Objective      To determine the correlation of radiation dose to late side effects in rectum (proctitis) and bladder (cystitis) following the 252Californium (252Cf) neutron intracavitary brachytherapy (ICBT) combined with external beam radiotherapy (EBT) in patients with cervical cancer.  Methods      A total of 286 cervical cancer patients treated by 252Cf neutron ICBT combined with EBT between January 2007 and August 2010 were enrolled into this study. A total dose of 40 Gy (10 Gy per fraction×4 fractions) was given at point A to determine the maximum dose delivered to the rectal anterior and bladder posterior walls. The distance from the maximum dose point of rectum and bladder to  tandem center was measured

respectively. Furthermore

all patients were divided into high-

moderate- and low-dose groups according to the dose they received in comparison to the reference maximum radiation dose. The incidence of severe (≥grade 2) late radiation-induced proctitis and cystitis was observed. Results      In rectum

the distance between the maximum dose point and the center of intrauterine applicator was positively correlated to increased number of treatment（r=0.990，P0.05）

whereas a negative correlation was deciphered between the radiation dose and treatment number (r=-0.959，P0.05). No such correlation was found in the bladder. The incidences of late radiation-induced proctitis for high-

moderate- and low-dose groups were 13.2%

2.0%

and 1.1%. The difference among groups was statistically significant（P0.01）. Correspondingly

the incidences of late radiationinduced cystitis were 4.2%

2.6%

and 4.5%

without significant difference （P=0.270）. Conclusion     The incidences of late radiation proctitis and cystitis can be predicted through monitoring the delivered radiation dose to rectum and bladder by 252Cf neutron ICBT.