“Does my radiotherapy treatment start when the machine switches on?”
“What happens when I lie down on the radiotherapy machine?”
“Why can’t I feel the radiation entering my body?”
“If I cannot feel it, what is radiation actually doing to the cancer?”
“Why do I need so many radiotherapy sessions?”
“How do you know that the correct radiation dose was actually delivered?”
“If radiotherapy is working, shouldn’t I develop side effects?”
“Should I worry if I feel completely normal after my radiotherapy session?”
“When will we know whether the radiotherapy worked?”
“So what should I remember when I am lying on the machine thinking, ‘Nothing is happening’?”
Radiotherapy Feels Like a CT Scan. Is It Really Working?
“Doctor, I don’t feel anything during radiotherapy. Is it really working?”
Yes. Radiotherapy is working exactly as planned even when you feel absolutely nothing.
You lie on the treatment table. The machine moves around you. You may hear a few mechanical sounds.
But there is no heat, no shock and usually no pain.
It can feel so uneventful that you may wonder:
“Is anything actually happening?”
We are used to thinking that a treatment should feel like a treatment. So when radiotherapy is painless and smooth, it can almost seem too simple to be real.
But radiotherapy is not meant to be felt .
Think of a skilled dancer performing a very difficult routine: when expertise, preparation and precision come together, something extremely complicated can look almost effortless.
Radiotherapy is similar.
Those few quiet minutes on the machine are only the final step of detailed imaging, planning, calculations, verification, quality checks and precise treatment delivery.
Let me take you behind the scenes.
“Does my radiotherapy treatment start when the machine switches on?”
No. Your radiotherapy treatment planning starts well before your first treatment session.
It usually begins with a planning CT scan .
You are positioned carefully, often using a mask, support, cushion or other positioning device depending on the part of the body being treated.
Your radiation oncologist then identifies:
The tumour or area that needs treatment
Areas at risk of microscopic cancer cells, when relevant
Nearby normal organs that should be protected
A treatment-planning system is then used to calculate how the prescribed radiation dose can be delivered to the required target while limiting unnecessary radiation to surrounding healthy tissues.
So while you are at home wondering,
“Why is my treatment taking time to start?”
a very important part of your treatment may already be happening behind the scenes:
Your personalised radiation treatment plan is being prepared.
“What happens when I lie down on the radiotherapy machine?”
Your position is carefully reproduced according to the treatment plan.
Those small marks on your skin, the mask over your head and neck, or the particular position of your arms and legs are not random.
They help us reproduce your treatment position accurately.
Modern radiotherapy machines can also take images while you are lying on the treatment couch.
These images can be compared with your planned position. If necessary, small corrections can be made before radiation is delivered.
This is called image-guided radiotherapy (IGRT).
There is a planned target, a prescribed dose, planned beam arrangement and a system for verifying your position.
Only then is the treatment delivered.
“Why can’t I feel the radiation entering my body?”
Because therapeutic radiation itself cannot normally be felt.
External-beam radiotherapy commonly uses high-energy photons. They are similar in physical nature to X-rays, but are generated and delivered at energies and doses appropriate for cancer treatment.
You cannot normally feel these radiation beams passing through your body.
You should not feel the beam:
Burning you
Shocking you
Heating you
Entering or leaving your body
The machine may rotate and you may hear mechanical sounds, but the radiation itself is invisible and normally painless.
Not feeling radiation does not mean radiation was not delivered.
“If I cannot feel it, what is radiation actually doing to the cancer?”
Radiation is producing biological damage inside cells in the treatment area.
Radiation deposits energy in tissue and can damage important cellular structures, particularly DNA.
When sufficient damage accumulates, cancer cells may lose their ability to continue dividing successfully and may eventually die. The body then gradually clears these damaged cells.
Importantly, this process does not necessarily happen the instant the radiation beam reaches the tumour.
Radiotherapy is therefore very different from surgery.
With surgery, a tumour may physically be removed during an operation.
With radiotherapy, the biological response develops over time.
Cancer cells can continue to die for days or weeks after radiation has been delivered.
That is why you should not expect the tumour to disappear immediately after each radiation session.
“Why do I need so many radiotherapy sessions?”
Because many radiotherapy treatments are intentionally divided into smaller treatments called fractions.
The number of fractions depends on several factors, including:
Type of cancer
Location of the tumour
Treatment goal
Total prescribed dose
Radiation technique
Nearby normal organs
Whether other treatments are being given
Each fraction contributes to the overall planned biological effect.
Between fractions, normal tissues often have a greater ability than cancer cells to repair certain forms of radiation injury.
Fractionation therefore allows us to repeatedly treat the cancer while providing normal tissues opportunities for recovery.
So that seemingly uneventful daily session is actually one carefully calculated component of your complete treatment course.
“How do you know that the correct radiation dose was actually delivered?”
Radiotherapy involves extensive quality assurance and safety checks.
Your radiation oncologist prescribes the treatment dose, number of fractions and treatment area.
Medical physicists perform measurements and quality checks to ensure that the radiotherapy equipment is functioning appropriately and radiation can be delivered accurately.
Radiation therapists/technologists carefully reproduce your treatment position and operate the treatment equipment according to the approved plan.
Modern radiotherapy also uses computerised treatment-planning systems, imaging and verification procedures.
So behind those few minutes on the machine are multiple professionals, calculations, measurements and safety systems.
Much of radiotherapy is deliberately invisible to the patient.
“If radiotherapy is working, shouldn’t I develop side effects?”
No. Side effects are not a test of whether radiotherapy is working.
Depending on the area being treated, some patients may develop:
Skin reactions
Tiredness
Mouth or throat soreness
Difficulty swallowing
Bowel symptoms
Urinary symptoms
Other site-specific effects
Another patient receiving effective radiotherapy may experience relatively few problems.
Side effects depend on factors such as the dose, treatment area, volume of normal tissue exposed, concurrent chemotherapy and individual sensitivity.
Therefore:
More side effects do not automatically mean better cancer treatment.
And fewer side effects do not mean that your treatment is ineffective.
Effective cancer treatment does not have to hurt.
“Should I worry if I feel completely normal after my radiotherapy session?”
Usually, no. Feeling nothing during treatment is expected.
Many radiation side effects, when they occur, develop gradually rather than immediately after the machine switches on.
Their timing also depends strongly on which part of the body is being treated.
Do not try to judge whether your treatment is working based on what you feel immediately after each session.
Your treatment team has much better ways of verifying treatment delivery than your symptoms.
“When will we know whether the radiotherapy worked?”
The answer depends on your cancer and the reason radiotherapy was given.
Response may be assessed using:
Clinical examination
Improvement in symptoms
Blood tests or tumour markers in selected cancers
CT
MRI
PET-CT
Other disease-specific investigations
Importantly, earlier is not always better when it comes to scanning after radiotherapy.
Radiation can temporarily cause inflammation, swelling and other tissue changes. Imaging performed too early can therefore sometimes be difficult to interpret.
Your oncologist will decide the appropriate investigation and timing based on your particular disease and treatment.
“So what should I remember when I am lying on the machine thinking, ‘Nothing is happening’?”
Remember this:
You are not supposed to feel the radiation.
While you are lying still, your position may be checked and a treatment designed specifically for your anatomy and cancer is being delivered according to a carefully prepared plan.
And when those few quiet minutes are finished, the biological effects of radiation do not simply switch off.
They continue within the treated cells.
Radiotherapy can be silent, painless and invisible.
That does not make it inactive.
Sometimes the most important part of your treatment is the part you cannot feel.