Development and Implementation of Intensity Modulated Radiation Therapy for Small Animal Irradiator
Translational cancer research has been around for many years and has resulted
in many advancements in cancer treatment. Preclinical radiation therapy is an important
tool used in some studies to better understand the biological effects due to radiation.
Current preclinical radiation treatment techniques do not emulate the advanced
techniques used in cancer clinics, such as intensity modulated radiation therapy (IMRT).
In this work we explore the possibility of developing and implementing an IMRT
treatment capability for an orthovoltage micro irradiator used for small animal research.
In order to implement IMRT to the micro irradiator, every step of the radiation
therapy treatment process had to be evaluated, developed, and tested. The first step was
to develop and treatment planning software that can be used for small animal studies.
Using the open source Computational Environment for Radiotherapy Research (CERR)
and adapting it for use with an orthovoltage irradiator, monte carlo dose calculations
could be performed for small animal data sets. CERR does not have the ability to
optimize dose calculations, so a Matlab script was developed and written for inverse
optimization for treatment planning. Treatment plans were designed and optimized for
several small animal cases to evaluate the optimization algorithm. Following successful
simulation development, treatment delivery techniques needed to be developed. 3D
printing was used as a tool to create physical compensators that could be used as an
add-on device to the micro irradiator. With the capability of submillimeter printing
resolution, 3D printing has the capability to handle the high resolution required for very
small structures inside of small animals. Using the simulation data, another Matlab
script was developed to create both compensator and inverse compensator 3D models.
Many materials and techniques were evaluated to determine the best method for
compensator production. Materials were tested for attenuation properties, printing
capabilities, and ease of use until a satisfactory result was achieved.
Once the simulation and delivery techniques were developed to a satisfactory
level, an end to end test was designed to verify the IMRT capability. Using a 2.2 cm
diameter cylindrical Presage® dosimeter as the quality assurance (QA) device/patient, a
treatment plan was created based on the geometry of the Radiologic Physics Center
(RPC) Head and Neck phantom design. The dose tolerances used for the inverse
optimization were the same as the RPC Head and Neck protocol with a stricter tolerance
for the organ at risk (OAR). Compensators were produced for the plan and both 2D and
3D analysis was performed. Radiochromic film was used for 2D dose map analysis.
Gamma analysis was performed using 2D film data with varying criteria for distance to
agreement and dose difference. 3D analysis was done by delivering the treatment plan
to the Presage® dosimeter. Using optical-CT for dose readout of the dosimeter,
qualitative analysis was performed to show the 3D delivered dose data.
The end to end test showed strong evidence that IMRT could be implemented on
the small animal irradiator. The 9 field treatment plan was delivered in under 30
minutes with no mechanical or collisional issues. The 2D dose analysis showed 7 out of 9
treatment fields had a passing rate greater than 90% for a gamma analysis using 10%/0.5
mm tolerances. 3D dose analysis showed promising spatial resolution of the dose
modulation. As a feasibility and an initial testing study for a new treatment technique on
the small animal irradiator, these results showed the capability of the 3D printed
compensators to modulate dose with high spatial precision and moderately accurate
Intensity Modulated Radiation Therapy
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