Evaluation of kidney motion with and without a pneumatic abdominal compression belt: Considerations for stereotactic radiotherapy.

INTRODUCTION: The optimal delivery of stereotactic radiotherapy for kidney tumours requires an effective motion management strategy. This study assessed the effectiveness of a pneumatic abdominal compression belt in reducing kidney motion during free breathing. METHODS: Thirteen patients, with four-dimensional computed tomography (4DCT) of the abdomen in free breathing with and without a pneumatic abdominal compression belt, were retrospectively reviewed. Points of Interest (POI) were placed on each kidney to determine the greatest magnitude of displacement in all directions. RESULTS: Without compression, all patients had >5.0 mm motion in the craniocaudal (CC) direction in at least one kidney. Median CC excursion of the left superior pole was reduced with compression from 8.0 mm (range 2.0 mm-18.0 mm) to 4.0 mm (range 2.0 mm-10.0 mm, P = 0.047) and right superior pole from 10.0 mm (range 4.0 mm-16.0 mm) to 6.0 mm (range 2.0 mm-10.0 mm, P=value 0.051). A benefit was less evident for the left and right inferior poles with median CC excursion of 6.0 mm versus 4.0 mm and 5.0 mm versus 4.0 mm without and with compression, respectively. Median displacement in the anteroposterior direction (≤3.2 mm) and lateral directions (≤1.3 mm) was similar for left and right kidneys and not significantly altered by compression. Overall, seven patients had kidney motion reduced by >5.0 mm with two reduced by 10.0 mm. CONCLUSION: A pneumatic abdominal compression belt reduced kidney motion by >5.0 mm in seven of thirteen patients. The relative benefit is patient and location specific and should be assessed on an individual basis.

Evaluation of accuracy and reproducibility of a relocatable maxillary fixation system for fractionated intracranial stereotactic radiation therapy.

INTRODUCTION: Accurate localisation is an essential component for the delivery of intracranial stereotactic treatment. For fractionated stereotactic radiotherapy, we compared the daily localisation accuracy of a standard thermoplastic mask with a new maxillary fixation device (MFD). METHODS: Daily pre-treatment kV cone-beam computed tomography (CBCT) scans of 23 patients (12 localised in the MFD and 11 in the mask) with benign skull-based lesions were reviewed retrospectively. The set up accuracy was measured in 6° of freedom, to ascertain both individual and population random and systematic errors. The appropriate clinical target volume to planning target volume margin was computed from set up error data. RESULTS: A total of 682 CBCT scans were evaluated. Systematic (Σ) and random (σ) population errors were Σ = 0.8 mm, 0.2 mm and 0.2 mm and σ = 0.3 mm, 0.3 mm and 0.2 mm, respectively, for the standard mask in the left/right (LR), superior/inferior (SI), and anterior/posterior (AP) translational planes, and Σ = 0.2 mm, 0.1 mm and 0.2 mm and σ = 0.2 mm, 0.3 mm and 0.2 mm, respectively, for the MFD. There was a reduction in rotation errors in the MFD compared to the mask. Margin calculations suggested an isotropic margin could be safely reduced to 2 mm for the MFD. CONCLUSION: The two devices demonstrate similar daily positional accuracy for fractionated stereotactic treatment of intracranial lesions. Combined with daily image guidance and couch correction, either of these devices is a viable frameless option for fractionated stereotactic radiation therapy.