End-to-end verification of DIBH Treatment technique using CIRS Dynamic Thorax phantom
Sankar Pillai,
United Kingdom
PO-1585
Abstract
End-to-end verification of DIBH Treatment technique using CIRS Dynamic Thorax phantom
Authors: Sankar Pillai1, Natalie McInally1, Ashley Lambert2, Zoe Monteith2, Fiona Robertson2, David Sutton3, William Nailon4, Zhihong Huang5
1Ninewells Hospital & Medical School, Medical Physics, Dundee, United Kingdom; 2Ninewells Hospital & Medical School, Radiotherapy, Dundee, United Kingdom; 3University of Dundee, Medical Physics, Dundee, United Kingdom; 4University of Edinburgh, Medical Physics, Dundee, United Kingdom; 5University of Dundee, Biomedical Engineering, Dundee, United Kingdom
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Purpose or Objective
Deep Inspiration Breath Hold (DIBH)
technique is most commonly used when treating left-sided breast cancer due to the potential
reduction in cardiac toxicity. Though this technique has been in clinical use
since 2012, patient specific dose verification is not well established and also not widely reported
in the literature. The aim of this study
is to address this and to provide a method for identifying the dose delivered from
DIBH technique involving gated fields using individual patients’ breathing
traces.
Material and Methods
DIBH data from 10 left sided breast cancer patients treated with four to
six conformal treatment fields delivering 26Gy in five fractions were selected
for this study. All breathing traces
were acquired using a 3D real-time patient position monitoring (Varian, UK)
system during CT scanning process and subsequently used to drive a 0.015cc pin
point chamber (PTW, Germany) inside a thoracic phantom (CIRS, USA). Two sets of CT Scans were acquired for the
phantom, one in static mode and the other in dynamic mode driven by each
patient’s breathing trace. Treatment planning parameters for all patients
were transferred to the respective CIRS phantom image sets and dose calculations
were performed using collapsed cone algorithm in Raystation (Ver.9B, Raysearch
Laboratories, USA). The treatment plans were delivered to the CIRS dynamic
phantom in static and dynamic mode from TrueBeam (Varian, USA) linear accelerator.
Results
At the point of measurement, the average calculated dose is 97% for the
static phantom plans and 95% for the dynamic phantom plans from the prescribed clinical
dose. From static phantom measurements, the measured doses agree with the treatment
planning estimated values within ±3% for 7 plans, for three plans the agreement
was between -4.0% to -8.0%. Whereas, for
the dynamic phantom measurements the agreement was within ±4% for 6 plans and
within ±9% for the remaining 4plans.
Conclusion
In this study, individual patient’s breathing traces were used in a
dynamic thoracic phantom to simulate exactly the planning CT Scanning and
treatment process used with the DIBH technique. Though the patients breathing
traces acquire the movements in 3 axes
(Left-Right, Ant-Post, Sup-Inf) , due to design limitations of the CIRS phantom
the ant-post and left-right movements were combined into a single rotational
movement by the motion control software.
This limitation restricts the replication of the real transfer of patients
3 axis movements during phantom based dose verifications. But, this is not having any impact on the
gated treatment delivery as it is managed through the sup-inf motion only. Though most of the measured single point
doses from this study agreed within +/- 4.0% from the treatment planning doses,
either 2-d or 3-d dose verification using suitable phantom capable of
replicating the motions in all 3 axes will possibly support to co-relate the
accuracy of dose delivered to nearby normal organs.