High-dose-rate intracavitary brachytherapy: results of analyses of late rectal complications.
OBJECTIVE
To examine the incidence of radiation-induced late rectal complications by analyzing the data of measured rectal doses in patients with cancer of the uterine cervix treated with high-dose-rate intracavitary brachytherapy.


METHODS
We measured doses to the rectum in 105 patients with cancer of the cervix during high-dose-rate intracavitary brachytherapy with a semiconductor dosimeter that can measure five points in the rectum simultaneously. On the basis of these measurements, equivalent doses, to which the biologically equivalent doses were converted as if given as fractionated irradiation at 2 Gy/fraction, were calculated as components of the cumulative dose at five rectal points in intracavitary brachytherapy combined with the external whole pelvic dose.


RESULTS
The calculated values of equivalent doses for late effects at the rectum ranged from 15 to 100 Gy (median 60 Gy for patients who did not develop complications and 76 Gy for patients who subsequently developed Grade II or III complications). When converted to a graph of absolute rectal complication probability, the data could be fitted to a sigmoid curve. The data showed a very definite dose-response relationship, with a threshold for complications at approximately 50 Gy and the curve starting to rise more steeply at approximately 60 Gy. The steepest part of the curve had a slope equivalent to approximately 4% incidence/1 Gy increase in equivalent doses.


CONCLUSIONS
The radiation tolerance dose, 5% and 50% complication probability, was about 64 and 79 Gy, respectively. Our data almost agree with the prescribed dose for the rectum for the radiation tolerance doses on the basis of the recorded human and animal data. The probability of rectal complications increased drastically after the maximal rectal dose was >60 Gy.
Sakata
Koh-ichi
K
Department of Radiology, Sapporo Medical University School of Medicine, Sapporo, Japan. sakatako@sapmed.ac.jp
Nagakura
Hisayasu
H
Oouchi
Atushi
A
Someya
Masanori
M
Nakata
Kensei
K
Shido
Mitsuo
M
Koito
Kazumitsu
K
Sagae
Satoru
S
Kudo
Ryuichi
R
Hareyama
Masato
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001918:Brachytherapy / Q000379:methods*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008875:Middle Aged; D011874:Radiometry; D012007:Rectum / Q000528:radiation effects*; D013997:Time Factors; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*