Dosimetry and quality control
Development and application of dosimetric and QA techniques.
Scope and outline
Radiotherapy treatments in our department are becoming increasingly complex due to the wide application of advanced techniques such as stereotactic (body) treatments, IMRT and IGRT, for example with the Cyberknife and the Synergy systems. The dosimetry and quality control programs provided by the medical physicists are essential to ensure the correct and safe functioning of all involved equipment. The major part of the clinical QA program consists of proactive measurements on -and monitoring of -well chosen device parameters to verify correct functioning within the required narrow tolerances.
An important aspect of IGRT QA is development of specific end-to end tests that prove the desired performance of the entire IGRT procedure and minimize the physics time investment in QA at the same time. Other QA activities are aimed at the safe clinical introduction of advanced treatments. All this requires development and maintenance of high precision dosimetry procedures, e.g. for radiochromic film dosimetry, and development of special purpose phantoms.
Below is a picture of an in-house constructed modular anthropomorphic thorax phantom with realistic dimensions and body contours. The phantom has been used to compare measured Cyberknife dose distributions, obtained with radiochromic film, with distributions calculated with the conventional ray-tracing dose calculation algorithm in Multiplan and with the novel module using Monte Carlo simulations.
Anthropomorphic thorax phantom with inserts to mimic a spherical lung tumor.
Comparisons of measured and calculated dose distributions for irradiation a lung tumor in the Thorax phantom. Upper panel: film in thorax phantom. Left panel: g -distribution (3%, 1 mm, absolute dose), comparing Ray-tracing with film measurement. Right panel: comparison of Monte Carlo dose calculation with film.
Selected publications
- Schembri V, Heijmen BJM. Optically stimulated luminescence (OSL) of carbon-doped aluminum oxide (Al2O3:C) for film dosimetry in radiotherapy. Med Phys. 2007; 34(6): 2113-8.
Contact
Dr. J.P.A. Marijnissen