Efficient X-Ray Source Probe Adjustment of the Intrabeam Intraoperative Radiotherapy System

Intraoperative radiotherapy (IORT) delivers, at the time of surgery, a large dose of radiation in a single fraction to a target area directly accessible to the surgeon in the operating room (OR), allowing for increased dose to the target and decreased dose to nearby normal tissues. Delivery of IORT to a patient requires that pertinent quality assurance (QA) checks of the system be successfully executed to ensure appropriate treatment. A widely used IORT system presently is the Intrabeam unit (Carl Zeiss Meditec AG, Jena, Germany), an electronic brachytherapy system which uses a compact low-energy X-ray source (XRS) mounted on a semi-robotic arm. To deliver IORT treatments using the Intrabeam system, two initial QA tests must be conducted to ensure that the isotropy and the output of the radiation source are both within tolerance. Whenever the initial isotropy check fails, indicating that the probe of the XRS is misaligned, an additional QA procedure meant to realign the probe becomes mandatory. This latter probe-adjustment procedure involves an interplay between the operator manipulating a special QA device around the XRS probe while the system monitors, continuously and in real time, the extent of misalignment of the probe. With a system-specified tolerance for probe eccentricity to be <0.1 mm, this interplay can result repeatedly in false-negative results due to artifacts unrelated to probe alignment, such as XRS manipulation by the user, potentially causing significant delays in initiation of the IORT treatment. We suggest a modified probe realignment procedure whereby measuring artifacts arising while the user manipulates the QA device are disregarded, and instead only artifact-free misalignment readings, i.e., while the device is not being manipulated, are considered. This modification is meant solely to improve efficiency, is based on workflow experience rather than any related quantitative measurements, and does not involve any changes to system tolerances or QA test acceptance criteria. A more efficient realization of the required set of preoperative QA tests could save significant time for the medical teams involved, as well as reduce the total time a patient is maintained under general anesthesia.