gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

Comparison of dose volume histograms of normal structures between proton and conventional photon irradiation with adaptive radiotherapy in Stage IV head and neck cancer

Meeting Abstract

  • C. Simone II - Radiation Oncology Branch, National Cancer Institute, Bethesda, USA
  • J. Ondos - Radiation Oncology Branch, National Cancer Institute, Bethesda, USA
  • H. Ning - Radiation Oncology Branch, National Cancer Institute, Bethesda, USA
  • D. Ly - Radiation Oncology Branch, National Cancer Institute, Bethesda, USA
  • H. Gates - Radiation Oncology Branch, National Cancer Institute, Bethesda, USA
  • K. Kramer - Radiation Oncology, Henry Jackson Foundation, Rockville, USA
  • A. Belard - Radiation Oncology, Henry Jackson Foundation, Rockville, USA
  • K. Camphausen - Radiation Oncology Branch, National Cancer Institute, Bethesda, USA
  • R. Miller - Radiation Oncology Branch, National Cancer Institute, Bethesda, USA
  • N. Simone - Radiation Oncology Branch, National Cancer Institute, Bethesda, USA

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog187

DOI: 10.3205/09ptcog187, URN: urn:nbn:de:0183-09ptcog1873

Published: September 24, 2009

© 2009 Simone II et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.en). You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.


Outline

Text

Background: Concurrent chemoradiation is standard therapy for head and neck malignancies despite high rates of normal tissue toxicity. Furthermore, good treatment responses often result in rapid tumor shrinkage that markedly alter head and neck anatomy. Standard practice does not account for this and can lead to overtreatment of normal tissue and undertreatment of tumor. Pilot studies have used adaptive photon IMRT (ART), re-simulating patients during therapy and modifying target volumes and plans, to try to adapt therapy to these changes. We propose that proton therapy for head and neck tumors may provide a better toxicity profile and tumor coverage than photon therapy, with or without adaptive therapy.

Methods: CT images from 5 patients who required re-simulation during their course of standard irradiation were used to quantify dosimetric differences between photon and proton therapy. Planning tumor volumes (PTVs) and normal tissue structures (parotids, larynx, spinal cord, brainstem, mandible) were contoured on the initial and re-simulation CT. Three plans were generated for each patient: IMRT photon, ART photon, and proton plans using the initial CT. Dose volume histograms were generated to compare doses to tumor and normal structures.

Results: IMRT, ART, and proton plans all provided acceptable and comparable PTV coverage. In all cases, ≥99% of the PTV received 97% of the prescribed dose and no point dose was >108% of the prescribed dose. Although ART trended towards improved dose conformality over IMRT for most critical structures, significant reduction in mean dose was only seen for the left parotid gland (22.7 Gy vs. 26.8 Gy , p=0.039). Proton therapy demonstrated further sparing of most normal tissues, with significantly decreased mean doses to left parotid gland (mean dose 20.1 Gy, p=0.04 for IMRT, p=0.05 for adaptive), spinal cord, and brainstem. The mean spinal cord maximum dose for protons was 27.3 Gy, compared with 40.9 Gy for IMRT (p=0.005) and 41.3 Gy for adaptive therapy (p=0.002). The mean brainstem maximum doses were 25.5 Gy vs. 47.7 Gy (p=0.004) vs. 40.9 Gy (p=0.009), respectively. Proton therapy also trended towards lower mean doses to the right parotid gland (21.0 Gy vs. 27.3 Gy vs. 25.3 Gy) and glottic larynx (25.7 Gy vs. 34.7 Gy vs. 31.5 Gy). There was no difference in mandible maximum dose.

Conclusions: Proton therapy has a more favorable toxicity profile than either standard IMRT or adaptive radiotherapy with IMRT especially with respect to the spinal cord, brainstem and left and right parotid glands. In this study, adaptive radiotherapy did not prove to be significantly better than standard IMRT despite smaller target volumes. With larger study population set, longitudinal studies may prove that proton therapy is superior to decrease normal tissue toxicity while still providing full coverage to the tumor and PTVs.