O6. Radiotherapy dosimetry audit: The Charlotte Maxeke Johannesburg Academic Hospital Experience

• Published in: Physica medica 2016-09, Vol.32, p.142-143
• Main Authors: Nhachissambe, F, Maselesele, V, van der Merwe, D.G
• Format: Article
• Language: English
• Subjects: Radiology
• ISSN: 1120-1797; 1724-191X
• DOI: 10.1016/j.ejmp.2016.07.014

Introduction Dosimetry audits are a set of tests that are used to assess and scrutinize the commissioning data, quality control and accuracy of dose delivery by radiotherapy equipment. They are important for continuous quality improvement. Charlotte Maxeke Johannesburg Academic Hospital (CMJAH) Medical Physics participated in an external dosimetry audit as the first pilot site for the national radiotherapy audit project (IAEA SAF6/018). Materials and methods Three types of measurements were conducted, i.e. absolute dosimetry measurements under reference conditions, dosimetry in non-reference conditions and end-to-end phantom measurements. Two linear accelerators were used. Under the reference conditions measurements, the IAEA-TRS-398 code of practice was applied. A water tank was used for the photon dosimetry with a calibrated PTW 30011 Farmer 0.6 cc ionization chamber. Electron measurements were conducted using an acrylic phantom and a calibrated PTW 34045 Advanced Markus ionization chamber. Non-reference measurements included wedge factors and output factor measurements. The end-to-end measurements were based on procedures recommended by IAEA-TECDOC-1583; wherein the CIRS IMRT thorax phantom was used. The end to end test included performing a CT scan of the phantom and developing a typical 3 field plan with 1 Gy per fraction dose prescription to the isocentre. The plan was then transferred to the treatment unit via the LANTIS record and verify system. The collapsed cone dose calculation algorithm (Oncentra Treatment Planning System V 4.5) was used for planning. Measurements were performed, at three fixed points in the phantom, with a 0.6 cc ionization chamber as well as a PTW 31006 Pinpoint ionization chamber, and were found to give consistent results. Results All measurements (reference conditions, non-reference conditions and end-to-end) were found to be within ± 2% agreement with the hospital data. Conclusion The full scope of the audit was achieved but it did not include the input or participation of other specialties like radiotherapists and radiation oncologists.