3D CT-based volumetric dose assessment of 2D plans using GEC-ESTRO guidelines for cervical cancer brachytherapy
Received 6 October 2008; received in revised form 12 May 2009; accepted 15 May 2009. published online 23 October 2009.
Abstract
Purpose
To investigate two-dimensional (2D) radiograph-based plans using three-dimensional (3D) dose–volume histogram (DVH) parameters following guidelines from Gynecologic GEC-ESTRO Working Group (GEC-ESTRO).
Methods and Materials
Nineteen high-dose-rate (HDR) fractions from 8 patients were studied. Prescription was 45Gy from external beam radiation therapy plus 30Gy in five fractions from HDR using tandem and ring/ovoids. Both radiographs and CT scan were obtained. Treatment was planned using radiographs following American Brachytherapy Society (ABS) guidelines. Retrospective evaluation of above 2D plans on a 3D volumetric basis was achieved by generating CT image-based 3D plans using same dwell times.
Results
In 2D plans, International Commission on Radiation Units and Measurement (ICRU) bladder and rectal point doses were 3.8±0.4 and 3.0±0.5Gy, respectively. In 3D plans, rectum D2cc is 4.0±1.0Gy and bladder D2cc is 5.4±0.9Gy. Position of actual hottest spot in 3D rectum volume was close to the position of ICRU rectal point. ICRU bladder point did not match with the actual hottest spot in 3D bladder volume. In 2D plans, H-point dose was 5.8±0.2Gy. In 3D plans, dose to CT-based cervix (D90) reduced from 7.1 to 4.2Gy as the cervical volume increased from 12 to 39cc. Average D2cc/ICRU dose ratio was calculated to be 1.36/1.01 for bladder/rectum, respectively.
Conclusions
The DVH analysis of 2D plans revealed a suboptimal coverage of CT-based cervix and a negative correlation between coverage and cervical size. Rectum dose to 2cc weakly correlated with ICRU point dose. Currently published constraint for bladder in 3D planning is tighter than ABS guidelines in past 2D planning.
Department of Radiation Oncology, Loyola University Medical Center, Maywood, IL
Corresponding author. Department of Radiation Oncology, Loyola University Medical Center, Maguire Center Room 2944, 2160 South First Avenue, Maywood, IL 60153. Tel.: +1-708-216-2594; fax: +1-708-216-6076.
ABSTRACT