Jeremy Coulot

Role of FDG PET/CT and Chest CT in the Follow-up of Lung Lesions Treated with Radiofrequency Ablation

PURPOSE To compare fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) combined with computed tomography (PET/CT) and chest CT in the evaluation of the effectiveness of lung radiofrequency (RF) ablation. MATERIALS AND METHODS Institutional review board approved the study, and all patients gave written informed consent. Thirty-four patients (22 men and 12 women; mean age, 64 years) planned to undergo lung RF ablation were prospectively included and underwent FDG PET/CT and chest CT before (pre-RF ablation PET) and 24 hours, 1 month, and 3 months after RF ablation. Persistent equivocal findings up to 3 months were followed up. RESULTS Pre-RF ablation PET led to changes in the treatment strategy in nine patients (26%) by depicting unexpected metastases. Two patients without FDG uptake in lesions to be treated were excluded. Overall, 28 patients (46 lesions: five primary cancer, 41 metastases) were treated and followed up. Within 3 months after RF ablation, incomplete treatment was diagnosed in four of 28 patients (14%, three at 1 month and one at 3 months). Findings of FDG PET/CT were true-positive in four, false-positive in one, and true-negative in 23 patients. Findings of chest CT were true-positive in one, false-positive in one, false-negative in three, and true-negative in 23 patients. Inflammatory FDG uptake in mediastinal lymph nodes and at the needle path puncture site used for RF ablation was observed in 15%, 21%, and 15% of patients and in 19%, 11%, and 15% of patients at 24 hours, 1 month, and 3 months, respectively. CONCLUSION FDG PET/CT can be used for the evaluation of the effectiveness of lung RF ablation. Inflammatory FDG uptake in mediastinal lymph nodes or at the needle path site used for RF ablation may occur.

/sup 18/F-FDG PET images segmentation using morphological watershed: a phantom study

Segmentation of 18F-FDG PET images could be helpful for delineation of tumor volume in radiotherapy and patient follow-up. The most commonly implemented method on clinical workstations is maximum intensity thresholding, which is inappropriate for heterogeneous uptakes. Our aim was to develop and evaluate a more sophisticated segmentation method, based on the morphological watershed. We developed a segmentation method taking into account PET images characteristics. We evaluated it first on phantom images, using an integrated PET/CT unit and taking CT images as reference images. To simulate tumors in a background activity, we used 6 homogeneous spheres of various volumes in a cylindrical phantom and 3 heterogeneous cylinders in an anthropomorphic phantom. The quality of segmentation was evaluated in terms of volume, shape and position. We compared the results with a maximum intensity threshold segmentation method fitting the volume, taken as reference segmentation. A quantitation analysis completed the phantom study. For both phantom acquisitions, the segmentation obtained with the watershed based algorithm gave satisfying results with the index integrating volume, shape and position. Results considering this index were not significantly different from the reference segmentation (p > 0.5). Errors of volume recovery reached 18% for watershed segmentation. The quantitation analysis on phantoms highlighted partial volume effect, with an error of activity concentration measurement on segmented images ranging between 42% and 51%. Performances of the watershed method evaluated in this study were comparable with an optimized segmentation on phantom images. The quantitation recovery of PET regions with this method was similar with to other segmentation methods.

Thyroid Cancer Patients Treated with 131I: Radiation Dose to Relatives After Discharge from the Hospital

BACKGROUND Thyroid cancer patients treated with radioiodine are potential source of radiation exposure for other individuals. Thus, we evaluated the radiation dose received by family members of thyroid cancer patients treated with (131)I after hospital discharge. MATERIALS AND METHODS Seventy-six family members of 56 thyroid cancer patients were included in the study. Thyroid cancer patients were given 3.7 GBq of (131)I and remained in a radiation protection ward for 3 days. Radiation protection recommendations were given to patients and relatives. Life conditions were recorded and radiation doses were monitored using a personal dosimeter. RESULTS AND DISCUSSION At discharge, the mean residual activity was 188 MBq. The mean radiation dose delivered to relatives during the 7 days after discharge was low (51.5 μSv) and was similar with either recombinant human thyrotropin (rhTSH) (59 μSv) or withdrawal (50 μSv) (p = 0.37). CONCLUSION With our current practice, radiation doses to relatives are low and well below international recommendations.

Validation of the EGS usercode DosE3D for internal beta dose calculation at the cellular and tissue levels

Internal radiotherapy is currently focusing on beta emitters such as 90Y or 131I because of their high-energy emissions. However, conventional dosimetric methods (MIRD) are known to be limited for such applications. They are unable to take into account microscopic radionuclide distribution because standardized anthropomorphic phantoms are used, and absorbed dose is calculated at the organ level. New tools are therefore required for dose assessment at cellular and tissue level (10-100 microm). The purpose of this study was to validate, at this scale, a Monte Carlo usercode (DOSE3D), based on the MORSE combinatorial geometry package and the EGS code system. Dose point-kernel calculations in water were compared to those published by Cross et al and Simpkin and Mackie. They confirm that DOSE3D is a reliable tool for cellular dosimetry in various geometric configurations.

Dosimetry of Beta-Emitting Radionuclides at the Tissular Level Using Monte Carlo Methods

Abstract Standard macroscopic methods used to assess the dose in nuclear medicine are limited to cases of homogeneous radionuclide distributions and provide dose estimations at the organ level. In a few applications, like radioimmunotherapy, the mean dose to an organ is not suitable to explain clinical observations, and knowledge of the dose at the tissular level is mandatory. Therefore, one must determine how particles lose their energy and what is the best way to represent tissues. The Monte Carlo method is appropriate to solve the problem of particle transport, but the question of the geometric representation of biology remains. In this paper, we describe a software (CLUSTER3D) that is able to build randomly biologically representative sphere cluster geometries using a statistical description of tissues. These geometries are then used by our Monte Carlo code called DOSE3D to perform particle transport. First results obtained on thyroid models highlight the need of cellular and tissular data to take into account actual radionuclide distributions in tissues. The flexibility and reliability of the method makes it a useful tool to study the energy deposition at various cellular and tissular levels in any configuration.