Comparison of Dose-Volume Histogram Between Intensity-Modulated Proton Therapy Versus Volumetric-Modulated Arc Therapy for the Irradiation of Pelvic Lymph Nodes and Prostate in High-Risk Prostate Cancer

Abstract

To compare DVH of the organs at risk (OAR) and clinical target volumes (CTV1: prostate and seminal vesicles; CTV2: regional pelvic lymph nodes) between IMPT and VMAT for high-risk Pca. A study of moderate hypofractionation proton therapy treating CTV1 and CTV2 is in progress for high-risk Pca since August 2016. CTV1 and CTV2 receive 6750 cGy and 4500 cGy in 25 fractions over 5 weeks, respectively, with an IMPT plan. Seven accrued patients, as of November 2016, were the subjects for DVH comparison between IMPT and VMAT. Two treatment plans (IMPT and VMAT) were prepared for each patient with pre-defined planning objectives for CTVs, PTVs, and OARs. IMPT plans were prepared with 2 lateral beams, and VMAT plans with 2 arcs. Coverage of CTV1 and CTV2 was adequate for both plans with 99% of CTVs receiving 100.7 - 101.7% of the prescription doses. Mean doses to the bladder, rectum, large bowel, and small bowel were lower with IMPT vs. VMAT. Mean dose to femoral heads was slightly higher with IMPT. % volumes of rectum and large bowel receiving V10-45 Gy, % volumes of small bowel receiving V10-40 Gy, and % volumes of bladder receiving V10-30 Gy were smaller with IMPT vs. VMAT. IMPT did not produce the typical low-dose ‘‘bath’’ to the pelvis seen with VMAT. % volumes of femoral heads receiving V20-30 Gy were smaller with VMAT, while that of femoral heads receiving V10 Gy were smaller with IMPT.Abstract 2532; TableBladderRectumLarge bowelSmall bowelLeft femurRight femurIMPTVMATIMPTVMATIMPTVMATIMPTVMATIMPTVMATIMPTVMATMean (Gy)39.246.834.8*48.731.1*43.510.5*26.323.222.224.421.7V66Gy (%)3.53.1*4.83.8*00000000V61Gy (%)5.95.1*8.06.900000000V57Gy (%)7.66.7*10.19.200000000V45Gy (%)16.316.616.3*20.14.17.22.62.20000V40Gy (%)23.123.820.0*28.817.923.25.77.10.500.30V30Gy (%)37.446.936.3*55.940.250.810.120.211.04.314.92.9V20Gy (%)57.976.150.9*81.952.3*79.115.7*42.042.431.643.428.2V10Gy (%)80.3*10063.7*89.464.0*89.821.5*61.265.369.668.871.6*Statistically significant, paired t-test Open table in a new tab *Statistically significant, paired t-test IMPT can significantly reduce the dose to OARs while providing adequate target coverage, compared with VMAT, when the pelvic lymph nodes, along with prostate and seminal vesicles, are irradiated.