Benefits of online in vivo dosimetry for single-fraction total body irradiation.

Use of a patient test dose before single-fraction total body irradiation (TBI) allows review of in vivo dosimetry and modification of the main treatment setup. However, use of computed tomography (CT) planning and online in vivo dosimetry may reduce the need for this additional step. Patients were treated using a supine CT-planned extended source-to-surface distance (SSD) technique with lead compensators and bolus. In vivo dosimetry was performed using thermoluminescent dosimeters (TLDs) and diodes at 10 representative anatomical locations, for both a 0.1-Gy test dose and the treatment dose. In total, 28 patients were treated between April 2007 and July 2013, with changes made in 10 cases (36%) following test dose results. Overall, 98.1% of measured in vivo treatment doses were within 10% of the prescribed dose, compared with 97.0% of test dose readings. Changes made following the test dose could have been applied during the single-fraction treatment itself, assuming that the dose was delivered in subportions and online in vivo dosimetry was available for all clinically important anatomical sites. This alleviates the need for a test dose, saving considerable time and resources.

A verification study of proposed pelvic lymph node localisation guidelines using nanoparticle-enhanced magnetic resonance imaging.

BACKGROUND AND PURPOSE: Normal sized pelvic lymph nodes are not easily identifiable on conventional imaging, but can be visualised with contrast-enhanced magnetic resonance imaging (MRI) using intravenous ultra-small particles of iron-oxide (USPIO). We have previously reported pelvic node clinical target volume (CTV) delineation guidelines for use with conventional imaging, derived from nodal mapping studies using USPIO. This study aims to verify these guidelines using an independent observer in a further patient cohort. MATERIALS AND METHODS: Ten patients with gynaecological cancer underwent MRI with and without intravenous USPIO. The guidelines were used to outline a pelvic node CTV on pre-contrast T2-weighted images. On post-contrast T2-weighted images the pelvic nodes were identified and outlined. The pre- and post-contrast images were co-registered and CTV examined for node coverage. RESULTS: By applying the guidelines, full coverage of 737 of 741 node outlines was achieved (>99%). Four nodes were not completely encompassed, two anterior external iliac nodes and two lateral external iliac nodes. CONCLUSIONS: MRI with USPIO contrast enabled the production of guidelines for localising a pelvic node CTV with conventional imaging. Application of these guidelines to a further patient cohort resulted in coverage of 99.5% node outlines demonstrating the reliability of this technique.