METHODS
Five different VMAT-SIB schemes were designed using the Varian Trilogy IX linear accelerator (Varian
Medical Systems) for total scalp irradiation and bilateral neck irradiation. These different VMAT scehemes
were compared with respect to a dose volume histogram of obtained data, homogeneity, indices,
conformity index, OAR, and doses of target volumes.
RESULTS
The patient-designed bolus plan 1 with two isocenters was chosen as the most appropriate plan. Plans 2, 3,
4, and 5 were inappropriate plans because the application of the virtual bolus in plan 2 was difficult, plan
3 with one isocenter was unacceptable with respect to the value of conformity index, plan 4 with three
isocenters had a matching field, and plan 5 in which different priority values were used had an increase
in OAR doses.
CONCLUSION
VMAT-SIB can be preferred as an appropriate radiotherapy technique as it can provide optimum and
allowable OAR doses in tumors requiring an intensive treatment planning effort.
Keywords: Agiosarcoma of the Scalp, Radiotherapy, VMAT
Diagnostic procedures
Angiosarcoma was diagnosed in the patient after incisional
biopsy for pathological diagnosis. Mitosis 2,
histological grade 2, CD31 (positive), CD34 (positive),
vimentin (positive), pan-CK (negative), Ki-67 proliferation
index 15%?20%, and common perineural invasion
were reported to be present.
Staging
Because of the high possibility of distant and locoregional
metastases, brain MR and PET CT were requested for
staging. The results detected an appearance with an irregular
FDG uptake (SUV max: 6.2) compatible with
residual disease in the left parietal scalp, a lymph node
with the size of 6×7 mm, retaining FDG (SUV max: 6.2)
in the left mastoid localization, a lymph node with the
size of 6×9 mm retaining FDG (SUV max: 9.2) in the
left cervical chain level 2, and a lymph node with the size
of 5×6 mm retaining FDG (SUV max: 1.8) in the left
cervical level 5. It is noteworthy that distant metastasis
was not detected in the patient, and sizes of metastatic
lymph nodes of the primary mass were small and their
SUVmax values were low.
Surgical procedure
Local wide excision and left neck dissection of the mass
on the scalp were performed. Pathologically, angiosarcoma,
tumor diameter: 5×1.5 cm, differentiation: score
2, mitosis: >20/10BBA score 2, tumor necrosis, perineural
invasion, and lymphovascular invasion were present;
the tumor was found to be at a distance of 0.1 cm
to the base surgical border. A total of four metastatic
lymph nodes were detected in 65 dissected lymph nodes
comprising level 2 (two nodes), level 4 (one node), and
postauricular (one node) ones and capsule invasion was
reported to be present in two lymph nodes consisting of
postauricular 0.8 cm and level 2 0.5 cm ones.
Adjuvant treatment
Because the risk of postoperative locoregional recurrence
and distant metastasis was high, the patient underwent
RT and was administered 80 mg/m2 of paclitaxel
weekly and he underwent CT concomitantly.
Radiotherapy Determination of CT simulation and
target volume
Treatment planning
Plan 1 (Horizontal dual isocenters, four arcs, special
bolus): In this plan used for treatment, a patient-specific
bolus was designed during CT, as shown in (Fig.
Plan 2 (two isocenters and four arcs, 0.5 bolus): Plan
1 used for treatment was considered as a template. Similar
to the plan applied in real settings, the bolus was
virtually created using the treatment planning system.
The plan"s CI appeared to be applicable as HI values;
however, because of difficulties and uncertainties in the
application of the bolus, it was thought that this plan
was not be suitable in practice.
Plan 3 (single isocentric planning): A plan was created
by placing the field center at the center of the total
PTV volume and by trying different collimator angles.
The most suitable angles were determined to be 315°,
45°, and 0°. Although it had the lowest monitor unit
value based on the multi-isocentric planning, it was
still insufficient for reducing the dose in critical organs,
such as the brain, and for providing CI for target volumes.
Plan 4 (three isocentric planning): Planning was performed
using the Arc Geometry Tool and by selecting
three isocenters. The field isocenters were positioned
to the right and left of the larynx, the vertical midpoint
of the PTV60 area. Thirty degree and 330° collimator
angles were used in the areas in the scalp region, while
a 30° collimator angle was used in the lower area. There
was an increase in critical organ doses in the lower area,
while there was no significant change in the doses in
the upper area compared with the other plans. In addition,
because the device did not allow three isocenters
to be set automatically, the target volume was manually
divided to try to overcome this problem. However, we
think that this plan is not suitable because of the development
of area overlap and hot spots.
Plan 5 (two isocenters, different priority): This plan
was designed based on Plan 2 but with different values
of priority. Priority values were increased for target
volumes, but an increase was observed in OAR doses
and total monitor unit values. Acceptable planning was
achieved with the least accuracy in the dosimetric measurement
analyses involving the treatment verification.
In the study by Kelly et al.[
Dosimetric analyses>
Homogeneity index (HI)
The minimum, maximum, mean dose, homogeneity
and CI values, and MU values that PTVs take in the
five different VMAT plans were compared, and these
values are shown in (Table
Treatment administration and verification
The patient was immobilized in a supine position with
a head and neck thermoplastic mask. CT simulation including
the head and neck was performed with a 3-mm
slice thickness and 3-mm slice spacing. The target was
drawn according to the International Commission on
Radiation Units and Measurements Reports (ICRU) 50
and 62guidelines for each CT section with the volumes
and OAR eclipse treatment planning system.[
All operations were performed using a Varian Trilogy
IX linear accelerator (Varian Medical Systems). The
dose calculation used the Anisotropic Analytical Algorithm
Model (2.5 mm×2.5 mm×2.5 mm) with the Varian
Eclipse Version: 13.6 Arc Geometry tool, RapidArc
(VMAT) planning. Five different VMAT plans were designed
using the same dose prescription and optimization
constraints. The RapidArc plan would include two
coplanar full arcs that rotate counter clockwise from
179° to 181° and clockwise from 181° to 179°. The plan
was designed by also considering the recommendations
provided by Kelly et al.[
Conformity Index (CI)
CI is a parameter used for estimating the degree of conformity
of a plan. According to RTOG publications, CI
1 indicates that the plain is ideal. If the index value is
1?2, the treatment is compatible with the plan. If it is
2?2.5 or 0.9?1, a small deviation exists. If the index is
<0.9 or >2.5, it means that there is a large deviation.
[12,13] CI values are shown in (Table
HI is a parameter indicating the homogeneity of the
dose distribution in the target volume. Different formulas
are used in the literature to describe HI.[
A patient-specific dose verification procedure was performed
with portal dosimetry for the RapidArc plans.
Hybrid phantom plans were constructed by recalculating
dose distribution with QA phantom geometry using
the same beam parameters of the patients" plans.
In addition, MUs and the duration of the application
were recorded for each plan to assess the application
efficiency of different treatment techniques. Daily field verification was performed using the kv-port cbct to
ensure correct administration of the treatment.
The etiology of angiosarcoma includes exposure to
radiation. Radiation-induced angiosarcoma typically
develops 5-10 years after irradiation, whereas longer
latency periods have also been shown after head and
leg irradiation.[
Because scalp angiosarcoma is so rare, there is no
standardized treatment for the disease and treatment
decisions have often been made on retrospective heterogeneous
patient profiles and on judgments in other
soft tissue sarcoma treatment algorithms.[
Because of high recurrence rates, adjuvant RT is
provided postoperatively. During TSI, regional lymphatics
are also required to be coirradiated.[
In the 80s and 90s, TSI was attempted with electron
therapy techniques, and techniques, such as overlapping,
shifting, and overlaying, were used in electron
fields to create enough dosage to cover the target volumes
of the dermis and epidermis.[
Disclosures
Peer-review: Externally peer-reviewed.
Conflict of Interest: None declared.
Authorship contributions: Concept - S.Y.R; Design -
S.Y.R; Supervision - S.Y.R; Materials - S.Y.R; Data collection
&/or processing - S.Y.R, Y.Ç, M.E; Analysis and/or interpretation
- S.Y.R; Literature search - S.Y.R; Writing - S.Y.R;
Critical review - S.Y.R