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Impact of Patient-Specific Factors On Implant Uncertainty in Permanent Breast Seed Implant Brachytherapy

C Zhang1,2*, M Hilts1,2, D Batchelar1,2, J Andrews2, C Hvingelby2, E Watt3, J Crook1, (1) BC Cancer - Kelowna, Kelowna, BC, CA, (2) The University Of British Columbia Okanagan, Kelowna, BC, CA, (3) Okolo Health, Calgary, AB, CA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Permanent breast seed implant (PBSI) is a novel single-day breast cancer treatment. Appropriate margin definition is critical to treatment efficacy and safety. The quantitative analysis of PBSI implant uncertainty lays the foundation for future investigations on PBSI PTV margin adequacy. To this end, this study determines correlations between implant accuracy and patient-specific factors (breast size, PTV volume, implant depth) in PBSI by evaluating the implant uncertainty of 4809 seeds from 63 patients who received PBSI at BC Cancer–Kelowna from 2012-2019.


Methods: Seed locations were identified on both planning and post-surgical (Day0) CTs. Implant accuracy was quantified by calculating seed displacements using a simulated annealing algorithm. The average seed displacement, including the magnitude and directional displacement in left-right (LR), shallow-deep (SD), and up-down (UD) directions from a needle insertion view, was calculated for each patient. Changes in the seed cloud from plan to Day0 were characterized by the volume of seed cloud. Pearson R tests were performed to analyze the correlation between patient-specific factors and patient-average seed displacement and seed cloud volume change.


Results: The mean seed displacement magnitude was 10±6 mm, and mean directional displacements were 0±5 mm (LR), 0±9 mm (SD), and -1±5 mm (UD). The mean seed cloud volumes were 45.1±18.9 cc (plan) and 50.0±25.0 cc (Day0). The magnitude of patient-average seed displacement showed moderate positive correlations with both breast size (r=0.31, p=0.01) and PTV volume (r=0.38, p=0.002). The relative seed cloud volume change showed a mild positive correlation with implant depth (r=0.26, p=0.04).


Conclusion: This work presents evidence-based data indicating an anisotropic pattern in seed implant uncertainty as well as a tendency for the seed cloud to expand during PBSI implantation. Some correlations between the implant accuracy and patient-specific factors were observed and may provide insights into establishing clinical planning guidelines.

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Funding Support, Disclosures, and Conflict of Interest: Funding Support: BC Cancer Foundation

Keywords

Brachytherapy, Permanent Implants, Statistical Analysis

Taxonomy

TH- Dataset Analysis/Biomathematics: biostatistics and clinical trial design

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