Download PET/CT in Radiotherapy Planning Dr Sze Ting LEE, MD

PET/CT in Radiotherapy Planning
Dr Sze Ting LEE, MD
Austin Health
Melbourne, Australia
ABSTRACT
Molecular imaging with PET/CT in radiotherapy allows better tumour staging, modification of treatment fields,
localised symptom control and therapy response evaluation. There is a clear dose-response relationship between
radiation dose and biochemical tumour control rates. The basics of radiotherapy relevant to nuclear medicine
will be outlined with a focus on intensity modulated radiotherapy planning, which is a strategy that has been
proposed to enable the delivery of high radiotherapy doses without giving an unacceptably high risk of toxicity.
There will be a review of the current literature and the emerging role of PET in radiotherapy planning, including
the role of new pharmaceuticals in this arena.
LECTURE TOPICS
1.
Basics of Radiotherapy
a) Nomenclature for Target Definition
Gross Tumour Volume (GTV)
- Includes the full extent of tumour as defined by any imaging or fused studies
Clinical Tumour Volume (CTV)
- Includes GTV and a margin for microscopic extent of disease (1-2cm)
Planning Target Volume (PTV)
- Includes a margin that envelops the CTV to account for day to day variations in setup and internal
organ motion (Prescription Dose)
Biologic Target Volume (BTV)
- Includes functional parameters that might affect radiation response
- To decrease dose to normal tissue, and prevent under-treatment of disease sites
b) Types of Radiation Therapy
External beam radiation therapy
- high XR beams provided by a linear accelerator
- short treatment sessions (Fr) to reduce side effects
- doses in Gy
- Types: Standard XRT; conformal 3D-RT & IMRT
Internal radiation therapy (brachytherapy)
- radiation source inserted into the body
Systemic radiation therapy
- unsealed source of radioactivity (iodine-131 / strontium-89)
2.
PET/CT in Radiotherapy Planning
a) Summary:
- Imaging modality with the most significant effect on RTP recently
- Estimated that 55%-60% of patients submitted for functional imaging have potential changes in target volumes
and/or dose distribution parameters
- Most commonly refers to FDG, but other radiopharmaceuticals are also used to assess underlying tumour
biology
- This is crucial for precise delivery of radiation dose to the tumour, whilst sparing the normal regions outside
the target volume
- Takes into account the functional information, and integrates it with the anatomical information
 Image-guided intensity modulated RT (IGRT)
- PET Radiopharmaceuticals (Table below)
Radionuclide
Tumour Biology
Clinical application
18
Glucose metabolism
All tumours
11
C-methionine
C-choline
18
F-DOPA
18
F-methyltyrosine (MET)
Proteins/amino acids
Brain tumour
Prostate cancer
Carcinoid tumour
Musculoskeletal tumour
18
DNA proliferation
Treatment response
18
Apoptosis
Treatment response
18
Hypoxia
Radiation planning
18
Receptor binding (avidity)
Breast cancer
18
Angiogenesis/perfusion
Integrin binding
18
Membrane/lipid synthesis
Proliferation
F-FDG
11
F-thymidine (FLT)
F-annexin V
F-misonidazole (FMISO)
F-estradiol
F-galacto-RDG
F-acetate
b) Role of PET/CT in Radiotherapy Planning
- Improves disease diagnosis and staging
- Assists tumour volume delineation
- Defines tumour phenotype or biological tumour volume
- Assessment of treatment response
- In-beam monitoring of radiation dosimetry
c) FDG PET/CT in Radiotherapy Planning in Solid Tumours
The role of FDG-PET/CT in Radiotherapy Planning of various solid tumours will be discussed, including head
& neck carcinoma, non-small cell lung carcinoma, mesothelioma, oesophageal carcinoma, pancreatic carcinoma,
rectal carcinoma & cerebral malignancies. Examples and discussion on standard conformal radiotherapy and
intensity modulated radiotherapy will be discussed.
3.
Non-FDG radiotracers in Radiotherapy Planning
a) Hypoxia
The importance of hypoxia in tumour biology
The role of hypoxia in radiotherapy
Hypoxic radiotracers – including FMISO & Cu-64
b) Proliferation
Utility of FLT PET in treatment response
Choline PET in prostate carcinoma
c) Amino Acid Proliferation
11
C-methionine PET in cerebral malignancies
References
1.
Delbeke D et al. Semin Nucl Med. 2009; 39(3):308-340.
2.
D. De Ruysscher et al. Lung Cancer. 2012; 75:141–145.
3.
Ahn PH et al. Sem Nucl Med. 2008; 38(2):141-148.
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Suggested Reading
1. Delbeke D et al. Semin Nucl Med 2009;39(3): 308-40.
2. Ahn PH et al. Sem Nucl Med. 2008; 38(2): 141-148.
3. D. De Ruysscher et al. Lung Cancer. 2012; 75:141–145.
4. Ford EC et al. J Nucl Med. 2009; 50(10): 1655-1665.