Dosimetric Comparison of Static Field Intensity-Modulated Radiotherapy and Volumetric Modulated Arc Therapy for Adjuvant Treatment of Patients with Endometrial Cancer
Olgun ELICIN1,Gülyüz ATKOVAR2,Şefika Arzu ERGEN2,Servet İPEK2,Songül KARACAM2,İsmet ŞAHINLER2
1Department of Radiation Oncology, University of Bern, Bern University Hospital, Bern-İsviçre
2Department of Radiation Oncology, İstanbul University Cerrahpaşa Faculty of Medicine, İstanbul-Türkiye
DOI : 10.5505/tjo.2017.1589 OBJECTIVE
The extent of previously published studies comparing static intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) in the adjuvant setting of endometrial cancer is limited and reports do not cover the whole landscape of today"s clinical practice. The aim of this study was to compare these treatment techniques.

Using 12 image sets, VMAT with double arcs and IMRT with 7 fields were planned. The femoral heads, rectum, bladder, iliac bone marrow, and bowels were contoured as organs at risk (OARs). Planned treatment volume (PTV) was prescribed to be 45 gray (Gy). Target and OAR parameters, conformity, and homogeneity indices were evaluated. P value under 0.05 was considered statistically significant.

Objectives for target volumes were achieved. No significant differences were found in conformity index, maximum dose (Dmax), or integral dose. Homogeneity index was better with IMRT (1.06 vs. 1.07; p<0.01). Dose received by 2% volume of PTV (D2%), D5%, the volume receiving 107% of prescribed dose (V107%), and V105% were lower with IMRT (p<0.05). PTV D98%, percent volume receiving ≥45 Gy (V45 Gy), and clinical target volume V45 Gy were higher with VMAT (p<0.05). Regarding OARs, only rectum V40 Gy, rectum PTV V40 Gy, and dose volume parameter D2cc were lower with VMAT (p<0.05). VMAT was superior with respect to monitor units and beam-on time per fraction: 465 vs. 1689 and 166 vs. 338 seconds, respectively (p<0.001).

Static IMRT is superior to VMAT regarding homogeneity, Dmax and OAR sparing, except for the rectum and the bladder. However, it is a marginal benefit with small differences. VMAT remains an attractive solution due to low number of monitor units needed and shorter treatment duration, which allows more time for patient imaging and positioning. Keywords : Intensity-modulated radiotherapy; volumetric modulated arc therapy; endometrial cancer; radiotherapy; gynecological neoplasms