[Evaluation of 3D Dose Distribution and Clinical Applications Using Polymer Gel Dosimeter].

Evaluation of dosimetric impact of the interplay effect between multi-leaf collimator (MLC) movement and tumor respiratory motion during volumetric modulated arc therapy (VMAT) delivery using polymer gel dosimeter was taken as an example in this article. An excellent gas barrier PAN (polyacrylonitrile) bottle filled with polyacrylamide-based gel dosimeter contained magnesium chloride as a sensitizer (iPAGAT dosimeter) was set to the QUASAR™ respiratory motion phantom (Modus), and was moved with motion amplitudes (peak-to-peak amplitude) of 1 and 2 cm with a 4 second period during VMAT delivery by the Novalis Tx linear accelerator (Varian/BrainLAB). Two spherical GTVs with 2 cm diameter and two PTVs were defined considering the respiratory motion and setup uncertainties. Three-dimensional (3D) dose distribution in iPAGAT dosimeter was read out by the 3T MRI system, and was evaluated by the dose profiles, gamma analysis and the dose-volume histogram (DVH) using in-house developed software. As a result, interplay effect was negligible since dose coverage of GTV was sufficient during VMAT delivery with simulated respiratory motion.

[Comparison of setup accuracy between ExacTrac X-ray 6 dimensions and cone-beam computed tomography for intracranial and pelvic image-guided radiotherapy].

The aim of this study was to compare the setup difference measured with ExacTrac X-ray 6D (ETX6D) and cone-beam computed tomography (CBCT) for non-invasive fractionated radiotherapy. Setup data were collected on a Novalis Tx treatment unit for both a head phantom and patients with intracranial tumors and a pelvic phantom and patients with prostate cancer. Initially, setup was done for a phantom using ETX6D. Secondly, a treatment couch was shifted or rotated by each already known value. Thirdly, ETX6D and CBCT scans were obtained. Finally, setup difference was determined: the registrations of ETX6D images with the corresponding digitally reconstructed radiographs using ETX6D fusion, and registrations of CBCT images with the planning CT using online 6D fusion. The setup difference between ETX6D and CBCT was compared. The impact of shifts and rotations on the difference was evaluated. Patients' setup data was similarly analyzed. In phantom experiments, the root mean square (RMS) of difference of the shift and rotation was less than 0.45 mm for translations, and 0.17 degrees for rotations. In intracranial patients' data, the RMS of that was 0.55 mm and 0.44 degree, respectively. In prostate cancer patients' data, the RMS of that was 0.77 mm and 0.79 degree, respectively. In this study, we observed modest setup differences between ETX6D and CBCT. These differences were generally less than 1.00 mm for translations, and 1.00 degrees for rotations, respectively.

[Influence of high-definition multileaf collimator for three-dimensional conformal radiotherapy and intensity-modulated radiotherapy of prostate cancer].

The focus of this work is to evaluate the dosimetric impact of treatment planning for three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT) of prostate cancer using Varian/BrainLAB 120-leaf high-definition multileaf collimator (HD120 MLC) with 2.5 mm leaf width and Varian 120-leaf millennium multileaf collimator (M120 MLC) with 5 mm leaf width. We measured the leaf transmission and dosimetric leaf gap (DLG) of two multileaf collimator (MLC) systems using Farmer ionization chamber. The dosimetric impact of treatment planning for 3DCRT and IMRT of prostate cancer for ten clinical cases using two MLC systems was evaluated quantitatively. 3DCRT was divided to 3DCRT(middle) as fitting at middle of leaf tip and 3DCRT(outside) as fitting at outside of leaf tip. The leaf transmission factor and DLG of HD120 MLC for 6 and 10 MV X-ray decreased by 0.2% and 1 mm, respectively, compared to M120 MLC. The mean conformity index of PTV of treatment planning for prostate 3DCRT(middle), 3DCRT(outside) , and IMRT decreased by 0.9%, 6.6%, and 0.9% and the mean homogeneity index increased 2.3%, 13.0%, and 4.2%, respectively. The mean V20, V40, and V65 decreased by 2.4%, 6.6%, and 4.5% for bladder and 3.3%, 6.1%, and 5.9% for rectum, respectively. The results of this work demonstrated that the dose conformity of PTV improved and the dose of bladder and rectum decreased for 3DCRT and IMRT of prostate cancer using HD120 MLC compared to M120 MLC, because of reduction of leaf width, leaf transmission, and rounded leaf end transmission.