ESTRO meets Asia 2024 - Abstract Book

S403

RTT – Treatment planning, OAR and target definitions

ESTRO meets Asia 2024

[1] Liu R, Bai J, Zhao K,et al. A New Deep-Learning-based Model for Predicting 3D Radiotherapy Dose Distribution In Various Scenarios[C]//2020 13th International Congress on Image and Signal Processing, BioMedical Engineering and Informatics (CISP-BMEI).2020.

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Proffered Paper

RELATIONSHIP BETWEEN THYROID DOSE-VOLUME PARAMETERS AND HYPOTHYROIDISM IN HEAD AND NECK RADIOTHERAPY

AMITH RAJ 1 , JOMON RAPHAEL C 2 , MATHEW VARGHEESE K 1 , JINI M P 3 , FEBIN ANTONY 1

1 RADIATION NCOLOGY, AMALA INSTITUTE OF MEDICAL SCIENCES, THRISSUR, India. 2 AMALA, AMALA INSTITUTE OF MEDICAL SCIENCES, THRISSUR, India. 3 COMMUNITY MEDICINE, AMALA INSTITUTE OF MEDICAL SCIENCES, THRISSUR, India

Purpose/Objective:

To investigate the correlation between dose-volumetric parameters of the thyroid gland and hypothyroidism in patients undergoing intensity-modulated radiation therapy (IMRT) for HN cancers.

Material/Methods:

We conducted an ambivalent study in patients of 18-70 years of age, who received radical and adjuvant RT for HN cancers and have completed 2 years of disease free follow up. The study period was from 2019-2021. After getting informed consent, we contoured the thyroid in the previously obtained planning images of these patients and following parameters including total thyroid volume, maximum dose, mean dose, minimum dose, were obtained from dose volume histogram using previously approved IMRT plan. Thyroid function was assessed by monitoring serum levels of thyroid-stimulating hormone (TSH), free thyroxine (T4), and free triiodothyronine (T3). Primary endpoint was incidence of hypothyroidism (clinical/subclinical) which was defined as TSH>4.5mu/l, T3<201ng/dl and T4< 1.7ng/dl Patients were monitored with these tests every six months until they developed hypothyroidism, or until the end of the study; whichever occurred first. Pearson correlation analysis was performed to find the relationship between total thyroid volume (TTV) and dose. Logistic regression used to analyze the risk of hypothyroidism. Fischer’s exact test was performed to find the relationship between hypothyroidism and TTV.

Results:

Forty-two patients were studied and 54.8% developed hypothyroidism, among them78.2% also received concurrent chemotherapy. Mean TTV was 12cc. Higher incidence of hypothyroidism was observed with TTV<12cc (71% and p = 0.030). Mean thyroid dose of among these patients were 56.53Gy± 5.02. Odds of developing hypothyroidism was 4 when TTV<12cc.

Conclusion:

Lower TTV is a risk factor for developing hypothyroidism in patients receiving HN IMRT. We recommend to keep the mean thyroid dose to as low as reasonably achievable in patients with TTV<12cc.

Keywords: Hypothyroidism, Head & neck IMRT