External radiotherapy is one of the most common treatments for lung cancer. The goalis to apply radiation to the tumour from an external sourceand at the same time protect the surrounding healthy tissue as much as possible, thus reducing the side effects on the patient. In the usual internshipthis goalis achieved by establishing safety margins around the tumour to ensure that the radiation dose is adequate, minimising the impact on the organs close to the tumour. 

What factors are decisive for the correct application of the treatment and is it possible to ensure that the tumour remains within the safety margins during the process? These are some of the questions addressed by Dr Carlos Huesa (Malaga, 27 years old) in his doctoral thesis entitled"Quantification of dosimetric uncertainties in lung stereotactic body radiation therapy".

One of the difficulties with these procedures - according to researcher- is the movement of the tumour caused by the patient's own breathing during the administration of the radiation, their anatomical changes throughout the different sessions and even the combined movement of the radiation beam and the tumour itself. "The added difficulty in lung cancer is that the patient breathes and therefore the tumour moves. In addition, during the application of the treatment, the patient may experience anatomical changes such as weight loss or gain, or simply the displacement of the tumour," says Dr Huesa.

The new techniques proposed in this researchare based on the use of images acquired from patients during treatment: CT images (obtained prior to treatment) and daily CBCT -Cone Beam Computed Tomography- images (obtained on the day of treatment). Both sets of images are spatially correlated, allowing a more reliable calculation of the radiation dose. "For a correct application of the treatment it is essential to know the impact of the patient's breathing (how much the tumour moves), of the anatomical variations present in each session (where exactly the tumour is on the day of the treatment) and of the combined movement of the radiation beam and the tumour," he adds.

These strategies proposed by Carlos Huesa make it possible to assess the quality of treatments in order to contribute to better clinical decision-making. "We have to quantify as accurately as possible the position of the tumour within the safety margins and the dose it has received, trying to safeguard healthy tissue.

Huesa believes it would be interesting to apply these tools to proton therapy treatments. "Unlike conventional radiation, in proton therapy the maximum amount of radiation is deposited in the tumour, considerably reducing side effects. To ensure this procedure, it is crucial to quantify the impact of the uncertainties that we have evaluated in this thesis doctoral study (respiration, anatomical changes and combined movement of the radiation beam and the tumour)".

According to the World Health Organisation, lung cancer is one of the cancers with the highest incidence in the population and a high mortality rate. In 2020, 1.8 million of the more than 10 million deaths from cancer will be due to lung cancer.

Carlos Huesa is a biomedical engineer, Master's Degree in Mathematics, and has developed his research in the department of Physics and Applied Mathematics in the School of Sciences of the University of Navarra under the direction of Full Professor Javier Burguete, and in the Radiophysics Service of the University of Navarra under the co-direction of Dr. Juan Diego Azcona. Clínica Universidad de Navarra under the co-direction of Dr. Juan Diego Azcona.

Bibliographical references

→ Huesa-Berral, C., Burguete, J., Moreno-Jiménez, M. and Azcona, J.D. A method using 4D dose accumulation to quantify the interplay effect in lung stereotactic body radiation therapy. Phys. Med. Biol. 2021; 66(3).

→ Azcona, J. D., Huesa-Berral, C., Moreno-Jiménez, M., Barbés, B., Aristu, J. J. and Burguete, J. A novel concept to include uncertainties in the evaluation of stereotactic body radiation therapy after 4D dose accumulation using deformable image registration. Med Phys. 2019; 46(10): 4346 - 4355.