Teletherapy: EBRT (External Beam Radiotherapy), source is at a distance,
Brachytherapy: source is nearer to the patient.
Brachytherapy is divided into 3 types:
Interstitial (into the tissue): Ca Prostate, Ca Breast
Intracavitatory (accessible cavity): Accessible tumors like Ca Cervix
Mold (Superficial cancers): Penis, Eye cancers
Disadvantage of Teletherapy as compared to Brachytherapy is the beam coming from outside, the target part along with adjacent parts are also exposed
Brachytherapy reduces the risk of exposure of adjacent parts to radiation.
In Teletherapy, Cobalt machine and LINAC (Linear Accelerator) are used.
The Cobalt machine produces an artificial radioisotope (Co60).
Half-life of Co60: 5.2 years
It decays into Ni60.
LINAC does not need any radioisotope, the fast moving electron beam generates radiation used for radiotherapy.
X-rays generated by LINAC have various energies. They are:
Ortho voltage < Super voltage < Mega voltage
Penetration is directly proportional to energy.
Mega voltage has higher energy and penetration power.
Ortho voltage has lower energy, can be used in superficial cancers and IORT (Intraoperative Radiotherapy).
Eg: A patient with carcinoma of pancreas, tumor is removed and the residual cells are to be killed which are superficial. Less energy or less permeable rays are enough. Hence, electron beam or ortho voltage is used.
Remember Whole body EBRT is used in Mycosis fungoides.
Overhead x-ray tube which emits x-ray beams.
It also has a robotic arm, which moves around the patient.
No frame is used to immobilize the patient.
Interstitial Brachytherapy has no cavity.
To insert the radioactive source, After loading is the technique to be followed.
Empty shell is put into the tissue, through which a robotic arm, a Lead-shielded storage container, sends the cable and automatically loads the shell.
Reduces the manual handling of radioactive materials.
Agents used for radiotherapy
X-rays (LINAC) are most commonly used.
Proton beams, neutrons, Gamma and beta rays are also used.
These pure emitters are used in Systemic Brachytherapy, where the isotope diffuses and reaches the site of action.
Seed Brachytherapy involves the localized action of the isotope.
Phosphorus 32 (P32) is used in treatment of polycythemia vera.
Strontium is used for metastatic bone pain.
Iodine 131 (I131) is a Beta emitter (not pure form). It emits gamma radiations as well.
Gamma radiation can be used in Systemic Brachytherapy.
Beta rays stay in the body and show the therapeutic effects, gamma rays exit the body.
I131: Half-life is 8 days.
Beta, Gamma rays are emitted from the nucleus of the atom.
X-rays are extranuclear.
In a proton beam, velocity is inversely proportional to dose given to the body.
As the beam travels deeper into the body, the velocity decreases and the dose increases suddenly.
Superficial structures are protected when proton beams are used.
Targeted pencil beams like radiotherapy can be given.
It affects only the tumor, surrounding cells are protected.
Example: A child with a brain tumor is given proton beam therapy, because the surrounding cells are not to be affected.
Image of comparison between X-ray with Bragg peak
X-rays give the maximum dose on the body.
Most common side effect of radiotherapy is skin erythema.
Comparison between X-ray with bragg peak in medulloblastoma
Treat Carcinoma of lungs, Non-small cell cancers like adenocarcinoma.
Given in Palliative treatment
It is given prophylactically in tumors which have drop metastasis.
Medulloblastoma, drops to the spine and causes spinal tumors like sugar coat (Zuckerguss in meninges with metastasis).
ALL (Acute Lymphoblastic Leukemia)
Small cell carcinoma of lungs
Previous Year Questions
Q. What does LINAC produce?
Ans: LINAC produces X-rays and electrons.
Q. What is the most common radiation used in IORT?
Ans: Electron beam or ortho voltage, as it has less penetration power.
Q. Afterloading is used in?
Q. Which radioisotopes are pure beta emitters?
Ans: Phosphorus 32 (P32), Strontium, Yttrium.
Q. Which is shown in Bragg peak?
Ans: Proton beam
Q. Which Radioisotopes are used as permanent implants in Brachytherapy?
Ans: C I G Y R P
Q. A child undergoing radiotherapy, which tissue may be least affected?
Ans: Nervous tissue
Q. What is the first hormone deficiency in Craniospinal Irradiation?
Ans: Growth hormone
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