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A. Caraman et al. / Journal of Advanced Research in Physics 6(1), 011601 (2016)
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A Comparison Between 3D Conformal
Radiotherapy, Intensity Modulated
Radiotherapy and Volumetric Modulated Arc
Therapy Techniques for Head and Neck
Cancer
Andrei Caraman1,*, Călin Gheorghe Buzea2, Silviana Ojica1,2, Mihaela Oprea1,2,
Alexandru Dumitru Zara1,2 and Dragoș Teodor Iancu1,3
Faculty of Physics, “Alexandru Ioan Cuza” University of Iași, Romania
Radiotherapy Department, Regional Institute of Oncology, Iași, Romania
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University of Medicine and Pharmacy „Grigore T. Popa”, Iași, Romania
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I. INTRODUCTION
Abstract — Although 3D Conformal Radiotherapy (3DCRT)
is the current standard technique in the treatment of head and
neck cancer, Intensity Modulated Radiotherapy (IMRT) and
the newly developed Volumetric Modulated Arc Therapy
(VMAT) are becoming increasingly used. VMAT is an
advanced form of IMRT that was introduced in 2007.
Volumetric Modulated Arc Therapy (VMAT) uses special
software and an advanced linear accelerator to deliver Intensity
Modulated Radiotherapy (IMRT) treatments up to eight times
faster than what was previously possible. The present study
compares treatment planning for a head and neck cancer case
using 3D Conformal Radiotherapy (3DCRT), Volumetric
Modulated Arc Therapy (VMAT) and Intensity Modulated
Radiotherapy (IMRT) techniques to find out which method is
most suitable in terms of target volume coverage and
preservation of organs at risk. The delivery of radiotherapy is
challenging due to the large size and constraints of normal
surrounding structures. Volumetric modulated arc therapy
(VMAT) allows for rapid delivery of highly conformal dose
distributions. To compare the Volumetric Modulated Arc
Therapy (VMAT) and Intensity Modulated Radiotherapy
(IMRT) plans to the original 3D Conformal Radiotherapy
(3DCRT) plan, dose-volume histograms (DVHs) were used. To
visualize the differences, average cumulative Dose Volume
Histograms (DVH) were calculated per examined tumor region
for each organ and treatment technique. For each patient 3D
Conformal Radiotherapy (3DRCT), Intensity Modulated
Radiotherapy (IMRT) and Volumetric Modulated Arc Therapy
(VMAT) plans were generated and the Conformity Index (CI),
organ at risk (OAR) doses and monitor unit (MU) were
evaluated. The investigation for head and neck cancer case
using Volumetric Modulated Arc Therapy (VMAT) technique
proved a significant sparing of organs at risk and healthy tissue
without compromising Planning Target Volume (PTV)
coverage compared to 3D Conformal Radiotherapy (3DCRT).
Keywords — 3D Conformal Radiotherapy, Intensity
Modulated Radiotherapy, Volumetric Modulated Arc Therapy,
Treatment Planning
Manuscript received May 11, 2016.
*Corresponding author ([email protected])
RADIATION therapy or radiotherapy, often abbreviated RT,
RT-x, or XRT, is therapy using ionizing radiation, generally
as part of cancer treatment to control or kill malignant cells
[1]. Radiation therapy may be curative in a number of types
of cancer if they are localized to one area of the body. It may
also be used as part of adjuvant therapy, to prevent tumor
recurrence after surgery to remove a primary malignant
tumor (for example, early stages of breast cancer) [2].
Radiation therapy is synergistic with chemotherapy, and has
been used before, during, and after chemotherapy in
susceptible cancers. Head and neck cancer is cancer that
starts in the lip, oral cavity (mouth), nasal cavity (inside the
nose), paranasal sinuses, pharynx, larynx or parotid glands.
Most head and neck cancers are biologically similar [3].
Around 90% of head and neck cancers are squamous cell
carcinomas, so they are called head and neck squamous cell
carcinomas (HNSCC) [2]. These cancers commonly
originate from the mucosal lining (epithelium) of these
regions. Head and neck cancers often spread to the lymph
nodes of the neck, and this is often the first (and sometimes
only) sign of the disease at the time of diagnosis. Head and
neck cancer is strongly associated with certain
environmental and lifestyle risk factors, including tobacco
smoking, alcohol consumption, UV light, particular
chemicals used in certain workplaces, and certain strains of
viruses, such as human papillomavirus [4]. These cancers
are frequently aggressive in their biologic behavior; patients
with these types of cancer are at a higher risk of developing
another cancer in the head and neck area. Radiotherapy (RT)
plays an important role in the treatment of oropharyngeal
cancer that is inoperable due to size or anatomical location
[5]. We compared the performance of 3D conformal
radiotherapy (3DCRT), intensity-modulated radiotherapy
(IMRT) and volumetric-modulated arc radiotherapy
(VMAT) to evaluate the best treatment technique for
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A. Caraman et al. / Journal of Advanced Research in Physics 6(1), 011601 (2016)
inoperable large volume oropharyngeal cancer. A
comparison of the Homogeneity Index (defined as (D2%D98%)/D50% (ICRU 83)), Conformity Index (defined as
the ratio between the volume receiving at least 95 % of the
prescribed dose and the PTV (ICRU 62)), OAR doses,
monitor units (MUs) and treatment delivery time was
evaluated.
II.
MATERIALS AND METHODS
The planning of radiation therapy treatment has been
revolutionized by the ability to delineate tumors and
adjacent normal structures in three dimensions using
specialized Computed tomography (CT) and/or Magnetic
Resonance Imaging (MRI) scanners and planning software.
Virtual simulation, the most basic form of planning, allows
more accurate placement of radiation beams than is possible
using conventional X-rays, where soft-tissue structures are
often difficult to assess and normal tissues difficult to protect
[5]. An enhancement of virtual simulation is 3-dimensional
conformal radiation therapy (3DCRT), in which the profile
of each radiation beam is shaped to fit the profile of the
target from a beam's eye view (BEV) using a multileaf
collimator (MLC) and a variable number of beams. When
the treatment volume conforms to the shape of the tumor, the
relative toxicity of radiation to the surrounding normal
tissues is reduced, allowing a higher dose of radiation to be
delivered to the tumor than conventional techniques would
allow [6]. An example can be seen in Figure 1 where the
radiation beams are set for one of the examined patients.
Intensity modulated radiation therapy (IMRT) is an
advanced type of high-precision radiation that is the next
generation of 3D Conformal Radiotherapy. IMRT also
improves the ability to conform the treatment volume to
concave tumor shapes, for example when the tumor is
wrapped around a vulnerable structure such as the spinal
cord or a major organ or blood vessel [7]. Computercontrolled x-ray accelerators distribute precise radiation
doses to malignant tumors or specific areas within the tumor.
The pattern of radiation delivery is determined using highly
tailored computing applications to perform optimization and
treatment simulation (Treatment Planning). The radiation
dose is consistent with the 3-D shape of the tumor by
controlling, or modulating, the radiation beam’s intensity.
The radiation dose intensity is elevated near the gross tumor
volume while radiation among the neighboring normal tissue
is decreased or avoided completely [8]. This results in better
tumor targeting, lessened side effects, and improved
treatment outcomes than even 3D Conformal Radiotherapy.
The beam setup in IMRT planning and also the better
coverage of tumor can be seen in Figure 2.
Volumetric modulated arc therapy (VMAT) is a new
radiation technique, which can achieve highly conformal
dose distributions on target volume coverage and sparing of
normal tissues. The specificity of this technique is to modify
the three parameters during the treatment. Volumetric
modulated arc therapy delivers radiation by rotating gantry
Fig. 1. 3D-CRT plan beam setup.
Fig. 2. Beam setup in IMRT planning.
Fig. 3. Volumetric Modulated Arc Therapy arc setup.
(usually 360° rotating fields with one or more arcs),
changing speed and shape of the beam with a multileaf
collimator (MLC) ("sliding window" system of moving) and
fluency output rate (dose rate) of the medical linear
accelerator [9]. VMAT also has the potential to give
additional advantages in patient treatment, such as reduced
delivery time of radiation, compared with conventional static
A. Caraman et al. / Journal of Advanced Research in Physics 6(1), 011601 (2016)
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field intensity modulated radiotherapy (IMRT) [9]. The
manner in which the treatment is delivered to the patient is
shown in Figure 3.
III. RESULTS
Our study analyzes the plans of treatment for 5 patients
with the age range from 20 to 64. Two subjects were female
and three were male. Patients were immobilized with a
thermoplastic mask in the supine position followed by
computed tomography (CT) scanning. The CT slices were
acquired every 3 mm. The 3D Conformal Radiotherapy,
Volumetric Modulated Radiotherapy and Intensity
Modulated Radiotherapy plans were created using the same
6 MV photon beams commissioned for a Varian Clinac iX
equipped with a 120 leaf Millennium MLC and variable
dose rate up to 600 MU/s. The treatment plans were
generated using the TPS (Treatment Planning System)
Eclipse (version 11) and Analitical Anisotropic Algorithm.
For the corresponding Volumetric Modulated Arc Therapy
and Intensity Modulated Radiotherapy plans we used ArcCheck 3D diode array from Sun Nuclear to check the
dosimetric accuracy. All cancers were large; a feature which
made surgery a less desirable treatment modality, with the
Planning Target Volume ranging from 417-745 cm3. The
minimum dose to the Planning Target Volume was
significantly lower for 3D Conformal Radiotherapy
compared to Intensity Modulated Radiotherapy and
Volumetric Modulated Arc Therapy plans, while there was
small difference in the maximum or mean dose to Planning
Target Volume. Due to significant inter-individual
variability in the homogeneity index within each plan type
(particularly for Volumetric Modulated Arc Therapy), the
overall homogeneity index was statistically similar for the
three plan types. Compared to Volumetric Modulated Arc
Therapy, Intensity Modulated Radiotherapy plans required
more Monitor Units (MU) on the machine (Table 1).
The mean dose to optic chiasm was statistically similar for
all three plan types. However, the mean dose to brainstem
was significantly lower for 3D Conformal Radiotherapy
(1730 cGy) compared to Intensity Modulated Radiotherapy
(2970 cGy) and Volumetric Modulated Arc Therapy (2830
cGy). There were no significant differences in the dose to
spinal cord for the Intensity Modulated Radiotherapy plans
compared to Volumetric Modulated Arc Therapy plans
(Table 2). The DVH (dose – volume histogram) for optic
chiasm at Intensity Modulated Radiotherapy and Volumetric
Modulated Arc Therapy were very similar. A typical plan
for a female patient with an oropharyngeal tumor is shown in
Fig. 4. Because VMAT technique uses several radiation
fields that means the tumor volume coverage will be better
than in case of 3DCRT, besides the treatment time will be
much shorter in VMAT case.
IV. DISCUSSION
Our findings confirmed the expectations that Volumetric
Modulated Arc Therapy achieves highly conformal dose
Fig. 4. PTV coverage comparison between 3DCRT and VMAT.
distribution with better target volume coverage and sparing
of normal tissues compared with conventional techniques. In
particular, Planning Target Volume coverage was found to
be similar for Intensity Modulated Radiotherapy and
Volumetric Modulated Arc Therapy, with both techniques
having superior conformity index compared to 3D
Conformal Radiotherapy (Table 1). We showed that
Volumetric Modulated Arc Therapy required less Monitor
Units (MU) on the machine compared to Intensity
Modulated Radiotherapy in this study. The lower Monitor
Units (MU) is also associated with less interleaf scatter dose
and reduced radiotherapy dose to normal tissues, thus
minimizing the risk of second radiation-induced
malignancies [10] which is of particular relevance when
delivering radiotherapy to young patients with
oropharyngeal cancer (age range 20–64 in our study).
Volumetric Modulated Arc Therapy was found to have
similar beam on time compared to Intensity Modulated
Radiotherapy and both required more beam on time
compared to 3D Conformal Radiotherapy. However, the
large number of fixed gantry field with Intensity Modulated
Radiotherapy approach increases the total treatment time
compared with Volumetric Modulated Arc Therapy and this
is likely to impact on intra-fractional patient movement and
clinical throughput of the radiotherapy department [11]. As
expected the mean dose to brainstem was significantly lower
for 3D Conformal Radiotherapy (1730 cGy) compared to
Intensity Modulated Radiotherapy (2970 cGy) and
Volumetric Modulated Arc Therapy (2830 cGy).
Nevertheless, reduced Organs At Risk (OAR) dose is
important to minimize late effects.
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A. Caraman et al. / Journal of Advanced Research in Physics 6(1), 011601 (2016)
TABLE I
VALUES OF THE CONFORMITY INDEX (CI), HOMOGENITY INDEX (HI) AND CALCULATED MONITOR UNITS (MU) FOR ALL TREATMENT
METHODS: 3D CONFORMAL RADIOTHERAPY (3DCRT), VOLUMETRIC MODULATED ARC THERAPY ( VMAT) AND INTENSITY MODULATED RADIOTHERAPY
(IMRT)
Patient
Patient 1
Patient 2
Patient 3
Patient 4
Patient 5
Conformity Index (CI)
3DCRT
VMAT
1.31
1.07
0.96
1.07
1.29
1.06
1.27
1.06
1.19
1.05
IMRT
1.09
1.20
1.10
1.14
1.18
Homogeneity Index (HI)
3DCRT
VMAT
IMRT
0.25
0.17
0.11
0.33
0.10
0.09
0.25
0.10
0.09
0.26
0.11
0.10
0.29
0.12
0.09
Monitor Units (MU)
3DCRT
VMAT
438
502
308
541
925
539
745
389
310
337
IMRT
1389
1101
1131
1221
1465
TABLE II ORGAN AT RISK (OAR) DOSE EVALUATION FOR ALL TREATMENT METHODS: 3DCRT, VMAT AND IMRT
Patient
Patient 1
Patient 2
Patient 3
Patient 4
Patient 5
Brainstem
3DCRT
VMAT
(cGy)
(cGy)
IMRT
(cGy)
4200
5170
5470
5330
5900
4900
5900
4920
5200
5000
5000
4630
4940
5900
5870
Maxim
admitted
value
(cGy)
5900
Organs At Risk (OAR) sparing was similar or only slightly
better for Volumetric Modulated Arc Therapy compared to
Intensity Modulated Radiotherapy in head and neck cancers
[9]. The endpoints for the target included mean, minimum,
and maximum Planning Target Volume doses. It also
included conformity index and homogeneity index. To
compare the Volumetric Modulated Arc Therapy and
Intensity Modulated Radiotherapy plans to the original 3D
Conformal Radiotherapy plan, dose-volume histograms
(DVHs) were used. To visualize the differences, average
cumulative DVHs were calculated per examined tumor
region for each organ and treatment technique. The
investigation for head and neck cancer case using
Volumetric Modulated Arc Therapy technique proved a
significant sparing of organs at risk and healthy tissue
without compromising target volume coverage compared to
3D Conformal Radiotherapy.
IMRT
(cGy)
4200
4570
4550
4560
4750
3700
4360
4170
4190
4340
3500
4100
3840
4390
4700
Maxim
admitted
value (cGy)
4500
reduced. This could allow dose escalation by Volumetric
Modulated Arc Therapy to tumor in close proximity to the
spinal cord, so that local tumor control could be enhanced.
In contrast, the reduction of the Organs At Risk (spinal cord)
irradiation in 3D Conformal Radiotherapy treatments to
avoid the risks of late toxicity necessitates a compromise of
the dose to the Planning Target Volume. Apart from the
above-mentioned superiority of the Volumetric Modulated
Arc Therapy plans, treatment time (beam on and set-up time)
and efficiency is another important issue. Since this
technique appeared a multitude of people have been treated
for cancer. There is no doubt that VMAT technique changed
the radiotherapy in better way.
REFERENCES
[1]
[2]
V. CONCLUSIONS
Our findings show that both Intensity Modulated
Radiotherapy and Volumetric Modulated Arc Therapy
provided superior Planning Tumor Volume coverage and
improved Organ At Risk (OAR) sparing compared to 3D
Conformal Radiotherapy. Volumetric Modulated Arc
Therapy was associated with reduced Monitor Units (MU)
compared to Intensity Modulated Radiotherapy. Compared
to 3D Conformal Radiotherapy plans, Volumetric
Modulated Arc Therapy plans provide better dose
homogeneity and highly conformal dose distributions. Doses
to Organs At Risk (OAR) such as the spinal cord were also
Spinal cord
3DCRT
VMAT
(cGy)
(cGy)
[3]
[4]
[5]
[6]
L. Licitra, J. Bernier, C. Grandi, M. Merlano, P. Bruzzi, and J.L.
Lefebvre, “Cancer of the oropharynx”, in Critical Review of
Oncology and Hematology, 1, 2002, pp. 107-122.
M.L. Gillison, et al., “Evidence for a causal association between
human papillomavirus and a subset of head and neck cancers”, J.
Natl. Cancer. Inst., 2000, 3, 2000, pp. 265-278, DOI:
10.1093/jnci/92.9.709.
J.J. Nuyttens, P.F. Rust, C.R. Thomas Jr, A.T. Turrisi 3rd, “Surgery
versus radiation therapy for patients with aggressive fibromatosis or
desmoid tumors: A comparative review of 22 articles”, Cancer, 14
2000, pp.132-140.
World Health Organization IARC monographs on the evaluation of
carcinogenic risk to humans. Vol.90: Human papillomaviruses, Ed.
Agency for Research on Cancer, Lyon (France), 2007, pp. 350-412.
L. Hammarstedt, et al., “Human papillomavirus as a risk factor for
the increase in incidence of tonsillar cancer”, Int. J. Cancer, 11,
2006, pp.119-125.
M. Teoh, C.H. Clark, K. Wood, S. Whitaker, A. Nisbet, “Volumetric
modulated arc therapy: a review of current literature and clinical use
in practice”, Br. J. Radiol., 84, 2011, pp. 1007-1012, DOI:
10.1259/bjr/22373346.
A. Caraman et al. / Journal of Advanced Research in Physics 6(1), 011601 (2016)
[7]
D. Lindquist, et al., “Human papillomavirus is a favourable
prognostic factor in tonsillar cancer and its oncogenic role is
supported by the expression of E6 and E7”, Mol. Oncol. J., 3, 2007,
pp. 350-355.
[8] B.A. Guadagnolo, G.K. Zagars, M.T. Ball, “Long-term outcomes for
desmoid tumors treated with radiation therapy”, Int. J. Radiat. Oncol.
Biol. Phys., 88, 2008, pp. 243-268.
[9] M.A. Spear, et al., “Individualizing management of aggressive
fibromatoses”, Int. J. Radiat. Oncol. Biol. Phys., 40, 1998, pp. 637–
645.
[10] C. Chew, R. Reid, P.J. O’Dwyer, “Evaluation of the long term
outcome of patients with extremity desmoids” Eur. J. Surg. Oncol.,
15, 2004, pp. 163-182.
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