490 Obstetrics and Gynecology Board Review •••
❍ At what doses of radiation, does radiation cystitis occur?
Radiation cystitis occurs with moderate doses of irradiation (above 3000 cGy). With doses above 6000 cGy,
chronic cystitis, fibrosis, and vesicovaginal fistula may occur.
❍ What doses of radiation will result in ovarian sterilization?
The dose of radiation that will result in ovarian castration is age dependent, with younger woman requiring
larger doses. In general, a single dose of 650 to 800 cGy or fractional doses of 1500 to 2000 cGy will bring about
permanent sterilization.
❍ What is the rationale for preoperative radiation therapy?
The rationale is based on its potential ability to eradicate subclinical disease beyond the anticipated margins of
surgical resection, to reduce tumor volume, to sterilize lymph node metastases, and to decrease the possibility for
dissemination of clonogenic tumor cells.
❍ What is the rationale for postoperative irradiation?
The rationale for postoperative irradiation is based on the assumption that subclinical foci of cancer cells will be
destroyed along with any residual disease.
❍ How are the effects of combined radiation therapy and chemotherapy helpful?
The effects of combined radiation therapy and chemotherapy can be independent, additive, and/or interactive.
Chemotherapy prior to irradiation results in a diminished tumor load for radiation treatment. Concurrent use of
chemotherapy with radiation therapy can bring about additive or supra-additive action, attenuating tumor kill.
Chemotherapy after radiation has been used as an adjuvant to control subclinical disease.
❍ What radiation modality provides for the most optimal treatment of carcinoma of the cervix?
The most optimal treatment combines external beam irradiation (teletherapy) with intracavity or interstitial
brachytherapy.
❍ What is the survival rate for stage IA and IB (smaller than 1 cm) cervical carcinoma with radiation therapy?
Intracavitary irradiation alone results in a 96% survival. External irradiation alone is much less successful, with
survival rates two-third of those for combined intracavitary and external beam radiation.
❍ What is the prescribed dose for external beam radiation in the treatment of cervical carcinoma?
The prescribed dose is dependent on tumor volume and the extent of combined brachytherapy. In general,
the relative proportion of external beam radiation increases with tumor volume and stage; it usually precedes
intracavitary brachytherapy with paracentral doses ranging between 70 and 85 cGy and pelvic sidewall doses
between 45 and 50 Gy.
❍ What are points A and B?
These are reference points in the pelvis that are used to describe the doses delivered. Point A is 2 cm lateral and
2 cm superior to the external cervical os and anatomically represents the area where the uterine artery crosses over
the ureter. Point B is 3 cm lateral to point A and corresponds to the pelvic sidewall.