Modeling treatment couches in the Pinnacle treatment planning system: Especially important for arc therapy.

This study is to demonstrate the importance and a method of properly modeling the treatment couch for dose calculation in patient treatment using arc therapy. The 2 treatment couch tops-Aktina AK550 and Elekta iBEAM evo-of Elekta LINACs were scanned using Philips Brilliance Big Bore CT Simulator. Various parts of the couch tops were contoured, and their densities were measured and recorded on the Pinnacle treatment planning system (TPS) using the established computed tomography density table. These contours were saved as organ models to be placed beneath the patient during planning. Relative attenuation measurements were performed following procedures outlined by TG-176 as well as absolute dose comparison of static fields of 10 × 10 cm(2) that were delivered through the couch tops with that calculated in the TPS with the couch models. A total of 10 random arc therapy treatment plans (5 volumetric-modulated arc therapy [VMAT] and 5 stereotactic body radiation therapy [SBRT]), using 24 beams, were selected for this study. All selected plans were calculated with and without couch modeling. Each beam was evaluated using the Delta(4) dosimetry system (Delta(4)). The Student t-test was used to determine statistical significance. Independent reviews were exploited as per the Imaging and Radiation Oncology Core head and neck credentialing phantom. The selected plans were calculated on the actual patient anatomies with and without couch modeling to determine potential clinical effects. Large relative beam attenuations were noted dependent on which part of the couch top beams were passing through. Substantial improvements were also noted for static fields both calculated with the TPS and delivered physically when the couch models were included in the calculation. A statistically significant increase in agreement was noted for dose difference, distance to agreement, and γ-analysis with the Delta(4) on VMAT and SBRT plans. A credentialing review showed improvement in treatment delivery after couch modeling with both thermoluminescent dosimeter doses and film analysis. Furthermore, analysis of treatment plans with and without using the couch model showed a statistically significant reduction in planning target volume coverage and increase in skin dose. In conclusion, ignoring the treatment couch, a common practice when generating a patient treatment plan, can overestimate the dose delivered especially for arc therapy. This work shows that explicitly modeling the couch during planning can meaningfully improve the agreement between calculated and measured dose distributions. Because of this project, we have implemented the couch models clinically across all treatment plans.

A study of finite discontinuity-volumetric modulated arc therapy for mid-and distal-Esophageal Carcinoma / 中华放射肿瘤学杂志

Objective To implement the finite discontinuity?volumetric modulated arc therapy ( FD?VMAT) in the Pinnacle planning system, and to investigate its clinical significance. Methods Eight patients with thoracic esophageal cancer in our hospital were enrolled as subjects. FD?VMAT was fulfilled in the Pinnacle planning system using a developed program. FD?VMAT, VMAT, and fixed?field intensity?modulated radiotherapy ( IMRT ) plans were designed for each patient. The conformity index ( CI ) and homogeneity index ( HI) of the planning target volume ( PTV) ,doses to organs at risk,passing rate for plan verification,number of monitor units,and treatment time were used to evaluate the plans. Comparison between different plans was made by paired t test. Results For the PTV,there was no significant difference in CI between FD?VMAT and VAMT ( P=0?186 );FD?VMAT had a significantly worse HI than VMAT ( P=0?001);however,both the CI and HI were significantly improved in FD?VMAT than in IMRT ( P=0?006, 0?002) . Compared with IMRT, FD?VMAT, retaining the advantage of VMAT, had pulmonary V20 and V30 significantly reduced by 19?79% and 20?32%,respectively (P=0?000,0?000).For the pulmonary low?dose regions (≤V5 ) ,FD?VMAT retained the advantage of IMRT and had lower doses than VMAT. Particularly, pulmonary V2 was significantly reduced by 16?79%(P=0?000).The mean lung dose was significantly lower in FD?VMAT than in VMAT or IMRT (P=0?001,0?000).There were no significant differences in D1cc to spinal cord PRV,heart V30,or passing rate for plan verification between the three therapies. The heart V40 and mean heart dose in FD?VMAT were similar to those in VMAT (P=0?175,0?468),but significantly lower than those in IMRT ( P=0?021,0?002) . FD?VMAT had a larger number of monitor units and longer treatment time than VMAT. Compared with IMRT, the number of monitor units and treatment time were reduced by 13?6% and 49?6% in FD?VMAT,respectively. Conclusions Compared with VMAT and IMRT, the application of the developed FD?VMAT in the treatment of thoracic esophageal cancer can further reduce the lung dose while keeping the PTV coverage,protection of the heart and spinal cord,and high efficacy. FD?VMAT is a new therapy available for thoracic esophageal cancer.