ABSTRACT
PURPOSE: To assess interobserver variability (IOV) in the delineation of structures during intensity-modulated radiation therapy for head and neck squamous cell carcinoma and the impact of fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) on such variability at the primary site. METHODS: Three experienced head-neck radiation oncologists, blinded to each other, delineated the primary site gross tumour volume (GTV) and specified organs-at-risk (OARs) viz parotid gland, spinal cord, and cochlea in 10 patients with pharyngolaryngeal cancers suited for definitive intensity-modulated radiation therapy. IOV was assessed by concordance index (CI), Dice similarity coefficient (DSC), and Fleiss' kappa. Subsequently, the observers refined their corresponding GTVs incorporating information from FDG-PET/CT. The impact of FDG-PET/CT on variability of GTV was assessed by comparing the overlap indices with and without FDG-PET/CT using paired 't' test. RESULTS: There was moderate IOV in the delineation of GTV as evidenced by mean CI, DSC, and Fleiss' kappa of 0.41, 0.57, and 0.56, respectively. The use of FDG-PET/CT improved consistency of target volume delineation with resultant improvement in the overlap indices (mean CI, DSC, and Fleiss' kappa of 0.54, 0.69, and 0.69, respectively) that was statistically significant (P < .001). There was good agreement between the three observers for delineation of spinal cord and parotid glands. Concordance was worst for the cochlea. CONCLUSION: This study demonstrates the presence of moderate IOV between three experienced head and neck radiation oncologists in an academic institutional setting for the delineation of GTV. The use of FDG-PET/CT for target volume delineation results in significant reduction of such variability.
ABSTRACT
AIM: The present study was to investigate the use of MOSFET as an vivo dosimeter for the application of Ir-192 HDR brachytherapy treatments. MATERIAL AND METHODS: MOSFET was characterized for dose linearity in the range of 50-1000 cGy, depth dose dependence from 2 to 7 cm, angular dependence. Signal fading was checked for two weeks. RESULT AND DISCUSSION: Dose linearity was found to be within 2% in the dose range (50-1000 cGy). The response varied within 8.07% for detector-source distance of 2-7 cm. The response of MOSFET with the epoxy side facing the source (0 degree) is the highest and the lowest response was observed at 90 and 270 degrees. Signal was stable during the study period. CONCLUSION: The detector showed high dose linearity and insignificant fading. But due to angular and depth dependence, care should be taken and corrections must be applied for clinical dosimetry.
