Page 95 - ARNM-3-2

Advances in Radiotherapy
& Nuclear Medicine Influence of photon beam quality in radiotherapy

and Measurements Reports 50 and 62, the total error A total of 90 patients – comprising 30 cases each of lung,
in radiotherapy, encompassing activities such as target gynecological, and prostate tumors – were selected to study
delineation, treatment planning, dose calculation, patient the impact of tissue inhomogeneities on dose calculation
positioning, and treatment delivery, should remain under in treatment planning. Each patient received treatment
5%. To maintain this degree of accuracy, systematic using the three-dimensional conformal radiotherapy
4,5
quality assurance procedures for computerized treatment (3DCRT) technique, facilitated by a Varian Clinac 2300CD
planning systems (TPSs) have been established by several linear accelerator equipped with 120 multileaf collimators
task groups over the past decades. These recommendations (MLCs) (Varian Medical System, Palo Alto, USA), at the
cover areas such as anatomical and beam descriptions, dose Maria Sklodowska-Curie National Research Institute of
calculations, as well as data output and transfer. Nowadays, Oncology in Warsaw, Poland. The treatment plans for lung,
3D TPSs that utilize a range of dose calculation algorithms gynecology, and prostate cases, represented in Figure 1A-C,
are widely employed in radiotherapy planning. 6-9 respectively, were recalculated without incorporating
For inhomogeneous geometries, comparing measured beam modifiers, and ICFs were determined for each beam
and calculated dose distributions in the presence of tissue angle by comparing dose distributions computed with and
inhomogeneities is essential, typically using inhomogeneity without inhomogeneity corrections. All calculations were
correction factors (ICFs). However, acquiring these carried out at the isocenter.
measurements is challenging due to the time and In addition, the ICFs for fifteen lung tumor patients
resources required. Some studies have reported findings treated using stereotactic body radiation therapy (SBRT)
on these measurements, 10-13 yet questions on whether ICFs were determined. For these cases, treatment plans were
determined by one institution can be applied universally created using 6 MV photons with a QI of 0.668 from a
and how variations in a user’s beam quality index (QI) Varian TrueBeam linear accelerator (equipped with a
might influence the results remain unanswered. 120-leaf MLC) (Varian Medical System, Palo Alto, USA)
This research aims to investigate the effects of changes and were generated using multiple arcs (clockwise and
in the beam QI, particularly the tissue phantom ratio anticlockwise, with angles defined according to the Varian/
(TPR 20,10 ) on ICFs in external beam radiation therapy IEC scale) (manufacturer, country). An example of SBRT
treatment plans. plan is shown in Figure 1D. These SBRT plans were then
recalculated with a 6 MV flattening filter-free (FFF) photon
2. Materials and methods beams employing beam quality of 0.632, and ICFs were
computed for both beam qualities. Along with the 3DCRT
Photon energies of 6 MV and 15 MV were utilized to cases, the ICFs for the SBRT plans were calculated at the
evaluate the correlation between ICFs and the beam QI isocenter.
(TPR 20,10 ). The TPR 20,10 values varied within the following
range: To compare ICFs calculated among various beam
qualities, we conducted a statistical analysis using Origin
20
(TPR = 0.67 k± *0.01) for 6 MV, k = −3, −2, −1, 0, 1, 2, 3
10
20
(TPR = 0.76 k± *0.01) for 15 MV, k = −3, −2, −1, 0, 1, 2, 3 A B
10
For each energy level, TPR 20,10 values were collected
from the Secondary Standard Dosimetry Laboratory at
the Maria Sklodowska-Curie National Research Institute
14
of Oncology in Warsaw, Poland. Subsequently, ICFs were
determined using the Eclipse version 13.6 TPS by Varian
Medical Systems (Palo Alto, CA) with the anisotropic C D
analytical algorithm.
For every TPR 20,10 value, a separate set of percent depth
dose (PDD) curves was generated for field sizes ranging
from 5 × 5 to 30 × 30 cm² using Gerbi’s formula. The same
15
beam profiles and output factors measured for 6 MV and
15 MV beams, corresponding to TPR 20,10 values of 0.670
and 0.760, respectively, were applied. As Gerbi’s formula
provides PDDs at a source-to-surface distance (SSD) of Figure 1. The three-dimensional conformal radiotherapy and stereotactic
body radiation therapy (SBRT) treatment plans generated using Eclipse
100 cm, these values were converted to an SSD of 90 cm treatment planning system: (A) Lung; (B) Gynecology; (C) Prostate; and
using Mayneord’s factor (F) before being input into the TPS. (D) Lung SBRT plan

Volume 3 Issue 2 (2025) 87 doi: 10.36922/arnm.6851