2D Medical Dosimetry Using Luminescent Techniques

SCK•CEN Mentor

Lebacq Anne Laure, alebacq@sckcen.be, +32 (0)14 33 21 32

Expert group

Dosimetric and Calibration Services

Introduction

The objective of this scientific visit is to develop a dosimetric system capable of reading 2D dose distributions from radiotherapy beams on patients. This system will be used for 2D dose mapping in real time in vivo dosimetry, and their possible applications in radiotherapy.

Objective

Two approaches are presented. Approach 1 will be developed and tested first. Approach 2 is also foreseen in case time is available. The two are described below:

Approach 1:  RL Al2O3:C droplets

Al2O3:C droplets were successfully tested as real time 1D radioluminescence (RL) detectors when coupled to optical fibres [44] . Droplets are composed of micro crystals (<4 μm) mixed with a photocurable polymer, with possibility of several sizes and shapes. The concept already tested for 1D dosimetry will be extended for a 2D matrix capable of reading real time (RL) dose rates.

The first challenge of this project is to arrange the matrix such that each droplet has similar shape, volume and sensitivity. Testing the matrix is connected to the readout process. Because radioluminescence doesn’t need external stimulation, such as light or heat, the optics needed is only related on acquiring the RL signal. For that, high-performance short-wave cameras will be tested. These cameras are optimized to acquire data in specific wavelength ranges and, together with dedicated optical filters, allow the radioluminescence from irradiated Al2O3:C droplets to be acquired. The image from the camera will give information of the position of the radiation fields, while the light intensity can be related to the dose-rate.

Approach 2: RPL Al2O3:C,Mg or OSL Al2O3:C droplets

Al2O3:C droplets were successfully tested as 1D passive OSL detectors [56] with detectors sizes smaller than 1 mm; the concept can be further developed to build a 2D matrix composed of such droplets. Both Al2O3:C and Al2O3:C,Mg are provided in powder (crystal sizes around 4 mm) by Landauer Inc., in collaboration with this project. 

This approach will focus on measuring passive absorbed doses from a 2D matrix composed of RPL Al2O3:C,Mg or OSL Al2O3:C detectors. The advantage of RPL solution is the non-destructive readout method, which allows the dosimetrist to assess the dose response as many times as necessary; while for OSL Al2O3:C the dose limits are much broader than from RPL Al2O3:C,Mg (from few mGy to 100 Gy). Ideally, a combination of the RPL and OSL features would give a better passive system and this will be further tested.    

In recent years remarkable progress has been made towards the understanding of proposed hallmarks of cancer development and treatment. However with its increasing incidence, the clinical management of cancer continues to be a challenge for the 21st century. Treatment modalities comprise of radiation therapy, surgery, chemotherapy, immunotherapy and hormonal therapy. Radiation therapy remains an important component of cancer treatment with approximately 50% of all cancer patients receiving radiation therapy during their course of illness; it contributes towards 40% of curative treatment for cancer. The main goal of radiation therapy is to deprive cancer cells of their multiplication (cell division) potential.[ref[SCK1] ]

An ever-present difficulty in radiotherapeutic procedures in oncology is the accurate measurement of absorbed doses at localised sites within the body. The effective use of radiation as a therapeutic tool requires accurate delivery of prescribed radiation doses to the organ of interest, while limiting the doses given to surrounding healthy tissue [ref]. Additionally, step dose gradients and high LET beams (such as Proton and Carbon therapies), impose new challenges to the dosimetrists.

As the radiotherapy community makes the transition from the conventional two-dimensional (2D) to three-dimensional (3D) conformal and intensity modulated dose delivery, it is recommended that new treatment techniques be checked systematically for a few patients, and to perform in vivo dosimetry a few times for each patient for situations where errors in dose delivery should be minimized. Entrance in vivo dosimetry using several types of dosimetric detectors, such as diodes, ion chambers, and MOSFETS, has been demonstrated to be valuable for the standard quality assurance methods used in a radiotherapy treatment [[SCK2] ]. Although in vivo dosimetry is generally recognized for its usefulness, the additional workload generated is one of the factors that impedes a widespread implementation.

All current dosimetric systems used in in vivo dosimetry have their inherent limitations and are not optimal; therefore the scientific community has as common interest to develop new and more reliable tools.

This project proposal presents a new approach for in vivo dosimetry based on luminescent techniques in a 2 dimensional (2D) matrix. Our proposal focuses on the assessing the 2D entrance dose distribution, with the advantage of real time and/or near real-time dose calculations.  The system is optical, reliable and easy to use in the clinics.

Due to its small volume and high sensitivity, Al2O3:C, and Al2O3:C,Mg detectors can be used for in vivo dosimetry. The different techniques (RPL, OSL, and RL) allow different application methods.  In this project proposal we suggest two approaches for 2D dosimetry using the luminescence properties of Al2O3:C and Al2O3:C,Mg. The two options can be summarized as follows:

Approach 1: 2D matrix consisting of RL Al2O3:C droplets, with detectors sizes smaller than 1 mm. Droplets are composed of micro crystals (<4 mm) mixed with a photocurable polymer, with possibility of several sizes and shapes. This approach allows the real time dose rate assessment.

Approach 2: 2D system to assess post-irradiation passive doses using either radiophotoluminescence (RPL) from Al2O3:C,Mg or optically stimulated luminescence (OSL) from Al2O3:C detectors. The detectors would be disposed on a matrix, as the RL droplets from approach 1, and readout optically in a 2D scan system.  

 [SCK1]Baskar, R., Lee, K. A., Yeo, R., & Yeoh, K. W. (2012). Cancer and radiation therapy: current advances and future directions. International journal of medical sciences, 9(3), 193.

 [SCK2]Leunens, G., Van Dam, J., Dutreix, A., & Van der Schueren, E. (1990). Quality assurance in radiotherapy by in vivo dosimetry. 1. Entrance dose measurements, a reliable procedure. Radiotherapy and Oncology, 17(2), 141-151.

The minimum diploma level of the candidate needs to be

PhD

The candidate needs to have a background in

Physics

Estimated duration

3 weken