Title:Evolution of Ipsilateral Head and Neck Radiotherapy
Volume: 10
Issue: 4
Author(s): Ke Sheng, Peng Dong, Archana Gautam, Chee-Wai Cheng, Dan Ruan, Daniel Low, Minsong Cao, Steve P. Lee and Patrick Kupelian
Affiliation:
Keywords:
Non-coplanar, radiotherapy, head and neck, proton.
Abstract: 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 4π, 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, 4π plans using 6 MV non-coplanar beams, and a non-intensity-modulated 3-field proton plan. The 4π
plans 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 4π 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 4π 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, 4π 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, 4π 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.
