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Int. J. Radiation Oncology Biol. Phys., Vol. 77, No. 3, pp. 942–949, 2010
Copyright Ó 2010 Elsevier Inc.
Printed in the USA. All rights reserved
0360-3016/$–see front matter
doi:10.1016/j.ijrobp.2009.09.053
PHYSICS CONTRIBUTION
VOLUMETRIC MODULATION ARC RADIOTHERAPY COMPARED WITH STATIC
GANTRY INTENSITY-MODULATED RADIOTHERAPY FOR MALIGNANT PLEURAL
MESOTHELIOMA TUMOR: A FEASIBILITY STUDY
MARTA SCORSETTI, M.D.,* MARIO BIGNARDI, M.D.,* ALESSANDRO CLIVIO, M.SC.,y LUCA COZZI, PH.D.,y
ANTONELLA FOGLIATA, M.SC.,y PAOLA LATTUADA, M.SC.,* PIETRO MANCOSU, M.SC.,*
PIERA NAVARRIA, M.D.,* GIORGIA NICOLINI, M.SC.,y GAETANO URSO, M.SC.,* EUGENIO VANETTI, M.SC.,y
SABRINA VIGORITO, M.SC.,* AND ARMANDO SANTORO, M.D.*
*Department of Radiation Oncology, Istituto Clinico Humanitas, Rozzano, Italy; yMedical Physics Unit, Oncology Institute of Southern
Switzerland, Bellinzona, Switzerland
Purpose: A planning study was performed to evaluate RapidArc (RA), a volumetric modulated arc technique, on
malignant pleural mesothelioma. The benchmark was conventional fixed-field intensity-modulated radiotherapy
(IMRT).
Methods and materials: The computed tomography data sets of 6 patients were included. The plans for IMRT with
nine fixed beams were compared against double-modulated arcs with a single isocenter. All plans were optimized
for 15-MV photon beams. The dose prescription was 54 Gy to the planning target volume. The planning objectives
for the planning target volume were a minimal dose of >95% and maximal dose of <107%. For the organs at risk,
the parameters were as follows: contralateral lung, percentage of volume receiving 5 Gy (V5Gy) <60%, V20Gy
< 10%, mean <10.0 Gy; liver, V30Gy <33%, mean <31 Gy; heart, V45Gy <30%, V50Gy <20%, dose received by
1% of the volume (D1%) <60 Gy; contralateral kidney, V15Gy <20%; spine, D1% <45 Gy; esophagus, V55Gy
<30%; and spleen, V40Gy <50%. The monitor units (MUs) and delivery time were scored to measure the treatment
efficiency. The pretreatment portal dosimetry scored delivery to the calculation agreement with the Gamma
Agreement Index.
Results: RA and IMRT provided equivalent coverage and homogeneity. Both techniques fulfilled objectives on organs at risk with a tendency of RA to improve sparing. The conformity index was 1.9 ± 0.1 for RA and IMRT. The
number of MU/2Gy was 734 ± 82 for RA and 2,195 ± 317 for IMRT. The planning vs. delivery agreement revealed
a Gamma Agreement Index for IMRT of 96.0% ± 2.6% and for RA of 95.7% ± 1.5%. The treatment time was 3.7 ±
0.3min for RA and 13.4 ± 0.1min for IMRT.
Conclusion: RA demonstrated compared with conventional IMRT, similar target coverage and better dose sparing
to the organs at risks. The number of MUs and the time required to deliver a 2-Gy fraction were much lower for
RA, allowing the possibility to incorporate this technique in the treatment options for mesothelioma
patients. Ó 2010 Elsevier Inc.
RapidArc, Intensity-modulated radiotherapy, IMRT, mesothelioma.
Malignant pleural mesothelioma (MPM) is a rare, aggressive
tumor often associated with a poor prognosis. The incidence
of MPM is increasing in most of the world owing to the widespread exposure to asbestos during the past decades with a latent period of 20–30 years from the first exposure (1). Poor
median survival rates of 4–12 months have been reported,
with sarcomatoid histologic features, poor performance status, extensive disease, and N2 lymph node involvement associated with a worse prognosis (2).
In general, single modality treatment has not been able to
substantially increase the survival, and a multimodality
approach is the preferred treatment regimen for patients
with resectable disease. Trimodal treatment, including chemotherapy, surgery (extrapleural pneumonectomy), and adjuvant radiotherapy (RT) have been used to improve the
disastrous prognosis of MPM (3, 4). In particular, postoperative RT has been proposed to reduce the risk of local
progression, which developed in 80% of patients who underwent extrapleural pneumonectomy alone (5).
Reprint requests to: Luca Cozzi, Ph.D., Department of Radiation
Oncology, Oncology Institute of Southern Switzerland, Medical
Physics Unit, Bellinzona 6504 Switzerland. Tel: (+41) 91-8119202; Fax: (+41) 91-811-8678; E-mail: [email protected]
Conflict of interest: L. Cozzi acts as Scientific Advisor to Varian
Medical Systems and is Head of Research and Technological Development, Oncology Institute of Southern Switzerland, IOSI, Bellinzona, Italy.
Received June 2, 2009, and in revised form Aug 12, 2009.
Accepted for publication Sept 18, 2009.
INTRODUCTION
942
RapidArc for malignant pleural mesothelioma tumor d M. SCORSETTI et al.
943
Fig. 1. Isodose distributions in two axial planes, one sagittal and one coronal view for 1 case. Color wash cut between
7 and 66 Gy. Also shown, overlay of planning target volume and main organs at risk. IMRT = intensity-modulated
radiotherapy; RA = RapidArc.
Many RT procedures have been evaluated to cover the large
and irregular target and to limit the dose to the organs at risk
(OARs) (i.e., contralateral lung, liver, spinal cord, heart,
esophagus, kidneys). The details of various RT techniques, including three-dimensional conformal RT and electron matching (6–8), intraoperative RT (9, 10), and, more recently,
intensity-modulated RT (IMRT) (8, 11–14) and tomotherapy
(15), have been published and clinically evaluated.
RapidArc (RA) is an innovative method of volumetric intensity-modulated arc therapy developed from the original investigations by Otto (16) and further developed and
implemented as the progressive resolution optimization algorithm in the Eclipse planning system (Varian Medical System,
Palo Alto, CA). The optimization process is based on an iterative inverse planning process aiming to simultaneously optimize the instantaneous multileaf collimator positions, dose
rate, and gantry rotation speed to achieve the desired dose distribution. RA has been investigated and compared with IMRT
or other approaches in a series of studies that included brain
tumors, prostate, head-and-neck, anal canal, and cervical
uterine cancer, and other indications (17–24).
The aim of the present study was to evaluate the RA technique for adjuvant RT for MPM. Thus, a planning comparison was performed between fixed-gantry IMRT and RA
techniques, evaluating the target conformity, target coverage,
integral dose, and normal tissue sparing. Pretreatment quality
assurance methods were applied to appraise the dosimetric
reliability of the two approaches. The treatment time was
measured to assess the efficiency of the two techniques.
METHODS AND MATERIALS
Patient selection, target, and organs at risk
Between 2004 and 2008, a relatively large number of patients
with histological confirmed MPM, who were scheduled to undergo
extrapleural pneumonectomy at the Istituto Clinico Humanitas Hospital, underwent RT simulation computed tomography with a 3-mm
slice thickness. In the present study, a retrospective treatment planning evaluation was performed of 6 randomly selected patients
(3 with left and 3 with right-sided disease). The local lymph node
stage was N0, and age and gender were not criteria for selection.
A radiation oncologist drew the clinical target volume (CTV) on
the computed tomography slices from the lung apex to the upper abdomen (usually up to L2), according to the study by Ahamad et al.
(25). CTV definition was helped by radiopaque clips marking the resection margins and other areas considered to be at high risk. The
planning target volume (PTV) was delineated by uniform margins
of 5 mm around the CTV. The PTV was bound to the external surface
of the body outline. Normal tissue organs, including the contralateral
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Volume 77, Number 3, 2010
Fig. 2. Mean dose–volume histograms for clinical target volume (CTV) and planning target volume (PTV).
lung, liver, heart, esophagus, kidneys, spleen, and spinal cord, were
delineated by a radiation oncologist. The dose prescription to the
PTV was set at 54 Gy in 2 Gy/fraction, with curative intent (26). Normalization was set to the PTV mean dose to avoid unnecessary biases
in the optimization and evaluation processes.
RT planning techniques and planning objectives
For each patient, two sets of dose plans were optimized. First,
IMRT plans were developed for sliding window dynamic delivery
with a beam arrangement according to the restricted fields technique
proposed by Allen et al. (14), using nine coplanar fields, with 15-MV
energy, excluding direct entrance through the contralateral lung. The
isocenter was positioned roughly at the geometric center of the PTV.
Second, RA plans were generated using two coplanar arcs of 360
optimized simultaneously with a beam energy of 15 MV. The same
isocenter of the IMRT plan was used. The collimator angle was kept
fixed and set to 15 for all patients.
For both IMRT and RA, the dose calculations and optimizations
were performed using the Eclipse treatment planning system (version 8.6), for a Clinac2100 equipped with the Millennium multileaf
collimator 120 leaves (leaf width at isocenter of 5 mm in the central
20 cm part of the field, 10 mm in the outer 2 10 cm, and a leaf transmission of 1.7%). For RA, the maximal dose rate was set to 600 MU/
min, and for IMRT, a fixed dose rate of 600 MU/min was used.
Dose calculation was performed with the AAA algorithm (27) using a grid of 2.5 mm.
The planning objectives for the PTV aimed to limit the minimal and
maximal dose (dose received by 99% and 1% of the volume [D99% and
D1%], respectively) to 95% and 107%, respectively, of the dose prescription. Although the PTV extension was not cropped inside the
body outline and, therefore, extended, in some cases, to the surface
of the body, no bolus was used during the optimization and dose calculation for any patient. Thus, it was anticipated that the minimal target
coverage would not be fulfilled using both techniques. This strategy
sought to assess the degree of coverage achievable for the most unfavorable conditions. For clinical treatment, either a bolus or different
normalization or structure cropping strategies could be applied.
The dose–volume planning objectives defined for the OARs were
as follows: contralateral lung, percentage of volume receiving 5 Gy
(V5Gy) <60%, V20Gy <10%, mean dose <10.0 Gy; liver, V30Gy
<33%, mean dose <31 Gy; heart, V45Gy <30%, V50Gy <20%, D1%
<60 Gy; contralateral kidney, V15Gy <20%; spinal cord, D1% <45
Gy; esophagus, V55Gy <30%; and spleen, V40Gy <50%.
Pretreatment quality assurance dosimetric measurements
To assess the delivery quality and agreement between the calculations and treatment, standardized pretreatment quality assurance
dosimetric measurements were performed to verify each individual
field or arc. Epiqa software (EPIdos, Bratislava, Slovakia) derived
from the GLAaS method was used in the present study. GLAaS
has been widely investigated (28, 29). In brief, it consists of measurements performed with the amorphous silicon portal imager
aS1000, attached to the treatment linear accelerator, with a calibration and processing method converting raw data into absorbed doses
at depth of maximum (2.5 cm in this case). Epiqa/GLAaS has been
previously tested for RA delivery and is the reference dosimetry tool
at our center for pretreatment verifications. With Epiqa/GLAaS, no
additional phantom is needed, and, for RA, the detector rotates together with the gantry, generating a sort of collapsed or composite
planar dose distribution. The spatial resolution of these measurements is 0.392 mm in the x and y directions (aS1000 pixel size).
Evaluation tools
Quantitative evaluation of the plans was performed using the standard dose–volume histogram (DVH). For the PTV, the D99% and D1%
were defined as metrics for the minimal and maximal doses and reported. To complement the appraisal of the minimal and maximal
dose, the volume receiving $95% or, at most, 107% of the prescribed
dose (V95% and V107%, respectively) are reported. The homogeneity
of the treatment was expressed in terms of the D5%–D95%. The conformality of the plans was measured with a conformity index, defined as
the ratio between the patient volume receiving $95% of the prescribed dose and the PTV receiving >95%, as in the study by Sterzing
et al. (15). For the OARs, the analysis included the mean dose, maximal dose expressed as D1%, and a set of appropriate Vx and Dy values.
The average cumulative DVH for the PTV, OARs, and healthy
tissue was built from the individual DVHs. These histograms
were obtained by averaging the corresponding volumes for the
whole patient cohort for each dose bin of 0.05 Gy.
The delivery parameters were recorded in terms of the monitor
units (MUs) per fraction and the effective beam on time, defined as
the pure beam on time plus the time needed to reset the system between beams without any additional dead time from external reasons.
The pretreatment quality assurance results were summarized in
terms of the Gamma Agreement Index (GAI), which scores the percentage of the modulated area fulfilling the g index criteria (30)
(computed with 3% of the maximal significant field dose [28] and
RapidArc for malignant pleural mesothelioma tumor d M. SCORSETTI et al.
945
Fig. 3. Mean dose–volume histograms for organs at risk and healthy tissue.
3-mm thresholds). Pretreatment dosimetry was considered satisfactory if the GAI was >95%.
The Wilcoxon matched-paired signed-rank test was used to compare the results. The threshold for statistical significance was
p #.05. All statistical tests were two-sided.
RESULTS
The dose distributions are shown for 1 patient in Fig. 1 for
two axial, coronal, and sagittal views. Figures 2 and 3 show
the average DVH for the CTV, PTV, healthy tissue, and
OARs. Table 1 reports the numeric findings from the DVH
analysis of the CTV, PTV, and healthy tissue; Table 2 lists
the findings for the OARs.
The data are presented as averages for the 6 investigated
patients, with errors indicated for interpatient variability at
1 standard deviation level.
Target coverage and dose homogeneity
The data summarized in Table 1 show that for the CTV,
the RA plans provided a systematic improvement in coverage and homogeneity, although the difference was not statistically significant, compared with the IMRT plans. For the
PTV, the situation was less clearly defined, with RA plans
showing a loss of 0.2 Gy in the minimal dose but a gain
of 1.3 Gy in the maximal dose and 0.2 Gy in homogeneity.
The conformity of the dose distribution was the same for the
I. J. Radiation Oncology d Biology d Physics
946
Table 1. Summary of DVH analysis for CTV, PTV, and
healthy tissue
Variable
Objective
IMRT
RA
p
CTV (2,495 1015 cm3)
Mean (Gy)
54.0
54.1 0.1 54.4 0.2 .03
D1% (Gy)
<57.8
58.6 2.1 57.6 0.9 .3
Minimize 5.3 1.6 4.5 0.6 .2
D5–95% (Gy)
>51.3
50.8 1.4 51.2 0.9 .2
D99% (Gy)
V95% (%)
>99
95.3 8.5 98.7 1.4 .3
<1
3.9 5.5 1.5 2.8 .1
V107% (%)
PTV (3,414 1,261 cm3)
Mean (Gy)
54.0
54.0 0.0 54.0 0.0 —
<57.8
58.8 2.0 57.5 0.8 .08
D1% (Gy)
Minimize 6.0 1.5 5.8 1.0 .2
D5–95% (Gy)
D99% (Gy)
>51.3
49.1 1.9 48.9 1.7 .04
>99
93.3 7.7 93.5 3.4 .9
V95% (%)
<1
4.1 5.7 1.3 2.3 .06
V107% (%)
Minimize 1.1 0.1 1.1 0.1 .9
CI95%
Healthy tissue (25,559
5,875 cm3)
Mean (Gy)
—
18.9 2.0 17.9 2.3 .04
V10Gy (%)
—
47.7 4.8 45.9 5.5 .16
—
4.8 0.1 4.6 0.1 .11
DoseInt
(Gy cm3 105)
Abbreviations: DVH = dose–volume histogram; CTV = clinical
target volume; PTV = planning target volume; IMRT = intensitymodulated radiotherapy; RA = RapidArc; Dx% = dose received by
x% of volume; Vx% = volume receiving $x% of prescribed dose;
CI = ratio between patient volume and the PTV volume receiving
$95% of prescribed dose DoseInt = integral dose.
IMRT and RA plans. The clinical relevance of the observed
minimal discrepancies is likely to be insignificant.
OARs and healthy tissue
Both IMRT and RA were shown to be capable of fulfilling
the planning objectives. In general, as proven also by the average DVH shown in Fig. 2, RA allowed additional improvement in sparing of the OARs for the maximal, mean, and
other dose–volume parameters. For left-sided targets, the
DVH of the spleen and the heart crossed at 40 Gy, with
RA more effective at lower values and IMRT slightly superior at higher doses, although both techniques respected the
corresponding planning objectives. Statistical significance
(or a tendency to significance with p #.07) for the differences
was observed for most parameters with explicit planning objectives. The results for healthy tissue indicated a substantial
equivalence between IMRT and RA.
Delivery parameters
The number of MUs per 2-Gy fraction was 2195 317 for
IMRT and 734 82 for RA (p <.001) with an IMRT/RA ratio of 2.99 0.28. The total treatment time from the loading
of patient data into the treatment console to the end of last delivery was 3.7 0.3 min (150 seconds of beam on time) for
RA compared with 13.4 0.1 min for IMRT. This difference, other than the MU ratio, mostly resulted from the
need to reprogram the linear accelerator between fixed gantry
Volume 77, Number 3, 2010
beams, rotate the gantry from one position to the next, and deliver split fields (fields were split because of the target size).
These values did not include any imaging or patient positioning procedures, which are common to any technique and not
relevant to our comparison.
Pretreatment dosimetric measurements
The GAI, scored with 3 mm and 3% thresholds was 96.0%
2.6% for IMRT and 95.7% 1.5% for RA. The time
needed to perform the pretreatment quality assurance was
as follows: time needed for data preparation, including
field-by-field calculations, 21.0 1.4 min for RA and 14.5
2.1 min for IMRT; time needed for measurements, 3.7 0.3 min for RA and 13.4 0.1 min for IMRT; time needed
for analysis of data, 1.2 0.1 min for RA and 5.1 0.6
min for IMRT, for a total time for quality assurance procedures of 25.6 1.5 min for RA with two arcs and 33.0 1.5 min for IMRT with nine split fields.
DISCUSSION
Radiotherapy after radical surgery for MPM has resulted in
better local control than surgery alone (5). Historically, threedimensional conformal RT techniques using photons and/or
electrons were tested. However, the low dose uniformity to
the target and the limited tolerance to neighboring OARs imposed a low-dose prescription using three-dimensional RT
techniques. The introduction of IMRT has allowed good target coverage and dose sparing of the OARs, as published by
many groups (11, 12, 25). However, the large volume to irradiate requires a long irradiation time with IMRT techniques.
Sterzing et al. (15) reported a mean radiation time of 19.9 min
for step-and-shoot IMRT and 19.7 min for high-intensity
modulation factor tomotherapy to fully cover the PTV.
This could result in involuntary patient motion during the
daily treatment, with the consequence of dose delivery different from that planned. Furthermore, patients’ co-morbidities
after radical surgery are severe, and, thus, they usually cannot
tolerate long treatment times. Moreover, high MUs are required to obtain good results, increasing the probability of
secondary tumors due to radiation leakage.
RapidArc was specifically modeled to reduce the delivery
time and the MUs, while maintaining adequate target coverage and dose sparing to the OARs, to improve the management of MPM. In the present study, 6 patients with
confirmed MPM, who were candidates for RT after surgery,
underwent treatment planning using static-gantry IMRT and
RA techniques. Particular attention was given to keeping the
mean dose to the contralateral lung to <10–15 Gy to avoid
pneumonitis, as suggested by Allen et al. (14).
Table 3 presents a synoptic overview of some of the dosimetric parameters and beam on times for the most recent
studies addressing the role of IMRT or helical tomotherapy
in the treatment of MPM compared with the corresponding
findings from the present investigation. Such comparisons
should be considered with care because the differences in patient characteristics, organ delineation and planning objective
RapidArc for malignant pleural mesothelioma tumor d M. SCORSETTI et al.
947
Table 2. Summary of DVH analysis for organs at risk
Contralateral lung (1,927 607 cm3)
Mean (Gy)
D1% (Gy)
V5Gy (%)
V20Gy (%)
Contralateral kidney (151 57 cm3)
Mean (Gy)
D1% (Gy)
V15Gy (%)
Ipsilateral kidney (155 54 cm3)
Mean (Gy)
D1% (Gy)
D30% (Gy)
V15Gy (%)
Heart (544 82 cm3)
Mean (Gy)
D1% (Gy)
V45Gy (%)
V50Gy (%)
Liver (1,423 200 cm3)
Mean (Gy)
D1% (Gy)
V30Gy (%)
Esophagus (30 7 cm3)
Mean (Gy)
D1% (Gy)
V50Gy (%)
Spine (66 24 cm3)
D1% (Gy)
Spleen (242 78 cm3)
Mean (Gy)
D1% (Gy)
V40Gy (%)
Objective
IMRT
RA
p
<10 Gy
Minimize
<60%
<10%
5.8 0.8
24.3 4.1
45.0 12.6
2.0 0.9
5.6 0.7
15.5 3.8
47.9 7.4
0.4 0.4
.6
.002
.6
.01
Minimize
Minimize
<20%
4.6 2.4
9.9 2.8
0.0 0.0
3.0 1.5
6.3 1.8
0.0 0.0
.013
.001
—
Minimize
Minimize
Minimize
Minimize
17.3 11.4
44.5 16.2
24.4 17.0
43.2 31.1
12.9 9.3
39.4 15.7
15.6 13.6
32.9 32.5
.06
.001
.08
.10
Minimize
<60 Gy
<30%
<20%
29.1 6.0
53.9 1.6
15.6 4.0
6.1 1.5
24.6 8.5
55.1 1.2
19.2 11.5
12.0 7.2
.02
.05
.38
.07
<30 Gy
Minimize
<33%
16.6 8.1
46.5 9.3
15.1 12.8
14.7 8.1
36.6 18.7
12.8 14.0
.04
.06
.07
Minimize
Minimize
<30%
30.9 7.9
50.7 2.7
8.2 14.4
26.8 6.1
48.7 5.6
4.4 9.2
.03
.26
.14
<45 Gy
39.7 2.5
38.6 2.1
.5
Minimize
Minimize
<50%
38.8 1.2
51.5 2.4
39.4 6.3
35.6 3.1
53.8 1.1
40.5 7.4
.1
.08
.6
Abbreviations as in Table 1.
strategies in the various studies have a strong influence on the
quantitative results. Nevertheless, it is clear that RA, the newest approach in the comparison is well positioned with respect to the alternative approaches from the conformal
avoidance viewpoint and could offer significant improvement from the logistic viewpoint.
In more detail and limiting the discussion to the data from
the present study, in which IMRT and RA were compared using the same patients, RA and IMRT showed an equivalent
degree of target coverage and homogeneity. The results for
PTV, which were less satisfactory than for CTV, were dominated by the insufficient coverage (93.5% instead of the required 99% for V95%). As anticipated, this was because no
bolus was used in the optimization and calculation and the
dose normalization was set to the PTV mean dose. The use
of a bolus to the entire surface of the hemithorax would put
the patient clinically at risk of severe toxicity and thus, if
needed, should be carefully tailored to the individual patient.
Hypothetical normalization to minimal dose levels, which
was not used in the present study and is not advisable because
of the forthcoming International Commission on Radiation
Units and Measurements recommendations for IMRT and
advanced techniques, could compensate for the observed insufficient coverage. Similar to a bolus, this strategy should be
tailored to specific cases. Nevertheless, regardless of the absolute value, IMRT and RA provided similar minimal doses
and RA reduced by about 3% the volume receiving doses
>107%. The present study was developed for 15-MV photon
beams and achieved satisfactory results in terms of conformal
avoidance of the OARs and homogeneity of the target dose.
Preliminary tests were performed to assess the difference between 6 and 15 MV with RA for these patients. The results
suggested that 15 MV provided better results in terms of target homogeneity and coverage. Given the low number of
MUs from RA, we believe that the use of higher energies
was not a concern; therefore, only the results for 15 MV
were presented. In general, other studies have investigated
MPM with low-energy beams. Previous investigations of
RA (17–24) were mostly performed for 6-MV beams.
The second objective of the present study was to assess the
treatment efficiency. In terms of the MUs/2 Gy, RA provided
the well-established reduction of a factor 3. This is particularly significant in the case of MPM because, to achieve a sufficient quality of plans for such large target volumes, highenergy photon beams are more beneficial than low-energy
beams. At energies >15 MV, the neutron contamination starts
to become significant. Thus, for radiation protection reasons,
it is often advised to avoid IMRT because of the too high
I. J. Radiation Oncology d Biology d Physics
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Volume 77, Number 3, 2010
Table 3. Synopsis of dosimetric findings from recent investigations on potential role of IMRT or tomotherapy for mesothelioma cancer
Sterzing et al. (15)
(tomotherapy)
Variable
Treatment time (min)
PTV
Prescription dose (Gy)
D1% or Dmax
D99% or Dmin
V95% (%)
CI95%
Contralateral lung
Mean (Gy)
V20Gy (%)
V5Gy (%)
Contralateral kidney
Mean (Gy)
V15Gy (%)
Heart
D1% or Dmax (Gy)
V45Gy (%)
Mean (Gy)
Liver
Mean
V30Gy (%)
Esophagus
Mean (Gy)
D1% or Dmax (Gy)
Spine
D1% or Dmax (Gy)
Present
study (RA)
Allen et al. (14) Krayenbuehl et al. (8) Chan et al. (12)
(IMRT)
(IMRT, SIB)
(IMRT)
Low IMF
High IMF
12.1 1.3
19.7 3.2
3.7 0.3
—
—
—
54
57.5% 0.8%
48.9% 1.7%
PTV: 93.5 3.4
CTV: 98.7 1.4
1.1 0.1
54
—
—
97.2
45.5/55.9
—
—
96.0 2.9
54
70 3.8 Gy
36 3.8 Gy
96.4
—
—
—
1.2 0.1
1.1 0.1
5.6 0.7
0.4 0.4
47.9 7.4
6.6
3
—
9.0 1.4
7.7 5.6
—
4.7
—
7.0 0.7
0.5 0.4
71.0 14.2
4.8 0.3
0.1 0.1
37.6 6.9
3.0 1.5
0
—
2.9
4.1 1.7
1.0 3.4
4.6 1.0
—
4.3 2.3
—
3.4 1.9
—
55.1 1.2
19.2 11.5
24.6 8.5
—
23 (left)
—
—
1.6 2.0
26.2 6.2
—
—
27.3 1.9
54.9 1.7
—
27.0 4.2
57.9 1.0
—
21.5 4.4
14.7 8.1 Gy
12.8 14.0
13.4–28.2%
10–29%
13.2 6.7
—
7.5 0.6 Gy
—
26.8 6.1
48.7 5.6
—
—
—
—
—
—
32.4 6.3
51.9 4.7
24.9 5.2
55.6 4.2
38.6 2.1
47.5
40.1 4.0
—
39.7 4.4
39.5 3.9
54
54
55.6 0.7 Gy 56.1 0.9 Gy
46.0 1.5 Gy 46.9 1.4 Gy
93.0 2.5
96.4 0.8
12.9 2.2 Gy 17.2 7.5 Gy
—
—
Abbreviations: Dmax = maximal dose; IMF = intensity modulation factor; other abbreviations as in Table 1.
number of MUs. The highly significant reduction in MUs
provided by RA, bringing the total number of MUs per
2-Gy fraction to within the same range of that for conventional
three-dimensional conformal RT when using 30 –60
wedges, made the use of high energy much safer than with
IMRT. Treatment efficiency was also scored in terms of the
total treatment time. The findings for RA confirmed the possibility of delivering single arcs within about 75 s/arc, leading
to a total beam on time of <3 min for double arcs with a single
isocenter and the rotation of the two arcs in opposite directions. In contrast, IMRT proved to be, as expected, significantly slower because of the beam multiplicity, the large
number of split fields, and the long dead times to move the
gantry to each start position and to reprogram the linear accelerator for each beam. Imaging and patient positioning are
common to both techniques and therefore were not accounted
for in the present study. Nevertheless, a large reduction in
treatment time, would allow, within normal scheduling slots,
all needed procedures to be performed with due diligence.
The third objective of the present study was to assess the
agreement between the calculations and effective delivery.
This was performed using a consolidated pretreatment quality assurance method measuring the dose absorbed to water
for each IMRT field or RA arc. The results showed, confirming the clinical experience of both centers (Istituto Clinico
Humanitas and Oncology Institute of Southern Switzerland)
and of other investigations (23, 24), that RA is as reliable and
accurate as normal IMRT and that the control systems embedded in the delivery machines are capable of guaranteeing
safe treatment for all treatment types offered to patients.
CONCLUSION
For RT for MPM, RA demonstrated similar target coverage and better dose sparing to the OARs compared with
fixed-gantry IMRT. The time required to deliver the dose
was much lower than that for other RT techniques and thus
could increase the population receiving RT for MPM after
radical surgery.
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