Page 150 - Organ motion in children for high-precision radiotherapy - Sophie Huijskens

Figure 8.2 | Comparison of dose distributions using conformal radiotherapy (CRT), intensity modulated radiotherapy (IMRT), and proton beam radiotherapy (PBT) for a neuroblastoma patient. Area irradiated with 95% (red), 70% (yellow), 40% (green), and 10% (blue) of prescribed dose are shown superimposed on the CT image. Figure adapted from [82].
Particle therapy
Irradiation of cancer with heavy particles (e.g., protons or carbon ions) has an important benefit compared to conventional photons, even when advanced photon techniques are used (i.e., VMAT, IMRT) (Figure 8.2). The volume in which an ion beam deposits most of its dose is much sharper defined than with a photon beam, and for carbon ions even sharper than with a proton beam. This leads to reduction of the integral dose and better saving of the surrounding healthy tissues. Clinical data supporting the benefits of particle therapy are promising, however still scarce [32, 108, 109]. Recently, the Pediatric Proton Consortium Registry, a collaboration of 13 major pediatric cancer centers with proton therapy, was established to facilitate long-awaited clinical outcomes of children irradiated with proton therapy, but results are not yet available [35, 110]. The number of children treated with particle therapy is growing since proton facilities are rapidly expanding worldwide. Therefore, treatment with protons is expected to become more easily accessible and expertise will continue to grow. In the Netherlands, childhood cancer is a standard indication for treatment with protons. Two proton facilities have opened, of which one center expects to treat 80-100 children per year. Carbon ion treatment facilities are still limited, and mainly situated in Japan and Germany, also treating children [111, 112]. With its physical and biological benefits, treatment with carbon ions is expected to play an emerging role in radiotherapy future [113].
Several dosimetric studies have clearly demonstrated that particle therapy limit the irradiated volume compared to photon techniques. Most commonly, childhood cancer types in the central nervous system and head and neck, with static and solid tumors and vital tissues in close proximity, have clear indications for treatment with particles [32, 110, 114, 115]. Also, tumors in the abdomen and thorax show promising results [25, 93, 116–120]. However, as shown in this thesis, substantial organ position variation is present in the abdominal and thoracic area. These uncertainties, in combination with volumetric changes in gas content in the abdomen, can affect the particle beam range, causing excessive dose irregularities [121]. Robustly optimizing treatment plans can account for these range and setup uncertainties [122, 123], by including the expected anatomical variations
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