In vivo dosimetry in external beam photon radiotherapy: Requirements and future directions for research, development, and clinical practice

Abstract

External beam radiotherapy with photon beams is a highly accurate treatment modality, but requires extensive quality assurance programs to confirm that radiation therapy will be or was administered appropriately. In vivo dosimetry (IVD) is an essential element of modern radiation therapy because it provides the ability to catch treatment delivery errors, assist in treatment adaptation, and record the actual dose delivered to the patient. However, for various reasons, its clinical implementation has been slow and limited. The purpose of this report is to stimulate the wider use of IVD for external beam radiotherapy, and in particular of systems using electronic portal imaging devices (EPIDs). After documenting the current IVD methods, this report provides detailed software, hardware and system requirements for in vivo EPID dosimetry systems in order to help in bridging the current vendor-user gap. The report also outlines directions for further development and research. In vivo EPID dosimetry vendors, in collaboration with users across multiple institutions, are requested to improve the understanding and reduce the uncertainties of the system and to help in the determination of optimal action limits for error detection. Finally, the report recommends that automation of all aspects of IVD is needed to help facilitate clinical adoption, including automation of image acquisition, analysis, result interpretation, and reporting/documentation. With the guidance of this report, it is hoped that widespread clinical use of IVD will be significantly accelerated.

Keywords: Electronic portal imaging device; External beam radiotherapy; In vivo dosimetry; Review; Task group report.

Fig. 1

Basics of an EIVD alert-inspection workflow.

Fig. 2

Probability density functions of delivered dose values corresponding to two D_IVD measurements, one inside (IVD_in) and one outside (IVD_out) the dosimetric tolerance limit values (D_P − T_L, D_P + T_H). The graph illustrates how the uncertainty of the IVD system influences the likelihood that the actual delivered dose deviation will exceed the tolerance limits (gray shaded areas). For simplicity, U_IVD is assumed to follow a normal distribution without bias.