Intraoperative computed tomography imaging for dose calculation in intraoperative electron radiation therapy: Initial clinical observations

Abstract

In intraoperative electron radiation therapy (IOERT) the energy of the electron beam is selected under the conventional assumption of water-equivalent tissues at the applicator end. However, the treatment field can deviate from the theoretic flat irradiation surface, thus altering dose profiles. This patient-based study explored the feasibility of acquiring intraoperative computed tomography (CT) studies for calculating three-dimensional dose distributions with two factors not included in the conventional assumption, namely the air gap from the applicator end to the irradiation surface and tissue heterogeneity. In addition, dose distributions under the conventional assumption and from preoperative CT studies (both also updated with intraoperative data) were calculated to explore whether there are other alternatives to intraoperative CT studies that can provide similar dose distributions. The IOERT protocol was modified to incorporate the acquisition of intraoperative CT studies before radiation delivery in six patients. Three studies were not valid to calculate dose distributions due to the presence of metal artefacts. For the remaining three cases, the average gamma pass rates between the doses calculated from intraoperative CT studies and those obtained assuming water-equivalent tissues or from preoperative CT studies were 73.4% and 74.0% respectively. The agreement increased when the air gap was included in the conventional assumption (98.1%) or in the preoperative CT images (98.4%). Therefore, this factor was the one mostly influencing the dose distributions of this study. Our experience has shown

Delivery of intensity-modulated electron therapy by mechanical scanning: An algorithm study

“…This study revealed that by adjusting the intensity of the scan beam, IMET can be achieved with nonuniform dose distributions according to the intraoperative images such as the CT image ( 34 ) and the three-dimensional ultrasound images ( 35 ). The electron beam is collimated by the applicator, which determines the scan beam size.…”

An open-source development based on photogrammetry for a real-time IORT treatment planning system

“…The use of intraoperative volumetric real-time imaging to evaluate applicator placement and optimize the treatment plan is only feasible if an imaging device that can calculate density relative to water, such as computed tomography (CT), O-arm cone beam CT (CBCT), and C-arms CBCT [5,6], is available in the operating room (OR) [7,8]. Other systems are under development to enhance the accuracy of the dose administered in IORT treatments [9].…”

Treatment Planning in Intraoperative Radiation Therapy (IORT): Where Should We Go?

“…The time is probably ripe for a change. Availability of accurate dose calculation algorithms for clinical use, such as real-time Monte Carlo calculation [ 4 , 5 , 6 ], the prospected coming of radically new irradiation schemes such as FLASH therapy [ 7 ], and the possibility to use in-room imaging [ 8 ] call for an evolution of treatment planning systems in IORT.…”