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Monte-Carlo and Grid-Based-Deterministic Models for Patient Dose Computation
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
Another ‘beautiful' example of the pedagogical value of MC simulation can be seen in Figure 3.16 in the chapter on charged-particle interactions: various electron-interaction phenomena have been successively ‘switched off' with dramatic effects on the shape of the depth-dose curve (Seltzer et al. 1978). The non-scattered electrons give rise to a Bragg peak, familiar from heavy charged-particle physics (see Chapter 25). For ‘real' electron beams, the straggling of the electron tracks due primarily to elastic nuclear scattering and to a lesser extent, energy-loss straggling ‘smears out' any such peak in fluence and thereby, in dose. The minor build-up at small depths, due to the forward transport of the most energetic delta-rays, is just discernible.
Proton Therapy Dosimetry
Published in Arash Darafsheh, Radiation Therapy Dosimetry: A Practical Handbook, 2021
Michele M. Kim, Eric S. Diffenderfer
As in all external beam treatment modalities, dosimetry for proton beam therapy must take into account a number of uncertainties. Aside from the inherent dosimetry uncertainties, positioning uncertainties play a significant role, and in many cases have a larger risk in proton therapy due to changes in water equivalent path length. In most modern uses of proton therapy, the Bragg peak is used to take advantage of the superior dosimetric properties of protons relative to x-rays, electrons, or neutrons. As discussed in Section 25.2, the positional depth of the Bragg peak depends on both the beam energy and the stopping power of the material through which the proton beam passes. In the case of a shoot through technique, the variability of stopping power through the material and the uncertainty in its determination has much less impact dosimetrically.
Adult Ocular and Orbital (Ocular Adnexa) Tumors
Published in Pat Price, Karol Sikora, Treatment of Cancer, 2020
P.N. Plowman, Rachel Lewis, J.L. Hungerford
Over the last two decades, it has become possible to avoid this important limitation of radioactive scleral plaques. The special properties of positively charged particulate external beam radiotherapy give this an advantageous dose distribution. Not only is the dose uniform from the base to apex of the tumor but the Bragg peak effect means that the entry dose is reduced and that the beam is extinguished behind the treated volume (Figure 2.3). By employing protons or helium ions generated by a cyclotron or next-generation, linear accelerator-based, proton beam machines, these properties have allowed a high dose prescription of 60–70 Gy in 4 or 5 fractions to be delivered to ocular melanomas over 4–5 days, with the 50% isodose occurring within 2 mm of the tumor edge and with successful tumor regression. Survival rates have been comparable with those following enucleation.8 Although charged particles can be used to treat melanomas that are too close to the optic disc to apply a radioactive scleral plaque or too thick for plaque brachytherapy, the surface-sparing advantages of the Bragg peak are progressively lost with increasing modulation of the beam to treat thicker and thicker tumors and tumors with anterior location. Consequently, eyelid damage limits the benefits of charged-particle therapy for larger and more anteriorly located melanomas. Moreover, the treatment of larger tumors may be followed by painful neovascular glaucoma, occasionally requiring enucleation.8
Dosimetric comparison between proton beam therapy, intensity modulated radiation therapy, and 3D conformal therapy for soft tissue extremity sarcoma
Published in Acta Oncologica, 2023
Brady S. Laughlin, Michael Golafshar, Matthew Prince, Wei Liu, Christopher J. Kutyreff, Safia K. Ahmed, Tamara Z. Vern Gross, Michael Haddock, Ivy Petersen, Todd A. DeWees, Jonathan B. Ashman
Proton beam therapy (PBT) may also be advantageous for eSTS patients with anatomically challenging presentations such as proximal medial thigh location or semi-circumferential tumor. Protons are heavy charged particles that undergo small angle scattering and deposit maximum energy per length close to the end of the range, termed the ‘Bragg’ peak [9]. PBT may be advantageous given the improved target conformality and reduction in integral dose [10–12]. In particular, PBT may lead to a reduction in dose to soft tissue and bone, allowing for a decreased risk of chronic lymphedema or late bone fracture. In this study, we performed a dosimetric comparison of pencil beam scanning PBT, IMRT, and 3D-CRT for patients with eSTS. We hypothesize that PBT will lead to better sparing of soft tissue and bone compared to IMRT and 3D-CRT.
DNA double-strand breaks in cancer cells as a function of proton linear energy transfer and its variation in time
Published in International Journal of Radiation Biology, 2021
Otilija Keta, Vladana Petković, Pablo Cirrone, Giada Petringa, Giacomo Cuttone, Dousatsu Sakata, Wook-Geun Shin, Sebastien Incerti, Ivan Petrović, Aleksandra Ristić Fira
Even though photons are still the most frequently used tool in radiotherapy, the therapeutic advantages of irradiations with ions have been increasingly recognized (Malouff et al. 2020). Due to their different physical characteristics, photon and ion beams, such as protons and carbon ions, differ in their energy transfer profiles. Protons and carbon ions display a specific, highly concentrated dose distribution in depth known as the Bragg peak which allows for radiation to be precisely delivered to the tumor. In addition, rather low levels of energy are deposited in tissues proximal and distal to the tumor, thus minimizing the damage to the adjacent, healthy tissue (Liu and Chang 2011; van de Water et al. 2011; Loeffler and Durante 2013; Vitti and Parsons 2019; Malouff et al. 2020). One of the main parameters which define the biological outcomes of ionizing radiation is the linear energy transfer (LET) (Tommasino and Durante 2015; Oeck et al. 2018). It is well recognized that high LET particles possess stronger cell killing abilities than low LET radiation. In contrast to photons, ion irradiation is characterized by higher LET because it deposits high density of energy along the particle track, increasing toward the end of the range (Hagiwara et al. 2019).
Is proton beam therapy ready for single fraction spine SBRS? – a feasibility study to use spot-scanning proton arc (SPArc) therapy to improve the robustness and dosimetric plan quality
Published in Acta Oncologica, 2021
Gang Liu, Xiaoqiang Li, An Qin, Jun Zhou, Weili Zheng, Lewei Zhao, Jun Han, Sheng Zhang, Di Yan, Craig Stevens, Inga Grills, Xuanfeng Ding
In the past decades, proton beam therapy has been implemented clinically, taking advantage of its unique physical characteristics of dose deposition from the ‘Bragg peak’. The development of the Pencil Beam Scanning (PBS) technique allows the proton system to optimize the energies and numerous spots to deliver the radiation dose layer by layer and spot by spot in 3-dimensional, just like a 3D-printer [9]. However, due to the prolonged proton PBS treatment delivery time, only a limited number of beam angles are normally used in the proton clinic [10,11]. Additionally, compared to the photon treatment, IMPT alone cannot provide high dose conformity and sharp dose fall-off, which is critical to SBRS/SBRT due to the large lateral penumbra from each individual proton spot [12–14]. As a result, only passive-scattering proton beam therapy using a collimator system was occasionally used in spine SBRT proton treatment cases through five or more fractions instead of a newer technique, PBS [15,16]. Single fractionation SBRS proton beam therapy for spine metastasis is not possible in most cases, even with passive-scattering technique due to the needs in the matching line feathering [17].