Needle‐free cervical cancer treatment using helical multishield intracavitary rotating shield brachytherapy with the 169Yb Isotope
Purpose
To assess the capability of an intracavitary 169Yb‐based helical multishield rotating shield brachytherapy (RSBT) delivery system to treat cervical cancer. The proposed RSBT delivery system contains a pair of 1.25 mm thick platinum partial shields with 45° and 180° emission angles, which travel in a helical pattern within the applicator.
Methods
A helically threaded tandem applicator with a 45° tandem curvature containing a helically threaded catheter was designed. A 0.6 mm diameter 169Yb source with a length of 10.5 mm was simulated. A 37‐patient treatment planning study, based on Monte Carlo dose calculations using MCNP5, was conducted with high‐risk clinical target volumes (HR‐CTVs) of 41.2–192.8 cm3 (average ± standard deviation of 79.9 ± 35.8 cm3). All patients were assumed to receive 25 fractions of 1.8 Gy of external beam radiation therapy (EBRT) before receiving 5 fractions of high‐dose‐rate brachytherapy (HDR‐BT). For each patient, 192Ir‐based intracavitary (IC) HDR‐BT, 192Ir‐based intracavitary/interstitial (IC/IS) HDR‐BT using a hybrid applicator with eight IS needles, and 169Yb‐based RSBT plans were generated.
Results
For the IC, IC/IS, and RSBT treatment plans, 38%, 84%, and 86% of the plans, respectively, met the planning goal of an HR‐CTV D90 (minimum dose to hottest 90%) of 85 GyEQD2 (α/β = 10 Gy). Median (25th percentile, 75th percentile) treatment times for IC, IC/IS, and RSBT were 11.71 (6.62, 15.40) min, 68.00 (45.02, 80.02) min, and 25.30 (13.87, 35.39) min, respectively. 192Ir activities ranging from 159.1–370 GBq (4.3–10 Ci) and 169Yb activities ranging from 429.2–999 GBq (11.6–27 Ci) were used, which correspond to the same clinical ranges of dose rates at 1 cm off‐source‐axis in water. Extra needle insertion and planning time beyond that needed for intracavitary‐only approaches was accounted for in the IC/IS treatment time calculations.
Conclusion
169Yb‐based RSBT for cervical cancer met the HR‐CTV D90 goal of 85 Gy in a greater percentage of the patients considered than IC/IS (86% vs 84%, respectively) and can reduce overall treatment time relative to IC/IS. 169Yb‐based RSBT could be used to replace IC/IS in instances where IC/IS treatment is not available, especially in instances when HR‐CTV volumes are ≥30 cm3.