3526 - Dosimetric Evaluation of a Novel HDR Brachytherapy Applicator for Intensity-Modulated Intracavitary Brachytherapy in Locally Advanced Cervical Cancers

Purpose/Objective(s): To evaluate the dosimetric properties of a high dose-rate (HDR) brachytherapy (BT) applicator for intensity-modulated intracavitary brachytherapy (IMBT) in the treatment of locally advanced cervical cancers.

Materials/

Methods: The HDR BT applicator, designed for this study, employs an Ir-192 source and features an IMBT tandem equipped with a rotatable radiation shield, alongside conventional ovoids or a ring, without interstitial needles. Twelve IMBT plans were created for 12 patients diagnosed with locally advanced cervical cancers, previously treated suboptimally per EMBRACE II recommendations. Optimization of all IMBT plans utilized a dose optimization algorithm integrating L0 and L2-norm regularization techniques. Optimal dwell positions, dwell times, and radiation emission angles were determined, minimizing the number of dwell positions and angles while maintaining optimized dose distribution. Resulting dose-volume histograms (DVHs) were compared with those of treatment plans under the same dose coverage of HR-CTV (V_{90 Gy} = 90%) including external beam dose (50.4 Gy in 28 fractions). Additionally, the number of violated dose constraints recommended by the EMBRACE II protocol for the patient group was compared.

Results: The average volume of the 12 HR-CTVs was 47 cm³, with volumes of 41.2 cm³ and 55.1 cm³ observed for 7 intracavitary (IC) applicators and 5 IC plus needles (ICIS) cases, respectively. DVH analysis demonstrated more conformal dose coverage of HR-CTVs by the prescription dose in IMBT plans compared to conventional ICR plans. In 7 ICR cases, IMBT plans showed better sparing of all organs at risk (OARs) when comparing volumetric doses delivered to 2 cm³ of OARs. The average dose reductions in EQD_2Gy(2 cm³) for bladder, rectum, sigmoid, and small bowel, were 6.6 Gy, 5.8 Gy, 3.7 Gy, and, 4.3 Gy, respectively. Further improvement in dose reduction may be achieved through enhanced dose optimization techniques. Additionally, the OAR sparing effect in IMBT plans was comparable to that in 5 ICIS cases.

Conclusion: The proposed IMBT applicator of locally advanced cervical cancers was developed and evaluated using a dose optimization algorithm. DVHs from IMBT plans indicate superior dosimetry over conventional intracavitary and hybrid applicator with needles in treating locally advanced cervical cancers.

Abstract 3526 – Table 1: Comparison of the violation number of EMBRACE II dose constraints in OARs (bladder, rectum, sigmoid, small bowel) for each patient under the same condition of HR-CTV volume coverage