Planning and treatment of multiple lung lesions using SABR

This research work aims to investigate the following areas of planning and treatment delivery to multiple lung lesions with SABR.

• Verify the correct computer planning algorithm to use for lung SABR planning and quantify the accuracy between the plan and treatment delivery within the target (high dose) and organs at risk (low dose).
• Better understand the expected magnitude of daily lesion position changes (baseline shifts from the original planning CT seen at treatment) in the lung and the effect that has on target delivery and Organ at Risk (OAR) doses.
• Complete a planning study to assess different planning strategies and the effect of studied motion differences likely to be encountered to inform computer planning technique.
• Create an audit protocol to assess the accuracy of treatment delivery when baseline shifts are present.

A description of each working package is given below:

1. Planning Algorithm and Static Treatment Delivery Verification Compare high and low radiation dose regions planned using the department’s current computer algorithm and the next generation (AAA Vs AXB) Verify planned doses within a lung-like phantom with point dose and planar dose measurements with simple and complex clinical SABR plans in high and low dose regions to determine the appropriate algorithm for the lung region and the differences that could be expected.

2. Quantifying motion between multiple lesions in the lung Retrospective selection of patients planned and treated for multiple lung lesions at the Royal Surrey Foundation Trust Hospital using a single SABR plan for each lesion to assess:

• Magnitude and frequency of lesion baseline shifts
• Impact of these shifts on the planned radiation dosimetry to the Planning Target Volumes (PTVs) and OAR Baseline shifts will be assessed using the on-line imaging acquired before treatment is delivered to each lesion. The differences measured from the initial patient setup position to the lesion’s treatment position is used to calculate the difference in the centre of the lesion with respect to the original treatment planning CT. Deviation away from the planned position for each lesion during treatment is used to determine the baseline shift in the lesions. These baseline shifts can then be simulated on the original planning CT to investigate the dosimetric impact to the PTV and OAR.

3. Planning study Based on the impact seen in the previous working package, retrospectively select MPLC lesions treated with SABR and re-plan using different optimisation strategies to better account for baseline shifts in the lesions. Investigation, including MDT working group and literature review to determine plan optimisation strategies to develop a local workflow. Assess whether conclusions from clinical planning algorithm (AAA) are also valid for next generation algorithm (AXB).

4. Treatment delivery verification to two or more simulated lung lesions Development of a 3D printed anthropomorphic lung phantom to measure planar and point doses before and after a lesion baseline shift. Aim to use this phantom to perform an end to end audit within RSFTH and potentially within a local audit group to assess treatment planning strategies and accuracy of delivered dose to lesions and OAR.