Outpatient template-guided permanent interstitial brachytherapy using ¹³¹Cs in gynecologic malignancies: Initial...

Optimal curative intent brachytherapy for certain gynecologic cancers requires interstitial brachytherapy, often using template-guided techniques such as a Syed-Neblett implant. Whether high or low dose rate (LDR), these procedures pose significant risks to patients, partly attributable to the prolonged period of bed rest. Published results of free-handed permanent interstitial brachytherapy (PIB) with ¹³¹Cs demonstrate it to be an effective modality for the management of small volume gynecologic cancers. This report is the first to describe a permanent template-guided interstitial technique using ¹³¹Cs for gynecologic cancers, performed as an LDR outpatient procedure.

Five sequential patients with recurrent or primary gynecologic malignancies underwent template-guided PIB using ¹³¹Cs. A posttreatment planning CT was obtained immediately after the procedure and again 3-4 weeks later. Both CT data sets were fused and the relative positions compared to assess for migration in the x, y, and z planes. Seed positions as well as dosimetric parameters including D₉₀, D₁₀₀, V₁₀₀, and the dose to 2 cc of rectum and bladder were compared to quantify migration of sources and the resulting effect, if any, on the treatment.

The median age was 69 years (range 64-85). All patients received a template-guided ¹³¹Cs PIB implant to treat gross disease. All 5 patients had significant medical comorbidities that limited treatment options. Considering all 5 patients, a total of 40 interstitial needles were placed. Ten needles carried only Vicryl-stranded sources, and 30 needles carried a combination of stranded ¹³¹Cs seeds and free seeds. Needle count was between 6 and 10 needles per patient, with active lengths of 4-10 cm. The median dose was 30 Gy (range 25-55 Gy) to permanent decay, enabling a cumulative median biological effective dose 91.5 Gy (range 60.9-92.1 Gy) and equivalent dose at 2 Gy per fraction 75.9 Gy (range 50.7-76.8 Gy). All implants were performed as outpatient procedures with only the first patient admitted for 23-hour observation. All calculated median migration distances were less than 1 cm in the axial, sagittal, or coronal planes. In 69.2% cases, the individual seed migration was <5 mm. Strand migration appeared directly related to peripheral placement and the use of stranded sources. The median D₉₀, D₁₀₀, and V₁₀₀ were compared between study sets, and no significant differences were identified. No Grade 3 or higher complications occurred.

Permanent LDR template-guided PIB using ¹³¹Cs can be safely performed on an outpatient basis. Compared to currently used template-guided techniques, the use of ¹³¹Cs avoids prolonged bed rest and hospitalization, significantly lowers cost, and enables a higher cumulative dose. Seed migration is minimal with this technique. Early experience suggests that the technique is safe and merits further study.