970 / 1096
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ESTRO 36
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comparison of planned to delivered plans for all TG-119
targets for IMRT and VMAT deliveries are shown in Figures
1 and 2 below, and for the two MLC systems. The
prototype MLC system produced higher passing rates for
both IMRT and VMAT than the TB MLC system for the
various test plans. In addition, the prototype MLC system
performs equally well for IMRT and VMAT, whereas the TB
MLC is less optimum for VMAT delivery compared to IMRT
(Fig. 1 and Fig. 2).
Conclusion
The TG-119 test plans were performed on a prototype MLC
system in comparison to the well-understood TB
Millennium MLC. Our investigation showed, in the context
of TG-119, this prototype MLC performs well for both IMRT
and VMAT plans.
1
Ezzel G., et al., 'IMRT commissioning: Multiple institution
planning and dosimetry comparisons, a report from AAPM
Task Group 119.” Med. Phys.
36
:5359-5373 (2009).
EP-1735 Total skin irradiation with helical
Tomotherapy: Planning and dosimetry feasibility
aspects
A. Haraldsson
1
, P. Engström
1
1
Skåne University Hospital, Radiation physics, Lund,
Sweden
Purpose or Objective
Mycosis fungoides (MF) is a lymhpatic disease that attacks
the skin. The primary treatment for treating MF is total
skin electron therapy (TSET). The procedure is technically
challenging both in terms of dosimetry and treatment
delivery. Helical TomoTherapy (HT) is due to its design
especially advantageous when irradiating very long and
complex targets. In this study we have explored the
possibility of employing HT in the treatment of total skin
irradiation (TSI).
Material and Methods
We used an anthropomorphic whole body phantom (PBU-
60 Kyoto Kaguka). The phantom was immobilized with
whole body vacuum bag, a five-point open head net mask
fixated to the couch and an individual neck rest. The
phantom was covered with a 7 mm thick wet suit made of
Neoprene (AquaLung) and CT scanned in two sets; from
vertex to thigh and from toes to hip. The CTV was defined
as skin with 5mm depth, with PTV as a 7 mm expansion.
An optimization bolus was added from the body and 12 mm
expansion, defined as mass density 1.0 g/cm
3
. The
prescribed dose was 12 Gy delivered in 6 fractions. The
dose planning was aimed to keep D
95%
> 95% to PTV and
minimizing dose to organs at risk, which was defined as
the rest of the body. An optimization structure was used
to create a tangential irradiation of the skin, minimizing
the dose to normal tissue. We tested the bolus effect of
Neoprene with Gafchromic EBT3 film by irradiating slabs
of 7mm, dry and soaked in water. To verify skin doses, the
phantom with wet suit was irradiated with several 2x2 cm
2
slabs of film taped to the body. The film were evaluated
at least 24 hours after irradiation. Corresponding detector
array measurements (Delta4, Scandidos) were done and
evaluated with gamma analysis. Further, a robustness test
was done by moving the phantom 10 mm in the x, y and z
directions, to evaluate the effect of mispositioning.
Results
Results of planning and robustness tests are presented in
table 1. Measured data fit to depth dose data yields a dose
maximum at 28 mm for Neoprene. Hence, 7 mm is
equivalent to 3 mm thick water bolus and lightly soaked
Neoprene adds another 1.2 mm thickness of water. Delta4
gamma analysis with 2 mm and 3%, global dose, is clinical
acceptable with regards to deliverability (M = 93%, SD =
3%). The verification of 27 film slabs for skin dose gave an
average difference from TPS dose of 4% (SD = 3%), figure
1.
Conclusion
The difference of measured dose compared to TPS, for
both film and Delta4 dosimetry is larger than most types
of targets treated with HT which is to be expected
considering the technique and size of target. The
deliverability is within limit of our clinic action levels
(gamma pass rate < 90%) and neoprene is feasible as bolus.
The benefits, in comparison with reported electron
treatments, are target homogeneity and target coverage
with good immobilization and complete irradiation with
two positions. The higher dose to organs at risk than
reported with electrons needs to be addressed if
acceptable with regards to toxicity.