Radiation Therapy

The goal of radiation therapy for cervical cancer is to deliver adequate doses over an acceptable period without exceeding normal tissue tolerance limits. The required dose varies according to the tumor burden in the cervix, paracervical sites, and regional lymph nodes. Factors that influence the tolerable dose of radiation include the patient’s vaginal and uterine anatomy, the degree of tumor-related tissue destruction and infection, and patient characteristics (e.g., body habitus, comorbid illnesses, smoking habits). The therapeutic ratio is optimized through careful integration of EBRT and brachytherapy, with the dose and intensity of treatment tailored according to estimates of the disease extent and the risk of complications.

 

 

External Beam Radiation Therapy

Microscopic disease in regional lymph nodes can usually be controlled with an external beam radiation dose of 40 to 50 Gy. However, this dose may not be sufficient to control some areas of heavy microscopic involvement. In particular, the sites of close or positive margins or extracapsular lymph node extension probably require a somewhat higher dose (e.g., 50 to 60 Gy). The risk of metastases within clinically uninvolved paracervical tissues in patients with locally advanced disease probably varies. If the uterus has not been removed, the combined dose from EBRT and ICRT addresses this risk. Adequate treatment of the paracervical tissues is more difficult after a hysterectomy has been performed because most of the paracervical tissues are no longer within the range of effective intracavitary therapy.

 

Patients with stage IB to IVA cervical carcinoma require irradiation of the external iliac, internal iliac, common iliac, and presacral nodes. If the posterior vaginal wall is extensively involved, the perirectal nodes also must be treated. If cancer is present in the distal vagina, the inguinal nodes must be irradiated.

 

EBRT fields must include the cervix (or operative bed) and paracervical tissues, including the broad ligaments and uterosacral ligaments. Treatment fields must be designed with the understanding that the central pelvic tissues are not static; the positions of the uterus, cervix, and upper vagina can change by 3 cm or more, depending on the filling of the bladder and rectum.

 

Integration with Brachytherapy

In addition to helping control regional metastasis, EBRT plays an important role in reducing the volume of central disease before intracavitary brachytherapy. Reduction of central disease volume facilitates insertion of brachytherapy applicators and permits delivery of a higher dose to gross disease by reducing the distance between the tumor periphery and intracavitary sources. Although patients are commonly treated with 40 to 45 Gy to the pelvis before brachytherapy, they should be examined regularly during treatment to determine the optimal point at which to begin brachytherapy. Because EBRT tends to cause some contraction of the upper vagina (limiting the size and packing of vaginal applicators), patients who have a narrow vagina should be considered for intracavitary therapy as soon as the cervix is 4 cm or less in diameter. However, when brachytherapy treatments are scheduled in the middle of EBRT, the procedures should be scheduled carefully to avoid more than a 2- or 3-day interruption in treatment of the regional nodes.