The 4 steps of radiation treatment planning and delivery

THE FIRST STEP : The  Simulation CT

A special computerised tomography  on  the exact  treatment position is first carried out. This is called a simulation CT and allows us to transfer the images of the area of interest  to the treatment planning system.

This CT is quick, simple and  easy . There are usually no needles or catheters involved. Your doctor is always  present and the procedure is done under her personal guidance.

After completion of the CT-sim  the experienced radiographer will mark your skin with tattoos, as safe reference points  to the  future treatment fields.

The simulation CT takes place a couple of days before the commencement of radiotherapy.

 

THE SECOND STEP : The treatment planning

The images are electronically transfered  to  the electronic  computer. Your doctor  will  now delineate the tumour on each image and spesify the area to be treated.

This delineation follows some strict rules and is guided by  protocols.  The currently used is the ICRU 62  protocol according to which :

1. GTV  is the Gross Tumour Volume  ,ie  the cancerous mass, the lump or simply the tumour bed after exsition
2. CTV  is the Clinical Tumour Volume,ie the possible spread of the cancer to its neibhouring area , the micrometastases  and/or   to the lymph nodes
3. PTV is the Planning Tumour Volume, that is the area that needs to be irradiated so that the CTV receives the therapeutic dose. It has a safety margin to compensate for the internal organ motion and for the random mistakes on the daily set- up.
4. OARS , ORGANS AT RISK  , these are  all the  healthy organs which must be excluded from the “hot” irradiation area.

The spinal cord ,the normal lung, the heart , the bladder or the rectum, the normal brain and  the major nerve plexuses are  all OARS. The dose to these organs must not exceed a certain level  as they can suffer serious damage ( Dose Constraints),  Different parts of these organs can accept small amounts of dose and these are calculated by the so called Dose Volume Histograms , DVH.

The treatment planning is the arrangement of the appropriate beams of radiation and the distribution of their energy to the PTV .

It is constructed by the Radiation Physicist,an experienced physicist with studies in Radiotherapy and in oncology.The procedure is meticulous and demanding.

The optimum plan is finally chosen in collaboration with the responsible doctor and the parameters are electronically transferred to the Linear Accelerator.

Your treatment is ready to commence.

 

THE THIRD STEP : The first session

On the first session you will be guided by the radiographer , who is the person who operates the machine, to the treatment room. Your doctor will be present. You will be set – up to the  your treatment position, according to the reference points. The Linac will take its position,  the Gantry position, the doctor will check the fields and you will be left alone for a few seconds . We are watching you and we can hear you  . During your treatment you can see the Linac change its positions and you can hear the “bip-bip” noise . Nothing touches you. The treatment is simple and quick.

Before you know the session will be  completed, your doctor and the radiographer will enter the room and you  will be helped off the treatment bed . You feel very relieved and you usually say “  is that all ? “

 

THE FOURTH STEP : the  following sessions and …the first radiation reactions

The treatment takes place on working days. Your visits are scheduled according to your convenience as the department works 9-5.

On the following sessions the treatment is  daily reproduced exactly as the first day.

As the sessions progress the first  acute reactions will appear. The skin will redden ( erythema ) , the mouth may be sore ( mucositis ) , the rectum may react with frequent bowel movements ( diarrhoea ) or you may find it difficult to pass urine ( dysuria ).

All these acute reactions are mild, self restricted  and very treatable.

They are caused by the damage of the rapidly proliferating tissues of the epidermis, mucosa , endothelium of the vessels from the irradiation. Your doctor will have you well prepared  and informed about their appearance and treatment.

After the completion of the radiotherapy ,usually 4-6 weeks after ,you will be asked to visit your doctor again. This is the real end of the treatment, as cells continue to die.

THE  LATE REACTIONS

These are  permanent radiation reactions that develop months  or even years  after the completion of Radiotherapy. They are caused by the damage of the slowing growing tissues like the endothelium of the greater vessels , the pneumocutes of the lung, the myocytes of the heart, the neuron cells and the glial cells in the brain ,the connective tissue cells ,or  the parotid cells  which excrete the saliva.

They manifest with non functioning organs in part or in whole.

Pneumonitis, pericarditis, cystitis, enteritis,a dry mouth  are all serious chronic radiation sequellae. The safer  treatment is their prevention during the treatment planning procedure and the treatment delivery period.

In experienced hands these  late reactions are minimal.
 

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