Dr. Aditi Tanwar

Radiation Oncologist

Dharamshila Cancer Hospital, New Delhi



Radiation therapy is one of the modalities of cancer treatment apart from surgery and chemotherapy that uses beams of intense energy to kill cancer cells. Radiation therapy most often uses X-rays, but protons or other types of energy also can be used.

Radiation is major of two types: external beam radiotherapy and brachytherapy. External beam radiation is delivered by invisible beams from various angles or in the form of an arc through computer-controlled plans.

Brachytherapy is the form of radiation wherein the source of radiation is placed inside the body near the site of the tumor with minimal radiation spill to the adjacent areas.

On the basis of technique, radiation can be broadly classified as CONVENTIONAL or CONFORMAL. In conventional radiation therapy, the beam of radiation uniformly irradiates the tumor as well as the adjacent normal tissues. While conformal radiation adapts to the shape of the tumor, delivering the majority dose to the tumor target while sparing adjacent organs.

Radiation therapy as a treatment modality has witnessed a lot of changes keeping at pace with the advancements in computers and technology.

Imaging is the backbone of successful radiation delivery. The past decade has observed a series of upgrades related to imaging thereby improving the precision with which radiation can be delivered.

Conformal radiation is now the state of arts wherein the targets to be irradiated and normal tissues to be spared are delineated on CT scans. This CT scan is separate from the scan acquired during the diagnostic workup, it is a part of the radiation planning process wherein cast fabrication (a method of immobilization) is done before acquiring the CT scan.


The radiation dose distribution is designed with the assistance of computers, it ensures that the objectives for target coverage and avoidance of healthy tissues are achieved. The beams of radiation are targeted from various angles, small beamlets within each beam are projected towards the tumor for best coverage. Sometimes the beam is also projected in the form of an arc, it reduces the treatment time and hence a majority of elderly patients can be benefited. The majority of the radiation delivery machines are now available with in-built imaging systems ensuring that the radiation is delivered as planned. On the basis of these imaging findings, the clinicians are able to assess the changes in tumor position, size, and shape. Accordingly, adjustments are done to maximize the geometric accuracy and precision of radiation delivery, reducing the volume of healthy tissue irradiated (thereby reducing the side effects such as mucositis, ulcers, etc). These adjustments finally allow dose escalation to the tumor, this is what is referred to as IMAGE GUIDED RADIOTHERAPY (IGRT). This form of treatment is of utmost benefit for patients whose tumor is in close vicinity to normal critical structures.

Conformal radiation is a blanket that covers under it a spectrum of techniques like THREE DIMENSIONAL CONFORMAL THERAPY (3DCRT), INTENSITY MODULATED RADIOTHERAPY (IMRT), IMAGE GUIDED RADIOTHERAPY (IGRT), VOLUMETRIC ARC THERAPY (VMAT). The most conformal radiation is brachytherapy wherein the entire radiation dose is delivered to the target and adjacent organs are spared. But brachytherapy cannot be used at all sites due to anatomical barriers like bone etc.

Radiation is not ‘one size fits all’. Many patients require upfront radiation (radical/definitive) as a part of cancer treatment but some require it after surgery, in the latter case it’s called adjuvant radiation. Some cases may require chemotherapy along with radiation while in some radiation is given alone. Also, the dose of radiation varies with the site of the tumor, dose escalation may be required in cases with adverse histopathological factors like unclean margins after surgery, the spread of cancer cells outside the nodes, etc.

Hence a variety of factors affect the dose of radiation like the site of the tumor, intent, histology, and various other factors so never can two patients be compared. No two patients are the same because even if they have tumors of the same site and same stage, their response to treatment will be different due to differences in genetics and tumor biology.

Despite the availability of a plethora of literature related to radiation, there exist numerous myths associated with it. Often confused with a sort of physiotherapy, radiation therapy does not generate heat nor does it induces any electric sensation in the body. Radiation is a localized form of treatment with side effects limited to the area being treated, although it causes suppression of the bone marrow to show systemic symptoms. The patient undergoing radiation treatment does not emit radiation that may harm anyone hence there is no need to isolate them.

The treatment of radiation cannot be taken at home, it has to be done on the treatment machine in the health institute. The biggest myth associated with radiation is that it alone can not cure any cancer which is not true as radiation can cure tumors of the anal canal (last part of the gut), cervical cancer, etc. Although with surgery and chemotherapy the potential of radiation for curing cancers increases. Radiation aims at sterilizing the surgical bed and destroy the microscopic disease. Also one should understand that the disease which can not be addressed surgically or medically may be benefited by radiation. Radiation still has a role to play in advanced-stage tumors, though the role may be the palliative the majority of times it is not rare to find cases where radiation may lead to complete eradication of the disease. Hence the scope of radiation cannot be completely defined by words, it is a ray of hope and sometimes all the sunshine you need!

This information is for general guidance and reflects the opinions and experience of the author. It is not intended to replace specialist consultation or provide treatment advice for specific cases

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