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Radiother Oncol. 2018 Oct;129(1):38-43. doi: 10.1016/j.radonc.2018.02.021. Epub 2018 Apr 30.

Submandibular function recovery after IMRT in head and neck cancer: A prospective dose modelling study.

Author information

1
Department of Radiation Oncology, Advanced Centre for Treatment Research and Education for Cancer (ACTREC), Tata Memorial Centre, Mumbai, India. Electronic address: vmurthy@actrec.gov.in.
2
Department of Radiation Oncology, Advanced Centre for Treatment Research and Education for Cancer (ACTREC), Tata Memorial Centre, Mumbai, India.
3
Clinical Research Secretariat, Advanced Centre for Treatment Research and Education for Cancer (ACTREC), Tata Memorial Centre, Mumbai, India.
4
Department of Nuclear Medicine, Tata Memorial Centre, Mumbai, India.
5
Medical Physics, Advanced Centre for Treatment Research and Education for Cancer (ACTREC), Tata Memorial Centre, Mumbai, India.

Abstract

PURPOSE:

To estimate the dose response relationship for submandibular gland (SMG) recovery using salivary scintigraphy in patients diagnosed with head and neck cancer treated with curative image guided chemoradiation.

MATERIAL AND METHODS:

Ninety newly diagnosed head and neck cancer patients (T1-3, N0-2c, M0) treated with intensity modulated radiotherapy on a prospective clinical trial were assessed for salivary toxicity at predefined intervals using dynamic salivary scintigraphy. The SMG function was measured using salivary excretion fraction (SEF) ratios at baseline and 6 monthly. Tolerance dose (TD) 50 for submandibular gland was estimated from dose response curves.

RESULTS:

The mean SEF ratio of 180 SMGs decreased at 6 months with a nadir at 12 months after treatment (SEF ratio 15%) and progressively recovered over time reaching 38% over 24 months. There was significant inverse correlation between SEF ratio and mean SMG dose at 6 months (r = -0.18, p = 0.04); 12-months (r = -0.36, p < 0.001); 18-months (r = -0.48, p < 0.001); 24-months (r = -0.42, p < 0.001); and more than 24-months (r = -0.56, p < 0.001). The estimated TD 50 values at 1 year and 2 year post treatment were 36 Gy and 44 Gy respectively with SEF ratio of ≤45% used to define severe xerostomia. For every 1 Gy reduction in mean dose below 54 Gy, there is 2-2.5% reduction in the probability of severe xerostomia.

CONCLUSION:

The submandibular gland function declines after radiotherapy with a nadir at 12 months and there is incomplete recovery over time with continued improvement over 24 months. The TD 50 at 1 year and 2 year was 36 Gy and 44 Gy with a 2-2.5% reduction in the probability of severe xerostomia for every 1 Gy reduction in mean dose.

KEYWORDS:

Salivary excretion fraction; Salivary scintigraphy; Submandibular gland; TD50

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