Radiation therapy dosimetry


Recent developments in radiation therapy treatment modalities (intensity modulated radiation therapy, volumetric modulated radiation therapy, stereotactic body radiation therapy, etc.) have increased the complexity of radiation therapy treatments, producing advanced patient dose deliveries. Due to this complexity, verification of dose delivery and quality assurance of new treatment techniques to validate that the dose delivery to the patient is accurate and precise is crucial. While many clinical dosimeters measure point dose or two-dimensional dose distributions, these new treatment modalities benefit from full, three-dimensional verification of dose delivery.

Gel dosimetry

Gel dosimeters have been shown to be promising tools for measuring and verifying radiation dose deliveries. Typically, gel dosimeters are read out using modalities such as magnetic resonance imaging, x-ray computed tomography (CT), or optical CT. Optical CT is becoming more frequently used as it is a simple and convenient method of acquiring dose distribution information. One major challenge with gel dosimetry is the extensive post-irradiation data processing time involved in registering and calibrating the gel dosimeter, and making the subsequent comparisons between the measured gel dosimeter dose and the planned dose distribution to confirm accurate dose delivery. Building on SlicerRT, a slicelet for gel dosimetry analysis was developed following the general workflow, greatly facilitating reproducible and timely 3D dosimetry analysis.

Use cases

Publications from the Cancer Centre Of Southeastern Ontario (CCSEO) using the gel dosimetry analysis slicelet:

  • Clinical management of tumour volume changes in VMAT head & neck radiation treatment
    K M Alexander et al 2017 J. Phys.: Conf. Ser. 847 012038
  • Dosimetric impact of a change in breathing period on VMAT stereotactic ablative body radiotherapy
    T Olding and KM Alexander 2017 J. Phys.: Conf. Ser. 847 012032

Film dosimetry

Radiochromic film is a convenient clinical dosimetry option as it is near tissue equivalent, energy and dose rate independent, and is an integrating dosimeter. Film dosimeter use is widely published and has been used for quality assurance, small field dose measurements, and as part of the commissioning of new machines and treatment techniques. On the analogy of the open-source 3D gel dosimetry analysis software, which streamlined gel dosimeter analysis from hours to 5-10 minutes, the more widespread film workflows could use a streamlined, unified workflow as well. Thus, an open-source film dosimetry analysis slicelet was also developed.