Seed placement in permanent breast seed implant brachytherapy: Are concerns over accuracy valid?

Publication date: Available online 2 February 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Daniel Morton, Michelle Hilts, Deidre Batchelar, Juanita Crook
PurposeTo evaluate seed placement accuracy in permanent breast seed implant brachytherapy (PBSI) in order to identify any systematic errors and evaluate their effect on dosimetry.Materials and MethodTreatment plans and post-implant CT scans for 20 PBSI patients were spatially registered and used to evaluate differences between planned and implanted seed positions, termed seed displacements. For each patient, the mean total and directional seed displacements were determined in both standard room coordinates and in needle coordinates relative to needle insertion angle. Seeds were labelled according to their proximity to the anatomy within the breast in order to evaluate the influence of anatomical regions on seed placement. Dosimetry within an ETV (seroma+5mm), skin, breast, and ribs was evaluated to determine the impact of seed placement on the treatment.ResultsThe overall mean difference between implanted and planned positions was 9 ± 5 mm for the aggregate seed population. No significant systematic directional displacements were observed for this whole population. However, for individual patients, systematic displacements were observed, implying intra-patient offsets occur during the procedure. Mean displacements for seeds in the different anatomical areas were not found to be significantly different from the mean for the entire seed population. However, small directional trends were observed within the anatomy, potentially indicating some bias in the delivery. Despite observed differences between the planned and implanted seed positions, the median (range) V90 for the 20 patients was 97% (66–100%), and acceptable dosimetry was achieved for critical structures.ConclusionsNo significant trends or systematic errors were observed in the placement of seeds in PBSI, including seeds implanted directly into the seroma. Recorded seed displacements may be related to intra-patient setup adjustments. Despite observed seed displacements, acceptable post-implant dosimetry was achieved.

Teaser

Permanent breast seed implant brachytherapy is an attractive treatment option for early stage breast cancer patients. In order to improve the accuracy and confidence in the procedure, uncertainties in the delivery must be identified. This study evaluates the accuracy of seed placement within the breast in order to identify any systematic errors in the delivery and evaluate the impact of seed placement on the treatment.


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