Session Item

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.

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.  

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.

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.