Abstract
BackgroundHypoxic cancer cells are thought to be radioresistant and could impact local recurrence after radiotherapy (RT). One of the major hypoxic imaging modalities is [18F]fluoromisonidazole positron emission tomography (FMISO-PET). High FMISO uptake before RT could indicate radioresistant sites and might be associated with future local recurrence. The predictive value of FMISO-PET for intra-tumoral recurrence regions was evaluated using high-resolution semiconductor detectors in patients with nasopharyngeal carcinoma after intensity-modulated radiotherapy (IMRT).MethodsNine patients with local recurrence and 12 patients without local recurrence for more than 3 years were included in this study. These patients received homogeneous and standard doses of radiation to the primary tumor irrespective of FMISO uptake. The FMISO-PET image before RT was examined via a voxel-based analysis, which focused on the relationship between the degree of FMISO uptake and recurrence region.ResultsIn the pretreatment FMISO-PET images, the tumor-to-muscle ratio (TMR) of FMISO in the voxels of the tumor recurrence region was significantly higher than that of the non-recurrence region (p < 0.0001). In the recurrent patient group, a TMR value of 1.37 (95% CI: 1.36–1.39) corresponded to a recurrence rate of 30%, the odds ratio was 5.18 (4.87–5.51), and the area under the curve (AUC) of the receiver operating characteristic curve was 0.613. In all 21 patients, a TMR value of 2.42 (2.36–2.49) corresponded to an estimated recurrence rate of 30%, and the AUC was only 0.591.ConclusionsThe uptake of FMISO in the recurrent region was significantly higher than that in the non-recurrent region. However, the predictive value of FMISO-PET before IMRT is not sufficient for up-front dose escalation for the intra-tumoral high-uptake region of FMISO. Because of the higher mean TMR of the recurrence region, a new hypoxic imaging method is needed to improve the sensitivity and specificity for hypoxia.
Highlights
Hypoxic cancer cells are thought to be radioresistant and could impact local recurrence after radiotherapy (RT)
We investigated whether locally recurrent nasopharyngeal carcinoma (NPC) would occur in the high-uptake region of FMISO-positron emission tomography (PET) imaging after prescribing a homogeneous dose of irradiation to primary tumors independent of the FMISO uptake
Our results suggested that the maximum FMISO uptake value, TMRmax, is not useful for predicting local recurrence
Summary
Hypoxic cancer cells are thought to be radioresistant and could impact local recurrence after radiotherapy (RT). The predictive value of FMISO-PET for intra-tumoral recurrence regions was evaluated using high-resolution semiconductor detectors in patients with nasopharyngeal carcinoma after intensity-modulated radiotherapy (IMRT). Full list of author information is available at the end of the article and hypoxic cell radio-sensitizers, and reports have indicated the usefulness of these approaches [4, 5]. Because of their adverse effects, the difficulty of patient selection, and several other limitations, these strategies have not seen wide clinical use [6]. Intensity-modulated radiotherapy (IMRT) with upfront dose escalation to hypoxic subvolumes is a potential method of overcoming tumor hypoxia [7]. The remarkable development of imaging and external beam radiotherapy has made dose escalation to small subvolumes in the primary tumor, or dose painting, technically
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