Proton Beam Treatment Research Articles

Ultrasonography and transillumination for uveal melanoma localisation in proton beam treatment planning.

The success of proton beam treatment (PBT) in uveal melanoma depends in part on the accuracy of tumour localisation. This study determined if using ultrasonography (US) to measure the distance between tumour margin and tantalum ring (DTR) in PBT planning improves local treatment success when compared with using intraoperative transillumination (TI) alone. Retrospective analysis of patients with uveal melanoma treated at one centre between January 2006 and June 2017 with ≥12-month follow-up (or until treatment failure). Local tumour control was compared among study groups based on methods for measuring DTR: Group 1 (TI alone), Group 2A (postoperative US alone) and Group 2B (combination). Fifty-four eyes (54 patients) with uveal melanomas were included: Group 1 (22 eyes, 41%), Group 2A (11 eyes, 20%) and Group 2B (21 eyes, 39%). Mean age at diagnosis was 64 years [median 66 years, range 23-86 years]. Fifty tumours (93%) involved the choroid, while four involved the ciliary body (7%). In Group 2B, PBT treatment was based on the DTR obtained using US; DTR differed between TI and US by ≥1 mm for 25 rings in 16 eyes and ≥2 mm for 12 rings in 7 eyes. Five-year Kaplan-Meier estimate revealed a difference in local treatment success between Groups 1 and 2, (0.82 vs. 1.0, p = 0.02) with no difference in overall survival estimate, (0.85 vs. 0.83, p = 0.8). US can be used to measure DTR in PBT planning for uveal melanoma. This may improve accuracy of tumour localisation and improve local treatment success.

The first prototype of spot-scanning proton arc treatment delivery

PurposeWe report the first prototype of spot-scanning arc treatment (SPArc) delivery on a clinical proton beam therapy machine and evaluate its delivery accuracy and efficiency. Methods and materialsA new module called Proton Dynamic Arc Delivery (PDAD) was developed to allow simultaneously delivering spot-scanning proton beam treatments while rotating the gantry on an IBA Proteus®One proton machine. A series of measurements was performed to validate the basic beam characteristics. Subsequently, patient specific quality assurance (QA) of a brain SPArc plan was performed. Total SPArc treatment delivery time was also recorded and compared to the clinically delivered intensity modulated proton therapy (IMPT) treatment time. Finally, the log file of the SPArc plan was analyzed and processed to reconstruct the actual delivered dose. ResultsAll the basic beam characteristics were confirmed in the PDAD mode, similar as those measured using fixed gantry deliveries in clinical mode. The brain SPArc plan with similar or superior plan quality was delivered in 4 mins compared to total 11 mins for the clinical treatment of the three-field IMPT plan. The patient QA result showed a good agreement between the measured and calculated dose distributions with the gamma index of 98.6% (3%/3 mm). The analysis of the log file confirmed the accuracy of the SPArc plan delivery, with the gamma index of 98.3% (1%/1 mm) between reconstructed and the planned doses. ConclusionThe first prototype of dynamic proton arc delivery on a clinical proton therapy system was successfully performed. The measurements and simulations demonstrated the feasibility of SPArc treatment within the clinical requirements.

Left ventricular function after noninvasive cardiac ablation using proton beam therapy in a porcine model

Noninvasive cardiac ablation of ventricular tachycardia (VT) using radiotherapy has recently gained interest among electrophysiologists. The effects of left ventricular (LV) ablative radiation treatment on global LV function and volumes are unknown. The purpose of this study was to investigate the effects of noninvasive ablation on LV function over time. Twenty domestic swine underwent proton beam treatment of LV sites in a dose-finding design and were followed for up to 40 weeks by cardiac magnetic resonance imaging at 4-week intervals. Doses investigated were either 40 Gy at 1 site (n = 8) or 30 Gy at 2 sites (n = 4) in the low-dose group and 40 Gy at 3 sites (n = 8) in the high-dose group. LV mean dose (13.2 ± 1.8 Gy vs 4.6 ± 1.8 Gy) and the volume receiving at least 20 Gy (V20Gy) (24.7% ± 4.8% vs 6.4% ± 3.0%) differed significantly between groups. Dose-dependent effects on left ventricular ejection fraction (LVEF) and LV end-diastolic volume became manifest about 3 months after treatment. LVEF decline was correlated to mean dose (correlation coefficient ρ= -0.69; P = .008) and V20Gy (ρ = -0.66; P = .01), as was LV dilation (ρ = 0.72; P = .005; and ρ = 0.75, P = .003 respectively). Possible adverse effects on LV function, seen about 3 months after treatment, are dose dependent. Therefore, precise target definition and focused energy delivery are paramount in catheter-free ablation.

Dosimetric comparisons of different hypofractionated stereotactic radiotherapy techniques in treating intracranial tumors > 3 cm in longest diameter.

The authors sought to compare the dosimetric quality of hypofractionated stereotactic radiosurgery in treating sizeable brain tumors across the following treatment platforms: GammaKnife (GK) Icon, CyberKnife (CK) G4, volumetric modulated arc therapy (VMAT) on the Varian TrueBeam STx, double scattering proton therapy (DSPT) on the Mevion S250, and intensity modulated proton therapy (IMPT) on the Varian ProBeam. In this retrospective study, stereotactic radiotherapy treatment plans were generated for 10 patients with sizeable brain tumors (> 3 cm in longest diameter) who had been treated with VMAT. Six treatment plans, 20-30 Gy in 5 fractions, were generated for each patient using the same constraints for each of the following radiosurgical methods: 1) GK, 2) CK, 3) coplanar arc VMAT (VMAT-C), 4) noncoplanar arc VMAT (VMAT-NC), 5) DSPT, and 6) IMPT. The coverage; conformity index; gradient index (GI); homogeneity index; mean and maximum point dose of organs at risk; total dose volume (V) in Gy to the normal brain for 2 Gy (V2), 5 Gy (V5), and 12 Gy (V12); and integral dose were compared across all platforms. Among the 6 techniques, GK consistently produced a sharper dose falloff despite a greater central target dose. GK gave the lowest GI, with a mean of 2.7 ± 0.1, followed by CK (2.9 ± 0.1), VMAT-NC (3.1 ± 0.3), and VMAT-C (3.5 ± 0.3). The highest mean GIs for the proton beam treatments were 3.8 ± 0.4 for DSPT and 3.9 ± 0.4 for IMPT. The GK consistently targeted the lowest normal brain volume, delivering 5 to 12 Gy when treating relatively smaller- to intermediate-sized lesions (less than 15-20 cm3). Yet, the differences across the 6 modalities relative to GK decreased with the increase of target volume. In particular, the proton treatments delivered the lowest V5 to the normal brain when the target size was over 15-20 cm3 and also produced the lowest integral dose to the normal brain regardless of the target size. This study provides an insightful understanding of dosimetric quality from both photon and proton treatment across the most advanced stereotactic radiotherapy platforms.

Effect of proton and ion beam treatment on cyclic olefin copolymer parts prepared via injection molding

The aim of this study is to analyze the effect of proton and ion beam treatment on injection molded plastic parts. We employed cyclic olefin copolymers (COCs) as a resin for the manufacturing. A light guide panel was designed and fabricated via injection molding. The size and fluence of ions were changed for the analysis. The physical and chemical properties of the samples irradiated with proton and nitrogen ion beams were investigated through UV–Vis spectroscopy, FT-IR, differential scanning calorimetry (DSC), nanoindentation, residual stress, and electrical analyses. The penetration behavior of ion beams was modeled numerically, and the injection molding process was simulated. The finding showed that the irradiation of proton and nitrogen ion beams led to a change in the chemical structure and energy level of the samples. We anticipate that this study could provide a meaningful strategic way to engineer a polymeric part for broader applications using proton and ion beams.

Periodic Measurements of Passive Proton Beam Width Using Radiochromic Film in Fixed Gantry System

Background and Aim: Irradiation methods such as double scattering method and spot scanning method have been used in proton beam treatment devices. In the scattering method, a ridge filter or a range modulation wheel is used to create a spread-out Bragg peak, but the distribution at the patient position may change due to positional deviation of the incident beam. Therefore, assessment of the incident position of the beam is very important even in the scattering method. To investigate the width and distribution of the proton beam before entering the RMW, a radiochromic film was installed at the outlet of the transport pipe and the entrance of the profile-monitoring detector. Methods: In this study, the distributions of the beam at the exit of the transport pipe and the entrance of the monitor detector were measured using films. The beam width was measured from the full width at half maximum of the profile obtained from the distribution. Measurements were conducted every month for 10 months. Results: Beams of widths ranging from 1.82 to 2.30 mm in the horizontal direction and 4.25 to 5.33 mm in the vertical direction were outputted from the exit of the transport pipe. Beams of widths ranging from 2.16 to 2.67 mm in the horizontal direction and 4.06 to 5.31 mm in the vertical direction were outputted from the entrance of the monitor detector. The maximum width fluctuation for 10 months was 0.55 mm in the horizontal direction and 1.26 mm in the vertical direction at the entrance of the monitor detector. Conclusions: The distribution was obtained before the proton beam was scattered by the scatterer, and then we propose a method to periodically measure and monitor the changes in the beam distributions every month.

Long Term Follow Up of Patients Treated at a Single Institution using a Passively Scattered Proton Beam; Observations Around the Occurrence of Second Malignancies

To report our observations around whether any patterns of secondary malignancies occurred in patients treated at a single institution, all with the same passively scattered proton beam delivery system. We examined case records from a single national particle therapy facility offering proton and neutron therapy over a 23 year period. Proton beam treatment at the institution started in October 1993 and uses a 200 MeV fixed horizontal beam line combined with a robotic chair. The vast majority of patients was treated for intracranial and cranial lesions and positioned using the stereophotogrammetric positioning system (SPG). Follow up was achieved by way of medical records, telephone calls to patients, and home visits by social workers or community nurses. All patients with 24 or fewer months of follow up were excluded, as well as patients who had previous photon therapy. Rates of observed malignancies in the patient population were compared with expected rates, which were obtained from the national cancer statistics. We analyzed the group as a whole, and also particular sub-populations, including children who were treated with the proton therapy. From October 1993 to May 2016 a total of 524 patients received proton beam therapy, with 322 patients evaluable (164 females & 158 males). Age ranged from 2 – 85 years, with a median of 40 years. Their follow up ranged from 25 to 276 months, with a median of 150 months (12.5 years). 9 patients developed new intracranial lesions consisting of 8 meningiomas and 1 carcinoma. Eight patients had new extracranial primary malignancies. No significant increased risk was observed in the patients who received proton therapy when compared with the expected risk in the general population. 37 pediatric patients (<20 years of age) were treated. No observed second malignancies were seen in this subgroup after a median follow-up of 15 years. No patient developed a second in field malignancy, and no apparent increased risk for a second out of field malignancy was observed. This is reassuring, especially in children and young adults. A solitary patient developed an intracranial carcinoma but this followed combined modality treatment with neutrons plus a proton boost. All other observed intracranial lesions were meningiomas. The findings of this study bode well for patients treated with pencil beam scanning systems, given the lower secondary neutron dose associated with that technique.

Explore the Potential Clinical and Dosimetric Improvements for Brain Cancer Proton Beam Treatment Based on the New Delivery and Planning Technique Developments - Collimator Based Intensity Modulated Proton Therapy and Spot-Scanning Proton Arc Therapy

Utilizing Intensity Modulated Proton Therapy (IMPT) for brain cancer patient has been reaching its dosimetric limitation due to the large lateral penumbra of the pencil beam spots and secondary proton scattering in the air and tissue. To improve the plan quality of using IMPT, new merging techniques were under development including collimator base IMPT (co-IMPT) and Spot-Scanning Proton Arc (SPArc) therapy. This is the first study to quantitatively investigate the dosimetric outcome and benefits among these three different treatment modalities (IMPT, co-IMPT and SPArc) for brain cancer treatment. A glioblastoma (GBM) patient CT and structure data set was used in this study whose clinical target volume (CTV) is abutting the brainstem. 3mm expansion from CTV to PTV is used. PTV is prescribed to 66 Gy with acceptable minor deviation 95% PTV covered by 95% of prescription dose (6270 Gy) due to the brainstem location. 3-field IMPT uses single field optimization technique to ensure the uniform PTV coverage through all three beams (PA; LT-LAT; Vertex directions); 3-field co-IMPT uses the same beam arrangement but adding a block margin 5mm for PTV to reduce the lateral penumbra; SPArc used two non-coplanar arcs. All theplans use the same objective functions for the optimization. Final objective values of each plan were analyzed. The lower of objective value means a better agreement to the plan optimization goal. Plan qualities were evaluated via Homogeneity Index (GI = D5%/D95%); Comformity Index (CI = Target volume covered by the prescription/ total volume received prescription dose); Brainstem maximum dose (0.03cc); Brainstem mean dose; mean brain dose. Treatment delivery time is estimated based on 2ms spot switching time, gantry rotation speed = 6 degree per second. Proton therapy systems with different energy layer switching time (ELST) from 0.1s to 4s were simulated as well. Comparing SPArc, co-IMPT and IMPT plans, the brainstem maximum dose received 49.99Gy, 53.41Gy and 54.10Gy; The brainstem mean dose received 16.99Gy, 23.19Gy and 25.18Gy and the mean brain dose received 6.12Gy, 8.12Gy and 9.11Gy respectively. Furthermore, CI of PTV is 0.97 for SPArc, 0.86 for co-IMPT and 0.83 for IMPT respectively. HI of PTV is 0.76 for SPArc; 0.79 for co-IMPT and 0.78 for IMPT. SPArc treatment delivery time is close to 3 field IMPT or co-IMPT when the ELST is close to 0.1s (Table 1). The final plan objective value is 0.1857 for SPArc; 0.2927 for co-IMPT; 0.3041 for IMPT.Abstract TU_26_3150; Table 1Estimated treatment delivery time vs. ELST using IMPT; co-IMPT and SPArcEnergy Layer Switching Time (s)IMPT (s)co-IMPT (s)SPArc (s)0.17878950.295851270.5108108222114514638122202216993295298101743603741335 Open table in a new tab The study shows both co-IMPT and SPArc could improve the plan quality and spare the dose to organs abutting the target. SPArc demonstrated a significant potential to further improve the plan quality. More developments are needed in order to deliver SPArc therapy in a clinical machine.

Facile Synthetic Route to a Nitrogen‐doped Titanium Oxide with Enhanced Photoelectrochemical Property via Proton Beam Irradiation

A layered titanate with a light harvesting property only in a UV region was irradiated with a proton beam in the presence of nitrogen source like ammonium cation, in order to modify its band gap from UV to visible region. According to X‐ray diffraction and X‐ray absorption spectroscopy results, a protonic titanate maintains its lamellar structure even after proton beam bombardment, showing that the crystal structure of layered titanate was preserved even after the ammonium adsorption and successive proton beam irradiation for nitrogen doping. However, UV–vis and X‐ray photoelectron spectra clearly show that the proton beam irradiation could provide enough energy to introduce ~0.5 at. % of nitrogen atoms into the titanium oxide for absorbing not only UV but also visible light. Photocurrent measurement clearly reveals that the nitrogen‐doped titanium oxide via the proton beam treatment shows highly enhanced photocurrent in comparison with that of the bare titanium oxide, suggesting that the proton beam irradiation could be a potential method for band gap engineering of a wide variety of semiconducting materials.

An end-to-end assessment of range uncertainty in proton therapy using animal tissues

Accurate assessment of range uncertainty is critical in proton therapy. However, there is a lack of data and consensus on how to evaluate the appropriate amount of uncertainty. The purpose of this study is to quantify the range uncertainty in various treatment conditions in proton therapy, using transmission measurements through various animal tissues.Animal tissues, including a pig head, beef steak, and lamb leg, were used in this study. For each tissue, an end-to-end test closely imitating patient treatments was performed. This included CT scan simulation, treatment planning, image-guided alignment, and beam delivery. Radio-chromic films were placed at various depths in the distal dose falloff region to measure depth dose. Comparisons between measured and calculated doses were used to evaluate range differences.The dose difference at the distal falloff between measurement and calculation depends on tissue type and treatment conditions. The estimated range difference was up to 5, 6 and 4 mm for the pig head, beef steak, and lamb leg irradiation, respectively.Our study shows that the TPS was able to calculate proton range within about 1.5% plus 1.5 mm. Accurate assessment of range uncertainty in treatment planning would allow better optimization of proton beam treatment, thus fully achieving proton beams’ superior dose advantage over conventional photon-based radiation therapy.

Proton Beam Radiation for Head and Neck Cancers: A Single-Institution Report on Feasibility and Early Outcomes

Definitive radiation of the head and neck has become a mainstay for locally advanced head and neck malignancies. This combined with initial surgery and/or adjuvant chemotherapy yields significant morbidity to the patients both short term and long term. This is a review of our prospective registry database of head and neck patients treated with proton beam radiation at our hybrid community practice/academic proton center to highlight our initial experience with relative long term follow up. All patients in our study were treated with the uniform scanning proton beam technology via the IBA system. Standard fractionation schemes with or without chemotherapy were delivered with curative intent. Acute and late toxicities were assessed by the National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0 and the by the Radiation Therapy Oncology Group late radiation morbidity scoring system, respectively. The cumulative incidence of locoregional failure (LRF) was calculated with death as a competing risk. The actuarial freedom from distant metastases (FFDM) and overall survival (OS) rates were calculated with the Kaplan-Meier method. A total of 66 patients were analyzed from our prospective registry. We focused on the 36 de-novo patients as our 30 re-irradiation patients are in process in upcoming literature. The scope of our patient population included patients with malignancies of the paranasal sinuses, nasopharynx, oropharynx, hypopharynx, and major salivary gland. Squamous Cell Carcinoma was the predominant histology, but others were Mucoepidermoid Carcinoma, Adenoid Cystic Carcinoma, Undifferentiated Carcinomas and Esthesioneuroblastomas. The median follow up was 33 months (9 – 53). The 2 and 5 year OS rates were 83% and 75%, respectively. The 2 and 5 year FFDM rates were 92% and 80%, respectively. There was 17% and 25% 2 and 5 year LRF rate. The mean time to failure was 17 months post initial proton beam treatment. Acute grade 3+ toxicity rate was 30.5% (mainly skin, mucositis, odynophagia, dysphagia, and anorexia), while the long term grade 3+ toxicity rate was 6% (anorexia and dysphagia). Ten patients had feeding tubes at some point during the radiation therapy, but none remained on tube feedings beyond 6 months post proton radiation therapy. Proton beam radiation of the head and neck can provide excellent disease control along with great sparing of the OARs. Longer follow up is needed with a less heterogeneous population to validate this modality. In addition, with the advent of intensity modulated proton beam radiation, even better conformality of proton beam will hopefully improve the toxicity profiles of even the acute toxicities.

SU‐F‐T‐209: Multicriteria Optimization Algorithm for Intensity Modulated Radiation Therapy Using Pencil Proton Beam Scanning

Purpose:To provide a multicriteria optimization algorithm for intensity modulated radiation therapy using pencil proton beam scanning.Methods:Intensity modulated radiation therapy using pencil proton beam scanning requires efficient optimization algorithms to overcome the uncertainties in the Bragg peaks locations. This work is focused on optimization algorithms that are based on Monte Carlo simulation of the treatment planning and use the weights and the dose volume histogram (DVH) control points to steer toward desired plans. The proton beam treatment planning process based on single objective optimization (representing a weighted sum of multiple objectives) usually leads to time‐consuming iterations involving treatment planning team members. We proved a time efficient multicriteria optimization algorithm that is developed to run on NVIDIA GPU (Graphical Processing Units) cluster. The multicriteria optimization algorithm running time benefits from up‐sampling of the CT voxel size of the calculations without loss of fidelity.Results:We will present preliminary results of Multicriteria optimization for intensity modulated proton therapy based on DVH control points. The results will show optimization results of a phantom case and a brain tumor case.Conclusion:The multicriteria optimization of the intensity modulated radiation therapy using pencil proton beam scanning provides a novel tool for treatment planning.Work support by a grant from Varian Inc.

Randomized Clinical Trial Comparing Proton Beam Radiation Therapy with Transarterial Chemoembolization for Hepatocellular Carcinoma: Results of an Interim Analysis

To describe results of a planned interim analysis of a prospective, randomized clinical trial developed to compare treatment outcomes among patients with newly diagnosed hepatocellular carcinoma (HCC). Eligible subjects had either clinical or pathologic diagnosis of HCC and met either Milan or San Francisco transplant criteria. Patients were randomly assigned to transarterial chemoembolization (TACE) or to proton beam radiation therapy. Patients randomized to TACE received at least 1 TACE with additional TACE for persistent disease. Proton beam radiation therapy was delivered to all areas of gross disease to a total dose of 70.2 Gy in 15 daily fractions over 3 weeks. The primary endpoint was progression-free survival, with secondary endpoints of overall survival, local tumor control, and treatment-related toxicities as represented by posttreatment days of hospitalization. At the time of this analysis 69 subjects were available for analysis. Of these, 36 were randomized to TACE and 33 to proton. Total days of hospitalization within 30 days of TACE/proton was 166 and 24 days, respectively (P<.001). Ten TACE and 12 proton patients underwent liver transplantation after treatment. Viable tumor identified in the explanted livers after TACE/proton averaged 2.4 and 0.9 cm, respectively. Pathologic complete response after TACE/proton was 10%/25% (P=.38). The 2-year overall survival for all patients was 59%, with no difference between treatment groups. Median survival time was 30 months (95% confidence interval 20.7-39.3 months). There was a trend toward improved 2-year local tumor control (88% vs 45%, P=.06) and progression-free survival (48% vs 31%, P=.06) favoring the proton beam treatment group. This interim analysis indicates similar overall survival rates for proton beam radiation therapy and TACE. There is a trend toward improved local tumor control and progression-free survival with proton beam. There are significantly fewer hospitalization days after proton treatment, which may indicate reduced toxicity with proton beam therapy.

Long-term evaluation of the effect of hypofractionated high-energy proton treatment of benign meningiomas by means of (11)C-L-methionine positron emission tomography.

To determine if (11)C-L-methionine PET is a useful tool in the evaluation of the long-term effect of proton beam treatment in patients with meningioma remnant. Included in the study were 19 patients (4 men, 15 women) with intracranial meningioma remnants who received hypofractionated high-energy proton beam treatment. Patients were examined with (11)C-L-methionine PET and MRI prior to treatment and after 6months, and 1, 2, 3, 5, 7 and 10years. Temporal changes in methionine uptake ratio, meningioma volume, meningioma regrowth and clinical symptoms throughout the follow-up period were evaluated. In 17 patients the tumour volume was unchanged throughout the follow-up. The methionine uptake ratio on PET decreased over the years in most patients. In two patients the tumour remnant showed progression on MRI. In these patients, prior to the volume increase on MRI, the methionine uptake ratio increased. One patient experienced transient clinical symptoms and showed radiological evidence of a radiation-induced reaction close to the irradiated field. Proton beam treatment is a safe and effective treatment for achieving long-term growth arrest in meningioma remnants. Follow-up with (11)C-L-methionine PET may be a valuable adjunct to, but not a replacement for, standard radiological follow-up.

Proton Beams Inhibit Proliferation of Breast Cancer Cells by Altering DNA Methylation Status.

Proton beam therapy has been gaining popularity in the management of a wide spectrum of cancers. However, little is known about the effect of proton beams on epigenetic alterations. In this study, the effects of proton beams on DNA methylation were evaluated in the breast cell lines MCF-10A and MCF-7. Pyrosequencing analysis of the long interspersed element 1 (LINE1) gene indicated that a few specific CpG sites were induced to be hypermethylated by proton beam treatment from 64.5 to 76.5% and from 57.7 to 60.0% (p < 0.05) in MCF-10A and MCF-7, respectively. Genome-wide methylation analysis identified “Developmental Disorder, Hereditary Disorder, Metabolic Disease” as the top network in the MCF-7 cell line. The proliferation rate significantly decreased in proton beam-treated cells, as judged by colony formation and cell proliferation assay. Upon treatment with the proton beam, expression of selected genes (MDH2, STYXL1, CPE, FAM91A1, and GPR37) was significantly changed in accordance with the changes of methylation level. Taken together, the findings demonstrate that proton beam-induced physiological changes of cancer cells via methylation modification assists in establishing the epigenetic basis of proton beam therapy for cancer.

Evaluation of beam delivery and ripple filter design for non-isocentric proton and carbon ion therapy

This study aims at selecting and evaluating a ripple filter design compatible with non-isocentric proton and carbon ion scanning beam treatment delivery for a compact nozzle. The use of non-isocentric treatments when the patient is shifted as close as possible towards the nozzle exit allows for a reduction in the air gap and thus an improvement in the quality of scanning proton beam treatment delivery. Reducing the air gap is less important for scanning carbon ions, but ripple filters are still necessary for scanning carbon ion beams to reduce the number of energy steps required to deliver homogeneous SOBP. The proper selection of ripple filters also allows a reduction in the possible transverse and depth-dose inhomogeneities that could appear in non-isocentric conditions in particular.A thorough review of existing ripple filter designs over the past 16 years is performed and a design for non-isocentric treatment delivery is presented. A unique ripple filter quality index (QIRiFi) independent of the particle type and energy and representative of the ratio between energy modulation and induced scattering is proposed. The Bragg peak width evaluated at the 80% dose level (BPW80) is proposed to relate the energy modulation of the delivered Bragg peaks and the energy layer step size allowing the production of homogeneous SOBP. Gate/Geant4 Monte Carlo simulations have been validated for carbon ion and ripple filter simulations based on measurements performed at CNAO and subsequently used for a detailed analysis of the proposed ripple filter design.A combination of two ripple filters in a series has been validated for non-isocentric delivery and did not show significant transverse and depth-dose inhomogeneities. Non-isocentric conditions allow a significant reduction in the spot size at the patient entrance (up to 350% and 200% for protons and carbon ions with range shifter, respectively), and therefore in the lateral penumbra in the patients.

Dental amalgam artifact: Adverse impact on tumor visualization and proton beam treatment planning in oral and oropharyngeal cancers

PurposeWe evaluated the incidence and impact of dental filling artifacts on the definition of clinical target volume (CTV) for oropharyngeal/oral cavity cancers receiving radiation therapy. We performed phantom proton beam dosimetric analyses using a low-density composite filling to investigate artifact reduction and dose distribution. Methods and materialsWe reviewed oral cavity/oropharynx radiation treatment plans between 2010 and 2012. Plans were evaluated for artifacts and impact on CTV visualization. We constructed a head and neck phantom, obtaining planning computed tomography images at baseline (native tooth) and for each filling (composite and metal amalgam) interchanged into a tooth adjacent to the tumor. We performed uniform scanning proton plans with each filling, evaluating for planning target volume (PTV) coverage and overall dose distribution. ResultsA total of 110 treatment plans were reviewed (71 oropharynx, 39 oral cavity). Artifacts were identified in 81 plans (73.6%), including 53 oropharynx (74.6%) and 28 oral cavity (71.8%). Artifacts obscured the CTV in 77 cases (95%), including 49 of 53 oropharynx cases (92.5%) and all 28 oral cavity cases. On phantom testing, the metal amalgam obscured the tumor while the composite did not. Hounsfield unit (HU) values (range, mean) for the tumor were: baseline (−484.0 to 700.0 HU, 104 HU), composite (−728.5 to 1038.0 HU, 105 HU), metal amalgam (−1023.0 to 807.0 HU, 90.74 HU). The percent of planning target volume receiving 95% of prescription dose of the PTV was baseline (100%), composite (100%), and metal amalgam (92.3%). PTV dose ranges were baseline (98%-106%), composite (98%-107%), and metal amalgam (66%-111%). PTV coverage and dose distributions of the composite and native tooth plans were identical. ConclusionsA high incidence of artifacts was found on the planning scans of oral/oropharyngeal cancer patients, adversely impacting CTV visualization. In our phantom model, metal amalgam impacted tumor and tissue density. The PTV was underdosed with the metal amalgam compared with the composite filling. A potential solution involves exchanging metal fillings with composite before proton treatment planning for improved tumor visualization and dosimetry.

SU‐E‐J‐72: Geant4 Simulations of Spot‐Scanned Proton Beam Treatment Plans

Purpose:To evaluate density inhomogeneities which can effect dose distributions for real‐time image gated spot‐scanning proton therapy (RGPT), a dose calculation system, using treatment planning system VQA (Hitachi Ltd., Tokyo) spot position data, was developed based on Geant4.Methods:A Geant4 application was developed to simulate spot‐scanned proton beams at Hokkaido University Hospital. A CT scan (0.98 × 0.98 × 1.25 mm) was performed for prostate cancer treatment with three or four inserted gold markers (diameter 1.5 mm, volume 1.77 mm3) in or near the target tumor. The CT data was read into VQA. A spot scanning plan was generated and exported to text files, specifying the beam energy and position of each spot. The text files were converted and read into our Geant4‐based software. The spot position was converted into steering magnet field strength (in Tesla) for our beam nozzle. Individual protons were tracked from the vacuum chamber, through the helium chamber, steering magnets, dose monitors, etc., in a straight, horizontal line. The patient CT data was converted into materials with variable density and placed in a parametrized volume at the isocenter. Gold fiducial markers were represented in the CT data by two adjacent voxels (volume 2.38 mm3). 600,000 proton histories were tracked for each target spot. As one beam contained about 1,000 spots, approximately 600 million histories were recorded for each beam on a blade server. Two plans were considered: two beam horizontal opposed (90 and 270 degree) and three beam (0, 90 and 270 degree).Results:We are able to convert spot scanning plans from VQA and simulate them with our Geant4‐based code. Our system can be used to evaluate the effect of dose reduction caused by gold markers used for RGPT.Conclusion:Our Geant4 application is able to calculate dose distributions for spot scanned proton therapy.

Long-Term Results After Proton Beam Therapy for Retinal Papillary Capillary Hemangioma

To evaluate the potential benefit and risk of proton beam therapy in the treatment of symptomatic retinal papillary capillary hemangioma. Retrospective interventional case series. This study included patients presenting with symptomatic exudative retinal papillary capillary hemangioma with or without association with von Hippel-Lindau disease. All patients were treated either as a first or a secondary treatment option by proton beam therapy between 2001 and 2009. The minimum follow-up was 30 months. Eight eyes of 8 patients (3 male and 5 female, with a mean age of 36 years [range 22-80 years]) were treated for symptomatic papillary retinal hemangioma. The median interval between onset of macular edema and proton beam therapy was 1.7 months (range 0.5-3.3 months). The median follow-up period was 84 months (range 32-106 months) between proton beam treatment and last follow-up. Exudation completely resolved in all but 1 patient after 4.2 months on average (range 2.8-7.2 months). Mean visual acuity prior to proton beam irradiation was 0.7 logMAR (0.2 DIN (DIN 58220 norm)) (range 2-0.3 logMAR) and declined to 0.8 logMAR (0.16 DIN; range 2-0.1 logMAR) at last follow-up examination (no statistical significance, P=.071). The anatomic outcome after proton beam therapy for retinal papillary hemangioma is convincing, whereas functional outcome may be compromised because of tumor location, long-persisting macular edema, extensive exudation, and poor initial visual acuity. In patients with extended retinal detachment surgical intervention was still necessary. Although proton beam therapy is proven to be a therapeutic option, treatment will remain challenging.

Acute skin toxicity associated with proton beam therapy in spine and brain patients

Objective The purpose of this retrospective study is to determine the dependence of acute skin toxicity on physical parameters associated with the proton beam treatment.