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Comparing Non-Invasive High-Dose-Rate Brachytherapy Using Partially-Shielded Applicators to Intracavitary/Interstitial Brachytherapy for Cervical Cancer

K Hopfensperger1*, Q Adams2, Y Kim2, X Wu3, W Xu3, K Patwardhan2, B Thammavong2, R Flynn2, (1) Department of Biomedical Engineering, University of Iowa, Iowa City, IA, (2) Department of Radiation Oncology, University of Iowa Hospitals and Clinics, Iowa City, IA, (3) Department of Electrical and Computer Engineering, University of Iowa, Iowa City, IA.

Presentations

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

Room: AAPM ePoster Library

Purpose: applicators have been proposed as alternative to invasive intracavitary/interstitial (IC/IS) high-dose-rate brachytherapy for cervical cancer treatment. These approaches include rotating shield brachytherapy (RSBT) and direction modulated brachytherapy (DMBT), which are based on partially-shielded intracavitary applicators. In this work we dosimetrically compare IC/IS, RSBT, DMBT, and conventional IC for cervical cancer treatment.


Methods: treatment plans for each of 37 patients were generated. Average HR-CTV volumes were 79 ± 37 cm3 (41.2 -191.83 cm³). The RSBT plans were modeled as multi-shield plans with 45° and 180° emission angles. ¹?²Ir and ¹6?Yb dose distributions were modeled corresponding to the same range of dose rates at 1 cm off-source-axis in water, 4.3 – 10 Ci for ¹?²Ir and 11.6 – 27 Ci for ¹6?Yb. All treatments were modeled with 5 brachytherapy fractions and 25 fractions of 1.8 Gy/fraction external beam radiotherapy. Treatment times were calculated based on time needed to reach 85 Gy, if possible, and needle placement time was accounted for in treatment time calculations for IC/IS plans.


Results: ¹?²Ir-based IC, DMBT, RSBT, and IC/IS, 38%, 73%, 73%, and 84% of plans, respectively, met the 85 Gy GEC-ESTRO HR-CTV D90 goal without violating OAR tolerance doses, with treatment times of 11.6 ± 5.7 min,16.6 ± 6.6 min, 16.6 ± 6.5 min, and 63.2 ± 18.4 min, respectively. For ¹6?Yb- DMBT and RSBT, 76% and 86% of plans, respectively, met the 85 Gy goal, with average treatment times of 59.8 ± 31.1 min and 27.8 ± 18.1 min, for DMBT and RSBT, respectively.


Conclusion: DMBT and RSBT provided poorer results than IC/IS, but multi-shield ¹6?Yb-based RSBT met the 85 Gy planning goal in 86% of patients, which was a larger percentage of patients than ¹?²Ir-based RSBT, IC, IC/IS, and DMBT and ¹6?Yb-based DMBT. The treatment times for multi-shield RSBT are considered clinically reasonable.

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Funding Support, Disclosures, and Conflict of Interest: Research reported in this abstract was supported by the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health under award number R01 EB020665. RTF is the founder of pxAlpha, LLC, which is developing rotating shield brachytherapy technology.

Keywords

Brachytherapy, HDR, Intensity Modulation

Taxonomy

TH- Brachytherapy: HDR Brachytherapy

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