Dosimetric comparison of postoperative interstitial high-dose-rate brachytherapy and modern external beam radiotherapy modalities in tongue and floor of the mouth tumours in terms of doses to critical organs.

BACKGROUND: The aim of the study was to dosimetrically compare interstitial high-dose-rate (HDR) brachytherapy (BT) and modern external beam radiotherapy modalities, as volumetric modulated arc therapy (VMAT) and stereotactic radiotherapy with Cyberknife (CK) of tumours of the tongue and floor of the mouth in terms of dose to the critical organs. PATIENTS AND METHODS: In National Institute of Oncology, Budapest, 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) tumours received postoperative radiotherapy because of close/positive surgical margin and/or lymphovascular and/or perineural invasion. High-dose-rate interstitial brachytherapy applying flexible plastic catheters with a total dose of 15 × 3 Gy was used for treatment. In addition to BT plans VMAT and stereotactic CK plans were also made in all cases, using the same fractionation scheme and dose prescription. As for the organs at risk, the doses to the mandible, the ipsilateral and the contralateral salivary glands were compared. RESULTS: The mean volume of the planning target volume (PTV) was 12.5 cm3, 26.5 cm3 and 17.5 cm3 in BT, VMAT and CK techniques, respectively, due to different safety margin protocols. The dose to the mandible was the most favourable with BT, as for the salivary glands (parotid and submandibular) the CK technique resulted in the lowest dose. The highest dose to the critical organs was observed with the VMAT technique. The mean values of D2cm3 and D0.1cm3 for the critical organs were as follows for BT, VMAT and CK plans: 47.4% and 73.9%, 92.2% and 101.8%, 68.4% and 92.3% for the mandible, 4.8% and 6.7%, 7.3% and 13.8%, 2.3% and 5.1% for the ipsilateral parotid gland, 3.5% and 4.9%, 6.8% and 10.9%, 1.5% and 3.3% for the contralateral parotid gland, 7.3% and 9.4%, 9.0% and 14.3%, 3.6% and 5.6% for the contralateral submandibular gland. CONCLUSIONS: The present results confirm that BT, despite being an invasive technique, is dosimetrically clearly beneficial in the treatment of oral cavity tumours and is a modality worth considering when applying radiotherapy, not only as definitive treatment, but also postoperatively. The use of the CK in the head and neck region requires further investigation.

Results of postoperative interstitial brachytherapy of resectable floor of mouth tumors.

PURPOSE: The purpose of this study was to describe the results of postoperative sole interstitial brachytherapy (BT) in patients with resectable floor of mouth tumors. METHODS AND MATERIALS: Between January 1998 and December 2017, 44 patients with squamous cell histology, stage T1-3N0-1M0 floor of mouth tumor were treated by excision of the primary lesion with or without neck dissection followed by sole high-dose-rate tumor bed BT with an average dose of 22.7 Gy (10-45 Gy) using rigid metal needles (n = 14; 32%) or flexible plastic catheters (n = 30; 68%). RESULTS: During a median followup time of 122 months for surviving patients, the probability of 5- and 10-year local and regional tumor control, overall survival (OS), and disease-specific survival (DSS) was 89% and 89%, 73% and 67%, 52% and 32%, 66% and 54%, respectively. In univariate analysis, lymphovascular invasion was a negative predictor of regional tumor control (p = 0.0062), DSS (p = 0.0056), and OS (p = 0.0325), whereas cervical recurrence was associated with worse DSS (p < 0.0001) and OS (p < 0.0001). The incidence of local Grade 1, 2, and 3 mucositis was 25%, 64%, and 11%, respectively. Grade 4 side effect, that is soft tissue necrosis occurred in four cases (9%). CONCLUSIONS: Results of postoperative sole high-dose-rate BT of floor of mouth tumors are comparable with those reported with low-dose-rate BT, and this method could improve local tumor control and DSS compared with exclusive surgical treatment.

Image guided high-dose-rate brachytherapy versus volumetric modulated arc therapy for head and neck cancer: A comparative analysis of dosimetry for target volume and organs at risk.

Background The aim of the study was to present dosimetric comparison of image guided high-dose-rate brachytherapy (IGBT) with volumetric modulated arc therapy (VMAT) for head and neck cancer regarding conformity of dose distribution to planning target volume (PTV) and doses to organs at risk (OARs). Patients and methods Thirty-eight consecutive patients with T1-4 mobile tongue, floor of mouth and base of tongue cancer treated with IGBT were selected. For these patients additional VMAT treatment plans were also prepared using identical computed tomography data. OARs and PTV related parameters (e.g. V98, D0.1cm3, Dmean, etc.) were compared. Results Mean V98 of the PTV was 90.2% vs. 90.4% (p > 0.05) for IGBT and VMAT, respectively. Mean D0.1cm3 to the mandible was 77.0% vs. 85.4% (p < 0.05). Dmean to ipsilateral and contralateral parotid glands was 4.6% vs. 4.6% and 3.0% vs. 3.9% (p > 0.05). Dmean to ipsilateral and contralateral submandibular glands was 16.4% vs. 21.9% (p > 0.05) and 8.2% vs. 16.9% (p < 0.05), respectively. Conclusions Both techniques showed excellent target coverage. With IGBT dose to normal tissues was lower than with VMAT. The results prove the superiority of IGBT in the protection of OARs and the important role of this invasive method in the era of new external beam techniques.

Dose-volume analysis of target volume and critical structures in computed tomography image-based multicatheter high-dose-rate interstitial brachytherapy for head and neck cancer.

PURPOSE: To evaluate dose-volume relationships of target volume and critical structures in computed tomography (CT) image-based brachytherapy for head and neck cancer. MATERIAL AND METHODS: Thirty-seven patients with mobile tongue, floor of mouth, and base of tongue cancer treated with brachytherapy (post-operative alone and as a boost after external beam radiotherapy [EBRT], or definitive alone or as a boost after EBRT) were selected. Treatment plans were made using post-implant CT images. The fractionation schedule was 7-15 × 3-5 Gy for post-operative (with or without EBRT), 14-15 × 3 Gy for definitive alone, and 5-10 × 3 Gy for boost treatments. For the target volume, V100, D90, and dose non-uniformity ratio (DNR) were calculated. For the mandible, spinal cord and salivary glands doses to specified volumes were reported. RESULTS: The median values of V100 and D90 were 89.9% and 99.9%, respectively; the median values of DNR was 0.46. The median D2cm3 of the mandible and spinal cord were 48.3% and 5.8%, respectively. The ipsilateral median D2cm3 of parotid and submandibular glands were 6.4% and 12.5%, whereas on the contralateral side, the corresponding values were 5.3% and 7.0%, respectively. CONCLUSIONS: Using conformal treatment planning, it was desirable to keep the dose to the mandible, spinal cord, and salivary glands at an acceptable level. The quantitative plan evaluation may help us find correlations between dosimetric parameters and clinical outcome, which may lead to improve the quality of the treatment, but it requires longer follow-up and results from other studies.