TH‐D‐303A‐09: Daily Image Guided Localization for Pediatric Brain Tumor Patients

• Published in: Medical Physics 2009-06, Vol.36 (6), p.2815-2815
• Main Authors: Beltran, C, Panandiker, A Pai, Krasin, M, Merchant, T
• Format: Article
• Language: English
• Subjects: Brain; Cancer; Cone beam computed tomography; Dosimetry; Medical imaging; Radiation therapy; Special unitary groups; Therapeutics
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.3182692

Purpose: Establish the setup uncertainty (SU) for intracranial pediatric radiotherapy patients based on daily pre‐treatment CBCT and quantify the residual uncertainty (RU) based on post‐treatment CBCT. Also, quantify the inter‐observer uncertainty (OU) and mechanical uncertainty (MechU) of the CBCT system. Methods and Materials: 94 intracranial pediatric patients have completed therapy under an IRB approved localization protocol, and stratified based on treatment position (Supine/Prone) and the use of general anesthesia (GA). Patients received a localization CBCT prior to each fraction and at the end of every other fraction. The CBCT used was an investigational MV imaging beam line; the output was adjusted such that the patient isocenter dose was 1cGy per CBCT. The offset based on the registration of the pre‐fraction CBCT to the Sim‐CT, comprising the SU, were recorded in an electronic database and the patient moved into the correct position. The offset in the post‐fraction CBCT to the Sim‐CT comprised the RU. Nine individuals independently registered the first five CBCTs of the same five randomly chosen patients. The comparison established the inter‐observer uncertainty (OU). The mechanical uncertainty (MechU) was determined by acquiring a CBCT of a localization phantom monthly and recording the discrepancy between the known positions of landmarks within the phantom and the positions based on the CBCT. Results: The mean age of the 94 patients was 12.7±7.3 years. 69 were treated supine and 25 prone; 41 with GA and 53 without. The various uncertainties in mm were as follows: SU_Supine=3.5, SU_Prone=3.8, SU_GA=3.7, SU_noGA=3.6; RU_Supine=1.8, RU_Prone=2.4, RU_GA=1.5, RU_noGA=2.3. The OU was 0.9 and the MechU was 0.5 mm. Conclusion: The 1cGy CBCTs produced with the investigational imaging beam line can be used to confidently localize the patient before treatment and thereby reduce the setup uncertainty. Conflict of Interest: Supported in part by Siemens Medical USA.