In Silico Clinical Trial on Adaptive Radiotherapy in Oropharynx Cancer, Comparing Photon & Proton Therapy: A Multicentric ROCOCO Planning Study Based on a Reference Dataset.

Given that the cost of particle therapy (PT) is considerably higher than that of conventional radiotherapy (RT) with photons, it is necessary to establish whether these higher costs are worthwhile in light of the expected advantages. Thus, clear evidence of the situations in which PT outperforms conventional photon treatment is needed. ROCOCO (Radiation Oncology COllaborative Comparison) is commenced at MAASTRO in May 2007 to evaluate PT's cost-effectiveness .

It is well known that during radiation treatment of head and neck cancer (HN), shrinkage and displacement of tumour and organs at risk (OARs, e.g. parotid glands), as well as weight loss may cause significant radiation dose changes to target volumes and organs at risk , , . These phenomena may cause the necessity to re-plan the treatment at a certain moment in time. In the last years many different treatment planning studies have been performed showing that the optimum moment for re-planning varies: after 20 Gy, 35 or 46 Gy. But what the actual effect of the deformation is on dose in actually treated patients has not been reported.

The investigators propose an in silico trial to investigate the relevance of contour changes for OAR as well as tumor during chemo radiation in H&N patients which will eventually lead to replanning. In that way the investigators will be able to assess and compare the optimal timing for replanning for photon and proton therapy.

The investigators compare different treatments focusing on the effect of deformation on PTV coverage and normal tissue radiation exposure. A fixed tumor dose, using the same delineation of gross target volume (GTV), clinical target volume (CTV) is used. The planning target volume (PTV) will be determined by each treatment modality.

For the initial plan the best possible dose distribution will be determined using the planning-CT (reference scan). For every time point (CT-scan) the reference treatment plan will be projected on the actual CT scan and the dose will be recalculated without changing the treatment parameters. This will be done using both photons and protons. All treatment uncertainties including robustness will be taken into account. Dose differences in the target volume (CTV-GTV and PTV) and the OAR, as a result of tumor shrinkage during treatment will be evaluated for each time point and each treatment modality.