[Treatment Planning and Dose Verification for Combined Internal and External Radiotherapy (CIERT)]. / Bestrahlungsplanung und Dosisverifikation für die kombinierte interne und externe Strahlentherapie (CIERT).

AIM: The combined internal and external radiotherapy (CIERT) take advantage of the benefits from radionuclide therapy and external beam irradiation. These include steep dose gradients and a low toxicity to normal tissue due to the use of unsealed radioisotopes as well as homogeneous dose distribution within the tumor due to external beam irradiation. For a combined irradiation planning, an infrastructure has to be developed that takes into account the dose contributions from both modalities. A physical verification of the absorbed dose distribution should follow by measurements using OSL detectors. METHOD: Internal irradiation was performed using Re-188 in a cylindrical phantom with three inserts. SPECT images were acquired to calculate the internal dose using the software STRATOS. The dose distribution was exported as DICOM-RT data and imported in the software Pinnacle. Based on the internal dose distribution the external irradiation using 6 MV photons was planned. The dose contributions of both modalities separately as well as for combined irradiation was measured using OSL detectors made out of Beryllium oxide. RESULTS: The planed doses of combined irradiation (1 Gy, 2 Gy, 4 Gy) could be verified within the uncertainty of the detectors. The mean energy response to Re-188 was (88.6 ± 2.4) % with respect to the calibration with 200 kV X-ray irradiation. The energy response to 6 MV photons was (146.0 ± 4.9) %. CONCLUSION: A workflow for the treatment planning of combined internal and external radiotherapy has been developed and tested. Measurements verified the calculated doses. Therefore, the physical and technical basis for the dosimetry of combined irradiation were worked out.

Radiobiological hypoxia, histological parameters of tumour microenvironment and local tumour control after fractionated irradiation.

OBJECTIVE: To investigate the relationships between radiobiological hypoxic fraction (rHF), pimonidazole hypoxic fraction (pHF) as well as other histological parameters of the tumour microenvironment, and local tumour control after fractionated irradiation in human squamous cell carcinomas (hSCCs). MATERIAL AND METHODS: Ten different hSCC cell lines were transplanted into nude mice and rHF was calculated from local tumour control rates after single dose irradiation under normal or clamped blood flow conditions. In parallel, tumours were irradiated with 30 fractions within 6 weeks. Radiation response was quantified as dose required to cure 50% of tumours (TCD(50)). Unirradiated tumours were excised for histological evaluation including relative hypoxic area (pHF), relative vascular area (RVA), and fraction of perfused vessels (PF). RESULTS: A weak but significant positive correlation between rHF (R(2)=0.6, p=0.014) and TCD(50) after fractionated irradiation was found. The pHF did not correlate with rHF but was significantly associated with the TCD(50) after single dose clamp (R(2)=0.8, p=0.003) and showed a trend for an association with TCD(50) after fractionated irradiation (R(2)=0.4, p=0.067). Relative vascular area and fraction of perfused vessels did not show an association with rHF or TCD(50) after fractionated irradiation. CONCLUSIONS: Our data suggest that radiobiological hypoxia contributes to the response after fractionated irradiation but that also other radiobiological mechanisms are involved. In the present study, pimonidazole labelling does not reflect rHF and has a limited value to predict local tumour control after fractionated irradiation. The association between pHF and TCD(50) after single dose clamp warrants further investigation.

Filmless evaluation of the mechanical accuracy of the isocenter in stereotactic radiotherapy.

BACKGROUND AND PURPOSE: The Winston-Lutz test verifies the mechanical accuracy of the isocenter in stereotactic radiotherapy. A lead ball inside a small beam is exposed to film applying different combinations of the gantry angle and the table angle. The increasing replacement of films by digital images requires alternative imaging methods. The suitability of two different electronic portal imaging systems and of a system based on digital luminescence radiography was investigated. MATERIAL AND METHODS: The imaging systems included the portal imaging devices BEAMVIEW PLUS and OPTIVUE1000 (both Siemens Medical Solutions, Erlangen, Germany) and the luminescence system KODAK ACR 2000 RT (Eastman Kodak Comp., Rochester, NY, USA). 6-MV photons from the linear accelerators PRIMUS and ONCOR (both Siemens Medical Solutions) were applied. First, only the small beam covering the lead ball was exposed. Second, an additional bigger open beam part in a certain distance to the small beam was applied. RESULTS: For all three investigated imaging systems, which are using preprocessing imaging software, only for the beam arrangement with additional open beam parts, the lead ball could be detected inside the small beam. Only for the application of a dosimetric software tool to the luminescence system, the metal ball inside the small beam became visible without an additional open beam part. CONCLUSION: Applying the proposed beam arrangements, the Winston-Lutz test can be done by digital and filmless imaging systems, thereby saving time as well.