Simultaneous Integrated Boost (Sib) For Treatment Of Gynecological Malignancies: Intensity Modulated Radiation Therapy (Imrt) Versus Volumetric Modulated Arc Therapy (Vmat)

Delivering the boost simultaneously rather than sequentially is an attractive option radiobiologically because it reduces the treatment duration and delivers a greater biological effective dose. It also results in better organs at risk (OAR) sparing and higher conformality with respect to concomitant boosts. The aim of this study was to quantitatively compare dosimetric criteria between IMRT and VMAT plans for patients undergoing radiation treatment of gynecologic carcinoma with an SIB technique. IMRT and VMAT plans were retrospectively analyzed for 20 patients. The elective volume was planned to receive 45 Gy (PTV45) in 25 fractions of 1.8 Gy with the integrated boost volume (involved nodes) receiving 55 Gy (PTV55) simultaneously. The same dose constraints were employed during the optimization of both techniques. IMRT plans consisted of 9 to 11 fields at equally spaced gantry angles. VMAT plans consisted of 3 full arcs of 360o. A large variety of dose metrics across PTV45, PTV55, bladder, rectum, sigmoid, bowel, kidneys, and femoral heads were extracted per patient, per plan. Conformity and homogeneity indices (CI and HI) were calculated. The total number of monitor units (MU) as well as the integral dose (ID) was also compared between IMRT and VMAT. The Wilcoxon signed rank (WSR) test was performed to evaluate any significant differences between parameters (significance level P<0.05). Both IMRT and VMAT were successful in achieving the dose constraints set forth by the physician. Out of a total of 86 studied parameters, only 16 total parameters revealed a statistically significant difference in favor of the IMRT plan. The average and standard error of the differences between IMRT versus VMAT for the most clinically relevant metrics with associated P values were reported as follows (Δ + SD, P-value): PTV55 D98% (12 + 1cGy, 0.2), Bladder D2cm3 (109 + 4cGy, 0.004), Rectum D2cm3 (104 + 4cGy, 0.09), Sigmoid D2cm3 (107 + 4cGy, 0.13), Bowel D2cm3 (108 + 4cGy, 0.7), Left Femoral Head V30Gy (10 + 0.4%, 0.5), Right Femoral Head V30Gy (10 + 0.5%, 0.2), Left Kidney V20Gy (12 + 0.7%, 0.6), and Right Kidney V20Gy (13 + 0.6%, 0.15). ID and CI also did not show meaningful differences in the comparison, but HI for PTV45 did (2.29 + 0.1, 0.025). Last, the total MU was significantly lower for VMAT (1374 + 29 MU, 0.0001). The findings of this study suggest that IMRT and VMAT are both acceptable options for applying simultaneous integrated boost techniques for the treatment of gynecologic cancers. IMRT provides slightly more favorable dosimetry and VMAT provides a shorter treatment time. The technique of choice will be dependent upon departmental resources and patient needs, and should be considered on a case-by-case basis.