Transcript Atypical Chordoma Case in Pediatric Patient

Radiation Oncology Case
with Pre-RT Images
Clival Chordoma Case
in Pediatric Patient
•RT and IMRT slides
courtesy of Paul Read, MD
Clival Chordoma – Overview
•Congenital tumors believed to originate from notochordal
cell rests
•Rare in childhood, more common in 3rd and 4th decades
•Chordomas generally occur in 3 locations: the sacrum, the
clivus, and along the spinal axis
•For clival tumors, diplopia, headache, widening sutures,
and enlarging head size are most common sx
•About ½ patients have cranial nerve palsies (VI, V, III)
Clival Chordoma – Overview
•Male predominance in pediatric population for unclear reasons
•10 month average time from the onset of sx to dx
•Tumors usually large in size at dx with innocuous presenting sx
•CT exam often reveals a midline soft tissue mass around the clivus
associated with osteolytic bone destruction and intralesional
calcifications.
• MRI delineates the exact site and extension, but also defines neural
and vascular relationship for planning surg
• Location of these tumours proximal to vital neural and vascular
structures makes surgical removal difficult and the ultimate clinical
course malignant
Clival Chordoma – Overview
•Combination of a ‘radical debulking’ operation followed by
high dose radiation therapy appears to be an effective mode
of treatment in older children.
•Chemotherapy appears to be of no value
• Survival for 4-11 years without recurrence is recorded in
children under 10 years of age who received such a
combination of treatment
• The 5-year survival 51%, 10-year survival 35%
• Good prognostic factors are young age, complete
resection, and the addition of radiation therapy
Clival Chordoma Case
•Pediatric patient with an extremely
aggressive atypical chordoma that locally
destroyed the clivus
•Tumor extension to brainstem, upper
spinal cord, nasopharynx, cavernous sinus,
retropharyngeal space, left parapharyngeal
space
•Plan high dose RT to tumor (65-70 Gy)
while respecting CNS tolerance
Axial and Sagittal CT views of an Atypical
Chordoma
Axial view
Sagittal view
What is Radiation Therapy?
• Radiation therapy is the treatment of cancer
using energy in the form of high voltage
radiation.
• Radiation Oncologists prescribe a radiation dose
in units of Gray (Gy) like other physicians
prescribe drugs in units of milligrams.
• A Gray is defined as an amount of energy
deposited per unit mass of tissue.
• Radiosurgery uses 10-40 Gy per treatment.
• Fractionated Radiotherapy uses 1.8-2.0 Gy per
treatment.
Standard Parallel Opposed Radiotherapy
Isodose Distribution
tumor
patient
The high dose isodose lines span the entire patient volume
damaging normal tissues.
Conformal Isodose Distribution
tumor
patient
The high dose isodose lines conform to the target volume
and spare normal tissues.
Improved Dose Conformality
Goals to maximize the dose of radiation delivered to target
volume and minimize dose to surrounding tissue
Each normal tissue has its own inherent threshold dose for
irreparable damage
Three-dimensional conformal therapy was the first application of
improved dose conformality
IMRT furthers this concept
Standard Linear Accelerator (Linac):
produces megavolt x-rays for 3D Conformal
radiotherapy and IMRT
What is Intensity Modulated Radiotherapy
(IMRT) ?
• Intensity modulated radiotherapy is very complex
radiotherapy in which the radiation beam is “modulated” by
blocking part of the beam using a motorized array of
paired tungsten blocks called a multi-leaf collimator within
a linear accelerator.
• With radiation beam modulation and the use of multiple
radiation beam angles one can achieve conformal
radiotherapy with a standard linear accelerator (linac).
• IMRT is usually delivered with fractionated radiotherapy
with 25-35 treatments of 1.8-2.0 Gy of radiation each.
• Currently UVA has a linear accelerator (linac) based IMRT
program which is described below.
Linear Accelerator Multi-Leaf
Collimator Based IMRT
Multi-leaf Collimator
The multi-leaf collimator is inside the linear accelerator. It is comprised of
multiple 1 cm thick metal radiation blocks each driven by an independent
motor and controlled by a central computer. The multi-leaf collimator
allows for multiple blocking patterns in each radiation field which in turn
allows for intensity modulation of the radiation dose.
9 field IMRT conformal treatment plan for
an atypical chordoma
IMRT in Practice
Physician outlines areas of interest on each slice
Then describes desired doses to CTV and restraints
to structures.
Then assigns numerical priority score to these goals.
There are several trade-offs and some of them are
more important in pediatric patients…
IMRT conformal plan for an atypical
chordoma (55-100% isodoses)
Isodoses
Axial view
Sagittal view
3D view of the dose intensity of IMRT
plan for an atypical chordoma
Isodoses
Right-inferior 3D view
3D view of dose intensity of IMRT
conformal radiotherapy plan for an
atypical chordoma
Isodoses
3D Inferior view
ACR CODE:
Presented by Tim Showalter, Class of 2004
Many of the RT and IMRT slides courtesy of Paul Read, MD of
UVA Department of Radiation Oncology