ABSTRACT
PURPOSE: To assess the reliability of soft tissue alignment by comparing pre- and post-treatment cone-beam CT (CBCT) for image guidance in stereotactic body radiotherapy (SBRT) of lung cancers. METHODS: Our lung SBRT procedures require all patients undergo 4D CT scan in order to obtain patient-specific target motion information through reconstructed 4D data using the maximum-intensity projection (MIP) algorithm. The internal target volume (ITV) was outlined directly from the MIP images and a 3-5 mm margin expansion was then applied to the ITV to create the PTV. Conformal treatment planning was performed on the helical images, to which the MIP images were fused. Prior to each treatment, CBCT was used for image guidance by comparing with the simulation CT and for patient relocalization based on the bony anatomy. Any displacement of the patient bony structure would be considered as setup errors and would be corrected by couch shifts. Theoretically, as the PTV definition included target internal motion, no further shifts other than setup corrections should be made. However, it is our practice to have treating physicians further check target localization within the PTV. Whenever the shifts based on the soft-tissue alignment (that is, target alignment) exceeded a certain value (e.g. 5 mm), a post-treatment CBCT was carried out to ensure that the tissue alignment is reliable by comparing between pre- and post-treatment CBCT. RESULTS: Pre- and post-CBCT has been performed for 7 patients so far who had shifts beyond 5 mm despite bony alignment. For all patients, post CBCT confirmed that the visualized target position was kept in the same position as before treatment after adjusting for soft-tissue alignment. CONCLUSIONS: For the patient population studied, it is shown that soft-tissue alignment is necessary and reliable in the lung SBRT for individual cases.
ABSTRACT
INTRODUCTION: Providing effective palliative treatment in childhood malignancies is a challenging task. This study evaluated the role of palliative radiotherapy in the management of incurable paediatric malignancies. METHODS: Records of 40 paediatric patients treated between January 2003 and November 2005 were reviewed and analysed retrospectively. All had received palliative external beam radiotherapy for symptom control either as a single modality or in addition to surgery, chemotherapy and drugs for symptomatic relief. RESULTS: Predominant symptoms noticed were swelling with or without pain, bleeding, and weakness of limbs. Median duration of symptoms was 90 days. Malignant round cell tumours were most common followed by retinoblastoma, neuroblastoma, Ewing's sarcoma and acute myeloid leukaemia with chloromas. 45 percent of children had disseminated disease at presentation. Nine underwent surgery, while 32 patients received chemotherapy, and all but two received drugs for symptomatic relief in addition to palliative radiotherapy. Dose schedules were either 5 Gy or 8 Gy in single fraction, while for fractionated radiotherapy, the range was 20 Gy in five fractions to 30 Gy in ten fractions. With regard to symptomatic relief, four patients had complete relief, 20 showed good relief, 15 had little and one did not have any relief. On completion of multimodality treatment, tumour response was complete in two patients, 18 had partial response, eight had stable disease, eight had progressive disease, and the disease status of four was unknown. CONCLUSION: The role of radiotherapy as a palliative modality in children with locally-advanced lesions provides better symptomatic relief in combination with other treatment modalities.
