Purpose To evaluate the efficacy of low-dose pulsed radiation therapy (PRT) in 2 head and neck squamous cell carcinoma (HNSCC) xenografts and to investigate the mechanism of action of PRT compared with standard radiation therapy (SRT). Methods and Materials Subcutaneous radiosensitive UT-SCC-14 and radioresistant UT-SCC-15 xenografts were established in athymic NIH III HO female mice. Tumors were irradiated with 2 Gy/day by continuous standard delivery (SRT: 2 Gy) or discontinuous low-dose pulsed delivery (PRT: 0.2 Gy × 10 with 3-min pulse interval) to total doses of 20 Gy (UT14) or 40 Gy (UT15) using a clinical 5-day on/2-day off schedule. Treatment response was assessed by changes in tumor volume, 18F-fluorodeoxyglucose (FDG) (tumor metabolism), and 18F-fluoromisonidazole (FMISO) (hypoxia) positron emission tomography (PET) imaging before, at midpoint, and after treatment. Tumor hypoxia using pimonidazole staining and vascular density (CD34 staining) were assessed by quantitative histopathology. Results UT15 and UT14 tumors responded similarly in terms of growth delay to either SRT or PRT. When compared with UT14 tumors, UT15 tumors demonstrated significantly lower uptake of FDG at all time points after irradiation. UT14 tumors demonstrated higher levels of tumor hypoxia after SRT when compared with PRT as measured by 18F-FMISO PET. By contrast, no differences were seen in 18F-FMISO PET imaging between SRT and PRT for UT15 tumors. Histologic analysis of pimonidazole staining mimicked the 18F-FMISO PET imaging data, showing an increase in hypoxia in SRT-treated UT14 tumors but not PRT-treated tumors. Conclusions Differences in 18F-FMISO uptake for UT14 tumors after radiation therapy between PRT and SRT were measurable despite the similar tumor growth delay responses. In UT15 tumors, both SRT and PRT were equally effective at reducing tumor hypoxia to a significant level as measured by 18F-FMISO and pimonidazole.
|Original language||English (US)|
|Number of pages||9|
|Journal||International Journal of Radiation Oncology Biology Physics|
|State||Published - Jul 15 2015|
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging
- Cancer Research