ABSTRACT
Delivering accurate radiation dose to blood specimens during biological irradiations is essential in quantifying damage of ionizing radiation. To estimate dose to blood samples as accurately as possible, pieces of EBT2 model GAFCHROMIC™ film were placed within an approximately 10 mm finely ground rice layer that was used to simulate test specimens inside 40 mL plastic flasks. Irradiations of flasks were carried out using an X-RAD 320 irradiator with a beam quality of 320 kVp and a measured half value layer of 1.12 mm Cu, in air and in a full scattering setup which consisted of either rice or Solid Water™ (SW) surrounding flasks, filled to the same level at top of the flasks, together with a 5 cm thick SW slab beneath them. Outputs, per cent depth doses and beam profiles at different depths were measured and compared between setups. For the same setting, the dose delivered to the middle flask under the full scattering setup is 22% larger than with the in-air setup at the depth of the specimen and 9.2% more homogeneous across the specimen thickness of 10 mm (2.3% variation in comparison to the surface). Rice showed a fairly similar performance to SW within 1% at the same depth of 10 mm. Experimental setup based on full scattering conditions was shown to provide faster, more homogenous and fairly uniform dose delivery to biological specimens in comparison to conventionally used in-air setups.
Subject(s)
Film Dosimetry/methods , Radiation DosageABSTRACT
Monte Carlo simulation is currently considered to be the most accurate method of calculating dose distributions for electron beam therapy, and commercial treatment planning software using simplified macro Monte Carlo is available for electron treatment planning. In this work, Eclipse V8.1.18 is being investigated in preparation for the clinical use of CT-based electron treatment planning. Water tank measurements of percentage depth doses (PDDs) and absolute outputs at depth of maximum dose (Zmax ) under different geometric conditions are compared to the results calculated by Eclipse. The measurements are carried out for a range of electron energies (6, 9, 12, and 16 MeV) for the standard open field (10×10 cm2 ) and for circular cutouts (2, 3, and 6 cm diameters) at SSD of 100 cm. In addition, extended SSDs (105 and 110 cm) and oblique beam incident (gantry 345 degree) for the open field and 3 cm diameter cutout are measured and compared to Eclipse. For PDDs, the results predicted by Eclipse are generally acceptable, falling mostly within 5% of those measured in water. For output, the results predicted by Eclipse are similar, falling mostly within 3% of those measured in water. We observed the greatest differences between Eclipse and measurements near the water surface and in high dose gradients for PDDs. A similar observation is noted for a small field in the case of outputs.
