Assessment of nodal target definition and dosimetry using three different techniques: implications for re-defining the optimal pelvic field in endometrial cancer

Susan Guo,Manjeet Chadha,Jinesh Shah,Frieda Trichter,Benjamin Bashist,Stephen Bhatia,Ronald D Ennis

doi:10.1186/1748-717x-5-59

Abstract

Purposes1. To determine the optimal pelvic nodal clinical target volume for post-operative treatment of endometrial cancer. 2. To compare the DVH of different treatment planning techniques applied to this new CTV and the surrounding tissues.Methods and MaterialsBased on the literature, we selected a methodology to delineate nodal target volume to define a NEW-CTV and NEW-PTV. Conventional 2D fields, 3D fields based on anatomic guidelines per RTOG 0418, 3D fields based on our guidelines, and IMRT based on our guidelines were assessed for coverage of NEW-CTV, NEW-PTV, and surrounding structures. CT scans of 10 patients with gynecologic malignancies after TAH/BSO were used. DVHs were compared.ResultsFor NEW-PTV, mean V45Gy were 50% and 69% for 2D and RTOG 0418-3DCRT vs. 98% and 97% for NEW-3DCRT and NEW-IMRT (p < 0.0009). Mean V45Gy small bowel were 24% and 20% for 2D and RTOG 0418-3DCRT, increased to 32% with NEW-3DCRT, and decreased to 14% with IMRT (p = 0.005, 0.138, 0.002). Mean V45Gy rectum were 26%, 35%, and 52% for 2D, RTOG 0418-3DCRT, and NEW-3DCRT, and decreased to 26% with NEW-IMRT (p < 0.05). Mean V45Gy bladder were 83%, 51%, and 73% for 2D, RTOG 0418-3DCRT, and NEW-3DCRT, and decreased to 30% with NEW-IMRT (p < 0.002).ConclusionsConventional 2D and RTOG 0418-based 3DCRT plans cover only a fraction of our comprehensive PTV. A 3DCRT plan covers this PTV with high doses to normal tissues, whereas IMRT covers the PTV while delivering lower normal tissue doses. Re-consideration of what specifically the pelvic target encompasses is warranted.

Highlights

Whole pelvic radiation therapy (WPRT) is commonly used in the post-operative treatment of endometrial malignancies as adjuvant therapy targeting the pelvic lymph nodes, in addition to the vaginal apex
Conventional 2D fields, 3D fields based on anatomic guidelines per RTOG 0418, 3D fields based on our guidelines, and intensity modulated radiation therapy (IMRT) based on our guidelines were assessed for coverage of NEW-CTV, NEW-PTV, and surrounding structures
Definition of target structures and subsequent planning We comprehensively reviewed the literature for articles that identified the locations of the pelvic lymph nodes rather than assuming a location

Summary

Introduction

Whole pelvic radiation therapy (WPRT) is commonly used in the post-operative treatment of endometrial malignancies as adjuvant therapy targeting the pelvic lymph nodes, in addition to the vaginal apex. Conventional pelvic fields reference anatomical structures of the bones to establish the pelvic radiation therapy fields. Data from studies including lymphangiograms, intraoperative measurements, or placed surgical clips have found that radiation fields determined by bony landmarks alone results in suboptimal coverage of the nodal areas [1,2,3,4]. With routine use of CT simulation, contouring vessels on the CT image is used as surrogate for lymph node localization. This method provides more complete, precise, and individualized field delineation compared to that achieved when using conventional pelvic fields[5]. Attempting to do this raises several issues that were heretofore not addressed

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