Yongsook Cecilia Lee, Presenter: Nothing to Disclose

Dominique Rash, Abstract Co-Author: Nothing to Disclose

Robin L. Stern PhD, Abstract Co-Author: Nothing to Disclose

Mathew Mathai, Abstract Co-Author: Nothing to Disclose

Jyoti S. Mayadev MD, Abstract Co-Author: Nothing to Disclose

Definitive radiation therapy for locally advanced cervical cancer involves both external beam radiation therapy (EBRT) and high dose rate (HDR) brachytherapy. There remains controversy and practice patterns variation among the optimal radiation prescription dose to metastatic pelvic lymph nodes. This study investigates the contribution of the pelvic lymph node dose from HDR brachytherapy.

From September 2007 to October 2011, 68 patients were treated with curative intent. Of these, 17 patients with 36 positive pelvic lymph nodes were included in this retrospective analysis. All patients were treated with EBRT to the pelvis with a supplemental boost to the involved pelvic node, plus HDR brachytherapy. Each lymph node was contoured on the Computed Tomography (CT) plan for the EBRT and on each of the 4 to 5 CTs for the brachytherapy planning. The mean dose from the EBRT and brachytherapy plans was recorded. The Equivalent Dose in 2-Gray Fractions (EQD2) was calculated with the equation EQD2 = D × [(d + α/β)/2 Gy + α/β] where D is total dose, d is dose per fraction and α/β-ratio is the dose at which the linear and quadratic components are equal. A student t-test was performed to determine if the mean received dose is significantly different from the mean prescribed dose and the mean EQD2.

The average prescribed dose from the EBRT, including the initial pelvic fields and boost contribution, was 54.09Gy. The average prescribed HDR dose to International Commission on Radiation Units (ICRU) point A was 26.81Gy. The average dose delivered to the involved pelvic lymph nodes from EBRT and brachytherapy were 54.25Gy and 4.31Gy, respectively, with the corresponding EQD2 of 53.45Gy and 4.00Gy. The statistics showed that the means of the received dose and prescribed dose for EBRT are not significantly different (p < 0.05). The similar results between the received dose and the EQD2 for EBRT and brachytherapy were observed.

The equivalent dose contribution to the involved pelvic lymph nodes in locally advanced cervical cancer from HDR brachytherapy was 4.00Gy. Our study shows that is the HDR contribution is 7.5% of the EBRT EQD2 (53.45Gy). The HDR contribution needs to be accounted for when prescribing the EBRT boost dose to pelvic lymph nodes for the optimal therapeutic dose.

This study provides the information for the optimal EBRT boost prescription dose to involved pelvic lymph nodes.

Lee, Y, Rash, D, Stern, R, Mathai, M, Mayadev, J, The Equivalent Dose Contribution from High Dose Rate Brachytherapy to Pelvic Lymph Node Positive Cervical Cancer.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12043908.html