Recommendations for implementing stereotactic radiotherapy in peripheral stage IA non-small cell lung cancer: report from the Quality Assurance Working Party of the randomised phase III ROSEL study
Recommendations for implementing stereotactic radiotherapy in peripheral stage IA non-small cell lung cancer: report from the Quality Assurance Working Party of the randomised phase III ROSEL study
Coen W Hurkmans 2
Johan P Cuijpers 1
Frank J Lagerwaard 1
Joachim Widder 0
Uulke A van der Heide 3
Danny Schuring 2
Suresh Senan 1
0 Department of Radiation Oncology, University Medical Center Groningen , Groningen , The Netherlands
1 Department of Radiation Oncology, VU University Medical Center , Amsterdam , The Netherlands
2 Department of Radiation Therapy, Catharina Hospital , Eindhoven , The Netherlands
3 Department of Radiation Oncology, University Medical Center Utrecht , Utrecht , The Netherlands
Background: A phase III multi-centre randomised trial (ROSEL) has been initiated to establish the role of stereotactic radiotherapy in patients with operable stage IA lung cancer. Due to rapid changes in radiotherapy technology and evolving techniques for image-guided delivery, guidelines had to be developed in order to ensure uniformity in implementation of stereotactic radiotherapy in this multi-centre study. Methods/Design: A Quality Assurance Working Party was formed by radiation oncologists and clinical physicists from both academic as well as non-academic hospitals that had already implemented stereotactic radiotherapy for lung cancer. A literature survey was conducted and consensus meetings were held in which both the knowledge from the literature and clinical experience were pooled. In addition, a planning study was performed in 26 stage I patients, of which 22 were stage 1A, in order to develop and evaluate the planning guidelines. Plans were optimised according to parameters adopted from RTOG trials using both an algorithm with a simple homogeneity correction (Type A) and a more advanced algorithm (Type B). Dose conformity requirements were then formulated based on these results. Conclusion: Based on current literature and expert experience, guidelines were formulated for this phase III study of stereotactic radiotherapy versus surgery. These guidelines can serve to facilitate the design of future multi-centre clinical trials of stereotactic radiotherapy in other patient groups and aid a more uniform implementation of this technique outside clinical trials.
Until recently, conventionally fractionated high-dose
radiation therapy was the preferred treatment in patients
with stage I NSCLC who were unfit to undergo surgery or
declined surgery. This is, however, a poor alternative to
surgery in operable patients as the mean reported crude
local recurrence rates are as high as 40% (range 670%),
resulting in a three year overall and cause-specific survival
of only 34 and 39%, respectively .
Recently, stereotactic radiotherapy has gained much
interest in the treatment of medically inoperable patients with
stage I lung cancer, as local control rates are dramatically
improved with this technique compared to conventional
fractionation. In studies where schedules with a
biologically effective dose (BED) larger than 100 Gy are used,
typical local control rates are approximately 90%. The largest
series were reported from Japan [2,3], United States 
and the Netherlands , comprising experience in over
750 patients. Onishi et al.  retrospectively described the
results of 257 patients treated in 14 Japanese centres using
a number of different fractionation schedules and delivery
approaches. This Japanese study also included nearly 100
patients who refused surgery, and the 5-year overall
survival rate of 70.8% observed after a BED of 100 Gy among
those patients is at least equivalent to the outcome after
surgery [7-9]. Currently, several phase II trials have started
in operable lung cancer patients  (RTOG 0618 and
JCOG 0403), however, to date no prospective
multi-centre randomized studies have been performed to compare
stereotactic radiotherapy with surgery in patients with
operable lung cancer.
A randomized phase III trial of Radiosurgery Or Surgery
for operable Early stage (stage 1A) non-small cell Lung
cancer (ROSEL, ClinicalTrials.gov ID = NCT00687986)
has been opened for accrual in August 2008. The study is
initiated by the VU medical centre Amsterdam and the
Dutch Lung Cancer Research Group. The primary study
objectives are to compare local and regional control,
quality of life and treatment costs at 2 and 5 years in patients
who are randomized to either surgery or radiosurgery
(Figure 1). Treatment costs are a primary end-point, as the
costs associated with surgery for stage IA in The
Netherlands are far higher than the present costs of stereotactic
radiotherapy . These costs are expected to be even
more if the costs of post-operative revalidation and loss of
economic activity are taken into account. However,
patients treated with stereotactic radiotherapy could incur
costs for salvage treatment if a higher incidence of local or
regional recurrences is detected. Therefore, treatment costs
were considered to be a relevant end-point.
(both direct and indirect). In case of surgery, a lobectomy
should be carried out, but limited resections are
acceptable. Careful radiological follow-up is performed within
the trial in patients treated by SRT, as salvage surgery or
mediastinal radiation therapy might still be possible in
case of clinical, radiological or histological evidence of
local or hilar disease progression.
Accreditation and dosimetry guidelines have been
previously developed for trials of stereotactic radiotherapy such
as RTOG 0236 and JCOG 0403 [12-14]. However, a
reassessment was considered necessary because a new patient
group was being treated with stereotactic radiotherapy,
namely patients who were fit to undergo both primary
and salvage surgery. As a result, normal tissue
dose-constraints had to be more stringently defined in order to
minimize the risk of increased complications after salvage
surgery. Furthermore, IGRT technology from different
vendors has been rapidly adopted at various Dutch
centres, which had to be taken into account. The resulting
guidelines include both minimum requirements that
must be met by each participating centre as well as
recommendations for possible further improvements. They are
presented here in order to facilitate the implementation of
future multi-centre studies, to stimulate and improve the
implementation of stereotactic techniques in clinical
practice and to improve the comparability of results.
A ROSEL Quality Assurance Working Party was formed by
radiation oncologists and medical physicists from both
academic as well as non-academic hospitals that had
already implemented stereotactic radiotherapy for lung
cancer. Several working party meetings were organised in
which both the knowledge from literature and clinical
experience were shared and amalgamated. In support of
these meetings, a literature search was conducted by
searching MEDLINE with different key words and their
permutations such as stereotactic radiotherapy, stage I
lung cancer, treatment planning, CT scan, patient
positioning and tumour mobility. Abstract books of the
ASTRO, ASCO, AAPM and ESTRO/ECCO from 2004 to
2008 were reviewed. It was recognized that there was little
data available in the literature about the influence of
different planning algorithms on the planning of stereotactic
radiotherapy. Therefore, an additional planning study was
performed in 22 stage IA and 4 stage 1B non-small cell
lung cancer patients in order to develop and evaluate the
planning guidelines differentiated according to type of
dose calculation algorithm used. Patient characteristics
and treatment planning details have been reported
Secondary objectives include overall survival, pulmonary
function tests, quality adjusted life years and total costs
In brief, a four-dimensional (4D)-CT was reconstructed in
ten equally spaced time bins using respiratory phase
binning for each patient. From these phases, a maximum
intensity projection (MIP) was reconstructed . The
datasets were then imported in the Pinnacle3 treatment
planning system (Philips Medical Systems, Wisconsin).
Using the MIP dataset, an experienced radiation
oncologist delineated the internal target volume (ITV). Organs at
risk were delineated on an average-density CT
reconstruction. The PTV was created by expanding the ITV with a 3
mm margin. The treatment plans consisted of 9 equally
spaced coplanar 6 MV beams which were not allowed to
enter through the oesophagus, heart, spinal cord or
contralateral lung. The plans were inversely optimized using
the direct aperture optimization module of the Pinnacle3
treatment planning system with the same objectives as
used in the ROSEL trial. Three different plans were
created; using an advanced (type A) dose calculation
algorithm, a less advanced (type B) algorithm and a plan
assuming all tissues within the body to have unit density,
in accordance with the RTOG study 0236 and 0618
In order to facilitate the clinical use of these
recommendations, we divided the process of implementing high-dose
radiotherapy into the following headings: CT scanning
and patient positioning, target volume definition, organs
at risk definition, Dose calculation algorithms and
fractionation, dose prescription, coverage and constraints,
treatment planning and treatment execution.
Patient positioning and CT scanning
The patient should be scanned in the treatment position
which should be supine with both arms raised above the
head using an arm-rest or other fixation device. Positions
which are less comfortable for the patient should be
avoided so as to prevent the likelihood of uncontrolled
movement during scanning or treatment.
Four-dimensional (4D) CT scanning is strongly recommended in
order to account for an individualised assessment and
incorporation of tumour motion [19-21]. Preferably 10
but no less than 6 breathing phases should be
reconstructed in order to determine the tumour movement for
treatment planning. Using 10 phases, it was found that
generally the full amplitude of motion can be captured
. Within the ROSEL trial, acquisition of a slow-CT
scan or multiple (at least 3) rapid planning scans covering
the entire range of tumour motion is also allowed, as
4DCT scanners are not widely available yet. However, target
volume delineation might be more difficult as the images,
and thus also the tumour volume, of slow-CT scans are
blurred [23,24]. All centres participating in the ROSEL
study will most likely be able to implement 4D-CT
scanning in the near future. Generally, intravenous contrast is
not necessary for planning CT scans for early stage lung
cancer, but contrast-enhanced CT images may still be used
for dose calculations. Although the effect of intravenous
(IV) contrast on dose calculations for lung patients is not
specifically studied, the influence of IV contrast in head
and neck intensity modulated radiotherapy plans was
proven to be insignificant . The slice spacing between
reconstructed CT images should be 3 mm over the
complete tumour trajectory and 5 mm elsewhere. The scan
should encompass the entire lung volume in order to
calculate meaningful lung dose-volume parameters.
Target volume definition
The gross tumour volume (GTV) will generally be
contoured using CT pulmonary windows; however, soft tissue
windows may be used to avoid inclusion of adjacent
vessels or chest wall structures within the GTV. The
correctness of the GTV delineation should be checked in axial,
sagittal and coronal views. The clinical target volume
(CTV) is assumed to be identical to the GTV, i.e. with no
margin for microscopic disease added, which appears to
be justified by the high local control rates observed in
patients undergoing careful post-treatment follow-up
. This approach has also been accepted in the
ASTROACR recommendations on stereotactic radiotherapy .
For PTV definition, two main treatment planning and
execution techniques can be distinguished; planning and
irradiation based on the internal target volume (ITV)
concept or the time-averaged mean position of the tumour.
PTV based on the ITV concept
For 4D CT scans, the ITV can be derived from the union of
GTV delineations on all breathing phases or alternatively,
from contouring on a maximum intensity projection
(MIP) CT-dataset [28,29]. The appropriateness of the
MIP-delineation should at least be confirmed by a visual
inspection of the projected ITV contours on the
CT-datasets of the end-inspiration and end-expiration phase bins
using axial, sagittal and coronal views. In addition to the
MIP contouring, the GTV should also be contoured in a
single phase (preferably the end-expiration phase,
because this is the most stable tumour position and the
phase with the least breathing artefacts) in all patients in
order to determine the GTV size. For checking the ITV
contour based on the MIP it is not necessary to delineate the
end-inspiration and end-expiration phase bins (visual
assessment suffices). Alternatively, the ITV may be
constructed by the union of all delineations of the GTV in all
breathing phases. If only 3D CT data is available, the ITV
should be based on either multiple slow CT-scans
covering the whole tumour trajectory or an additional margin
of 35 mm in all directions around the CTV determined
on a single slow CT-scan . The ITV to PTV margin is
primarily meant to take into account patient set-up
uncertainties. However, small intra-fractional variations in the
tumour motion and mean position may be present. Also
inter-fractional variations may be present, but these might
be corrected for using tumour based image guided
position verification and correction . In addition, small
delineation uncertainties will exist. Thus, a minimum of 3
mm ITV to PTV margin is required in all dimensions, even
if a set-up error of <3 mm can be guaranteed. On the other
hand, the ITV to PTV margin should not exceed 5 mm, as
this would unnecessarily enlarge treated volumes. In case
an institution would need to apply a larger margin, e.g.
because of their set-up accuracy, it is advised to first
improve its (set-up) technique (see also paragraph about
PTV based on the mean tumour position
As an alternative to the ITV concept, planning and
irradiation based on the time-averaged mean position of the
tumour has been developed . In contrast to the ITV to
PTV margin discussed previously, the CTV to PTV margin
needed here should take the tumour motion into account.
However, similar to the reasoning given for the ITV to PTV
margin, a minimum margin of 3 mm should be used for
the incorporation of the other uncertainties.
Organs at risk definition
Dose volume criteria for organs at risk (OAR) given in a
next paragraph are all constraints to the highest doses
received by the OAR. As a consequence, the impact of
differences in delineation protocols between institutions is
not expected to be high, as these differences are likely to
be primarily of influence on the delineations located
outside the high dose region. However, in order to support
future normal tissue complication probability (NTCP)
modelling studies, the OAR delineation guidelines as used
in the ROSEL protocol are given below.
When 4D-CT scans are used for treatment planning, the
critical OAR should be contoured on the relevant
reference reconstruction (i.e. the scan used for dose
calculations, see also paragraph about treatment planning). This
can generally be performed without taking into account
potential mobility of these organs, as current experience is
based on this type of delineations. However, extremes of
motion of organs such as the oesophagus may influence
the choice of beam arrangements in case of 'peripheral'
lesions located in the proximity of the mediastinum .
Also, patient set-up corrections due to tumour shifts lead
to a change in the dose given to the OAR. To avoid
excessive doses to OAR, it is recommended to evaluate the
impact of such shifts on the OAR dose during treatment
planning. This might be accomplished by using Planning
organ at Risk Volumes (PRV) .
The spinal cord and oesophagus should be contoured
starting at least 10 cm above the superior extent of the PTV
and continuing on every CT slice to at least 10 cm below
the inferior extent of the PTV. For patients with tumours
located in the mid- or lower zones of the lungs, the
pericardium and/or heart should be contoured as a single
structure. The superior aspect (or base) for purposes of
contouring will begin at the level of the inferior aspect of
the aortic arch (aorto-pulmonary window) and extend
inferiorly to the apex of the heart.
The defined ipsilateral brachial plexus originates from the
spinal nerves exiting the neural foramen on the involved
side from around C5 to T2 [35,36].
For peripheral tumours in the upper lobes, the major
trunks of the brachial plexus should be contoured, using
the subclavian and axillary vessels as surrogates. This
neurovascular complex will be contoured starting proximally
at the bifurcation of the brachiocephalic trunk into the
jugular/subclavian veins (or carotid/subclavian arteries)
and following along the route of the subclavian vein to
the axillary vein ending after the neurovascular structures
cross the 2nd rib.
The trachea and proximal bronchial tree are contoured as
two separate structures using mediastinal windows on CT
to correspond to the mucosa, submucosa and cartilage
rings and airway channels associated with these structures.
For this purpose, the trachea will be divided into two
sections: the proximal trachea and the distal 2 cm of trachea.
The proximal trachea will be contoured as one structure,
and the distal 2 cm of trachea will be included in the
structure identified as proximal bronchial tree (main carina,
right and left main bronchi, right and left upper lobe
bronchi, intermedius bronchus, right middle lobe
bronchus, lingular bronchus, right and left lower lobe
Delineation of the chest wall has not been regularly
performed. Little is known about chest wall morbidity in
relation to dose in stereotactic radiotherapy, and therefore
delineation is not mandatory within the ROSEL trial .
However, it is recommended to delineate the chest wall in
case of tumours in close proximity to the chest wall. This
will aid the development of NTCP models concerning
chest wall toxicity.
Dose calculation algorithms and fractionation
A number of different dose fractionation schedules have
been reported for lung SRT [38,39], but the optimal dose
fractionation schedule may vary with tumour stage and
location. Although no randomized studies comparing
different fractionation schedules have been conducted for
stage I tumours, most of the clinical experience is based
on schedules with 3 fractions of 20 Gy. In RTOG study
0236, RTOG study 0618 and in the ROSEL study, this
fractionation scheme is used. In all studies, eligibility for
inclusion was limited to lesions located 2 cm distal to
the hilar structures. Within the ROSEL study, a more
conservative fractionation scheme of 5 fractions of 12 Gy is
also allowed for patients with a tumour with broad
contact to the thoracic wall or adjacent to the heart or
mediastinum. Lung function is not considered to affect the
scheduling or fractionation. The largest clinical experience
published thus far did not exclude any patient on the basis
of poor lung function , and did not observe excessive
lung toxicity when 'risk-adapted' SRT schemes were used
This is supported by 2 recent reviews [40,41]. A report by
Timmerman  which suggested that toxicity rates were
high for central tumors treated with SRT has been
criticized on the grounds of the toxicity definitions used .
However, it is recognized that differences between
calculation algorithms in the various treatment planning
systems may be as high as 30% in individual cases .
These differences are largest for lung tumour treatment
plans, and generally increase with decreasing field size,
which is especially relevant in stereotactic radiotherapy of
stage 1A lung tumours. Thus, depending on the treatment
planning algorithm used, one should actually use an
alternative nominal fraction dose to deliver the same actual
dose to the patient. Unfortunately, extensive data
comparing all the calculation algorithms that are likely to be used
in the ROSEL study are not available. For the nominal
dose fractionation schedules allowed within the ROSEL
trial two main type of algorithms are distinguished
Type A models: Models primarily based on electronic
path length (EPL) scaling for inhomogeneity corrections.
Changes in lateral transport of electrons are not (well)
modelled. The algorithms in this group are e.g. Eclipse/
ModBatho and Eclipse/ETAR from Varian, OMP/PB and
Plato/ETAR from Nucletron, PrecisePLAN from Elekta,
Iplan Dose/PB from BrainLAB, and XiO/Convolution from
Type B models: Models that in an approximate way
consider changes in lateral electron transport. The models in
this group are e.g. Pinnacle/CC from Philips Medical
Systems, Eclipse/AAA from Varian, OMP/CC from Nucletron,
I-Plan-dose with XVMC Monte-Carlo algorithm from
BrainLAB and XiO/Superposition from CMS.
As a guideline, the fractionation schedule(s) and dose
constraints one wants to implement should be adapted to
the dose algorithm used. For example, within the ROSEL
trial, it was decided that for type A models, a standard
fractionation schedule of 3 fractions of 20 Gy or 3 fractions of
18 Gy and a conservative fractionation schedule of 5
fractions of 12 Gy or 5 fractions of 11 Gy could be allowed.
For type B models, the standard fractionation should be 3
fractions of 18 Gy and the conservative fractionation
should be 5 fractions of 12 Gy or 5 fractions of 11 Gy. A 3
fractions of 20 Gy schedule is not allowed in combination
with type B models in the ROSEL trial, as this might lead
to dose levels being approximately 10% higher than the
dose levels with which extensive experience has been
gained in the VU Medical Centre Amsterdam, using a type
A algorithm. These higher dose levels might lead to
increased morbidity. The fractionation of 5 times 12 Gy is
still allowed with type B models since the errors of type A
algorithms in calculating dose to the thoracic wall, heart
or mediastinum are expected to be less significant.
Although this also would lead to approximately 10%
higher dose levels, the biologically effective dose for the
PTV will still be well below the BED of the 3 fractions
schedule. There are no indications in the literature that
this would lead to an unacceptable level of morbidity. It is
highly recommended to include dose algorithm specifics
in future reports about stereotactic radiotherapy for lung
tumours. If a more accurate algorithm becomes available
to the authors of such articles, one should also consider
the publication of the recalculated data. These data can be
used to improve our dose-effect models, which aid the
further improvement of stereotactic radiotherapy.
Dose prescription, coverage and constraints
In line with current multi-institutional trials and multiple
single-centre experiences, the dose prescription should be
based on 95% of the target volume (PTV) receiving at least
the nominal fraction dose (e.g., 20 Gy per fraction = 60 Gy
total), and 99% of the target volume (PTV) receiving a
minimum of 90% of the fraction dose. The dose
maximum within the PTV should preferably not be less than
110% or exceed 140% of the prescribed dose, similar to
the criteria formulated in RTOG protocol 0618 . The
location of the treatment plan normalization point,
which is in fact only influencing the display of the dose
distribution, can be left to the institutions preference.
RTOG trial 0236 defined a set of parameters to quantify
the conformity of the dose and PTV coverage. The same
parameters were used in RTOG trial 0618 and are used
here. However, the ROSEL trial requires the use of
inhomogeneity corrections, whereas this is not allowed within
the RTOG trials. Consequently, the dose conformity
requirements in the ROSEL study differ from the RTOG
recommendations. Moreover, a distinction in these values
is made between type A and B algorithms, because of the
significant differences in calculation results between them
From Figure 2 it is clear that using a type B algorithm, it is
more difficult to conform the planned dose to the PTV
than using a type A algorithm, especially for a small PTV.
This is caused by the increased influence of lateral scatter
disequilibrium for smaller PTV, which is modelled better
using a type B algorithm. Thus, a less strict conformity
requirement was formulated. The difference between type
B and type A or unit density calculations is even more
pronounced for the R50% values (Figure 3). Also for the dose
at 2 cm from the PTV (Figure 4) and the percentage of the
lung receiving more than 20 Gy (Figure 5), it is clear that
a type B algorithm will result in higher values, due to the
fact that the change in lateral scattering in lung tissue is
taken into account much better. Again, the conformity
requirements for type B algorithms were relaxed for these
parameters. However, relaxation of these requirements
does not result in an actual inferior patient treatment. On
the contrary, because these more advanced algorithms
provide a better description of the actual dose
distribution, the user has a greater opportunity to optimize the
dose distribution to the stated requirements. Therefore,
the use of these more advanced algorithms is strongly
encouraged. Please note that the figures presented here are
based on the treatment plans generated without
recalculation with a more advanced algorithm, thus representing
treatment planning clinical practice within the ROSEL
trial, while in the article of Schuring and Hurkmans the
results were presented after recalculation, thus
quantifying the actual delivered dose differences arising from the
use of different algorithms . To emphasize the
improvement that can be achieved using a more advanced
algorithm over a type A algorithm or a unit density
calculation, the dose to the PTV after recalculation is given in
Figure 6 (reprinted with permission from Schuring and
Hurkmans . The figure clearly shows that The EPL
plans (Type A algorithm) consistently overestimate the
dose to the PTV, resulting in an average D95 of 48 Gy, 20%
lower than the prescribed value. The overestimation of the
dose increased with decreasing PTV size, although large
variations are observed between individual patients. For
the unit density calculations the recalculated D95 ranged
between as much as 63 and 42 Gy for individual patients.
Dose-volume constraints for OAR within the ROSEL
protocol are given in Table 2 and differ from the ones used in
RTOG 0236 and 0618 (for lung constraints, see previous
Table 1). A reassessment was considered necessary
because a new patient group will be treated with
stereotactic radiotherapy within the ROSEL trial, namely patients
who are fit to undergo both primary and salvage surgery.
As a result, normal tissue dose-constraints have to be
more stringently defined in order to minimize the risk of
increased complications after salvage surgery.
Additionally, new constraints were formulated to be used for the 5
fraction scheme. Furthermore, the constraints are based
on 1 cc volumes (except for the spinal cord), to prevent an
excessive dependency on the calculation grid size in the
evaluation of these parameters. Skin dose, with the
constraint that no point within the skin should receive a dose
higher than 24 Gy as dictated in RTOG 0618 is not
included in Table 2, as dose calculations within this
region are often not very accurate and this dose parameter
is often very labour intensive to score. However, this will
be evaluated in a dummy run procedure planned before
trial participation for each institution.
If treatment planning and irradiation are based on the ITV
concept, the PTV incorporates the complete respiratory
Type A algorithm
Type B algorithm
sFRtiaagtgiueor1oeBf2Ptruemscoruiprstio(wnitIshoPdToVses Voofl5u9mcec,to85thcec,P1T0V7 (cRc10a0n%d) 1fr0o8mcca)total of 22 patients with stage IA tumours and 4 patients with
Ratio of Prescription Isodose Volume to the PTV (R100%) from a total of 22 patients with stage IA tumours and
4 patients with stage 1B tumours (with PTVs of 59 cc, 85 cc, 107 cc and 108 cc).
tumour mobility. Several studies indicate that the use of
the ITV concept leads to the use of larger margins than
necessary to compensate for tumour motion due to
breathing [45-48]. This may in turn lead to the
unnecessary exposure of relatively large volumes of organs at risk,
especially for patients with very mobile tumours.
However, Lagerwaard et al. have shown that the incidence of
toxicity is low using this concept and a risk-adapted
fractionation schedule . Therefore, the use of this concept
is accepted within the ROSEL trial. However, one might
want to avoid unnecessary exposure of organs at risk due
to breathing motion, and four techniques can be
distinguished : 1) adaptation of margin recipe [32,50,40],
2) tumour tracking, 3) gating and 4) reduction of
breathing motion . These methods are not mutually
exclusive, for example, one might use abdominal compression
in combination with the mean-position margin recipe. It
must be emphasised that introduction of these techniques
is not needed for the majority of the patients. In a study
performed by Underberg and colleagues, it was shown
that only 15% of their patients would have a clinically
relevant PTV reduction (defined as 50% or more) using
gating compared to the PTV based on the ITV concept .
They also showed that the PTV reduction correlated well
with the tumour mobility. Thus, the abovementioned
techniques should be primarily considered when treating
very mobile tumours or for example tumours close to the
It has been shown that the use of a different margin recipe
leads to a similar reduction of the PTV as gating [45,50].
From a patients' perspective, the use of an adapted margin
recipe might be preferred, as gating significantly prolongs
the treatment time and this, in turn, leads to significantly
more intra-fractional changes in tumour position .
Also, the use of an abdominal compression plate or active
breathing control device might be less comfortable for a
patient. This less comfortable position might lead to
Type A algorithm
Type B Algorithm RTOG 25 50
FRwiaigthiuorsoteafg35e01%BPtruemscoruiprtsi o(wn iItshoPdTosVes Voofl5u9mcec,to85thcec,P1T0V7 (cRc50a%n)dfr1o0m8 cact)otal of 22 patients with stage IA tumours and 4 patients
Ratio of 50% Prescription Isodose Volume to the PTV (R50%) from a total of 22 patients with stage IA tumours
and 4 patients with stage 1B tumours (with PTVs of 59 cc, 85 cc, 107 cc and 108 cc).
increased patient movement and no data about this
possible effect is available yet. Tumour tracking by means of
an external marker does not cause any patient discomfort
and might be seen as a patient friendly alternative.
However, it is shown that variations in external/internal
motion correlation are present, making their use
potentially less accurate [54,55]. The use of internal markers is
considered more accurate, but is associated with an
increased risk of pneumothorax . Furthermore, gating
and tracking are also technically challenging techniques.
They can only be used on a wide scale if existing technical
problems can be solved .
Due to the wide penumbra of high energy ( 15 MV)
beams, it is recommended to only use photon (x-ray)
beams with energies of 610 MV. Experience has been
gained with both coplanar and non-coplanar techniques,
with in general a 713 beam angles in case static beams
are used. Dynamic conformal arcs can be used, although
For ITV based treatment plans, dose calculations can be
performed on the 3D CT scan reconstruction generated
without breathing phase binning. (i.e. an average scan or
untagged scan reconstruction). This has proven to be a
good approximation of 4D dose calculations if combined
with a type B algorithm [47,58].
For mid-position based treatment plans, dose calculations
should be either performed on the CT reconstruction
phase which represents the time-averaged mean position
of the tumour or on scan reconstruction generated
without breathing phase binning.
It is advised to keep the inter-fraction interval at a
minimum of 40 hours, in line with the RTOG protocol 0618.
Type A algorithm
Type B algorithm
aFMniagdxui4mrepuam4tiednotsew2itchmstfargoem1PBTtVuminoaunrys d(wirietchtiPoTnV(sDo2fcm5)9acsc%,8o5fcpcr,e1s0cr7ibcecdadnods1e0f8rocmc) a total of 22 patients with stage I tumours
Maximum dose 2 cm from PTV in any direction (D2 cm) as % of prescribed dose from a total of 22 patients with
stage I tumours and 4 patients with stage 1B tumours (with PTVs of 59 cc, 85 cc, 107 cc and 108 cc).
The maximum inter-fraction interval should be 4 days.
Within the ROSEL trial, the standard fractionation should
be given over 58 days, while the conservative
fractionation should be given over 1014 days. In general, it is
recommended to keep the treatment time as short as possible
in order to limit possible patient movement and patient
discomfort. Longer sessions have been correlated with
significantly more inter-fractional changes in tumour
Patient positioning should be determined by imaging at
the treatment unit itself by means of kV-CT imaging,
MVCT imaging or orthogonal kV imaging. It is strongly
recommended that the target position should be compared
to the target position in the images used for treatment
planning, and appropriate patient set-up corrections
should be applied when tumour shifts are detected .
As a minimum requirement within the ROSEL protocol,
an on-line set-up correction protocol based upon bony
anatomy should be applied.
The ROSEL trial Quality Assurance Working Party in this
article has tried to present a broad overview of all the
technical aspects of stereotactic radiotherapy for early stage
lung cancer. Our aim was to develop widely applicable
guidelines in view of the number of stereotactic
radiotherapy systems used at centres in The Netherlands which will
participate in the ROSEL trial. However, we also
formulated recommendations assuming the most advanced
technical possibilities are at ones disposal. Hopefully,
these recommended techniques can be implemented on a
large scale in the near future. As stereotactic radiotherapy
techniques are in general highly sophisticated, our paper
cannot possibly cover all areas in detail. As many aspects
of implementation depend on the available equipment,
we recommend that centres should familiarize themselves
Type A algorithm
Type B algorithm
4PFeipgracuterienentt5osfwluitnhg s(tbaogteh1luBntgusmmoiunruss(GwTitVh)PrTeVcesivoifn5g920ccG,8y5ocrcm,1o0r7e c(cV2a0nGdy)10fr8omcc)a total of 22 patients with stage I tumours and
Percent of lung (both lungs minus GTV) receiving 20 Gy or more (V20 Gy) from a total of 22 patients with stage
I tumours and 4 patients with stage 1B tumours (with PTVs of 59 cc, 85 cc, 107 cc and 108 cc).
with technical details of the equipment to be used.
Appropriate quality assurance systems should also be
implemented. A comprehensive overview of quality assurance
issues can be found in a special edition about quality
assurance of the Int. J. Radiat. Oncol. Biol. Phys. (71S,
To the best of our knowledge, this is the first trial in
stereotactic lung radiotherapy which makes a distinction in
dose prescription and dose to OAR criteria based on the
calculation algorithm used. As was clearly shown, the
dosimetric differences from the use of different
algorithms can be large, and it is more difficult to plan a
conformal dose distribution using a more advanced
algorithm. Without making a distinction based on type of
algorithm, this might lead to the incorrect assumption
that centres with such algorithms use less conformal
techniques. However, it is shown that the actually delivered
dose using type A algorithms can deviate as much as 30%,
which is highly dependent on the patient specific
anatomy and in general the deviation increases with
decreasing target volume . Therefore, relationships between
treatment outcome and dose generated from stereotactic
lung cancer trials which not primarily applied type B
calculation algorithms should be interpreted with caution.
Guidelines and recommendations have been formulated
to aid the implementation of stereotactic radiotherapy for
early stage lung cancer patients in both individual centres
as in future multi-institutional trials. They are formulated
such that stereotactic treatment can safely and effectively
be implemented in clinical practice in a wide variety of
hospitals and treatment results become better
The authors declare that they have no competing interests.
Dose to 95% of the PTV as a function of the PTV after recalculation using a type B algorithm (Collapsed Cone
(CC) algorithm, Pinnacle 8.0 h) from a total of 22 patients with stage IA tumours and 4 patients with stage 1B
tumours (with PTVs of 59 cc, 85 cc, 107 cc and 108 cc) (reprinted with permission from ref 20). Plans were
optimized using a type A algorithm (EPL), a unit density calculation (UD) or a type B algorithm (CC).
CH drafted the manuscript, coordinated and participated
in the Quality Assurance Working Party designing the
guidelines, and participated in performing the
calculations comparing dose calculation algorithms. JC, FL, JW
and UH were all members of the Quality Assurance
Working Party. DS participated in performing the calculations
comparing dose calculation algorithms. SS conceived of
the study, and participated in its design and coordination.
All authors read and approved the final manuscript.
The ROSEL study is supported by a grant from ZonMW. Grants for the
ROSEL radiotherapy quality assurance work from Elekta, Philips Medical
Systems and Promis Electro-Optics are gratefully acknowledged.
Deviation given as cumulative absolute dose (Gy)
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