Radiation therapy always had a strategic role in the treatment of lung cancer. Recently it became even more crucial thanks to the development of stereotactic radiotherapy.
This article will focus on techniques of radiotherapy used in the treatment of primitive lung cancer. Metastases and brain metastases will be subject to a new publication.
Several aspects must be examined to deliver a radiotherapy treatment on a lung cancer:
- The lung is a vital organ. Then the treatment must be delivered with a very high precision to spare the healthy lung.
- The preservation of critical organs located in the mediastinum such as the heart or oesophagus which are close to the lung.
- Due to respiration, lung tumours move. Then 2 options can be considered: to increase the volume of radiation or to reckon the breathing movement through different methods. In that case, technologies analysing the breathing movements are integrated in the most advanced radiotherapy techniques.
Let’s have a focal point on radiation therapy techniques used in lung tumour treatment:
- 3-D Conformal Radiation Therapy: the three dimensions of the tumour and at-risk organs are examined. The radiation beams are shaped to target the tumour very precisely and spare healthy tissues.
- Intensity Modulated Conformal 3-D Radiation Therapy (IMRT, Dynamic Arc-Therapy): this technique allows to spare at-risk organs and a better adaptation to the shape of the tumour by varying the intensity of the beam. Recent studies also confirmed a better cardiac protection in lung cancer treatment.
- Stereotactic Radiotherapy (RTS) is exclusively delivered for tumours without node invasion. Its principle is to deliver, with millimetre precision, high doses of radiation in a few sessions (3 to 10). This radiotherapy is considered ablative because its results are close to those of surgery.
We can now introduce the breathing motion techniques:
- The 4D scanner: the tumour movement will be recorded during the different phases of the respiratory cycle. The volume treated will then correspond to each position of the tumour during this cycle.
- The gating or respiratory blockage: patients are asked to block breathing either during inspiration or expiration. The treatment is exclusively delivered during one of this phase of the respiratory cycle which reduces the volume of radiation. The only constraint is to be able to hold the respiration long enough to deliver the radiation.
- The tracking: it consists of real-time monitoring of the tumour. The tumour can be identified by radio-opaque markers such as gold grains or directly on stereoscopy imaging. Thanks to this technique, radiation therapy will have a major role in every stage of lung cancer treatment. In the early stages, stereotactic radiation therapy may be performed in patients who could not benefit from surgery. In the most advanced stages, it allows in combination with chemotherapy to treat inoperable tumours.