A declarative implementation of the DICOM-3 network protocol.

We describe a new design for programs using the Digital Imaging and Communications in Medicine (DICOM) protocol, which we have implemented in a DICOM image storage server and a radiation treatment plan transfer facility for our locally developed radiation treatment planning system, Prism. This design is declarative, representing DICOM as a language for describing messages and sequencing of messages. The coding involved implementing an interpreter for this language. The DICOM protocol specifies messages, message formats, and sequencing. In our design, the specification translates almost directly into computer-readable declarative expressions that closely resemble the relevant tabulated DICOM specifications. The resulting programs are small, simple, and extensible, because most of the details of the DICOM protocol are not coded in the procedural control statements but are in the expressions and state table that the interpreter uses to perform all its functions. This approach provides a way to validate the consistency of a specification and the correctness of the implementation. The same method can be generalized to other such protocols. It may also be used to assist the design of new protocols.

Random and systematic beam modulator errors in dynamic intensity modulated radiotherapy.

This paper reports on the dosimetric effects of random and systematic modulator errors in delivery of dynamic intensity modulated beams. A sliding-widow type delivery that utilizes a combination of multileaf collimators (MLCs) and backup diaphragms was examined. Gaussian functions with standard deviations ranging from 0.5 to 1.5 mm were used to simulate random positioning errors. A clinical example involving a clival meningioma was chosen with optic chiasm and brain stem as limiting critical structures in the vicinity of the tumour. Dose calculations for different modulator fluctuations were performed, and a quantitative analysis was carried out based on cumulative and differential dose volume histograms for the gross target volume and surrounding critical structures. The study indicated that random modulator errors have a strong tendency to reduce minimum target dose and homogeneity. Furthermore, it was shown that random perturbation of both MLCs and backup diaphragms in the order of sigma = 1 mm can lead to 5% errors in prescribed dose. In comparison, when MLCs or backup diaphragms alone was perturbed, the system was more robust and modulator errors of at least sigma = 1.5 mm were required to cause dose discrepancies greater than 5%. For systematic perturbation, even errors in the order of +/- 0.5 mm were shown to result in significant dosimetric deviations.