Page 96 - ARNM-3-2

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

(version 9.1, OriginLab Corporation, USA). A paired t-test tissue inhomogeneities at certain quality levels. However,
was performed to compare the means of ICFs. This test beyond the reference beam quality, ICFs begin to rise
is appropriate to evaluate whether the mean difference again – a behavior likely driven by complex alterations in
between paired observations is statistically significant. In scatter and attenuation within lung tissue. Relative to the
our analysis, a p<0.05 indicates a significant difference. reference, ICFs varied by 16.3% for 6 MV and 12.5% for 15
MV beams, emphasizing the sensitivity of dose corrections
3. Results and discussion to beam quality fluctuations. These observations highlight
This study thoroughly evaluated how variations in the beam the critical importance of precise ICFs determination
QI (TPR 20,10 ) influence ICFs in 3DCRT treatment plans by during treatment planning, particularly for lung tumors,
employing 6 MV and 15 MV photon beams, which are to maintain accurate dose delivery. 19,20
widely used for clinical purposes. A substantial number In contrast, the mean ICFs for gynecology cases show
16
of treatment plans were analyzed, ensuring a robust dataset only minor variation – remaining below 2.0% for 6 MV
for interpretation. The ICF values for lung, gynecological, and below 1.0% for 15 MV beams (Figure 3C and D) –
and prostate tumors are illustrated in Figure 2A and B (at
a specific gantry angle, with the baseline beam qualities indicating that beam quality exerts a minimal influence
established at 0.670 for 6 MV and 0.760 for 15 MV. In lung on dose distribution in these tissues. Prostate treatments
cases, ICFs were observed to increase with higher beam also display a non-linear relationship between ICFs and
quality indices, while gynecology cases exhibited only beam quality, with maximum variations of 8.5% for 6 MV
minimal changes, and prostate cases showed a decrease. and 6.3% for 15 MV beams (Figure 3E and F), suggesting
These trends confirm a consistent relationship between that ICFs in prostate cases are somewhat more sensitive
beam quality and ICFs across different treatment sites, in to changes in beam quality. In addition, in intensity-
line with previous studies. 17,18 Specifically, for 6 MV beams, modulated radiation therapy using 6 MV beams,
ICFs variations were 5.6% for lung, <1.0% for gynecology, incorporating inhomogeneity corrections resulted in an
and 1.7% for prostate tumors. For 15 MV beams, the average decrease of 5.0% in the prescription point dose. 21
corresponding variations were 4.9%, 0.5%, and 1.0%, For lung SBRT treatment plans, a 5.6% difference in
respectively. the beam QI – from 0.632 to 0.688 – between 6 MV and

Figure 3A-F presents the mean ICFs as a function of 6 MV FFF beams resulted in an ICFs variation of <3.0%
the beam QI for lung, gynecological, and prostate tumors (Figure 4). This relatively small change indicates that,
treated with 3DCRT with both photon energies. In lung within the SBRT setting, beam quality variations have
cases, the ICFs behavior is non-linear for both 6 MV and only a limited effect on dose distribution in lung tissue,
15 MV beams (Figure 3A and B). Initially, ICFs decline regardless of the use of a flattening filter. However, it is
as the beam QI increases, suggesting a reduced impact of important to note that Ding et al. reported that differences

A B

Figure 2. The relationship between inhomogeneity correction factors (ICFs) and the beam quality index as a function of beam quality index (TPR 20,10 )
for lung, gynecology, and prostate tumors treated with the three-dimensional conformal radiotherapy technique using 6 MV (A) and 15 MV (B) photon
energies. At a TPR 20,10 of 0.670, the absolute ICFs values were 1.233 for lung, 1.051 for gynecology, and 0.916 for prostate tumors. At a TPR 20,10 of 0.760, the
corresponding ICFs were 1.117 for lung, 1.032 for gynecology, and 0.940 for prostate tumors.

Volume 3 Issue 2 (2025) 88 doi: 10.36922/arnm.6851