Utrecht Applicator for Combined Intracavitary/Interstitial Brachytherapy in Locally Advanced Cancer Cervix: Feasibility and Plan Comparison

Purpose: To find out whether additional interstitial component provides better dose distribution and less organ at risk (OAR) doses compared to treatment plan without needles for locally advanced carcinoma cervix cases with residual disease after chemoradiation. Methods: Nine patients with residual disease after chemoradiation for locally advanced cancer cervix were selected for MRI-based brachytherapy planning with hybrid intracavitary/interstitial (IC/IS) Utrecht applicator. The doses of external beam radiotherapy and brachytherapy were added and converted to 2 Gy dose equivalent (EQD2). Two additional sets of plans were created for each patient with and without optimization, before incorporating the interstitial component. A dosimetric comparison was carried out between the plans. Results: The mean high-risk clinical target volume (HRCTV) D90 dose was 87.78 Gy, and HRCTV D98 was 77.4 Gy for the combined IC/IS plans. The mean 2 cc rectal, bladder, and sigmoid doses were 61.3 Gy, 82.2 Gy, and 57.02 Gy, respectively. The mean D90 and D98 doses for plans without optimization were 90.01 Gy and 78.61 Gy, and for optimized plans were 89.8 Gy and 78.03 Gy, respectively. The corresponding 2 cc rectal, bladder, and sigmoid doses were 76.54 Gy, 99.48 Gy, and 69.58 Gy, respectively, for non-optimized plans and 76.1 Gy, 101.94 Gy, and 69.5 Gy, respectively, for optimized plans. The differences of doses of OAR were significantly favoring IC/IS plans with p-value of 0.027, 0.025, and 0.044 for D2cc of bladder, rectum, and sigmoid, respectively. Conclusion: The combined IC/IS plans with optimization resulted in statistically significant lower OAR doses while maintaining the optimal HRCTV doses compared to the intracavitary alone plans with or without optimization.