Reference volume, milligram-hours and external irradiation for the Fletcher applicator.

The ICRU Report 38 recommends the use of reference point doses and reference volumes for the reporting of intracavitary gynecologic therapy. The reference volume enclosed by the 60 Gy isodose for intracavitary therapy alone (which can be represented by hwt) and for combined external and intracavitary therapy (HWT) has no conceptual counterpart in the standard intracavitary systems. We report the relationship of the reference volumes (hwt and HWT) to milligram-hours (mgh) radium equivalent and to dose of external irradiation (XRT) for the Fletcher system. HWT and hwt are directly proportional to mgh, the proportionality constant depending on XRT but not appreciably on moderate changes in source geometry. HWT increases slowly with increasing XRT to about 30 Gy, then increases dramatically with even small increases in XRT. The reasons for this behavior and the possible clinical significance are discussed.

Dose-volume analysis and the prevention of radiation sequelae in cervical cancer.

We report a 9 year (1975-1983) experience of treatment of carcinoma of the uterine cervix by radiation alone. Computerized dosimetry conforming to the ICRU 38 recommendations was performed for all 348 patients analyzed. Late sequelae were graded as mild (grade 1), moderate (grade 2) and severe (grade 3). The overall rates were grade 3: 9.8%, grade 2: 18%, and grade 1: 19.5%. Of the moderate to severe sequelae, 48% were rectal, 15% rectosigmoid and 21% urinary. The complication rate was highly dependent on the type of intracavitary applicator: lowest for patients treated by two insertions of a standard Fletcher-Suit applicator (grade 3: 5.4%, grade 2: 14.4%) and highest for those receiving uterine stem plus vaginal line sources (grade 3: 29.5%, grade 2: 26%). For 183 patients treated with stem and standard ovoids, moderate and severe rectal and bladder sequelae were analyzed according to critical organ reference doses and reference treatment volumes as defined by ICRU 38, with the addition of a mean rectal dose. Zones of low, moderate and high risk could be defined on dose-volume plots using these parameters. Modification of treatment plans at the Cancer Institute G. F. Leclerc (CGFL) of Dijon according to these concepts produced a reduction in moderate and severe sequelae (grade 3: 14.4-3.4%) without a concurrent increase in pelvic failures. Although the zones of risk proposed can be used directly only with standard Fletcher-Suit applicators and comparable computer dosimetry, the concept can be applied to other systems.