The presence of contrast agent increases organ radiation dose in contrast-enhanced CT

Objectives Routine dosimetry calculations do not account for the presence of iodine in organs and tissues during CT acquisition. This study aims to investigate the impact of contrast agent (CA) on radiation dose. Methods First, relation between absorbed radiation dose and iodine concentrations was investigated using a cylindrical water phantom with iodine-saline dilution insertions. Subsequently, a retrospective study on abdominal dual-energy CT (DECT) patient data was performed to assess the increase of the local absorbed radiation dose compared to a non-contrast scan. Absorbed doses were estimated with Monte Carlo simulations using the individual CT voxel data of phantom and patients. Further, organ segmentations were performed to obtain the dose in liver, liver parenchyma, left kidney, right kidney, aorta, and spleen. Results In the phantom study, a linear relation was observed between the radiation dose normalized by computed tomography dose index (CTDI) and CA concentrations Iconc (mg/ml) for three tube voltages; $$ \frac{D_{80 kVp}}{CTDI_{vol}} $$ D 80 kVp CTDI vol = 0.14 × Iconc + 1.02, $$ \frac{D_{120 kVp}}{CTDI_{vol}} $$ D 120 kVp CTDI vol = 0.16 × Iconc + 1.21, $$ \frac{D_{140 kVp}}{CTDI_{vol}} $$ D 140 kVp CTDI vol = 0.16 × Iconc + 1.24, and for DECT acquisition; $$ \frac{D_{DECT}}{CTDI_{vol}} $$ D DECT CTDI vol = 0.15 × Iconc + 1.09. Similarly, a linear relation was observed between the dose increase and the organ iodine contents (R2 = 0.86 and pvalue < 0.01) in the patient study. The relative doses increased in the liver (21 ± 5%), liver parenchyma (20 ± 5%), right kidney (37 ± 7%), left kidney (39 ± 7%), aorta (34 ± 6%) and spleen (26 ± 4%). In addition, the local dose distributions changed based on patient’s anatomy and physiology. Conclusions Compared to a non-contrast scan, the organ doses increase by 30% in contrast-enhanced abdominal CT. This study suggests considering CA in dosimetry calculations, epidemiological studies, and organ dose estimations while developing new CT protocols. Key Points • The presence of contrast media increases radiation absorption in CT, and this increase is related to the iodine content in the organs. • The increased radiation absorption due to contrast media can lead to an average 30% increase in absorbed organ dose. • Iodine should be considered in CT radiation safety studies.

Radiomics Analysis for 177Lu-DOTAGA-(l-y)fk(Sub-KuE) Targeted Radioligand Therapy Dosimetry in Metastatic Prostate Cancer—A Model Based on Clinical Example

177Lu-DOTAGA-(l-y)fk(Sub-KuE) a.k.a. 177Lu-PSMA I&T is currently used for radioligand therapy (RLT) of metastatic castration-resistant prostate cancer (mCRPC) in several centers in Europe. Background: Dosimetry is mandatory according to EU guidelines, although routine methods for dosimetry, i.e., absorbed radiation dose calculations for radiopharmaceuticals, are missing. Methods: We created a model of dosimetric analysis utilizing voxel-based dosimetry and intra-lesion radiomics to assess their practicality in routine dosimetry. Results: As an example for the model, our patient with mCRPC had excellent therapy response; quantitatively more than 97% of the metastatic tumor burden in local and distant lymph nodes and skeleton was destroyed by four cycles of RLT. The absorbed radiation doses in metastases decreased towards later cycles of RLT. Besides the change of prostate-specific membrane antigen (PSMA) concentration and absorbed doses in the tumor, further response to RLT could be predicted from biomarker changes, such as LDH and PSA. Conclusions: Individual dosimetry is needed to understand large variations in tumor doses and mixed responses; for that purpose, routine tools should be developed. The Dosimetry Research Tool (DRT) fluently performed automated organ delineation and absorbed radiation dose calculations in normal organs, and the results in our patient were in good concordance with the published studies on 177Lu-PSMA dosimetry. At the same time, we experienced considerable challenges in voxel-based dosimetry of tumor lesions. Measurements of 177Lu-PSMA activity concentrations instead of absorbed radiation dose calculations could make routine dosimetry more flexible. The first cycle of RLT seems to have quantitatively the biggest impact on the therapy effect. Radiomics analyses could probably aid in the treatment optimization, but it should be tested in large patient populations.

RADIATION RESISTANT COMPOSITE FOR BIOLOGICAL PROTECTION OF THE PERSONNEL

Results of scientific and practical justification of use as a part of designs of biological protection of polymer concrete on the basis of non - isocyanates polyurethane are presented. Influence of a ratio polymer is established: radiation - resistant filler on strength and protective properties of a polymer concrete. Regression dependences of change of the main properties of the specified polymer concrete on the power of the absorbed radiation dose are given. The synergetic effect in weakening of radiation when sharing a hydrogenous polymeric basis and radiation resistant powders is shown.

ESTIMATION OF HUMAN DOSE OF 188/186RE-HEDP COCKTAIL BASED ON OLINDA/EXM AND DISTRIBUTION DATA IN RATS

188Re and 186Re are two applicable rhenium medical radioisotopes with complementary features that make them beneficial for different sizes of tumours. The aim of this study is to investigate 188/186Re-HEDP efficacy as a cocktail by calculating absorbed radiation dose in human organs based on biodistribution data obtained by injecting it to normal rats. Three rats were sacrificed at different time intervals and the percentage of injected dose per gram of each organ was measured by direct counting from rat data. By calculating accumulated activities in each organ and extrapolating rat data to human data by the radiation dose assessment resource method and by using OLINDA/EXM software, the injected dose in various human organs was obtained. The calculated absorbed dose showed that the 188/186Re-HEDP has noticeable properties that can be more helpful in comparison with using each of the rhenium radioisotopes separately.

SUN-510 Prolonged RAIA Induced Thyroiditis After 131 I Therapy for Graves’ Hyperthyroidism

Radioactive iodine ablation (RAI) has been used for the treatment of Graves’ hyperthyroidism since 1946 and it is the primary recommended modality for Graves’ disease treatment in many countries. Acute painful radiation thyroiditis after radioiodine treatment for hyperthyroidism of Graves’ disease is considered uncommon. The prevalence is 1-5% in patients treated with 131I therapy for hyperthyroidism. Dose of RAI and thyroid volume can be precipitating factors for post radiation thyroiditis. The higher RAI dose increases the chance of RAI thyroiditis while the larger goiter size decreases the absorbed radiation dose in the thyroid gland. We present a 25-year-old Emirati male previously healthy, who was referred to our service for hyperthyroidism management. He presented with thyrotoxicosis in absence of goiter. All investigations revealed that graves’ disease is the primary cause of his hyperthyroidism. He was treated with RAI ablation 18.3 mCi. Day four after RAI, he presented with severe pain in the anterior neck associated with fatigue, tremor, palpitation and weight loss. Symptoms lasted for 6 weeks post RAI. There was laboratory evidence of thyrotoxicosis presented with further suppression of TSH and higher fT4 than the baseline. Acute radiation thyroiditis was diagnosed and has been commenced on propranolol 10mg BID. Symptoms completely resolved after 6 weeks of treatment and thyroid function returned to normal level. The patient has remained asymptomatic on continued follow up care till eventually became hypothyroid clinically and biochemically. Our case reflects that radioiodine thyroiditis can last for longer period and occur after larger doses of 131I treatment in absence of goiter. Our patient has RAIA induced thyroiditis lasted for 6 weeks post 18.3mCi of 131I, and has no goiter, which were both contributing factors for RAIA induced thyroiditis