Even though arc therapy is regularly used in photon therapy, it is not commercially available in proton therapy. We developed a concept to deliver proton arcs in an effective and practical way and discuss its application and advantages through a proof-of-principle dosimetric planning study. The concept of proton arc therapy which uses a tertiary energy modulator has been suggested so that only a single energy is requested from the cyclotron per arc (one gantry revolution). A dose plane with 1-2 cm thickness perpendicular to the beam is assigned for each gantry angle, where each angle will be used as a control point. This plane sweeps the target volume while the gantry moves. Comparison plans were created between a two field single field optimization (SFO) proton plan, a 6x photon volumetric arc plan, and 24 SFO plans from different gantry angles each day, using a cylindrical phantom with 25 cm diameter. Plan quality were evaluated based on volumetric integral dose, robustness of the technique, and distribution of relative biological effectiveness (RBE) dose. Plans with PTVs of varying size and position were evaluated to investigate the advantages of this method compared to current methods. Worst case GTV robustness D95% increased from 80.2%, to 90.8%, to 90.2% for the proton arc as the target diameter increased from 1cm, to 3 cm, to 11 cm. As the target was shifted from the surface to the center of the volume, the robustness did not change significantly. For the target closer to the surface the VMAT integral dose was similar to that of the proton plans, but the difference increased markedly as the depth of the target increased. With VMAT, almost the entire volume receives 10% of the dose, while the V10% is substantially less for all the proton techniques. The integral dose was about a factor of 2 less for proton arcs compared to VMAT and even less than for the standard two field technique, although the V5% was less for the two-field technique the V20% was less for proton arc method, thus decreasing the integral. The mean RBE’s of the 5 cm diameter PTV volume were 1.11 and 1.26 for the single field SFO plan and for the arc plan, respectively. The peak of the RBE distribution is at the center of the PTV for the arc plan, while it is at the distal end of the PTV for the single beam plan. This planning study shows that proton arc is a promising delivery method, even if it is perceived to give up the largest advantage of protons, i.e. no dose to a large volume. It gave less integral dose to a simulated volume than VMAT and even current proton treatment techniques. The method proposed here also provides significant advantages in RBE dose distribution.
The radiotherapy of malignant diseases has reached much progress during the past decade. Thus, intensity modulated radiation therapy (IMRT) and VMAT (Rapidarc) now belong to the standard modalities of tumor treatment with high energy radiation in clinical practice. In recent time, the particle therapy (protons and partially with heavy carbon ions) has reached an important completion of these modalities with regard to some suitable applications. In spite of this enrichment essential features need further research activities and publications in this field: Nuclear reactions and the role of the released neutrons, electron capture of positively charged nuclei at lower projectile energies (e.g. in the environment of the Bragg peak and at the distal end of the particle track), correct dose delivery in scanning methods by accounting for the influence of the lateral scatter of beam-lets. Deconvolution methods can help to overcome these problems, which already occur in radiotherapy of very small photon beams [1 - 8].
For Hodgkin Lymphoma (HL), proton therapy has been shown to potentially reduce therapeutic dose to healthy tissue and therefore the risk of developing a radiogenic second cancer (RSC) relative to photon therapy. Currently, commercial treatment planning systems (TPS) do not account for stray radiation doses for these treatments and their risks of late effects. Treatment plans were created and therapeutic doses were calculated with commercial TPSs for the breast, lung, and thyroid of nine HL patients. Stray dose contributions were added by thermoluminescent dosimeter (TLD) measurements in an anthropomorphic phantom for the intensity modulated radiation therapy (IMRT) treatments and personalized Monte Carlo simulations for the proton treatments. The mean relative risk (RR) of developing a RSC following HL treatment with proton therapies was then calculated and compared to photon IMRT, and reported with the metric ratio of relative risk (RRR). Results showed generally lower RSC risks after proton therapy than photon IMRT when averaged over all patients in the cohort for the breast (RRR = 0.84±0.03), lung (RRR = 0.77±0.03), and thyroid (RRR = 0.83±0.05), but were not universal across all patients examined. Our findings revealed that it is important to include stray dose contributions when comparing the RSC risks for different HL treatment techniques and demonstrated the importance of personalized dose and risk calculations for modern HL radiotherapy.
The total nuclear cross-section Qtot(E) resulting from the interaction of protons with nuclei is decomposed in 3 different contributions: 1. elastic scatter at the complete nucleus, which adopts a part of the proton kinetic energy; 2. inelastic scatter at a nucleus, which changes its quantum numbers by vibrations, rotations, transition to highly excited states; 3. proper nuclear reactions with change of the mass and/or charge number. Then different particles leave the hit nucleus (neutrons, protons, etc.), which is now referred to as 'heavy recoil' nucleus. The scatter parts of Qtot(E) according to points 1 and 2 can be removed by a deconvolution acting at Qtot(E) in the energy space. The typical nuclear reaction channels are mainly characterized by resonances of a reduced cross-section function Qred(E). The procedure is applied to cross-sections of therapeutic protons and also to Cs55137 as an example with technical relevance (transmutations with the goal to drastically reduce its half-time).
Purpose:A rapid cycling proton beam has several distinct characteristics superior to a slow extraction synchrotron: The beam energy and energy spread, beam intensity and spot size can be varied spot by spot. The feasibility of using a spot scanning beam from a rapidc‐ycling‐medical‐synchrotron (RCMS) at 10 Hz repetition frequency is investigated in this study for its application in proton therapy.Methods:The versatility of the beam is illustrated by two examples in water phantoms: (1) a cylindrical PTV irradiated by a single field and (2) a spherical PTV irradiated by two parallel opposed fields. A uniform dose distribution is to be delivered to the volumes. Geant4 Monte Carlo code is used to validate the dose distributions in each example.Results:Transverse algorithms are developed to produce uniform distributions in each transverseplane in the two examples with a cylindrical and a spherical PTV respectively. Longitudinally, different proton energies are used in successive transverse planes toproduce the SOBP required to cover the PTVs. In general, uniformity of dosedistribution within 3% is obtained for the cylinder and 3.5% for the sphere. The transversealgorithms requires only few hundred beam spots for each plane The algorithms may beapplied to larger volumes by increasing the intensity spot by spot for the same deliverytime of the same dose. The treatment time can be shorter than 1 minute for any fieldconfiguration and tumor shape.Conclusion:The unique beam characteristics of a spot scanning beam from a RCMS at 10 Hz repetitionfrequency are used to design transverse and longitudinal algorithms to produce uniformdistribution for any arbitrary shape and size of targets. The proposed spot scanning beam ismore versatile than existing spot scanning beams in proton therapy with better beamcontrol and lower neutron dose.This work is supported in part by grants from the US Department of Energy under contract; DE‐FG02‐12ER41800 and the National Science Foundation NSF PHY‐1205431.
The Journal of Proton Therapy is a new kid on the block in the myriad of clinical oncology journals. However, this new kid on the block comprises of a group of experienced and dynamic practitioners in proton therapy on the editorial board . One of the concerns of potential contributors to a journal is the total length of time from receipt of a manuscript to its publication in the journal, if accepted. Members of the editorial board will address this directly by ensuring that peer reviews will be completed in 3-6 weeks. Just as important as a fast turnaround time, the authorities in the relevant area of research in the review system are provided by the members of the editorial board and their selection of reviewers. The open access system adopted by the journal but with no processing and publication fee should encourage submission of research studies by authors who may otherwise worry about the burden of having to pay a substantial publication fee.
The purpose of this study is to compare the dosimetric results between the uniform scanning proton therapy (USPT) and intensity modulated proton therapy (IMPT) plans for the prostate cancer in patients with a unilateral metallic hip prosthesis. Five prostate cancer cases with left (n = 3) and right (n = 2) metallic hip prostheses were included in this retrospective study. For each case, the USPT and IMPT plans were generated using two anterior-oblique beams and one lateral beam for a total dose of 79.2 Gy(RBE) to be delivered in 44 fractions. For a given case, the beam parameters, dose prescription, and delivery schema in the IMPT plan were kept identical to the ones in the USPT plan. The IMPT and USPT plans were compared for various dosimetric parameters. The mean dose to the target volume was comparable. Both the IMPT and USPT techniques achieved the target coverage goals. Dose homogeneity was found to be similar in the IMPT and USPT plans. For both the rectum and bladder, the IMPT plans produced favorable dosimetric results in the low-, medium-, and high-dose regions when compared to the USPT plans. For the high dose regions, the rectal V 70 was lower in the IMPT plans by about 3.89 cc when compared to the one in the USPT plans. The rectal V 80 in the IMPT plans (1.10 cc) was almost half than the one in the USPT plans (2.39 cc). In comparison to the USPT plans, the mean dose to the rectum, bladder, and femoral head were lower in the IMPT plans by about 8.91%, 4.15%, and 41.09%, respectively. Based on the preliminary results of five cases presented in this study, the IMPT plans provided slightly better dosimetric results compared to the USPT plans, especially in sparing the rectum and bladder in the low-, medium-, and high-dose regions, for the treatment of the prostate cancer in patients with a unilateral metallic hip prosthesis. Future studies need to address the impact of the setup uncertainties and intra-fraction prostate motion in the IMPT planning of the prostate cancer patients with prosthetic hip replacements.
Standard methods for determining dose per monitor unit values in a patient do not yet exist for proton therapy. Indeed, some aspects of D/MU estimation remain poorly understood, such as the conversion of absorbed dose in a water phantom to absorbed dose in a patient. This study focused on the water-to-patient absorbed dose conversion factor, F CSPS , which accounts for differences in scatter (from the range compensator and internal patient anatomy) between patient treatments and their corresponding calibration irradiation in a homogeneous water-box-phantom. We estimated F CSPS for 32 prostate fields using a pencil beam dose algorithm in the treatment planning system (TPS). The mean F CSPS value was 1.006; its standard deviation of the mean was ±0.001. The lower bound for uncertainty in F CSPS , μF CSPS , was estimated for a sub-set of fields through comparisons of TPS dose predictions with measurements and Monte Carlo (MC) simulations. Comparison of TPS predictions and measurements yielded μF CSPS of 0.4% - 0.8%. Comparison of TPS predictions and MC simulations yielded μF CSPS < 0.3%. For a prostate treatment, a comparison of F CSPS values from TPS predictions with the historical value of 1.0 yielded μF CSPS < 3% and a mean μF CSPS of 0.6%. Regardless of estimation method, μF CSPS was approximately 1%, suggesting that uncertainty in F CSPS for proton treatments of prostate cancer is clinically acceptable.
During the past decade, many proton therapy facilities have been established or are planned to become available very soon. Thus it is amusing that in the meantime much more vendors of proton treatment machines offer these facilities than corresponding machines working either with bremsstrahlung or fast electrons. Many researchers in the field of radiotherapy have expressed the opinion that about 20 % of malign tumors can be better treated with protons due to the rapid fall-off behind the Bragg peak than with the conventional radiotherapy with ultra-hard photons or electrons. Thus the normal tissue can be better protected by this behavior, whereas photons may travel long distances behind the target.
Post-mastectomy radiotherapy (PMRT) has been shown to improve disease-free survival and overall survival for locally advanced breast cancer. However, long term survivors may develop life threatening acute and chronic treatment-related toxicities after radiotherapy, like cardiac toxicity and second cancers. The more advanced techniques like volumetric arc therapy (VMAT), and proton therapy have the potential to improve treatment outcome by constraining doses to radiosensitive organs, but evidence from outcome study will not be available until years or decades later. Furthermore, the literature is largely incomplete regarding systematic comparison of potential benefits of advanced technologies for PMRT. The purpose of this study was to compare proton therapy, both passively scattered (PSPT) and intensity modulated (IMPT), to VMAT and develop an evidence-based rationale for selecting a treatment modality for left sided post-mastectomy radiotherapy (PMRT) patients. Eight left-sided PMRT patients previously treated with VMAT were included in this study. Planning target volumes (PTV) included the chest wall and regional lymph nodes. PSPT and IMPT plans were created using a commercial proton treatment planning system. The resulting plans were compared to the corresponding VMAT on the basis of dosimetric and radiobiological endpoints. The uncertainties in risk from proton range, set-up errors, and dose-response models were also evaluated. All modalities produced clinically acceptable treatment plans with nearly 100% tumor control probability. Both proton techniques provided significantly lower normal tissue complication probability values for the heart (p < 0.02) and lung (p < 0.001). Patient-averaged second cancer risk for the contralateral breast and lungs were also significantly lower (p < 0.001) with protons compared to VMAT. The findings of this study were upheld by the uncertainty analysis. All three techniques provided acceptable PMRT treatment plans. Proton therapy showed significant advantages in terms of predicted normal tissue sparing compared to VMAT, taking into account possible uncertainties.
Purpose: We have previously developed for nuclear cross-sections of therapeutic protons a calculation model, which is founded on the collective model as well as a quantum mechanical many particle problem to derive the S matrix and transition probabilities. In this communication, we show that the resonances can be derived by shifted Gaussian functions, whereas the unspecific nuclear interaction compounds can be represented by an error function, which also provides the asymptotic behavior. Method: The energy shifts can be interpreted in terms of necessary domains of energy to excite typical nuclear processes. Thus the necessary formulas referring to previous calculations of nuclear cross-sections will be represented. The mass number A N determines the strong interaction range, i.e. R Strong = 1.2·10 -13 ·A N 1/3 cm. The threshold energy E Th of the energy barrier is determined by the condition E strong = E Coulomb . Results and Conclusion : A linear combination of Gaussians, which contain additional energy shifts, and an error function incorporate a possible representation of Fermi-Dirac statistics, which is applied here to nuclear excitations and reaction with release of secondary particles. The new calculation formula provides a better understanding of different types of resonances occurring in nuclear interactions with protons. The present study is mainly a continuation of published papers. 1-3 -------------------------------- Cite this article as : Ulmer W. A new calculation formula of the nuclear cross-section of therapeutic protons. Int J Cancer Ther Oncol 2014; 2(2):020211. DOI: 10.14319/ijcto.0202.11
The benefit of proton therapy over conventional photon and electron therapies has been recognized in the past few decades. The physical characteristics of proton beams are exploited to enhance the dose to the target and to reduce the dose to healthy tissues. It has been shown that there is a great advantage in using proton therapy for treatment of medulloblastoma, lung, head and neck, gastrointestinal, and other sites. The innovation in proton therapy equipment has and will help to reduce the cost of acquiring this modality and will enable many cancer centers to employ this technique to their current practice for cancer patients’ treatment. It is foreseen that this methodology will be a common practice in almost all the cancer centers in the US and abroad as intensity modulated radiotherapy is currently.
Proton therapy is an evolving force in the future of radiation therapy and cancer management. As the technology becomes more readily available and the cost becomes feasible for smaller centers, proton therapy utilization and indications will become more extensive. Improved planning systems, expanded vendor competition, and diminished proton unit sizes will make proton therapy more available to the greater public. In a world of personalized medicine with increasing use of targeted agents and reduced systemic cytotoxic therapy utilization, proton therapy will be a necessary partner.
