












































International Journal of Cancer Therapy and Oncology
www.ijcto.org

Copyright © Gill ISSN 2330-4049

Treatment planning for the lung cancer

Sukhdeep Gill

Department of Radiation Oncology, University of Toledo, Toledo, Ohio, USA.

Received February 13, 2014; Revised March 10, 2014; Accepted March 12, 2014; Published Online March 16, 2014

Letter to editor

Volumetric modulated arc therapy (VMAT) and intensity
modulated radiation therapy (IMRT) are commonly used
treatment techniques for cancer treatment, and both the
VMAT and IMRT techniques use the photon beam
(mega-voltage X-rays) to deliver radiation dose to the tumor.
The capability of modulating radiation beam has increased
the ability of delivering more conformal dose distributions to
tumor volume while minimizing dose to the normal tissues.
The VMAT planning generally involves one or multiple arcs
with gantry rotating around the patient, whereas the IMRT
planning involves multiple static beams.

Current literature on radiation therapy for the lung cancer
shows the publication of good number of dosimetric studies,
which are typically focused on the treatment planning tech-
niques 1-7 and dose calculation algorithms.8-16 The treatment
planning studies comparing the dosimetric quality between
the IMRT and VMAT, however, do not provide the defini-
tive conclusion, especially for the normal lung tissue. For
example, Verbakel et al. 1 performed the dosimetric study on
14 lung cancer cases and compared the IMRT and VMAT
plans. It was reported that the V5 of the normal lung tissue
was higher in the VMAT plans than in the IMRT plans. Ong
et al. 2 and Jiang et al. 3 also reported higher V5 of the lung in
the VMAT plans. The V5 of the lung from these studies 1-3
show that the IMRT could be better at sparing the lung than
the VMAT. However, the VMAT plans could produce lower
values for the lung if dosimetric evaluation is done using
different parameters. In the study by Jiang et al. 3, normal
lung was also evaluated for the mean dose, V20, and V30,
and the results showed lower values in the VMAT plans than
in the IMRT plans.3 This leads to the question- which dosi-
metric parameter for the normal lung tissue is more im-
portant when plan evaluation is done?

In addition to the sparing of normal tissues, the target cov-
erage and dose homogeneity within the target volume are
also equally important in radiation therapy. Jiang et al. 3
found that the VMAT could produce better target coverage
when compared to the IMRT. However, Rao et al. 4, who
performed study on 8 lung cases, found comparable target
coverage in the VMAT and IMRT plans. Dose to the target
volume was found to be similar in the VMAT and IMRT
plans.3-5

The variation in the reported results from various studies on
lung cancer 1-7 can be attributed to different factors such as
plan optimization technique, experience of the treatment
planner, treatment volume margins, dose prescription, loca-
tion of the tumor, and dose calculation algorithms. The
treatment plan optimization interface within the treatment
planning system can let the user to assign weightings and
objectives for the target and normal tissues. The final dosi-
metric results in the treatment plan may depend on the se-
lection of weightings and objectives for the structures. Addi-
tionally, the plan optimization can be repeated with same set
of optimization parameters or different ones if the dosimetric
results have deviation from the compliance criteria.

Dose calculation algorithm incorporated in the treatment
planning system can also affect the dosimetric results of the
treatment plans, especially for the lung cancer, which in-
cludes the low-density medium. When radiation beam
traverses the human body before it reaches the tumor, tissues
of different electron density are encountered in the beam
path. Presence of heterogeneity along the beam path may
change the dose contribution to the tumor when compared
to the homogeneous geometry. Such situation requires the
dose calculation algorithm to consider the tissue heterogene-
ity correction when dose computations are performed on the
cancer treatment plans.

Recent literature shows that the Monte Carlo based dose
calculation algorithm is more appropriate for dose computa-
tions in the lung plans.8-10 Several investigators compared the
analytical anisotropic algorithm (AAA) with the most recent
algorithm called Acuros XB for the lung plans 9-16, and vali-

Corresponding author: Sukhdeep Gill; Department of Radiation
Oncology, University of Toledo, Toledo, Ohio, USA.

Cite this article as:
Gill S. Treatment planning for the lung cancer. Int J Cancer Ther
Oncol 2014; 2(1):020117. DOI: 10.14319/ijcto.0201.17

http://ijcto.org/index.php/IJCTO/index
http://dx.doi.org/10.14319/ijcto.0201.17


2 Gill: Treatment planning for the lung cancer International Journal of Cancer Therapy and Oncology
www.ijcto.org

Copyright © Gill ISSN 2330-4049

dation studies on Acuros XB show its superiority over the
AAA, especially in inhomogeneous media.8-9, 11, 17-18 The
beam modeling within the Acuros XB algorithm considered
to be based on the Monte Carlo approach.18

The literature comparing the AAA and Acuros XB in the
lung plans showed that the Acuros XB could produce higher
values for the V20 11, 12 and V5.10-12 If the Acuros XB is con-
sidered to be more accurate than the AAA, does the AAA
underestimate the lung dose? It was also reported that the
higher number of monitor units (MUs) will be required for
the Acuros XB in order to achieve the target coverage similar
to that of the AAA.9 The decreased target coverage using
Acuros XB for the same number of MUs as in the AAA plans
may not be clinically acceptable. If the treatment planning
systems have an option to normalize the plan (e.g., target
volume receiving certain percentage of the prescription
dose), the Acuros XB plans can be normalized to achieve the
desired target coverage, but such method may also increase
the MUs, and this will increase the normal tissue dose and
hot spot. Hence, treatment plans computed with different
dose calculation algorithms are likely to provide different
dosimetric results. Treatment plans calculated with different
beam energy may also produce difference dosimetric re-
sults.19, 20

Although there are uncertainties in the dosimetric results
between the IMRT and VMAT plans, the common agree-
ment among different published studies 1-7 is the decreased
delivery time and a smaller number of MUs using the VMAT
than using the IMRT. Clinical trials comparing the IMRT
and VMAT may be more helpful in establishing superiority
of one technique over another. Multi-institutional study
using the same dataset, beam parameters, and dose calcula-
tion algorithms/treatment planning system would help in
reducing the uncertainties in the dosimetric results of the
lung treatment plans. Studies based on the radiobiological
models in the treatment planning could also be beneficial for
more accurate prediction of tumor control and normal tissue
complication.21

Conflict of interest

The authors declare that they have no conflicts of interest.
The authors alone are responsible for the content and writ-
ing of the paper.

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