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

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 x 2.39 Gy for the protons and IMRT and 35 fractions x 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.