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

Abstract

PurposeOptimal 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. Methods and MaterialsFive 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. ResultsThe 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. ConclusionsPermanent 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.