer option for long-term follow-up, as MRI does not involve ionizing radiation and provides high sensitivity for detecting recurrence. The comparison between CT and MRI for detecting relapse in AIP patients further strengthens the argument for considering MRI as a primary follow-up modality. MRI’s ability to detect subtle pancreatic changes and its higher sensitivity for AIP relapse make it a valuable tool in clinical practice. The study results align with prior research indicating that MRI can provide superior soft-tissue contrast and better visualization of inflammatory changes in the pancreas, which may not be detectable on CT scans. However, despite its advantages, MRI comes with its own limitations, such as higher costs, longer scan times, and limited availability in some settings. Moreover, the study’s findings reinforce the importance of a balanced approach to imaging in AIP management. While CT may still be preferred in certain clinical scenarios (e.g., for patients with MRI contraindications, for emergency assessments, or where MRI is unavailable), the cumulative risks of radiation exposure necessitate a reevaluation of imaging strategies. A tailored, individualized follow-up approach that alternates between CT and MRI could minimize radiation risks while maintaining high diagnostic accuracy. Despite the strengths of this study, some limitations should be acknowledged. First, the retrospective design and the reliance on a single senior radiologist for clinical data review could introduce potential biases. Additionally, the absence of a standardized definition for AIP relapse across studies makes comparisons with other research challenging. Further prospective studies with larger, more diverse cohorts are needed to validate the findings and refine follow-up strategies for AIP patients. In conclusion, the study calls for a more thoughtful and individualized approach to AIP follow-up. While CT remains a useful tool in certain circumstances, the high cumulative radiation dose and the limitations in sensitivity for detecting relapse suggest that MRI may be a more appropriate choice for long-term follow-up, particularly when relapse is suspected or when reducing radiation exposure is a priority. Clinicians should consider the strengths and weaknesses of both imaging modalities and tailor follow-up strategies to each patient’s specific needs and circumstances. Dr. Francesco Gigante is a fourth-year Radiology resident at the University of Verona, Italy. He completed his undergraduate medical degree at "Tor Vergata, University of Rome". He has a wide range of interests in diagnostic imaging, especially regarding abdominal imaging and the hepatobiliary system. Comments may be sent to: gigante.fr@gmail.com |