Dosimetric characteristics of intensity-modulated radiation therapy and RapidArc® therapy using a 3D N-isopropylacrylamide gel dosimeter

Chun-Hsu Yao,Ting-Yu Tsai,Yuan-Jen Chang,His-Ya Chao,Bor-Tsung Hsieh,Yuk-Wah Tsang,Chung-Yu Chiu

doi:10.1142/s2010194516602210

Abstract

This study aimed to investigate the dosimetric characteristics of intensity-modulated radiation therapy (IMRT) and RapidArc therapy by using 3D N-isopropylacrylamide (NIPAM) polymer gel. Optical computed tomography, specifically OCTOPUSTM-10X fast optical computed tomography scanner, was used as a readout tool. Two cylindrical acrylic phantoms (10 cm in diameter, 10 cm in height, and 3 mm in thickness) were filled with NIPAM gel and used for IMRT and RapidArc irradiation by using the Clinac iX treatment machine. The irradiation energies for IMRT and RapidArc® were set as 6 MV photons, but their irradiation angles and dose rates differed during irradiation. The irradiation angles of IMRT were 120°, 155°, 180°, 215°, and 245°, and the dose rate was fixed at 400 cGy/min. RapidArc® rotated continuously during irradiation, and the dose rate varied from 330 cGy/min to 400 cGy/min. The pass rates were 98.02% and 97.48% for IMRT and RapidArc®, respectively, and the rejected area appeared at the edge of the irradiated region. The isodose lines of IMRT and RapidArc® were consistent with those of TPS in most regions. Scattering and edge enhancement effects are main factors that cause dose inaccuracy in the edge region and reduced pass rates. Considering dose rate dependence, we used variable dose rates during irradiation with RapidArc®. Results showed that the dose distribution of NIPAM gel was consistent with that of TPS. The pass rates were also the same for IMRT and RapidArc® irradiation. This study proposes a preliminary profile of dosimetric characteristics of IMRT and RapidArc® by using a NIPAM gel dosimeter.

Highlights

Intensity-modulated radiation therapy (IMRT) has been widely adopted for clinical use because it can generate dose distributions that precisely conform to the tumor target while minimizing the dose delivered to the surrounding healthy tissues.[1]
The images on the top row are the results of IMRT, and the images on the bottom row are the results of RapidArc®
A NIPAM gel dosimeter combined with an optical computed tomography (CT) scanner was applied on IMRT and RapidArc® therapy to investigate the dosimetric characteristics

Summary

Introduction

Intensity-modulated radiation therapy (IMRT) has been widely adopted for clinical use because it can generate dose distributions that precisely conform to the tumor target while minimizing the dose delivered to the surrounding healthy tissues.[1] IMRT requires high monitoring units and long treatment times. RapidArc (Varian Medical Systems), a novel radiation treatment technique, is based on volumetric-modulated arc delivery and differs from intensity modulation, which uses fixed gantry beams. The treatment time of RapidArc is four to eight times faster than IMRT.[2] The complex 3D dose distribution generated by RapidArc is difficult to verify using conventional techniques, such as a 1D ion chamber or 2D detector. A true 3D dosimeter must be developed to verify the dose distribution

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Methods

Results

Conclusion