Shinshu Med J, 65⑵：93～98, 2017

Dosimetric Comparisons of Volumetric Modulated Arc Therapy
with Three-Dimensional Conformal Radiation Therapy for Locally
Advanced Non-Small Cell Lung Cancer
Takesumi Ozawa＊, Keiichiro Koiwai, Hirohide Matsushita and Masumi Kadoya
Department of Radiology, Shinshu University School of Medicine

Purpose : To evaluate the dosimetric differences between volumetric modulated arc therapy (VMAT) andthree-dimensional conformal radiation therapy (3D-CRT) for locally advanced non-small cell lung cancer (NS­
CLC).
Materials and methods : A planning study was performed with the data of 17 patients with inoperable NSCLC
who actually underwent definitive radiotherapy. VMAT and 3D-CRT plans were created for each patient. The
primary objectives of these plans were to prescribe 60 Gy in 30 fractions to 95% of the planning target volume
and to limit the dose delivered to the spinal cord to less than 50 Gy. The secondary objectives were to keep thedoses delivered to other risk organs as low as possible.
Results : The 3D-CRT plans for two patients did not achieve the primary objectives, although they wereachieved by the VMAT plans for these patients. In a comparison of the acceptable plans, the VMAT plans im­proved the dose conformity, V20 and mean dose of the lung, and V35 of the oesophagus. There were no signifi­
cant differences in V10 or V5 of the lung, or the maximum dose and mean dose of the oesophagus.
Conclusion : The advantage of VMAT compared to 3D-CRT may facilitate appropriate use of VMAT for pa­
tients with locally advanced NSCLC. Shinshu Med J 65 : 93―98, 2017
(Received for publication October 31, 2016 ; accepted in revised form December 7, 2016)
Key words : non-small cell lung cancer, volumetric modulated arc therapy, three-dimensional conformal
radiation therapy, treatment planning comparison

Ⅰ Introduction

the organs at risk (OAR) is often difficult to achieve.
Although this dilemma has been partially resolved

Radiotherapy plays a key role in the treatment ofwith the advent of three-dimensional conformal ra­

inoperable locally advanced non-small cell lung can­diation therapy (3D-CRT), a number of problems re­1）

cer (NSCLC) . Although radiotherapy is recognized

main. Intensity-modulated radiation therapy (IMRT)

as the standard of care for advanced NSCLC, signifi­

has been expected to solve some of these issues,

cant challenges remain regarding this therapy. The

and has recently been utilized in clinical settings2）-4）.

lungs are surrounded by critical organs, such as theVolumetric modulated arc therapy (VMAT) is an

spinal cord, oesophagus, and heart. Furthermore, theadvanced form of IMRT that efficiently provides

lung itself is vulnerable to radiation. Delivering

highly conformal dose distributions with rotation

the prescribed doses to the planning target volumeof the gantry. Several planning studies showed that

(PTV) while preventing intolerable irradiation of

VMAT, especially partial arc (PA)-VMAT, has some＊Corresponding author : Takesumi Ozawa
Department of Radiology, Shinshu University School of
Medicine, 3-1-1 Asahi, Matsumoto, Nagano 390-8621 Japan
E-mail : tozawa@shinshu-u.ac.jp

No. 2, 2017

advantages compared with conventional IMRT in
the treatment of locally advanced NSCLC5）6）. Howev­
er, there have been few studies related to the benefitsof VMAT compared with 3D-CRT in consecutive
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Ozawa・Koiwai・Matsushita et al.

patients. In this study, we investigated the dosimetricwith the anisotropic analytical algorithm. The 3D-

differences between VMAT and 3D-CRT plans and

CRT plans typically consisted of four beams ar­evaluated whether VMAT is more beneficial than 3D-

ranged with anterior-posterior (AP) opposed beams

CRT in the treatment of locally advanced NSCLC.
Ⅱ

Materials and Methods

The institutional review board of our hospital ap­
proved this retrospective study, and the require­and oblique off-cord opposed beams. The VMAT
plans typically consisted of two partial coplanar arcs.
Irradiation was avoided on the lateral sectors (40°140°, 220°-320°) to prevent excessive irradiation of
the normal lung tissue.

ment to obtain informed consent from study patients

The primary objectives of planning were to pre­was waived. Seventeen patients with inoperable lo­

scribe 60 Gy in 30 fractions to 95% of the PTV andcally advanced NSCLC who underwent definitive

to limit the dose delivered to the spinal cord PRV <radiotherapy between January 2013 and August

50 Gy. The secondary objectives were to keep the2014 at our institution were selected for this study.

doses delivered to other PRVs as low as possible.

The patient characteristics are listed in Table 1. All

The dose-volume constraints for the PRVs were set

patients were staged by the 7th edition of the UICC-

as follows : lung PRV, volume receiving > 20 Gy (V20)

TNM staging system. Ten of 17 patients were staged< 35% and mean lung dose (MLD) < 20 Gy ; oesopha­

as T4 or N3. Computed tomography (CT) images

gus PRV, mean dose (Dmean) < 34 Gy ; heart PRV, vol­were acquired for radiation treatment planning in all

ume receiving > 40 Gy (V40) < 80%. Plans in which

patients. The entire thorax was scanned in the supine

both the primary and secondary objectives wereposition with both arms raised above the head.

achieved were considered acceptable.

Respiratory movement was evaluated with either

To compare the VMAT with the 3D-CRT plans,four-dimensional CT images or breath-held CT images

the dose-volume histograms (DVHs) of the PTV andat inhaling and exhaling positions.

the PRVs were calculated in each plan. The homoge­

On those planning CT images, we newly contoured

neity index (HI) and conformity index (CI) were com­target volumes and OARs according to the follow­

puted from the data of DVH to assess the quality of

ing definitions. The gross tumour volume (GTV)

planning. The HI was defined as the ratio of thewas defined as the primary lesion that was mac­maximum dose (Dmax) over the minimum dose (Dmin)roscopically identifiable and lymph nodes > 1 cm inin the PTV. Greater HI values indicated doses ex­

diameter. Fluorodeoxyglucose-positron emission

ceeding the prescription dose and a greater degree

tomography (FDG-PET) images were utilized for de­of dose heterogeneity in the PTV. The CI was de­lineation of GTV when available. The GTV was de­fined as the ratio of the prescription-isodose volume

lineated considering respiratory movement. The

over the PTV. Greater CI values indicated a greater

clinical target volume (CTV) enclosed the GTV withvolume of the prescription dose delivered outside

a margin of 0.5－1 cm. The PTV enclosed the CTV

the PTV.

with a margin of 0.5 cm. The OARs consisted of the

The collected data were statistically analysed

lung, spinal cord, oesophagus, and heart. Planning

based on Wilcoxon’s signed rank test using JMP

organ at-risk volumes (PRVs) were extended as 0.3(version 5.1.1 ; SAS Institute, Cary, NC, USA). In all

cm to the spinal cord, oesophagus, and heart. The

analyses, a value of P < 0.05 was considered to belung PRV included both ipsi- and contralateral lungs,

significant.

but the GTV was excluded.
Both 3D-CRT and the VMAT plans were createdⅢ

Results

on the Eclipse treatment planning system (version

The primary objectives were not achieved in the

11 ; Varian Medical Systems, Palo Alto, CA, USA)

3D-CRT plans for two patients (Patients 3 and 14).

with 10-MV photon beams. Doses were calculated

Delivery of 60 Gy to 95% of the PTV could not be

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Comparison of VMAT with 3D-CRT for NSCLC
Table 1
Patient

TNM

Patient characteristics

Location

PTV (cm3)

T4/N3 descriptor

1

T4N0M0

Right lower lobe

216

Invasion to the heart

2
3
4
5
6

T4N2M0
T4N1M0
T4N2M0T1N2M0
T3N3M0

Right upper lobe
Right upper lobe
Left upper lobe
Right upper lobe
Right upper lobe

853
581
251
147
481

Invasion to the great vessels
Invasion to the vertebral bodyInvasion to the oesophagus

7
8
9
10
11
12
13

T3N2M0
T4N2M0
T4N2M0T3N2M0T1N1M0T2N2M0T1N3M0

Right upper lobe
Left hilus
Left upper lobe
Right upper lobe
Right upper lobe
Left lower lobe
Left upper lobe

280
58
611
508
147
273
281

14

T4N3M0

Left upper lobe

776

15
16
17

T4N0M0T2N1M0T2N1M0

Left hilus
Left lower lobe
Left upper lobe

89
262
240

Metastasis in the ipsilateralsupraclavicular lymph nodes
Invasion to the carina
Invasion to the heart

Metastasis in the ipsilateralsupraclavicular lymph nodes
Invasion to the mediastinum/
metastasis in the contralateral
mediastinal lymph nodes
Invasion to the carina

PTV, planning target volume.

achieved within the limit of dose to the spinal cord
PRV because their PTVs were near the spinal cord
PRV and the off-cord fields could not encompass

lung.
Ⅳ

Discussion

the entire PTVs. We were able to create acceptable

This planning study was performed on the data of

VMAT plans with full arcs for these patients. In thepatients with inoperable NSCLC who underwent de­remaining 15 patients, all of the created plans were

finitive radiotherapy at our institution. The majority

considered acceptable. Further analyses were per­of the patients were staged as T4 or N3, i.e. com­formed on the acceptable plans for these 15 patients.

pletely unresectable. This is thought to be the gen­Comparisons of the DVH-based parameters of theeral case in clinical situations, so our study reflects

PA-VMAT with 3D-CRT plans for the 15 patientsthe conditions in actual clinical practice. In thisare shown in Table 2. The conformity of the dosestudy, the 3D-CRT plans for two of 17 patients were

distribution to the PTV was significantly improved

considered unacceptable because the off-cord fields

in the PA-VMAT plans (P < 0.001). On the otherin the plans could not encompass the entire PTVs.

hand, the homogeneity of the dose distribution to

The 3D-CRT plans were obviously inadequate for

the PTV was significantly better in the 3D-CRT

these cases, but the VMAT plans delivered suffi­plans (P＝0.041). Compared with the 3D-CRT plans,

cient dose to the PTV while maintaining the dose to

the PA-VMAT plans significantly reduced the dose

the PRVs within acceptable levels.

of V 20 (P＝0.003) and mean dose of the lung (P＝In this study, the dose conformity was improved

0.002), V35 of the oesophagus (P＝0.033), and V40 ofin the VMAT plans, although the dose heterogeneity

the heart (P＝0.020). There were no significant dif­increased. The dose distributions in IMRT/VMAT

ferences between 3D-CRT and PA-VMAT plans

plans commonly have more hot and cold spots com­with regard to V10 (P＝0.258) and V5 (P＝0.923) of thepared with 3D-CRT plans, which is not regarded

No. 2, 201795

Ozawa・Koiwai・Matsushita et al.
Table 2Comparisons of dose distributions between VMAT and 3D-CRT plans
3D-CRT

Dose
constraints

MedianRange

Median

63.7
1.27
2.04

62.6 - 64.6
1.20 - 1.70
1.54 - 2.93

63.7
1.50
1.33

62.5 - 64.9
1.25 - 5.34
1.08 - 2.05

0.916
0.041
< 0.001

19.0
9.7

7.8 - 29.8
4.5 - 17.1

14.3
8.8

5.3 - 28.9
3.7 - 17.2

0.003
0.002

PTV
Dmean (Gy)
HI
CI
Lung
V20 (%)MLD (Gy)
V10 (%)
V5 (%)

Esophagus
Dmean (Gy)

< 35
< 20

< 34

Dmax (Gy)V35 (%)Heart
V40 (%)

VMAT

< 80

Range

P-value

22.9

12.0 - 33.8

20.1

8.7 - 36.7

0.258

31.0

15.8 - 44.2

27.9

13.6 - 48.5

0.923

15.8

1.5 - 23.0

15.1

1.4 - 22.7

0.182

64.6

23.6 - 66.3

62.9

13.2 - 65.3

0.241

22.7

0.0 - 36.3

20.6

0.0 - 30.0

0.033

0.4

0.0 - 31.5

0.4

0.0 - 20.0

0.020

3D-CRT, three-dimensional conformal radiation therapy ; VMAT, volumetric modulated arc
therapy ; PTV, planning target volume ; MLD, mean lung dose.

as a serious problem, although efforts to evaluate

DVH parameters, such as V35, were reported to be

and optimize is needed, if precise inspections confirm

potentially relevant for prediction of RO16）17）. The

that the IMRT/VMAT plans are clinically accept­

present study indicated that VMAT plans poten­

7）tially reduced the V35 of the oesophagus. Althoughable .

Radiation pneumonitis (RP) is a life-threatening

there are some uncertainties in predicting RO, re­adverse event occurring in 13%-37% of patients re­duction of the dose to the oesophagus with VMAT

8）

ceiving thoracic radiotherapy for NSCLC . DVH pa­

may improve the QOL of NSCLC patients treatedrameters, especially V20 and MLD, have been accept­

with radiotherapy.

ed as predictors of RP after radiotherapy for lungcancer9）-12）. Other parameters, such as V5 and V10,
13）
14）

In our study, the median doses of the heart werequite low in both 3D-CRT and VMAT plans. This. Our

was attributed to the inclusion of only a few patients

data showed that the VMAT plans resulted in bet­

with left lower lobe tumour in our study population.

ter sparing of the lung, i.e. reducing V20 and MLD,

Therefore, we cannot conclude that the difference incompared with the 3D-CRT plans, while suppress­

heart dose between 3D-CRT and VMAT plans ob­

ing expansion of low-dose areas in the lung. The ef­

served in the present study is clinically significant.

ficiency of VMAT in sparing of the lung was consis­

Although reports of the clinical usefulness oftent with previous studies comparing VMAT plans

IMRT/VMAT are still sparse18）-20）, several planningwith conventional IMRT plans5）6）. We confirmed thestudies indicated the advantages of IMRT/VMAT

superiority of VMAT to 3D-CRT, which has beenin the treatment of locally advanced NSCLC2）5）6）21）.

utilized in actual clinical settings more frequently

However, it is impractical to treat every patient withthan conventional IMRT.

IMRT/VMAT as it usually requires more time

were also reported to be associated with RP

Radiation oesophagitis (RO) is a common acute andfor preparation than 3D-CRT. The dose verification

chronic toxicity, especially in the setting of concur­

and quality assurance required for IMRT/VMAT

rent chemoradiotherapy, and is known to adversely

are burdensome for medical staff, especially in under­

affect the quality of life (QOL) of patients15）. Several

staffed institutions. Therefore, prioritizing patients

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Comparison of VMAT with 3D-CRT for NSCLC

should be considered. The results of the present

mours in the lung were biased, and plans createdstudy directly comparing VMAT plans with 3D-with 10-MV photon beams and lower-energy pho­

CRT plans represent meaningful information for suchton beams, which may improve the dose distribution

prioritization. Based on our findings, patients in whomof lung cancer treatment, were not tested due to theoff-cord fields in 3D-CRT plans cannot encompass

limitations of our radiation therapy equipment.

their entire PTVs should be highly prioritized as
candidates for VMAT.

We demonstrated the advantages of VMAT planscompared to 3D-CRT plans for locally advanced NS­

This study had several limitations. First, we did
not consider motion-reducing approaches, such as

CLC. These findings may facilitate appropriate us­age of VMAT for such cases.

breath holding and respiratory gating, although theⅤinterplay effects may have only a small dosimetricimpact on fractionated radiotherapy22）. The numberof the patients was small, the locations of the tu­

Acknowledgements

The authors are grateful to Mrs. I. Koiwai and Mrs.
Y. Ogawa for technical assistance.

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