Page 27 - ARNM-2-1

Advances in Radiotherapy
& Nuclear Medicine Is 5-mm PTV margin 4D-CT-based radiotherapy

to unnecessary irradiation of at-risk organs. In contrast, of 0.15,0.33, and 0.21 cm and δ x,y,z of 0.14,0.46, and 0.23 cm
the plans generated based on the 4D-CT-based volume with a required PTV margin of 0.69 cm, 1.16 cm, and
are smaller and cannot adequately cover the FBCT-based 0.47 cm in the X, Y, and Z axes. The corrected translational
volume. This does not necessarily mean inferior PTV vector resulted in a systematic and random error of 0.11
coverage, as we have seen in our study that none of the and 0.3 cm, with a required PTV margin of 0.48 cm. Shifts
patients experienced locoregional recurrence. of more than 5 mm in the X, Y, and Z axes were noted in
Response assessment scans were performed 4 weeks 1%, 32.67%, and 7.9% of cases, respectively.
to 3 months after the completion of concurrent 4. Discussion
chemoradiotherapy. Those planned for adjuvant durvalumab
had a response assessment CT scan at 4 – 6 weeks; otherwise, Our study revealed that 4D-CT-based radiotherapy
patients underwent a response assessment scan 3 months planning for locally advanced lung cancer with a reduced
after the completion of treatment. Forty percent of patients PTV margin of 5 mm can significantly reduce PTV and
developed a complete response. Forty-eight percent of the OAR doses without compromising PTV coverage compared
patients developed a partial response. Two patients had a to FBCT-based planning with a population-based PTV
stable disease (Table 4). Locoregional progression was not margin. This study will also help other centers set up 4D-CT
observed. Four patients who developed progressive disease image-based guided radiotherapy for locally advanced lung
recurred distally (two patients progressed in the brain, one cancer with a reduced PTV margin, provided they meet
in the abdominal nodes, and the other in the liver). These standard licensing requirements and have trained staff
four patients already had M1 disease but were treated and facilities for real-time position management systems,
radically in view of oligometastatic disease. infrared cameras, and infrared reflective markers.

We retrospectively analyzed the setup data (CBCT) of Previously, most radiotherapy centers used helical
1,010 fractions of 50 patients for PTV coverage and shifts. FBCT for lung radiotherapy contouring and planning.
Offline imaging verification of uncorrected setup errors This FBCT is associated with several inherent problems:
revealed that 95% (960 fractions) of the time, the primary (i) it does not account for breathing movement; (ii) it often
tumor was within the PTV. After image matching and produces distorted images owing to motion artifacts during
correction, we got a systematic and random error of ∑ x,y,z the CT scan; (iii) it may result in blurred gross tumors
due to respiratory and tumor motion and may create
uncertainties in target delineation, which will eventually
lead to suboptimal target coverage and unnecessary
dose to OARs. Considering the respiratory motion, the
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4D-CT scan reconstructs the 3D volume as a function of
time. Multiple 3D imaging datasets reflecting the entire
trajectory of the lung tumor and OARs were produced by
the 4D-CT scan. The ITV, consisting of the total GTV, is
determined by considering all imaging datasets. Therefore,
when planning 4D-CT-based lung radiation, a narrower
PTV margin can be employed, but only to account for daily
setup uncertainties. 21
Numerous researchers have assessed 4D-CT’s
usefulness in radical lung radiation treatment. In their
study, Rietze et al. demonstrated that the GTV contoured
on a helical CT scan was less than the GTV calculated as a
Figure 2. Histogram showing Dice similarity coefficient.
summation of all phases of the respiratory cycle from 4D
datasets (39.9 vs. 24.4 cm ). They also highlighted how the
3
Table 4. Radiological response to treatment geometry of the GTV obtained from a helical scan was
RECIST criteria response Number (N=50) Percentage modified by image artifacts[14]. Alasti et al. compared
Complete response 20 40 4D-CT-based planning and helical CT-based planning in
Partial response 24 48 24 NSCLC patients, revealing that the GTV determined
by helical CT was approximately 25% smaller than that
Stable disease 2 4 determined by 4D-CT. In addition, they demonstrated that
Progressive disease 4 8 in comparison to traditional helical CT-based planning,

Volume 2 Issue 1 (2024) 6 https://doi.org/10.36922/arnm.2784