Patient-size based dose optimization in projection radiography examinations: A BMI-guided approach

Purpose

The increasing prevalence of obesity poses challenges for dose optimization in projection radiography due to greater anatomical thickness in overweight and obese patients worldwide. Diagnostic reference levels (DRLs) alone may not adequately account for variations in body habitus, potentially leading to suboptimal patient protection. This study aimed to explore benchmark doses (BMDs) based on patient body mass index (BMI) for projection radiography examinations of major anatomical regions in Sri Lanka, providing a complementary approach for dose optimization alongside DRLs.

Methods

This prospective study included 1989 adult patients (≥18 years) undergoing abdomen anteroposterior (AP), chest posteroanterior (PA), kidney–ureter–bladder (KUB) AP, lumbar spine AP, lumbar spine lateral (LAT), and pelvis AP examinations at six major tertiary care hospitals. For each examination, patient demographics (age, weight, height, and BMI) and exposure parameters (kilovoltage peak [kVp] and tube current-exposure time product [mAs]) were recorded, and the patient doses in terms of kerma-area product (P_KA) were measured using a P_KA meter. DRLs (achievable doses) were proposed at the median of the median P_KA distribution across hospitals for a standard-sized patient group (58 ± 20 kg). For BMI-based BMDs, patients were classified into four standard BMI categories: underweight, normal weight, overweight, and obese. The median P_KA distributions across hospitals were used to formulate BMI-based BMDs, which were then compared with the proposed DRLs for the standard-sized patient group.

Results

The results showed a progressive increase in BMI-based BMDs across BMI categories for all examinations studied. BMI-based BMDs (in Gy.cm²) for underweight, normal weight, overweight, and obese patients were as follows: 1.46, 1.94, 2.88, 3.00 (abdomen AP); 0.17, 0.21, 0.22, 0.25 (chest PA); 1.70, 1.76, 2.30, 3.60 (KUB AP); 1.00, 1.03, 1.29, 1.48 (lumbar spine AP); 1.94, 2.09, 2.57, 2.56 (lumbar spine LAT); and 0.60, 1.85, 1.86, 2.24 (pelvis AP). Compared to normal weight patients, underweight patients exhibited percentage reductions in BMI-based BMDs of 24.7%, 3.4%, 2.9%, 7.1%, 4.5%, and 67.6% for abdomen AP, KUB AP, lumbar spine AP, lumbar spine LAT, chest PA, and pelvis AP, respectively. Conversely, overweight patients demonstrated percentage increases of 48.5%, 30.7%, 25.2%, 23.0%, 4.8%, and 0.5% across the same examinations, while obese patients showed increases of 54.6%, 104.5%, 51.5%, 22.5%, 19.0%, and 21.1%, respectively. DRLs for the standard-sized patient group were 1.82, 0.22, 2.03, 1.27, 2.21, and 1.90 Gy.cm², respectively.

Conclusion

These findings underscore the importance of BMI-based BMDs as an effective tool for personalized dose optimization, accounting for variations in patient body habitus. Their integration into clinical practice, alongside DRLs, could enhance patient protection and promote good radiographic practices. Furthermore, the findings underscore the need for the introduction of international guidelines for DRLs in intervals of BMI to ensure standardized implementation across countries.