The Modified Danish Technique for adjuvant irradiation after
mastectomy
P.F.Kukołowicz, A.Wieczorek, B.Selerski, T.Kuszewski
Introduction
Adjuvant postmastectomy teleradiotherapy is a standard of care for a group of breast
cancer patients at high risk of locoregional recurrence [1,2]. Despite long history of use of
postmastectomy irradiation only recently survival benefit was proved in randomized trials
[3,4,5].. The main disadvantage of the use of the ionizing radiations in the breast cancer clinic
was the considerable excess of cardiac death in the irradiated compared to the non-irradiated
patients [6,7,8]. Patients with left-sided tumors had bigger probability of ischaemic heart
disease than those with the right-sided. The old techniques with big volume of the heart
included in the high dose region and inappropriate fractionation were considered to be the
main reason of the excess in cardiac mortality in the past, whereas the application of adequate
technique and fractionation did not effect this toxicity [4,9]. The dose to the heart strongly
depends on the technique applied and the energy and type of radiation used for the treatment.
The highest dose to the heart was delivered in the era of the orthovoltage and cobalt
radiotherapy and when the so called wide tangent technique was used irrespective on the
radiation type[10,11]. The second important dose-limiting organ for radiation therapy of the
breast is lung [12,13,14], however the significant lung injury; the radiation pneumonitis and
fibrosis, were noticed very rarely and especially in patients previously treated with systemic
therapy [15,16,17]. The better knowledge concerning the dose-volume dependence of the
probability of the lung and heart injury and parameters that can be easily obtained from the
dose volume histogram curves help in evaluation of the dose distribution for the treatment
plan prepared for each single patient. The breast cancer is the most common malignancy in
women so the application of a good and safe treatment technique is of the special importance
in the management of this disease. There is a very large number of several techniques used for
postmastectomy irradiation: a) the most common technique based on two tangential opposite
beams, b) very modern IMRT techniques with or without active breathing control, c) several
electron based techniques, stationary and arc techniques, d) complicated rotational photon
techniques and e) mixed photon electron techniques. Nevertheless no single technique is
accepted as the „gold standard” [18-23]. The choice of the technique applied in each
radiotherapy department depends on the technical availabilities , preferences and traditions.
The aim of this paper is to describe the post-mastectomy irradiation technique of breast cancer
patients applied in the Holycross Cancer Centre (HCC) in Kielce . Our technique is referred
Summer School of Radiotherapy, Kielce, Poland 2003
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as the Modified Danish Technique (MDT), because this method is applied for many years in
Aarhus in Denmark. In the literature this technique is sometimes called as inverted hockeystick technique [24].
Materials and methods
Patients
The study group of patients consisted of 40 women suffered from breast cancer
treated with adjuvant postmastectomy radiotherapy directed to chest wall and loco-regional
lymphonodes. The indications for postoperative irradiation were: histologically confirmed
involvement of excised axillary lymphonodes (pN+) and/or tumor stage pT3 or pT4 revealed
in pathologic report of radical mastectomy. Patient previously diagnosed stage III, who were
subjected to neoadjuvant preoperative chemotherapy were also qualified to postmastectomy
radiotherapy irrespective of findings in pathologic specimen. The irradiation was carried out
in conjunction with systemic adjuvant treatment. The radiotherapy usually started right after
II cycle of CMF chemotherapy with III cycle given concomitantly with irradiation. When
antracyclin based regimen was prescribed the postmastectomy radiation was postponed till the
finish of this treatment. In case of adjuvant hormonotherapy the postoperative radiotherapy
was initiated when healing of surgical scar was adequate. In the evaluated group there were
23 patients irradiated on the left side and 18 patients irradiated on the right side of the chest
wall. The treatment plans of the patients were renumbered for the use of this article: 1-23
were left-sided patients and 24-42 were right sided patients.
Data preparations for the treatment planning.
All data needed for the treatment planning were collected in the treatment position.
The patient was lying supine on the flat table with both arms along the body. The arm on the
treated site was slightly bended so it did not touch the chest wall in the irradiated region. In
order to make the treatment position as comfortable as possible the KneeFix immobilization
system was used. The position of a patient is shown in figure 1. The two tattoos BL and BR
were made in accordance with external laser system on both lateral surfaces of the thorax .
Third point GR was tattooed on the frontal surface of the thorax at the mid-line near the
sternum. This point was used as a geometrical reference point which was used for obtaining
the entrance point for both photon and electron beams. All three points were used to
reproduce the position of the patients during the irradiation. At the time of patient’s CT the
radioopaque small wire crosses were placed on the patients skin at points GR. The scar was
marked with the thin wire. CT images were acquired at 10 mm thick intervals from the level
of the mandible through the lung bases. The CT images were transferred to contouring station
where the CTV and organs at risk contours were delineated by radiotherapists.
Summer School of Radiotherapy, Kielce, Poland 2003
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Figure 1
The lung contours were defined by means of the automated density gradient tracing method
and if needed corrected by the physicists responsible for treatment planning. The heart
contours were delineated manually by physicians. The CTV including the chest wall, the
axillary , the parasternal and the supraclavicular lymph nodes was entered by radiotherapist.
The PTV was defined by expanding the CTV of 5 mm in the medio-lateral direction only.
This margin was to compensate the set-up errors only. Then the data were send to the
treatment planning system, TMS Nucletron Ver.6.0. The PTV and organ at risk were checked
and corrected by senior radiotherapist before the start of planning of the treatment .
Treatment planning
The typical treatment field arrangement was shown in figure 2 and 3.
Figure 2
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tattoo
Figure 3
In most cases one AP 6 MV photon and one AP electron fields of individually chosen
energy were used. The energy of the electron beam was chosen from 6, 9, 12 and 15 MeV.
The supraclavicular and axillary regions were irradiated with the photon field only. The chest
wall was irradiated with photon and electron fields. There was no fixed position of the
upper(superior) border of the electron beam. The position of this edge was defined during the
treatment planning. The most often this edge was located near the second rib. The lateral
border of the electron beam and consequently the medial edge of the photon block were
located a few millimeters internally of the lung-chest wall edge. The lateral edge of the
electron field was shaped with an individual boomerang-shaped block. For the photon field
this part of the PTV which was irradiated by electron beam was covered by shielding block.
The photon and boomerang-shaped electron blocks matched to each other - there was no gap
between two fields. In the figure 4 the electron and photon blocks were shown.
Figure 4
The energy of electron field was chosen individually for each patient. The dose in the
therapeutic region covered with electron field could not be lower than 85% of the maximum
dose at the central axis with one exception. At the upper border of the electron field the
minimum dose was allowed to be of 80%. Preferably the minimum dose should be 90%. This
requirement influenced the decision where to place the upper border of the electron field. In
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order to spare the lung tissue and the heart for the left-sided patient the highest energy of the
electron beam was 15 MeV. If the thickness of the chest wall required usage of the higher
energy of the electron beam the standard tangential photon field techniques was preferred
[18].
The treatment planning process usually begun with the choice of the energy of the
electron beam. Then the shape of the electron field was designed. After that, the size and the
shape of the photon field was chosen. The dose distribution was calculated and the first trial
of designing of the individual bolus started. The dose distribution was calculated and the
physicist reviewed the dose distribution. The shape of the bolus was corrected until the 90%
isodose followed the internal border of the PTV. There was acceptable to have the minimum
dose of 85% in some small regions. The process of bolus design was usually time consuming
because the change of the shape in one slice influenced the dose distribution in the
neighboring slices. After completion of the bolus design the dose distribution in the smaller
calculation grid size was calculated. The dose distribution was normalized to the maximum
dose at the central axis of the electron beam. The photon weight was chosen to have the
minimum dose in the supraclavicular region bigger than 80%. If it was required to set the
weight larger than 110% than additional PA photon beam was added. The dose distribution
was evaluated by physicists and if accepted it was presented to referring doctor. After
acceptance the dose distribution in the central scan and the protocol was printed for record
purpose. Also the shape of outer contour of the patient in all slices where the bolus was
defined was printed and delivered to mould room staff. The shape of the photon and electron
blocks were send to the computer block cutter. The typical dose distribution in the plane,
where both electron and photon fields delivered dose to the PTV was presented in figure 5
(the plane near the central axis of the electron beam) .
The patients were treated with a prescribed dose of 50 Gy with fraction dose of 2 Gy.
The dose was prescribed at the maximum dose on the central axis of electron beam.
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Figure 5
Bolus preparation.
The bolus was made manually from the mixture of the wax and paraffin. It was made
of 1 cm thick pieces. A paper shape represented the bolus in one CT slice were glued to the
every piece of the bolus and than cut-off. After preparation of all pieces of boluses they were
joint to each other. Later the surface of the bolus were rounded. For each bolus a special form
made from plaster-bands were prepared. The form protected the bolus from a deformation.
The bolus was placed into the form and put into the heater at temperature of about 45oC until
the right shape of the bolus is restored if the technologists noticed that it had changed the
shape during the irradiation course. An example of the bolus and the form is shown in the
figure 5 .
Figure 6
Treatment simulation and treatment execution
Patient was placed in the treatment position on the simulator treatment. The
simulation started from the photon field. The entrance points of the photon fields was
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obtained by the appropriate shifts of the table with respect to the geometrical reference point GR. The entrance point was tattooed. After the photon block was placed in the block holder
the shadow of the block edge was marked on the skin with the marker. Along this line a few
tattoos were made. Next the entrance point of the electron beam was defined and the bolus
was placed on the skin (see figure 3). The position of the block was carefully defined with
respect to the medial edge of the electron field and the outline of the bolus was marked with a
marker on the skin. The irradiation was performed in a similar way and during every
treatment session before the irradiation the outline contour of the bolus was remarked.
Evaluation of the dose distribution
For each patient the DVH in the PTV, lungs and heart were calculated. In order to
compare the dose distributions for all patients the dose was normalized to the mean dose to
the PTV. For the PTV the standard deviation of the dose was calculated as a metrics of the
dose homogeneity. The percentage of the PTV volume that received the dose larger than
110% - PTV110 and less than 90% - PTV90 were also calculated. For the lungs the volume of
the organ that receives at least 20 Gy was calculated – LV20. Hurkmans [9] showed a good
correlation between the probability of the pneumonitis and the LV20. For the heart the
volume of the organ that received at least 30 Gy was calculated – HV30. In the Stockholm
trial it was shown that the risk of heart injury correlates with the HV30.
Results
The distribution of electron energies used for the group of 150 patients was shown in
figure 7 .The standard deviation of the dose distribution for left sided patients was presented
in figure 8 . The LV20 for patients irradiated on the left and right side were shown in figure 9
and 10. The H30 for patients irradiated on the left side was shown in figure 10.
Energy beams distribution
Number of patients
50
55.2%
40
30
23.9%
20
10
51.8%
left
27.7%
right
17.9%
3.0% 2,4%
0
6 MeV
9 Mev
12 MeV
15 MeV
electron energy
Figure 7 Percentages were calculated for left and right side separately.
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Standard deviation PTV
left sided patients
Value of St. Dev. (%)
12
10
8
6
Serie1
4
2
23
21
19
17
15
13
11
9
7
5
3
1
0
Patient's number
Figure 8
Discussion - advantages and disadvantages of the Modified Danish Technique
Energies of electron beams
The most common energy used for MDT technique was 12 MeV. This energy was
used in more than 50% of cases. The higher energies were used for right sided patients. The
average energy used for right and left side patients was 11.7 and 10.0 MeV respectively. The
energy of 6 MeV was never used for the right side. The 15 MeV was used for some patients .
The application of higher energy was not allowed by our protocol. The technique was change
to standard tangent technique if the higher energy had to be used.
LV20
left sided patients
Volume > 20 Gy (%)
30
25
20
15
VL20
10
5
23
21
19
17
15
13
11
9
7
5
3
1
0
Patient's number
Figure 9
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Volume > 20Gy (%)
LV20
right sided patients
40
35
30
25
20
15
10
5
0
VL20
24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
Patient's number
Figure 10
8
7
6
5
4
3
2
1
0
23
21
19
17
15
13
11
9
7
5
3
VH30
1
Volume > 30 Gy (%)
HV30
left sided patients
Patient's number
Figure 11
Treatment position
The very important feature of the MDT was the therapeutic position of a patient. The
natural body position makes this technique very convenient for a patient and consequently
very reproducible. Additionally the patient reproducibility was positively influenced by the
treatment geometry. Both fields enter the body from the same AP direction. Our results
showed that the random error of patients set-up described in terms of standard deviation was
of about 2.5 mm for both cranial-caudal and medial-lateral direction. In case of most other
techniques the arm at the irradiated site had to be raised over a head. The position then was
not as comfortable as in MDT. For some of them despite of rehabilitation it was difficult to
keep the hand in this position. Moreover raising an arm over a head changed the position of
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the muscles in the axillary and supraclavicular region and caused the lymph nodes lying
deeper. We tried to irradiate our patients with the arms raised over a head few times. The idea
was to be ready to use the same CT information for tangential field technique if the MDT
would be not acceptable. We noticed that it was never possible to use a single AP photon field
to irradiate the lymph nodes in the supraclavicular region, because the minimum dose was
always smaller than 80%. For patients lying in this position the additional PA beams had to be
applied in the supraclavicular and axillary region. Our experience showed that the MDT
allowed irradiation with only AP field in more than 95% cases. In most cases the minimal
dose delivered to the axillary lymph nodes differed from the prescribed dose of no more than
10%.
Dose distribution in the PTV
For all techniques for patients treated after mastectomy it was difficult to obtained the
homogenous dose distribution in the target volume [14]. The reasons for not having good
coverage of the dose were complicated and large target volume and the match field regions.
Also the application of the electron beam made the dose distribution homogeneity worse. For
techniques were the photon and electron beams were used the good matching was impossible
due to a very different penumbra of both fields. The typical penumbra of photon beam was of
about 5 mm while the electron beam was of about 12 mm. For electrons beams the penumbra
increased with the depth. For the MDT the unprofitable factor was a very long matching line
which was usually of more than two times longer that for standard tangent technique. As it
was shown in the figure 5 the standard deviation for patients irradiated on the left side was
about 10% which was much larger than the acceptable value according to international
standards. The similar results were obtained for right sided patients. There was no data in the
literature to be compared with our data. The information about the dose homogeneity was
limited only to the chest wall region. The only argument that despite of the lack of the good
homogeneity the MDT technique might be acceptable was the long clinical experience of
using the similar technique in Aarhus and Karolinska.
As it was shown in the histogram of the dose distribution in the PTV the disability of
good match of electron and photon beams led to deliver to the subvolume of the PTV the dose
higher of the prescribed dose of 10%. The volume of this region was usually less than 10% of
the total volume of the PTV. In the 5 years experience of the usage of the technique there was
no serious damages of the skin or other structures of the chest wall. The early reactions
disappeared in the period of 3 to 4 weeks after the completion of the treatment. However the
latent time of the fibrosis and teleangiectasia is much longer than 5 years so the clinical
evaluation of the technique with regard to possible consequences of the overdosage needs
longer observation. In all techniques applicable to the patients after mastectomy there were
problems of beams matching. Theoretical analysis reviles that the best dose distribution at the
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match line may be obtained for the monoisocentric standard tangential technique.
Unfortunately that technique may be performed only on the linear accelerators with
asymmetric collimator and, what one needs to remember, the match of the treatment beams is
the only one of many others parameter that should be taken into account in treatment
technique. Irrespective of the technique which was applied the good reproducibility should be
obtained. In case of systematic error the overdosage or underdosage region is present. In the
Holycross Cancer Centre the project was realized aimed on to improve the beams matching.
Of about 12% of the PTV volume received the dose smaller than the prescribed one of more
than 10%. This volume was situated in the axillary region mainly.
Dose to the radiosensitive organs.
The heart and the ipsilateral lung were considered as the organs at risk for
postmastectomy irradiation. The results of Stockholm trial showed (reviled) that the dose
delivered to the heart increased the number of fatal heart diseases. The mortality was
correlated with the volume of the heart that absorbed the dose larger than 30 Gy – HV30. For
patients treated on the left side the HV30 was in the range 0%-7.5% with the mean value of
3.5%. This dose was negligible for the heart with respect to the possibility of heart injury.
This result makes this technique fully safe. The probability of the serious heart injury was less
than 1%. The smaller dose to the heart was obtained by Pierce for the technique referred to as
partially wide tangent fields. However there was a difference between the definition of the
PTV used by Pierce and in our case. In his work the internal mammary nodes located in the
first two intercostals spaces were included in the PTV only. In our case also the IMN in the
third and fourth intercostals spaces were included in the PTV what surely increased the dose
to the heart.
For the MDT the dose to the lung depended on the anatomical structure and the
energy of the electron beam. As more curve was the outline contour in the region irradiated
with electron beam and larger the electron beam energy as higher was the dose to the
ipsilateral lung. For the patients irradiated on the left side the mean value of the LV20 was in
the range 14.6% and 24.4% with the mean value of 18.3%. For patients irradiated on the right
side the LV20 was in the range 23.0% and 32.0% with the mean value of 26.7%. Based on the
data published by Hurkmans one may evaluated that the risk of acute lung pneumonitis for
left sided patients is negligible and for right sided patients is smaller that a few percent. The
mean value of the LV20 calculated for the 20 patients treated with similar technique referred
as the inverse hockey stick published by Pierce was 34% [14]. For the MDT technique the
mean LV20 dose was smaller than the LV20 dose for the standard tangent for which the
smallest dose to the lung was obtained of all techniques analyzed by Pierce. In the inverse
hockey stick technique the individual bolus was not used so it was likely that the smaller dose
to the lung for the MDT was obtained thanks to the individual bolus. In our technique the
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important role in the diminishing of the dose to the lung and likely to the heart played the
individual bolus. The bolus shape was designed to keep the minimum dose at 90%. It may be
expected that the smaller dose to the lung could be delivered if the bolus would have been
designed tracing 80% isodose but then the inhomogeneity of dose distribution would be
larger. The additional advantage of the MDT was the possibility of choosing the match line
between the electron and photon beam individually. For thinner patients this border was
moved up so the dose to the upper lobe of the lung from the AP photon beam was diminished.
The change of this border for the most common technique as it was the tangential field
techniques was very limited.
Technical aspects of the MDT.
The MDT may be used only with the CT based data which enables the precise
information of the chest wall thickness. There is not possible to design appropriate individual
bolus without such information . The usage of the standard bolus may cause the excessive
irradiation of the lung and delivering to small dose at least to the part of the PTV. Therefore
in the authors’ opinion the MDT should be based on the 3D CT treatment planning. The
treatment planning of the MDT technique is very time consuming and may be performed by
experienced expert in treatment planning Also the bolus design is a challenge for the team of
the mould room. The average time of MDT preparation was about 6-8 hours what was about 2
to 3 times longer than the standard tangential technique. On the other hand the realization of
the MDT technique at the linear accelerator was relatively easy. The only problem was
placing a very heavy photon block in the block holder.
Conclusions:
1. Five year experience of using the Modified Danish Technique proved that it is good
and safe technique of irradiation after mastectomy.
2. The main advantages are: very convenient and reproducible position of a patient
which enables 3D treatment planning in the whole PTV, the small dose to the organs
at risk, to the ipsilateral lung and heart.
3. The disadvantage of the technique is the poor dose homogeneity in the target volume
and the long matching line of electron and photon beam.
4. The MDT is very time consuming at the stage of preparation and very convenient at
the irradiation.
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