Dosimetric measurements of (68)Ga-high affinity DOTATATE: twins in spirit - part III.

PURPOSE: 68Ga-labelled compounds are increasingly used for somatostatin-receptor scintigraphy because of their favourable biokinetic properties, a higher tumour-to-background contrast and higher diagnostic accuracy compared to the gamma-emitting tracer 111In-DTPA-octreotide. Recently, we have introduced the new tracer 68Ga-DOTA-3-iodo-Tyr3-Thr8-octreotide (68Ga-HA-DOTATATE). The present study demonstrates the biodistribution and radiation dosimetry of this tracer in humans. PATIENTS, METHODS: Seven men were enrolled in this analysis. Every patient underwent a 20 min dynamic PET scan after intravenous injection of about 114 ± 9 MBq of 68Ga-HA-DOTATATE. This was followed by two whole-body scans at 30 min p. i. and 120 min p. i. Blood radioactivity concentration was determined non-invasively from a ROI drawn over the aorta. Urine was collected until the time of the last scan. Liver, spleen, kidneys and urinary bladder wall were included in the dosimetric estimation that was carried out with the software package OLINDA 1.0. RESULTS: Physiological 68Ga-HA-DOTATATE uptake was observed in the pituitary gland, thyroid, salivary glands, liver, spleen, kidneys, urinary bladder, adrenals and intestine. Organs with the highest absorbed dose were spleen (0.26 ± 0.11 mSv/MBq), kidneys (0.14 ± 0.03 mSv/MBq) and liver (0.12 ± 0.02 mSv/MBq).The estimated effective dose was 0.024 ± 0.001 mSv/MBq. CONCLUSION: Our study demonstrates biokinetics and radiation exposure of the 68Ga-labelled tracer HA-DOTATATE to be comparable to other 68Ga-labelled SSR analogues in clinical use.

On the dose calculation at the cellular level and its implications for the RBE of (99m)Tc and ¹²³I.

PURPOSE: Based on the authors' previous findings concerning the radiotoxicity of(99m)Tc, the authors compared the cellular survival under the influence of this nuclide with that following exposure to the Auger electron emitter (123)I. To evaluate the relative biological effectiveness (RBE) of both radionuclides, knowledge of the absorbed dose is essential. Thus, the authors present the dose calculations and discuss the results based on different models of the radionuclide distribution. Both different target volumes and the influence of the uptake kinetics were considered. METHODS: Rat thyroid PC Cl3 cells in culture were incubated with either(99m)Tc or (123)I or were irradiated using 200 kV x-rays in the presence or absence of perchlorate. The clonogenic cell survival was measured via colony formation. In addition, the intracellular radionuclide uptake was quantified. Single-cell dose calculations were based on Monte Carlo simulations performed using Geant4. RESULTS: Compared with external radiation using x-rays (D37 = 2.6 Gy), the radionuclides (99m)Tc (D37 = 3.5 Gy), and (123)I (D37 = 3.8 Gy) were less toxic in the presence of perchlorate. In the absence of perchlorate, the amount of activity a37 that was necessary to reduce the surviving fraction (SF) to 0.37 was 22.8 times lower for (99m)Tc and 12.4 times lower for (123)I because of the dose increase caused by intracellular radionuclide accumulation. When the cell nucleus was considered as the target for the dose calculation, the authors found a RBE of 2.18 for (99m)Tc and RBE = 3.43 for (123)I. Meanwhile, regarding the dose to the entire cell, RBE = 0.75 for (99m)Tc and RBE = 1.87 for (123)I. The dose to the entire cell was chosen as the dose criterion because of the intracellular radionuclide accumulation, which was found to occur solely in the cytoplasm. The calculated number of intracellular decays per cell was (975 ± 109) decays/MBq for (99m)Tc and (221 ± 82) decays/MBq for (123)I. CONCLUSIONS: The authors' data indicate that extra-nuclear targets to Auger electrons exist, which is obvious from our dose calculations. When considering the dose to the cell nucleus, the authors found an enhanced RBE for(99m)Tc and (123)I relative to acute x-ray irradiation and pure extracellular irradiation with both radionuclides. Surprisingly, the authors did not find any radionuclide accumulation in the cell nucleus, indicating that there are additional radiosensitive targets besides the DNA. In addition, the authors demonstrated the necessity of cellular dose calculations in radiobiological experiments using unsealed radionuclides and identified the relevant parameters.

Potential of a Cetuximab-based radioimmunotherapy combined with external irradiation manifests in a 3-D cell assay.

Targeting epidermal growth factor receptor (EGFR)-overexpressing tumors with radiolabeled anti-EGFR antibodies is a promising strategy for combination with external radiotherapy. In this study, we evaluated the potential of external plus internal irradiation by [(90) Y]Y-CHX-A″-DTPA-C225 (Y-90-C225) in a 3-D environment using FaDu and SAS head and neck squamous cell carcinoma (HNSCC) spheroid models and clinically relevant endpoints such as spheroid control probability (SCP) and spheroid control dose 50% (SCD50 , external irradiation dose inducing 50% loss of spheroid regrowth). Spheroids were cultured using a standardized platform. Therapy response after treatment with C225, CHX-A"-DTPA-C225 (DTPA-C225), [(90) Y]Y-CHX-A"-DTPA (Y-90-DTPA) and Y-90-C225 alone or in combination with X-ray was evaluated by long-term monitoring (60 days) of spheroid integrity and volume growth. Penetration kinetics into spheroids and EGFR binding capacities on spheroid cells were identical for unconjugated C225 and Y-90-C225. Spheroid-associated radioactivity upon exposure to the antibody-free control conjugate Y-90-DTPA was negligible. Determination of the SCD50 demonstrated higher intrinsic radiosensitivity of FaDu as compared with SAS spheroids. Treatment with unconjugated C225 alone did not affect spheroid growth and cell viability. Also, C225 treatment after external irradiation showed no additive effect. However, the combination of external irradiation with Y-90-C225 (1 µg/ml, 24 hr) resulted in a considerable benefit as reflected by a pronounced reduction of the SCD50 from 16 Gy to 9 Gy for SAS spheroids and a complete loss of regrowth for FaDu spheroids due to the pronounced accumulation of internal dose caused by the continuous exposure to cell-bound radionuclide upon Y-90-C225-EGFR interaction.

[Determination of radioactivity by smartphones]. / Radioaktivität mit dem Smartphone messen.

UNLABELLED: The interest in the detection of radioactive materials has strongly increased after the accident in the nuclear power plant Fukushima and has led to a bottleneck of suitable measuring instruments. Smartphones equipped with a commercially available software tool could be used for dose rate measurements following a calibration according to the specific camera module. AIM: We examined whether such measurements provide reliable data for typical activities and radionuclides in nuclear medicine. METHODS: For the nuclides 99mTc (10 - 1000 MBq), 131I (3.7 - 1800 MBq, therapy capsule) and 68Ga (50 - 600 MBq) radioactivity with defined geometry in different distances was measured. The smartphones Milestone Droid 1 (Motorola) and HTC Desire (HTC Corporation) were compared with the standard instruments AD6 (automess) and DoseGUARD (AEA Technology). RESULTS: Measurements with the smartphones and the other devices show a good agreement: linear signal increase with rising activity and dose rate. The long time measurement (131I, 729 MBq, 0.5 m, 60 min) demonstrates a considerably higher variation (by 20%) of the measured smartphone data values compared with the AD6. For low dose rates (< 1 µGy/h), the sensitivity decreases so that measurements of e. g. the natural radiation exposure do not lead to valid results. The calibration of the camera responsivity for the smartphone has a big influence on the results caused by the small detector surface of the camera semiconductor. CONCLUSIONS: With commercial software the camera module of a smartphone can be used for the measurement of radioactivity. Dose rates resulting from typical nuclear medicine procedures can be measured reliably (e. g., dismissal dose after radioiodine therapy). The signal shows a high correlation to measured values of conventional dose measurement devices.

Sodium-iodide symporter positive cells after intracellular uptake of (99m)Tc versus α-emitter 211At. Reduction of clonogenic survival and characterization of DNA damage.

PURPOSE: We evaluated the DNA damaging potential of Auger electrons emitted in the decay of (99m)Tc compared to α-particles of 211At. MATERIAL AND METHODS: The impact of (99m)Tc and 211At was monitored in a NIS-expressing rat thyroid cell model PCCl3 with varying, yet defined intra- and extracellular radionuclide distribution (using ± perchlorate). The radiotoxicity of (99m)Tc and 211At was studied by the comet assay under neutral and alkaline conditions and colony formation. RESULTS: In the presence of perchlorate, the radioactivity yielding 37% cellular survival, A37, was estimated to be (0.27 ± 0.02) MBq/ml and (450 ± 30) MBq/ml for 211At and (99m)Tc, respectively. In absence of perchlorate, cellular radiotracer uptake was similar for both radionuclides (2.2%, 2.7%), yet the A37 was reduced by 82% for the α-emitter and by 95% for (99m)Tc. Cellular dose increased by a factor of 5 (211At) and 38 (99mTc). Comet assays revealed an increased DNA damage after intracellular uptake of both radiotracers. CONCLUSIONS: The data indicate damage to the cell to occur from absorbed dose without recognizable contribution from intracellular heterogeneity of radionuclide distribution. Comet assay under alkaline and neutral conditions did not reveal any shift to more complex DNA damage after radionuclide uptake. Cellular uptake of (99m)Tc and 211At increased cellular dose and reduced clonogenic survival.

Preincubation with Sn-complexes causes intensive intracellular retention of (99m)Tc in thyroid cells in vitro.

UNLABELLED: Technetium radiopharmaceuticals are well established in nuclear medicine. Besides its well-known gamma radiation, (99m)Tc emits an average of five Auger and internal conversion electrons per decay. The biological toxicity of these low-energy, high-LET (linear energy transfer) emissions is a controversial subject. One aim of this study was to estimate in a cell model how much (99m)Tc can be present in exposed cells and which radiobiological effects could be estimated in (99m)Tc-overloaded cells. METHODS: Sodium iodine symporter (NIS)-positive thyroid cells were used. (99m)Tc-uptake studies were performed after preincubation with a non-radioactive (cold) stannous pyrophosphate kit solution or as a standard (99m)Tc pyrophosphate kit preparation or with pure pertechnetate solution. Survival curves were analyzed from colony-forming assays. RESULTS: Preincubation with stannous complexes causes irreversible intracellular radioactivity retention of (99m)Tc and is followed by further pertechnetate influx to an unexpectedly high (99m)Tc level. The uptake of (99m)Tc pertechnetate in NIS-positive cells can be modified using stannous pyrophosphate from 3-5% to >80%. The maximum possible cellular uptake of (99m)Tc was 90Bq/cell. Compared with nearly pure extracellular irradiation from routine (99m)Tc complexes, cell survival was reduced by 3-4 orders of magnitude after preincubation with stannous pyrophosphate. CONCLUSIONS: Intracellular (99m)Tc retention is related to reduced survival, which is most likely mediated by the emission of low-energy electrons. Our findings show that the described experiments constitute a simple and useful in vitro model for radiobiological investigations in a cell model.

[Measurement of ocular lens ionizing radiation exposure after radioiodine therapy]. / Bestimmung der Augenlinsenexposition bei Patienten nach einer Radioiodtherapie.

AIM: Current reports for the radiation cataracts contained a warning for deterministic effects at 1-2 Gy radiation single exposure for lens. Recently, the German Radiation Protection Board (SSK) published a document (234. SSK-Board) in that threshold dose for radiation cataracts is claimed at 0.5 Gy. The lens of the eye is recognized as one of the most radiosensitive tissues in the human body, and the International Commission on Radiological Protection (ICRP 103) has defined a limit of 150 mSv for its exposure.Recently, the ICRP lowered this limit down to 20 mSv per year.However, this limit does not apply to patients. Therefore, the question of the lens radiation exposure for patients underwent a radioiodine therapy (RIT) is a point at issue. PATIENTS, METHODS: A total of 41 patients (age: 22-92 years) underwent a radioiodine therapy were included in the study. Optical stimulated luminescence dosimeters were used to measure the radiation exposure. The dosimeters were fastened nearby the patient's eye lens. The measurement was carried out up to 48 h after radioiodine application and the patients were divided into three groups. Group 1: patients underwent a diagnostic 131I whole body scan (mean activity: 370 MBq); group 2: thyriod carcinoma patients under RIT (mean activity: 3700 MBq); group 3: hyperthyroid patients under RIT (activity: 180-1237 MBq). RESULTS: The cumulative exposure of the eye lens during the stay at the therapy unit (48 h) was 4.8 ± 0.7 mGy in group 1, 24.5-50.5 mGy in group 2 and 2.7-26.3 mGy in group 3, respectively. For the calculation of the expected cumulative dose, including follow-up after patient's dismissal, the effective half-lives were involved. The cumulative doses were obtained to be 6 ± 1 mGy in the first group, 63 ± 15 mGy in the second and 5-148 mGy in the third. CONCLUSION: The results show that there exists a low risk for radiation cataract in a nuclear medicine therapy unit. After serial radioiodine therapies radiation-induced lens opacity cannot be expected.

[99mTc reduces clonogenic survival after intracellular uptake in NIS-positive cells in vitro more than 131I]. / 99mTc reduziert nach intrazellulärer Aufnahme in NIS-positiven Zellen in vitro das klonogene Uberleben stärker als 131I.

AIM: In addition to gamma radiation of 140 keV 99mTc emits during the transition to 99Tc electrons of low energy and tiny path-lengths. These Auger electrons cannot be utilized in diagnostic procedures. However, they were discussed frequently for therapeutic application. Hitherto proof of effect of the Auger electrons from 99mTc is missing which is supplied now in an in vitro-system in comparison to beta-emitter 131I. METHODS: The thyroid cell line PCCl3 (sodium iodide symporter (NIS)-positive) was incubated with 131I-sodium iodide (131I) or 99mTc-pertechnetate (99mTc) in presence or absence of perchlorate. For comparison the amount of radioactivity was adjusted to obtain the same dose from extracellular irradiation for both radionuclides. The colony forming assay detects the clonogenic cell survival as surviving fraction. In addition, intracellular radionuclide uptake was quantified. RESULTS: Dose effect curves were established for 131I and 99mTc for variable extra- and intracellular distribution of the radioactivity. In presence of perchlorate no cellular uptake of radioactivity was detectable. Survival curves were largely comparable confirming the dosimetric calculations. In absence of perchlorate cellular radiotracer uptake varied from 1.39% (131I) to 1.90% 99mTc). Effects on survival were twice for the beta-emitter and ten-fold higher for 99mTc. CONCLUSIONS: Intracellular uptake of 131I and 99mTc increases DNA-damage compared to strict extracellular radiotracer distribution which was demonstrated by means of colony forming assay. Increasing radiotoxicity from intracellular 99mTc is explained most likely by increased dose deposition in cellular structures due to Auger- and conversion-electrons of low range and high local energy deposition.

[BeO-OSL detectors for dose measurements in cell cultures]. / Anwendung von BeO-OSL-Detektoren zur Dosismessung in Zellkulturen.

AIM: The absorbed dose is an important parameter in experiments involving irradiation of cells in vitro with unsealed radionuclides. Typically, this is estimated with a model calculation, although the results thus obtained cannot be verified. Generally used real-time measurement methods are not applicable in this setting. A new detector material with in vitro suitability is the subject of this work. METHODS: Optically-stimulated luminescence (OSL) dosimeters based on beryllium oxide (BeO) were used for dose measurement in cell cultures exposed to unsealed radionuclides. Their qualitative properties (e. g. energy-dependent count rate sensitivity, fading, contamination by radioactive liquids) were determined and compared to the results of a Monte Carlo simulation (using AMOS software). OSL dosimeters were tested in common cell culture setups with a known geometry. RESULTS: Dose reproducibility of the OSL dosimeters was +/-1.5%. Fading at room temperature was 0.07% per day. Dose loss (optically-stimulated deletion) under ambient lighting conditions was 0.5% per minute. The Monte Carlo simulation for the relative sensitivity at different beta energies provided corresponding results to those obtained with the OSL dosimeters. Dose profile measurements using a 6 well plate and 14 ml PP tube showed that the geometry of the cell culture vessel has a marked influence on dose distribution with 188Re. CONCLUSION: A new dosimeter system was calibrated with beta-emitters of different energy. It turned out as suitable for measuring dose in liquids. The dose profile measurements obtained are suitably precise to be used as a check against theoretical dose calculations.

[DNA damage in lymphocytes after irradiation with 211At and 188Re]. / DNA-Schäden von Lymphozyten nach Bestrahlung mit 211At und 188Re - Quantifizierung mit dem alkalischen und neutralen Komet-Assay.

AIM: Ionising radiation produces many types of DNA lesions of different complexity. High linear energy transfer (LET) types of radiation are biological more effective than low LET radiation. In the present work we applied the single cell gel electrophoreses (comet assay) to study the induction of initial DNA damage, efficiency of repair and residual DNA damage in lymphocytes after treatment with 211At and 188Re. METHODS: Peripheral blood mononuclear cells (PBMC) were isolated from heparinized blood of healthy donors and irradiated with 211At and 188Re at different doses. The comet assay was performed under alkaline and neutral conditions in order to detect the initial DNA damage and its repair. The measure of damage was % tail DNA (percentage of DNA in the tail). RESULTS: After treatment of cells with 188Re the initial DNA damage (% tail DNA) detected with the alkaline comet assay was higher than the damage measured for 211At. The neutral comet assay estimated higher tail intensities for 211At in contrast to 188Re. Compared with the complete repair (10%) after irradiation with 188Re, the radiotoxicity of alpha particles indicated reduced rejoining of DNA strand breaks (60-80% residual damage). Rejoining of DNA damage measured by the neutral comet method detected about 70% unrepaired strand breaks for 211At and 188Re. CONCLUSIONS: There are major differences between the repair of strand breaks caused by 188Re and 211At detected by the alkaline comet assay. The DNA-damage induced by the high LET Emitter 211At remains nearly unrepaired detected by both alkaline and neutral comet assay. Represented data following irradiation of lymphocytes with alpha and beta particles demonstrated higher biological effectiveness of 211At by factors of 2.0-2.5.

[Cellular damage in vitro]. / Einfluss der mittleren Betaengergie und der intrazellulären Radionuklidaufnahme auf die Zellschädigung in vitro.

AIM: The cellular damage of ionising radiation depends on dose, physical radiation quality (e. g. LET) and intracellular radionuclide uptake. The influence of two beta emitters (188Re and 131I) on the thyroid cell line PCCl3 was studied. Furthermore, we analysed the effect of intracellular accumulation. METHODS: The thyroid cell line PCCl3 was irradiated with 188Re-perrhenate or 131I-sodium iodide in presence or absence of perchlorate. The initial DNA-damage was measured in the comet assay as olive tail moment (OTM). The colony forming assay detects the clonogenic cell survival as surviving fraction. Additional the intracellular radionuclide uptake was quantified. RESULTS: Dose response curves were established for irradiation with 188Re-perrhenate or 131I-iodine under various extra- and intracellular activity distribution conditions. In the presence of perchlorate DNA-damage and clonogenic cell survival for both radionuclides were comparable. In the absence of perchlorate radionuclide uptake of 1.39% (131I) and 4.14% (188Re) were measured causing twofold higher radiotoxicity. Although 131I uptake was lower than 188Re uptake the OTM values were higher und surviving fractions were lower. CONCLUSIONS: 131I, compared to 188Re, has lower mean beta energy and a higher LET, and therefore, it induced a higher DNA-damage even at lower intracellular uptake. An additional explanation for the higher radiotoxicity of 131I could be the higher dose exposition caused by cross-fire through neighborhood cells.

[Radiation exposure of patients during 68Ga-DOTATOC PET/CT examinations]. / Strahlenexposition der Patienten bei Untersuchungen mit 68Ga-DOTATOC am PET/CT.

AIM: Investigation of the biodistribution and calculation of dosimetry of Ga-68-DOTATOC- for patients imaged in the routine clinical setting for diagnosis or exclusion of neuroendocrine tumours. PATIENTS, METHODS: Dynamic PET/CT-imaging (Biograph 16) was performed over 20 min in 14 patients (8 men, 6 women) after injection of (112+/-22) MBq 68Ga-DOTATOC followed by whole body 3D-acquisition (8 bed positions, 3 or 4 min each) 30 min p.i. and 120 min p.i.. Urinary tracer elimination was measured and blood activity was derived non-invasively from the blood pool of the heart. The relevant organs for dosimetry were spleen, kidneys, liver, adrenals, urinary bladder and pituitary gland. Dosimetry was performed using OLINDA/EXM 1.0 software and specific organ uptake was expressed as standardized uptake values (SUVs). RESULTS: Rapid physiological uptake of the radiotracer could be demonstrated in liver, spleen and kidneys, adrenals and pituitary gland (mean SUVs were 6, 20, 16, 10, and 4, respectively). Radiotracer elimination was exclusively via urine (16% of injected dose within 2h); no redistribution could be observed. The spleen and the kidneys received the highest radiation exposure (0.24 mSv/MBq, 0.22 mSv/MBq resp.), mean effective dose yielded 0.023 mSv/MBq. CONCLUSION: 68Ga-DOTATOC is used extensively for diagnosis of somatostatin receptor positive tumours because it has several advantages over the 111In-labelled ligand. The derived dosimetric values are lower than first approximations from the biological data of OctreoScan. The use of CT for transmission correction of the PET data delivers radiation exposure up to 1 mSv (low dose).

A high-resolution radiation hybrid map of the human genome draft sequence.

We have constructed a physical map of the human genome by using a panel of 90 whole-genome radiation hybrids (the TNG panel) in conjunction with 40,322 sequence-tagged sites (STSs) derived from random genomic sequences as well as expressed sequences. Of 36,678 STSs on the TNG radiation hybrid map, only 3604 (9.8%) were absent from the unassembled draft sequence of the human genome. Of 20,030 STSs ordered on the TNG map as well as the assembled human genome draft sequence and the Celera assembled human genome sequence, 36% of the STSs had a discrepant order between the working draft sequence and the Celera sequence. The TNG map order was identical to one of the two sequence orders in 60% of these discrepant cases.

Exposure duration affects the perceived direction of cyclopean type II plaids.

This study investigated the effect of exposure duration on the perceived direction of cyclopean Type I and Type II plaids moving in the X/Y plane. The cyclopean plaids were created from grating components defined by binocular disparity embedded in a dynamic random-dot stereogram. The results showed that the cyclopean Type I plaid appeared to move in the intersection-of-constraints (IOC) direction across the range of exposures tested. However, the cyclopean Type II plaids appeared to move in a direction different from the IOC with short exposures but near the IOC with long exposures. This perceived directional shift was also obtained with luminance-defined Type II plaids. A common pattern-motion mechanism that processes cyclopean and luminance motion signals appears responsible for the perceived directional shift of the Type II plaids.