Abstract
The purpose of this study was to investigate whether a new O‐ring design radiotherapy delivery system has advantages in radiotherapy planning for skull‐base tumors. Twenty‐five patients with skull‐base tumors were included in this study. Two plans were made using conventional (Plan A) or new (Plan B) techniques. Plan A consisted of four dynamic conformal arcs (DCAs): two were horizontal, and the other two were from cranial directions. Plan B was created by converting horizontal arcs to those from caudal directions making use of the O‐ring design radiotherapy system. The micromultileaf collimators were fitted to cover at least 99% of the planning target volume with prescribed doses, 90% of the dose at the isocenter. The two plans were compared in terms of target homogeneity, conformity, and irradiated volume of normal tissues, using a two‐sided paired t‐test. For evaluation regarding target coverage, the homogeneity indices defined by the International Commission on Radiation Units and Measurements 83 were 0.099±0.010 (mean ± standard deviation) and 0.092±0.010, the conformity indices defined by the Radiation Therapy Oncology Group were 1.720±0.249 and 1.675±0.239, and the Paddick's conformity indices were 0.585±0.078 and 0.602±0.080, in Plans A and B, respectively. For evaluation of irradiated normal tissue, the Paddick's gradient indices were 3.118±0.283 and 2.938±0.263 in Plans A and B, respectively. All of these differences were statistically significant (p‐values <0.05). The mean doses of optic nerves, eyes, brainstem, and hippocampi were also significantly lower in Plan B. The DCA technique from caudal directions using the new O‐ring design radiotherapy system can improve target homogeneity and conformity compared with conventional DCA techniques, and can also decrease the volume of surrounding normal tissues that receives moderate doses.PACS numbers: 87.55.‐x, 87.55.D‐, 87.55.dk
Highlights
227 Ogura et al.: O-ring design RT system beam’s eye view is fitted to the target volume throughout the arc length, which yields high dose conformity to the targets.In conventional C-arm linear accelerator systems, arc arrangement from caudal directions is usually difficult because of the risk of collision between the gantry head and the patient
Clinical target volume (CTV) was defined as residual gross tumors — except cases of craniopharyngioma, in which the CTV was defined as residual gross tumors and 5 mm thick areas of the normal brain tissue attached to the tumors on preoperative magnetic resonance imaging (MRI) images
In terms of irradiated normal tissues, Paddick’s gradient index (PGI) decreased and modified PGI (mPGI) increased in Plan B, both with statistical significance
Summary
227 Ogura et al.: O-ring design RT system beam’s eye view is fitted to the target volume throughout the arc length, which yields high dose conformity to the targets.In conventional C-arm linear accelerator (linac) systems, arc arrangement from caudal directions is usually difficult because of the risk of collision between the gantry head and the patient. For large tumors, these are occasionally insufficient because the dose distribution within the targets becomes inhomogeneous from the cranial to caudal direction, such that fewer doses are delivered to the caudal part of the target In this regard, we hypothesized that the characteristics of a new O-ring design radiotherapy system, vero4DRT (Mitsubishi Heavy Industries, Ltd., Tokyo, Japan, and BrainLAB, Feldkirchen, Germany) would yield further improvements in target conformity and homogeneity, compared with conventional DCA techniques. The treatment couch can translate right-to-left, superior-to-posterior, and anterior-to-posterior, and can rotate in both the pitch and roll planes Use of such tools allows of high-precision, image-guided patient setup.[4] The MLC of the delivery systems is regular in type, as opposed to a binary MLC (such as employed in tomotherapy). The MLC is of single-focus, has 30 pairs of 5 mm wide leaves at the isocenter, and produces a maximum treatment field of 150 × 150 mm2.(5)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
