Image-Guided Adaptive Therapy for the Treatment of Lung Cancer

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Image-Guided Adaptive Therapy for the Treatment
of Lung Cancer C Ramsey, S Mahan, D
Chase Thompson Cancer Survival Center,
Knoxville,TN
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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
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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
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Lung Adaptive Therapy
TomoImage Fraction 1
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
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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 therapys impact increases the larger
  the original GTV volume and the greater the tumor
  response

Adaptive Composite Plan
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Lung Adaptive Therapy
PTV
Ips. Lung
Lung mass reduced to 36 of the original tumor
volume
Non-Adaptive
Weekly Adaptive
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Lung Adaptive Therapy
PTV
Lung mass reduced to 25 of the original tumor
volume
Ips. Lung
Non-Adaptive
Weekly Adaptive
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Lung Adaptive Therapy
PTV
Ips. Lung
Lung mass reduced to 81 of the original tumor
volume
Weekly Adaptive
Non-Adaptive
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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 CTVs 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