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.

3D MRI-based evaluation of the 2D brachytherapy planning in patients with advanced cervical cancer: An analysis of the delivered dose.

PURPOSE: To analyze the dose distribution achieved during 2D radiography-based brachytherapy (BRT) planning, by using a 3D MRI-based BRT replanning evaluation, in patients with advanced cervical carcinoma, treated with definitive concomitant chemoradiation (CCRT). METHODS: The curative CCRT was applied to 30 patients with advanced cervical carcinoma. For each patient, 2D radiography-based planning and a 3D MRI-based BRT replanning were performed. Applying the same source positions and dwell times in both planning methods, it was possible to use the MRI replanning to evaluate the dose distribution, maximum organs at risk (OAR) doses and target volume coverage, that was obtained during 2D BRT planning. RESULTS: A statistically significant difference for bladder and rectum maximum doses, between 2D planning (Bmax, Rmax) and 3D replanning (D0.1ccm, D1ccm, D2ccm) was found, except between Bmax and bladder D2ccm dose (p=0.07), and Rmax and rectal D2ccm dose in the group of patients with symmetrical rectum position regarding the applicator system (p=0.47). MRI evaluation of the HR-CTV volume, according to the 2D planning achieved dose distribution, revealed total EQD2 HR-CTV doses: D90 (107.15±22.06 Gy) and D100 (80.66±14.58 Gy). CONCLUSION: 2D radiography-based BRT planning can provide a good estimation for the bladder and rectum 3D D2ccm dose with a significant statistical difference for the doses in the smaller OAR volumes (D0.1ccm, D1ccm). Inability to visualize tumor tissue during 2D BRT planning provides no option in tailoring the dose distribution to the tumor volume and patient anatomy, leading to potential under/over-treatment in some patients.