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Tumor Control Probability Incorporated in SAVI Brachytherapy Treatment Planning Prevents Failure in Treatment Outcomes

Z Huang

Z Huang1*, M Farmer1 , Y Feng2 , K Rasmussen3 , S Lo4 , J Grecula5 , N Mayr4 , W Yuh4 , (1) Methodist Hospital, Germantown, TN, (2) East Carolina University, Greenville, NC, (3) University of Texas HSC SA, San Antonio, TX, (4) University of Washington, Seattle, WA, (5) Ohio State University, Columbus, OH


SU-I-GPD-T-5 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Accelerated partial breast irradiation (APBI) with high dose rate (HDR) brachytherapy provides an excellent compact treatment course of radiation due to its limited number of fractions for early-stage carcinoma of breast. SAVI (strut-adjusted volume implant) applicator has 6, 8 or 10 peripheral source channels with one center channel. Our previous analysis on about 200 SAVI patients suggested that the large V200 may be associated with increased toxicity. This study focuses on tumor control probability (TCP), normal tissue complication probability (NTCP) and dosimetry aspects of HDR brachytherapy treatment planning.

Methods: The APBI balloon devices normally inflate above 35 cc range, and hence these balloon type devices cannot be accommodated in small lumpectomy cavity sizes. CT images were obtained and 3-D dosimetric plans were done with Oncentra planning system for 5 patients. The 3-D treatment planning and dosimetric data were evaluated with planning target volume (PTV)_eval V90, V95, V150, V200, skin dose and minimum distance to skin. TCP and NTCP based on the equivalent uniform dose (EUD) incorporating differential Dose-Volume Histogram (DVH) were calculated in the plans with two different optimizations: inverse planning of simulated annealing (IPSA) and graphic optimization (GO).

Results: We were able to accomplish an excellent coverage — V90, V95, V150 and V200 to 98%, 95%, 37 cc (<50 cc volume) and 16 cc (<20 cc volume), respectively in both IPSA and GO. TCP was averaged over 5 patients to be 88.28% in IPSA plans and 58.95% in GO plans. NTCP was averaged to be 0.16% in IPSA verses 1.30% in GO plans for lung and 8.1% vs. 6.6% for skin. The lower TCP was associated with the larger V200 as well as lower normalized dose in the differential DVH.

Conclusion: TCP calculations in HDR brachytherapy treatment planning would be helpful in avoiding radiation induced toxicities.

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