The Choice of 2D-Brachytherapy or 3D-Brachytherapy for Cervical Cancer Patients after External Beam Radiation Based on Residual Gross Tumor Volume

Purpose/Objective(s)The purpose of this study was to analyze the choice of 2-dimensional brachytherapy (2D-BT) or 3-dimensional brachytherapy (3D-BT) for cervical cancer patients after external beam radiotherapy (EBRT), based on residual gross tumor volume (GTV res).Materials/MethodsBetween September 2019 and April 2020, 106 local advanced cervical cancer patients (FIGO stage IB3-IVA) who received primary radiation or chemoradiation followed by BT were analyzed retrospectively. We divided patients into large tumor group (GTV res > 30 mm3 or the width ≥ 4 cm) and small tumor group (GTV res ≤ 30 mm3). Point A and high-risk clinical target volume (CTVHR) planning were designed for each patient; all patients received 4–5 fractions of intra-cavity BT with a single dose of 6 Gy. The CTVHR, the bladder, and rectum were delineated, respectively, the D2cc (minimum dosage to the most irradiated 2 cc of an organ at risk) of bladder and rectum, D90 (dose to 90% of a target) of the target, vaginal dose point, and vaginal reference length (VRL) were compared.ResultsThe patients who received BT fewer than 4 times (n = 2), had double primary tumors (n = 1), or had incomplete data (n = 3) were excluded. Thus, 106 patients were eligible and analyzed in this study. Of the 106 patients, 45 (42.5%) had an initial tumor size of > 4 cm before EBRT. After EBRT, 92 (86.8%) patients had small GTV res, the median of GTV res and CTVHR were 2 cm3 and 17.85 cm3. The CTVHR does not change with GTV res (r2 = 0.16, P < 0.001), no matter the size of GTV res, both the point A dose and CTVHR can satisfactorily reach the prescribed tumor coverage dose. However, when evaluated by volume dose, the CTV-HR D90 was higher than the Point A dose; with reduced organs at risk (OARs) dose (bladder, rectum-, and vaginal dose point) (P < 0.05). The remainder of the patients had large GTV res, with a median of 64cm3, which is not covered by the Point A dose. While evaluated by volume dose, the median of CTVHR was 71.6 cm3; as GTV res increased, the CTVHR increased significantly (r2 = 0.68, P < 0.001). The CTVHR D90 to Point A dose ratio was negatively correlated with GTV res (r = -0.61, P < 0.001), and the Point A dose typically varied between 47% and 230% of the CTVHR D90. In the OARs dose evaluation, only the vaginal dose points were lower in the CTVHR plan. The 1-year and 2-year local controls for small and large tumor groups were 94.3% versus 78.6% and 91.9% versus 70.7%, respectively.ConclusionAfter EBRT, 86.8% of locally advanced cervical cancer (LACC) patients had small residual tumors, and 2D-BT can achieve adequate prescription dose coverage and meet treatment needs. Only 13.2% of patients had large residual tumors, and these patients should receive 3D-BT or treatment combined with interstitial needles to deliver a higher dose to the CTVHR. To protect the OARs and reduce radiation damage in small resident tumor patients, 3D-BT would be the best choice.