Compared to conventional radiotherapy with photons (CRT), particle therapy (PT) has the potential to inflict maximum damage on tumors with minimum collateral damage to neighboring healthy tissue. 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.

In a previous ROCOCO study (lung stage I-IIIB) an inhomogeneous group of patients with regard to tumor stage and size was included1. Conformal radiotherapy and Intensity Modulated Radiotherapy were used in the comparison. In this study patients with smaller tumors are included (stage I). A stereotactic treatment schedule and more advanced treatment techniques, such as CyberKnife, RapidArc, IMRT and Tomotherapy, are eligible for these kind of lesions. As a result the comparison as demonstrated in our previous study maybe invalid. We propose to investigate to what extend proton and 12C-ion therapy decrease the amount of irradiated normal tissue compared to state of the art photon modalities in stage I lung cancer patients.

For this in silico planning study all treatment plans will be performed in centers that are already operating and have experience in treatment planning. IMRT treatment plans will be calculated in Eindhoven (NL), Tomotherapy plans in Deventer (NL), Cyberknife plans in Liege (BE) and RapidArc treatment plans in Hasselt (BE). Proton treatment plans will be performed at the University of Pennsylvania (USA) and the C-ion treatment plans at the University of Marburg (GE).

A dataset with state-of-the-art image data is available. 25 patients will be included according to a-priori defined selection criteria. Each patient will function as his or her own control. For this reason, the number of patients per tumor group can be limited to 25 patients per tumor group (power = 80%, alpha = 5%).

The datasets will be stored on a secure website hosted by MAASTRO. High quality CT-images will be used for radiotherapy treatment planning. Secondary image information such as FDG-PET and MRI will be used for GTV delineation. GTV and all relevant OARs will be delineated in MAASTRO (NL). The GTV to PTV margin will be determined by the individual institutes according to the treatment technique and treatment modality.

Photons will be planned with state of the art treatment techniques. Protons will be planned using active beam delivery with Intensity Modulated proton therapy (IMPT)and carbon-ions with a pencil beam delivery treatment planning technique with gantry. Each participating center will use its own treatment planning system according to standard practice at that center. The same tumor dose, overall treatment time (OTT) and an equal number of fractions will be used for all treatment modalities.

Photon, proton and C-ion treatments will be compared based on dosimetric parameters on normal tissues. DVH's will be calculated for the OARs. In addition, the NTCP for a fixed tumor dose will be determined. Cobalt Gy equivalent doses will be used when reporting the proton and carbon-ion dose. In the case of protons, a constant RBE value of 1.1 will be used for both the tumor and the normal tissues. The RBE of carbon-ions will be calculated based on the models used by the participating centers.

Inclusion Criteria:

• >18 years of age
• referred for primary radiotherapy or chemo radiation
• NSCLC stage I
• received respiratory gated CT (4DCT) scans

The study population consists of 25 NSCLC patients; stages I (cT1/cT2aN0M0). Consecutive patients were identified from October 2009 onwards in MAASTRO clinic, Maastricht. All patients received respiratory gated CT (4DCT) scans. All were patients referred for primary radiotherapy or chemo radiation.