Pencil Beam and Collapsed Cone Algorithm Calculations for a Lung-Type Volume Using Ct and the Omp Treatment Planning System

Topics: Percent difference, Monte Carlo method, Measurement Pages: 21 (7815 words) Published: May 17, 2012
Pencil Beam and Collapsed Cone Algorithm Calculations for a Lung-type Volume Using CT and the OMP Treatment Planning System Methods
Measurements have been carried out in both phantom and a specifically designed phantom which simulated human lung volume. Samples were taken from the Lung Planning CT images for 15 patients using the Oncentra Masterplan OMP Treatment Planning System. The X-axis was, following convention, taken to be horizontal, and the Y-axis to be vertical; accordingly, abscissa and ordinate distances to the skin, heart and the lungs were measured (see figure 8). Figures 4 and 5 show typical CT images for a patient’s lungs, while Tables 1 and 2 give the beam information and dose information for typical patients. The X-ray images were taken using CT-SIM: Philips Brilliance Big Bore. A print out of the planning CT images was produced by the Oncentra Masterplan OMP treatment Planning system (see section 3.3).

Figure 4: Lungs Image for Patient by CT-SIM: Philips Brilliance Big Bore Beam Information|
Beam| 1ANT| 2RPO| 3RPO| 4ARO|
Nom. Acc. Pot.(MV or MeV)| 6| 6| 6| 6|
FX (cm)| 8.2| 8.2| 8.6| 8.6|
FY (cm)| 9.4| 10.6| 8.2| 8.6|
SSD (cm)| 87.2| 86.8| 85.6| 84.7|
Gantry (degrees)| 0| 223| 267| 320|
Wedge Angle(degrees)| 60/60| 60/33| 60/25| |
Dose Information: Absolute dose 5500 cGy (275 cGy / fraction)| Number of Fraction| 20| 20| 20| 20|
MU or min / Fraction| IN = 424.77OUT = 0| IN = 185.78OUT = 85.22| IN = 92.85OUT = 69.34| 16.39| Table 1: Beam Information and Dose Information for Patient

Figure 5: Lungs Image for Patient by CT-SIM: Philips Brilliance Big Bore

Beam Information|
Beam| 3LPO THORAX| 4ANT| 5MINI-ANT| 6LAO|
Nom. Acc. Pot.(MV or MeV)| 6| 6| 6| 6|
FX (cm)| 10.6| 10.1| 9.7| 14.2|
FY (cm)| 9.7| 14.3| 11| 10.1|
SSD (cm)| 86.3| 87.2| 87.2| 82.4|
Gantry (degrees)| 120| 0| 0| 60|
Wedge Angle(degrees)| 60/25| 60/28| 60/60| 60/9|
Dose Information: Absolute dose 4000 cGy (267 cGy / fraction)| Number of Fraction| 15| 15| 15| 15|
MU or min / Fraction| IN = 2291.07OUT = 1711.09| IN = 1277.72OUT = 793.65| IN = 1974.08OUT = 0| IN = 476.08OUT = 1301.50| Table 2: Beam Information and Dose Information for Patient
Design of multi-block chest phantoms
The first phantom was introduced to the experiment as shown in figure 7, in order to reduce the uncertainty within the results and to increase the accuracy all that because of the very inhomogeneous lung region that may led to poor dose distribution.

Figure 7: for Design 1 of the Multiblock phantom (first phantom) The specially designed phantom
Using measurements taken from 15 patients, who had previously been scheduled for lung radiotherapy, a second phantom consisting of multi-block components was designed. A multi-block phantom is essentially a phantom containing a number of blocks with different shapes and materials used to form an approximate cross-section of the patient. This facilitates taking measurements on the phantom volume to confirm the prescribed dose. A plan for the phantom was designed using similar field parameters, for example collimator settings, beam weightings, wedge fractions, and gantry angles as the clinical plan. The two lungs are presented in a lateral position, as shown in Figure 8 the heart is represented in the middle to reflect the correct anatomy and the lighter color in both Figures 7 and 8 represent the lungs.

Figure 8: Design 2 for the Multiblock phantom (second phantom), where (S-L) is skin and lung, and (L-H) is lung and heart. Table 3 shows the average distance between the skin, lungs and heart of the patient from the X-ray for the X and Y axes. The table also illustrates the maximum and minimum values for the X and Y axes, as well as the range of maximum and minimum values. Figure 8 illustrates the distance for X and Y axes between the skin, lungs and heart in the Multi-Block...

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