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

Sparing the salivary glands with scanned protons in head and neck radiotherapy: Benefits of 6-field Intensity Modulated Proton Therapy (IMPT) as compared to 3-field IMPT

Meeting Abstract

  • T. van de Water - Department of Radiation Oncology, University Medical Center Groningen/University of Groningen, Groningen, The Netherlands
  • T. Lomax - Center for Proton Radiation Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland
  • H. P. Bijl - Department of Radiation Oncology, University Medical Center Groningen/University of Groningen, Groningen, The Netherlands
  • C. Schilstra - Department of Radiation Oncology, University Medical Center Groningen/University of Groningen, Groningen, The Netherlands
  • E. Hug - Center for Proton Radiation Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland
  • J. A. Langendijk - Department of Radiation Oncology, University Medical Center Groningen/University of Groningen, Groningen, The Netherlands

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog213

DOI: 10.3205/09ptcog213, URN: urn:nbn:de:0183-09ptcog2137

Published: September 24, 2009

© 2009 van de Water 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

Purpose: The aim of this planning comparative study was to determine the potential benefits of a 6-field scanned IMPT technique as compared to a 3-field scanned IMPT technique in the treatment of oropharyngeal cancer. In a previous study, we showed that 3-field IMPT was superior to 7-field photon IMRT with regard to sparing organs at risk (OARs) involved in salivary function after curative irradiation in the head and neck region, while the target volume coverage was similar. In this subsequent study, we investigated whether a 6-field IMPT technique could further improve two aspects of the dose delivery: (1) the reduction of radiation dose to salivary glands, and (2) the avoidance of those air cavities and other heterogeneities that may impair the accuracy of dose delivery due to density uncertainties, setup variations and anatomical variations.

Methods: The study population was composed of ten patients with oropharyngeal cancer with various stages (T2-T4N0). Target dose prescriptions were similar for both techniques, i.e., 54 Gy to the elective target volume and 70 Gy to the boost target volume, using a simultaneous integrated boost (SIB) technique. The 6-field IMPT technique was a split field set up including: (1) two anterior beams, irradiating the caudal part of the target volume up to the lower edge of the jaw bone, and (2) three posterior beams and one lateral beam, irradiating the cranial part of the target volume. The 3-field IMPT technique used three beams, all irradiating the entire target volume. The parotid and submandibular glands were spared as much as possible.

Results: The target volume coverage was equal for IMRT and both IMPT techniques. No significant differences were found between 3-field IMPT and 6-field IMPT regarding the mean dose to the parotid glands and the ipsilateral submandibular gland. However, the mean dose to the contralateral submandibular gland could be reduced significantly from 44.7 Gy with 3-field IMPT to 42.8 Gy with 6-field IMPT (Table 1 [Tab. 1]). In addition, although no specific constraints were defined for the sublingual glands and the oral cavity, mean dose values to these structures were significantly reduced with 6-field IMPT (Table 1 [Tab. 1]).

No significant differences were obtained for the mean dose to the submandibular glands when 3-field IMPT was compared to IMRT. However, with 6-field IMPT the mean dose to the contralateral submandibular gland was significantly lower than with IMRT (p<0.05).

The most important air cavities and other sources of heterogeneity could be avoided effectively with the 6-field IMPT technique, in contrast to the 3 field IMPT technique.

Conclusions: 6-field IMPT is superior to 3-field IMPT for two reasons: (1) the dose to the contralateral submandibular gland, the sublingual glands, and the oral cavity is significantly reduced and; (2) irradiation through sources of heterogeneity can be avoided more adequately.