Depth dose measurement in water phantom for two X-ray energies (6MeV and 10MeV) in comparison with actual planning

Abstract

The purpose of this study is to measure doses delivered at different depths in water phantom at vertical position in comparison with the actual planning in order to verify the dose delivered to the tumor in addition to the measurement of the effect penumbra dose to assess the dose leaking to the healthy soft tissue.
 Percentage depth dose (PDD) values was measured at field sizes (5×5,10×10,15×15, and 20×20) cm2, and the depth dose was measured between (0-16) cm deep at 4cm intervals, for both energies 6 MeV and 10 MeV X-ray beam. Other readings were taken at different distances 1cm and 2cm outside of the actual beam in orthogonal directions at depth of 4 cm. These measurements were designed to measure the penumbra dose produced outside the central beam.
 Results show that the high similarity between water phantom and actual tissue for this reason water is taken as phantom for Quality Assurance (QA) and calculation the depth dose. The similar results may appear strange as the actual planning depth dose is taken in the chest wall where there is bone and soft tissue. The increase in the field size, increases the percentage of surface dose, this could be caused by an increase in the amount of scattering in the larger fields. There is almost no difference in depth dose between homogenous and non homogenous planning also similar to the water phantom. Because of higher photon energy 6MeV and 10MeV the bone has no influence in absorption from the soft tissue. A slight change in the depth dose with increase in the field size may be caused by the scattered radiation.

Dosimetric Verification of Grid Radiotherapy Using Three Ionization Chamber Detectors o Dosimetry

“…Figure 4: The variation of the mean of the match percentage of the maximum, mean and point (cGy) radiation doses calculated by TPS with the measured radiation dose using three ionization chambers.These results of this study agree with the mechanical setup of the Grid plan with MLCs, where the Grid field is divided into many sub volumes by MLCs, which leads to increase radiation leakage through the MLCs; therefore, the ionization detectors measured radiation doses higher than that dose calculated by the TPS[13]. Also, factors like leak of photons from the Linac's head, collimators of the beam, and filters flattening (head scattering) caused increases in the measured doses[17]. Other researchers mentioned that the increase in the field size increases the surface dose, which is attributed to the scattered radiation.…”

Investigation on electron contamination of LINAC at different operating voltages using particle heavy ion transport code system (PHITS)

“…The output field area of the radiation field is set for a field area of 10 × 10 cm and a Source to Image Receptor Distance (SID) of 100 cm. At a distance of 100 cm is placed a water phantom with a cube geometry measuring 40 × 40 × 40 cm 3 (Hasan et al, 2019).…”

Verification of Depth Dose Curves Derived on Beeswax, Paraffin and Water Phantoms Using FLUKA Monte Carlo Code

“…These include determination of tissue equivalent depth dose curves used in treatment planning and to ensure that deviations between the prescribed and the delivered doses to the target volume are within the ± 5% range as recommended by the International Commission on Radiation Units and Measurements (ICRU) (IAEA 2000, Thwaites 2013, ICRU 2016. It is well established that depth doses measured in water phantom for various field sizes differ (Buzdar et al 2009, Araki et al 2017, Hasan et al 2019. What is not well known is whether these depth doses are the same as the depth doses in human tissues.…”