Page 83 - ARNM-3-1

Advances in Radiotherapy
& Nuclear Medicine Cone beam-focused GK dosimetric analysis

Table 1. Physical performance of ZND‑A Smart Knife
No. Physical quantity Item Nominal value/requirements
1 Isocenter deviation ≤0.5mm
2 Nominal dose rate at the focal point Head The absorbed dose rate of the biggest radiation-focusing field ≥3.0 Gy/min
The ratio of absorbed dose rates of the smallest to the biggest
radiation-focusing fields ≥0.7
Body The absorbed dose rate of the biggest radiation-focusing field ≥2.0 Gy/min
The ratio of absorbed dose rates of the smallest to the biggest
radiation-focusing fields ≥0.6
3 Nominal radiation field (in diameter) #1 Collimator 6 mm
#2 Collimator 12 mm
#3 Collimator 25 mm
#4 Collimator 35 mm
4 Dose gradient #1 Collimator ≤6 mm
#2 Collimator ≤8 mm
#3 Collimator ≤10 mm
#4 Collimator ≤10 mm
5 Comprehensive error in dose calculation Point dose ≤5%
Area overlap ratio ≥90% (biggest radiation field)

scanned by an EPSON V850 scanner to export 16-bit
grayscale images. The grayscale-dose values were fitted to
a second-order polynomial using ImageJ image analysis
software, resulting in the calibration curve equation:
y = 2.1706E − 2 −6x 0.1625x + 3.03 3E . The grayscale-dose
calibration curve is shown in Figure 6.
4.1.4. Focusing field size and dose gradient
Figure 5. Films irradiated by 1# collimator. XOY and YOZ planes of the
focusing field in phantom are shown. EBT3 films were cut to match the same size with the 1#, 2#,
3#, and 4# collimators, with two films allocated for each

where D is the dose rate to water at the focal point on collimator. For each collimator, one film was irradiated in
0
the installation date; ∆t is the number of years between the spherical phantom for the XOY plane, while another
installation date and measurement date; T is the half-life was irradiated for the YOZ plane. The irradiated films were
1/2
of radioactive decay (= 5.27 years for Cobalt-60). then scanned using an EPSON V850 scanner to generate
16-bit grayscale images at a resolution of 400 dpi. Figure 7
4.1.3. Film calibration
displays images of the focusing field irradiated by the 1#, 2#,
EBT3 is a specialized film that undergoes radiation- 3#, and 4# collimators. These images were analyzed using
induced crosslinking, causing a color change that reflects an in-house MATLAB program. The program uses the
the absorbed dose. Its advantages include no requirement calibration curve equation to convert the image grayscale
for chemical development or a darkroom, water resistance, matrices into dose matrices for further evaluation. The
cuttability, a wide dose range, and an energy-independent focusing field size is defined by the 50% isodose curve
dose response. EBT3 film exhibits varying grayscale levels area within the radiation field’s dose distribution. The
depending on radiation exposure and must be calibrated dose gradient of the focusing field is characterized by the
for dose-grayscale correlation before use. distance between the 20% and 80% isodose curves within
For the film calibration, EBT3 films were cut into the radiation field’s dose distribution.
small pieces to fit into the film holder in the spherical 4.1.5. TMR-OAR data
phantom. The films were exposed in the phantom using
the biggest collimator, with doses ranging from 0 to 1000 The TMR-OAR physical model is the core component
cGy in 100 cGy increments. The irradiated films were then of the TPS. It plays an essential part in calculating

Volume 3 Issue 1 (2025) 75 doi: 10.36922/arnm.6280