During the 3rd ESTRO Forum that took place in Barcelona last week, researchers presented a new breathing movement model that allows for the exact measurement of narrow beams to a tumor model by simulating the physical properties and the motion of the chest anatomy. The new method was presented by Dr Rosalind Perrin, from the Centre for Proton Therapy at the Paul Scherrer Institute in Villigen, Switzerland. The led researcher described how she and her team developed this model to test the feasibility of proton therapy targeting lung cancer, using a rescanning technique that mitigates motion effects, and to create practical methods to implement this technique in cancer treatment.
“This involved experiments using an advanced breathing model of the patient, a so-called ‘anthropomorphic phantom,’ with integrated measurement devices to accurately measure the dose distribution. We found that our rescanning technique worked well to overcome the effect of motion on the dose delivered to the tumor, and for tumor motions of up to 1 cm,” said Dr. Perrin in a recent news release.
The researchers used a sphere mimicking a tumor moving in an inflating lung, sheltered in a rib cage including adjacent skin and muscle layers. This new technique can be programmed to move according to each patient’s breathing patterns.
In their research, the investigators measured the dose of radiation during movement and discovered that rescanning allowed the delivery of an adequate dose distribution to the tumor, with only a minimal dose distributed to the surrounding tissues.
This scanning proton radiotherapy approach to cancer treatment is an emerging technology, in which a narrow particle beam with accelerated hydrogen nuclei is scanned across the tumor and a highly directed radiation is administered to cancer cells. Because of the large mass of the protons, the beam delivers the majority of the radiation dose towards the end of its path in the tissue. Consequently, proton therapy can limit the dose of radiation affecting the surrounding tissues.
The proton beam only pierces the tissue up to a specific depth, which is controlled by energy levels. As such, in comparison to traditional radiotherapy techniques, proton therapy allows a maximal tumor dose while reducing the radiation dosage in surrounding tissues.
For liver or lung tumors, which are mobile tumors, tumor and organ motion weakens dose distribution due to the possibility of rifts between the radiation delivery time-line and the time-line of the tumor motion: also called the “interplay” effect.
To address this issue, researchers developed a state-of-the art delivery system. “This makes it possible to average out the dose to the moving tumor, and also reduce the effect of motion on the dose delivered to it. Because of the sensitivity of the lung to radiation, as well as the proximity of the heart, oesophagus and spinal cord, it is particularly important to keep the radiation dose to surrounding tissues as low as possible in lung cancer,” said Dr Perrin.
Researchers now want to apply this novel technique into the clinic to improve cancer radiotherapy. However, the associated costs are still an important issue. “The cost-benefit of proton therapy is a hotly-debated topic amongst national healthcare bodies and insurers. But if we can show, through randomized clinical studies, that proton therapy is better for certain cancer types, this may influence politicians and insurance providers to make appropriate decisions. This is particularly important for cancer types with a poor outcome that are subject to motion, especially advanced-stage liver and lung cancers,” Dr Perrin explained.
Professor Philip Poortmans, President of ESTRO, commented: “Proton therapy is currently attracting a lot of attention in the field of oncology as well as in the lay press. This study points out very accurately that a lot of work still has to be done before its applicability to most tumor sites will be broadly acceptable outside the field of clinical trials. The investigators focused on the challenge of the movement of the tumor within the patient’s body, for example with a normal breathing cycle. The rescanning technique they describe, which compensates for tumor motion, averages out the delivered dose while keeping the dose to surrounding normal tissues at a low level. The next challenge will be to bring this novel technique to the point of clinical applicability.”