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Dr D Ghosh
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Cancer is considered to be a deadly and incurable disease with dismal outcomes. But with newer treatment technologies and early detection this notion is changing in today’s era. The treatment of most of the cancers is multimodality. The field of radiation oncology is an ever changing branch with new technological innovations.
Delivery of radiation therapy is a team work which includes the radiation oncologist, who after evaluating the patients decides the best course of treatment for the individual patient, medical physicist who makes the best possible plan and makes sure that the proper dose gets delivered to the tumour and maintains the quality assurance, and last but not the least, the radiation therapist technologist who operates the machine and delivers the dose according to the plan made.
The greatest challenge to a radiation oncologist is to attain high probability of cure with minimal possible morbidity. The field of radiotherapy has evolved over a period of years. The multileaf collimator (MLC), along with intensity modulated radiotherapy (IMRT) is a major breakthrough.
Radiation therapy at Batra Hospital
The Varian clinic 2100 C linear accelerator at Batra Hospital is a state-of-the-art machine. It has dual photon energies 6X and 15X, with 5 high electron energies 6, 9,12,16,20 MeV. The dose rate varies from 100MU/min to 400MU/min and has a 120 micro multileaf collimator which can take the shape of tumour under treatment.
The department is fully supported by well equipped medical physics department which is approved by AERB/BARC.
Some of the available radiation therapy techniques at Batra Hospital are as follows: CT simulation for radiation therapy planning, 3D conformal radiation therapy (3DCRT), intensity modulated radiation therapy (IMRT), image guided radiation therapy (IGRT), rapid arc, cone beam computed tomography (CBCT), high dose rate brachytherapy (HDRBT), and 3-dimensional brachytherapy.
Conventional 2-dimensional radiation therapy (2-D): This is a simple treatment delivered with two to four beam angles and beam shapes being either rectangular or square. The dose was limited by the normal structures lying along the path of beam which also receives the same radiation dose. Blocks, wedges and compensators were used in the path of beam for sparing the critical organs and better dose distribution in the tumour.
3-dimensional radiation therapy (3DRT): With the availability of CT scan the tumour could be visualised in three dimensions and with the help of automated multileaf collimators the normal tissues could be spared in a better way, simultaneously delivering curable dose to the tumour.
Intensity modulated radiation therapy (IMRT): A type of 3-dimensional conformal radiotherapy that focuses multiple radiation beams directly on the tumour itself. Beam intensities vary, so that the highest possible doses can be used to destroy cancerous tissue keeping the dose to the critical normal tissues to the minimum. This technique is best for tumours which are surrounded by the normal and critical organs like head and neck, prostate, brain tumours close to visual pathway, abdomen tumours surrounded by normal organs like kidneys, spinal cord etc. This results in very low complication rate following extended radiotherapy treatments because dose is modulated and adjusted with the help of multileaf collimator. Computer-aided optimisation derives desired treatment plan with intensity modulated beams so special planning software is required to determine the most accurate treatment.
Image-guided radiotherapy (IGRT): The organs in the human body are not static and the range of movement varies from organ to organ (most organs move a few millimetres or more in all the directions). When the radiation oncologists plan specialised treatments like 3-dimensional conformal radiotherapy (3DCRT) or intensity modulated radiotherapy (IMRT), they keep the margins around the tumour very tight in order to reduce dose to the surrounding normal tissues. However, there is a possibility of the treatment field to shift on either side by a few millimetres everyday, particularly in organs like lungs, prostate, urinary bladder which moves with respiration. Taking this into account bigger margins around the tumour are required, thus including more surrounding normal tissues thereby compromises the purpose of highly precise treatment. With IGRT facility, very tight margins can be taken, since the treatment fields and organ position will be verified by image guidance every day by taking the image in the treatment room itself by KV and CBCT ( imaging facilities) just before the treatment is given and adjustments made for field and organ shift on a daily basis before delivery of radiation. Thus IGRT helps in reducing the side effects dramatically in patients and is the ultimate in precision radiation therapy.
Rapid arc: It shapes the radiation beam to match the exact contour of the tumour, ensuring the maximum prescribed dose of radiation delivered to the tumour and protects the surrounding healthy tissue. The technique is non-invasive and lasts for five to 10 minutes, rather than long treatment time as with conventional techniques, which makes the treatment delivery comfortable. It reduces the likelihood of patient and tumour movements thus ensuring the highest possible level of accuracy and reducing the side effects which in turn results in improved quality of life. With these newer techniques, tumours which were initially considered to be untreatable can now be treated very well.
Computed tomography (CT): It is an immobilisation device that is fabricated in the mould room for each individual patient to ensure a better set up during the treatment delivery. Data from the CT simulator ensures that patients get the appropriate dose of radiation before treatment begins. Each patient will undergo a CT scan (CT simulation) for planning a radiotherapy procedure. Treatment planning based on CT scans is the most accurate method available all over the world today. Some patients with brain tumours and prostate carcinoma may require MRI scans along with CT scans, where the CT and MRI images are fused for treatment planning. Facility is also available for fusing data obtained from PET scan for an excellent tumour target delineation and refined treatment planning.
Brachytherapy: It is defined as a form of radiation therapy where radiation is delivered by arranging the radioactive sources in a geometrical fashion, in and around the tumour. It is used as an adjunct to external beam radiation therapy. The advantage is prescription of high dose to a small limited region in shorter time period and sparing of the normal tissues because of rapid dose fall off. HDR brachytherapy has high dose rate delivery system and the treatment gets completed in few minutes. Various forms of brachytherapy are available in form of intracavitary (cancer cervix), intraluminal (oesophagus) and interstitial (head and neck, soft tissue sarcoma, breast cancer). Radioactive sources are placed into the tumour through the applicators in situ. Now the concept of 3-dimensional base brachytherapy is growing, wherein normal organs are contoured and accurate dose is identified through specialised treatment planning softwares.
Role of imaging in oncology
The development and use of computed tomography (CT) and magnetic resonance imaging (MRI) to define the target volume and map the patient’s external contour, as well as internal organs and target volumes have an unprecedented impact on radiation therapy. The use of CT images as an aid in calculating the effect of tissue in homogeneities has improved the accuracy with which the dose can be calculated. The precision with which radiation therapy can be delivered has been greatly improved and may have an impact on the cancer cure rates. CT scans for treatment planning is different from diagnostic images because they are obtained with the patient in the treatment position on the flat table insert on the CT table and with some external reference marks that are visible on the CT image. As mentioned above, every organ in the human body has a tendency to move with respiration and some organs like bladder and rectum changes their volume with filling and evacuation. These movements can be divided into interfraction motion which means the changes in the position caused by day-to-day set-up conditions and intrafraction motion which are the changes in position during a treatment session because of respiratory and organ motion. Both these types of motions create treatment uncertainties. If the motion is greater than the treatment planning margin, the prescription dose to the target may not be achieved or the tolerance dose to the normal tissues may exceed. This would defeat the very purpose of treatment. kV imaging uses high resolution, low-dose digital imaging in the treatment room. With digital kV radiographic, cone -beam CT (CBCT) and fluoroscopic images one can very well manage the patient and target movement. Cone beam CT is designed for fast image acquisition to speed up the clinical process. Image acquisition is fast using a single, one minute rotation around the patient regardless of the patient anatomy being scanned. Hence, it would not be wrong to say that imaging is the backbone of radiation oncology which provides improved tumour targeting and better treatment delivery that is the ultimate goal of radiation therapy.