RPS 913 - Striving for lower radiation dose and better image quality

Author Block: A. S. L. Dedulle, T. Vanaudenhove, K. Van Slambrouck, A. Fremout; Brussels/BE
Purpose: In Belgium, diagnostic reference levels (DRLs) are established based on periodical patient dose surveys carried out by the regulatory body. This study evaluates trends in doses from CT scans, using data from these surveys.
Methods or Background: From 2012 to 2021, 10 periodical patient dose surveys were conducted in Belgium, covering CT equipment nationwide, as participation in the surveys is mandatory. Anonymous patient dose data were collected for 10 types of CT examinations (abdomen, chest angiography, coronary angiography, colon, cervical spine, lumbar spine, skull, sinus, thorax, thorax-abdomen). For each type of examination, dose data (CTDIvol, DLP) were registered for minimal 30 adult patients per CT device. The typical dose value was calculated (median) for each type of examination and each CT device. DRLs for each type of examination along with other statistical parameters were derived from the distribution of these values.
Results or Findings: The participation rate exceeded 85% across all 10 surveys. Between 2012 and 2021, the 75th percentile of the typical DLP-values for complete examinations showed a decrease between 22% and 63%, depending on the type of examination. Additionally, the data spread narrowed between 8% and 65%, and the 95th percentiles decreased between 16% and 62%. The DRL for CTDIvol per acquisition reduced between 31% and 71%, while the 95th percentile of the typical CTDIvol-values decreased between 38% and 71%. For most examination types, the largest decrease in DRL was obtained during the first five periodical surveys.
Conclusion: Over the 10-year period, patient doses from CT scans in Belgium substantially decreased. This is reflected in both lower DRLs and a reduced spread in dose data. This decrease is likely the result of improved protocols and the introduction of advanced CT technology.
Limitations: No limitations were identified.
Funding for this study: No funding was received.
Has your study been approved by an ethics committee? Not applicable
Ethics committee - additional information: Not applicable.

Author Block: M. Azizi¹, M. Romero-Expósito², I. Múñoz², A. Gkavonatsiou², O. Norrlid², C. Goldkuhl³, D. Molin², I. Toma-Dasu¹, A. Dasu²; ¹Stockholm/SE, ²Uppsala/SE, ³Gothenburg/SE
Purpose: This project aimed to fill a knowledge gap on the magnitude of secondary doses including the out-of-field and the imaging doses contributing to the risks from photon and proton radiotherapy.
Methods or Background: A framework was developed for determining and integrating the imaging and therapy doses for individual determination of total organ doses. VirtualDose software [1] was used for dose determinations from individual CT scans, while Monte Carlo simulations were used for CBCT dose determinations. Synthetic whole body CTs from the individual planning CTs were generated using IS2aR-software [2]. Neutron doses in proton radiotherapy were calculated using MCNP. Out-of-field doses in photon therapy patients were determined with Periphocal3D [3].
Results or Findings: To our knowledge, this was the first systematic assessment of total dose administered to patients throughout the course of the radiotherapy, encompassing clinically relevant frequency of use of the imaging procedures. The numbers of kV-CBCT ranged from 3 to 17 and 3 to 11 CTs, respectively in photon and proton plans. Imaging doses contribute 60-570 mSv for photon and 6-200 mSv for proton treatments over the entire treatment course for organs close to the target. Distant organs like the stomach, bladder, and liver showed a 13.5% increase in imaging dose relative to the photon treatment dose, while PBS indicates a 400% increase (though with lower absolute doses), indicating its greater relative impact.
Conclusion: Radiation burden in high precision radiotherapy depending on the imaging protocols will have to be taken into account in epidemiological studies on the incidence of second cancers in future patient cohorts.


References:
[1] A. Ding et al., Phys Med Biol; 2015.
[2] I. S. Muñoz-Hernández et al., Phys. Medica, 2023.
[3] B. Sánchez-Nieto, et al., Front. Oncol., 2022.
Limitations: No limitation was identified.
Funding for this study: This project has received funding from Euratom’s research and innovation programme 2019-20 under grant agreement no. 945196.
Has your study been approved by an ethics committee? Not applicable
Ethics committee - additional information: The study is retrospective.

Author Block: J. Pluim¹, J. Van De Kamer², E. Heeling², I. Ploeg², D. Hulsen¹; ¹'s-Hertogenbosch/NL, ²Amsterdam/NL
Purpose: The treatment of breast cancer during pregnancy (PrBC) requires careful consideration of consequences for both maternal and fetal health. In non-pregnant patients, the use of radioactive iodine-125 (125I)-seeds is standard practice for localising non-palpable breast tumors before breast-conserving surgery. However, the use of 125I-seeds in pregnant patients has been avoided due to concerns about fetal radiation exposure.
Methods or Background: This study developed a mathematical model to estimate the fetal absorbed dose based on several factors: the radioactivity of the 125I-seed, the duration of implantation, and the distance between the 125I-seed and fetus as a function of maternal anatomy, gestational age, and fetal development. Three scenarios, representing a range of maternal and fetal anatomy, were evaluated, including a worst-case scenario from a radiation safety perspective.
Results or Findings: The results show that the fetal absorbed dose varies across the three scenarios, with ranges of 0–1.6 mGy, 0.0–1.0 mGy, and 0.0–0.4 mGy, depending on when the 125I-seed was implanted and when it was removed. These dose ranges are similar to conventional diagnostic x-ray scans. The maximum calculated absorbed dose (1.6 mGy) is unlikely to be reached in practice and is well below the 100 mGy threshold associated with possible fetal malformations. The associated cancer risk increase (0.016%) is minimal.
Conclusion: The use of 125I-seeds as localisation method of breast tumors in pregnant patients results in low fetal radiation doses and should not be avoided due to dose concerns.
Limitations: No limitations were identified.
Funding for this study: No funding was received for this study.
Has your study been approved by an ethics committee? Not applicable
Ethics committee - additional information: Not applicable

Author Block: R. Massera, N. W. Marshall, H. Bosmans; Leuven/BE
Purpose: To apply novel optimization strategies in the search for optimal x-ray technique factors in paediatric interventional cardiology examinations.
Methods or Background: A simulation framework previously developed for adult interventional radiology examinations was adapted to use paediatric phantoms. The optimization framework implemented the Monte Carlo (MC) code PENELOPE(2018)/penEasy(2020) for dose and image quality (IQ) calculations, combined with a ray-tracing routine to calculate the attenuation through the patient and table. A figure of merit (FOM) defined as SDNRw²(u)/Dose was used. SDNRw(u) is a signal-difference-to-noise ratio weighted for the impact of geometric blurring from the focal spot and from object motion. This was evaluated for the task of detecting a 0.36 mm diameter iron guidewire. Dosimetric quantities comprised incident air kerma (AK) at the reference point, used to approximate skin dose, and the effective dose (Deff), used to estimate stochastic risk. To calculate Deff and SDNRw(u), ICRP female paediatric phantoms of 1- and 5-year-old were used. The tube voltage, spectral copper filtration and x-ray focus that yielded the highest FOM value for a particular dose quantity were found, taking into consideration x-ray tube loading limitations.
Results or Findings: For the 1-year-old and 5-year-old phantoms, optimal FOM values were achieved at respectively 65kV/0.7 mm Cu/micro focus and 64kV/0.5 mm Cu/small focus, when AK was the cost function. Using effective dose as the cost function gave optimal factors of 59kV/0.5 mm Cu/micro focus and 60kV/0.3 mm Cu, for the 1-year-old and 5-year-old cases, respectively.
Conclusion: The framework was successfully adapted to work with paediatric phantoms. Optimization based on effective dose selected lower tube voltages and copper spectral filtration thicknesses compared to a typical optimization using incident air kerma.
Limitations: A limited number of phantoms were used in the simulations.
Funding for this study: This study is the result of a research agreement with Siemens Healthineers.
Has your study been approved by an ethics committee? Not applicable
Ethics committee - additional information: Na

Author Block: K. Torfs¹, D. Petrov¹, L. D'Hondt², M. Lefere³, K. Bacher², A. Snoeckx⁴, W. De Wever¹, H. Bosmans¹; ¹Leuven/BE, ²Gent/BE, ³Bonheiden/BE, ⁴Zandhoven/BE
Purpose: Current guidelines for lung-cancer-screening (LCS) with low-dose chest CT (LDCT) are focused on dose, without specifying image quality (IQ) targets. This study compares noise and resolution in patient scans between the NELSON LCS trial, an ultra-low-dose (ULDCT) LCS study and current clinical standard-dose (SDCT) and LDCT on both energy-integrating (EIDCT) and photon-counting CT (PCCT).
Methods or Background: IQ was measured in 54 patient scans (24-26cm water-equivalent-diameter, sharp, 1mm slice-thickness reconstructions) of 6 protocols: LDCT-NELSON (Siemens Sensation 16), SDCT-EIDCT, LDCT-EIDCT and ULDCT-EIDCT (Siemens SOMATOM Force) and LDCT-PCCT and SDCT-PCCT (Siemens Naeotom Alpha).

Noise was computed per scan by averaging global-noise-levels (GNL) for soft tissue (0-170HU) from 50 equidistant slices. Resolution was quantified using AUC of the digital modulation-transfer-function (MTF) measured from the patient skin-air-interface. Protocol averages were presented as: [kVp|reconstruction kernel|CTDIvol(mGy)|GNL-soft(HU)|MTF-AUC(mm-1)].

To assess standardized-condition-protocols, patient-specific influence of pixel-size and dose was removed by predicting GNL at 1.6mGy CTDIvol and measuring presampled-MTF.
Results or Findings: The results can be summarized as follows:
LDCT-NELSON [120|B50|1.6±0.2mGy|155±8HU|0.52±0.06mm-1]
ULDCT-EIDCT [Sn100|Br64-IR3|0.16mGy|151±7HU|0.49±0.04mm-1]
SDCT-EIDCT [120|Br54|5.8±1.6mGy|70±4HU|0.49±0.06mm-1]
SDCT-PCCT [120|Bl56|4.8±0.6mGy|127±9HU|0.86±0.05mm-1]
LDCT-PCCT [Sn100|Bl56-IR1|1.08±0.15mGy|129±3HU|0.71±0.06mm-1]

Compared to LDCT-NELSON scans, noise was significantly lower (p<0.001) in SDCT-EIDCT, SDCT-PCCT and LDCT-PCCT and the AUC-MTF significantly sharper (p<0.001) in SDCT-PCCT and LDCT-PCCT. ULDCT had similar noise and resolution properties as LDCT-NELSON, at a mean dose of only 0.16mGy versus 1.6mGy.

However, for standardized-conditions, LDCT-PCCT, SDCT-EIDCT and ULDCT-EIDCT protocols were inherently less noisy (p<0.01) than NELSON, with SDCT-PCCT, LDCT-EIDCT and LDCT-PCCT being significantly sharper (p<0.001).
Conclusion: We have proposed a method to compare IQ of successful historical LCS scans to current state-of-the-art candidates with a dose – image quality evaluation from patient CT scans. Taking the NELSON setting as minimal reference, there are several candidate (ultra)LDCT protocols, with the LDCT on PCCT outperforming.
Limitations: Limited no. cases
Funding for this study: This work was performed with a grant from Kom op Tegen Kanker (G0B1922N), a Flemish NGO active in the fight against cancer
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: Study approved under internal reference number S68527

Author Block: O. Sandvold¹, R. Proksa¹, A. Perkins², P. Noël¹; ¹Philadelphia, PA/US, ²Cleveland, OH/US
Purpose: This work presents a CT acquisition paradigm utilizing sparse spectral imaging to deliver both high spatial resolution and spectral imaging, specifically designed for pediatric imaging.
Methods or Background: Combining spectral imaging with high spatial resolution at ultra-low doses is challenging with current technology. In our method, most of the scan is captured using single low tube voltage with the detector operating in non-spectral, high-resolution mode by combining x-ray photons across energy bins (excluding electronic noise). During sparse intervals, the system switches to rapid kVp mode, leveraging the detector's spectral capabilities. Data is continuously acquired and combined to generate both high-resolution and spectral images. A Monte Carlo simulation demonstrated this pediatric imaging protocol, using 70 kVp with intermittent 110 kVp pulses for spectral data. The detector pixel size was set to 0.5x0.5 mm², with an additional sampling protocol investigated using 1x1 mm² pixels. The simulated phantom represented a 150 mm pediatric patient. Spectral SNR in monoenergetic images was estimated using the Cramér-Rao Lower Bound, and the area under the monoenergetic curve (AUMC) was calculated as the total SNR over 35–120 keV.
Results or Findings: The sparse spectral protocol improved AUMC spectral SNR by 220% compared to a constant 100 kVp photon-counting scan using the same dose level and pixel size. Binning pixels to measure 1x1 mm², the sparse spectral performance was 475% the 100 kVp reference scan AUMC. At 62% of the 100 kVp dose, the sparse protocol AUMC was 170% greater than reference AUMC.
Conclusion: Pediatric spectral CT faces three main challenges: achieving high spatial resolution, obtaining low-noise spectral data, and minimizing radiation dose. Our proposed acquisition method combines multiple technologies to address these challenges. Future clinical translation promises improved pediatric care with minimal radiation exposure.
Limitations: None
Funding for this study: None
Has your study been approved by an ethics committee? Not applicable
Ethics committee - additional information: Not applicable

Author Block: A. Sarno¹, R. Massera², G. Paternò³, P. Cardarelli³, N. W. Marshall², H. Bosmans², K. Bliznakova⁴; ¹Milan/IT, ²Leuven/BE, ³Ferrara/IT, ⁴Varna/BG
Purpose: To investigate the use of a machine learning algorithm and patient-derived digital breast phantoms for predicting normalized glandular dose (DgN) coefficients and factors that influence the DgN uncertainty in digital mammography (DM) and digital breast tomosynthesis (DBT).
Methods or Background: Monte Carlo dosimetry calculations were performed for a set of 126 anatomically realistic digital breast phantoms to establish the ground truth DgN. The DgN was then predicted using a linear regression with an Automatic Relevance Determination Regression algorithm from 5 anatomical breast features: compressed breast thickness, glandular fraction, total glandular volume, center of mass and standard deviation of the glandular tissue distribution in the cranio-caudal direction. An algorithm for data imputation was explored to account for the cases where the latter two features are not available. The regression algorithm was validated using 5-fold Cross Validation.
Results or Findings: With the use of all 5 selected anatomical features, average difference between predicted DgN and the ground truth was 1%, with 50% of cases differing from the ground truth by less than 3%; estimated uncertainty on the DgN values was 9%. Uncertainty on DgN coefficients increased to 17% when the features related to the glandular distribution were excluded; however, this had only a minor impact on the prediction accuracy. The data imputation algorithm reduced the uncertainty on the predicted values, but could not match the prediction performance obtained by using all the available anatomical features.
Conclusion: The proposed methodology predicts the normalized glandular dose in DM and DBT with an error of 1%, on average, and with an estimated uncertainty of only 9%. 50% of the predicted DgN coefficients differed by less than 3% from the ground truth.
Limitations: Limited to single DM/DBT geometry
Funding for this study: None
Has your study been approved by an ethics committee? Not applicable
Ethics committee - additional information: Not applicable