Evolution of ipsilateral head and neck radiotherapy

Purpose: For patients with early stage lateralized head and neck cancer, unilateral radiotherapy has been shown a superior treatment than bilateral radiotherapy. Unilateral treatment not only maintains the same level of tumor control, it reduces treatment related toxicity. To take the advantage of treating a lateralized and smaller volume, radiotherapy has experienced evolution from mixed photon/electron fields, to wedge pair and IMRT treatment. The recent available proton treatment can offer further contralateral organ sparing but at a significantly higher financial cost, in addition to its technical complexities and limited accessibility. A new non-coplanar radiotherapy technique that is deliverable on existing C-arm linacs, term 4 p, is in traduced in this article. Methods: Two patients with unilateral head and neck cancer were included in the planning study. The first patient was a post-surgical head-and-neck patient with a tumor involving posterior right maxillary sinus. The second patient had a primary parotid tumor. A single-level 60 Gy was prescribed to the PTV. Three treatment plans were developed including volumetric modulated arc therapy (VMAT, clinically used) using 2 partial arcs, 4p plans using 6 MV non-coplanar beams, and a non-intensity-modulated 3-field proton plan. The 4pplans were created using an in-house optimization program. Both VMAT and the proton plans were generated on Eclipse (Varian). Results: All photon plans achieved 95% coverage of the PTV and less than 10% hot spots in the PTV. The proton plan showed greater dose heterogeneity in the PTV and greater high dose spillage to the surrounding normal tissue. For the first patient, comparison of the maximum doses between VMAT, 6 MV 4p and proton plans shows that for the contralateral cochlea, it was reduced from 15.6 to 4.6 and 0 Gy; the chiasm, it was from 31 to 10.6 and 7.2 Gy; for the contralateral lens, it was reduced from 6.2 to 1 and 1 Gy; for the contralateral optical nerve, it was reduced from 31.5 to 16.4 and 10.9 Gy; for the brain stem, it was reduced from 28.6 to 14.5 and 14.2 Gy. For the second patient, the same comparison shows that the spinal cord dose was reduced from 35.7 to 21.7 and 5 Gy, contralateral optical nerve dose was reduced from 35.1 to 16.3 and 8.7 Gy, contralateral eye dose was reduced from 12.1 to 7.5 and 0.1 Gy, contralateral lens dose was reduced from 5.5 to 3.1 and 0.1 Gy, contralateral cochlea dose was reduced from 24.6 to 8.52 and 0.05 Gy and contralateral parotid dose was reduced from 14.5 to 5.11 and 0.15 Gy. Conclusion: The 4p plan’s capacity to spare normal organs is benchmarked against the state of the art partial arc VMAT and proton plans. For well lateralized target in the case study, 4p plans showed remarkable potentials to further reduce distant organ doses compared to VMAT. While the level of distant organ sparing is not equivalent to proton therapy, 4p was able to attain the majority of the gains from using the proton therapy at the same time achieving superior PTV coverage and proximal organ sparing.