Dosimetric Comparison Of 3d Treatment Planning And Conventional Planning In Post-Operative Vaginal Mold Brachytherapy (Vbt) For Patients With Gynecological Malignancies

To compare the dose to target and organs at risk in conventional planning versus CT based 3D planning in Vaginal mound brachytherapy and to compare the effect of bladder distension on target dose distribution as well as dose to organs at risk. Patients diagnosed with carcinoma cervix or carcinoma endometrium with indication for vaginal mound brachytherapy were included in the study after a detailed gynecological assessment. All patients underwent planning CT with a full bladder and an empty bladder protocol. Target volumes and organs at risk were contoured in a planning system and brachytherapy planning was done in a brachytherapy planning system. For each CT, two plans were generated – one 2D based standard unoptimized plan and another 3D based optimized plan. Dosimetric parameters like D90, D95, V100 and V150 were reported for clinical target volume (CTV) and D0.1cc, D1cc, D2cc and D5cc were reported for organs at risk (OARs). Dosimetric comparison was done between 2D and 3D based plans and between full bladder and empty bladder protocols and the data was analyzed. 92 observations were made from data collected from 43 patients. Median age was 49 years (Range – 24 – 69). All patients had undergone hysterectomy and 54% (n = 23) of patients were diagnosed with carcinoma endometrium, followed by carcinoma cervix (30%) and carcinoma cervical stump (16%). Mean CTVsurface volume was 28.8cc (range 18.6cc– 39cc) and mean CTVdepth volume was 53cc (range 36.3cc – 68cc). Difference between CTV coverage in terms of optimized and non-optimized plans were not statistically significant for CTVsurface (p=0.286) and CTVdepth (p=0.11). Significant reduction in D0.1cc, D1cc, D2cc and D5cc dose parameters were observed in bladder, rectum, sigmoid and bowel with 3D optimized plan (p<0.001). Bladder distension did not have significant effect on CTVdepth and CTVsurface dose parameters. However, bladder distension showed a 35% reduction in dose for bowel (p<0.001) and 8% reduction in sigmoid dose which was not statistically significant (p=0.068). Bladder distension also showed a sharp 8.3% (p=0.04) increase in bladder dose correlating to the proximity of posterior bladder wall with the applicator on distension but there was a significant reduction in the mean dose to bladder. This study demonstrates the dosimetric benefits with CT based 3D planning for vaginal brachytherapy over 2D based conventional planning. 3D CT based planning helps to decrease dose to critical organs without compromising target volume coverage by individualizing the dosimetry according to each patient’s anatomy. This study also illustrated the dosimetric benefits of bladder distension and kindles the need for a consensus contouring and reporting guideline for vaginal cuff brachytherapy.