Radiotherapy can be used to treat all stages of cervical cancer, with cure rates of about 70% for stage I, 60% for stage II, 45% for stage III, and 18% for stage IV (3). A comparison of surgery and radiation for treatment of low-stage disease is shown in Table 36.5. Primary radiation treatment plans consist of a combination of external teletherapy to treat the regional lymph nodes and to decrease the tumor volume, and brachytherapy delivered by intracavitary applicators or interstitial implants to provide a treatment boost to the central tumor. Intracavitary therapy alone may be used in patients with early disease when the incidence of lymph node metastasis is negligible.
The treatment sequence depends on tumor volume. Stage IB lesions smaller than 2 cm may be treated first with an intracavitary source to treat the primary lesion, followed by external therapy
Table 36.5 Comparison of Surgery versus Radiation for Stage IB/IIA Cancer of the Cervix to treat the pelvic lymph nodes. Larger lesions require external radiotherapy first to shrink the tumor and to reduce the anatomic distortion caused by the cancer. Such a treatment strategy enables the therapist to achieve intracavitary dosimetry. The usual doses delivered are 7,000 to 8,000 cGy to point A (defined as 2 cm superior to the external cervical os and 2 cm lateral to the internal uterine canal) and 6,000 cGy to point B (defined as 3 cm lateral to point A), limiting the bladder and rectal dosage to less than 6,000 cGy. To achieve this level, it is necessary to adequately pack the bladder and bowel away from the intracavitary source. Localization films and careful calculation of dosimetry are mandatory to optimize the dose of radiation and to reduce the incidence of bowel and bladder complications. Local control depends on delivering an adequate dose to the tumor from the intracavitary source.
Although brachytherapy was traditionally prescribed using a low-dose rate technique, high-dose rate techniques are becoming more popular, and controversy exists over which technique is superior. Low-dose rates use caesium-137 as the source, whereas high-dose rates use iridium-192. Proponents of high-dose rate techniques argue that the exposure of radiation to medical personnel is less, ambulatory therapy is possible, and total treatment time is less. Advocates of low-dose rate techniques cite literature suggesting that complication rates are higher with higher-dose rate therapy. Several published trials show that there may be slight stage-related differences in survival between patients treated with low-and high-dose rate regimens, but the techniques have comparable survival and complication rates (116–118).
As noted, clinical staging is imprecise and fails to accurately predict disease extension to the para-aortic nodes in 7% of patients with stage IB, 18% with stage IIB, and 28% with stage III disease (119). Such patients will have “geographic” treatment failures if standard pelvic radiotherapy ports are used. As a result, treatment plans for these patients are individualized based on CT scans, PET scans, and biopsies of the para-aortic lymph nodes for consideration of extended-field radiotherapy. The routine use of extended-field radiation for prophylactic para-aortic radiation without documentation of distant metastasis to the para-aortic nodes was evaluated and is not practiced because of the increased enteric morbidity associated with this treatment modality.