Proton therapy spares healthy tissue

Radiation therapy for cancer in the head and neck region with protons leads to less damage to surrounding healthy tissue than the usual treatment with photons. As a result, patients should be less troubled by side effects such as problems with swallowing and a dry mouth. In preparation for the introduction of proton therapy in the Netherlands, PhD student at the University Medical Center Groningen (UMCG) Tara van de Water investigated the advantages involved. Van de Water was awarded a PhD by the University of Groningen on 13 March 2013.

The aim of radiation therapy is to eradicate cancerous tissue while leaving the surrounding healthy tissue as undamaged as possible. Using protons has the advantage that they lose momentum after entering the body and release most of their energy at the desired location in the tumour prior to stopping. Photons, on the other hand, release most of their energy directly under the skin. The energy released then gradually decreases as the photons pass further into the body. Many photons leave the body without releasing any of their energy, including some aimed at the tumour. Head and neck cancer often involves tumours adjacent to healthy tissue such as the salivary glands, the anatomical structures involved in swallowing and the spinal cord. Less radiation passing through these vulnerable tissues means the patients will suffer fewer side effects.

Radiation treatment plans

When radiation therapy is indicated for a patient, a CT scan is made first providing a detailed view of the location of the tumour and the surrounding tissues and organs. The radiotherapist-oncologist uses the scan to define the target area for radiation and the healthy tissues that need to be left intact as far as possible. The CT scan is then used to draw up a treatment plan and to calculate the radiation dose involved.

Potential advantages

Van de Water used the treatment plans of patients who had already received photon therapy to draw up improved plans for photon and proton therapy. She then used these simulated radiation treatment plans to investigate the potential advantages of protons over photons in preventing damage to the salivary glands and structures involved in swallowing. She demonstrated that with the same effective dose in the tumour, a lower radiation dose was found in the salivary glands and swallowing structures using protons. Van de Water expects that proton therapy will lead to fewer complaints involving a dry mouth and problems swallowing than photon therapy, thus potentially contributing to improved quality of life during and after radiation treatment. Her study also shows that some patients gain little or no advantage from proton therapy due to the size, shape and location of the tumour involved.

Choice

Proton therapy is not yet available in the Netherlands. The Ministry of Health, Welfare and Sport (VWS) is planning a phased introduction, which could incorporate UMCG’s plans to build a proton facility. If proton therapy does become available, patients will be evaluated on whether it would be advantageous for them as opposed to photon therapy, using similar methods to those used by Van de Water in her study of patients with head and neck cancer.

Cost

According to Van de Water, the Health Care Insurance Board (CVZ) is working on guidelines for the introduction of proton therapy. ‘The guidelines will be drawn up with the aid of comparative studies on radiation planning like the one I conducted. Such a study shows you which patients can expect a clinically relevant advantage and for whom proton therapy could be indicated’, says Van de Water. ‘CVZ will also want to investigate the cost effectiveness. Although the cost of proton therapy may be higher than that of photon therapy, if the treatment causes far fewer side effects, savings in medical care will be made in the long run.’ The cost effectiveness can only be properly established after proton therapy has been introduced and patients treated have been monitored.

Curriculum Vitae

Tara van de Water (Bombay, India, 1981) studied Applied Physics at the University of Groningen. She conducted her PhD research at the Department of Radiotherapy of the University Medical Center Groningen (UMCG) and at the Center for Proton Therapy at the Paul Scherrer Institute in Switzerland. Since 2010 Van de Water has been in training to become a clinical physicist in radiotherapy at the UMCG. Her thesis is entitled ‘Potential benefits of intensity-modulated proton therapy in head and neck cancer’.