Session Item

To study the doses in the critical organs using different irradiation techniques - on the basis of a model experiment - in operated tongue and floor of mouth tumors.

Between March 2013 and August 2022 twenty patients (11 male/9 female) with stage T1-3N0M0 tongue (n=14) and floor of mouth (n=6) tumors received postoperative radiotherapy because of near/positive surgical margin and/or lymphovascular and/or perineural invasion using high-dose-rate (HDR) interstitial brachytherapy (BT) with a total dose of 15 x 3 Gy applying flexible plastic catheters. For the purpose of comparison volumetric modulated arc therapy (VMAT) and stereotactic irradiation (SRT) plans were also prepared in all cases, using the above mentioned fractionation and total dose. In terms of organs at risk, the doses of the mandible, the ipsilateral and the contralateral salivary glands were compared.

Using a non-parametric variance analysis (Friedman ANOVA) the mean values of D2(%) and D0.1(%) were as follows for BT, VMAT and stereotaxic planning: mandible D2(%) 51.3% and D0,1(%) 70.0%, ipsilateral parotid gland D2(%) 5.7% and D0,1(%) 9.1%, contralateral parotid gland D2(%) 4.1% and D0,1(%) 7.1%, contralateral submandibular gland D2(%) 7.9% and D0,1(%) 11.6%. The mean extent of the planning target volume (PTV) was 12.5 cm3, 26.6 cm3 and 20.1 cm3 with BT, VMAT and stereotaxic planning, respectively.

All the three investigated irradiation techniques result in adequate dose distribution in the radiotherapy of operated tongue and floor of the mouth tumors. While the dose coverage of the target volume and the dose in the the mandible were best with BT, in terms of salivary glands, the SRT technique resulted in the lowest dose. The highest dose of critical organs was observed by the VMAT technique. The above results confirm that BT is definitely effective in the treatment of oral cavity tumors and a worth considering modality when using radiation therapy, not only with a definitive intention, but also postoperatively, taking into account its radiobiological advantages known from the literature.