KEY POINTS
- This multicentre retrospective study included 33 patients with 40 retroperitoneal nodal lesions located partially within previously irradiated fields. Patients were unsuitable for or declined further EBRT; 32 of 33 also had distant metastatic disease.
- CT-guided iodine-125 implantation used seed activities of 11.1–29.6 MBq and prescription doses of 80–140 Gy. Treatment planning expanded the GTV by 5 mm, and complex procedures could incorporate ultrasound guidance or a three-dimensional printed template.
- Disease-control rates per lesion were 90.0% at three months and 77.5% at six months. Median local tumour progression-free survival was 9.0 months, and median overall survival was 20.0 months.
- Overall survival rates at 6, 12, 18, and 24 months were 81.8%, 60.5%, 50.2%, and 28.2%, respectively. Most patients received additional systemic therapy, limiting attribution of survival outcomes to brachytherapy.
- Among eight patients with pain, mean numerical-rating score decreased from 3.50 to 1.75 one month after implantation (p=0.009).
- A postoperative GTV D90 of at least 108 Gy was associated with longer local progression-free survival (HR 0.209, 95% CI 0.087–0.502; p<0.001). The threshold was derived by dichotomizing this small dataset rather than prospectively validated.
- One patient developed a grade 3 sigmoid-colon fistula four months after implantation; the lesion had invaded the bowel wall before treatment. Intestinal-wall invasion independently predicted worse overall survival (HR 5.672, 95% CI 2.032–15.836; p<0.001), while four patients reported mild transient back discomfort.
CLINICAL TAKEAWAY
Iodine-125 implantation may provide temporary local control and pain relief when further external-beam treatment is not feasible. The apparent D90 relationship should not be treated as a validated prescription target, and bowel-wall invasion demands particular caution because efficacy and severe-toxicity risks compete directly.