Impact of intensity-modulated radiotherapy (IMRT) on salivary gland function in early-stage nasopharyngeal carcinoma (NPC) patients: a prospective randomized study.

Reviewer: Walter Sall, MD
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Last Modified: May 15, 2005

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Presenter: M.K. Kam
Presenter's Affiliation: Prince of Wales Hospital
Type of Session: Scientific

Background

  • In early stage nasopharyngeal carcinoma, local control approaches 90% with radiation therapy alone.  Unfortunately, 50-80% of these patients develop long term xerostomia which causes difficulties with speech, swallowing and dental health and increases risk of osteonecrosis.
  • Though IMRT has been shown to decrease radiation dose to the parotid glands, phase III randomized data comparing IMRT to 2D treatment planning is lacking.
  • This phase III randomized study intended to compare the effects of IMRT and 2D radiation on salivary function.

Materials and Methods

  • Eligibility criteria:  Patients had stage T1-2b, N0-1 nasopharynx carcinoma.  No chemotherapy was given. 
  • Primary endpoint was the rate of delayed xerostomia 1 year after completion of therapy.  Secondary endpoints were rates of acute xerostomia measured 6 weeks after RT completion.
  • All patients received 66Gy in 33 fractions of 200cGy.  14-18Gy of this radiation was delivered with brachytherapy. 
  • Xerostomia was assessed by the treating physician and by patient completed questionaire as well as by direct measurement of salivary flow.

Results

  • 60 patients enrolled from 11/2001 to 12/2003.  Minimum F/U was 1 year.
  • Patients were well balanced with regard to age, sex and stage.
  • Parotid glands received an average of 61Gy when treated with 2D RT vs 32Gy when treated with IMRT.
  • 1  year rate of grade II-IV xerostomia was 39% with IMRT and 82% with 2D RT.  Stimulated parotid flow rates were much higher at all time points with IMRT vs 2D RT.
  • However, patient self-assessment of xerostomia showed no significant difference between IMRT and 2D RT.
  • Threshold dose for RT induced xerostomia was 26Gy.  Threshold volume for RT induced xerostomia was 20% of total parotid volume.  No xerostomia was seen below these thresholds.

Author's Conclusions

  • IMRT is superior to 2D RT in preserving parotid gland function and preventing xerostomia as measured by RTOG toxicity scale and stimulated parotid salivary flow rates.
  • No subjective difference in xerostomia was reported by patients between IMRT and 2D RT.  This may reflect an inadequacy in the patient questionaire, making it difficult to discern subtle differences in xerostomia between patient groups.
  • A threshold dose and threshold volume were found, below which clinically apparent xerostomia did not occur.

Clinical/Scientific Implications
This is one of the first randomized studies to demonstrate improvement in salivary gland function and xerostomia by the use of parotid sparing IMRT vs conventional 2D RT planning.  The fact that improvement in salivary function was not supported by patient questionaire is more likely due to inadequacies in the survey instrument than an actual lack of parotid sparing by IMRT.  However, more dramatic improvements in xerostomia may be possible.  Sparing of submandibular glands and/or the addition of amifostone may be beneficial.  These options should be evaluated in future randomized studies.