Highlights
- •Conventional image similarity metrics are insufficient to assess the quality of sCT.
- •Water equivalent depth (WED) calculation can evaluate dosimetric quality of sCT.
- •The mean WED difference () between the sCT and reference CT can be calculated.
- •The can facilitate the development process of the new sCT generation method.
Abstract
Purpose
To provide a metric that reflects the dosimetric utility of the synthetic CT (sCT)
and can be rapidly determined.
Methods
Retrospective CT and atlas-based sCT of 62 (53 IMRT and 9 VMAT) prostate cancer patients
were used. For image similarity measurements, the sCT and reference CT (rCT) were
aligned using clinical registration parameters. Conventional image similarity metrics
including the mean absolute error (MAE) and mean error (ME) were calculated. The water equivalent depth (WED) was automatically determined for each patient on the rCT and sCT as the distance
from the skin surface to the treatment plan isocentre at 36 equidistant gantry angles,
and the mean WED difference ) between the two scans was calculated. Doses were calculated on each scan pair for
the clinical plan in the treatment planning system. The image similarity measurements
and were then compared to the isocentre dose difference () between the two scans.
Results
While no particular relationship to dose was observed for the other image similarity
metrics, the ME results showed a linear trend against with R2 = 0.6, and the 95 % prediction interval for between −1.2 and 1 %. The results showed an improved linear trend (R2 = 0.8) with a narrower 95 % prediction interval from −0.8 % to 0.8 %.
Conclusion
highly correlates with for the reference and synthetic CT scans. This is easy to calculate automatically
and does not require time-consuming dose calculations. Therefore, it can facilitate
the process of developing and evaluating new sCT generation algorithms.
Keywords
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Article info
Publication history
Published online: December 17, 2022
Accepted:
November 26,
2022
Received in revised form:
November 24,
2022
Received:
May 18,
2022
Identification
Copyright
© 2022 Associazione Italiana di Fisica Medica e Sanitaria. Published by Elsevier Ltd. All rights reserved.
