237P - Dosimetric effects of conscious sparing of contralateral lobe of thyroid gland in select head and neck patients receiving intensity modulated radiotherapy to ipsilateral neck

Background

The purpose of this paper is to report the dosimetric effects of conscious sparing of contralateral lobe of thyroid gland in select head and neck patients receiving intensity-modulated radiotherapy to ipsilateral neck only. In unilaterally treated neck, the thyroid lobe present contralaterally is passively spared. We compared the effects of consciously sparing it and associated dosimetric results and their statistical significance.

Methods

Treatment plans of 38 buccal mucosa cancer patients, treated to ipsilateral side only, receiving same dose and fractionation to buccal mucosa & elective neck irradiation were evaluated. Since October 2021 we adopted a department protocol of conscious sparing of contralateral thyroid in unilaterally treated head and neck cancer patients. 19 of these had conscious sparing of contralateral thyroid (group A) whereas 19 of old plans were evaluated when C/L thyroid were not given constraints & are being passively spared due to location on contralateral/non treatment side of neck (group B). Treatment planning was done using 7 beam (6 MV) IMRT in Eclipse 13.7 TPS in all of these patients. The best treatment plans were selected ensuring 95% PTV dose coverage and acceptable dose to organs at risk (OARs). Uniform contouring, plan optimization and evaluation protocols were followed for all of these patients.

Results

The mean dose of thyroid in group A was 10.23Gy whereas in group B it was 19.35Gy which is statistically significant (P value – 0.0001). The mean thyroid volume in group A was 4.76cc and in group B was 5.86cc which is not significant statistically different from group B, thyroid dose. Table: 237P

Unpaired ‘t’ test applied. P value = 0.0001, Significant

Conclusions

Unilateral treatment of neck passively reduces dose to OARs present on the contralateral side. This study emphasizes that conscious sparing of contralateral thyroid lobe can further reduce the dose to significant levels. This reduction can preserve thyroid function further. Larger clinical trials are required to corroborate this dosimetric gain with clinical thyroid function preservation.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.