|Title:||Dosimetric effect of belly board position on small bowel and bladder volume irradiated for postoperative 3-dimensional conformal radiotherapy of rectal cancer|
|Subject:||Hong Kong Polytechnic University -- Dissertations.|
Rectum -- Cancer -- Radiotherapy.
Rectum -- Cancer -- Treatment.
|Department:||Department of Health Technology and Informatics|
|Pages:||viii, 73 leaves : ill. (some col.) ; 30 cm.|
|Abstract:||Purpose/objectives: To evaluate the effect of belly board position on dose to the small bowel and bladder in rectal cancer patients receiving 3DCRT. Materials/Methods: Fourteen rectal cancer patients planned to receive 3DCRT were included. With full bladder, three sets of CT scans were performed with the patients positioned at three different levels against the lower border of the aperture of the belly board: Position 1 (PI), at the interspace of L5/SI; Position 2 (P2), at the lower end of the sacroiliac joint; Position 3 (P3), at the upper end of the symphysis pubis. Three-dimensional conformal plans were generated on each of the CT set. The dose given was 40 Gy followed by a 10 Gy boost in 25 fractions. The dose distribution to the small bowel and bladder was evaluated by the dose-volume histogram from 5 to 50 Gy in 5 Gy steps and analyzed using one-way repeated measures of ANOVA. Regression analysis was used to evaluate the relationship between bladder and small bowel changes. Results: The volume of small bowel irradiated at 5-10 Gy increased in the order of PI, P2, and P3 with an average of 126.8+-4.95 (S.D.) cm3, 145.6+-1.25 (S.D.) cm3, 221.05+-27 (S.D.) cm3 respectively and tested to be significantly different (p<0.05). However from 15 Gy - 20 Gy, the volume of irradiated small bowel was much reduced with an average of 83.05 cm3 at PI, 66.95 cm3 at P2 and 73 cm3 at P3 with significant difference between PI and P2 (p<0.05). At >25 Gy, very little difference was found among the three positions. For the bladder, the volume irradiated was expressed as the percentage volume of the whole bladder. Between 5-10 Gy, over 98% of the bladder volume was included. Above 10 Gy, the percentage volume of the bladder irradiated was about the same at PI and P2 but significantly lower at P3 at 15 Gy with a difference of 18.6% (p<0.02). The bladder volume was the largest at P3 for all cases in the CT slices. The CT scans were performed in the order of PI, P2 and P3 with P3 being the last so the bladder was the most filled by the time the P3 position was scanned. Regression analysis revealed a negative correlation between the bladder volume and the small bowel volume. Conclusions: Total volume of small bowel irradiated was the lowest at PI. Bladder sparing was the best at P3 as there was more space at the anterior abdomen wall for the fall down of bladder. The increase in bladder volume has a displacement effect on the volume of irradiated small bowel. The optimum position for using the belly board for small bowel sparing would be at PI with a more distended bladder.|
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