Time- and dose-dependent volume decreases in subcortical grey matter structures of glioma patients after radio(chemo)therapy

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Radiotherapy causes atrophy of the hippocampus, amygdala, putamen, thalamus and pallidum.

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Atrophy is dose dependant and progressive over time.

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The hippocampus shows the highest atrophy rates at a given mean dose and time.

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The caudate shows no significant atrophy.

Background and purpose

Radiotherapy (RT) is an adjuvant treatment option for glioma patients. Side effects include tissue atrophy, which might be a contributing factor to neurocognitive decline after treatment. The goal of this study was to determine potential atrophy of the hippocampus, amygdala, thalamus, putamen, pallidum and caudate nucleus in glioma patients having undergone magnetic resonance imaging (MRI) before and after RT.

Materials and methods

Subcortical volumes were measured using T1-weighted MRI from patients before RT (N = 91) and from longitudinal follow-ups acquired in three-monthly intervals (N = 349). The volumes were normalized to the baseline values, while excluding structures touching the clinical target volume (CTV) or abnormal tissue seen on FLAIR imaging. A multivariate linear effects model was used to determine if time after RT and mean RT dose delivered to the corresponding structures were significant predictors of tissue atrophy.

Results

The hippocampus, amygdala, thalamus, putamen, and pallidum showed significant atrophy after RT as function of both time after RT and mean RT dose delivered to the corresponding structure. Only the caudate showed no dose or time dependant atrophy. Conversely, the hippocampus was the structure with the highest atrophy rate of 5.2 % after one year and assuming a mean dose of 30 Gy.

Conclusion

The hippocampus showed the highest atrophy rates followed by the thalamus and the amygdala. The subcortical structures here found to decrease in volume indicative of radiosensitivity should be the focus of future studies investigating the relationship between neurocognitive decline and RT.

Reduced diffusion in white matter after radiotherapy with photons and protons

BACKGROUND AND PURPOSE

Radio(chemo)therapy is standard in the adjuvant treatment of glioblastoma. Inevitably, brain tissue surrounding the target volume is also irradiated, potentially causing acute and late side-effects. Diffusion imaging has been shown to be a sensitive method to detect early changes in the cerebral white matter (WM) after radiation. The aim of this work was to assess possible changes in the mean diffusivity (MD) of WM after radio(chemo)therapy using Diffusion-weighted imaging (DWI) and to compare these effects between patients treated with proton and photon irradiation.

MATERIALS AND METHODS

70 patients with glioblastoma underwent adjuvant radio(chemo)therapy with protons (n = 20) or photons (n = 50) at the University Hospital Dresden. MRI follow-ups were performed at three-monthly intervals and in this study were evaluated until 33 months after the end of therapy. Relative white matter MD changes between baseline and all follow-up visits were calculated in different dose regions.

RESULTS

We observed a significant decrease of MD (p < 0.05) in WM regions receiving more than 20 Gy. MD reduction was progressive with dose and time after radio(chemo)therapy (maximum: -7.9 ± 1.2% after 24 months, ≥50 Gy). In patients treated with photons, significant reductions of MD in the entire WM (p < 0.05) were seen at all time points. Conversely, in proton patients, whole brain MD did not change significantly.

CONCLUSIONS

Irradiation leads to measurable MD reduction in white matter, progressing with both increasing dose and time. Treatment with protons reduces this effect most likely due to a lower total dose in the surrounding white matter. Further investigations are needed to assess whether those MD changes correlate with known radiation induced side-effects.

Overestimation of grey matter atrophy in glioblastoma patients following radio(chemo)therapy

Objective

Brain atrophy has the potential to become a biomarker for severity of radiation-induced side-effects. Particularly brain tumour patients can show great MRI signal changes over time caused by e.g. oedema, tumour progress or necrosis. The goal of this study was to investigate if such changes affect the segmentation accuracy of normal appearing brain and thus influence longitudinal volumetric measurements.

Materials and methods

T1-weighted MR images of 52 glioblastoma patients with unilateral tumours acquired before and three months after the end of radio(chemo)therapy were analysed. GM and WM volumes in the contralateral hemisphere were compared between segmenting the whole brain (full) and the contralateral hemisphere only (cl) with SPM and FSL. Relative GM and WM volumes were compared using paired t tests and correlated with the corresponding mean dose in GM and WM, respectively.

Results

Mean GM atrophy was significantly higher for full segmentation compared to cl segmentation when using SPM (mean ± std: ΔV_GM,full = − 3.1% ± 3.7%, ΔV_GM,cl = − 1.6% ± 2.7%; p < 0.001, d = 0.62). GM atrophy was significantly correlated with the mean GM dose with the SPM cl segmentation (r = − 0.4, p = 0.004), FSL full segmentation (r = − 0.4, p = 0.004) and FSL cl segmentation (r = -0.35, p = 0.012) but not with the SPM full segmentation (r = − 0.23, p = 0.1).

Conclusions

For accurate normal tissue volume measurements in brain tumour patients using SPM, abnormal tissue needs to be masked prior to segmentation, however, this is not necessary when using FSL.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10334-021-00922-3.

Measurement of relative lung perfusion with electrical impedance and positron emission tomography: an experimental comparative study in pigs

BACKGROUND

Electrical impedance tomography (EIT) with indicator dilution may be clinically useful to measure relative lung perfusion, but there is limited information on the performance of this technique.

METHODS

Thirteen pigs (50-66 kg) were anaesthetised and mechanically ventilated. Sequential changes in ventilation were made: (i) right-lung ventilation with left-lung collapse, (ii) two-lung ventilation with optimised PEEP, (iii) two-lung ventilation with zero PEEP after saline lung lavage, (iv) two-lung ventilation with maximum PEEP (20/25 cm H₂O to achieve peak airway pressure 45 cm H₂O), and (v) two-lung ventilation under unilateral pulmonary artery occlusion. Relative lung perfusion was assessed with EIT and central venous injection of saline 3%, 5%, and 10% (10 ml) during breath holds. Relative perfusion was determined by positron emission tomography (PET) using ⁶⁸Gallium-labelled microspheres. EIT and PET were compared in eight regions of equal ventro-dorsal height (right, left, ventral, mid-ventral, mid-dorsal, and dorsal), and directional changes in regional perfusion were determined.

RESULTS

Differences between methods were relatively small (95% of values differed by less than 8.7%, 8.9%, and 9.5% for saline 10%, 5%, and 3%, respectively). Compared with PET, EIT underestimated relative perfusion in dependent, and overestimated it in non-dependent, regions. EIT and PET detected the same direction of change in relative lung perfusion in 68.9-95.9% of measurements.

CONCLUSIONS

The agreement between EIT and PET for measuring and tracking changes of relative lung perfusion was satisfactory for clinical purposes. Indicator-based EIT may prove useful for measuring pulmonary perfusion at bedside.

Somatostatinrezeptor-PET/CT

Die vorliegende Handlungsempfehlung dient als Grundlage zur Qualitätssicherung der Somatostatinrezeptor (SSTR-) PET/CT bei onkologischen Patienten. Die Leitlinie wurde interdisziplinär erarbeitet und enthält neben der Definition und Zielsetzung einen Konsens hinsichtlich der erforderlichen klinischen Hintergrundinformationen, Indikationsstellung, Durchführung, Auswertung, Dokumentation und Befunderstellung. Dabei werden die beiden gebräuchlichsten Radiotracer der SSTRPET/ CT (68Ga-DOTATOC und 68Ga-DOTATATE) vertieft dargestellt. Die SSTR-PET/CT erfordert eine enge Interaktion zwischen den zuweisenden und ausführenden Fachdisziplinen unter Berücksichtigung bereits vorhandener Leitlinien und Handlungsempfehlungen europäischer und deutscher Fachgesellschaften, namentlich der European Association of Nuclear Medicine (EANM), der Deutschen Gesellschaft für Endokrinologie (DGE), Deutschen Gesellschaft für Nuklearmedizin (DGN) und Deutschen Röntgengesellschaft (DRG).

Wertigkeit der Hoden Perfusionsszintigraphie

Perfusion scintigraphy of the testicles has still its place, in addition to scrotal ultrasound imaging, in the investigation of the “acute scrotum”. It reveals scintigraphic patterns typical for twisted testicle and acute or subacute epididymitis. Especially in the Bundeswehr, with its large number of young men, this method enhances the diagnostic spectrum and helps in making surgical decisions. However, in the examination of scrotal masses, ultrasound imaging or surgery is to be preferred.

Dosimetrische Grundlagen für die endo vaskuläre Therapie mit Re-188 zur Prävention der Restenose nach Angioplastie

Ziel: Für die endovaskuläre Brachytherapie stehen unterschiedliche Radionuklide zur Verfügung. Ein interessantes Konzept ist die Nutzung eines flüssigen Betastrahlers in einem Ballonkatheter. Re-188 kann aus einem Generatorsystem gewonnen werden und steht somit täglich zur Verfügung. Es sollten dosimetrische Daten erhoben werden. Methode: Es wurde die radiale Abnahme der Dosis von Re-188 bei einem typischen Dilatationskatheter (Durchmesser 3 mm, Länge 20 mm) berechnet und mit TLD-Messungen verglichen. Ergebnisse: Bei einer spezifischen Aktivität von 370 MBq/ml konnten 0,3 Gy pro 1 min in 0,5 mm Abstand von der Ballonwand gemessen werden. Doppelmessungen wiesen eine Abweichung von 3% auf. Ein schneller Dosisabfall von 50% innerhalb von 0,5 mm bzw. von 90% innerhalb von 2,5 mm wurde beobachtet. Meßwerte und Berechnungen stimmten gut überein. Die Daten von Re-188 und Y-90 entsprechen sich weitgehend. Schlußfolgerung: Berechnungen über die Dosisverteilung von Re-188 stimmen mit TLD-Messungen gut überein. Bei einer spezifischen Aktivität von 1,85 GBq/ml können in 2-3 Minuten 10-15 Gy an der Gefäßwand einer Koronararterie appliziert werden. Gegenüber radioaktiven Stents oder radioaktiven Drähten bietet sich hiermit eine einfache Alternative für die Prävention der Restenose an.

F-18-FDG-PET zur Primärdiagnostik und Dignitätsbeurteilung pleuraler Prozesse

Ziel: Zahlreiche Studien belegen die hohe Treffsicherheit der Positronen-Emissions-Tomographie (PET) mit 2-[F-18]-Fluoro-2-desoxy-D-Glukose (FDG) bei der Dignitätsbeurteilung nicht-verkalkter Lungenrundherde. Ziel dieser Untersuchung war die Evaluation der Wertigkeit der FDG-PET in der Primärdiagnostik und Dignitätsbeurteilung pleuraler Veränderungen. Patienten/Methode: Dreizehn Patienten mit computertomographisch bekannten pleuralen Raumforderungen, von denen drei zusätzlich einen Pleuraerguß aufwiesen, sowie drei Patienten mit ätiologisch unklarem Pleuraerguß wurden einer FDG-PET unterzogen. Die PET wurde 50 min nach i.v. Injektion von 400-670 MBq F-18-FDG in Standardtechnik (ohne Schwächungskorrektur) durchgeführt. Die Sicherung der endgültigen Diagnose erfolgte in allen Fällen histologisch. Ergebnisse: Histologisch hatten zwölf Patienten pleurale beziehunsgweise pulmonale Malignome (neun Pleuramesotheliome, drei Adenobronchialkarzinome mit Pleuritis carcinomatosa), vier Patienten wiesen benigne pleurale Veränderungen auf (ein Fibrom, ein tuberkulöse Pleuritis, ein Pleuraschwarte, ein Pleuraempyem). Mittels FDG-PET wurden alle pleuralen Prozesse richtig klassifiziert, wobei zwölf richtig positive und vier richtig negative Befunde erhoben wurden. Schlußfolgerung: Unsere Daten zeigen, daß FDG-PET mit hoher Sensitivität maligne pleurale Prozesse detektieren kann.

Präoperative Dignitätsbeurteilung asymptomatischer Adnextumoren mittels Positronen-Emissions-Tomographie und F-18-FluordeoxygIukose

Ziel: Es wurde untersucht, ob die FDG-PET zu einer Verbesserung der Dignitätsbeurteilung asymptomatischer, sonographisch malignomsuspekter Ovarialtumoren beitragen kann. Methode: 85 Patientinnen mit malignomsuspekten, asymptomatischen Adnextumoren unterzogen sich einer FDG-PET Untersuchung. Emissionsaufnahmen des Abdomens wurden ca. 1 h nach i. v. Injektion von 222-555 MBq F-18-FDG angefertigt (Exact HR+ bzw. ECAT 931). Die Bildrekonstruktion erfolgte iterativ. Die PET-Aufnahmen wurden visuell ausgewertet, zum einen ohne andere bildgebende Verfahren, zum anderen zusammen mit der Kernspintomographie. Die Validierung erfolgte mittels Histologie. Ergebnisse: Histologisch fanden sich 8 Malignome, von denen 4 mittels FDGPET als richtig positiv erkannt wurden. Falsch negative Resultate ergaben sich bei 2 Adenokarzinomen im Stadium pT1a und bei 2 Borderline-Tumoren. Bei 60 der 77 benignen Ovarialtumoren konnte das Vorliegen von Malignität mittels PET ausgeschlossen werden. Falsch positive Ergebnisse lagen bei 3 akut entzündlichen Veränderungen, 1 Teratom, 1 benignen Schwannom, 1 Dermoidzyste, 1 benignen Thekom, 1 serösen Zyste, 1 serösen Zystadenom, 2 muzinösen Zystadenomen, 2 Corpusluteum-Zysten, 3 Endometriosezysten und 1 Sactosalpinx vor, wobei in mindestens 6 Fällen der falsch positive FDG-Uptake einer Fehlinterpretation von physiologischer Darmaktivität zuzuschreiben war. Die Sensitivität und Spezifität der FDG-PET betrugen 50% und 78%. Die retrospektive Befundung zusammen mit der Kernspintomographie steigerte die Spezifität auf 86% (bei gleichbleibender Sensitivität). Schlußfolgerung: Die Sensitivität der FDG-PET bezüglich der Detektion von Borderline-Tumoren und Frühkarzinomen des Ovars ist deutlich eingeschränkt. Die sich aus der geringen Inzidenz maligner Ovarialtumoren ergebende Anforderung höchster Spezifität an ein Verfahren zur Dignitätsdiagnostik wird von der FDG-PET auch unter Einbeziehung kernspintomographischer Informationen nicht erfüllt. Die FDG-PET ist somit in der klinischen Situation der präoperativen Dignitätsbeurteilung suspekter, asymptomatischer Ovarialtumoren nicht empfehlenswert.

99mTc reduziert nach intrazellulärer Aufnahme in NIS-positiven Zellen in vitro das klonogene Überleben 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 PC Cl3 (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.

DNA damage in lymphocytes after irradiation with 211At and 188Re

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.

Radiation exposure of patients during 68Ga-DOTATOC PET/CT examinations

Aim: Investigation of the biodistribution and calculation of dosimetry of Ga-68-DOTATOCfor 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).

Dosimetry of cell-monolayers in multiwell plat

Aim: Irradiation of cells in-vitro with unsealed radionuclides is often carried out in cylindrical multi-well-plates. For calculation of the absorbed dose using the sphere model is common. This model assumes a spherical distribution of activity. However, by physical aspects a dose reduction in the peripheral area of the activity volume is expected and predicted especially for high-energy beta-emitting radionuclides. The impact on cellular dosimetry shall be depicted in this paper. Methods: The dose-distribution inside a multi-well-plate was calculated by convolving the dose distribution around a point source with a given activity. This was performed for the radionuclides I-131, Re-188 and Y-90 in wells of different sizes. For comparison the sphere dose was also calculated. Results: Depending on the beta-energy differences up to 40% between the mean calculated dose and the mean sphere dose were found, whereby calculated dose was always lower than the sphere model prediction. Furthermore a fall-off was calculated for the bottom-dose compared to dose in the centre. An analytical expression was revealed for the bottom-dose with respect to the filling level for three different wells. Conclusion: The shape of geometry and the influence on dose distribution must be considered especially at in-vitro exposure with low energy and short range beta-emitting radionuclides. There could be a great impact for exact dose estimation, which is especially necessary to know for comparison of different irradiation experiments (e.g. different radionuclides, various irradiation geometries or comparison with x-rays).

Cellular damage 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 PC Cl3 was studied. Furthermore, we analysed the effect of intracellular accumulation. Methods: The thyroid cell line PC Cl3 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 perchlorat 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 crossfire through neighborhood cells.

Where does subclinical hypothyroidism start?

The upper limit of the TSH reference range is currently under discussion. In its recent guidelines, the National Academy of Clinical Biochemistry (NACB) recommended the use of ~2.5 mIU/L, rather than ~4 mIU/L, due to the fact that reference populations, on which the definition of the reference range is based, contain persons undergoing an initial phase of autoimmune thyroid disease. This will skew the upper reference limit of TSH. Ultrasonography, in addition to measurement of thyroid autoantibodies, should be used to exclude these persons. Objective: The present study investigates whether the NACB recommendation also applies for a region of mild iodine deficiency. Methods: According to NACB criteria, a reference population (713 persons) was defined out of a total study population of 1442. The TSH reference range was calculated in this reference group and in further subgroups by percentiles. The results were compared with the total study population and the NACB recommendation. All assays used were provided by BRAHMS Diagnostica AG, Hennigsdorf, Germany. Results: As expected, all median TSH values, excluding the median of the group with a hypoechogenic thyroid were close to 1.2 mIU/L. The 97.5th percentile in the reference population was 3.35 mIU/L. However, there was no difference compared to the total study population. Conclusion: The upper reference limit for TSH based on a reference population according to NACB criteria came down to 3.35 mIU/L, but not to ~2.5 mIU/L. Interestingly, there is no difference compared to the total study population.

Predictive value of thyrotropin receptor antibodies using the second generation TRAb human assay after radioiodine treatment in Graves’ disease

The detection of TSH-receptor antibodies (TRAb) in patients with Graves’ disease is routinely used in nuclear medicine laboratories. This determination has been possible for approximately 3 years with a second generation human TRAb assay. Studies showed that this TRAb determination is diagnostically more sensitive compared to established, porcine TRAb assays. Objective: The aim of our study was to investigate, based on a ROC analysis, whether TRAb determination with the new, second generation assay allows a dependable statement about probability of occurence of relapse after radioiodine therapy in patient suffering from Graves’ disease. Methods: 57 patients were examined with the DYNOtest® TRAKhuman (BRAHMS Diagnostica AG, Hennigsdorf) directly before and six months after therapy with radioiodine (dose: 150 Gy). A ROC-analysis was performed to determine positive/negative predictive values depending on different cut-off values. Results: Whereas 21/57 patients became eu- or hypothyroid after six months, 36/57 patients relapsed. Nonrelapsed patients showed a significant lower median TRAb titer (4.2 IU/l vs. 19.2 IU/l; p <0.05) compared to relapsed patients. But the positive predictive value conducted 63 and 66, 62 and 66 as well as 63 and 69% (before and after therapy) linked with the cut-offs 1.0, 1.5, and 2.0 IU/l. So it was in areas also achieved by the first generation porcine radioreceptorassay. Conclusion: An increased sensitivity is achieved undoubtedly with the new DYNOtest® TRAKhuman in the diagnostic of Graves’ disease. It is not held over the established radioreceptorassay concerning the positive predictive value for relapsing patients.

Beta-radiation exposure at the finger tips during the radionuclide synovectomy

Ziel: Der Anstieg der Therapiezahlen bei der Radio-synoviorthese (RSO) und die neue Strahlenschutzverordnung (StrSchV) erfordern, die -Strahlenbelastung, HP(0,07), des Personals bei der RSO zu dokumentieren. Methode: Da die amtlichen Teilkörperdosimeter (TLDFingerringdosimeter) die -Strahlenbelastung bei der RSO ungenügend wiedergeben, wurden Thermolumineszenzdosimeter (TLD) auf allen Fingerkuppen des Therapeuten, Radiochemikers und der assistierenden Schwester platziert. An 6 Therapietagen mit insgesamt 155 behandelten Gelenken erfolgte die Messung der HP(0,07) für die Nuklide 169Er, 186Re, 90Y. Ergebnisse: Die höchste Dosis zeigten linker Zeigefinger- (ZF li.) und Daumenkuppe (Daumen li.) des Therapeuten (Rechtshänder). Für drei Therapiesitzungen mit 52 Finger- (1204 MBq 169Er), 31 großen Gelenken (2405 MBq 186Re) sowie 15 Kniegelenken (3100 MBq 90Y) betrug die kumulative Dosis für den ZF li. 190 mSv , für den Daumen li. 48 mSv. Als maximale Ortsdosen ergeben sich: 0,56 Sv/MBq (169Er) bzw. 1,52 Sv/MBq (186Re) am ZF li. Durch Einsatz eines Manipulators für die Fixierung der Injektionsnadel konnte die Fingerbelastung für 90Y am li. ZF von 22,09 auf 0,42 Sv/MBq reduziert werden. Die kumulative Fingerbelastung betrug 119 mSv am Daumen li. (Radiochemiker) und 16 mSv am ZF li. (Assistenz). Schussfolgerung: Bei üblicher Durchführung der RSO wird der größte Teil der HP(0,07) durch 90Y verursacht. Besonders am ZF li. besteht die Gefahr, den Grenzwert der Organdosis für die Haut §55 StrlSchV zu überschreiten. Mit einem Manipulator zur Fixierung der Injektionsnadel kann die maximale Fingerbelastung um den Faktor 50 reduziert und der gesetzlich vorgeschriebene Grenzwert eingehalten werden.

Peptidrezeptor-Radionuklidtherapie Somatostatinrezeptor- exprimierender Tumore

Diese Handlungsempfehlung soll eine Grundlage für die Qualitätssicherung der Peptid - rezeptor-Radionuklidtherapie (PRRT) von Patienten mit Somatostatinrezeptor-exprimierenden Tumoren schaffen, die zurzeit in Deutschland bei fehlenden gleichwertigen oder besseren Therapiealternativen im Rahmen eines individuellen Heilversuches erfolgt. Sie wurde interdisziplinär erarbeitet und enthält neben Definition, allgemeiner Zielsetzung und klinischen Hintergrundinformationen Angaben zu Indikationen und Kontraindikationen der PRRT. Im Mittelpunkt stehen die Anforderungen, die an das Behandlungszentrum gestellt werden, wie die enge Zusammenarbeit der an der Behandlung beteiligten Fachgebiete. Weiterhin wird spezifiziert, welche Untersuchungsbefunde vor der Therapie vorliegen müssen und wie die PRRT technisch und organisatorisch durchzuführen ist. Nach der Behandlung ist eine langfristige Nachsorge/Kontrolle der therapierten Patienten – u. a. zur Gewinnung onkologischer Qualitätsparameter – unabdingbar. Die gesamte Behandlung einschließlich der Nachsorge muss in enger Abstimmung und Zusammenarbeit der beteiligten Fachdisziplinen erfolgen, wobei in der Regel die Empfehlung zur PRRT durch ein multidisziplinäres Tumorboard erfolgen sollte.

β-radiation exposure with 188Re-labelled pharmaceuticals

Aim: The number of therapies with radiopharmaceuticals labelled with 188Re is increasing requiring the documentation of the beta radiation exposure Hp(0.07) of the staff at all working and production sites and during the application and follow-up of the patient according to the new German Radiation Protection Law (StrlSchV). However, data for β-radiation exposure are rare. Therefore, we determined the personal dose Hp(0.07) of the skin of the hands handling 188Re radiopharmaceuticals to identify steps of high radiation exposure and to optimize working conditions. Method: Thermoluminescence dosimeters (TLD 100) were fixed to the fingertips of the radiochemist, the physician and the nurse and compared to official ring dosimeters. In addition, to monitor radiation exposure continuously readable electronic beta- and gamma dosimeters EPD (Siemens) were used. At eight days in which therapies were performed these readings were evaluated. Results: Considering one therapy with a 188Re-labelled radiopharmaceutical the middle finger of the radiochemist (production) and the physician (application) showed a radiation burden of 894 and 664 μSv/GBq, respectively. The cumulative dose of the fingertips after eight days of therapy was 249 and 110 mSv for the radiochemist and physician, respectively. A cumulative finger dose after eight days of therapy of 17 and 38 μSv/GBq was found for physician and nurse leading to a Hp(0.07) of 3 and 6 mSv, respectively. Preparing the radiopharmaceutical labelled with 20GBq of 188Re the reading of the personal electronic dosimeter of the radiochemist showed a γ-dose rate H . p(10) of 55 μSv/h and a β-dose rate H . p(0.07) of 663 μSv/h which are obviously not representative for the true radiation dose to the skin of the fingertips. Conclusion: During therapy with 188Re-labelled radiopharmaceuticals the true radiation dose to the skin of the finger tips exceeds by far the readings of the official ring dosimeters as well as the continuously readable beta- and gamma dosimeters. This means a risk in exceeding the radiation limit of 500 mSv/a given in the German Radiation Protection Law (§55 StrSchV) primarily in the working field of the radiochemist and the administering physician.

Therapy of malignant ascites in vivo by 211At-labelled microspheres

Aim: Determination of the biological effect of the alpha emitter 211At on cellular level as well as the assessment of dosimetric data in a tumour model in vivo. Methods: Transplantation of malignant ascitic cells in mice intraperitoneally and estimation of tumour characteristics (doubling time of the cells, mean survival of the animals following an i.p. application of a defined tumour cell number). 211At labelled human serum albumine microspheres B-20 (MSP) of variing activity were injected into tumour bearing mice intraperitoneally. The effectiveness of the therapy was evaluated by means of determination of the duration of cell cycle arrest as well as the microscopic analysis of the rate of abnormal mitotic cells due to radiation induced damage. Furthermore, dose dependence of survival was evaluated. Results: Three days following the intraperitoneally application of 8 x 106 tumour cells, 50-600 kBq 211At-MSP were applied into the abdominal cavity. Considering the volume of ascites at this time and the administered activity, dose calculations were performed. An activity of 50 kBq caused a dose of 0.84 Gy. The increase of radiation induced effect on ascitic tumour cells was correlated with the dose. Between the duration of the cell cycle arrest and the administered activity, a directly proportional correlation was found. The mean survival of non-treated animals was 16.9 ± 3.7 days. The prolongation of the survival was proportional to the activity administered. Using a dosage of 10 Gy, five animals out of 16 survived. Conclusion: Therapy of malignant ascitic cells using 211At-MSP was effective in vivo. For tumour therapy, the 211At represents a highly effective alternative to usually applied beta emitters.

Intraindividual comparison of [11C]acetate and [11C]choline PET for detection of metastases of prostate cancer

In a pilot trial we investigated whether significant differences in prostate cancer (PCA) imaging would be observed using [11C]acetate and [11C]choline positron emission tomography (PET). Methods: Twelve patients were studied with both radiotracers. Whole body PET without attenuation correction was performed after injection of 0.95 ± 0.15 GBq [11C]acetate and 0.84 ± 0.13 GBq [11C]choline, respectively, from 5 to 60 min p. i. Focally increased uptake in bone, below the urinary bladder or in a lymph node region was considered as tumour. Primary tumour, lymph node involvement, bone metastases, local recurrence; and no evidence of disease were known in 2, 4, 2, 2; and 2 patients, respectively. Results: [11C]Acetate uptake was highest in spleen and pancreas while [11C]choline uptake was predominant in liver and kidney parenchyma. However, interindividual variation was high. The potential of both radiotracers to detect known bone lesions, lymph node metastases, and imaging of the primary tumour was identical. However, both failed to detect a small local recurrence in two patients as well as to demonstrate lymph node involvement in one patient, which was confirmed by surgery. Conclusions: In this preliminary study, uptake of both radiotracers in prostate cancer or its metastases was nearly identical and none of them should be favoured. At present, both radiotracers influence patient management by detection of local recurrence, lymph node, or bone metastases of PCA.

Influence of time-dose-relationships in therapeutic nuclear medicine applications on biological effectiveness of irradiation

Aim: The biological effectiveness of irradiation is influenced not only by the total dose but also the rate at which this dose is administered. Tolerance dose estimates from external radiation therapy with a conventional fractionation protocol require adaptation for application in targeted radionuclide therapy. Methods: The linear-quadratic model allows for calculation of the biologically effective dose (BED) and takes into consideration tissue specific factors (recovery capacity) as well as dose rate effects (recovery kinetics). It can be applied in radionuclide therapy as well. For relevant therapeutic radionuclides (e. g. 188Re, 90Y, 177Lu, and 131I), the effect of different physical decay times and variable biological half-lives on BED was calculated for several organs. Results: BED is markedly increased using 188Re compared to longer-lived radionuclides. The effect is dose-dependent and tissue-specific, resulting, for example, in higher effects on the kidneys compared to bone marrow. Therefore, in unfavourable conditions (e. g. reduced recovery capacity due to concomitant diseases or previous therapy), the BED may exceed organ dose tolerance. Conclusion: Time-dose-relationships have to be taken into consideration by the calculation of BED for internal radionuclide therapy. The biological effectiveness depends on dose- and tissue-specific factors and is much more pronounced in 188Re than in 90Y and other longer living radionuclides. Determination of organ tolerance dose values should take into account these radiobiological differences, since it is currently not considered in dosimetry programs.

Radiation treatment planning in brain tumours

Aim: Amino acid PET has become an important diagnostic tool for brain tumour imaging. In this data analysis, the potential impact of amino acid PET with 3-O-methyl- 6-[18F]fluoro-L-DOPA ([18F]OMFD) on radiation treatment planning is addressed by the following questions: 1. Was tumour tissue identified with OMFD-PET which was not covered by the conventionally derived planning target volume (PTV)? 2. Would the PTV have been changed incorporating OMFD-PET? Patients, methods: OMFD-PET of 25 patients after subtotal resection of malignant glioma was evaluated. The region of elevated tracer uptake of PET and of contrast enhancing masses on MRI were outlined as separate gross tumour volumes (GTVMRI and GTVOMFD) and reconstructed in the planning CT for comparison with the conventionally drawn GTVconv. A PTVnew based on GTVconv+MRI was calculated. Pairwise differential volumes were calculated to estimate overlap and differential volumes delineation by each image modality and the PTVconv and PTVnew respectively. Results: Differential volume analysis showed > 10 cm3 of GTVOMFD outside GTVconv and GTVMRI in 5/25 patients respectively. From GTVMRI >10 cm3 were found outside GTVOMFD in 8/25 patients. Although all tumour areas indicated by [18F]OMFD were covered by the conventionally derived PTV, based on a GTVOMFD+MRI, the PTVnew would have been enlarged >20% in seven patients. In seven patients the PTVnew would have been reduced. Conclusion: OMFD-PET indicated tumour tissue outside the tumour region identified with MRI, adding valuable information for the delineation of the GTV in radiation treatment planning. OMFD-PET contains the potential to tailor the high dose radiation to the appropriate tumour volume, especially if dose escalation is desired.

Preincubation with Sn-complexes causes intensive intracellular retention of 99mTc in thyroid cells in vitro

Technetium radiopharmaceuticals are well established in nuclear medicine. Besides its well-known gamma radiation, 99mTc 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 99mTc can be present in exposed cells and which radiobiological effects could be estimated in 99mTc-overloaded cells. Methods: Sodium iodine symporter (NIS)- positive thyroid cells were used. 99mTc-uptake studies were performed after preincubation with a non-radioactive (cold) stannous pyro - phosphate kit solution or as a standard 99mTc 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 99mTc and is followed by further pertechnetate influx to an unexpectedly high 99mTc level. The uptake of 99mTc pertechnetate in NIS-positive cells can be modified using stannous pyrophosphate from 3–5% to >80%. The maximum possible cellular uptake of 99mTc was 90 Bq/cell. Compared with nearly pure extracellular irradiation from routine 99mTc complexes, cell survival was reduced by 3–4 orders of magnitude after preincubation with stannous pyrophosphate. Conclusions: Intra cellular 99mTc 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.

Sodium-iodide symporter positive cells after intracellular uptake of 99mTc versus α-emitter 211At

Purpose: We evaluated the DNA damaging potential of Auger electrons emitted in the decay of 99mTc compared to α-particles of 211At. Material and methods: The impact of 99mTc and 211At was monitored in a NIS-expressing rat thyroid cell model PC Cl3 with varying, yet defined intra- and extracellular radionuclide distribution (using ± perchlorate). The radiotoxicity of 99mTc 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 99mTc, 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 99mTc. 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 99mTc and 211At increased cellular dose and reduced clonogenic survival.

Very stable 188Re-S4 chelates for labelling biomolecules

Aim: The preparation and stability of a new 188Re-S4-complex [S4 = (1-aza-18-crown-6)(O)C-C(SH)-C(SH)- C(O)NH-(CH2)3-NH-(CH2)3-NHC(O)-C(SH)-C(SH)- C(O)(1-aza-18-crown-6] was studied at therapeutic relevant radioactive concentrations. The results were compared with 188Re-MAG3 (MAG3: mercaptoacetyltriglycine) and 188Re-DMSA preparations (DMSA: dimercaptosuccinic acid) performed with the same highly concentrated [188Re]perrhenate solution (12-15 GBq/ml). Methods: The 188Re complexes were prepared by direct reduction of perrhenate (188Re-S4-complex) as well as via the 188Re- EDTA precursor complex (188Re-MAG3, 188Re-DMSA). The preparations were stabilised with 15 mg of ascorbic acid and analysed after 1, 2, and 24 hours by TLC and HPLC. Additionally, in vitro and in vivo stability studies were performed with the purified complexes. Results: After stabilisation with 15 mg of ascorbic acid, all of the complexes were nearly stable under nitrogen for hours, and only 2–8 % of perrhenate was observed after 24 h. In contrast, only the 188Re-S4 complex was completely stable in vitro and in all investigated in vivo samples after separation of ligand excess and reducing agent by HPLC. Conclusion: The bridging amine group or free carboxylic groups of the S4-ligand framework make available reactive positions for coupling biomolecules to the chelate. Thus it appears that the new 188Re-S4 complexes offer the possibility of stable and high specific activity labelling of biomolecules for therapeutic application.

Nuklearmedizin in Deutschland

Aim: To explain the spectrum and number of in-vivo nuclear medicine examinations and therapies based on official statistics about out-patient and in-patient care. Trends in time of the frequency and spectrum of procedures as well as data on the health care structure for nuclear medicine in Germany should be collected. Methods: Data from the Gesundheitsberichterstattung des Bundes, from the frequency statistics of the statutory health insurance for out-patients and from the Bundes - ärztekammer were used. Customized queries were performed to analyse temporal changes. Results: Nuclear medicine physicians are more frequently consulted by out-patients over the last years (2008: 2 024 498; 2009: 2 164 664) and the number of colleagues in private practice increased. For in-patients, the frequency of conventional nuclear medicine procedures (mainly for brain, lymphatic system, lung and heart) increased since 2008 after a decline in previous years (2009: 323 515; +4.6%) and the number of PET(/CT) examinations continued to rise (2009: 25 123; +18%), even if changes in OPS keys may hamper comparisons. Nearly 600 gamma cameras and 76 PET(/CT) scanners were installed in hospitals in 2008. Nuclear medicine procedures are increasingly performed as cross sectional imaging like SPECT(/CT) and PET(/CT). With the supply shortfall with 99Mo, the frequency of thyroid scans with 123I iodine increased as well as the use of 18F PET as a substitute for conventional bone scans. The number of radionuclide therapies, in particular non-thyroid treatments, increased since the mid-nineties and stabilized at nearly 50 000 cases per year with shorter lengths of stay. Conclusion: The details of the present analysis may help to understand the positive evolution of key numbers for nuclear medicine.

Improving external beam radiotherapy by combination with internal irradiation

The efficacy of external beam radiotherapy (EBRT) is dose dependent, but the dose that can be applied to solid tumour lesions is limited by the sensitivity of the surrounding tissue. The combination of EBRT with systemically applied radioimmunotherapy (RIT) is a promising approach to increase efficacy of radiotherapy. Toxicities of both treatment modalities of this combination of internal and external radiotherapy (CIERT) are not additive, as different organs at risk are in target. However, advantages of both single treatments are combined, for example, precise high dose delivery to the bulk tumour via standard EBRT, which can be increased by addition of RIT, and potential targeting of micrometastases by RIT. Eventually, theragnostic radionuclide pairs can be used to predict uptake of the radiotherapeutic drug prior to and during therapy and find individual patients who may benefit from this treatment. This review aims to highlight the outcome of pre-clinical studies on CIERT and resultant questions for translation into the clinic. Few clinical data are available until now and reasons as well as challenges for clinical implementation are discussed.

[Positron emission tomography 2013 in Germany. Results of the query and current status]

AIM

Five years after the first survey the positron emission tomography (PET) council of the German Society of Nuclear Medicine (DGN) repeated a survey to re-evaluate the status of PET diagnostics in Germany based on the data of the year 2013.

METHODS

A web-based questionnaire was used for gathering information retrospectively. Details regarding the physicians involved in PET operations, PET systems, and radiopharmaceuticals were also part of the survey as well as indications and number of studies. Furthermore, the role of PET and PET/CT within the diagnostic process was evaluated. In addition, official statistical hospital reports were analysed.

RESULTS

Responses from 52 sites were analysed. They reported a total of 38,350 PET studies in 2013. In the majority of cases PET was used in oncologic indications (87%). Further main applications were: neurology 6%, cardiology 1%, and inflammation 5%. University or other hospitals performed 85% of the studies. The portion of in-patients was 26%. Hybrid systems (56 PET/CT, 5 PET/MRT, and 2 stand-alone PET) were most frequently used for imaging. The radiotracers were labelled with F-18 in 90% of the studies, whereas Ga-68 was used in 9% and C-11 in 1%. Lung tumours were the most investigated tumour entity (40%), followed by malignant lymphoma (8%), tumours of the gastrointestinal tract (5%), and NET (5%). 20% of the 333 physicians hold a PET certificate awarded by the DGN. More than 50% of the facilities were certified according ISO9001, KTQ or QEP standard. The findings of nearly 60% of the oncological studies were discussed interdisciplinary in a tumour board. In federal statistical reports a 56% increase of in-patient PET operations during 5 years was found.

CONCLUSION

In Germany, a moderate increase (9% per year) of PET studies is observed, but compared with other industrialised countries PET is still less established.

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.

Wie schreibe ich eine gute Übersichtsarbeit?

Übersichtsarbeiten stellen einen wichtigen Teil medizinischer Literatur dar und ermöglichen dem Leser innerhalb kurzer Zeit einen umfassenden Überblick über ein bestimmtes Thema zu bekommen. In der Radiologie und der Nuklearmedizin haben Übersichtsarbeiten oft einen erzählenden/narrativen Charakter und somit ein hohes Maß an Subjektivität. Diese Subjektivität ist letztlich ausschlaggebend dafür, dass narrative Übersichtsarbeiten bei der Erstellung wissenschaftlicher Leitlinien nicht berücksichtigt werden.

Ziel dieser Arbeit ist es, die Kriterien für die Erstellung einer systematischen Übersichtsarbeit zu beleuchten und den Leser so bei der Erstellung einer systematischen und strukturierten Übersichtsarbeit zu unterstützen.

[Peptide receptor radionuclide therapy for patients with somatostatin receptor expressing tumours. German Guideline (S1)]

This document describes the guideline for peptide receptor radionuclide therapy (PRRT) published by the German Society of Nuclear Medicine (DGN) and accepted by the Association of the Scientific Medical Societies in Germany (AWMF) to be included in the official AWMF Guideline Registry. These recommendations are a prerequisite for the quality management in the treatment of patients with somatostatin receptor expressing tumours using PRRT. They are aimed at guiding nuclear medicine specialists in selecting likely candidates to receive PRRT and to deliver the treatment in a safe and effective manner. The recommendations are based on an interdisciplinary consensus. The document contains background information and definitions and covers the rationale, indications and contraindications for PRRT. Essential topics are the requirements for institutions performing the therapy, e. g. presence of an expert for medical physics, intense cooperation with all colleagues involved in the treatment of a patient, and a certificate of instruction in radiochemical labelling and quality control are required. Furthermore, it is specified which patient data have to be available prior to performance of therapy and how treatment has to be carried out technically. Here, quality control and documentation of labelling are of great importance. After treatment, clinical quality control is mandatory (work-up of therapy data and follow-up of patients). Essential elements of follow-up are specified in detail. The complete treatment inclusive after-care has to be realised in close cooperation with the involved medical disciplines. Generally, the decision for PRRT should be undertaken within the framework of a multi-disciplinary tumour board.

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.

An automatic method for accurate volume delineation of heterogeneous tumors in PET

PURPOSE

Accurate volumetric tumor delineation is of increasing importance in radiation treatment planning. Many tumors exhibit only moderate tracer uptake heterogeneity and delineation methods using an adaptive threshold lead to robust results. These methods use a tumor reference value R (e.g., ROI maximum) and the tumor background Bg to compute the volume reproducing threshold. This threshold corresponds to an isocontour which defines the tumor boundary. However, the boundaries of strongly heterogeneous tumors can not be described by an isocontour anymore and therefore conventional threshold methods are not suitable for accurate delineation. The aim of this work is the development and validation of a delineation method for heterogeneous tumors.

METHODS

The new method (voxel-specific threshold method, VTM) can be considered as an extension of an adaptive threshold method (lesion-specific threshold method, LTM), where instead of a lesion-specific threshold for the whole ROI, a voxel-specific threshold is computed by determining for each voxel Bg and R in the close vicinity of the voxel. The absolute threshold for the considered voxel is then given by Tabs=T×(R-Bg)+Bg, where T=0.39 was determined with phantom measurements.

VALIDATION

30 clinical datasets from patients with non-small-cell lung cancer were used to generate 30 realistic anthropomorphic software phantoms of tumors with different heterogeneities and well-known volumes and boundaries. Volume delineation was performed with VTM and LTM and compared with the known lesion volumes and boundaries.

RESULTS

In contrast to LTM, VTM was able to reproduce the true tumor boundaries accurately, independent of the heterogeneity. The deviation of the determined volume from the true volume was (0.8±4.2)% for VTM and (11.0±16.4)% for LTM.

CONCLUSIONS

In anthropomorphic software phantoms, the new method leads to promising results and to a clear improvement of volume delineation in comparison to conventional background-corrected thresholding. In the next step, the suitability for clinical routine will be further investigated.

Periacetabular bone metabolism following hip revision surgery. PET-based evaluation of allograft osteointegration

The treatment of loosened total hip replacement (THR) acetabular components may require the management of severe bone defects. Although being applied for decades, there is only limited scientific data about the osteointegration of cancellous bone allografts (CBA) and other void fillers. Monitoring of periprosthetic bone regeneration could possibly help to optimize this process thereby reducing late failure rates. The aim of this study was to show osteometabolic changes in periprosthetic CBA after THR revision with the use of sodium-[18F]-fluoride (NaF) and positron emission tomography (PET).

PATIENTS, METHODS

Twelve patients undergoing THR revision with the use of CBA were prospectively enrolled in the study. Nine patients completed all necessary examinations and were included in the evaluation. The temporal pattern of osteointegration was assessed via NaF-PET at one (PET1) and six weeks (PET2) after surgery. CBA, tantalum implants, supraacetabular regions ipsilateral and contralateral, and parasymphyseal pubic bones were delineated as volumes of interest (VOI) in postop CT scans, which were then merged with the PET data.

RESULTS

In comparison to the contralateral supraacetabular reference bone, a significant 1.5-fold increase of osteometabolic activity from PET1 to PET2 was seen in the CBA region. Also, the ipsilateral supraacetabular host bone showed a higher NaF-influx in week 6, compared to the first postoperative week. The supraacetabular site exhibited a significantly 1.8- to 2-fold higher influx and uptake than bone regions in non-operated sites. Tantalum implants had a low NaF influx at both time points investigated.

CONCLUSION

Using NaF-PET osteometabolic changes of CBA and implant-bone-interfaces can be monitored. Applying this method we demonstrated early periprosthetic temporal bone regeneration patterns in THR cup revision patients.

Evaluation of PET quantification accuracy in vivo. Comparison of measured FDG concentration in the bladder with urine samples

Quantitative positron emission tomography (PET) requires accurate scanner calibration, which is commonly performed using phantoms. It is not clear to what extent this procedure ensures quantitatively correct results in vivo, since certain conditions differ between phantom and patient scans.

AIM

We, therefore, have evaluated the actual quantification accuracy in vivo of PET under clinical routine conditions.

PATIENTS, METHODS

We determined the activity concentration in the bladder in patients undergoing routine [18F]FDG whole body investigations with three different PET scanners (Siemens ECAT EXACT HR+ PET: n = 21; Siemens Biograph 16 PET/CT: n = 16; Philips Gemini-TF PET/CT: n = 19). Urine samples were collected immediately after scan. Activity concentration in the samples was determined in well counters cross-calibrated against the respective scanner. The PET (bladder) to well counter (urine sample) activity concentration ratio was determined.

RESULTS

Activity concentration in the bladder (PET) was systematically lower than in the urine samples (well counter). The patient-averaged PET to well counter ratios for the investigated scanners are (mean ± SEM): 0.881 ± 0.015 (ECAT HR+), 0.898 ± 0.024 (Biograph 16), 0.932 ± 0.024 (Gemini-TF). These values correspond to underestimates by PET of 11.9%, 10.2%, and 6.8%, respectively.

CONCLUSIONS

The investigated PET systems consistently underestimate activity concentration in the bladder. The comparison of urine samples with PET scans of the bladder is a straightforward means for in vivo evaluation of the expectable quantification accuracy. The method might be interesting for multi-center trials, for additional quality assurance in PET and for investigation of PET/MR systems for which clear proof of sufficient quantitative accuracy in vivo is still missing.

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.