Uncertainty of small bowel dose?volume and normal tissue complication probability assessment due to small bowel motility during intensity?modulated radiotherapy for rectal cancer
Author(s): Qian Jianjun, Sun Yanze, Yang Yongqiang, Chen Liesong, Tian Ye
Pages: 310-315
Year: 2017 Issue: 3
Journal: Chinese Journal of Radiation Oncology
Keyword: Rectal neoplasms/intensity?modulated radiotherapy; Small bowel; Normal tissue complication probability;
Abstract: Objective To evaluate the uncertainty of the small bowel dose?volume and the normal tissue complication probability (NTCP) during intensity?modulated radiotherapy (IMRT) for rectal cancer, and to provide a reference for the dose limit and protection of the small bowel during IMRT for rectal cancer. Methods A total of 20 patients with rectal cancer who received postoperative adjuvant radiotherapy from March 2014 to August 2015 were enrolled in this study, including 10 patients receiving CT scan in the supine position and 10 patients in the prone position. All patients received computed tomography ( CT) scan before the treatment and at weeks 1, 2, 3, and 4 of treatment, and they were defined as Plan, 1W, 2W, 3W, and 4W CT groups, respectively. The small bowel loop ( BL ) and peritoneal space ( PS ) were delineated on the images. The IMRT plan based on the Plan CT was copied to the 1W, 2W, 3W, and 4W CT groups, and then the small bowel dose?volume and NTCP were assessed for all CT groups. The paired t?test was used for comparison between groups. The Pearson method was used to analyze the correlation between NTCPC(chronic NTCP) and dose?volume. Results A total of 89 CT images of 20 patients were obtained. In all the patients, the volumes of BL and PS were 25121 cm3 and 132416 cm3 , respectively, and the shift% was 2315% and 1134%, respectively. The V15 of BL and PS was 18486 cm3 and 79245 cm3 , respectively, and the shift% was 3169% and 370%, respectively. The V30 of BL and PS was 8801 cm3 and 64573 cm3 , respectively, and the shift% was 3766% and 1049%, respectively. The V15 of BL in 35% of patients and V15 of PS in 20% of patients, the Dmax of BL in 50% of patients, and the NTCP of 15% of patients in the course of treatment exceeded the safety limits. The 1?4W CT groups had a significantly higher NTCPC than the Plan CT group (402% vs. 320%, P=0104), and their SD% was 4168%. There was a significant correlation between NTCPC and V30?V50 of BL (R>0400, P=0000). The NTCPA ( acute NTCP ) and NTCP C in the supine position were significantly higher than those in the prone position ( 6230% vs. 5674%, P=0061;488% vs. 322%, P=0145 ) . Conclusions Small bowel motility leads to an uncertainty of the adverse event assessment during IMRT for rectal cancer. The change in BL is significantly larger than that in PS and the change in BL and PS in the supine position is significantly larger than that in the prone position. Using the prone position and minimizing V15 and V30 when designing the treatment plan can reduce the NTCP A and NTCP C in the small bowel.
Pages: 310-315
Year: 2017 Issue: 3
Journal: Chinese Journal of Radiation Oncology
Keyword: Rectal neoplasms/intensity?modulated radiotherapy; Small bowel; Normal tissue complication probability;
Abstract: Objective To evaluate the uncertainty of the small bowel dose?volume and the normal tissue complication probability (NTCP) during intensity?modulated radiotherapy (IMRT) for rectal cancer, and to provide a reference for the dose limit and protection of the small bowel during IMRT for rectal cancer. Methods A total of 20 patients with rectal cancer who received postoperative adjuvant radiotherapy from March 2014 to August 2015 were enrolled in this study, including 10 patients receiving CT scan in the supine position and 10 patients in the prone position. All patients received computed tomography ( CT) scan before the treatment and at weeks 1, 2, 3, and 4 of treatment, and they were defined as Plan, 1W, 2W, 3W, and 4W CT groups, respectively. The small bowel loop ( BL ) and peritoneal space ( PS ) were delineated on the images. The IMRT plan based on the Plan CT was copied to the 1W, 2W, 3W, and 4W CT groups, and then the small bowel dose?volume and NTCP were assessed for all CT groups. The paired t?test was used for comparison between groups. The Pearson method was used to analyze the correlation between NTCPC(chronic NTCP) and dose?volume. Results A total of 89 CT images of 20 patients were obtained. In all the patients, the volumes of BL and PS were 25121 cm3 and 132416 cm3 , respectively, and the shift% was 2315% and 1134%, respectively. The V15 of BL and PS was 18486 cm3 and 79245 cm3 , respectively, and the shift% was 3169% and 370%, respectively. The V30 of BL and PS was 8801 cm3 and 64573 cm3 , respectively, and the shift% was 3766% and 1049%, respectively. The V15 of BL in 35% of patients and V15 of PS in 20% of patients, the Dmax of BL in 50% of patients, and the NTCP of 15% of patients in the course of treatment exceeded the safety limits. The 1?4W CT groups had a significantly higher NTCPC than the Plan CT group (402% vs. 320%, P=0104), and their SD% was 4168%. There was a significant correlation between NTCPC and V30?V50 of BL (R>0400, P=0000). The NTCPA ( acute NTCP ) and NTCP C in the supine position were significantly higher than those in the prone position ( 6230% vs. 5674%, P=0061;488% vs. 322%, P=0145 ) . Conclusions Small bowel motility leads to an uncertainty of the adverse event assessment during IMRT for rectal cancer. The change in BL is significantly larger than that in PS and the change in BL and PS in the supine position is significantly larger than that in the prone position. Using the prone position and minimizing V15 and V30 when designing the treatment plan can reduce the NTCP A and NTCP C in the small bowel.
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