Spatially fractionated radiotherapy (SFRT) is one of the radiotherapy techniques utilized to treat patients with advanced bulky tumours. This study aims to estimate the difference in biological and dosimetric parameters of the SFRT technique and compare it to the three-dimension conformal radiotherapy (3D-CRT) of bulky shoulder and pelvic sarcoma tumours. 3D-CRT and SFRT were designed by the Monaco treatment planning system. Sex bulky shoulder and pelvic sarcoma cases were selected, a single fraction 15Gy were used. Dose-volume histogram of the organs at risk (OARs) was used to calculate the equivalent uniform dose (EUD) (Gy) by Matlab program. SFRT achieves more EUD (Gy) for OARs were compared to 3D-CRT. In SFRT, where organs at risk in close to the tumours and the shielding it by multi-leaf (1 cm) that leads to more effective than other techniques, and lead to a decrease of EUD(Gy) according to its definition by Niemierko. EUDs showed significant differences between the two methods for OARs in right and left lungs and heart as p-value = 0.001,0.001 and 0.03, respectively. While, others OARs, right and left femurs, bladder, rectum and bowel is non-significant different between them as p-valve > 0.05. The OARs have differed from patient to patient, that is due to differences in tumours site, shape, size, depth and how far from OARs, such as pelvic sarcoma tumours. SFRT achieves more sparing and fewer complications for OARs and provides an accurate assessment of the radiation dose that is actually received.