Trial Information

Localization of Anatomic Point A in Cervical Cancer Patients

Radiation therapy (RT), with a relevant integration of external beam radiotherapy (EBRT) and
intracavitary brachytherapy (ICBT), is an important part in the treatment of cervical
cancer. Even though concurrent chemoradiation therapy (CCRT) improves the control of
locoregional recurrence and distant metastasis for locally advanced disease, the role of RT
remains important and essential. ICBT is an essential component of RT and has been used to
deliver a high localized dose to the primary cervical lesion and adjacent parametria with an
attempt to minimize dose to nearby normal tissues. The conventional point-based dose
prescription systems have been applied for decades. Incorporation of modern imaging
techniques, namely computerized tomography (CT), magnetic resonance imaging (MRI) and
positron emission tomography (PET) to ICBT, enable radiation oncologists to individualize
treatment volumes but yet, not applicable for routine practice. Point A, since defined by
Tod and Meredith in 1938 and revised in 1953, has been widely accepted as a sacrosanct
reference point for dose prescription of ICBT. Point A was defined as a point 2 cm above the
cervical os and 2 cm apart from os on the line perpendicular to uterine axis. It is a
hypothetical point representing the crossover of the ureter and uterine artery, located in
the paracervical triangle, and is considered as a critical point for radiation tolerance.
This definition of point A provides an easy way to prescribe dose in ICBT and integrate with
EBRT. However, its dosimetry according to orthogonal radiographs would depend solely on the
applicator geometry but not the individual tumor volume or location. The International
Commission on Radiation Units and Measurements (ICRU) report 38 proposed a set of guidelines
for uniform reporting. Reporting of the dimensions of reference volumes still depends on the
geometry of applied applicator and remains difficult for reporting of ICBT. Thus, point A is
still used as a reference point for dose prescription and for correlating the treatment
outcome in clinical trials. CCRT has been considered as a standard of care for locally
advanced cervical cancer. To further dissect the patient population, which may have a
benefit of less morbidity from CCRT, but not radical surgery plus subsequent RT, the
sampling of pelvic and paraaortic lymph nodes prior to decision of intended surgery has been
utilized by performing laparoscopy or laparotomy for stages IB and IIA. Moreover, this
sampling procedure can also provide a pathological proof and delineation of lymph nodes at
risk for an important reference of RT field design. During sampling procedures, we observed
that the point crossing over the ureter and uterine artery could be visualized and marked by
using hemoclips. Therefore, the anatomic position of point A could be visualized on the
orthogonal films after closure of abdominal wound. In this study, we attempt to compare the
location of and the radiation doses to anatomic point A (APA) and hypothetical point A (HPA)
during fractionated ICBT.