Effect of Gross Tumor Volume (GTV) after Pelvic External Irradiation on Radiation Dose Selection and Prognosis in Vaginal Stump Cancer

Abstract

<h3>Purpose/Objective(s)</h3> Radical radiotherapy is safe and effective for patients with vaginal stump cancer after hysterectomy. The tumor volume after external irradiation is important for selecting irradiation dose and local control. For patients with less residual tumor volume after external irradiation, the total irradiation dose < 70Gy does not affect survival. <h3>Materials/Methods</h3> Ninety-nine patients with vaginal stump cancer after hysterectomy between January 2011 and November 2018 were retrospectively analyzed in this study. All patients received radical radiotherapy without prior antitumor therapy. After pelvic irradiation of 45-50Gy, the residual tumor was further irradiated to 60-82Gy (EQD2, a/β=10) by external irradiation or brachytherapy. Cisplatin-based chemotherapy was performed concurrently with radiotherapy. The overall survival (OS), progress-free survival (PFS), local control (LC), and toxicity were analyzed. <h3>Results</h3> Seventy patients (70.7%) had received 70-82Gy (EQD2, a/β=10) for vaginal stump lesions, and external irradiation is responsible for 84.8% of patients. The Median follow-up was 49.9 months (7.4-114.7months). The 4-year actuarial OS, PFS, and LC were 84.4%, 79.2%, and 89.3%, respectively. In multivariable analysis, GTV > 9cc after pelvic radiotherapy an only independent prognostic factor for worse OS, LC (OS: hazard ratio [HR] = 6.87, CI, 1.90 to 24.83, p=0.003; LC: HR = 8.47, CI, 2.18 to 32.82, p = 0.002). In a subgroup analysis, among patients with GTV > 9cc after pelvic radiation, those with an irradiation dose ≥ 70Gy had better LC than those with a dose < 70Gy (86.5% VS. 44.4%, p=0.009). However, the OS or PFS did not show significant differences between the two groups. In patients with GTV ≤9cc, the irradiation dose ≥ 70Gy didn't show a benefit of LC (93.2% VS.100%, p=0.267). 6 patients (6.06%) developed acute grade 3 rectal toxicity, 4 of which occurred at irradiation dose ≥ 70Gy. None of the patients had complications of late G3-4 grade urinary, rectal toxicity, or lymphedema. <h3>Conclusion</h3> Radical radiotherapy is safe and effective for patients with vaginal stump cancer after hysterectomy. The tumor volume after external irradiation is important for selecting irradiation dose and local control. For patients with less residual tumor volume after external irradiation, the total irradiation dose < 70Gy does not affect survival.