E Klein

The world’s first single-room proton therapy facility: Two-year experience

PURPOSE This is a review of our 2-year experience with the first single-gantry proton therapy (PT) system. METHODS AND MATERIALS All patients were consented to participate on an institutional review board-approved prospective patient registry between December 2013 and December 2015. PT was delivered in a single-room facility using a synchrocyclotron with proton beam energy of 250 MeV. The dataset was interrogated for demographics, diagnosis, treatment modality, and clinical trial involvement. Cases were classified as simple or complex based on fields used and immobilization. The volume of photon patients treated in our department was collected between January 2011 and December 2015 to evaluate the impact of PT on our photon patient volume. RESULTS A total of 278 patients were treated with PT, including 228 (82%) adults and 50 (18%) pediatric cases. PT patients traveled a mean distance of 83.3 miles compared with 47.4 miles for photon patients queried in 2015. Rationale for treatment included reirradiation (20%), involvement in prospective clinical trial (14%), and proximity to critical structures to maximally spare organs at risk (66%). Forty patients were enrolled on 5 adult and 3 pediatric prospective clinical trials. The most common histologies treated were glioma (27%) and non-small cell lung cancer (18%) in adults, and medulloblastoma (22%) and low-grade glioma (24%) in pediatric patients. Prostate cancer composed 6% of PT. Complex cases composed 45% of our volume. Our photon patient volume increased yearly between 2011 and 2015, with 2780 patients completing photon treatment in 2011 and 3385 patients in 2015. PT composed 4% of overall patients treated with external beam radiation. CONCLUSIONS The installation of our single-gantry proton facility has expanded the treatment options within our cancer center, helping to increase the number of patients we see. Patients travel from twice as far away to receive this treatment, many for typical PT indications such as pediatrics or to participate in prospective clinical trials.

WE-E-204-01: ASTRO Based Journals

Research papers authored by Medical Physicists address a large spectrum of oncologic, imaging, or basic research problems; exploit a wide range of physical and engineering methodologies; and often describe the efforts of a multidisciplinary research team. Given dozens of competing journals accepting medical physics articles, it may not be clear to an individual author which journal is the best venue for disseminating their work to the scientific community. Relevant factors usually include the Journals audience and scientific impact, but also such factors as perceived acceptance rate, interest in their topic, and quality of service. The purpose of this symposium is to provide the medical physics community with an overview of scope, review processes, and article guidelines for the following journals: Radiology, Medical Physics, International Journal of Radiation Biology and Physics, Journal of Applied Clinical Medical Physics, and Practical Radiation Oncology. Senior members of the editorial board for each journal will provide details as to the journals review process, for example: single blind versus double blind reviews; open access policies, the hierarchy of the review process in terms of editorial board structure; the reality of acceptance, in terms of acceptance rate; and the types of research the journal prefers to publish. Other journals will be discussed as well. The goal is to provide for authors guidance before they begin to write their papers, not only for proper formatting, but also that the readership is appropriate for the particular paper, hopefully increasing the quality and impact of the paper and the likelihood of publication. LEARNING OBJECTIVES 1. To review each Journals submission and review process 2. Guidance as to how to increase quality, impact and chances of acceptance 3. To help decipher which journal is appropriate for a given work A. Karellas, Research collaboration with Koning, Corporation.

WE-E-204-00: Where to Send My Manuscript

Research papers authored by Medical Physicists address a large spectrum of oncologic, imaging, or basic research problems; exploit a wide range of physical and engineering methodologies; and often describe the efforts of a multidisciplinary research team. Given dozens of competing journals accepting medical physics articles, it may not be clear to an individual author which journal is the best venue for disseminating their work to the scientific community. Relevant factors usually include the Journals audience and scientific impact, but also such factors as perceived acceptance rate, interest in their topic, and quality of service. The purpose of this symposium is to provide the medical physics community with an overview of scope, review processes, and article guidelines for the following journals: Radiology, Medical Physics, International Journal of Radiation Biology and Physics, Journal of Applied Clinical Medical Physics, and Practical Radiation Oncology. Senior members of the editorial board for each journal will provide details as to the journals review process, for example: single blind versus double blind reviews; open access policies, the hierarchy of the review process in terms of editorial board structure; the reality of acceptance, in terms of acceptance rate; and the types of research the journal prefers to publish. Other journals will be discussed as well. The goal is to provide for authors guidance before they begin to write their papers, not only for proper formatting, but also that the readership is appropriate for the particular paper, hopefully increasing the quality and impact of the paper and the likelihood of publication. LEARNING OBJECTIVES 1. To review each Journals submission and review process 2. Guidance as to how to increase quality, impact and chances of acceptance 3. To help decipher which journal is appropriate for a given work A. Karellas, Research collaboration with Koning, Corporation.

SU-F-T-602: Central Moments to Analyze Dose Distributions in Planning Target Volumes.

PURPOSE To quantify the dose distribution inside planning target volumes (PTV), the coefficient of variation, skewness (third central moment) and kurtosis (fourth central moment) were used to analyze the dose distributions of PTVs for lung and prostate cases. Those variables can be used to measure the shape of the dose distribution. METHODS The mean dose, coefficient of variation, skewness, and kurtosis were used to analyze the dose distributions inside PTVs for 24 randomly selected patients. The bin width of the relative dose distribution is 0.1 percent. The coefficient of variation (ratio of the standard deviation to the mean), skewness (third standardized moment), kurtosis (fourth standardized moment) were calculated by using the calculated dose distribution. The coefficient of variation measures the ratio of noise to signal. Skewness measures the asymmetry of the distribution, and negative values indicate that data is skewed left (more low dose). Kurtosis measures the peak of the distribution, where a value of 3 is for a standard normal distribution. RESULTS The average mean dose was found to be (101.17±5.26)% of the prescribed dose. The averaged standard deviation is (2.07±0.68)%. The average coefficient of variation is 0.020±0.007. The average skewness is -1.17±0.50, with range from -2.12 to -0.24. Because the values of the skewness are negative for all patients, that means more voxels were in lower dose regions. The average kurtosis is 5.89±2.29 with a range from 3.58 to 12.06. The dose distributions are wider than standard normal distributions. CONCLUSION The coefficient of variation, skewness and kurtosis were used to analyze PTV dose distributions. It was found that these variables can be used to quantify the dose distributions inside PTVs, and maybe a preferred way to assess PTV coverage.

SU-F-T-321: The Effect of an Electromagnetic Array Used for Patient Localization and Tumor Tracking On OSLD in Vivo Dosimetry

PURPOSE The purpose of this study was to observe the effect of an electromagnetic array used for patient localization and tumor tracking on optically-stimulated luminescent in-vivo dosimetry. METHODS A linear accelerator equipped with four photon energies was used to irradiate optically stimulated luminescent dosimeters (OSLDs) at the respective dmax depths and in the buildup region, with and without the presence of an electromagnetic array used for tumor tracking and patient localization. The OSLDs were placed on solid water slabs under 5 mm bolus and on each face of an octagonal phantom, and irradiated using both static beam and arc geometry, with and without the electromagnetic array under our setup. The electromagnetic array was placed 6 cm above the phantom to coincide with similar distances used during patient treatment. Ionization chamber measurements in a water phantom were also taken initially for comparison with the simple geometry OSLD measurements and published data. RESULTS Under simple geometry, a negligible change was observed at dmax for all energies when the electromagnetic array was placed over the setup. When measuring at five millimeter depth, increases of 1.3/3.1/16/18% were observed for energies 4X/6X/10X/15X respectively when the electromagnetic array was in place. Measurements using the octagonal phantom yielded scattered results for the lateral and posterior oblique fields, and showed increases in dose to the OSLDs placed on the anterior and lateral anterior faces of the phantom. CONCLUSION Placing the electromagnetic array very close to the patients surface acts as a beam spoiler in the buildup region (at 5 mm depth), which in turn causes an increase in the measured dose reading of the OSLD. This increase in dose is more pronounced when the OSLD is placed directly underneath the electromagnetic array than off to one side or the other.

SU-F-T-53: Treatment Planning with Inhomogeneity Correction for Intraoperative Radiotherapy Using KV X-Ray Beams

PURPOSE The current standard in dose calculation for intraoperative radiotherapy (IORT) using the ZEISS Intrabeam 50 kV x-ray system is based on depth dose measurements in water and no heterogeneous tissue effect has been taken into account. We propose an algorithm for pre-treatment planning including inhomogeneity correction based on data of depth dose measurements in various tissue phantoms for kV x-rays. METHODS Direct depth dose measurements were made in air, water, inner bone and cortical bone phantoms for the Intrabeam 50 kV x-rays with a needle applicator. The data were modelled by a function of power law combining exponential with different parameters. Those phantom slabs used in the measurements were scanned to obtain CT numbers. The x-ray beam initiated from the source isocenter is ray-traced through tissues. The corresponding doses will be deposited/assigned at different depths. On the boundary of tissue/organ changes, the x-ray beam will be re-traced in new tissue/organ starting at an equivalent depth with the same dose. In principle, a volumetric dose distribution can be generated if enough directional beams are traced. In practice, a several typical rays traced may be adequate in providing estimates of maximum dose to the organ at risk and minimum dose in the target volume. RESULTS Depth dose measurements and modeling are shown in Figure 1. The dose versus CT number is shown in Figure 2. A computer program has been written for Kypho-IORT planning using those data. A direct measurement through 2 mm solid water, 2 mm inner bone, and 1 mm solid water yields a dose rate of 7.7 Gy/min. Our calculation shows 8.1±0.4 Gy/min, consistent with the measurement within 5%. CONCLUSION The proposed method can be used to more accurately calculate the dose by taking into account the heterogeneous effect. The further validation includes comparison with Monte Carlo simulation.

SU-F-P-23: Setup Uncertainties for the Lung Stereotactic Body Radiation Therapy

PURPOSE The Exactrack X-ray system with six degree-of-freedom (6DoF) adjustment ability can be used for setup of lung stereotactic body radiation therapy. The setup uncertainties from ExacTrack 6D system were analyzed. METHODS The Exactrack X-ray 6D image guided radiotherapy system is used in our clinic. The system is an integration of 2 subsystems: (1): an infrared based optical position system and (2) a radiography kV x-ray imaging system. The infrared system monitors reflective body markers on the patients skin to assistant in the initial setup. The radiographic kV devices were used for patient positions verification and adjustment. The position verification was made by fusing the radiographs with the digitally reconstructed radiograph (DRR) images generated by simulation CT images using 6DoF fusion algorithms. Those results were recorded in our system. Gaussian functions were used to fit the data. RESULTS For 37 lung SBRT patients, the image registration results for the initial setup by using surface markers and for the verifications, were measured. The results were analyzed for 143 treatments. The mean values for the lateral, longitudinal, vertical directions were 0.1, 0.3 and 0.3mm, respectively. The standard deviations for the lateral, longitudinal and vertical directions were 0.62, 0.78 and 0.75mm respectively. The mean values for the rotations around lateral, longitudinal and vertical directions were 0.1, 0.2 and 0.4 degrees respectively, with standard deviations of 0.36, 0.34, and 0.42 degrees. CONCLUSION The setup uncertainties for the lung SBRT cases by using Exactrack 6D system were analyzed. The standard deviations of the setup errors were within 1mm for all three directions, and the standard deviations for rotations were within 0.5 degree.

SU-F-T-323: A Post-Mastectomy Radiation Therapy Dose Distribution Study Using Nanodots and Films

PURPOSE In post-mastectomy radiation therapy (RT), skin dose must be accurately estimated to assess skin reactions such as erythema, desquamation and necrosis. Planning systems cannot always provide accurate dosimetry for target volumes distal to skin. Therefore, in-vivo dosimetry is necessary. A female anthropomorphic phantom was used with optically stimulated luminescence dosimeters (nanoDots) to measure dose to chest wall skin. In addition, EBT2 films was employed to measure dose to left lung and heart in post-mastectomy RT. METHODS Films and nanoDots were calibrated under full buildup conditions at 100cm SAD for 6MV photons. Five pieces of films were placed between slabs of Rando phantom to assess dose to left lung and heart. Two layers of 0.5cm thick bolus were used to cover the whole left chest. Six pairs of nanoDots were placed at medical and lateral aspects on the bolus surface, between the 0.5cm bolus layers, and under the bolus. Three control nanoDots were placed on chest wall to quantify imaging dose. The phantom was CT scanned with all dosimeters in place, and treatment planning was performed with tangential fields (200cGy). All dosimeters were contoured on CT and dose was extracted. NanoDots were read using nanoDot reader and films were scanned using film scanner. The measured and calculated doses were tabulated. RESULTS Dose to 12 nanoDots were evaluated. Dose variance for surface nanoDots were +3.8%, +2.7%, -5% and -9.8%. Those at lateral positions, with greater beam obliquity had larger variance than the medial positions. A similar trend was observed for other nanoDots (Table1). Point doses from films for heart and the left lung were 112.7cGy and 108.7cGy, with +10.2% and +9.04% deviation from calculated values, respectively. CONCLUSION Dosimetry provided by the advanced planning system was verified using NanoDots and films. Both nanoDots and films provided good estimation of dose distribution in post-mastectomy RT.

SU-E-T-296: Single Field Per Day Vs. Multiple Fields Per Day and the Impact On BED in Proton Therapy Treatment

PURPOSE A common practice, in proton therapy, is to deliver a rotating subset of fields from the treatment plan for the daily fractions. This study compares the impact this practice has on the biological effective dose (BED) versus delivering all planned fields daily. METHODS For two scenarios (a phantom with a geometry approximating the anatomy of a prostate treatment with opposing lateral beams, and a clinical 3-field brain treatment), treatment plans were produced in Eclipse (Varian) to simulate delivery of one, two, and three fields per fraction. The RT-Dose file, structure set, and α/β ratios were processed using in-house MATLAB code to return a new RT-Dose file containing the BED (including a proton RBE of 1.1) which was imported back into Eclipse for analysis. RESULTS For targets and regions of field overlap in the treatment plan, BED is not affected by delivery regimen. In the phantom, BED in the femoral heads showed increased by 20% when a single field was used rather than two fields. In the brain treatment, the minimum BED to the left optic nerve and the pituitary gland increased by 13% and 10% respectively, for a one-field regime compared to three-fields per fraction. Comparing the two-field and threefield regimes, the optic nerve BED was not significantly affected and the minimum pituitary BED was 4% higher for two fields per day. CONCLUSION Hypo-fractionation effects, in regions of non-overlap of fields, significantly increase the BED to the involved tissues by as much as 20%. Care should be taken to avoid inadvertently sacrificing plan effectiveness in the interest of reduced treatment time.

TH‐C‐144‐05: Distal and Lateral Dose Perturbation From Collimator Scattering in Proton Radiotherapy

PURPOSE Dose perturbation from collimator scattering is not modeled by current treatment planning systems and is usually ignored in proton radiotherapy. In this work we study the dosimetric impact of collimator scattering and possible solutions. METHODS Three sets of apertures with non-diverging edge, diverging edge and stepped edges that averaged divergence for each single piece, were milled by CURA to produce a 10cm×10cm field at isocenter. Cross-plane profiles were measured at a shallow (2cm) and deep (7.5cm) depths with EBT3 films, delivered with the Mevion S250 system, which has a relatively shorter SAD (∼2m). Films were irradiated with a fully modulated proton beam with range of 15cm in water. In-plane profiles were also acquired on a coronal plane along the central axis. RESULTS Although negligible changes in lateral penumbra were observed in all cases, collimator scattering added up to 11% extra dose near the field edge for the non-diverging edge aperture. For diverging and stepped edge apertures, extra dose from collimator scattering were reduced to less than 5% at 2cm depth, and was negligible at 7.5cm depth. Deterioration of distal penumbra was observed in both non-diverging and stepped edged apertures, broadened to 13mm from 8mm, which was measured for the diverging edge aperture. CONCLUSION Collimator scattering from apertures not only introduce extra dose near the field edge at shallow depths, but also deteriorates the distal penumbra. A diverging-cut aperture can eliminate both contaminations. Divergent edges should be considered in apertures when sensitive organs are lateral at shallow depths, or distal to the target. blown MC. The method can be integrated in existing TPS to enable PET-based treatment verification in the daily clinical routine of proton therapy.