Image-Guided Adaptive Therapy for the Treatment of Lung Cancer C Ramsey, S Mahan, D Chase Thompson Cancer Survival Center, Knoxville,TN

Adaptive IGRT for Lung The first Lung Cancer patient was treated with Helical Tomotherapy at the Thompson Cancer Center in July 2003 7 lung cancer patients have been treated for a total of 199 fractions Each patient had CT imaging prior to treatment delivery Lung Window Bone Window

TCSC-RT 0301: Lung Tomo Protocol Prescription Initial: 44 Gy (2.0 Gy/fraction) Boost: 20 Gy (2.5 Gy/fraction) Margins Initial: GTV + 2-cm Boost: GTV + 1-cm (with DIBH) Plan Optimization Parameters: Pitch: 0.333 Thickness: 2.5 Modulation: 2.5 The total lung volume (right and left lung minus the gross tumor volume) receiving greater than 20 Gy must be 35% or less

Lung Adaptive Therapy Tumor Response TomoImage Fraction #1 5 10 15 20 25 30 40 50 60 70 Elapsed Days Volume (cc) Patient #1 Patient #2 Patient #3 GTV TomoImage Fraction #30 Tumor Response During the course of the therapy (with or without concurrent chemotherapy), the GTV can reduce in volume by a factor of 3 As the GTV shrinks, the target is effectively being treated with an increasing margin GTV

Lung Adaptive Therapy Original Treatment Plan The PTV is reduced every five fractions based on GTV volume reduction in the previous five TomoImages The GTV is reduced in the planning CT image to match each weeks measured tumor volume The GTV is still expanded into the PTV (i.e. margins are the same) Adaptive therapy’s impact increases the larger the original GTV volume and the greater the tumor response Adaptive Composite Plan

Lung Adaptive Therapy PTV Ips. Lung 5 10 15 20 25 30 40 50 60 70 Elapsed Days Volume (cc) Patient #1 Patient #2 Patient #3 Ips. Lung Lung mass reduced to 36% of the original tumor volume Non-Adaptive Weekly Adaptive

Lung Adaptive Therapy PTV 5 10 15 20 25 30 40 50 60 70 Elapsed Days Volume (cc) Patient #1 Patient #2 Patient #3 Lung mass reduced to 25% of the original tumor volume Ips. Lung Non-Adaptive Weekly Adaptive

Lung Adaptive Therapy PTV Ips. Lung 5 10 15 20 25 30 40 50 60 70 Elapsed Days Volume (cc) Patient #1 Patient #2 Patient #3 PTV Ips. Lung Lung mass reduced to 81% of the original tumor volume Weekly Adaptive Non-Adaptive

Adaptive IGRT for Lung Based on the results of this feasibility study, adaptive therapy at a minimum has the potential to decrease radiation induced damage to healthy lung tissue The level of improvement increases with larger initial CTV’s and with increased volume reduction during treatment The potential pitfall of this type of adaptive therapy is the potential for underdosing microscopic extension As the visible GTV decreases, the assumption is that the microscopic extension is also shrinking at the same rate However, margin is still added around the GTV in adaptive therapy, and the final PTV is typically the same size or larger than the initial CTV