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

1. Introduction with locally advanced lung cancer between helical FBCT
and 4D-CT. In addition, we assessed the feasibility of
Lung cancer ranks as the second most common cancer with achieving a lower PTV margin with 4D-CT planning.
an incidence of 11.6% and carries the highest mortality
rate at 18.4%. Radiotherapy is a common component of 2. Methods
1
the multimodal management of lung cancer. The most
common course of treatment for locally advanced or stage 2.1. Participants
III non-small cell lung cancers (NSCLCs) is concurrent This prospective, non-randomized cohort study was
chemoradiotherapy or radical radiotherapy alone. conducted at a tertiary cancer care center in Eastern
2,3
Similarly, patients with limited-stage small-cell lung cancer India between January 2021 and March 2023. Ethical
and certain stage IV NSCLC patients with oligometastatic approval for this study was obtained from the Institutional
disease are also treated with radical radiotherapy. For Ethics Committee of Apollo Multi-Speciality Hospital,
patients with early-stage NSCLC (stages I and II) who are Kolkata (approval no.: IEC/2021/DNB/04/17). The
not suitable candidates for surgery or stereotactic adjuvant inclusion criteria were as follows (i) Age: 18 – 70 years
radiotherapy (SABR), radiotherapy alone or combined old; (ii) biopsy-proven lung cancer (NSCLC or SCLC);
with other multimodality management strategies can be (iii) locally advanced NSCLC (stage III); (iv) early-stage
employed. However, a significant percentage of lung NSCLC (stages I and II) who are not suitable for surgery
4-6
cancer patients experience locoregional recurrence after or SABR; (v) limited stage small cell lung cancer; and
treatment with radiotherapy or chemo-radiotherapy. (vi) patients receiving a radiotherapy dose of 60 – 66 Gy in
1,7
Although the reason for such recurrence is multifactorial, 30 – 33 fractions over 6 – 6.6 weeks, possessing adequate
geographical misses and suboptimal doses of gross lung function to undergo definitive radiotherapy, and
disease secondary to tumor motion play a pivotal role. willingness to provide consent for participation in the
Conventionally, helical free-breathing CT scans (FBCT) study. The exclusion criteria were as follows (i) patients not
have been the standard for lung radiotherapy treatment willing to provide consent; (ii) patients unable to cooperate
planning for many years. during 4D-CT scanning; and (iii) patients receiving

In general, a population-based safety margin is used palliative radiotherapy.
around both gross disease (gross tumor volume [GTV]) 2.2. Helical FBCT and 4D-CT procedure
and microscopic disease (clinical target volume [CTV]) to
determine the final radiotherapy planning target volume Helical FBCT and 4D-CT planning scans were derived
(PTV). However, lung tumors can move erratically during during the same session with the patient in the same
8
respiration in an unpredictable manner. The inability treatment position. The standard institutional protocol was
to encompass the range of tumor motion might lead to adhered to for FBCT imaging. The patient’s breathing cycle
inadequate tumor coverage, and using larger generalized was monitored for 4D-CT image capture using either the
population-based margins can cause unnecessary toxicity real-time position management system (Varian Medical
to nearby organs at risk (OARs). 9-11 4D-Computed Systems Inc., USA) or the Philips bellows device (Philips
tomography (4D-CT) has shown promising results in Healthcare, USA), employing infrared reflector markers
10,16
mitigating motion management issues associated with and infrared cameras. The GTV_3D was contoured
radiotherapy in lung cancer. 4D-CT scans have become on an FBCT scan using fluorodeoxyglucose positron
12
the standard to derive detailed information regarding the emission tomography (PET) image fusion to identify
pattern and range of respiratory motion. Since tumor primary and/or nodal illness. The number of nodes and
13
motion is inherently considered when using 4D-CT scans, mediastinal disease were contoured on the mediastinal
a smaller safety margin for set-up error (PTV) can be window, whereas parenchymal tumors were contoured
used during lung radiotherapy planning. In 76% of the at the lung window level. The CTV_3D was created by
14
treatment fractions, Steiner et al. demonstrated that a 5-mm expanding the GTV_3D by 5 mm in all directions and
PTV margin was sufficient to capture the 4D-CT-based then modifying it to remove natural barriers, such as air
motion data, with brief intervals of excess motion (varying and bone. To account for internal margin and setup faults,
from 1% to 20% of the treatment period). However, there the PTV_3D was calculated as CTV_3D + 1 cm axial and
15
is a risk of geographical miss with a very small PTV margin 1.3 cm superior/inferior expansions. Organs at risk were
when setting up 4D-CT-based image-guided radiotherapy contoured according to the standard Radiation Therapy
17
(IGRT) for lung cancer. In this study, we aimed to compare Oncology Group (RTOG) contouring guidelines.
the dosimetric and volumetric differences in target volume A fusion of PET-CT was used for 4D-CT-based
delineation for radical radiotherapy planning in patients contouring whenever available, although it was not

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