Chemotherapy uses medicines, which travel in the blood and reach cancer cells anywhere in the body [1, 3]. Radiotherapy (radiation therapy) uses high-energy radiation to damage the DNA of cancer cells and is a local treatment: it treats only the part of the body the radiation is aimed at [4, 5]. Neither is always "better" or "stronger"; the choice depends on the type of cancer, where it is and whether it has spread [1], and in some cancers, such as cervical and head and neck cancer, giving both together has worked better than radiotherapy alone [9, 10].
Key points
- Chemotherapy is a treatment for the whole body, while external radiotherapy is a local treatment: if the cancer is in the lung, only the chest receives radiation, not the whole body [3, 4].
- Hair loss: some chemotherapy causes hair loss on the head and other parts of the body; radiotherapy causes hair loss only in the area being treated [7].
- Radiotherapy without chemotherapy can also cure cancer [4]: in prostate cancer that had not spread outside the prostate, deaths from the cancer were as low with radiotherapy as with surgery; after 15 years, fewer than 3 in 100 men had died of it [8].
- Together, sometimes better than alone: in cervical cancer and head and neck cancer, chemotherapy given at the same time as radiotherapy helped people live longer than radiotherapy alone [9, 10].
Chemo vs radiation at a glance
| Chemotherapy | External radiotherapy | |
|---|---|---|
| What is used? | Medicines [1] | High-energy radiation [4] |
| How does it work? | Kills fast-growing cells or stops them growing [1] | Damages the DNA of cancer cells so that they die or grow more slowly; it takes days to weeks of treatment for the cells to die, and this goes on for weeks or months after treatment ends [4] |
| Which part of the body does it reach? | The whole body, through the blood [3] | Only the area that receives the radiation [4, 5] |
| How is it given? | Drip into a vein, tablets or injections, in cycles with rest periods in between [1] | A machine outside the body aims radiation at the tumour without touching you; usually once a day, 5 days a week [4, 5] |
| How long does each session take? | It depends on the medicines; ask your treatment team [2] | Usually 30 minutes to an hour, most of it spent getting you into the right position; the radiation itself takes 1 to 5 minutes [5] |
| Side effects | Can affect the whole body: tiredness, nausea, low blood counts, hair loss and mouth sores [2] | Mostly in the treated area; tiredness is also common [6] |
| Hair loss | Some medicines cause hair loss on the head and body [7] | Only in the treated area [7] |
| Safety of the people around you | For a while after each session, your family should avoid contact with your body fluids [2] | External radiotherapy does not make your body radioactive [5] |
Internal radiotherapy (brachytherapy) and radiotherapy given by mouth or injection have other safety rules and differ from external radiotherapy [4].
Radiotherapy vs chemotherapy: which is better, and which is stronger?
Neither is always better or stronger; the two treatments do different jobs. The treatment you need depends on the type of cancer, whether it has spread and where to, and any other health problems you have [1].
- When the cancer is in one area, a local treatment such as radiotherapy can cure it or stop it coming back [4]; for example, in prostate cancer confined to the prostate, radiotherapy prevented deaths from the cancer as well as surgery did [8].
- When the cancer is in the blood or has spread to several parts of the body, a treatment that reaches the whole body, such as chemotherapy, is needed [1, 3]. Radiotherapy can still be used in this situation to ease symptoms such as pain [4].
- In many cancers both are needed, with or without surgery; radiotherapy may be given before, during or after other treatments [4].
So a better question is: "In my cancer, what role does each treatment play, and what is its aim?" Ask your doctor. Read more: What is chemotherapy and how is it given? and What is radiotherapy, and what are its side effects?
Are chemotherapy and radiotherapy given together? (Chemoradiotherapy)
Yes. When chemotherapy is given at the same time as radiotherapy, it is called "chemoradiotherapy"; the chemotherapy helps the radiotherapy work better [2]. Some examples from large studies:
- Cervical cancer: adding chemotherapy to radiotherapy helped women live longer and made the cancer come back less often [9].
- Head and neck cancer: chemotherapy at the same time as radiotherapy helped people live longer; chemotherapy given before or after radiotherapy did not [10].
- Lung cancer that has grown within the chest but not spread further: giving chemotherapy and radiotherapy at the same time worked better than giving them one after the other and helped people live longer, but it caused more severe inflammation of the gullet (pain and difficulty swallowing) [11].
- Rectal cancer: chemoradiotherapy before surgery, compared with after surgery, roughly halved the number of cancers coming back in the pelvis and caused fewer side effects; people lived just as long in both groups [12].
Chemoradiotherapy causes more side effects; in cervical cancer, for example, early effects on the blood and the gut were more common [9]. Tiredness may also be more severe when chemotherapy and radiotherapy are given together [2]. Related pages: Cervical cancer, Head and neck cancer and Lung cancer.
How do the side effects of chemotherapy and radiotherapy differ?
Chemotherapy reaches the whole body, so its side effects can affect the whole body too: tiredness, nausea and vomiting, low blood counts, hair loss, mouth sores and pain [2]. Most of these get better or go away after treatment ends [2].
Radiotherapy side effects depend mostly on the area being treated [6]: for example, radiotherapy to the pelvis may cause diarrhoea and urinary problems, and radiotherapy to the head and neck may cause mouth problems and difficulty swallowing [6]. Many people feel tired during radiotherapy [6]. Healthy cells that are damaged usually recover within a few months after treatment ends, but some side effects may appear months or years later [6].
Hair loss is an important difference: radiotherapy only causes hair loss in the area being treated; for example, radiotherapy to the breast does not make the hair on your head fall out [7]. Hair often grows back 2 to 3 months after chemotherapy ends and 3 to 6 months after radiotherapy ends [7].
Read more: What are the side effects of chemotherapy?, When do chemotherapy side effects start?, Skin care during radiotherapy and Does hair grow back after chemotherapy?
When should I call my doctor?
During chemotherapy or chemoradiotherapy, call your treatment team straight away in these situations, even at night or at the weekend [2]:
- A temperature of 38°C or higher (or whatever temperature your team has told you), chills or sweats; talk to your team before taking any medicine that lowers fever [2]
- Diarrhoea for more than 24 hours, or diarrhoea with pain and cramps [2]
- Vomiting for more than a day, or bringing up everything you drink [2]
During radiotherapy, also tell the radiotherapy team about any new or worsening side effect at your next session. If you suddenly feel very unwell, for example with severe breathlessness or confusion, call your local emergency number.
Frequently asked questions
Are chemo and radiation the same thing?
Which one has fewer side effects?
It depends on the medicines and on the area treated with radiotherapy. The side effects of chemotherapy depend on the type and amount of medicine and can affect the whole body [2]; the side effects of radiotherapy depend mostly on the area treated [6]. Ask your doctor which side effects are most likely with your treatment plan.
Will radiotherapy make me radioactive? Am I a risk to my family?
External radiotherapy does not make you radioactive, and you can safely be around other people, even pregnant women, babies and young children [5]. Internal radiotherapy and radiotherapy given by mouth or injection have particular safety rules [4]; read: What is radiotherapy, and what are its side effects?
Why has my doctor prescribed both chemotherapy and radiotherapy?
Because in some cancers the two together have given better results: chemotherapy helps radiotherapy work better [2], and in studies in cervical and head and neck cancer it helped people live longer [9, 10]. Chemotherapy can also destroy cancer cells that have travelled to other parts of the body [1].
Can the same area be treated with radiotherapy again?
Each area of the body can safely receive only a certain amount of radiation over a lifetime; that is why an area that has already been treated sometimes cannot be treated again [4]. If you have had radiotherapy before, always tell any new doctor.
How many sessions of radiotherapy and of chemotherapy will I need?
External radiotherapy is usually given once a day, 5 days a week, for several weeks, and how long it lasts depends on the type of cancer and the aim of treatment [5]. Chemotherapy is given in cycles with rest periods in between [1]. Read more: How many chemotherapy sessions will I need? and How many radiotherapy sessions are needed?
Evidence on chemoradiotherapy and curative radiotherapy (for doctors)
For physicians
- Cervix (CCCMAC individual-patient-data meta-analysis, 18 trials): in 13 trials comparing chemoradiotherapy with the same radiotherapy, 5-year survival improved by 6% (HR 0.81, P<0.001); the benefit was seen with both platinum-based (HR 0.83) and non-platinum regimens (HR 0.77), and local and distant recurrence were reduced; acute haematological and gastrointestinal toxicity increased [9]. Regimen: Weekly cisplatin with radiotherapy.
- Head and neck (MACH-NC 2021; 101 trials, 18,951 patients, about 90% stage III or IV): the survival benefit was limited to concomitant chemotherapy: HR 0.83 (95% CI 0.79–0.86), absolute benefit 6.5% at 5 years and 3.6% at 10 years. Adding induction (HR 0.96) or adjuvant chemotherapy (HR 1.02) did not improve survival, and the benefit decreased with increasing age [10]. Regimen: Cisplatin with radiotherapy in head and neck cancer.
- Locally advanced NSCLC (Aupérin meta-analysis; 6 trials, 1,205 patients): concomitant vs sequential: HR for death 0.84 (95% CI 0.74–0.95), absolute benefit 5.7% at 3 years (from 18.1% to 23.8%) and 4.5% at 5 years; less locoregional progression (HR 0.77) with no effect on distant progression (HR 1.04); acute grade 3–4 oesophagitis rose from 4% to 18% [11]. Afterwards: Durvalumab after chemoradiotherapy (PACIFIC).
- Rectum (CAO/ARO/AIO-94; 823 patients, cT3–4 or node-positive): 5040 cGy in 180 cGy fractions, 5 days a week, with fluorouracil 1000 mg/m² per day as a 120-hour continuous infusion in weeks 1 and 5, before vs after surgery: 5-year local recurrence 6% vs 13% (P=0.006), grade 3 or 4 acute toxicity 27% vs 40% and long-term toxicity 14% vs 24%; 5-year survival 76% vs 74% (P=0.80) [12]. A more recent approach: Total neoadjuvant therapy (RAPIDO).
- Curative radiotherapy in localised disease (ProtecT): 1,643 men aged 50–69 with PSA-detected localised prostate cancer; after a median follow-up of 15 years, death from prostate cancer was 2.9% with radiotherapy, 2.2% with prostatectomy and 3.1% with active monitoring (P=0.53); metastases 5.0%, 4.7% and 9.4% [8].
References
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Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
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This page is based on reputable scientific sources and was last updated on 28 October 2026. The content of this website is for educational and informational purposes only and does not replace consultation, diagnosis or treatment by a specialist physician. Consult your treating physician about any treatment decision.
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