Permanent Low-Activity ¹²⁵I Seed Placement for the Treatment of Pediatric Brain Tumors: Preliminary Experience

Abstract

Although external beam radiation therapy is effective in the treatment of many pediatric brain neoplasms its use in this patient population has been associated with the development of significant cognitive and endocrine dysfunction and is severely limited as an option in previously irradiated patients. Therefore, we have adopted a strategy for management of residual microscopic disease by implantation of low-activity ¹²⁵I seeds in the tumor bed at the time of surgery. Six patients aged 2–14 years with recurrent tumors including two supratentorial primitive neuroectodermal tumors (n = 2), one medulloblastoma, one malignant ependymoma (n = 1), glioblastoma (n = 1) and one pleomorphic xanthoastrocytoma were implanted at the time of reoperation. A total of 11–126 seeds were implanted resulting in total doses of 16–21.8 Gy (after theoretical infinite time) at a depth of 5 mm from the implanted resection bed. Five patients had prior external beam radiation while the other patient (2 years old at initial diagnosis) progressed after surgery and chemotherapy. Two patients had lasting local tumor control. One patient is alive at 390 weeks of follow-up and another who died of distant failure at 366 weeks had no recurrence on MRI at 333 weeks’ follow-up. Only 2 patients had first local failures. These results suggest that the use of permanent low-activity ¹²⁵I seeds as an adjunct to surgery can provide good local tumor control and is a suitable treatment option for pediatric patients.

Safety and efficacy of concomitant chemotherapeutic wafers and iodine-125 seeds for recurrent glioblastoma

“…For SAR, however, previous chemotherapy ( P = 0.06) and implantation of iodine-125 seeds ( P = 0.09) trended toward significance. Previous studies have suggested that an increased radiation activity per tumor volume may have an effect on survival,[81729] and the analysis was repeated for patients receiving <0.8 mCi/mL (including patients receiving wafers only) versus those receiving a higher activity implant. This showed a statistically significant advantage in SAR (median 60 weeks and 31 weeks, P = 0.02) for those patients receiving the higher activity per tumor volume [Table 3] [Figure 2].…”

“…Dosages are usually calculated to a depth from surgical cavity perimeter of 0.5 cm, dropping off rapidly with approximately the 30% isodose volume at 1.0 cm depth. [29]…”

Study on treating glioblastoma with 125I seed implantation during operations

“…The form of radionuclide most frequently used for intracranial glioma is 125 I seeds [3,4] which posseses advantages of low average energy, quick energy attenuation beyond an effective distance, long half-life time, and an ease in safe guarding and preserving the radioactivity. Some studies have shown that 125 I can be tolerated by brain tissue, and can produce a satisfactory therapeutic efficacy [5,6] . The 125 I seeds implanted permanently into tissue usually have been of low activity with a low dose rate (LDR) so as to reduce injury to the surrounding normal tissue, prolong the time of continuous exposure and more effectively control the growth of remnant tumor cells.…”

Pediatric CNS Tumors

“…Six patients with recurrent disease were enrolled, 5 of whom had received prior EBRT, and all of whom had reoperations after recurrence; only 2 patients had local failures at the fi rst site of recurrence, leading the authors to conclude that low-activity permanent 125 I seed implants can help to provide good local control while diminishing the risk of signifi cant treatment-related morbidity (Rostomily et al 2001) . Six patients with recurrent disease were enrolled, 5 of whom had received prior EBRT, and all of whom had reoperations after recurrence; only 2 patients had local failures at the fi rst site of recurrence, leading the authors to conclude that low-activity permanent 125 I seed implants can help to provide good local control while diminishing the risk of signifi cant treatment-related morbidity (Rostomily et al 2001) .…”