About Surgery

About Radiation

Radiation Oncology: Therapeutic use of Ionising radiation

External Beam Therapy

External beam therapy is a method for delivering a beam of high-energy x-rays to a patient's tumor. The beam is generated by a linear accelerator and is targeted at the tumor site. These high energy x-rays can deposit their dose to the area of the tumor to destroy the cancer cells and spare the surrounding normal tissues.

External beam therapy can be used to treat many diseases like Breast Cancer Cervical Cancer, Colorectal Cancer (large Bowel Cancer), Head and Neck Cancer, Lung Cancer Prostate Cancer, Brain Tumors.

Delivery of external beam therapy requires a treatment team, including a radiation oncologist, radiation physicist, dosimetrist and radiation therapy Technologist. The radiation oncologist is a physician who evaluates the patient and determines the appropriate therapy determines area to be treated and dose to be delivered and the techniques to be used to deliver the prescribed dose. The physicist and the dosimetrist make treatment calculations and quality assurance checks prior to treatment delivery. The radiation therapy Technologists are specially trained to deliver the daily treatments

Linear accelerators or cobalt machines are used to deliver external beam therapy. The linear accelerator is the most commonly used device for external beam therapy.

Radiation Oncology: Therapeutic use of Ionising radiation

Linear Accelerator

The Linear Accelerator is operated by a highly trained technologist. The overall treatment plan is created by the radiation oncologist, a highly trained physician specializing in treating cancer with radiotherapy

The process of external beam therapy can be divided into three parts:

Simulation

The goal of simulation is to determine the treatment position that will be used daily, to make devices that will help the patient maintain that position, and to obtain the necessary images for treatment planning. The radiation therapist places the patient in the treatment position on a special x-ray machine or CT scanner. Masks, pads or other devices may be used to help the patient to hold still and in a specific position during the simulation. These devices will be used for the treatment to achieve the same position daily, so it is important that the patient can maintain that position. Images of the treatment area are taken in the treatment position. The radiation therapist places small marks on the patients to help guide the daily treatments. Marker seeds may be placed in the target tumor or organ at simulation or during a separate surgical procedure.

Treatment Planning

For treatment planning the dosimetrist, radiation physicist and radiation oncologist use a special computer to calculate the radiation dose that will be delivered to the patient's tumor and the surrounding normal tissue. The radiation oncologist will determine the volume of the tumor and other areas that needed to be treated and outline those on the treatment planning films. He or she will also outline normal structures that should be avoided or considered in devising the treatment plan. Together, the oncologist, dosimetrist and physicist will generate a treatment plan that delivers the appropriate dose to the tumor while minimizing dose to surrounding normal tissues. In certain cases, this process may employ such techniques as three-dimensional conformal therapy or intensity-modulated radiation therapy. This planning is based on CT, MRI and PET/CT scans which may be done in the Radiology Department or the Radiation Oncology Department.

Treatment Delivery

The patient is placed on the treatment couch of the linear accelerator in exactly the same position that was used for simulation using the same immobilization devices. The therapist carefully positions the patient using the alignment lasers and the marks that had been placed on the patient during simulation. Some form of imaging is often used prior to the treatment delivery to verify the accuracy of the patient setup. Some of the types of imaging that can be used include x-rays, ultrasound, and cone beam CT. The therapist goes outside the room and turns on the linear accelerator from outside. Beams from one or more directions may be used and the beam may be on for as long as several minutes for each field.

The treatment process can take 10 to 30 minutes each day and most of the time is often spent positioning and imaging the patient. The duration of a patient's treatment depends on the method of treatment delivery such as IMRT and the dose given. The length of each treatment will usually be the same from day to day.

Patients usually receive radiation treatments once a day, five days a week for a total of two to nine weeks. The patient's diagnosis determines the total duration of treatment.

Temporary brachytherapy:

In temporary brachytherapy, a delivery device, such as a catheter, needle, or applicator, is placed into the tumor using fluoroscopy, ultrasound, MRI or CT to help position the radiation sources. The delivery device may be inserted into a body cavity such as the vagina or uterus (intracavitary brachytherapy) or applicators (usually needles or catheters) may be inserted into body tissues (interstitial brachytherapy). Treatments may be delivered at a high dose-rate (HDR) or a low dose-rate (LDR). Treatment may also be delivered in periodic pulses (pulsed dose-rate or PDR). High-dose rate (HDR) brachytherapy is usually an outpatient procedure although patients are sometimes admitted to the hospital to have several HDR treatments using the same applicator. With HDR brachytherapy, a specified dose of radiation is delivered to the tumor in a short burst using a remote-afterloading unit. The treatment lasts only a few minutes although the entire procedure (including placement of the delivery device) may take up to several hours. This may be repeated several times in a day before the delivery device is removed and the patient returns home. Patients may receive up to 10 separate HDR brachytherapy treatments over one or more weeks. With low-dose rate (LDR) brachytherapy, the patient is treated with radiation delivered at a continuous rate over several hours or days. A patient receiving LDR brachytherapy stays overnight at the hospital so the delivery device can remain in place throughout the treatment period. Pulsed dose-rate (PDR) brachytherapy is delivered in a similar way but the treatment occurs in periodic pulses (usually one per hour) rather than continuously. The physician may insert the radioactive material manually through the delivery device and later remove the material and delivery device when the treatment is done

Alternatively, the patient may be moved to a shielded treatment room that contains a remote afterloading unit, which inserts the radioactive material to the delivery devise within the tumor site. The radioactive material is automatically withdrawn when someone enters the patient's room and when the treatment is completed When the treatment is completed, the delivery device is removed from the patient

Intensity-Modulated Radiation Therapy (IMRT)

Intensity-modulated radiation therapy (IMRT) is an advanced mode of high-precision radiotherapy that utilizes computer-controlled linear accelerators to deliver precise radiation doses to a malignant tumor or specific areas within the tumor. IMRT allows for the radiation dose to conform more precisely to the three-dimensional (3-D) shape of the tumor by modulating—or controlling—the intensity of the radiation beam in multiple small volumes. IMRT also allows higher radiation doses to be focused to regions within the tumor while minimizing the dose to surrounding normal critical structures. Treatment is carefully planned by using 3-D computed tomography (CT) images of the patient in conjunction with computerized dose calculations to determine the dose intensity pattern that will best conform to the tumor shape. Typically, combinations of several intensity-modulated fields coming from different beam directions produce a custom tailored radiation dose that maximizes tumor dose while also minimizing the dose to adjacent normal tissues.

Because the ratio of normal tissue dose to tumor dose is reduced to a minimum with the IMRT approach, higher and more effective radiation doses can safely be delivered to tumors with fewer side effects compared with conventional radiotherapy techniques. IMRT also has the potential to reduce treatment toxicity, even when doses are not increased. IMRT does require longer daily treatment times and delivers a low dose to larger volumes of normal tissue than conventional

Delivery of external beam therapy requires a treatment team, including a radiation oncologist, radiation physicist, dosimetrist and radiation therapy Technologist. The radiation oncologist is a physician who evaluates the patient and determines the appropriate therapy determines area to be treated and dose to be delivered and the techniques to be used to deliver the prescribed dose. The physicist and the dosimetrist make treatment calculations and quality assurance checks prior to treatment delivery. The radiation therapy Technologists are specially trained to deliver the daily treatments

Linear accelerators or cobalt machines are used to deliver external beam therapy. The linear accelerator is the most commonly used device for external beam therapy.

Brachytherapy

Brachytherapy is one type of radiation therapy used to treat cancer., brachytherapy involves placing a radioactive material directly inside or next to the tumor.

Brachytherapy, also called internal radiation therapy, allows a physician to use a higher total dose of radiation to treat a smaller area and in a shorter time than is possible with external radiation treatment.

Brachytherapy is used to treat cancers throughout the body, including the:

  • prostate
  • cervix
  • head and neck
  • skin
  • gallbladder
  • uterus
  • vagina
  • lung
  • rectum
  • eye
Brachytherapy may be either temporary or permanent:

In temporary brachytherapy, the radioactive material is placed inside or near a tumor for a specific amount of time and then withdrawn. Temporary brachytherapy can be administered at a low-dose rate (LDR) or high-dose rate (HDR).

Permanent brachytherapy, also called seed implantation, involves placing radioactive seeds or pellets (about the size of a grain of rice) in or near the tumor and leaving them there permanently. After several weeks or months, the radioactivity level of the implants eventually diminishes to nothing. The inactive seeds then remain in the body, with no lasting effect on the patient.

For permanent implants, radioactive material (which is enclosed within small seeds or pellets) is placed directly in the site of the tumor using a specialized delivery device. For temporary implants, needles, plastic catheters or specialized applicators are placed in the treatment site. Different types of radioactive material may be used according to the type of brachytherapy; some types of radiation sources used in brachytherapy are: iodine, palladium, cesium and iridium. In all cases of brachytherapy, the source of radiation is encapsulated which means that the radioactive material is enclosed within a non-radioactive metallic capsule.

RECENT DEVELOPMENTS IN RADIATION ONCOLOGY

The accurate targeting of tumours with maximal sparing of normal tissues has been the foremost goal of radiotherapy practice. Over the past two decades, the ability to achieve this goal has improved greatly through advances in imaging technology, specifically the development of computerized tomography (CT), magnetic resonance imaging (MRI), positron-emission tomography (PET) and fusion PET/CT

Intensity modulated radiation therapy (IMRT)

Intensity modulated radiation therapy (IMRT) is a sophisticated type of three-dimensional conformal radiotherapy that assigns non-uniform intensities to a tiny subdivision of beams called beamlets. The ability to optimally manipulate the intensities of individual rays within each beam leads to greatly increased control over the overall radiation fluence (i.e. the total number of photons/particles crossing over a given volume per unit time). This in turn allows for the custom design of optimal dose distributions. Improved dose distributions often lead to improved tumour control and reduced toxicity in normal tissue .

Image guided radiation therapy (IGRT)

IGRT is a technology aimed at increasing the precision of radiotherapy by frequently imaging the target and/or healthy tissues just before treatment and then adapting the treatment based on these images. There are several image guidance options available: non-integrated CT scans, integrated X-ray (kv) imaging, active implanted markers, ultrasound, single-slice CT, conventional CT or integrated cone-beam CT

The aim of image guided radiation therapy is to improve accuracy by imaging tumours and critical structures just before irradiation The availability of high quality imaging systems and automatic image registration has led to many new clinical applications such as the high precision hypofractionated treatments of brain metastases and solitary lung tumours with real time tumour position corrections.

Helical tomotherapy

Helical tomotherapy is a modality of radiation therapy in which the radiation is delivered slice-by-slice This method of delivery differs from other forms of external beam radiation therapy in which the entire tumour volume is irradiated at one time . The overall treatment time is relatively short which is the main advantage of this method.

Volumetric modulated arc therapy

Volumetric modulated arc therapy is a technique that delivers a precisely sculptured 3D dose distribution with a single 360-degree rotation of the linear accelerator gantry

Volumetric modulated arc therapy differs from other techniques such as helical tomotherapy or intensity modulated arc therapy (IMAT) in that it delivers doses to the whole volume, rather than slice-by-slice. The treatment planning algorithm contributes to the treatment precision helping to spare normal healthy tissue.

B.5 Stereotactic radiotherapy

Stereotactic radiotherapy (also called ‘radiosurgery’ ) consists of the delivery of a relatively high dose of radiation to a small volume using a precise stereotactic localization technique. This modality is usually applied in the treatment of intracranial tumours. Stereotactic radiotherapy can be delivered using a gamma knife device. This machine uses 201 small cobalt-60 sources collimated to converge in a small volume where the lesion is located.

Small intracranial tumours in general, pituitary adenomas, small meningiomas, acoustic neuroma, craniopharyngioma, pineal tumours, brain metastasis or non-malignant conditions such as arterio- venous malformations are often treated with stereotactic radiotherapy. Stereotactic body radiotherapy is also being used to treat localized liver tumours.

B.6 Robotic radiotherapy

Robotic radiotherapy is a frameless robotic radiosurgery system The two main elements of robotic radiotherapy are the radiation produced from a small linear accelerator and a robotic arm which allows the energy to be directed towards any part of the body from any direction.

The robotic radiotherapy system is a method of delivering radiotherapy with the intention of targeting treatment more accurately than standard radiotherapy. The robotic radiotherapy system is used for treatment of malignant and benign tumours, as well as other medical conditions.

PET in radiotherapy treatment planning

Recent years have seen an increasing trend in the use of positron emission tomography (PET) and PET/CT imaging in oncology. Along with diagnosis, staging, relapse detection and follow-up, one of the main applications of PET/CT is the assessment of treatment response and treatment planning. PET provides molecular information about the tumour microenvironment (“functional imaging”) in addition to anatomical imaging. Therefore, it is highly beneficial to integrate PET data into radiotherapy treatment planning. The use of functional imaging to better delineate the treatment target is a good example of individualized treatment.

Particle therapy: proton beam and heavy ions

There is an increasing use of particle therapy in the field of radiation oncology with increasing focus on the application of proton beam therapy.

The advantage of particle therapy, including proton therapy, is that the particle beam can provide a more precise dose distribution compared to photon beam (X-ray) radiotherapy. A particle beam deposits its energy at a certain depth as a sharp energy peak called Bragg peak, releasing a much lower dose before and almost none after this peak. Thus, by manipulating this characteristic, particle therapy can yield better dose distributions than photon therapy, providing the therapeutic dose to the tumour while minimizing unnecessary doses to healthy tissues

Brachytherapy

Brachytherapy is the administration of radiation therapy by placing radioactive sources adjacent to or into tumours or body cavities. With this mode of therapy, a high radiation dose can be delivered locally to the tumour with rapid dose fall-off in the surrounding normal tissues. The use of HDR brachytherapy has the advantage that treatments can be performed in a few minutes allowing them to be given in an outpatient setting with minimal risk of applicator movement and minimal patient discomfort. Remote controlled afterloading brachytherapy devices eliminate the hazards of radiation exposure.