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Information for patients having Radiotherapy to the Rectum

Preparing for Radiotherapy


It is very important that you are well hydrated (drinking lots of fluid every day) and have a ‘comfortably full’ bladder for your CT Planning scan and treatment. A comfortably full bladder means your bladder is full but that you do not feel that you urgently need to empty it. Therefore we ask that you drink a minimum of two litres (four pints) of fluid per day, but no more than 4 litres. This should mainly be water, squash or other non-caffeinated drinks. You should also reduce your intake of caffeinated, fizzy and alcoholic drinks.

A suggested way to keep hydrated is to drink a glass of water every 1-1.5 hours during the daytime (more if the weather is hot or if you are exercising). Aim to drink a glass of water measuring about 150mls at these time intervals. In addition to thinking about keeping yourself well hydrated, we need you to practice filling your bladder and keeping it full. We suggest that when you are well hydrated, you empty your bladder and then drink 350ml (approx two small glasses) of water. After 30 minutes you should have a comfortably full bladder and be able to hold it comfortably for a further 15 minutes. Please do this every day from the day you consent to treatment.



It is also important to empty your bowels daily when you have your planning CT scan and treatment – being well hydrated will help you to do this but do not strain to open your bowels as this may cause problems. This section is not relevant if you have a stoma or colostomy.


Flatulence / Wind

If you are normally prone to flatulence, it is important to reduce the amount of gas you produce by avoiding food and drink that you know causes you be flatulent, these food or drinks maybe different for different people. 

Following these instructions will help to reduce the side effects of your treatment.

This will also make sure that your bowels are in the same relative position each day, helping to ensure that the treatment is accurate.


What if I am unable to hold the water in my bladder? 

If you are unable to hold your bladder with 350ml of fluid, try reducing the amount to 300ml. If you still can’t hold on, try decreasing the amount of fluid you drink until you find an amount of fluid that is comfortable for you to hold on to for the full 45 minutes. Aim to increase the volume of water daily until you are comfortable holding 350ml. Following your initial outpatient appointment with the Oncologist, you will be telephoned by the radiotherapy assistants informing you of the time and date of your CT scan / Planning Scan appointment.


Computerised tomography (CT) scan / Planning Scan

A CT scanner is a special x-ray machine that produces a series of detailed pictures showing the structures of the pelvis.

This scan is only for planning your treatment. The images are sent to a planning computer and used to reconstruct a three dimensional image of your pelvis. The clinical oncologist will then use this image to accurately plan your radiotherapy. 

When you arrive for your scan 

A member of the pre-treatment radiotherapy team will explain what is going to happen, and during this discussion, you will be asked to confirm your name, address and date of birth. You will also be asked for this information before every procedure or treatment undertaken in the department.

We will then ask you to re-confirm consent to make sure you are certain that you would still like to go ahead with the proposed treatment. 

You will then need to go to a toilet to try and empty your bladder and bowel (do not strain), after that you will need to drink 350mls of water. We have a water dispenser in the waiting area and it should take you no more than 10 minutes to drink the water, then we will wait 30 minutes to give your bladder time to fill. 

You will need an empty bowel and a full bladder for the scan and also for all of your treatments. If however you cannot manage this, which can happen, the radiographers will give you advice to help achieve this. We understand that with a rectal tumour this may be more difficult so we may accept your bowel as it is if it is tumour related.

If you have a stoma or colostomy, bowel emptying/preparation is not required.

Although you may be more comfortable with an empty bag for your appointment.  

We may wish to insert a cannula (needle) into to your arm to allow us to inject dye/contrast media during your scan.

Please make sure you eat normally and drink plenty on the day of your scan and throughout your treatment appointments. There is no harm in you being around other people after treatment, as you will not be radioactive in anyway.

During the CT scan 

For the scan you will need to remove your trousers/shorts/skirt and shoes. You will need to lie on the CT table on your back, with your hands on your chest. Your head, knees and ankles will be supported in specially-shaped rests.

The radiographers will make you as comfortable as possible so that you are able to lie very still. The radiographers will then scan your bladder with ultrasound to check your bladder volume.

Then a radiographer will make some pen marks on your pelvis and place a sticker on it to mark the area that needs to be scanned. This is done so that the mark shows up on your scan. The pen marks and stickers will be removed after the scan is completed. 

The CT table will be raised to go through the scanner and the radiographers will then leave the room. The radiographers will be watching you at all times through the window. All you need to do is relax, breathe normally and stay still. 

The radiographers will start the scan from outside the room. You will feel the bed slowly move in and out of the scanner and hear the machine buzzing. The scan should only take a few minutes. We may inject a dye/contrast media into a vein on your arm to enhance the clarity of the CT images which helps the Clinical Oncologist plan your treatment.

If your bladder or bowel is too full or too empty we may need to get you off the bed to try and rectify this. Sometimes it may take a couple of attempts’ to achieve the best scan which will then allow us to plan an optimal and individualised treatment for you.

After the CT scan 

Once the scan is complete and satisfactory, the radiographers will come back into the room. They will take some measurements and make some very small permanent ink marks (tattoos) on your pelvis. These marks help to position you correctly for your future treatments. The radiographers will assist you down from the scanning table and you may then get dressed and leave the department. If you have had dye/contrast during your scan we will ask you to wait in the waiting room for 30 minutes before removing your cannula and then you can go home.

Before you leave, you will be given a parking permit for the hospital and a letter with your provisional start date and time. You will be given a confirmed full list of appointments on your first day of radiotherapy treatment, approximately two to three weeks after your CT scan.


Radiotherapy Treatment

When you arrive for your appointment, you will be directed to the treatment waiting area. 

One of the treatment radiographers will discuss your treatment with you and confirm that you consent to have the treatment; you will also be able to ask any questions that you may have before the treatment begins. 

What will I need to do during my treatment?

You will need to have an empty bowel and a full bladder for your treatment. There are water dispensers in the waiting areas of the department if you need them. Having a full bladder and empty bowel helps to ensure the position of your internal anatomy and helps to reduce the side effects of treatment. 

Each day, please arrive in the department one hour before your appointment time to allow you to empty your bowel and bladder, then to drink water to fill your bladder for your appointment time. Alternatively you can arrive with a comfortably full bladder and empty rectum ready for your appointment time.

Please be aware that sometimes your treatment appointment may be delayed. You will be escorted into the room, where the radiographers will introduce themselves and ask you to identify yourself by telling them your name, first line of your address and your date of birth. After which, you will be asked to remove your trousers/shorts/skirt and shoes. 

You will be asked to lie on the treatment table, which will be set up with the same equipment as when you had your CT scan. You should try to relax, lay still and breathe normally.


The Radiotherapy Treatment

Radiotherapy treatment is given by a machine called a linear accelerator, often referred to as a Truebeam.

The lights will be dimmed so that the radiographers can see the room lasers that will help them to position you correctly. You will hear the machine move around you. It will come close to you but will not touch you.

You will hear radiographers taking various measurements and feel the bed moving. Once you are in the right position, the radiographers will leave the room, and you will hear a beeping sound – this is the door safety interlock. You will be alone in the room during your treatment but the radiographers will be watching you and can hear you on closed circuit television (CCTV).

If you need assistance at any point, just wave a hand and the radiographers can immediately return to the room. Digital x-ray images are taken regularly during your treatment to ensure that the treatment is being delivered accurately. There will be a short delay while these images are assessed and you may feel the bed move as the radiographers adjust its position from outside the room. 

Once we are happy that you are in the correct position, the treatment will then be delivered and the machine will move around you to treat you from different angles.

During the treatment delivery you will not see or feel anything from the treatment, all you will notice is a buzzing noise. This whole process will take approximately 15 minutes. 

Afterwards, the radiographers will return to the room, and help you down from the treatment table. The treatment table will be quite high up, so it is very important that you do not move or attempt to get off the table without assistance. The radiographers will tell you when it is safe to sit up and get off the table.


Important Information

If you have a pacemaker or ICD, please tell your doctor/radiographer as soon as possible.

Although your device is not near the area being treated, you will need to have it checked before your treatment. If you are diabetic you will need to have appropriate drinks without sugar. If you take regular pain medication or have any condition that may cause you pain or discomfort when lying flat on a hard surface, ensure you bring your pain medications with you when on treatment or for the CT scan.

If you have or have had haemorrhoids in the past and they come back on treatment, please check with your staff before using ANY creams or ointments as they may cause problems if used during radiotherapy.


Who will look after me while on treatment?

A number of healthcare professionals will be involved in your treatment and care. Below is a list of all of the doctors, nurses, specialists and departments who will look after you while you are having radiotherapy. 

Clinical oncologists are doctors who are trained in the use of radiotherapy and chemotherapy. The consultant clinical oncologist will be in charge of your care. Clinical oncologists are supported by a team of specialist registrars, therapy radiographers, nurses and administrative staff. 

Therapy radiographers are specifically trained to plan and deliver the radiotherapy. They provide support and advice on radiotherapy side effects and their management. The radiographers will have day-to-day responsibility for you while you are receiving radiotherapy.

Your advanced practice radiographers will provide support and advice on all aspects of your treatment including regular reviews during treatment.

Macmillan Oncology Nurses provide support and advice on the side effects of radiotherapy/chemotherapy and their management. 

Chemotherapy Nurses and Pharmacists will be involved in preparing and delivering chemotherapy treatment if necessary. 

The Emergency Assessment Bay (01604 545851) will provide emergency medical advice or care for any side effects of treatment or problems relating to the cancer itself and are available 24 hours a day, 7 days a week.


Useful websites


Other information

Northampton General Hospital operates a smoke-free policy. This means that smoking is not allowed anywhere on the Trust site, this includes all buildings, grounds and car parks.

Leaflets, information, advice and support on giving up smoking and on nicotine replacement therapy are available from the local Stop Smoking helpline on 0845 6013116, the free national helpline on 0300 123 1044, email: and pharmacies.

Car parking at Northampton General Hospital is extremely limited and it is essential to arrive early, allowing ample time for parking. You may find it more convenient to be dropped off and collected.

This information can be provided in other languages and formats upon request including Braille, audio cassette and CD. Please contact (01604) 544516 or the Patient Advice & Liaison Service (PALS) on (01604) 545784, email:


 This information was taken from Northampton General Hospital leaflet NGV2445 (Feb 2022).

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