Researchers have developed a method that could help apply a more effective form of radiotherapy even on diseased mobile organs such as the lung.Radiotherapy using protons can deliver more accurate treatment to a tumour while reducing the dose to surrounding tissue. However, in mobile organs such as the lung, precise targeting of the dose is difficult.The researchers used in a dummy tumour a delivery technique called rescanning, which helps to mitigate the effect of motion. The findings could lead to practical ways to implement it in the clinic for patient treatments."We found that our rescanning technique worked well to overcome the effect of motion on the dose delivered to the tumour, and for tumour motions of up to one cm," said Rosalind Perrin from the Paul Scherrer Institute, Villigen, Switzerland.
The model developed by the researchers was made up of a sphere representing a tumour moving within an inflating lung, enclosed in a rib cage complete with surrounding muscle and skin layers.The model can be programmed to move with breathing patterns specific to each patient.Radiation dosage was measured during movement, and the researchers found that the rescanning technique allowed the application of clinically acceptable dose distribution to the tumour, and only a minimal dose to surrounding tissues.Scanning proton therapy is an emerging technology in cancer therapy, in which a narrow particle beam, consisting of accelerated hydrogen nuclei, is scanned through the tumour and administers highly targeted radiation to the cancer cells.Compared with conventional radiotherapy techniques, the therapy allows a maximal dose to the tumour, while reducing the dose elsewhere, the researchers noted.
However, for mobile tumours in the liver or lung, organ and tumour motion deteriorates the dose distribution because there may be a rift between the radiation delivery time-line and the time-line of the tumour motion: the "interplay" effect.The rescanning technique involves scanning the tumour several times by the proton beam."This makes it possible to average out the dose to the moving tumour, and also reduce the effect of motion on the dose delivered to it," Perrin noted.The findings are scheduled to be presented at the third ESTRO (European Society for Radiotherapy & Oncology) Forum in Barcelona, Spain.