SU-E-T-99: Small Field Output Factor Measurement Using MAGIC Gel Dosimeter in 3T MRI.

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Small field dosimetry is crucial for modern radiation therapy techniques like IMRT and radiosurgery.
• Accurate measurement of output factors (OFs) in small radiation fields is essential for dose calculation accuracy.

Purpose of the Study:

• To investigate the efficacy of a MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper) gel dosimeter for quantitative measurement of small field output factors (OFs).
• To evaluate the performance of MAGIC gel dosimeters for 6MV x-ray beams across various small field sizes.

Main Methods:

• MAGIC gel phantoms were prepared and irradiated with 6MV x-rays for field sizes ranging from 1x1 cm² to 10x10 cm².
• Output factors were measured using MAGIC gel, ion chambers, Gafchromic film, and TLDs under identical conditions.
• Dose distributions in MAGIC gel were read out using a 3T MRI scanner and analyzed with custom Matlab code.

Main Results:

• The MAGIC gel dosimeter yielded an OF of 0.612 for a 1x1 cm² field, showing a deviation of approximately 2% from small volume dosimeters.
• Larger ion chambers exhibited significantly lower OFs (0.26 for 1x1 cm²) due to nonequilibrium and partial volume effects.
• The study confirmed good agreement between MAGIC gel and other validated small field dosimetry methods.

Conclusions:

• The MAGIC gel dosimeter, when read out with a 3T MRI scanner, is a suitable and accurate tool for small field dosimetry.
• Its quantitative capabilities make it valuable for precise dose verification in advanced radiation therapy applications.
• MAGIC gel offers a promising alternative for measuring output factors in small radiation fields, complementing existing dosimetry techniques.