Objectives: To compare 3-Dimensional Conformal Radiotherapy (3D-CRT) with Intensity Modulated Radiotherapy (IMRT) with Volumetric - Modulated Arc Therapy (VMAT) for PTV coverage and OAR sparing in rectal cancer. Methods: Radiotherapy plans for 30 patients with stage II-III rectal cancer were prospectively developed for 3D-CRT, IMRT and VMAT using Varian Eclipse planning system in Ho Chi Minh City Oncology Hospital from 01/01/2019 to 31/12/2019. Results: Radiotherapy plans for 30 patients, average age 57.2 years old. Ratio of male: women = 1 : 2.3. Tumors were in the lower (53.3%), inguinal lymph node radiotherapy accounted for 23.3%. The dosimetric for PTV_4500 and PTV_5040 of IMRT and VMAT is better than 3D-CRT: D98%, Dmean, V95, V100, HI and CI (p<
0.05)
VMAT is better than IMRT at D2% and IMRT is better than VMAT in V100 and HI (p<
0.05). The MU of the IMRT is the highest, then VMAT and then 3D-CRT (p<
0.05)
therefore, the radiotherapy time of the 3D-CRT technique is the fastest, IMRT complexity involves the requirement of longest treatment times. The dosimetric of IMRT and VMAT in the bladder, femoral head and bowel bag is better than 3D-CRT especially with V45 (femoral head and bowel bag), VMAT better than IMRT dose V45 of bowel bag. The bladder volume of group II (250 - 350ml) and group III (>
350ml) helps reduce the dose of the bowel bag than group I (<
250ml). The dosimetric of IMRT and VMAT in the femoral head during inguinal lymph node radiotherapy is better than 3D-CRT, the dosimetric of VMAT is better than IMRT in V30, V40 and V45 (p<
0.05). Conclusions: The dosimetric of IMRT and VMAT techniques are better than 3D-CRT into the target PTV_4500, PTV_5040 and the OARs (bladder, femoral head and bowel bag). VMAT is superior to IMRT. The optimal bladder volume is 250 - 350ml.