Yttrium-90 Activity Quantification in PET/CT-Guided Biopsy Specimens from Colorectal Hepatic Metastases Immediately after Transarterial Radioembolization Using Micro-CT and Autoradiography.

PURPOSE: To evaluate the yttrium-90 (90Y) activity distribution in biopsy tissue samples of the treated liver to quantify the dose with higher spatial resolution than positron emission tomography (PET) for accurate investigation of correlations with microscopic biological effects and to evaluate the radiation safety of this procedure. MATERIALS AND METHODS: Eighty-six core biopsy specimens were obtained from 18 colorectal liver metastases (CLMs) immediately after 90Y transarterial radioembolization (TARE) with either resin or glass microspheres using real-time 90Y PET/CT guidance in 17 patients. A high-resolution micro-computed tomography (micro-CT) scanner was used to image the microspheres in part of the specimens and allow quantification of 90Y activity directly or by calibrating autoradiography (ARG) images. The mean doses to the specimens were derived from the measured specimens' activity concentrations and from the PET/CT scan at the location of the biopsy needle tip for all cases. Staff exposures were monitored. RESULTS: The mean measured 90Y activity concentration in the CLM specimens at time of infusion was 2.4 ± 4.0 MBq/mL. The biopsies revealed higher activity heterogeneity than PET. Radiation exposure to the interventional radiologists during post-TARE biopsy procedures was minimal. CONCLUSIONS: Counting the microspheres and measuring the activity in biopsy specimens obtained after TARE are safe and feasible and can be used to determine the administered activity and its distribution in the treated and biopsied liver tissue with high spatial resolution. Complementing 90Y PET/CT imaging with this approach promises to yield more accurate direct correlation of histopathological changes and absorbed dose in the examined specimens.

Raman scattering for dosimetry using GAFCHROMIC EBT3 radiochromic dosimetry film.

PURPOSE: Raman scattering spectra can be thought of as the "fingerprints" of the investigated material. The purpose of this work was to link the absorbed doses of irradiated radiochromic film at the micrometer level with changes in their Raman spectra. METHODS: Raman spectra of irradiated GAFCHROMIC EBT3 film with doses ranging from 0 to 40 Gy were acquired. The excitation wavelengths used in the experiments (457.9 and 647.1 nm) coincided with electronic transitions of the active layer of the film. The effect of resonance Raman scattering enhanced Raman peaks in the resonance region. Spectra were taken in the range of room temperature to around the temperature of liquid nitrogen (-190°C). RESULTS: The Raman peak intensity redistribution is shown for films with different absorbed doses. The ratio of intensities of the 1445 cm-1 band with respect to the 1330 cm-1 band increases with the increase in absorbed dose. This allows building a dose calibration curve for the film. CONCLUSION: The dose distribution of the irradiated film can be identified based on the intensity ratio of the 1445 and 1330 cm-1 bands by means of Raman mapping. This is a noninvasive and computerized readout method which provides micrometer resolution results for the film surface. This is beneficial in the use of radiochromic films as dosimeters for high-precision radiotherapies.