Volumetric Modulated Arc Therapy (VMAT): A modern radiotherapy technique - A single institutional experience

Abstract

Objective: To evaluate VMAT plans for conformity and homogeneity of radiation dose to the target in order to share our experience as a pioneering institute to use VMAT technology in Pakistan.

Methods: Since December 2014 to January 2018, 530 patients of various anatomical sites were treated by VMAT technique at Neurospinal Cancer Care Institute (NCCI) Karachi Pakistan. ERGO++ planning system (Version 1.7.2) was used to develop VMAT plans with single or multiple arcs by the rotation of couch and gantry. The plans were evaluated by calculating Conformity Index (CI) and Homogeneity Index (HI) and critical organ (OARs) doses of individual tumor sites.

Results: The average CI of various sites was 1.4 (range: 1.0-2.0) and average HI of various sites was 1.20 (range: 1.07-1.374), respective critical organ doses were adequately achieved.

Conclusions: VMAT treatment planning technique showed good conformal and homogeneous target coverage with sparing of organs at risk and reduced treatment delivery time. With these features, safety of VMAT technique may allow its routine clinical use, though it is still under investigation in many areas.

Keywords: Conformity Index; Homogeneity Index; Radiotherapy; VMAT.

Fig.1

(a): Contouring of GTV and remaining brainstem on MR images. (b): Fusion of MRI & CT images. (c): After fusion, contouring shifted to CT images for planning.

Fig.2

(a): Crown technique used for brain tumor with different couch angles. (b): Prescription was made on 75% isodose line(green) covering peripheral part of PTV, while blue line represents 50% isodose line.

Fig.3

VMAT-SBRT, Fan shaped beam planning display: (a) Right rib metastases was planned for 10 Gy x 3 Fr @ 70% isodose line. (b) Planning with CT images (c) Three dimensional view.

Fig.4

VMAT-SRS mono-isocentric planning display for multiple (six) brain metastases from non-small cell lung cancer. Dose prescription was 20 Gy single fraction at 70% isodose line. a) Location and Volume of Six brain metastases, Left temporal met: 1.8 cc, Left parietal met: 2.1 cc, left posterior parietal met: 2.2 cc, Left Occipital met: 1.2 cc, Right parietal met: 0.3cc, Right cerebellar met: 2.9cc. b) Plan was prepared with the help of two arcs, all the contoured metastases were well covered with prescription isodose line of 70%. Total treatment time was 11 minutes. c) Computerized planning on treatment planning system ERGO++. Green line around the target is prescription isodose line of 70%. Blue line is 50% isodose line.