(Thursday, 7/18/2019) 7:30 AM - 9:30 AM
Room: 301
Purpose: To present a mechanically simple intracavitary rotating shield brachytherapy (RSBT) system for cervical cancer based on the commercially-available ¹��Yb radioisotope. The system uses a conventional afterloader to produce similar high-risk clinical target volume (HR-CTV) D₉₀-values as the gold-standard intracavitary/interstitial (IC/IS) high-dose-rate brachytherapy in clinically acceptable treatment times.
Methods: Two redundant motors rotate a threaded catheter within a threaded tandem applicator, causing helical advancement of two rotating shields with 180° and 45° emission angles. The catheter has a rigid proximal portion and a flexible distal portion that travels through the curved applicator. The platinum shields are 1.6 mm thick, and the dual-shield approach enables an optimized trade-off between treatment time and D₉₀. The partially-shielded ¹��Yb source of 0.6 mm diameter and 10.5 mm length was dosimetrically modeled using MCNP5. ¹��Yb source activities of 11.6 – 27 Ci were considered, which deliver the same date rate at 1 cm in water as an ¹�²Ir source with a clinical activity range of 4.3 – 10 Ci. The RSBT system was compared to IC/IS in a 37-patient treatment planning study.
Results: HR-CTV volumes in the patients considered were 79 ± 37 cm³. 89% of RSBT and 81% of IC/IS-BT treatment plans reached the GEC-ESTRO-supported 85 Gy HR-CTV D₉₀ goal of 85 GyEQD2 without exceeding the bladder, rectum, or sigmoid colon D2cc constraints of 90, 75, and 75 GyEQD2. The RSBT and IC/IS deliveries were assumed to be in 5 fractions, and the external beam radiotherapy dose of 45 Gy, 1.8 Gy in 25 fractions, was accounted for. RSBT treatment time was 36 ± 28 min, and IC/IS treatment time, accounting for extra time needed for needle insertion and planning, was 63 ± 19 min.
Conclusion: Multi-shield, helical RSBT using ¹��Yb met the planning goals for more patients than IC/IS, with reduced delivery times.
Funding Support, Disclosures, and Conflict of Interest: The authors acknowledge funding from the National Institute of Biomedical Imaging and Bioegineering (R01 EB020665) and the National Cancer Institute Phase 1 Small Business Technology Transfer grant (1 R41 CA210737-01). Ryan Flynn has ownership interest in pxAlpha, LLC, which is developing a commercial rotating shield brachytherapy system.
Keywords
Brachytherapy, HDR, Intensity Modulation
Taxonomy
Not Applicable / None Entered.
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