Characteristic X-ray imaging for palliative therapy using strontium-89 chloride: understanding the mechanism of nuclear medicine imaging of strontium-89 chloride.

Strontium-89 (Sr-89) chloride is a targeted palliative therapy used for painful bone metastasis in which repeated doses can be administered, and its usefulness has been reported in the case of bone metastasis of various primary tumors. However, the effectiveness of the pain relief treatment is only described using a subjective index such as the visual analog scale, which lacks objectivity. Although various attempts at quantifying the effectiveness of Sr-89 chloride therapy have been reported using nuclear medicine imaging for energy peaks around 70-80 keV, the principle of Sr-89 chloride imaging has not been explained. In this study, the principle of nuclear medicine imaging for Sr-89 chloride was evaluated using a fundamental study. Additionally, the optimal collimator for acquiring Sr-89 chloride image data was evaluated. Based on the results, the principle of nuclear medicine imaging for Sr-89 chloride could be explained: the energy peaks were characteristic X-rays produced by interactions between gamma rays (514 keV) emitted from Sr-85, which is included during the manufacturing process of the Sr-89 chloride solution, and the lead collimator used in the imaging. The optimal collimator for generating characteristic X-rays efficiently was identified as a middle-to-high energy collimator.

New knowledge about the bremsstrahlung image of strontium-89 with the scintillation camera.

OBJECTIVE: Strontium-89 ((89)Sr) chloride has been used to treat metastases in bone. A method to visualize the distribution of (89)Sr chloride with a scintillation camera was developed in 1996. Studies using bremsstrahlung imaging have shown that (89)Sr accumulates in bone and that the bremsstrahlung generated from biological tissue surrounding bone does not exceed 30 keV. However, it was not clear how low-energy bremsstrahlung from bone can produce peak energy levels of around 75 keV. We speculate that a different (unidentified) factor is involved. METHODS: The energy spectrum of an (89)Sr source was acquired with a scintillation camera with or without a low-to-medium-energy general-purpose collimator. The energy window was set at 20-650 keV for 4 windows. A 50-mm thick acrylic block was placed between the scintillation camera and the (89)Sr source to exclude the effects of bremsstrahlung. The energy spectrum of (89)Sr covered with lead was acquired using the scintillation camera without a collimator. RESULTS: With the collimator the energy spectrum curve was similar to that without the 50 mm of acrylic. The energy spectrum curve showed peaks at about 75, 170, and 520 keV. Without the collimator the energy spectrum showed a similar curve but no peak at 75 keV peak. The curve was similar to that obtained with the scintillation camera and the collimator; however, the curve obtained when the (89)Sr source had been placed in a lead container was similar to that obtained when the source was unshielded, and the collimator was not attached to the scintillation camera. CONCLUSION: If bremsstrahlung of (89)Sr produces an image, a low-energy spectrum region should decrease when acrylic is placed between the (89)Sr source and the scintillation camera. However, similar curves were obtained both with the acrylic in place and without the acrylic. Therefore, we believe that the radiation detected by the scintillation camera was not bremsstrahlung due to the beta rays of (89)Sr. Most (89)Sr preparations are contaminated by (85)Sr, and most of the gamma ray energy of (85)Sr is 514 keV. The scintillation camera detected the characteristic X-ray energy of about 75 keV from the materials of the collimator (lead and others) through interaction with the gamma rays of (85)Sr.

[Development of a simple quantitative method for the strontium-89 concentration of radioactive liquid waste using the plastic scintillation survey meter for beta rays].

Strontium-89 (89Sr: pure beta, E; 1.495 MeV-100%, halflife: 50.5 days) chloride is used as pain relief from bone metastases. An assay of 89Sr is difficult because of a pure beta emitter. For management of 89Sr, we tried to evaluate a simple quantitative method for the 59Sr concentration of radioactive liquid waste using scintillation survey meter for beta rays. The counting efficiency of the survey meter with this method was 35.95%. A simple 30 minutes measurement of 2 ml of the sample made the quantitative measurement of 89Sr practical. Reducing self-absorption of the beta ray in the solution by counting on the polyethlene paper improved the counting efficiency. Our method made it easy to manage the radioactive liquid waste under the legal restrictions.

[A questionnaire about radiation safety management of the draining-water system at nuclear medicine facilities].

We conducted a questionnaire survey about radiation-safety management condition in Japanese nuclear medicine facilities to make materials of proposition for more reasonable management of medical radioactive waste. We distributed a questionnaire to institutions equipped with Nuclear Medicine facilities. Of 1,125 institutions, 642 institutes (52.8%) returned effective answers. The questionnaire covered the following areas: 1) scale of an institution, 2) presence of enforcement of radiotherapy, 3) system of a tank, 4) size and number of each tank, 5) a form of draining-water system, 6) a displacement in a radioactive rays management area, 7) a measurement method of the concentration of medical radioactive waste in draining water system, 8) planned and used quantity of radioisotopes for medical examination and treatment, 9) an average displacement of hospital for one month. In most institutions, a ratio of dose limitation of radioisotope in draining-water system was less than 1.0, defined as an upper limitation in ordinance. In 499 hospitals without facilities of hospitalization for unsealed radioisotope therapy, 473 hospitals reported that sum of ratios of dose limits in a draining-water system was less than 1.0. It was calculated by used dose of radioisotope and monthly displacement from hospital, on the premise that all used radioisotope entered in the general draining-water system. When a drainage including radioactivity from a controlled area join with that from other area before it flows out of a institution, it may be diluted and its radioactive concentration should be less than its upper limitation defined in the rule. Especially, in all institutions with a monthly displacement of more than 25,000 m3, the sum of ratio of the concentration of each radionuclide to the concentration limit dose calculated by used dose of radioisotope, indicated less than 1.0.