核医学と放射線治療

Liver metastases are a common source of morbidity and mortality. Despite significant improvements in outcome with systemic therapy in recent years, it is infrequent that liver metastases or sites of macrometastatic disease are controlled permanently. Furthermore, most liver metastases are not amenable to what is considered the gold standard locally ablative therapy, surgical resection and consequently there has been a surge in interest in non surgical ablative therapies. Review of patient selection factors for two such liver directed radiation therapies, radioembolization and stereotactic body radiation therapy (SBRT) will be addressed.

Purpose: To investigate the risk of false positive MRI and 18F-Fluorocholine (FCH) or 11Cacetate (AC) PET/ CT in prostate cancer patients with long term biochemical and clinical remission after curative radiation therapy (RT).
Methods and Materials: Twenty patients underwent MRI studies including T2-weighted, diffusion weighted, dynamic contrast-enhanced, and spectroscopic imaging. Nine of these patients were selected to have FCH and 10 AC PET/CT studies.
Results: MR spectroscopy suggested positive or equivocal results in 16/20 patients. However, the combined interpretation of all MRI sequences dropped the rate of suspicious or equivocal studies to 8/20. All but one patient underwent also PET/CT and early PET frames showed suspicious or equivocal local images in 15/19 patients (8/10 with AC, 7/9 with FCH). However, a combined evaluation of early and late PET frames was judged equivocal in only 1 patient.
Conclusions: Multimodal MRI, early single FCH or AC PET frames of the prostate after curative RT may not be accurate enough to differentiate remission from early recurrence. Multiple-phase evaluation of PET images, however, may reduce significantly the risk of reporting equivocal or false positive results.

While undergoing nuclear medicine therapy using 131I radioisotope at a hospital, patients generate wastewater with a considerable amount of radioactivity. Thus, contamination can reach levels of as much as 90% of the radioactive dose administered to the patient, depending on the type of therapy the patient underwent [1,2]. Given its radioactive half life of 8.02070 days, there is a significant risk of 131I radioisotope accumulation after its discharge into the sewer network (through sanitary wastewater) and into the environment. Therefore, it is advisable to collect this effluent in a separate system for its treatment prior to final discharge to the municipal sewer [3-8]. In spite of the clear scientific evidence of the severe contamination of this specific type of wastewater, a harmonised legal framework has still not been devised for all member states of the European Union. A survey conducted by the Radiological Protection Institute of Ireland clearly spotlights the discrepancies existing among concepts for managing radioactively contaminated effluents. The survey examined thirteen countries, six of which stipulate the installation of wastewater treatment systems (Table 1), three of which permit the wastewater to be discharged directly following dilution (Table 2) and four of which permit both options (Table 3), depending on the specific conditions of the respective sanitary system.

In radiation therapy of cancer, any possible mistakes that may occur in prescribed tumour dose calculation and/ or in treatment set up could also be checked by the biological dosimetry. In order to verify this, 20 patients having pelvic area tumours with no prescribed chemotherapy were selected. Their peripheral blood samples were collected before starting fractionated radiotherapy and at some definite time during treatment. Equivalent whole body doses (EWBD) were calculated from patient’s weights, irradiated volumes and total tumor doses given until the date of blood sample collection during treatment. Each patient’s EWBD was given in vitro to blood samples that were collected before starting radiotherapy. Radiation induced chromosome damage in lymphocytes were measured by micronucleus (MN) induction.

The relationship between the micronucleus frequencies (MN/BN) scored during therapy ( in vivo ) and the micronucleus frequencies scored after the application of in vitro EWBD was investigated. MN/BN rates scored following in vitro application of EWBD differed between 0.195 and 0.540, whereas MN/BN rates obtained during radiotherapy equivalent to EWBD differed between 0.213 and 0.625. It was shown that there was no significant difference (p=0.653) between the MN scores following in vitro applied EWBD and MN scores obtained in vivo . The existence of this correlation has confirmed the correct application of fractionated radiotherapy and treatment setup for the patients.

The carrier free radioisotopes play a vital role in the rapidly emerging fields of science and technology, emphatically in the areas of biomedical sciences. Again, the carrier free radioisotopes of transition series elements have achieved special importance due to their favourable nuclear and chemical properties, either in material research or in biomedical applications. In the present review article, the beneficial uses of some carrier free radioisotopes of the second transition series elements such as 90Y, 89Zr, 97,103Ru, 99mTc, 101mRh, 111Ag, 107,109Cd, etc. in the field of nuclear medicine has been discussed. Some probable routes for production of these radionuclides have also been indicated.

A case of rapid cancer progression causing impending spinal cord compression at the margin of a previously irradiated treatment volume close to the thoracic spinal cord in a patient with non-small cell lung cancer is presented. The patient and treating physicians were faced with a difficult decision. Either reirradiate and accept a considerable risk of delayed radiation myelopathy or risk paraplegia as a result of tumour progression. To prevent rapid development of neurological deficits, the patient was reirradiated only 34 days after he had finished his initial course of simultaneous radio- and chemotherapy. The high cumulative spinal cord dose (corresponding to 84 Gy in 2-Gy fractions) and short interval to reirradiation resulted in a high risk of radiation myelopathy according to a previously published risk score. However, no treatment-related toxicity developed and neurological function was preserved for almost 5 months. Eventually, tumour progression resulted in paraplegia. This case illustrates important issues around palliative reirradiation of target volumes close to the spinal cord.