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Proton therapy
1. Proton Therapy
Dr. Md. Ruhul Amin
MD (Oncology), Phase B Resident
Department of Oncology
KYAMCH
2. Rationale:
• To reduce dose to non target regions
• Dose escalation
• To reduce probable second malignancies
• Better constraints to Organ at Risk
3. Basic Physics:
The Existence of proton was first demonstrated by Ernest Rutherford in 1919
Proton is the nucleus of hydrogen atom
• It has a positive charge of 1.6 x 1019 c
• Its mass is 1.6x10-27 kg(1840 times of electron)
• It consists of 3 Quarks(two up and one down)
• It is the most stable particle in universe with half life of >1032 years
5. Spread Out Bragg Peak:
In a typical treatment plan for proton therapy, the
Spread Out Bragg Peak, is the therapeutic radiation
distribution. The SOBP is the sum of several individual
Bragg peaks (thin blue lines) at staggered depths.
In most treatments, protons of different energies with
Bragg peaks at different depths are applied to treat the
entire tumor
6. Proton Generation:
Protons are produced from hydrogen gas:
1. Either obtained from electrolysis of deionized water
or
2. Commercially available high-purity hydrogen gas
High-voltage electric current is applied to hydrogen gas, stripping electrons from the
hydrogen atoms, leaving positively charged proton particles
8. Cyclotron:
A cyclotron produces a monoenergetic proton beam,
typically 250 MeV
• Energy Degradators
Modify Range and intensity of beam
• Energy selection system (ESS)
consist of energy slits, bending magnets, and focusing
magnets, is then used to eliminate protons with excessive
energy or deviations in angular direction.
9. Synchrotron:
• Produce proton beams of selectable energy,
thereby eliminating the need for the energy
degrader and energy selection devices
• Beam currents are typically much lower than
with cyclotrons, thus limiting the maximum
dose rates that can be used for patient
treatment, especially for larger field sizes
10. Proton Beam Transport:
A series of large bending and focusing
magnets along with diagnostic
measuring tools guides the proton
beam from the cyclotron or
synchrotron to the patient treatment
rooms
11. Proton Beam Delivery:
The pencil-shaped proton beam has to be modified for clinical use by
the following techniques:
• Scattering Beam Technique
• Scanning Beam Technique
12. Scattering Beam Technique:
The pencil beam passes through a range modulator followed by first and
second scatterer then through a compensator to treat the patient. The
variable thickness range modulator spins in front of the pencil beam
creating a flat top Bragg peak. By using the two scatterers and the
compensator, the pencil beam shaped proton beam is spread laterally for
clinical use. The scatterers and the compensator are custom-made for
each proton beam.
14. Tailoring the Beam in Depth:
The range modulator (fan like The
modulator spins around in front of
the proton beam pulling the beam
back and forward causing a flat
topped dose distribution providing
the tumor with a uniform dose
15. Scanning Beam Technique:
Multiple variable strength magnets scan
the pencil beam shaped proton beam
laterally to conform to the tumor/target
volume. The scanning beam technique
does not require patient-specific
hardware
16. Treatment Planning:
A CT simulation of the patient is performed for imaging data collection. The CT
values are converted to proton stopping power (as opposed to electron densities for
photon treatment planning). This is followed by delineation of the target volume.
Finally, selection of beam direction and plan optimization is performed. A field
patching technique to match multiple beams at the 50% isodose lines laterally and at
the distal level produces the desired treatment plan. The planning system designs the
aperture and the compensator for each single field. Pencil beam algorithms are used
for the dose calculation and the radiation dose unit is cobalt Gray equivalent (CGE).
17. IMPT:
Currently, intensity-modulated proton therapy (IMPT) is in use in the clinical
environment. With this technique, Bragg peaks of pencil beams are distributed
around the target volume and beam weights are optimized by inverse planning.
Finally, several magnets are used to deflect and focus the pencil beams to the target
to treat the patient. Using the IMPT technique can dramatically reduce the proton
treatment time because of its complexity and labor-intensity in making the 3D
compensators
18. Potential Application:
• Central nervous system cancers (including chordoma, chondrosarcoma, and malignant
meningioma)
• Eye cancer (including uveal melanoma or choroidal melanoma)
• Head and neck cancers (including nasal cavity and paranasal sinus cancer and some
nasopharyngeal cancers)
• Lung cancer
• Liver cancer
• Prostate cancer
• Spinal and pelvic sarcomas (cancers that occur in the softtissue and bone)
• Some noncancerous tumors of the brain may also benefit from proton therapy
24. Other Heavy Ion Therapy:
Heavy ions also have excellent biological
properties because their DNA damage is difficult to
repair. Carbon ions (C) have similar biological
effectiveness to fast neutrons but better physics
dose distribution thanks to the Bragg peak and the
pencil-beam scanning. Protons (p+) have dose
distribution similar to that of carbon, slightly worse
because of the high lateral scattering, and a
biological effectiveness similar to x-rays.
