A dosimetric evaluation of ureteric doses with and without ureter as avoidance organ in patients treated with MR hybrid brachytherapy for cervical cancer.

PURPOSE

Ureteric stenosis is a known complication with radiotherapy with studies showing correlation of ureteric dose with stenosis. This study was done to assess the dose delivered to the ureters with and without ureter as avoidance organ in cervical cancer patients treated with hybrid brachytherapy.

MATERIAL AND METHODS

Cervical cancer patients treated with EBRT and MR hybrid brachytherapy were retrospectively analyzed. They were treated without ureter contoured as organ at risk. The right and left ureters were retrospectively contoured on T2 weighted MRI images. Dose to 0.1cc volume of ureter was documented.

RESULTS

26 patients treated with hybrid brachytherapy were analyzed. The median HRCTV volume was 23.9cc. The median HRCTV D90 & GTV D98 EQD2 were 91.09Gy (IQR 92.36-87.28) and 104.67Gy (IQR 113.90-95.04) respectively. The median D2cc for bladder, rectum and sigmoid were 75.46Gy, 58.10Gy and 61.3Gy EQD2 respectively. The mean minimum distance of the left ureter from HRCTV was 3.2mm (IQR 6.75-1) & right ureter was 2.3mm (IQR 8-0). The mean D to the left ureter was 75.16Gy EQD2 (IQR 88.28-58.20) and to the right ureter was 69.73Gy EQD2 (IQR 76.77-56.01). The ureter D exceeded 77Gy in 13/26 patients. Replanning and reducing needle loading near the ureter resulted in reduction of ureter 0.1cc dose to less than 77Gy in all but 2 patients, without compromising the HRCTV coverage.

CONCLUSION

The ureter is at risk of receiving high doses when we use hybrid applicator. MR planning to delineate the ureter and careful optimization of needles can result in significant reduction of ureter dose with similar target coverage.