Assessing dose contribution to pelvic lymph nodes in intracavitary brachytherapy for cervical cancer

Abstract

PurposeIn radical radiotherapy for cervical cancer, high-dose-rate (HDR) brachytherapy is commonly used after external beam radiation therapy (EBRT) to deliver a cumulative EQD2 of 80 to 90 Gy to the primary tumor. However, there is less certainty regarding brachytherapy dose contribution to the pelvic lymph nodes. This poses a challenge as to how high a preceding EBRT dose should be prescribed to gross nodal disease, in order to achieve a cumulative tumoricidal effect. Hence, this study aims to quantify brachytherapy dose contribution to individual pelvic nodal groups, using computed tomography (CT) planning with the Manchester system.Material and methodsThis is a single institution retrospective dosimetric study. CT planning datasets from 40 patients who received EBRT followed by intracavitary HDR brachytherapy (5 or 6 Gy fractions) were retrieved. The external iliac (EI), internal iliac (II), and obturator (OB) lymph node groups were contoured on each CT dataset. Applying the initial brachytherapy plan, mean doses to each nodal group were calculated for every patient, and averaged across the respective (5 or 6 Gy) study populations.ResultsWith a brachytherapy dose of 5 Gy to Manchester point A, the mean absolute doses received by the EI, II, and OB groups were 0.79, 1.12, and 1.34 Gy respectively, corresponding to EQD2s (α/β = 10) of 0.71, 1.04, and 1.27 Gy respectively. With a brachytherapy dose of 6 Gy, the mean absolute doses received by the EI, II, and OB groups were 1.16, 1.56, and 1.80 Gy respectively, corresponding to EQD2s of 1.08, 1.49, and 1.77 Gy, respectively.ConclusionsOur study demonstrates that pelvic lymph nodes receive substantial dose contributions from HDR brachytherapy in cervical cancer. This should be taken into account by the radiation oncologist during EBRT planning, and adequate external beam boost doses calculated to achieve cumulative tumoricidal doses to pelvic nodal disease.

Equivalent dose in 2 Gy (EQD2) to pelvic lymph nodes using volume based prescription for three brachytherapy applicators — a dosimetric retrospective analysis

“…Similar studies have been done by Chua et al [8], Lee et al [11], Lee Y et al [12] and Matsukawa et al [13], where they did CT based planning but prescribed to point A.…”

“…With a brachytherapy dose of 5 Gy to point A, the mean EQD2 doses received by the EI, II and OB groups were 0.71, 1.04, and 1.27 Gy, respectively. With a brachytherapy dose of 6 Gy, the mean EQD2 doses received by the EI, II, and OB groups were 1.08, 1.49, and 1.77 Gy, respectively [8]. In our study, using volume based prescription to a dose of 6.5 Gy per fraction, the median EQD2 ranged between 3.92-5 Gy for point B, 1.78-2.16 Gy for the ELN groups, 2.88-3.56 Gy for the ILN groups and 4-5.2 Gy for the OBT groups across the three arms.…”

“…In addition to the targets and OARs, the pelvic lymph nodes were contoured by a radiation oncologist according to the consensus guidelines formulated by Chua et al [8]. The ELN, ILN, OBT group of lymph nodes were contoured for each patient bilaterally.…”

Dose to pelvic lymph nodes in image based high dose rate brachytherapy of carcinoma cervix

“…The average dose delivered to the external iliac, internal iliac and obturator lymph nodes was 4 Gy, 5.09 Gy and 5.47 Gy, respectively. In a similar study by Ying Chua et al, 21 the mean absolute dose received by the external iliac, internal iliac and the obturator lymph nodes was 0.79 Gy, 1.12 and 1.34 Gy, respectively with a point A dose of 5 Gy and 1.16 Gy, 1.56 Gy and 1.80 Gy, respectively, with a point A dose of 6 Gy.…”

Assessment of the anatomical position of point B and the relationship between point B dose and the dose delivered to pelvic lymph nodes in CT-based high-dose-rate brachytherapy for uterine cervical cancer

“…quantified the brachytherapy dose contribution to pelvic node groups using the Manchester method. They indicated that the mean cumulative EQD 2 doses to the external iliac, the internal iliac, and the obturator nodes were 4.30 Gy, 5.95 Gy, and 7.09 Gy, respectively, in patients who received 6 Gy × 4 fractions [25]. Thus, the brachytherapy dose was reported to make a significant contribution in these studies, and the accurate evaluation of the dose delivered to the pelvic lymph nodes by brachytherapy is essential.…”