Amr Taha

BACKGROUND AND PURPOSE: To quantify the organ motion relative to bone in different breathing states in pediatric neuroblastoma using cone beam CT (CBCT) for better definition of the planning margins during abdominal IMRT.

METHODS AND MATERIALS: Forty-two datasets of kV CBCT for 9 pediatric patients with abdominal neuroblastoma treated with IMRT were evaluated. Organs positions on planning CT scan were considered the reference position against which organs and target motions were evaluated. The position of the kidneys and the liver was assessed in all scans. The target movement was evaluated in four patients who were treated for gross residual disease.

RESULTS: The mean age of the patients was 4.1 ± 1.6 years. The range of target movement in the craniocaudal direction (CC) was 5mm. In the CC direction, the range of movement was 10mm for the right kidney, and 8mm for the left kidney. Similarly, the liver upper edge range of motion was 11 mm while the lower edge range of motion was 13 mm.

CONCLUSIONS: With the use of daily CBCT we may be able to reduce the PTV margin. If CBCT is not used daily, a wider margin is needed.

AIM: To compare the accuracy of radiotherapy set-up using an electronic portal imaging device (EPID) versus megavoltage cone beam computed tomography (MV-CBCT) in paediatric patients.

MATERIALS AND METHODS: In total, 204 pairs of EPID and MV-CBCT were carried out for 72 patients in the first 3 treatment days and weekly thereafter.

RESULTS: For the whole group, the mean systematic EPID set-up errors were 1.8 (±1.7), 1.6 (±1.3), 1.4 (±1.5) mm and 2.3 (±1.7), 1.6 (±1.3), 2.4 (±1.6) mm for MV-CBCT in the longitudinal, lateral and vertical directions, respectively, whereas the mean EPID random errors were 2.0 (±1.7), 1.4 (±1.5), 1.2 (±1.6) and 1.9 (±1.5), 1.5 (±1.3), 2.1 (±1.7) mm for MV-CBCT in the longitudinal, lateral and vertical directions, respectively. For systematic errors of head and neck patients, there was a statistically significant difference in the lateral and vertical directions (P=0.027, 0.003), whereas in the non-head and neck patients there was a statistically significant difference in the lateral direction only (P=0.031). In head and neck patients, the mean random errors were significantly different in the vertical and lateral directions, whereas in non-head and neck patients, they were significantly different in the vertical direction only. The larger values alternate between the two modalities. The systematic and random errors (detected by EPID and MV-CBCT) were significantly correlated in almost all direction in all tumour sites.

CONCLUSIONS: The comparison between set-up error in EPID and MV-CBCT was not in favour of any of the two modalities. However, the two modalities were strongly correlated but fairly agreed and the differences between the shifts reported were small and hardly influenced the recommended planning target volume margin.