Imaging as Part of a Quality Assurance Program: Predictors of Interobserver Variability for Pretreatment Image Registration for Lung SBRT

Purpose: To evaluate the magnitude of interobserver variability in pretreatment image registration for lung stereotactic body radiation therapy patients in aggregate and within 3 clinical subgroups and to determine methods to identify patients expected to demonstrate larger variability. Methods and Materials: Retrospective image registration was performed for the first and last treatment fraction for 10 lung stereotactic body radiation therapy patients by 16 individual observers (5 physicians, 6 physicists, and 5 therapists). Registration translation values were compared within and between subgroups overall and between the first and the last fractions. Four metrics were evaluated as possible predictors for large interobserver variability. Results: The mean 3-dimensional displacement vector for all patients over all comparisons was 2.4 ± 1.8 mm. Three patients had mean 3-dimensional vector differences >3 mm. This cohort of patients showed a significant interfraction difference in variance ( P value = .01), increasing from first fraction to last. A significant difference in interobserver variability was observed between physicians and physicists ( P value < .01) and therapists and physicists ( P value < .01) but not between physicians and therapists ( P value = .07). Three of the 4 quantities evaluated as potential predictive metrics showed statistical correlation with increased interobserver variation, including target excursion and local target/lung contrast. Conclusion: Variability in pretreatment image guidance represents an important treatment consideration, particularly for stereotactic body radiation therapy, which employs small margins and a small number of treatment fractions. As a result of the data presented here, we have initiated weekly “registration rounds” to familiarize all staff physicians with the target and normal anatomy for each stereotactic body radiation therapy patient and minimize interobserver variations in image registration prior to treatment. The metrics shown here are capable of identifying patients for which large interobserver variations would be anticipated. These metrics may be used in the future to develop thresholds for additional interventions to mitigate registration variations.

Variability Over Time of Normal-Sized Fetal Renal Pelvis During the Second Trimester Scan

Purpose To investigate the variability of the normal-sized fetal renal pelvis (≤5 mm) over time and to analyze repeatability of measurements. Materials and Methods 98 fetal renal pelvises and 49 fetal urinary bladders were analyzed at a gestational age of 17–20 weeks at St. Olavs Hospital, Trondheim, Norway. The anterior-posterior diameter (APD) of the fetal renal pelvis and two diameters of the fetal bladder were measured with an interval of at least 30 min. Intra- and interobserver variations and variations over time and in association with bladder size were investigated. Results The mean difference in renal pelvis size between the first and second measurements was 0.09 mm (95% CI, −0.09 to 0.26 mm). The variation over time was ≤1 mm in 85% of cases and the renal pelvis was ≤4 mm in both the first and second examinations in 92% of cases. The intraclass correlation coefficient (ICC) was 0.54 (95% CI: 0.31 to 0.69). We did not observe any association between variation of bladder size and variation of APD. The difference in fetal renal pelvis size was ≤1 mm in 70% of observations for the first examiner and 58% for the second examiner. The intraobserver ICCs were 0.71 (95% CI: 0.62–0.78) and 0.60 (95% CI: 0.50–0.70) for the two observers respectively. The interobserver difference was ≤1 mm in 72% of cases and the interobserver ICC was 0.56 (95% CI: 0.34–0.71). Conclusion The variation of the APD of the fetal renal pelvis over time was small in fetuses with the APD in the lower range and can mainly be explained by intraobserver variation.

Are therapeutic radiographers able to achieve clinically acceptable verification for stereotactic lung radiotherapy treatment (SBRT)?

PurposeThe aim of this study was to assess the feasibility of radiographer led verification of cone-beam computed tomography (CBCT) images for patients with solitary lung tumours treated with stereotactic body radiotherapy treatment (SBRT).Material and methodsCBCT setup images of 20 patients from the first fraction of each patient were retrospectively registered by therapeutic radiographers. The displacements recorded were compared with the clinical oncologist’s original online match. The time taken by radiographers to verify the CBCT images was also recorded.ResultsOverall agreement for all radiographers when compared with the clinical oncologist match was 91%. Interobserver variations between radiographers were X plane 0·87 (0·76–0·94); Y plane 0·74 (0·51–0·88); and Z plane 0·88 (0·78–0·95) intraclass correlation coefficient and 95% confidence interval. The average time taken for verification was 128 seconds.ConclusionTherapeutic radiographers are able to verify CBCT images for thorax SBRT with results comparable to the ‘gold standard’ clinical oncologists’ match, however additional training will be provided for online verification. The time taken was within acceptable limits.