Low­dose radiation­induced apoptosis in human leukemia K562 cells through mitochondrial pathways.

High­dose total body irradiation (TBI) has an established role as preparative regimen for bone­marrow transplantation in the treatment of chronic myelogenous leukemia (CML), but this regimen still has a relatively high rate of acute and late toxicity. Low­dose radiation (LDR) induces apoptosis of tumor cells and has numerous beneficial effects on normal tissues, including radiation homeostasis and adaptive response. Based on the previous evidence, in the present study, K562 cells were exposed to LDR, high­dose radiation (HDR), and LDR in combination with HDR to investigate the possible mechanism of the apoptotic effect and hypersensitivity induced by LDR. The apoptotic rate increased in all radiation groups in a time­dependent manner. An upregulation of Bax protein expression and a downregulation of Bcl­xl in a dose­dependent manner in human leukemia K562 cells was observed. However, the expression of p53 protein did not change in all of the radiation cell groups. The mitochondrial membrane potential (ΔΨm) in K562 cells decreased in all of the radiation cell groups in a dose­dependent manner. Furthermore, the decrease of ΔΨm was enhanced in the LDR/HDR group compared with that in the LDR or HDR groups. The activity of caspase­3 was enhanced in all of the radiation groups. In the LDR/HDR group, the activity of caspase­3 was higher than that in the HDR or LDR groups. The present study provided preliminary experimental evidence of LDR being beneficial in combination with TBI in the treatment of CML.

Dosimetric verification for primary focal hypermetabolism of nasopharyngeal carcinoma patients treated with dynamic intensity-modulated radiation therapy.

OBJECTIVE: To make sure the feasibility with (18F)FDG PET/CT to guided dynamic intensity-modulated radiation therapy (IMRT) for nasopharyngeal carcinoma patients, by dosimetric verification before treatment. METHODS: Chose 11 patients in III~IVA nasopharyngeal carcinoma treated with functional image-guided IMRT and absolute and relative dosimetric verification by Varian 23EX LA, ionization chamber, 2DICA of I'mRT Matrixx and IBA detachable phantom. Drawing outline and making treatment plan were by different imaging techniques (CT and (18F)FDG PET/CT). The dose distributions of the various regional were realized by SMART. RESULTS: The absolute mean errors of interest area were 2.39%±0.66 using 0.6 cc ice chamber. Results using DTA method, the average relative dose measurements within our protocol (3%, 3 mm) were 87.64% at 300 MU/min in all filed. CONCLUSIONS: Dosimetric verification before IMRT is obligatory and necessary. Ionization chamber and 2DICA of I'mRT Matrixx was the effective dosimetric verification tool for primary focal hyper metabolism in functional image-guided dynamic IMRT for nasopharyngeal carcinoma. Our preliminary evidence indicates that functional image-guided dynamic IMRT is feasible.