Quality Assurance of Ultrasound Imaging Systems for Target Localization and Online Setup Corrections

Comparison of 2 transabdominal ultrasound image guidance techniques for prostate and prostatic fossa radiation therapy

PURPOSE

Our clinic is a long-term user of a first-generation transabdominal (TA) biplanar (2.5-dimensional [2.5D]) ultrasound image guidance (USIG) system for prostate cancer treatments. We are also an early adopter and development partner for a new, second-generation, fully 3D USIG system that allows for volumetric TA localization of the prostate. This new system has been evaluated at our institution by direct comparison with the previously established first-generation TA method for prostate alignment.

METHODS AND MATERIALS

We compared the 2 TA-USIG methods on the same subjects and same treatment sessions. A total of 1428 fractions delivered to 41 treated patients (16 intact prostate, 25 fossa) were analyzed regarding the agreement of alignments between the 2 US positioning systems. Patients were first aligned to tattoos using treatment room lasers. TA-USIG using the 3D system was then performed to align contours derived during the computed tomography simulation process to their corresponding daily US-visualized structures. The US-3D system image guidance shifts were performed and recorded as the "initial" shifts. A 2.5D system alignment was then immediately performed using the same computed tomography derived reference contours and the indicated shifts, relative to the 3D system, were recorded as the difference between the 2 alignment methods.

RESULTS

The average difference between the 2 TA-USIG alignments for all patients was 0.4 ± 0.7 mm, 0.7 ± 0.9 mm, and 0.5 ± 0.9 mm in the left-right, anteroposterior, and superoinferior directions, respectively. No significant difference in system agreement between intact prostate versus fossa patients was observed.

CONCLUSION

Our comparison of an established 2.5D USIG method with a newer, fully 3D approach for prostate alignment of 41 different patients (1428 fractions) shows excellent agreement with each other, despite the nontrivial difference in imaging approaches. This shows that the 2 specific USIG approaches yield results that are consistent with each other, and that the USIG modality yields consistent results within the modality.

Review of ultrasound image guidance in external beam radiotherapy: I. Treatment planning and inter-fraction motion management

In modern radiotherapy, verification of the treatment to ensure the target receives the prescribed dose and normal tissues are optimally spared has become essential. Several forms of image guidance are available for this purpose. The most commonly used forms of image guidance are based on kilovolt or megavolt x-ray imaging. Image guidance can also be performed with non-harmful ultrasound (US) waves. This increasingly used technique has the potential to offer both anatomical and functional information.This review presents an overview of the historical and current use of two-dimensional and three-dimensional US imaging for treatment verification in radiotherapy. The US technology and the implementation in the radiotherapy workflow are described. The use of US guidance in the treatment planning process is discussed. The role of US technology in inter-fraction motion monitoring and management is explained, and clinical studies of applications in areas such as the pelvis, abdomen and breast are reviewed. A companion review paper (O'Shea et al 2015 Phys. Med. Biol. submitted) will extensively discuss the use of US imaging for intra-fraction motion quantification and novel applications of US technology to RT.