(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: study the change in bladder volume and its position on daily basis using the CBCT images for the patients following water protocol and its effect on the bladder and bowel dose.
Methods: 21 patients were selected for this study with water intake of 500mL withhold time of 40-45 minutes. All the patients were immobilized with 4 clamp pelvic orfit and scanned with Philips PET-CT scanner (PET-CT TOF, Amsterdam, The Netherlands) with 3mm slice thickness for dose planning. Contouring and Planning was done on the MONACO V5.11.01 treatment and planning station. For all these patients VMAT full double arc plans were generated and PTV volume, bladder volume, bladder mean dose, D50% of bladder on the planning CT was noted down. KV CBCT images taken on first and alternative days were transferred on planning station and all the contours were drawn on these images. The change in the bladder volume and maximum shift in the bladder position in the patient left, right, cranial and caudal direction was observed. After that the same plan was copied to these CBCT images and dose was calculated on kV CBCT images.
Results: this study we found that change in the bladder volume from planning CT day was almost 5 % and change in bladder mean dose was 6.4 % and of bowel dose was 4.5 % for all the patients and the maximum shifts observed in the bladder position was 1.6±0.37 cm in patient right, 1.8±0.25 cm in patient left, 1.7±0.27 cm in patient cranial, 1.9±0.39 cm in patient caudal direction.
Conclusion: to change in the bladder position and its volume the bladder mean dose was also changed which in turn increase the bowel dose marginally.
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