ESTRO 2025 - Abstract Book

S931

Clinical – Head & neck

ESTRO 2025

Results: Of the 17 patients, 10 (59%) had tonsil and 7 (41%) had base of tongue primary sites. All patients received definitive RT (66-70 Gy/30-35 fractions). The IMPT clinical plans had a median of 46.99 Gy to the ipsilateral tubarial gland, which decreased to 38.83 Gy in the reoptimized plan ( p <0.01); the contralateral tubarial gland dose decreased from 22.1 Gy to 18.7 Gy ( p <0.01). In the IMRT plans, the ipsilateral tubarial gland dose decreased from 58.8 Gy to 48.8 Gy ( p <0.01), and the contralateral tubarial gland decreased from 26.6 Gy to 20.5 Gy ( p <0.01). A difference in the mean dose of 0-18.2 Gy was observed between the plans. IMPT plans met tubarial gland mean dose constraints more often than did IMRT plans. (Figure 2) All the plans met the institutional dosimetric goals in terms of target coverage. No significant difference was observed in IMPT plans: mean difference in HR-CTV D 99% - 0.09 (95% CI: -0.21-0.01; p =0.09), IR-CTV D 99% - 0.05 (95% CI: -0.01-0.12; p =0.1), LR-CTV D 99% -0.07 (95% CI: -0.14-0.3; p =0.1). A small decrease in high risk target coverage was noted in IMRT plans (mean difference in HR-CTV D 99% - 0.8% (95% CI: 0.48-1.26%; p <0.01), IR-CTV D 99% - 0.7% (95%CI:-2.35-3.78; p =0.62) and LR-CTV D 99% -1.4% (95%CI: -3.04-5.94; p =0.5).

Conclusion: This pilot study demonstrates the feasibility of sparing tubarial glands without compromising target coverage using both IMPT and IMRT. Future studies are warranted to establish a definite dose constraint for this new OAR.

Keywords: Tubarial glands, IMPT, IMRT

References: 1 Valstar MH, de Bakker BS, Steenbakkers RJHM, de Jong KH, Smit LA, Klein Nulent TJW, et al. The tubarial salivary glands: A potential new organ at risk for radiotherapy. Radiother Oncol J Eur Soc Ther Radiol Oncol 2021;154:292–8. https://doi.org/10.1016/j.radonc.2020.09.034.

454

Digital Poster Evaluation of Submandibular Gland Function Using Quantitative Pertechnetate Scintigraphy in Submandibular-Sparing Radiation for Head and Neck Cancers Shyama Prem S 1 , Prasoon Garg 2 , Madhusudhanan Ponnusamy 3 , Saravanan Kandasamy 4 , Muthuveerappan S 5 1 Radiation Oncology, JIPMER, Pondicherry, India. 2 Radiation Oncology, TMH, Mumbai, India. 3 Nuclear Medicine, JIPMER, Pondicherry, India. 4 Medical Physics, JIPMER, Pondicherry, India. 5 Medical Oncology, JIPMER, Pondicherry, India Purpose/Objective: Radiation-induced xerostomia and its complications have a profound impact on a patient's quality of life after treatment. Since the submandibular gland, contributes significantly to unstimulated salivary flow, sparing it is crucial in preventing radiation-induced xerostomia. However, few studies on salivary scintigraphy specifically