ESTRO 2024 - Abstract Book

S1514

Clinical - Lower GI

ESTRO 2024

and R-RT were compared by t-test. P < 0.05 was considered statistically different. Besides, routine blood tests were conducted regularly during and within 1 month after radiotherapy.

Results:

a) Patients information. Among 11 patients, 7 were male and 4 were female. The median age was 54 years old (27 to 72 years old). According to UICC/AJCC 8 th edition, 9 cases were stage IIIB, 1 case and 1 case were stage IIA and stage IIIA respectively. 9 cases were low rectal cancer, whereas 2 cases were middle/high. b) Target volume and OARs. The average volume of PGTVp/nd and PCTV were 165cc (99 - 235cc) and 1063cc (741 - 1273cc) respectively. The average volume of BM-w and BM-a were 427cc (285 - 584cc) and 191cc (121 - 247cc) respectively. BM-a volume accounted for 45.2% (36.3 – 60.9%) of BM-w volume. c) Comparison of BM doses. In FA-RT and R-RT, BM-w D mean was 22.5Gy vs. 26.1Gy ( P < 0.01), BM-w equivalent uniform dose (EUD) was 8.7Gy vs. 11.4Gy ( P < 0.01), BM-a D mean was 22.1Gy vs. 27.7Gy ( P < 0.01), and BM-ia D mean was 24.0Gy vs. 24.1Gy ( P > 0.05). Those results suggested that the exposure doses of both BM-a and BM-w were significantly reduced in FA-RT. d) Comparison of OARs doses. In FA-RT and R-RT, bowel V 30 was 190cc vs. 177cc ( P > 0.05), bladder V 45 was 50.2cc vs. 52.0cc ( P > 0.05), and femoral heads D mean was 20.7Gy vs. 20.1Gy ( P > 0.05). The results indicated that dose distributions of bowel, bladder and femoral heads were not significantly affected in FA-RT. e) Comparison of target doses. In FA-RT and R-RT, PGTVp/nd D 95 was 50.33Gy vs. 50.37Gy ( P > 0.05); PCTV D 95 was 45.46Gy vs. 45.60Gy ( P > 0.05). It revealed that there were no significant differences in target doses in two plannings, both of which were in line with the planning requirements. f) Among the 11 patients who received FA-RT, the most severe degree of neutropenia, anemia and thrombocytopenia were grade 2 (4 cases), grade 1 (4 cases), and grade 1 (1 case) respectively.

Figure 1. One case as an example to illustrate the difference of dose distribution in FA-RT (A) and R-RT (B). BM-a areas were contoured by red line (indicated by red asterisks).