Speaker
Dr
Slobodan Devic
(McGill Univeristy)
Description
Purpose: To test the feasibility of FDG based PET/CT data on target volume
delineation in radiotherapy treatment planning of NSCLC patients, and impact of
these outlined biological target volumes (BTV) for IMRT treatment.
Materials and methods: Patient diagnosed with non-operable NSCLC in the right upper
lobe had a 3D conformal planning based on CT data with our hypo-fractionated regimen
of 52.5 Gy in 15 fractions. Planning was redone with fusion of PET/CT data and 3D
CT. Three target volumes were created: necrotic BTV (same as seen in CT),
proliferating BTV (based on PET signal to background ratio 1:3) and hypoxic BTV
(based on PET signal to background ratio of 1:19, believed to be related to
anaerobic glycolisis inefficacy in ATP production). Two IMRT plans were created
based on these three BTVs with the intention of giving different doses to each BTV.
The first plan (“conservative plan”) delivers 52.5 Gy to the necrotic BTV and 65 Gy
to the hypoxic BTV. The second plan (“radical change”) delivers 30 Gy to the
necrotic BTV, 52.5 Gy to proliferating BTV and 65 Gy to hypoxic BTV.
Results: The use of BTVs in IMRT plan seems attractive because it increases dose to
targets considered to need higher doses. It reduces considerably dose to the heart
and spinal cord, organs considered to limit dose escalation approaches in NSCLC
treatment. However, lower dose to the spinal cord comes at the expense of slight
increase in the contra lateral lung dose, still way below V20 limit.
Conclusions: The “conservative” IMRT approach can be understood as a PET/CT based
concomitant boost to the tumor expressing the highest FDG uptake. The “radical” IMRT
planning implies a deviation from the traditional uniform dose target coverage
approach, with the intention of achieving a better surrounding tissue sparing and
ultimately allowing for dose escalation protocols in NSCLC patients. Several issues
should be considered before treating patients using PET/CT based BTVs: tumor motion
(patients could be scanned with 4D PET/CT and treated with gated RT), dose
calculation accuracy with Monte Carlo based treatment planning algorithms, and
specific tumor metabolic activity should be imaged with better radiopharmaceutical
markers. We also intend to present four current recommendations for tumor outlining
using PET: Qualitative Visual Method (Ciernik), CTV = 2.5 SUV units (Paulino and
Johnstone), CTV = 40 % Iso of max Uptake Value (Erdi) and Linear SUV threshold
function method (Black).
Author
Dr
Slobodan Devic
(McGill Univeristy)
Co-authors
Mr
Chris Kaufman
(McGill University)
Dr
Ervin Podgorsak
(McGill University)
Dr
Geoffrey Dean
(McGill University)
Mrs
Nada Tomic
(McGill University)
Dr
Robert Lisbona
(McGill University)
Dr
Sergio Faria
(McGill Univeristy)
Mr
William Parker
(McGill University)
