Document Type: Original Paper
MD (medical doctorate), Consultant of National cancer institute, Cairo University, Egypt King Fahad Specialist Hospital, Dammam, Saudi Arabia
Assistant Professor of medical physics, Faculty of Medicine, Menofiya University, Egypt Consultant of radiation oncology Physics, King Fahad Specialist Hospital, Dammam, Saudi Arabia
Radiation oncology department, Medical physics unit King Fahad Specialist Hospital, Dammam, Saudi Arabia
Radiation Oncology Department, King Fahad Specialist Hospital, Dammam, Saudi Arabia
Purpose: To compare volumetric-modulated arc therapy (VMAT) technique with conventional intensity modulated radiation therapy (IMRT) technique in locally advanced rectal cancer (LARC) patients.
Materials and methods: Ten Computed tomography (CT) scans of LARC patients were selected. For each CT scan two plans were calculated (IMRT and VMAT). The average cumulative dose volume histograms (DVHs) of VMAT plans for planning target volumes (PTVs), organs at risk (OARs) and normal tissues were calculated and compared with the corresponding IMRT technique.
Results: VMAT was equivalent to IMRT for target coverage. For PTV primary, average homogeneity index (HI) for IMRT is significantly lower than the VMAT plans (0.10 ± 0.04 vs. 0.11 ± 0.03, p < 0.0001). The average conformity index (CI) values for IMRT and VMAT were 1.21 and 1.12, respectively, with a non-significant trend for better results with VMAT (p = 0.1). For PTV boost, there was a non-significant trend for better results with VMAT in average HI and CI. VMAT was superior to IMRT in OAR sparing. For small bowel, VMAT had significant sparing improvement on V35 Gy, V40 Gy and V45 Gy. For bladder, VMAT showed significant sparing improvement on V45 Gy and V50 Gy with a non-significant trend for better results with VMAT on V40 Gy. For femoral heads, VMAT demonstrated a statistically significant benefit for V40 Gy and V45 Gy. For monitor units (MUs), VMAT plans required 70% less than IMRT.
Conclusion: For LARC patients, VMAT was able to deliver dosimetrically equivalent treatment plans to IMRT in terms of PTV coverage. VMAT provided better OAR sparing and significant reductions of MUs.