Experimental validation of Monte Carlo based treatment planning system in bone density equivalent media

Irradiation set-ups for measurements in 6 MV photon beam used for experimental verification of the Monaco ver. 5.11 treatment planning systems (TPS) calculation algorithm in the semi-anthropomorphic CIRS Thorax phantom. Reference and measuring points (I₁ to I₁₀) are shown in the last two columns; subscripts 1 to 10 correspond to the labelling in Figure 1

Set-up	Irradiation geometry	Field size [cm²]	SSD/SAD	Gantry angle [°]	reference point	measuring points
1	Single square fields	10×10	SSD	0	I₅	I₁, I₃, I_5-10
2		10×10	SAD	0	I₅	I, I, I_135-10
3		4×4	SAD	0	I₅	I_1-9
4		10×10	SAD	90	I₃	I_2-10
5	Rectangular field	10× 15	SAD	300	I₁	I₁, I₄, I_6-8, I₁₀
6	Single asymmetric fields	(6+8)×15	SAD	0	I₅	I_1-10
7		(3+8)×15	SAD	90	I₅	I, I_15-10
8		(4+10)×15	SAD	180	I₅	I_1-3, I_5-10
9		(3+7)×15	SAD	300	I₅	I_2-10
		12×10	SAD	0
10	4 fields (box)	12×10	SAD	180	I₅	I_2-5
		12×8	SAD	90
		12×8	SAD	270
		4×4	SAD	30
11	3 fields	16×4	SAD	90	I₅	I₂, I_5-9
		16×4	SAD	270
12	Diamond-shaped field	14×14	SAD	0	I₃	I₁, I₃, I_5-10
13	Irregular L shaped field	/	SAD	45	I₁	I_1-2, I_4-6, I_8-10
14	MLC cylinder shaped field	/	SAD	0	I₂	I_1,2, I₅, I_8,9, I₁₀
		16×4	SAD	90
15	3 non-coplanar fields	16×4	SAD	270	I₅	I₁, I_5-6, I_8, I₁₀
		4×4a	SAD	30

SAD = source to axis distance; SSD = source to surface distance

a Couch angle = 270^°

CT image of the CIRS Thorax phantom: water equivalent insert inside BDE part of the phantom **(A)**; a BDE insert inside bone density equivalent (BDE) part of the phantom **(B)** and cross-section of small “water cylinders” of different dimensions delineated inside BDE part of the phantom to find limits for calculating geometry where cavity theory applies (top right).

Mean percentage dose differences ${\bar{δ D}}_{m}$ and ${\bar{δ D}}_{w}$ between calculated and measured doses in different parts of the CIRS Thorax phantom (water, lung, and bone density equivalent materials) for both calculation options built in the Monaco TPS: dose-to-medium *D_m* and dose-to-water *D_w*. Error bars represent corresponding combined uncertainties.

Table 2

Differences $δ D_{m}$ and $δ D_{w}$ between two different calculation options in the Monaco ver. 5.11. treatment planning systems (TPS) and measured data obtained in the bone density equivalent (BDE) part of the CIRS Thorax phantom, according to Eqs. [1] and [2]. Two phantom assemblies and three simple beam setups were considered for this part of the study

Irradiation geometry (field, gantry)	Phantom assembly	$δ D_{m} [%]$	$δ D_{w} [%]$
(6+8) x 15 cm² Gantry = 0^°	standarda	- 2.9	2.9
(6+8) x 15 cm² Gantry = 0^°	non-standardb	- 0.7	- 0.2
(3+8) x 15 cm² Gantry = 90^°	standarda	- 3.0	5.1
(3+8) x 15 cm² Gantry = 90^°	non-standardb	- 0.7	- 0.1
(4+10) x 15 cm² Gantry = 180^°	standarda	- 5.7	5.4
(4+10) x 15 cm² Gantry = 180^°	non-standardb	0.5	1.3

a BDE insert with the ionization chamber placed in the BDE part of the phantom

b Water equivalent insert with the ionization chamber placed in the BDE part of the phantom

a BDE insert with the ionization chamber placed in the BDE part of the phantom

b Water equivalent insert with the ionization chamber placed in the BDE part of the phantom

a BDE insert with the ionization chamber placed in the BDE part of the phantom

b Water equivalent insert with the ionization chamber placed in the BDE part of the phantom

Table 3

Mean differences, ${\bar{δ D}}_{m}$ and ${\bar{δ D}}_{w}$ between calculated and measured doses in the bone density equivalent (BDE) part of the CIRS Thorax phantom for D_m and D_w calculation approaches, respectively. The absorbed doses were calculated using the Monaco ver. 5.11 treatment planning systems (TPS) in the center of delineated “water cylinders” of volume V, in the BDE part of the phantom. Corresponding combined uncertainties are denoted as u_c,m and u_c,w for dose-to-medium and dose-to-water calculation options, respectively

V [cm³]	${\bar{δ D}}_{m}$ [%]	u_c,m[%]	${\bar{δ D}}_{w}$ [%]	u_c,w[%]
0	- 3.9	2.1	4.4	1.9
0.035	- 2.6	1.5	2.5	1.9
0.141	- 1.4	1.3	1.8	1.7
0.279	- 0.3	1.2	1.2	1.5
0.573	0.3	1.4	0.4	1.3

Average differences ${\bar{δ D}}_{m}$ and ${\bar{δ D}}_{w}$ between calculated and measured doses in the bone density equivalent (BDE) part of the CIRS Thorax phantom, as a function of the volumes of the simulated “water cylinders” (see Figure 2 and Table 3). ${\bar{δ D}}_{m}$ and ${\bar{δ D}}_{w}$ are presented as individual values/points calculated using Eqs. [1] to, [4], and in the form of two analytical functions from Eqs. [9] and [10]. Error bars represent corresponding uncertainties within 95% confidence limits.

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DOI: https://doi.org/10.2478/raon-2020-0051 | Journal eISSN: 1581-3207 | Journal ISSN: 1318-2099

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Language: English

Page range: 495 - 504

Submitted on: Jun 10, 2020

Accepted on: Jul 9, 2020

Published on: Sep 16, 2020

Published by: Association of Radiology and Oncology

In partnership with: Paradigm Publishing Services

Publication frequency: 4 issues per year

Keywords:

treatment planning system,

dose-to-medium,

dose-to-water,

experimental validation of dose calculation,

Related subjects:

© 2020 Djeni Smilovic Radojcic, Bozidar Casar, David Rajlic, Manda Svabic Kolacio, Ignasi Mendez, Nevena Obajdin, Dea Dundara Debeljuh, Slaven Jurkovic, published by Association of Radiology and Oncology
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Volume 54 (2020): Issue 4 (December 2020)

Experimental validation of Monte Carlo based treatment planning system in bone density equivalent media

Figures & Tables

Figure 1

Table 1

Figure 2

Figure 3

Table 2

Table 3

Figure 4

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