Radiation therapy or Radiotherapy: Treatment of Cancer using ionizing radiation such as X rays or Gamma Rays
Mechanism of Action: By damaging the DNA of cancerous tissue leading to cellular death
Radiation therapy may be used for majority of cancers either as Curative (where the therapy has long survival benefit) or as
palliative treatment (where cure is not possible and the aim is for local disease control or symptomatic relief).
It is curative in a number of types of cancer if they are localized to one area of the body. It may also be used as part of adjuvant therapy, to prevent tumor recurrence after surgery to remove a primary malignant tumor. Radiation therapy is synergistic with chemotherapy and can be used before, during, and after chemotherapy in susceptible cancers.
The precise treatment intent (curative, adjuvant, neoadjuvant, therapeutic, or palliative) depends on the tumor type, location, and stage, as well as the general health of the patient.
Radiation is produced by a linear accelerator, or LINAC. It employs microwave energy to accelerate electrons to nearly the speed of light within a contained area. The electrons collide with a metal barrier, creating powerful X-rays called photons. The photons are shaped into beams and delivered to the patient through a gantry that moves 360 degrees around the treatment table.
A single dose of radiation is called a fraction. Most radiation treatments require several fractions. A typical radiation treatment plan has five fractions a week for 4-6 weeks. The total radiation dose is fractionated (spread out over time) for several important reasons. Fractionation allows normal cells time to recover, while tumor cells are generally less efficient in repair between fractions. Fractionation also allows tumor cells that were in a relatively radio-resistant phase of the cell cycle during one treatment to cycle into a sensitive phase of the cycle before the next fraction is given. Similarly, tumor cells that were chronically or acutely hypoxic (and therefore more radioresistant) may reoxygenate between fractions, improving the tumor cell kill. The unit of radiation dose (Absorbed Dose) measurement is Gray (Gy).
Example of the conventional Curative Radiation Therapy schedule:
For Throat Cancer: 66-70 Gy in 33-35 fractions over 6-7 weeks, five days a week treatment with concurrent chemotherapy, on Saturday and Sunday no treatment.
For Gynecological Cancers: 50 Gy in 25 fractions over 5 weeks with concurrent chemotherapy
Intensity-modulated radiation therapy (IMRT) is an advanced type of high-precision radiation. IMRT improves the ability to conform the radiation treatment volumes/fields to irregular tumor shapes while surrounding normal and critical organs such as spinal cord, eyes, brain can be spared. The radiation dose is consistent with the 3-D shape of the tumor by controlling, or modulating, the radiation beam’s intensity. The radiation dose intensity is elevated near the gross tumor volume while radiation among the neighboring normal tissues is decreased or avoided completely. This results in better tumor targeting, lessened side effects, and improved treatment outcomes.
Image-guided radiation therapy (IGRT) is the use of imaging during radiation therapy to improve the precision and accuracy of treatment delivery. IGRT is a high precision technique used to treat tumors in areas of the body that move, such as the lungs. Radiation therapy machines are equipped with imaging technology to allow your doctor to image the tumor before and during treatment. By comparing these images to the reference images taken during simulation, the patient’s position and/or the radiation beams may be adjusted to more precisely target the radiation dose to the tumor. Some IGRT procedures may use fiducial markers, electromagnetic transponders or colored ink tattoos on the skin to help align and target the radiation equipment.
Volumetric modulated arc therapy (VMAT) is a new radiation technique, which can achieve highly conformal dose distributions on target volume coverage and sparing of normal tissues. The specificity of this technique is to modify the three parameters during the treatment. VMAT delivers radiation by rotating gantry (usually 360° rotating fields with one or more arcs), changing speed and shape of the beam with a multileaf collimator (MLC) ("sliding window" system of moving) and fluence output rate (dose rate) of the medical linear accelerator. VMAT also has the potential to give additional advantages in patient treatment, such as reduced delivery time of radiation, compared with conventional static field intensity modulated radiotherapy (IMRT).
Sterotactic Radiotherapy (SRS/SRT): A specialized technique which delivers large dosages of radiation in a single or few (4-5) fractions using highly focused radiation beam with extreme accuracy targeting a well defined tumor.
Stereotactic radiosurgery (SRS) is a non-invasive treatment that uses dozens of tiny radiation beams to accurately target brain tumors with a single high dose of radiation. Despite its name, SRS is not a surgical procedure and does not require an incision or anesthesia.
CyberKnife Radiosurgery system is a noninvasive alternative to surgery delivers radiation with the intention of targeting treatment
with pinpoint accurasy. The two main elements of the CyberKnife are:
1. the radiation produced from a small linear accelerator (linac)
2. a robotic arm which allows the energy to be directed at any part of the body from any direction (German Robot- KUKA KR 240)
CyberKnife System uses image guidance software to track and continually adjust treatment for any patient or tumor movement. It can be used for the treatment of both cancerous and non-cancerous tumors anywhere in the body, including the prostate, lung, brain, spine, liver, pancreas and kidney. Designed using a true robotic manipulator and a compact, lightweight linear accelerator, the CyberKnife System is versatile and can deliver beams from thousands of non-coplanar, isocentric or non-isocentric angles. Treatments have excellent tumor coverage, steep dose gradients and tight dose conformality, regardless of target shape. The system tracking capabilities eliminate the need for gating techniques and restrictive head frames, providing greater comfort for the patient.
In particle therapy (example: proton therapy) energetic ionizing particles (protons or carbon ions) are directed at the target tumor. The dose increases while the particle penetrates the tissue, up to a maximum (the Bragg peak) that occurs near the end of the particle's range, and it then drops to (almost) zero. The advantage of this energy deposition profile is that less energy is deposited into the healthy tissue surrounding the target tissue.
Intraoperative radiation therapy (IORT) is applying large dose of radiation to a target area (such as tumor bed/cavity after excision of breast tumor mass) while the area is exposed during surgery. The rationale for IORT is to deliver a high dose of radiation precisely to the targeted area with minimal exposure of surrounding tissues which are displaced or shielded during the IORT. Conventional radiation techniques such as external beam radiotherapy (EBRT) following surgical removal of the tumor have several drawbacks: The tumor bed where the highest dose should be applied is frequently missed due to the complex localization of the wound cavity even when modern radiotherapy planning is used. Additionally, the usual delay between the surgical removal of the tumor and EBRT may allow a repopulation of the tumor cells. These potentially harmful effects can be avoided by delivering the radiation more precisely to the targeted tissues leading to immediate sterilization of residual tumor cells. Another aspect is that wound fluid has a stimulating effect on tumor cells.
Brachytherapy: Brachytherapy is a type of radiation technique, in which a radiation source is placed inside or next to the area requiring treatment. It minimizes exposure to healthy tissue during radiation treatment while delivering maximum dose to the tumor area.
Side-effects: Side effects may affect you no matter which area of the body you’re having radiotherapy to. It’s important to remember that most people will have a few side effects and they will often be mild. Most people only experience a few of the following:
Early and Temporary Side-Effects: Nausea, diarrhoea, oral mucositis, Fatigue, skin redness discolouration (erythema), hair loss, Neutropenia etc.
Long term side effects: Dryness of mouth (xerostomia), skin fibrosis, infertility etc.