Treatment delivery software for a new clinical grade ultrasound system for thermoradiotherapy

A detailed description of a clinical grade Scanning Ultrasound Reflector Linear Array System (SURLAS) applicator was given in a previous paper [Med. Phys. 32, 230-240 (2005)]. In this paper we concentrate on the design, development, and testing of the personal computer (PC) based treatment delivery software that runs the therapy system. The SURLAS requires the coordinated interaction between the therapy applicator and several peripheral devices for its proper and safe operation. One of the most important tasks was the coordination of the input power sequences for the elements of two parallel opposed ultrasound arrays (eight 1.5 cm x 2 cm elements/array, array 1 and 2 operate at 1.9 and 4.9 MHz, respectively) in coordination with the position of a dual-face scanning acoustic reflector. To achieve this, the treatment delivery software can divide the applicator's treatment window in up to 64 sectors (minimum size of 2 cm x 2 cm), and control the power to each sector independently by adjusting the power output levels from the channels of a 16-channel radio-frequency generator. The software coordinates the generator outputs with the position of the reflector as it scans back and forth between the arrays. Individual sector control and dual frequency operation allows the SURLAS to adjust power deposition in three dimensions to superficial targets coupled to its treatment window. The treatment delivery software also monitors and logs several parameters such as temperatures acquired using a 16-channel thermocouple thermometry unit. Safety (in particular to patients) was the paramount concern and design criterion. Failure mode and effects analysis (FMEA) was applied to the applicator as well as to the entire therapy system in order to identify safety issues and rank their relative importance. This analysis led to the implementation of several safety mechanisms and a software structure where each device communicates with the controlling PC independently of the others. In case of a malfunction in any part of the system or a violation of a user-defined safety criterion based on temperature readings, the software terminates treatment immediately and the user is notified. The software development process consisting of problem analysis, design, implementation, and testing is presented in this paper. Once the software was finished and integrated with the hardware, the therapy system was extensively tested. Results demonstrated that the software operates the SURLAS as intended with minimum risk to future patients.