Dosimetric comparison of fixed field dynamic IMRT and VMAT techniques in simultaneous integrated boost radiotherapy of Prostate Cancer

Abstract

Background: As the high risk prostate cancer can be benefited from the combination of hypo-fractionated radiotherapy and pelvic conventional fraction radiotherapy, the comparison between fixed field dynamic IMRT and VMAT techniques can provide suggestion for clinical treatment. Methods: We selected 10 patients with high risk prostate cancer who received radiotherapy at Sun Yat-sen University Cancer Center from 2013 January to 2013 December. The target including the prostate, seminal vesicle and pelvic lymph nodes. With the same prescription and optimized parameters, 9 field IMRT, single arc and double arc VMAT treatment plans were designed, which are expressed by 9F, 1ARC and 2ARC respectively. The dose distribution of the targets, organs at risk (OAR), monitor units (MUs), treatment time and gamma pass ratios of dose verification were compared. Results: The D2%(69.37±0.89)Gy,D50%(66.92±0.63)Gy, HI(0.09±0.02) and CI(0.83±0.05) of PTV1 in 9F were slightly better than those of 1ARC which were (71.13±1.21) Gy, (68.50±0.76)Gy, (0.12±0.02), (0.74±0.07), except D98% , the difference were significant(p<0.05). All dosimetric indices of PTV1 in 9F and 2ARC were close and has no significant differences (p>0.05). The V95 %(99.45±0.78)% of PTV2 in 9F was slightly better than that in 1ARC (99.35±1.28)%, the difference was significant (p<0.05). All dosimetric indices of PTV2in 9F and 2ARC were close and the difference were no significant (p>0.05). The Dmean of bladder and the V67.5Gyof rectum between all three plans were similarity The Dmean of left and right femoral in 1ARC and 2ARC were lower than that in 9F, and the difference was significant (p<0.05). Other dosimetric indices of OARs in 9F were lower than those in 1ARC and 2ARC, and much lower than 1ARC, the difference were significant (p<0.05). The mean monitor units in 1ARC and 2ARC were fewer by 70.0% and 67.2% in comparison with 9F. The treatment mean time in 1ARC and 2ARC were shorter by 81.7% and 61% in comparison with 9F. The verification pass ratios of γ(3%/3mm)were 97.8% (9F), 98.9% (1ARC) and 99.4% (2ARC) respectively, the difference were significant(p<0.05). Conclusion: Compared with IMRT, VMAT improved delivery efficiency noticeably. Two arcs provided comparable tumor dosimetric coverage, but performed worse in dose sparing for bladder, rectum and small bowel. IMRT plan was better than VMAT in prostate cancer simultaneous integrated boost radiotherapy.