Role of High-Dose Salvage Radiotherapy for Oligometastases of Localized Abdominal/Pelvic Lymph Nodes

Abstract

To assess the utility of high-dose radiotherapy for abdominal/pelvic lymph node (LN) oligometastases. Between January 2008 and April 2018, patients who irradiated their abdominal/pelvic LN from 4 institutes were retrospectively analyzed. We included patients who developed localized abdominal/pelvic nodal recurrence of 1–5 LN metastases. The exclusion criteria were as follows: nonepithelial tumors, uncontrolled primary lesion, palliative intent, and re-irradiation. Since a conventional linear accelerator and robotic radiosurgery were used for treatment, fractionated schedules varied, such as 3D conformal/intensity-modulated radiotherapy and stereotactic body radiotherapy. We therefore calculated the EQD2 at D50% for all patients to compare the different treatment schedules and stratified patients with EQD2≧60Gy as the high dose group. With a median follow-up time of 23.7 months for surviving patients, 113 patients were analyzed. Median age was 65 years (range 36-83 years), and 68 patients (60%) were female. Initial treatment was surgery for 101 patients and radiotherapy for 12 patients. The median period from last treatment to this salvage radiotherapy (disease-free interval; DFI) was 8.5 months (range 0.5-86.6 months). The primary tumor sites included colorectum (n=28), uterine cervix (n=27), endometrium (n=15), and ovary (n=10). Most patients (n= 61) involved a solitary LN with a median size of 2 cm (range 1-5.5 cm). The 2-year overall survival (OS), local control (LC), and progression-free survival (PFS) rates were 63.1%, 59.7% and 19.4%, respectively. Univariate and multivariate analyses revealed that solitary metastasis, high dose irradiation, and long DFI were significantly associated with favorable OS, LC, and PFS, respectively. Although the high-dose group (n=55) had a significantly improved 2y-LC (74.9% in high dose vs 45.2% in low dose; p<0.001), it showed only a trend towards better 2y-OS (74.8% in high dose vs 52.7% in low dose; p=0.08). However, when analyzing only the subgroup of patients with solitary LN involvement (n=61), high-dose irradiation (n=33) had a significantly improved 2y-OS (88.8% in high dose vs 56.3% in low dose; p=0.009). Late Grade 3 toxicity or more included ileus in 7 cases (6%) and gastrointestinal bleeding in 4 cases (4%). There was no significant difference between the high and low dose groups in the incidence of late toxicities. This analysis found that salvage radiotherapy for oligometastases of abdominal/pelvic LN was effective with acceptable toxicity. This treatment is especially promising for solitary LN recurrence with high-dose treatment (EQD2≧60Gy), in which excellent local control and OS can be expected. We therefore believe that a prospective trial is warranted.