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modalities and choice of associated cases need to take
into consideration the utility for clinical trials.
Results
The Level III audit is an end-to-end test using a humanoid
thorax phantom (CIRS, Norfolk, VA). The custom phantom
has a central insert for either conformal modality with two
farmer chambers, or for IMRT and VMAT with seven CC13
ion chambers as the primary detectors. The IMRT/VMAT
central insert includes a film holder for supplementary
measurements. The custom phantom includes removable
lungs that are replaced with solid water inserts to
investigate the effect of inhomogeneity on IMRT and VMAT
deliveries. Figure 1 shows the custom phantom. The CC13
chambers are connected to the TomoTherapy
®
TomoElectrometer, an 8 channel reference class
electrometer for simultaneous measurement on all
chambers for each audit case.
The IMRT and VMAT planning cases were designed for
addition to the current Level III audit. Clinical plans were
prepared based on the AAPM Publication TG119 [1] and
adapted for use in the ACDS audit program. Table 1 shows
an example of how the audit outcomes are reported. Each
modality is scored separately, and assigned a Pass
(Optimal Level), Pass (Action Level), or Out of Tolerance
outcome. Field trials on the IMRT, VMAT and FFF
modalities began in September 2016. In 2017 the new
modalities scoring criteria will be finalised and the new
modalities will go live, and field trials on a SABR modality
are scheduled to begin.
Table 1
Example of modality scoring in the ACDS Level III
audit.
Figure 1
Images of the custom CIRS phantom for the new
ACDS Level III audit, showing the removable lungs and
removable central insert.
Conclusion
The ACDS is developing a comprehensive suite of audit
modalities aimed at ensuring patient safety across a range
of clinical practice. The new Level III (end-to-end) audit
joins the integrated range of multi-modality audits
provided by the ACDS including the Level Ib audit (on-site
linac output) covering reference beams, FFF and small
fields and the Level II audit (slab phantom combined with
array) audit covering conformal, IMRT, VMAT and FFF
treatments
plans.
EP-1756 Treatment planning and dosimetric validation
of bone oligomet SABR treatments on TomoTherapy
C. Thomas
1
, T. Burrows
1
, R. Lynn
1
, N. Milesi
1
, S. Petty
2
,
M. Stenson
1
, K. Blythe
1
, T. Greener
1
1
Guys and St Thomas NHS Foundation Trust, Medical
Physics, London, United Kingdom
2
Guys and St Thomas NHS Foundation Trust,
Radiotherapy Department, London, United Kingdom
Purpose or Objective
To establish whether the TomoTherapy helical delivery
system can accurately deliver high dose per fraction SABR
treatments to bone oligo-metastases within the NHS
England Commissioning through Evaluation SABR program.
Material and Methods
TomoTherapy Volo treatment planning system was used to
generate example SABR treatment doses of 10Gy and 15Gy
per fraction to a cylindrical PTV within a CT dataset of the
Delta-4 phantom. These treatments were delivered to the
Delta-4 phantom. Treatment plans for clinical oligo-
metastases in bone, with prescription doses of 27Gy/3#
and 30Gy/5# were generated and delivered to Delta-4
phantom, ionisation chamber and Gafchromic film.
Clinical treatment fractions were delivered in 2 half-
fractions in order to allow a mid-fraction imaging scan to
assess intra-fraction motion.
Results
Volo treatment planning system signalled when the
treatment planning objectives were not deliverable and
suggested modified treatment planning parameters. The
test cases measured on Delta-4 passed local gamma
analysis at 3%/3mm with >95% pass rate. Paddick and
CIRTOG conformity indices were improved with the use of
TomoTherapy compared with VMAT solution for the first
clinical case, and dose gradient between target and
critical structures was improved. For the first clinical case
measured on Delta-4, 100% of sampled detectors passed
within 3%/3mm gamma analysis and 98.5% passed within
2%/2mm.
Initial
transverse
EBT2
Gafchromic
measurement of the first clinical case showed satisfactory
qualitative agreement with treatment plan. Subsequent
EBT3 GAFchromic film measurements resulted in 97.5%
gamma passrate at 3%/3mm and mean dose deviation on
representative dose profiles of less than 2.2%. Average
intra-fraction motion between half fractions was 0.68mm
in X, 0.64mm in Y and 0.84mm in Z with standard deviation
of 0.62mm, 0.48mm and 0.79mm respectively.
Conclusion
GSTFT is the first centre with QA approval under the NHS
England CtE programme to treat bone oligometastatic
cases using the TomoTherapy treatment planning and
delivery system. Volo and Hi-Art systems are capable of
generating and accurately delivering homogeneous dose of
up to 15Gy per fraction in phantom studies. Clinically
approved treatment plans for bone oligomet cases
delivering up to 9Gy per fraction have been generated and
accurately delivered to diodes, ionisation chamber and
Gafchromic film. Intra-fraction motion was small and has
permitted the reduction of PTV margin from 4mm to 3mm.
EP-1757 QA of MLC Elekta Agility for Static fields
F. Tato de las Cuevas
1
1
Hosp. Univ. de Canarias, Medical Physics Dept., Santa
Cruz de Tenerife, Spain
Purpose or Objective
QA of MLC is one of the main points of any LINAC QA
program. Agility MLC (Elekta) have different properties
than most of the more common MLCs, like less interleaf
transmission. The objective is to perform the Agility MLC
QA in static mode using the electronic portal imaging