A 4D ultrasound real-time tracking system for external beam radiotherapy of upper abdominal lesions under breath-hold.

BACKGROUND AND PURPOSE: To evaluate a novel four-dimensional (4D) ultrasound (US) tracking system for external beam radiotherapy of upper abdominal lesions under computer-controlled deep-inspiration breath-hold (DIBH). MATERIALS AND METHODS: The tracking accuracy of the research 4D US system was evaluated using two motion phantoms programmed with sinusoidal and breathing patterns to simulate free breathing and DIBH. Clinical performance was evaluated with five healthy volunteers. US datasets were acquired in computer-controlled DIBH with varying angular scanning angles. Tracked structures were renal pelvis (spherical structure) and portal/liver vein branches (non-spherical structure). An external marker was attached to the surface of both phantoms and volunteers as a secondary object to be tracked by an infrared camera for comparison. RESULTS: Phantom measurements showed increased accuracy of US tracking with decreasing scanning range/increasing scanning frequency. The probability of lost tracking was higher for small scanning ranges (43.09% for 10° and 13.54% for 20°).The tracking success rates in healthy volunteers during DIBH were 93.24 and 89.86% for renal pelvis and portal vein branches, respectively. There was a strong correlation between marker motion and US tracking for the majority of analyzed breath-holds: 84.06 and 88.41% of renal pelvis target results and 82.26 and 91.94% of liver vein target results in anteroposterior and superoinferior directions, respectively; Pearson's correlation coefficient was between 0.71 and 0.99. CONCLUSION: The US system showed a good tracking performance in 4D motion phantoms. The tracking capability of surrogate structures for upper abdominal lesions in DIBH fulfills clinical requirements. Further investigation in a larger cohort of patients is underway.

A novel approach for superficial intraoperative radiotherapy (IORT) using a 50 kV X-ray source: a technical and case report.

The use of IORT as a treatment modality for patients with close or positive margins has increased over the past decade. For situations where a flat area (up to 6 cm in diameter) has to be treated intraoperatively, new applicators for superficial treatment with a miniature X-ray source (INTRABEAM system) were developed. Here we report our evaluation of the dosimetric characteristics of these new applicators and their first clinical use. Each of these flat and surface applicators consists of a radiation protective metal tube and a flattening filter, which converts the spherical dose distribution of the X-ray source into a flat one. The homogeneity of each dose distribution and depth-dose measurements were evaluated using film dosimetry in a solid water phantom and a soft X-ray ionization chamber in a water tank. The first patient was treated with 5 Gy delivered in 5 mm using a 4 cm FLAT applicator over 21 minutes. The flat applicators show the maximum homogeneity, with a uniformity ratio of 1.02-1.08 in certain depths. In 1 mm depth surface applicators show a uniformity ratio of 1.15-1.28. They also show a higher dose rate and a steeper dose gradient compared to the flat applicators. The results of this investigation demonstrated that the flat and surface applicators have unique dosimetric characteristics that need to be considered during the treatment planning stages. This work also showed that it is possible to perform a superficial localized IORT which provides new application possibilities for use of the INTRABEAM system.