Vaginal packing volume impact on dose parameters during radiography and computed tomography based postoperative brachytherapy of cervical carcinoma

PURPOSE: To investigate the influence of the vaginal packing volume on the registered dose parameters evaluated by radiography (2D) and computed tomography (CT) (3D) based brachytherapy planning in cervical cancer patients treated with postoperative radiotherapy.

METHODS: The postoperative radiotherapy was performed in 40 cervical cancer patients with increased risk for disease relapse. Both, radiography and CT based brachytherapy planning were done in all patients. Vaginal packing volume was evaluated by clinical target volume (CTV)uk, assessed on CT scans and analyzed according to the registered dose parameters: doses delivered to the organs at risk (OAR) and the defined CTV, using both planning methods.

RESULTS: CTVuk volume had statistically significant influence on CTV coverage with the prescribed brachytherapy doses D90 (p<0.01) and D100 (p<0.01), revealing a CTVuk cut-off value of 25.6 cm3. Dividing the patients into two groups according to the cutoff value, we found a statistical significance in the registered doses to the rectal wall and no significance in the bladder wall doses between the groups. Also, a statistically significant, negative correlation was found between CTVuk and following doses: Rmax (rho= -0.34, p<0.05), D0.1cc (rho= -0.76, p<0.01), D1cc (rho= -0.74, p<0.01) and D2cc (rho= -0.72, p<0.01), D90 (rho= -0.80, p<0.01), D100 (rho= -0.7, p<0.01).

CONCLUSION: If the brachytherapy vaginal packing is of a large volume (more than 25.6 cm3), an asymmetric deformation of the proximal part of the vaginal cavity might appear, leading to inappropriate dose coverage of the CTV part of the vaginal mucosa. Also, making a vaginal packing volume larger than 25.6 cm3 made no further reduction in the bladder dose, but it made a statistically significant further reduction in the rectal doses.