Room: Track 3
Purpose: this study, we investigate the dosimetric benefits of an MRI-compatible novel rotating shield IMBT system for cervical cancer cases treated with intracavitary (IC-BT) or intracavitary-interstitial (IC/IS-BT) HDR-BT compared to needle-free IMBT.
Methods: developed IMBT delivery system is compatible with any commercial HDR afterloader as an add-on device which resides between the applicator and the afterloader. The device controls the rotation of the shields within the tandem while the afterloader independently controls the source position along the channel. Thirty-six (30 IC-BT, IC/IS-BT) cervical cancer cases treated with MR-guided HDR-BT with high-risk-CTV (HR-CTV) ranging between 82-113.8 cm³, were planned and optimized in RapidBrachyMC-TPS, a MC-based research TPS. Clinical (¹?²Ir) and IMBT (¹?²Ir, 75Se, ¹6?Yb) plans were compared using a Wilcoxon signed rank test.
Results: For IC-BT cases, IMBT significantly reduced bladder, rectum and sigmoid D2cc relative to IC-BT by up to 7.3%±1.0%, 7.7%±0.6% and 4.8%±0.6% for ¹?²Ir, 75Se and ¹6?Yb-based IMBT, respectively; similarly, maximum achievable HR-CTV D98 and D90 were improved by up to 6.7% and 5.2% respectively. Overall, needle-free ¹?²Ir and 75Se-based IMBT were not significantly different to IC/IS-BT. Needle-free ¹6?Yb improved HR-CTV D98 and sigmoid D2cc by 1.5% and 1.9%, respectively.
Conclusion: Dynamic shield IMBT is a superior alternative to conventional IC-BT with ¹?²Ir and even greater improvements with 75Se and ¹6?Yb. Compared to IC/IS-BT, needle-free IMBT with ¹6?Yb improve tumor coverage and OAR sparing;75Se proved non-inferior; and ¹?²Ir lead to clinically acceptable plans. The ability to deliver a conformal, OAR-sparing dose without a single interstitial needle is an exciting avenue towards improving local control and reducing morbidity in cervical cancer patients.