ABSTRACT
Cone-beam computed tomography (CBCT) images are presently used for geometric verification for daily patient positioning. In this work, we have compared the images of CBCT with the images of conventional fan beam CT (FBCT) in terms of image quality and Hounsfield units (HUs). We also compared the dose calculated using CBCT with that of FBCT. Homogenous RW3 plates and Catphan phantom were scanned by FBCT and CBCT. In RW3 and Catphan phantom, percentage depth dose (PDD), profiles, isodose distributions (for intensity modulated radiotherapy plans), and calculated dose volume histograms were compared. The HU difference was within ± 20 HU (central region) and ± 30 HU (peripheral region) for homogeneous RW3 plates. In the Catphan phantom, the difference in HU was ± 20 HU in the central area and peripheral areas. The HU differences were within ± 30 HU for all HU ranges starting from -1000 to 990 in phantom and patient images. In treatment plans done with simple symmetric and asymmetric fields, dose difference (DD) between CBCT plan and FBCT plan was within 1.2% for both phantoms. In intensity modulated radiotherapy (IMRT) treatment plans, for different target volumes, the difference was <2%. This feasibility study investigated HU variation and dose calculation accuracy between FBCT and CBCT based planning and has validated inverse planning algorithms with CBCT. In our study, we observed a larger deviation of HU values in the peripheral region compared to the central region. This is due to the ring artifact and scatter contribution which may prevent the use of CBCT as the primary imaging modality for radiotherapy treatment planning. The reconstruction algorithm needs to be modified further for improving the image quality and accuracy in HU values. However, our study with TG-119 and intensity modulated radiotherapy test targets shows that CBCT can be used for adaptive replanning as the recalculation of dose with the anisotropic analytical algorithm is in full accord with conventional planning CT except in the build-up regions. Patient images with CBCT have to be carefully analyzed for any artifacts before using them for such dose calculations.
ABSTRACT
OBJECTIVE: (1) To study the feasibility, adverse effects and response of concurrent weekly Docetaxel with radical radiotherapy in inoperable locally advanced head and neck squamous cell carcinoma. (2) To assess the compliance and tolerance of weekly Docetaxel with radiotherapy. MATERIAL AND METHODS: Twenty one patients with stage III and IV head and neck squamous cell carcinoma satisfying inclusion criteria were selected and treated with conventional external radiotherapy of 70Gy in 35 fractions with weekly concurrent Docetaxel (15mg/sqm), administered one hour before radiotherapy. Assessment of toxicities and evaluationof response was carried out. RESULTS: Majority of patients had stage IV diseaseand 17/21 (81%) received the planned radiotherapydose of 70Gy and ≥4 cycles of weekly chemotherapy. Duration of treatment ranged from 7.1to 11.2 weeks. The toxicities noted were Grade III mucositis in 57% and grade III skin reaction in 23%, grade III dysphagia in 38% and grade II weight loss in 23% of patients. Systemic toxicities associated with chemotherapy were minimal and there was no dose limiting toxicities. The overall locoregional response at first follow up was 85%, with complete response of 70% and partial response of 15%. CONCLUSION: Concurrent Docetaxel is a feasible and suitable alternate to Cisplatin and 5-Fluorouracil chemotherapy with good patient compliance. The late toxicities and survival need to be followed up.
