Radiation doses from low-dose CT scans in SPECT/CT and PET/CT examinations: A survey in Germany.

AIM: Recently, dose reference levels (DRLs) have been defined in Germany for auxiliary low-dose CT scans in hybrid SPECT/CT and PET/CT examinations, based on data from 2016/17. Here, another survey from 2020 was evaluated and compared with the new DRLs as well as with similar surveys from foreign countries. METHODS: The survey, which had already been conducted in the Nordic countries, queried for various examinations including the following values: patient weight and height, volume CT dose index (CTDIvol), dose length product (DLP). For each examination, statistical parameters such as the third quartile (Q3) were determined from all submitted CTDIvol and DLP values. Additionally, for examinations comprising datasets from at least 10 systems, the third quartile (Q3-Med) of the respective median values of each system was calculated. Q3 and Q3-Med were compared with the newly published DRLs from Germany and values from similar studies from other countries. RESULTS: Data from 15 SPECT/CT and 13 PET/CT systems from 15 nuclear medicine departments were collected. For the following examinations datasets from more than 10 systems were submitted: SPECT lung VQ, SPECT bone, SPECT&PET cardiac, PET brain, PET oncology. Especially for examinations of the thorax and heart, the new DRLs are very strict compared to this study. The CTDIvol values for examinations of the head were lower in this study than the DRLs prescribe now. CONCLUSIONS: For certain examination types, there is a need for dose optimization at some clinics and devices in order to take into account the new DRLs in Germany in the future.

Epidermal growth factor receptor inhibitors for radiotherapy: biological rationale and preclinical results.

Blocking the epidermal growth factor receptor (EGFR) represents a role model for a successful biological targeting approach to improving outcomes after radiotherapy. This review summarizes data from several local tumour control experiments in which EGFR inhibitors were combined with radiation in FaDu human squamous cell carcinomas xenografted into nude mice. BIBX1382BS is an oral bioavailable inhibitor of the intracellular tyrosine kinase domain of EGFR. It was administered in different experimental settings: concurrent with fractionated radiotherapy, following completion of irradiation, and in the period between surgery and adjuvant irradiation. Despite beneficial effects on tumour growth, in none of these experimental settings did BIBX1382BS improve local tumour control. In contrast, cetuximab (Erbitux), an IgG1 monoclonal antibody against the extracellular ligand-binding domain of EGFR, improved local tumour control when given concurrently with radiation. Results from a series of local tumour control experiments designed to elucidate the underlying mechanisms of cetuximab suggest that multiple radiobiological mechanisms might contribute to the observed effects: decreased number of clonogenic tumour cells, increased cellular radiation sensitivity, decreased repopulation and improved reoxygenation of clonogenic tumour cells during the combined treatment. In summary, the data suggest that different classes of EGFR inhibitors may have a different potential to improve local tumour control after fractionated irradiation.

Effect of increase of radiation dose on local control relates to pre-treatment FDG uptake in FaDu tumours in nude mice.

OBJECTIVES: To investigate whether heterogeneity in [(18)F]2-fluoro-2-deoxy-d-glucose (FDG) uptake in a single tumour line, i.e. in tumours with identical genetic background, relates to radiation response. MATERIALS AND METHODS: Sixty-two human FaDu head and neck squamous cell carcinomas in nude mice with a diameter of 7mm entered the study. FDG-PET scanning was performed without anaesthesia on an animal PET scanner immediately prior to irradiation in order to determine maximum standardized uptake values (SUV(max)). Single dose irradiations of 25 or 35Gy were applied under normal blood flow conditions using 200kV X-rays (0.5mm Cu, approximately 1.2Gy min(-1)). The mice were observed for 120 days after irradiation, experimental endpoint was local tumour control evaluated using the Kaplan-Meier method. RESULTS: Analyzing all 62 animals, tumour control probability after irradiation with 25Gy was significantly lower than after irradiation with 35Gy (29% vs. 57%, log rank p=0.016). Pre-treatment SUV(max) values ranged from 0.72 to 3.47, the median SUV(max) value was 1.59. In tumours with FDG uptake less than the median SUV(max), local control was 37% after 25Gy vs. 47% after 35Gy (p=0.37). In contrast, substantial differences in local tumour control were found in tumours with FDG uptake above the median SUV(max) (24% vs. 71%, p=0.006). Multivariate Cox analysis revealed a significant decrease of hazard of recurrence with increasing dose and SUV(max). CONCLUSIONS: An increase of radiation dose had a greater effect on local control in FaDu tumours with higher FDG uptake than in tumours with lower FDG uptake. This supports the hypothesis that pre-treatment FDG-PET may provide useful information for heterogeneous radiation dose prescription in subvolumes of tumours of individual patients. As only one tumour model was studied and single doses were applied, confirmatory investigations using further tumour models and fractionated radiotherapy are warranted.

In vivo studies of the PARP inhibitor, AZD-2281, in combination with fractionated radiotherapy: An exploration of the therapeutic ratio.

BACKGROUND AND PURPOSE: Pre-clinical data have shown that PARP inhibitors (PARPi) may increase the efficacy of radiotherapy in prostate cancer. However, it is uncertain as to whether PARPi lead to clonogenic kill when combined with radiotherapy (RT). MATERIAL AND METHODS: We tested the PARP inhibitor AZD-2281 as a radiosensitizing agent under oxic and hypoxic conditions for clonogenic survival in vitro and in vivo using the human prostate cancer cell line, 22Rv1. In addition, the effects of PARPi+RT on normal tissue were investigated using a crypt clonogenic assay. RESULTS: AZD-2281 inhibited cellular PARP activity under both oxic and hypoxic conditions. The addition of AZD-2281 radiosensitized 22Rv1 cells under oxia, acute hypoxia and chronic hypoxia in vitro. The combination of AZD-2281 with fractionated radiotherapy resulted in a significant growth delay and clonogenic kill in vivo. No increased gut toxicity was observed using this combined PARPi+radiotherapy regimen. CONCLUSIONS: This is the first preclinical study to demonstrate direct clonogenic kill in vivo by the addition of AZD-2281 to radiotherapy. As we did not observe gut toxicity, the use of PARPi in the context of prostate cancer radiotherapy warrants further investigation in clinical trials.

Effect of [(18)F]FMISO stratified dose-escalation on local control in FaDu hSCC in nude mice.

OBJECTIVE: To investigate the effect of radiation dose-escalation on local control in hypoxic versus non-hypoxic hypoxic tumours defined using [(18)F]fluoromisonidazole ([(18)F]FMISO) PET. MATERIALS AND METHODS: FaDu human squamous cell carcinomas (hSCCs) growing subcutaneously in nude mice were subjected to [(18)F]FMISO PET before irradiation with single doses of 25 or 35Gy under normal blood flow conditions. [(18)F]FMISO hypoxic volume (HV) and maximum standardised uptake value (SUVmax) were used to quantify tracer uptake. The animals were followed up for at least 120days after irradiation. The endpoints were permanent local tumour control and time to local recurrence. RESULTS: HV varied between 38 and 291mm(3) (median 105mm(3)). Non-hypoxic tumours (HV below median) showed significantly better local control after single dose irradiation than hypoxic tumours (HV above median) (p=0.046). The effect of dose was significant and not different in non-hypoxic and in hypoxic tumours (HR=0.82 [95% CI 0.71; 0.93], p=0.002 and HR=0.86 [0.78; 0.95], p=0.001, respectively). Dose escalation resulted in an incremental increase of local tumour control from low-dose hypoxic, over low-dose non-hypoxic and high-dose hypoxic to high-dose non-hypoxic tumours. SUVmax did not reveal significant association with local control at any dose level. CONCLUSIONS: The negative effect of [(18)F]FMISO HV on permanent local tumour control supports the prognostic value of the pre-treatment [(18)F]FMISO HV. Making the assumption that variable [(18)F]FMISO uptake in different FaDu tumours which all have the same genetic background may serve as an experimental model of intratumoural heterogeneity, the data support the concept of dose-escalation with inhomogeneous dose distribution based on pre-treatment [(18)F]FMISO uptake. This result needs to be confirmed in other tumour models and using fractionated radiotherapy schedules.

Combination of EGFR/HER2 tyrosine kinase inhibition by BIBW 2992 and BIBW 2669 with irradiation in FaDu human squamous cell carcinoma.

PURPOSE: To investigate the effect of the dual EGFR/HER2 (ErbB2) tyrosine kinase inhibitors BIBW 2992 and BIBW 2669 on proliferation and clonogenic cell survival of FaDu human squamous cell carcinoma in vitro, and on tumor growth after single-dose irradiation in nude mice. MATERIAL AND METHODS: Cell proliferation, cell-cycle distribution and clonogenic cell survival after irradiation were assayed with and without BIBW 2992 or BIBW 2669 (3, 30, and 300 nM) in vitro. Tumor volume and tumor growth delay (GD(V2)) were determined in tumors growing in NMRI (nu/nu) nude mice, treated with (a) BIBW 2992 (20 mg kg(-1) body weight orally), BIBW 2669 (3-4 mg kg(-1) body weight orally) or carrier until a final tumor diameter of 15 mm, or, (b) 3 days before a 20-Gy single-dose irradiation or, (c) after a 20-Gy single-dose irradiation until reaching the final tumor diameter. RESULTS: BIBW 2992 and BIBW 2669 significantly increased the doubling time of FaDu cells in vitro. A marked dose-dependent antiproliferative effect with blockade of the cells in G0/G1-phase of the cell cycle was found. Incubation with BIBW 2669 or BIBW 2992 for 3 days marginally increased radiosensitivity of FaDu cells in vitro. For BIBW 2992, this effect was statistically significant (p = 0.006). Daily oral application of BIBW 2669 or BIBW 2992 in mice bearing unirradiated FaDu tumors showed a marked antiproliferative effect with a significant prolongation of tumor growth delay (p < 0.0001). After drug application for 3 days, followed by 20-Gy single-dose irradiation, a slight effect of both drugs on tumor growth delay was seen. For BIBW 2669, this effect was statistically significant (p = 0.007). However, this effect disappeared when tumor volumes were normalized to the time point of irradiation suggesting that both drugs showed no or only a slight radiosensitizing effect in vivo. Daily application of BIBW 2669 or BIBW 2992 after a single-dose irradiation showed a clear inhibition of tumor growth with a significantly longer tumor growth delay after drug treatment compared to control tumors (p < 0.002). Enhancement ratios were smaller for irradiated than for unirradiated tumors, suggesting an additive effect for combinations with radiotherapy. In all treatment arms, the effects of BIBW 2669 were not significantly different from BIBW 2992. CONCLUSION: BIBW 2669 and BIBW 2992 showed a clear antiproliferative effect in vitro, whereas radiosensitization was only marginal. The present data are the first to show an effect of combined irradiation and dual EGFR/ErbB2 inhibition on tumor growth delay in vivo. Further preclinical investigations using fractionated irradiation schedules and local tumor control as experimental endpoint are needed to evaluate a possible curative potential for the combination treatment.