Evaluation of doses to pelvic lymph node regions from image-guided high-dose-rate interstitial brachytherapy for carcinoma of the uterine cervix.

Purpose: Interstitial brachytherapy (ISBT) is indicated for intact cervical carcinoma (IN-CC) if intracavitary brachytherapy (ICRT) is not feasible and also in vault carcinoma (VA-C). We aimed to evaluate the doses to pelvic lymph node regions in IN-CC and VA-C treated with ISBT.

Material and methods: Ten patients (6 IN-CC, 4 VA-C) were chosen for this dosimetric study. IN-CC had a central tandem in addition to the needles. External iliac (EI-N), internal iliac (II-N), obturator (OB-N) and sacral (SA-N) groups of lymph nodes were delineated. A dose of 10 grays (Gy) and 8 Gy each × 2 fractions was prescribed to the target in IN-CC and VA-C respectively. Doses received by 100%, 90% and 50% volume (D₁₀₀, D₉₀, D₅₀) and D_2cc, D_1cc, D_0.1cc were evaluated. Doses to lymph nodal groups in IN-CC vs. VA-C were compared using Student's t-test.

Results: For 20 implants, the median number of needles was 18 (range, 16-20). Mean D₉₀ and D_2cc of the combined bilateral OB-N, II-N, EI-N and SA-N groups were 33.62 ±3.46% and 102.94 ±10.71%, 6.98 ±0.65% and 39.69 ±3.64%, 5.1 ±0.51% and 15.4 ±0.8%, 7.76 ±0.95% and 15.36 ±1.09% of the prescribed doses respectively. Patients with a central tandem (IN-CC) received significantly higher doses to external, internal iliac and sacral group of lymph nodes (p < 0.001) as compared to VA-C.

Conclusions: In patients with cervical carcinoma treated with ISBT, pelvic lymph node groups received significant doses. The dose contribution to pelvic lymph nodes is higher in patients with intact cervical cancer where a central tandem is used as compared to post-operative patients.