No abstract

A new magnetic resonance (MR) technique, gadolinium-enhanced subtraction MR imaging, was developed to evaluate the response of patients with osteosarcoma to chemotherapy. Ten patients, who had received chemotherapy for osteosarcoma of the lower extremity, underwent MR imaging 3 days before surgery. After routine MR imaging was performed, subtraction MR was performed in the plane in which the tumor was best visualized. With gadopentetate dimeglumine (0.1 mmol per kilogram) on a standard MR console, subtraction images were created by subtracting precontrast images from gadolinium-enhanced T1-weighted images. The time of maximal tumoral vascular uptake was 1 1/2 minutes after injection, and, therefore, the subtracted image obtained at this time was used for evaluation of viable tumor. Independently, radiologists and histopathologists examined their respective studies for viable tumor to differentiate responders from nonresponders. Four of 10 osteosarcomas were classified as good responders because they appeared as nonenhancing masses, with or without enhancing thin lines, or small nodules (< or = 3 mm wide). At histopathologic examination, all were good responders with less than 3% viable tumor. Six of 10 osteosarcomas were classified as nonresponders because they appeared as enhancing high-signal-intensity masses measuring more than 3 mm in width. Five tumors had between 18% and 43% viable tumor cells.

No abstract

Physical and biological dosimetry were investigated in 45 rheumatoid arthritis patients treated by radiosynoviorthesis (RSO) with 186Re-sulphide (medium-sized joints) and 169Er-citrate (digital joints). Biological dosimetry involved scoring dicentrics in lymphocytes, cultured from blood samples withdrawn just before and 6 h, 24 h and 7 days after treatment. Physical methods included repeated blood sample counts and scintigraphy data. For erbium-169 (pure beta emitter), only bremsstrahlung could be measured and solely in the injection area. For rhenium-186 (both beta and gamma emitter), whole body scans and static images of joints and locoregional lymph nodes were performed. Dosimetry calculations were in accordance with the MIRDOSE 3 software and tables. For erbium-169 (21 patients), either metacarpophalangeal (30 MBq) or proximal interphalangeal (20 MBq) joints of the hands were treated (one joint per patient); 18 patients (out of 21) were interpretable for biological dosimetry, 10 (out of 11) for physical dosimetry and six (out of 10) for both. For rhenium-186, 23 wrists, nine elbows, three shoulders and two ankles were injected in 24 patients, with a maximum of three joints per patient (70 MBq per joint); 20 patients (out of 24) and 10 (out of 10) were interpretable for biological and physical dosimetry, respectively, and eight (out of 10) for both methods. Erbium-169 biological dosimetry was negative in all interpretable patients, and physical dosimetry gave a blood dose of 15 +/- 29 microGy and an effective dose lower than 1 mSv/30 MBq. For rhenium-186, biological results were negative in 16 patients (out of 20), but showed a blood irradiation around 200 mGy in the last four. A significant cumulative increase of dicentrics 7 days after injection (16/10,000 instead of 5/10,000 prior to treatment; p < 0.04) was also noted. Gamma counts gave a blood dose of 23.9 +/- 19.8 mGy/70 MBq and the effective dose was found to be 26.7 +/- 5.1 mGy/70 MBq, i.e. about 380 microGy.MBq-1. Erbium-169 RSO is very safe from both physical and biological dosimetry standpoints. Rhenium-186 leak is greater, as demonstrated by the higher blood activity and the measurable, although limited, dicentrics induction in blood lymphocytes. However, the effective dose remains moderate, i.e. 30 times lower than in 131I therapy in benign thyroid diseases.

In internal dosimetry for both nuclear medicine and radiation protection, the adult morphology is represented by a limited number of anthropomorphic models that may not be suitable for all patients. To develop more patient-specific dosimetry, we derived six mathematical models for adults of different height. Three male models (160 cm, 170 cm and 180 cm) and three female models (150 cm, 160 cm and 170 cm), based on the MIRD model design, were developed from the statistical analysis of anthropometric data gathered from autopsies. Monte Carlo calculations were used to provide an example of estimations of S value for these new models for iodine 131 uniformly distributed successively in the stomach or in the urinary bladder. On average, for both male and female models, an increase in the model height of 10 cm leads to a mean reduction in the S value for iodine-131 by 20% and 29% when the stomach and the urinary bladder respectively are selected as source regions. Similarly, when the model height increases by 20 cm, the S values decrease on average by 35% and 48%. This study presents the use of anthropometric data to develop new mathematical models for adults of different height, and shows the significant influence of the morphology on dosimetric parameters.