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Radiation oncology is increasingly personalized

Dr Mathangi J
Wednesday, February 21, 2018, 08:00 Hrs  [IST]

Radiotherapy is the technique of treating a tumour with ionizing radiation like X-rays. It is painless and is an integral part of cancer treatment. It acts by damaging the DNA of the cells, either directly or indirectly, thereby killing the cells. In the process, the cells of normal tissues get damaged because of their proximity. As the survival in cancer is improving, our focus is now on ensuring good quality of life in the long term. This has resulted in a shift of focus from cure to cure with as less damage to adjacent normal tissues as possible.

The kill
The primary intention is to deliver a high dose to the tumour to improve the cure rate. There is little point in saving normal tissue at the cost of the tumour. The higher the dose, the better the kill. For example prostate, head and neck cancers need very high doses for cure, which will be toxic and damaging to the adjacent normal tissues.

The balance
A dead man with a wet mouth is as bad as a live person with a completely dry mouth in head and neck cancers. Similarly, prostate cancers should not be cured with lifetime bleeding from the rectum. The balance is the new thing to draw the line.

New techniques
The latest radiotherapy delivery techniques like IMRT (intensity modulated radiotherapy) and RapidArc (volumetric modulated arc therapy) help the radiation oncologist to go around the salivary glands, spinal cord, bladder or rectum, avoiding damage to these tissue while still achieving good tumor control.

However, in some sites, the advanced technology may be harmful. Here, the sparing can be done by boosting the tumour with brachytherapy (internal radiotherapy)

This is an age old technique of boosting the dose to the tumor from within. Though an invasive procedure, this gives the least dose to the normal tissues. The image guidance adds value to this tool.  

Tumours come with signatures. HPV DNA, IDH, P53, MIB index, 1p, 19q are some markers which help in judging the severity of the disease, patterns of recurrence, response to therapy etc. Personalized treatment is now possible with the use of these genomic signatures.

For planning - 4DCT is like a video CT scan of the tumour that moves as is in the case of lung/liver cancer. This gives the exact movement of the tumour for that patient, so that only the needed volume can be treated. 4DCT in left-sided breast cancer must be done when the breath is held in deep inspiration. This can help in avoiding radiation to the heart and reduces long term cardiac side effects.

PETCT in radiotherapy planning shows the real extent of the disease in esophageal and lung cancer. It also helps us in finding the missing primary in a patient presenting solely with a huge neck node. C Met PET helps in exactly delineating the brain tumor for each patient. PSA PET does the same job in a prostate cancer.

MRI scans help us to know the real extent of the brain tumor, the intracranial spread of head and neck cancers, the extent of the cervical cancer into the adjacent soft tissues etc. This helps the radiation oncologist to cover the entire tumor avoiding geographical misses, thus improving local control.

During treatment
The gold markers inserted in the prostate with USG scan guidance help the doctor to track and match the prostate everyday with X-ray or CT scan imaging during treatment. This improves the accuracy and reduces the dose delivered to the rectum in the back and the bladder in the front.

The new machines are incorporated with the facilities to perform an X-ray, CT scan or a fluoroscopy on the couch during treatment. This helps matching and correcting with sub millimeter accuracy. Imaging during treatment (Image guided radiotherapy/IGRT) is a powerful tool minimizing the errors and reducing the dose delivered to the normal tissues. This is of great help in critical treatments like ablation of the trigeminal nerve in a patient with trigeminal neuralgia with a very high dose, while avoiding damage to the brain stem which is just few millimeters away. The same is true while treating skull base tumors.

Adaptive radiotherapy
The planning and delivery of treatment should be adapted to the changes seen in the patient. When treating a patient with a large node bulging out, the response to the treatment should be monitored. The node size may regress resulting in dose delivery elsewhere, or to the nearby critical structures. Imaging/scanning during treatment helps us in assessing this, re-planning and tailoring it accordingly.

Similarly, a patient may lose weight due to many reasons, and the thickness of the body in the treated region may reduce. For example, in head and neck cancers, this may result in a higher dose to the skin or spinal cord, resulting in more reactions. So, this might call for attention to re-tailor it to the present condition.

In a cervical cancer patient, the growth might be obstructing, creating large fluid collections in the uterine cavity. During the treatment, when the tumor responds and reduces in size, the fluid gushes out as a result of the reduced size of the uterus. This place would now be occupied by the small intestines and may result in increased loose stools and long-term bleeding from intestines. The imaging integrated to the radiotherapy machine ensures that plans be modified frequently as the treatment progresses.

Depression and family counseling
Counseling should not only involve the patients but also the entire family and caregivers to advise them on how to support the patients physically and mentally. They need periodic diet-counseling and education to look for and manage the toxicities and emergencies. Economic and logistics counseling also plays an important role, as the treatment duration may runs into weeks.

In short, the tools present to fight cancer with radiotherapy are increasing. It is the wisdom and the experience of the doctor to choose which treatment and combination would be best suited to the patient, with a view of achieving good tumor control and the least amount of side effects. Not every tumor needs high end technique and not every patient the same treatment.

(Author is senior consultant, Radiation Oncologist, BGS Gleneagles Global Hospital)


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