[en] The aim of the study was to quantify the dose received by nuclear medicine technologists and radiotherapeutic technologists as a result of PET/CT applications with ¹⁸F-FDG as well as optimization of the procedures and working conditions. Thermo-luminescence dosimeters were used for the determination of the equivalent dose on the hands and for ambient dosimetry. Electronic personal dosimeters as well as the obligatory personal dosimeters provided information concerning the total body effective dose to the workers. The shielding of two shipping containers with different lead thickness for delivery of the FDG to the hospital as well as different dispenser designs for the preparation of the syringes and administration to the patient were evaluated..The effect of the use of a lead shield during supporting and positioning of the patient was also studied. All results were related to a single nuclear medicine technologist (NMT) performing 1000 patients/year, each patient receiving an activity of 370 MBq ¹⁸F-FDG. Dispensing the ¹⁸F-FDG into syringes, using a specifically designed shielded lead container, the so-called 'Koenders' system, resulted in a total equivalent dose on the fingers of 8.4 mSv for the MNT, while the use of the less extensively shielded syringe (the Docking station) resulted in an average finger dose of 71 mSv (p=0.000). Administration of the ¹⁸F-FDG to the patient resulted in a finger dose of 4.6 mSv for the 'Koenders' system, 6.3 mSv in case of the use of a ready made syringe and 23 mSv (p=0.000) in case of the Docking station. The proper use of the mobile lead shield during administration to the patient and removal of the intravenous access from the patient resulted in a significant decrease of the effective dose. Combined with the use of the thicker walled delivery container and the 'Koenders' system, the total effective dose for the NMT was 2.7 mSv, nearly half of the dose before optimization. The positioning of patients for the radiotherapy planning process by RT technologists attributed to an effective dose of 1.9 mSv. The different tasks of the NMT/RT technologists will be discussed. The results of the ambient dosimetry confirmed the effectiveness of the lead shielding present in the walls as well as the classification in supervised (< 6 mSv/yr), controlled (< 20 mSv/yr) and adjacent (< 1 mSv) zones. (author)

[en] Purpose: Because individual tumors are heterogeneous, including for ¹⁸F-deoxyglucose (FDG) uptake and, most likely, for radioresistance, selective boosting of high FDG uptake zones within the tumor has been suggested. To do this, it is critical to know whether the location of these high FDG uptake patterns within the tumor remain stable during radiotherapy (RT). Methods and Materials: Twenty-three patients with Stage I-III non-small-cell lung cancer underwent repeated FDG positron emission tomography computed tomography scans before radical RT (Day 0) and at Days 7 and 14 of RT. On all scans, the high and low FDG uptake regions were autodelineated using several standardized uptake value thresholds, varying from 34% to 80% of the maximal standardized uptake value. The volumes and overlap fractions of these delineations were calculated to demonstrate the stability of the high FDG uptake regions during RT. Results: The mean overlap fraction of the 34% uptake zones at Day 0 with Days 7 and 14 was 82.8% ± 8.1% and 84.3% ± 7.6%, respectively. The mean overlap fraction of the high uptake zones (60%) was 72.3% ± 15.0% and 71.3% ± 19.7% at Day 0 with Days 7 and 14, respectively. The volumes of the thresholds varied markedly (e.g., at Day 0, the volume of the 60% zone was 16.8 ± 20.3 cm³). In contrast, although the location of the high FDG uptake patterns within the tumor during RT remained stable, the delineated volumes varied markedly. Conclusion: The location of the low and high FDG uptake areas within the tumor remained stable during RT. This knowledge may enable selective boosting of high FDG uptake areas within the tumor

[en] This work compares Monte Carlo (MC) dose calculations for ¹²⁵I and ¹⁰³Pd low-dose rate (LDR) brachytherapy sources performed in virtual phantoms containing a series of human soft tissues of interest for brachytherapy. The geometries are segmented (tissue type and density assignment) based on simulated single energy computed tomography (SECT) and dual energy (DECT) images, as well as the all-water TG-43 approach. Accuracy is evaluated by comparison to a reference MC dose calculation performed in the same phantoms, where each voxel's material properties are assigned with exactly known values. The objective is to assess potential dose calculation accuracy gains from DECT. A CT imaging simulation package, ImaSim, is used to generate CT images of calibration and dose calculation phantoms at 80, 120, and 140 kVp. From the high and low energy images electron density ρ_e and atomic number Z are obtained using a DECT algorithm. Following a correction derived from scans of the calibration phantom, accuracy on Z and ρ_e of ±1% is obtained for all soft tissues with atomic number Z in [6,8] except lung. GEANT4 MC dose calculations based on DECT segmentation agreed with the reference within ±4% for ¹⁰³Pd, the most sensitive source to tissue misassignments. SECT segmentation with three tissue bins as well as the TG-43 approach showed inferior accuracy with errors of up to 20%. Using seven tissue bins in our SECT segmentation brought errors within ±10% for ¹⁰³Pd. In general ¹²⁵I dose calculations showed higher accuracy than ¹⁰³Pd. Simulated image noise was found to decrease DECT accuracy by 3-4%. Our findings suggest that DECT-based segmentation yields improved accuracy when compared to SECT segmentation with seven tissue bins in LDR brachytherapy dose calculation for the specific case of our non-anthropomorphic phantom. The validity of our conclusions for clinical geometry as well as the importance of image noise in the tissue segmentation procedure deserves further experimental investigation.

[en] We investigated the feasibility of serial dynamic contrast-enhanced computed tomography (DCE-CT) in patients with advanced/metastatic non-small cell lung cancer (NSCLC) receiving anti-angiogenic (sorafenib) and anti-EGFR (erlotinib) treatment, and correlated tumour blood flow (BF) with treatment outcome. DCE-CTs were performed at baseline and 3 and 6 weeks after starting treatment. Tumour BF, calculated with the maximum slope method, and percentage change were measured in 23 patients (14 male; median age 59 years). Tumour BF was compared at baseline and weeks 3 and 6; the relation with RECIST/Crabb response and progression-free survival (PFS) was assessed. Mean tumour perfusion decreased from 39.2 ml/100 g/min at baseline to 15.1 ml/100 g/min at week 3 (p < 0.001) and 9.4 ml/100 g/min at week 6 (p < 0.001). Tumour perfusion was lower in RECIST and Crabb responders versus non-responders at week 3 (4.2 versus 17.7 ml/100 g/min, p = 0.03) and week 6 (0 versus 13.4 ml/100 g/min, p = 0.04). Patients with a decrease larger than the median at week 6 tended to have a longer PFS (7.1 versus 5.7 months, p = 0.06). Serial DCE-CTs are feasible in patients with NSCLC and demonstrated a significant decrease in tumour BF following sorafenib/erlotinib therapy. Early changes in tumour BF correlated with objective response and showed a trend towards longer PFS. (orig.)

[en] Increased tumour hypoxia is associated with a worse overall survival in patients with head and neck squamous cell carcinoma (HNSCC). The aims of this study were to evaluate treatment-associated changes in ["1"8F]HX4-PET, hypoxia-related blood biomarkers, and their interdependence. ["1"8F]HX4-PET/CT scans of 20 patients with HNSCC were acquired at baseline and after ±20 Gy of radiotherapy. Within the gross-tumour-volumes (GTV; primary and lymph nodes), mean and maximum standardized uptake values, the hypoxic fraction (HF) and volume (HV) were calculated. Also, the changes in spatial uptake pattern were evaluated using ["1"8F]HX4-PET/CT imaging. For all patients, the plasma concentration of CAIX, osteopontin and VEGF was assessed. At baseline, tumour hypoxia was detected in 69 % (22/32) of the GTVs. During therapy, we observed a significant decrease in all image parameters. The HF decreased from 21.7 ± 19.8 % (baseline) to 3.6 ± 10.0 % (during treatment; P < 0.001). Only two patients had a HV > 1 cm"3 during treatment, which was located for >98 % within the baseline HV. During treatment, no significant changes in plasma CAIX or VEGF were observed, while osteopontin was increased. ["1"8F]HX4-PET/CT imaging allows monitoring changes in hypoxia during (chemo)radiotherapy whereas the blood biomarkers were not able to detect a treatment-associated decrease in hypoxia. (orig.)

[en] Purpose: To compare pretreatment scans with perfusion computed tomography (pCT) vs. dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in rectal tumors. Methods and Materials: Nineteen patients diagnosed with rectal cancer were included in this prospective study. All patients underwent both pCT and DCE-MRI. Imaging was performed on a dedicated 40-slice CT-positron emission tomography system and a 3-T MRI system. Dynamic contrast enhancement was measured in tumor tissue and the external iliac artery. Tumor perfusion was quantified in terms of pharmacokinetic parameters: transfer constant K^trans, fractional extravascular-extracellular space v_e, and fractional plasma volume v_p. Pharmacokinetic parameter values and their heterogeneity (by 80% quantile value) were compared between pCT and DCE-MRI. Results: Tumor K^trans values correlated significantly for the voxel-by-voxel-derived median (Kendall's τ correlation, τ = 0.81, p < 0.001) and 80% quantile (τ = 0.54, p = 0.04), as well as for the averaged uptake (τ = 0.58, p = 0.03). However, no significant correlations were found for v_e and v_p derived from the voxel-by-voxel-derived median and 80% quantile and derived from the averaged uptake curves. Conclusions: This study demonstrated for the first time that pCT provides K^trans values comparable to those of DCE-MRI. However, no correlation was found for the v_e and v_p parameters between CT and MRI. Computed tomography can serve as an alternative modality to MRI for the in vivo evaluation of tumor angiogenesis in terms of the transfer constant K^trans.