ESTRO 2024 - Abstract Book

S261

Brachytherapy - Gynaecology

ESTRO 2024

4 University of Louisville School of Public Health & Information Sciences, Bioinformatics and Biostatistics, Louisville, USA

Purpose/Objective:

Cervix cancer is the fourth most common malignancy in women worldwide, and the standard of care for locally advanced cervix cancer is concurrent chemoradiation followed by a brachytherapy boost (Potter, Tanderup et al. 2021). Syed-Neblett and tandem & ovoid applicators can be used for the administration of brachytherapy in these patients (Otter, Coates et al. 2018). The goal of this study was to compare patient and tumor characteristics and the dosimetry between Syed-Neblett vs Fletcher-Suit-Delclos Tandem and Ovoid (T&O) applicators used in high dose rate (HDR) gynecologic brachytherapy. Patient toxicities and dosimetric differences between the two applicators to the High-Risk Clinical Target Volume (HR-CTV) and Organs at Risk (OARs) were evaluated.

Material/Methods:

A retrospective study was conducted on patients who underwent HDR brachytherapy from 2009 to 2023. The equivalent dose in 2 Gy fractions (EQD2) was calculated with an Eclipse Scripting Application Programming Interface (ESAPI) program developed at our institution, assuming an alpha/beta ratio of 10 for the HR-CTV and 3 for the OARs. For the HR-CTV, the D50, D90, and D98 were obtained, and for the OARs, the D0.1cc, D1cc, and D2cc values were acquired. Patient and dose characteristics were compared between Syed and T&O applicators using t-tests, Fisher exact, and Mann-Whitney tests.

Results:

A total of 154 Syed patients (66%) and 80 T&O patients (34%) were included. The average age at completion of treatment was 55.4 years and 50.3 years for Syed and T&O patients, respectively (p = 0.014). The mean Karnofsky Performance Status (KPS) and mean Charlson Comorbidity Index were worse for those patients who underwent Syed brachytherapy (86 vs 89, p = 0.098, and 3.9 vs 3.4, p = 0.056, respectively), but did not reach statistical significance. There were no statistically significant differences in the mean body mass index (p = 0.735) or ethnicity (p = 0.384) between Syed and T&O patients. Patients treated with Syed brachytherapy were more likely to have FIGO stage 3 or 4 disease compared to patients treated with T&O brachytherapy (68% vs 30%, p < 0.001). The mean tumor diameter and median HR-CTV were larger in Syed brachytherapy patients (5.8 cm vs 4.7 cm and 49 cc vs 28 cc, p < 0.001). The mean EQD2 HR-CTV D90 was 83.5 Gy and 82.6 Gy for Syed and T&O patients, respectively (p = 0.489). Similarly, there were no statistically significant differences in HR-CTV D50 and D98 values between Syed and T&O brachytherapy. Syed brachytherapy demonstrated equivalent to improved dosimetry to the surrounding OARs compared to T&O brachytherapy. For OAR EQD2 dosimetry values, statistically significant differences were noted for the mean D0.1cc for the bladder and small bowel (100.6 Gy vs 117 Gy and 69 Gy vs 79.6 Gy for Syed and T&O, respectively, p < 0.05), D1cc for the bladder, small bowel, and sigmoid colon (81.3 Gy vs 96.8 Gy, 61.6 Gy vs 70.2 Gy, and 64.8 Gy vs 71.6 Gy for Syed and T&O, respectively, p < 0.05), and D2cc for the bladder, small bowel, and sigmoid colon (76.3 Gy vs 89.8 Gy, 59.3 Gy vs 66.9 Gy, and 62.2 Gy vs 68 Gy for Syed and T&O, respectively, p < 0.05). There were no statistically significant differences in the D0.1cc, D1cc, and D2cc values to the rectum between Syed and T&O applicators. Patients treated with Syed compared to T&O brachytherapy were significantly more likely to be free of any genitourinary (43% vs 23%, p = 0.002), gastrointestinal (55% vs 33%, p = 0.001), or vaginal toxicities (55% vs 31%, p < 0.001) within 6 months following treatment.

Conclusion:

Patients treated with a Syed applicator were more likely to have larger tumors and FIGO stage 3 or 4 disease. Syed brachytherapy was associated with average lower EQD2 D2cc and D1cc doses to the bladder, sigmoid colon, and