Effects of Bladder Distension on Organs at Risk in 3D Image-Based Planning of Intracavitary Brachytherapy for Cervical Cancer
Presented at the 50th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO), Boston, MA, September 21–25, 2008.
Received 7 October 2008; received in revised form 29 January 2009; accepted 30 January 2009. published online 20 May 2009.
Purpose
To investigate the effects of bladder distension on organs at risk (OARs) in the image-based planning of intracavitary brachytherapy for cervical cancer.
Methods and Materials
Thirteen patients with cancer of the cervix were treated with high-dose radiation brachytherapy (800 cGy/fraction for 3 fractions). For the three-dimensional (3D) analysis, pelvic CT scans were obtained from patients with indwelling catheters in place (defined as empty bladder) and from patients who received 180-cc injections of sterile water in their bladders (defined as full bladder). To compare the International Commission on Radiation Units and Measurements (ICRU) point doses with 3D-volume doses, the volume dose was defined by using two different criteria, D2cc (the minimum dose value in a 2.0-cm3 volume receiving the highest dose) and D50% (the dose received by 50% of the volume of the OAR) for OARs.
Results
The bladder D2cc was located more cranially in the bladder base and was distributed in multiple spots in 46% of patients. The rectal D2cc was located in the area of the ICRU point as a single “hot spot.” For patients with a full bladder, the mean bladder D2cc increased from 634 to 799 cGy (28.8%, p = 0.002). However, the bowel D2cc decreased from 475 to 261 cGy (45.0%, p < 0.001). There were no substantial differences in rectal and sigmoid D2cc values. However, the mean D50% values of both the bladder and the bowel decreased from 108 to 80 cGy (23.7%, p < 0.001) and from 282 to 221 cGy (19.7%, p = 0.004) with a full bladder, respectively.
Conclusions
An increase in bladder volume resulted in a significant reduction in bowel D2cc values at the expense of an increase in bladder D2cc values. Treatment with a distended bladder is preferable to protect the bowel.
∗Department of Radiation Oncology, University of Alabama Medical Center, Birmingham, AL
†Department of Medical Statistics Section of the Comprehensive Cancer Center, University of Alabama Medical Center, Birmingham, AL
Reprint requests to: Robert Y. Kim, M.D., Department of Radiation Oncology, University of Alabama at Birmingham, 1824 6th Avenue South, Birmingham, AL 35249-6832. Tel: (205) 975-0222; Fax: (205) 975-0784
ABSTRACT