An investigation of the dose distribution effect related with collimator angle in volumetric arc therapy of prostate cancer

Abstract

To investigate the dose-volume variations of planning target volume (PTV) and organ at risks (OARs) in eleven prostate cancer patients planned with single and double arc volumetric modulated arc therapy (VMAT) when varying collimator angle. Single and double arc VMAT treatment plans were created using Monaco5.0® with collimator angle set to 0°. All plans were normalized 7600 cGy dose to the 95% of clinical target volume (CTV) volume. The single arc VMAT plans were reoptimized with different collimator angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°), and for double arc VMAT plans (0–0°, 15°–345, 30–330°, 45–315°, 60–300°, 75–285°, 90–270°) using the same optimization parameters. For the comparison the parameters of heterogeneity index (HI), dose-volume histogram and minimum dose to the 95% of PTV volume (D95 PTV) calculated and analyzed. The best plans were verified using 2 dimensional ion chamber array IBA Matrixx® and three-dimensional IBA Compass® program. The comparison between calculation and measurement were made by the γ-index (3%/3 mm) analysis. A higher D95 (PTV) were found for single arc VMAT with 15° collimator angle. For double arc, VMAT with 60–300° and 75–285° collimator angles. However, lower rectum doses obtained for 75–285° collimator angles. There was no significant dose difference, based on other OARs which are bladder and femur head. When we compared single and double arc VMAT's D95 (PTV), we determined 2.44% high coverage and lower HI with double arc VMAT. All plans passed the γ-index (3%/3 mm) analysis with more than 97% of the points and we had an average γ-index for CTV 0.36, for PTV 0.32 with double arc VMAT. These results were significant by Wilcoxon signed rank test statistically. The results show that dose coverage of target and OAR's doses also depend significantly on the collimator angles due to the geometry of target and OARs. Based on the results we have decided to plan prostate cancer patients in our clinic with double arc VMAT and 75°–285° collimator angles.

Radiotherapy for maxillary sinus carcinoma: dosimetric comparison of volumetric modulated arc therapy with 0° and 90° collimator intensity modulated radiation therapy

“…He concluded that a higher D 95 (PTV) was found for single arc VMAT with 15°collimator angle. Lower rectum doses obtained for 75-285°collimator angles [28]. In our study, through changing the angle of the collimator from 0 to 90°with IMRT, it could reduce the maximum point dose of ipsilateral lens.…”

Dosimetric effects related to collimator angle optimization in intensity‐modulated radiotherapy planning for gastric cancer

“…We determined the collimator angle based on 2‐D beam's eye view images; in further studies, it might be useful to obtain the collimator angle in 3‐D directions according to the shape of the target, because it might be better to irradiate the target area and protect the OAR. Conventionally, volumetric modulated arc therapy (VMAT) plans generally only use one fixed collimator angle; however, the quality of VMAT plans are also related to the collimator angles 32–42 . More recently, dynamic collimator optimization has been proven to have a positive influence on dosimetric distribution in VMAT 43–47 .…”

“…Conventionally, volumetric modulated arc therapy (VMAT) plans generally only use one fixed collimator angle; however, the quality of VMAT plans are also related to the collimator angles. [32][33][34][35][36][37][38][39][40][41][42] More recently, dynamic collimator optimization has been proven to have a positive influence on dosimetric distribution in VMAT. [43][44][45][46][47] Similarly, acquiring multiple collimator angles during gantry rotation using the CLx technique in VMAT plans also warrants further investigation.…”

A Collimator Setting Optimization Algorithm for Dual-Arc Volumetric Modulated Arc Therapy in Pancreas Stereotactic Body Radiation Therapy

“…Previous studies demonstrated that dose coverage and dose-volume histogram (DVH) statistics were related to collimator angle selections in VMAT. [26][27][28][29] However, in clinics, collimator parameters are commonly set by a template with default values following institutional guidelines and conventions. One common practice is employing dual arcs with symmetric collimator angles (eg, 30 and 330 ) and full rotations.…”