Dose Contribution to the Regional Lymph-Node Metastases and Point B from Intracavity and Interstitial Hybrid Brachytherapy in Locally Advanced Cervical Cancer

Purpose: Analyzing dose distributions to regional lymph-node metastases (RLNMs) in locally advanced cervical cancer (LACC) patients undergoing intracavitary and interstitial hybrid brachytherapy (IC/IS).

Methods: Dose distributions of eleven LACC patients with 38 RLNMs, and who received 38 IC/IS sessions were analyzed in EQD₂, considering RLNM positions and ipsilateral interstitial needles; these RLNMs, excepting the para-aortic region, were classified into four groups.

Results: RLNMs had a median of two ipsilateral interstitial needles per session. Significant differences were observed in total RLNM D₉₀, depending on whether the position was cranial or caudal of the uterine base (85.5 vs. 378.9 cGy, p < 0.0001), and whether the RLNM D₉₀ was associated with a number of ipsilateral interstitial needles between 0-1 or 2 or more (68.4 vs. 112.2 cGy, p = 0.006) per session. At each session, Group 1 RLNMs (cranial of the uterine base, 0-1 ipsilateral interstitial needle) had a mean D₉₀ of 21.1 cGy; Group 2 (cranial, 2 or more), 73.8; Group 3 (caudal, 0-1), 94.7; and Group 4 (caudal, 2 or more), 136.1.

Conclusion: RLNMs located caudal of the uterine base associated with two or more ipsilateral interstitial needles in IC/IS had a higher dose contribution, which should be considered when calculating the RLNMs' dose of external beam boost irradiation.