Potential outcomes of modalities and techniques in radiotherapy for patients with hypopharyngeal carcinoma

Abstract

Background and purpose To determine potential improvements in treatment outcome for patients with hypopharyngeal carcinoma, T4N0M0, using proton and intensity modulated photon radiotherapy (IMRT) compared to a standard 3D conformal radiotherapy treatment (3D-CRT) in terms of local tumour control probability, TCP, and normal tissue complication probability (NTCP) for the spinal cord and the parotid glands using. Patients and methods Using the three-dimensional treatment-planning system, Helax-TMS™, 5 patients were planned with protons, IMRT, and 3D-CRT plans. The prescribed dose used was 30 fractions×2.39 Gy for the protons and IMRT and 35 fractions×2.00 Gy for 3D-CRT. The treatment plans were evaluated using dose volume data and dose response models were used to calculate TCP and NTCP. The target volumes were delineated to spare the parotid glands. A dose escalation was made for protons and IMRT using NTCP constraints to the spinal cord. Results On average, protons and IMRT increase TCP by 17% compared to 3D-CRT. For the spinal cord NTCP values are zero for all methods and patients. Average NTCP values for the parotid glands were >90% for 3D-CRT and significantly lower for protons and IMRT varying from 43–65%. The average parotid gland dose was 33 Gy for the protons, 38 Gy for IMRT and 48 Gy for 3D-CRT. Conclusions Protons and IMRT gave a significant TCP increase compared to 3D-CRT while no significant difference between protons and IMRT was found. Protons generally show lower non-target tissue doses, which indicates a possibility for further dose escalation. Large individual dose differences between protons and IMRT for parotid glands indicate that some patients may benefit more from protons and others from IMRT.