A Prospective Observational Study to Compare the Effect of Adaptive Radiation Therapy in Head and Neck Cancer Patients Treated with Helical Tomotherapy – Bangalore, Karnataka

BACKGROUND Establishing the usefulness of adaptive radiotherapy in our setting with limited data might help to ensure better conformity and reduce treatment related morbidity. Hence we conducted this study to elicit the benefit of adaptive radiotherapy with helical tomotherapy. METHODS This is a prospective study conducted among 25 head and neck cancer patients undergoing radiotherapy with helical tomotherapy. All patients underwent initial radiation therapy treatment planning simulation positron emission tomography computed tomography (PET CT/ CT scan) [CT-1], followed by repeat PET CT/ CT scan at 4th - 5th week of radiotherapy [CT-2]. Planning for full intended dose [66 Gy - 70 Gy] was done on both the scans, keeping the radiation therapy planning parameters same. Changes in the volume of the clinical target volumes (CTV), changes in the volume and dose to spinal cord, bilateral parotids, and mandible were compared. A p - value of < 0.05 was considered for statistical significance. RESULTS A significant reduction in the volumes of tumour - CTV-1 [CT-1 v/s CT-2: 166.82 cc v/s. 150.63 cc] and of lymph nodal region - CTV-2 [CT-1 v/s CT-2: 260.29 cc v/s 228.00 cc], contra lateral parotid gland [CT-1 v/s CT-2: 33.00 cc v/s 18.72 cc] were observed (P < 0.05). The mean doses received by contra lateral parotid gland [CT-1 v/s. CT-2: 23.14 Gy v/s 21.26 Gy] were significantly lesser in the CT2 scans (P < 0.05). The mean maximum doses were also significantly lesser to the mandible and spinal cord i.e., CT-1 v/s. CT-2: 68.528 Gy v/s 67.39 Gy and 39.45 Gy v/s. 37.33 Gy respectively (P < 0.05). A significant reduction in standardised uptake value (SUV), values of the primary tumour and involved lymph nodes was observed between CT-1 and CT-2. CONCLUSIONS During 4th to 5th week of radiation therapy, significant reductions in the CTVs and in dose to OARs were noted. Thus, we recommend at least one re-simulation scan and re-planning during radiation therapy, irrespective of the type of technique of radiation therapy. KEYWORDS Adaptive Radiation Therapy, IMRT, Tomotherapy