Evaluation of run-off computed tomography angiography on a first-generation photon-counting detector CT scanner - Comparison with low-kVp energy-integrating CT

PURPOSE

To assess the overall imaging performance (radiation dose and image quality) of a photon-counting detector CT (PCD-CT) in comparison with a state-of-the-art energy-integrating detector CT (EID-CT) in run-off CTAs.

METHODS

Consecutive patients who underwent run-off CTA on a PCD-CT were included (PCD-CT cohort). A retrospective cohort of patients who had undergone run-off CTA on an EID-CT was matched for gender, body mass index, height, and age (EID-CT cohort). Virtual monoenergetic imaging (VMI) reconstructions for various keV settings (40-120 keV) were generated. CT values and noise were semiautomatically measured for 13 vascular segments of the abdomen, pelvis, and lower extremities. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated for each segment. Subjective image quality was evaluated by two radiologists along the dimensions 'vessel attenuation', 'vessel sharpness', and 'overall image quality' using 5-point Likert scales.

RESULTS

Forty patients (age 70.9 ± 9.8 years; 14 women) were included in the PCD-CT cohort and matched with a corresponding number of EID-CT patients. Overall, there was an inverse correlation of signal and noise but also of SNR and CNR with keV levels used for VMI reconstructions. SNR and CNR in the 40 - 60 keV range exceeded EID-CT levels significantly. Subjective image quality was substantially higher at lower keV levels and showed no significant difference to EID-CT.

CONCLUSION

Low keV VMI reconstructions of run-off CTA scans on a PCD-CT result in substantially higher SNR and CNR than 80 kVp and 100 kVp EID-CT acquisitions with equal subjective image quality.

Timing of radiotherapy following breast-conserving surgery: outcome of 1393 patients at a single institution

BACKGROUND

The role of postoperative radiotherapy in breast-conserving therapy is undisputed. However, optimal timing of adjuvant radiotherapy is an issue of ongoing debate. This retrospective clinical cohort study was performed to investigate the impact of a delay in surgery-radiotherapy intervals on local control and overall survival.

PATIENTS AND METHODS

Data from an unselected cohort of 1393 patients treated at a single institution over a 17-year period (1990-2006) were analyzed. Patients were assigned to two groups (CT+/CT-) according to chemotherapy status. A delay in the initiation of radiotherapy was defined as > 7 weeks (CT- group) and > 24 weeks (CT+ group).

RESULTS

The 10-year regional recurrence-free survival for the CT- and CT+ groups were 95.6 and 86.0 %, respectively. A significant increase in the median surgery-radiotherapy interval was observed over time (CT- patients: median of 5 weeks in 1990-1992 to a median of 6 weeks in 2005-2006; CT+ patients: median of 5 weeks in 1990-1992 to a median of 21 weeks in 2005-2006). There was no association between a delay in radiotherapy and an increased local recurrence rate (CT- group: p = 0.990 for intervals 0-6 weeks vs. ≥ 7 weeks; CT+ group: p = 0.644 for intervals 0-15 weeks vs. ≥ 24 weeks) or decreased overall survival (CT- group: p = 0.386 for intervals 0-6 weeks vs. ≥ 7 weeks; CT+ group: p = 0.305 for intervals 0-15 weeks vs. ≥ 24 weeks).

CONCLUSION

In the present cohort, a delay of radiotherapy was not associated with decreased local control or overall survival in the two groups (CT-/CT+). However, in the absence of randomized evidence, delays in the initiation of radiotherapy should be avoided.