bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐130: Radiotherapy Treatment Plans with RapidArc for Head‐And‐Neck Cancer
Authors: Yoo S , Das S , Wu Q , Brizel D , Yoo D , Yin F
Published: April 2010

Purpose: The purpose of this study is to compare RapidArc plans and conventional IMRT plans for head‐and‐neck cancer treatment involving bilateral nodes. Methods and Materials: This study included 10 locally advanced head‐and‐neck cancer patients. The planning target volume (PTV) included a 3‐mm margin onto the clinical target volume. The prescription was 50Gy to the PTV (2Gy/fraction). Right/left parotids, oral cavity, larynx, brainstem, spinal cord and mandible were contoured as critical organs. For each patient, 9‐fixed‐field IMRT and 3‐arc RapidArc plans were generated. For IMRT plans, the beams were spaced 40° apart and the collimator jaws were fixed to avoid shoulders. RapidArc plans had a total of 600° rotation, one full rotation and two anterior 120° rotations (179°–181°, 60°–300° and 300°–60°). All plans were normalized to cover 90% of PTV with 100% of the prescribed dose. Dosimetric results and treatment time were compared. Results: The homogeneity index of PTV was (1.07; 1.06) and the normal‐tissue receiving dose greater than 110% of the prescription dose was (0.11%; 0.01%) for (RapidArc; IMRT). The average median doses were (right parotid; 46.6%; 43.1%), (left parotid; 39.9%; 34.5%), (oral cavity; 50.0%; 51.7%) and (larynx; 45.7%; 41.4%) for (structure; RapidArc; IMRT). The average maximum doses were (brainstem; 45.5%; 49.9%), (spinal cord; 52.9%; 65.6%) and (mandible; 108.5%; 107.1%) for (organ; RapidArc; IMRT). The statistical analysis showed that the differences in homogeneity index and median doses to right/left parotids and spinal cords were statistically significant (p<0.05), and all others were not. The MU values were reduced by 56% in average and the total treatment time was reduced by 7 minutes when RapidArc was compared to IMRT. Conclusions: IMRT performs better for parotid glands whereas RapidArc performs better for spinal cord. IMRT and RapidArc provide comparable plans for other organs. Treatment time with RapidArc is much reduced compared to IMRT.
SU‐FF‐T‐137: IMRT Treatment Delivery Efficiency — A Multi‐Institutional Retrospective Study
Authors: Chang S , Deschesne K , Chen H , Weeks K , Sibata C , Carey E , Hill P , Mackie T , Marks L
Published: April 2010

Purpose: To compare daily clinical IMRT delivery efficiency in 6 institutions using different accelerators, delivery techniques, treatment planning systems, and clinical practice environments; to deduce key contributing factors for IMRT delivery efficiency improvement. Method and Materials: IMRT treatment MUs, daily treatment delivery time (time elapsed between beam‐ON of the 1st field and beam‐OFF of the last field), and other parameters from Record & Verify systems for 421 patients using accelerators from 4 different vendors and 4 different accelerators treatment planning systems are retrospectively analyzed. IMRT treatments are delivered using compensator‐IMRT on Siemens, segmental MLC‐IMRT on Siemens, Elekta and Varian accelerators, and via TomoTherapy. RESULTS: In average the shortest average IMRT delivery times are associated with TomoTherapy (7.3 min.), plans using the least MLC segments (10.1 min.) and compensator‐IMRT (11.3 min.) (times quoted for 9‐fld IMRT). Longer delivery time is not mainly due to more MUs as beam‐ON time for all LINAC‐based IMRT were all < 2 min., which is only < 20% of the IMRT delivery time. The majority of the IMRT delivery time is spent on preparation of delivery such as segment field formation and verification. LINAC‐based IMRT MUs are < 7 times TomoTherapy‐IMRT MUs. The average MU ratio of LINAC‐based IMRT to non‐IMRT treatments is less than 2:1. CONCLUSION: Major improvement in the MLC‐IMRT delivery time requires significant reduction in MLC leaf motion and verification time. In meantime the most efficient approach to delivery time reduction is to reduce the total number of MLC segment. The retrospective study shows that compensator‐IMRT delivery time is comparable to the most efficient MLC‐IMRT, and TomoTherapy uses the shortest IMRT delivery time. Conflict of Interest: Thomas Mackie has financial interest in TomoTherapy Inc. Sha Chang has a research grant (unrelated to this work) from Siemens.
SU‐FF‐T‐138: Time Optimal Delivery of Intensity Modulated Arc Therapy
Authors: Rangaraj D , Yang D , Goddu S , Papiez L
Published: April 2010

Purpose: Delivery of arc therapy can be achieved with multiple solutions for speed of gantry rotation, beam dose rate variation in time and with various speed trajectories of MLC leaves. The goal is to find the most time efficient realization of the arc delivery provided all constraints of the delivery system are satisfied. Methods: The starting point for our considerations is that the specific plan of treatment has been derived for arc radiation therapy. The parameters of the plan that have to be kept unchanged during delivery to preserve the integrity of the plan include file defining apertures of MLC as function of gantry angle and file defining beam intensity (MU) as function of gantry angle. The other point of our considerations exemplifies limitations of delivery systems for arc therapies. These constraints include gantry angle angular speed limit, beam dose rate limit and MLC leaf speed limits. Provided above invariants and limitations are satisfied there exist multiple solutions for arc therapy delivery. We derive formula for such determination of gantry rotation speed, beam dose rate variation and MLC leaf speeds during delivery that lead to minimal time of arc delivery of a given plan. Results: We investigate example of arc therapy comparing delivery performed under Varian delivery algorithm and our time‐optimized delivery. We first solve the optimization problem, define delivery files. We simulate deliveries based on parameters derived from standard algorithms and from our solutions. In our preliminary study we find that both deliveries provide identical dose distributions and observe our algorithm leads to 10–15% decrease in delivery time. Conclusions: Investigation of minimal delivery time arc therapy demonstrates that this provides a viable option for arc therapy implemented with clinical TPS and linear accelerators. Simulation study shows that minimal delivery time arc RT improves treatment efficiency without compromising dosimetric integrity.
SU‐FF‐T‐139: Dosimetric Accuracy of Low Dose Region (V5‐V10) in TomoTherapy Planning of Lung IMRT
Authors: Krafft S , Jang S , Hamilton R , Watchman C
Published: April 2010

Purpose: To quantify the dosimetric accuracy of a TomoTherapy treatment planning system in areas of low dose (V5 to V10 regions) and in the presence of tissue heterogeneities in lung IMRT. Materials and Methods: CIRS anthropomorphic heterogeneous thorax phantom was used to generate clinical treatment plans using TomoTherapy's treatment planning system (TPS). Three plans were developed for treatment delivery using three different field widths (1.0, 2.5 and 5.0 cm) with standard planning parameters used in our clinic. A designated tumor volume was contoured in the phantom lung volume and was planned to receive 200 cGy fractions to a total prescription dose of 7000 cGy. Point measurements with a PTW Farmer chamber were conducted at two locations in the contralateral lung which fell with in the V5 to V10 region of low dose. Comparison of the experimental findings to the TPS results was performed to assess the dosimetric accuracy of TomoTherapy's convolution/superposition algorithm in low dose regions. Results: Comparison of the ion chamber measurements to the TPS dose calculation demonstrated an average difference of +4.5% and −3.0% at the medial and posterior points of measurement in the contralateral lung of the same axial slice. Variation as a function of field width was found to be 1–2% for chamber measurements. Over the total course of treatment of 35 fractions, differences between the TPS and measurement were 35 cGy regardless of field width or point of measurement. Conclusions: At low dose levels (V5 to V10 regions), dosimetric accuracy of conventional TPS systems is often underestimated, but our experimental results suggest the TomoTherapy TPS is reasonably accurate under the given conditions. Tomotherapy's TPS provides acceptable dosimetric accuracy in lung region areas of low dose.
SU‐FF‐T‐141: Initial Clinical Experience with Elekta VMAT
Authors: Shepard D , Cao D , Rao M , Chen F , Afghan M , Ye J , Wong T , Mehta V
Published: April 2010

Purpose: Elekta recently introduced a new delivery control system called PreciseBeam® VMAT that provides dynamic delivery capabilities including volumetric modulated arc therapy (VMAT). VMAT is a rotational approach to the delivery of IMRT that can be delivered on a conventional linear accelerator. In this study, we report on our initial clinical experience with Elekta VMAT. Method and Materials: The PreciseBeam® VMAT control system has been installed on an Elekta Synergy and an Elekta Precise linear accelerator in our clinic. We have tested the delivery system in conjunction with three inverse planning solutions: (1) an in‐house arc sequencing algorithm that translates optimized fluence maps into deliverable VMAT plans, (2) the Ergo++ planning system that utilizes anatomy based inverse planning, and (3) the SmartArc planning module in the Pinnacle3 treatment planning system. The optimized treatment plans have been verified using phantom irradiations with the IBA MatriXX 2D ion chamber array embedded in a MULTcube phantom. Results: Using our arc‐sequencing algorithm for VMAT planning, we treated our first Elekta VMAT patient under an institutional review board (IRB) protocol in July 2008. In January 2009, we treated our first Elekta VMAT case planned using Ergo++. Our initial focus was on more simple concave targets. More recently, we have opened up VMAT for all clinical sites. Conclusion: Elekta's Precise Beam® VMAT control system can safely and efficiently delivery highly complex VMAT treatment plans. For simple targets such as prostate, pancreatic, and lung cases, single arc VMAT plans are sufficient and be typically delivered in less than 3 minutes. For more complex cases such as head‐and‐neck, the use of multiple arcs provides a dosimetric benefit and plans typically take between 4 and 6 minutes to deliver.

Research sponsored in part through a grant from Elekta.
SU‐FF‐T‐288: Spot Position Uncertainty of Scanning Proton Pencil Beam
Authors: Li H , Zhu X , Ciangaru G , Sahoo N , Suzuki K , Lee A , Gillin M
Published: April 2010

Purpose: The accuracy of spot position is essential for scanning beam proton therapy. The purpose of this work is to assess the spot position uncertainty of scanning pencil beam by analyzing the daily treatment log files of the treatment control system (TCS). Methods: The entrance position and profiles of the pencil beam are monitored by the profile monitor. The spot positions in the treatment target are monitored by the spot position monitor. In every fraction, all spot positions are recorded in the TCS. To validate the accuracy of the spot positions in the log file, a test treatment plan containing 9 spot positions with 10 MU each was generated and delivered. The spot positions were measured with radiographic films placed at the isocenter plane and were compared with those from the treatment plan and the log file to determine the deviations. The statistics of the daily variance were then analyzed for patient data. Results: In the same treatment session, the reproducibility of the spot position for the same spot location is within ±0.2mm. The spot positions measured by film agreed with those from the treatment plan within ±1mm and the log file within ±0.5mm. The maximum day‐to‐day variance for any given spot position is within ±1 mm. For one field in a prostate patient with total of ∼35,000 spots in 28 fractions recorded, the mean spot deviation is (−0.15, 0.01)mm, the maximum displacement is (0.84, 1.08)mm, and the standard deviation is (0.14, 0.30)mm. Conclusion: We have investigated the possibility of utilizing the spot positions in the TCS log file as a QA tool to monitor the day‐to‐day variance of the treatment delivery. The analysis tool developed here could be very useful to assess the spot position uncertainty and thus the dose uncertainty for any patient receiving scanning beam proton therapy.
SU‐FF‐T‐323: Dosimetry Study On An Amorphous Silicon Electronic Portal Imaging Device(a‐Si EPID)
Authors: Wu Q , Hu Y
Published: April 2010

Purpose: To present exploratory research on the dosimetry of an amorphous silicon electronic portal imaging device(a‐Si EPID), and develop a software tool. Method and Materials: Based on MATLAB language, over 30 special functions are programmed with more than 3000 lines' code, and an in‐house software tool is developed to achieve the following functions: to read and write, process, analyze, show and chart the data. Varian 21EX Linac's PV aS500 a‐Si EPID is studied, the dose images from treatment planning system (TPS) and EPID are exported and read in ASCII, and the data's characteristics are analyzed. Based on some hypothesis, the relations between EPID value (EV) and monitor unit (MU) or EPID dose (ED) are developed. The dose calibration curves of the EPID are established, and the errors of curves are analyzed. The images of the EPID and TPS are spatial registered and scaled. Distance to agreement (DTA) analysis is applied to the EPID's dosimetric verification. Based on the above study, comparing to MapCheck, the EPID is used to do clinical dosimetric verification. One prostate cancer patient and one nasopharyngeal carcinoma (NPC) patient are selected to design some plans using 3 dimension conformal radiation therapy (3DCRT) and intensity modulated radiation therapy (IMRT) techniques. Results: The result of EPID is not as good as MapCheck. To get the similar pass rate, the DTA error criterion of MapCheck is better than EPID by one or two levels, which is possibly caused by EPID's narrow penumbra and the errors from the algorithms of spatial registration and DTA in this study. Conclusion: Although the current preliminary result is not good as expected, the study lays the foundations for the next step to dosimetry research of the a‐Si EPID.
SU‐FF‐T‐328: Dose Perturbation and Range Shift with High‐Z Medium in Proton Beam
Authors: Das I , Nichiporov D , Moskvin V , Shahnazi K , Fanelli L , Fitzek M , Johnstone P
Published: April 2010

Purpose: Treatment planning for proton beams requires accurate CT numbers to correlate with electron densities that define the proton range. When high atomic number (Z) and high density materials (prosthesis) are present in the patient, they produce significant image artifacts leading to pronounced uncertainties in CT numbers that introduce unknown error in proton range estimations. We provide an analytical expression for range shift and its experimental verification along with measurement of the dose perturbation from high‐Z media in a proton beam. Materials and Methods: An analytical expression is proposed for the range shift (DR) in water for a high‐Z material (M) of thickness, t and density _M, DR(t, ZM) = tr M (1.192 – 0.158Ln(ZM)). This expression was verified experimentally with various thicknesses and materials in a water phantom. The range shift was measured in a clinical proton beam having a range of 17 cm and a 10 cm SOBP for Z ranging from 13–82 (Al‐Pb). Measurements were also made at the medium‐to‐water interface to evaluate dose perturbation using a thin window parallel plate ion chamber. Results: When materials were placed in the beam, the measured range shift was in good agreement with the theoretical calculation within ±2% standard deviation. The range shift is predominantly a function of physical density, stopping power ratio, and atomic number. Measured dose perturbation downstream of the material is less than +5% for thicknesses up to 30 g/cm2. Conclusions: An experimentally verified analytical equation is proposed that establishes relation between the thickness of a high‐Z material and the corresponding range shift in water. The dose perturbations are not pronounced (less than +5%) in proton beams. For clinical situations, the analytical expression could be used to verify the range shift and hence provide adequate margin for the target volume.
SU‐FF‐T‐338: Dose Shadowing and Diode Consistency in Small Electron Fields
Authors: Anamalayil S , Doyle L , Harrison A , Shabason L , Yu Y , Xiao Y
Published: April 2010

Purpose: To investigate the appropriateness of using diodes for in‐vivo dosimetry for small electron cutouts in terms of output factor accuracy, reproducibility and disturbance of the dosimetry. Methods and Materials: Electron cutouts with diameters from 1.5cm–4cm in 0.5cm increments were measured using a 6×6 cone for electron energies of 6, 9, 12, 15, and 18MeV. Measurements were obtained by placing a pinpoint ionization chamber in solid water at dmax corresponding to the electron energy. The measurements were taken at 100cm SSD to the top of solid water with sufficient solid water to account for backscatter. A diode was placed on top of the solid water in the center of the cutout. Ion chamber readings were collected for 6 cutouts at 5 electron energies with and without the diode in place. A smaller subset of ion chamber measurements for the 1.5cm cutout at all energies was collected by replacing the diode with a MOSFET. Results: The output factor measured with diode over that with pinpoint chamber fluctuates from 0.07–0.79 for 1.5–2.5cm cutouts. The ion chamber reading was significantly decreased with diode on‐top. This effect was greatest for lower energies and smaller cutouts. The percentage decrease ranged from 37%–19% for 6MeV at various cutout diameters and 21%–10% for 18MeV. The MOSFET produced much smaller dose perturbation; with the smallest cutout, the ion chamber measurements decreased by ⩽5% for all energies. Conclusions: Using diodes in a clinical setting to measure dose from small electron fields is unlikely to provide consistent results. For small electron fields, the dose behind the diode is significantly decreased for all energies. From these observations, we don't recommend the usage of diodes for in‐vivo dosimetry for electrons using cones smaller than 6cm×6cm. Although diode accuracy improves for cutouts >3.5cm, the dose shadowing effect is significant for all cutouts considered.
SU‐FF‐T‐339: Small Field Electron Beam Dosimetry Using MOSFET Detector
Authors: Amin M , Heaton R , Norrlinger B , Islam M
Published: April 2010

Purpose: The dosimetry of very small electron fields can be challenging due to relative shifts in percent depth‐dose curves, including the location of dmax, and lack of lateral electronic equilibrium in an ion chamber when placed in the beam. Conventionally, a small parallel plate chamber or film is utilized to perform small field electron beam dosimetry. With the advent of electronic imaging, modern radiotherapy departments are moving to a filmless environment and an alternate clinical dosimeter is required for routine clinical dosimetry. In this work, we have studied the performance of MOSFET as a relative dosimeter for small field electron beams. Methods and materials: The reproducibility, linearity and sensitivity of a high sensitivity micro MOSFET were investigated for clinical electron beams. In addition, the percent depth doses, output factors and profiles have been measured in a water tank with MOSFET and compared with those measured by an ion chamber and film for a range of field sizes from 1 cm diameter to 10×10 cm2 for 6, 12, 16 and 20 MeV beams. Similar comparative measurements were also performed with MOSFET as well as with films in solid water phantom. Results: The MOSFET sensitivity was found to be stable over the range of field sizes investigated. The dose response was found to be linear and reproducible (within ±1% for 100 cGy). For 1, 1.5, 2, 2.5, 3, 4, 5, 6 cm circular and 10 cm square field, excellent agreement (within ±2% and ±2mm) was observed among the central axis depth dose curves measured using MOSFET, film and ion chamber. The output factors measured with MOSFET for small fields agreed to within 2% with those measured by film dosimetry. Conclusion: Overall results indicate that MOSFET can be utilized to perform dosimetry of small electron fields for routine clinical use.
SU‐FF‐T‐340: A New Parameterisation of Small Photon Fields in Off‐Axis Regions for the 160MLC
Authors: Poppe B , Riediger J , Suft G , Ruehmann A , Willborn K , Harder D
Published: April 2010

Purpose: Due to the improved over travel capacities of the SIEMENS MLC160, the application of small fields for stereotactic treatments as well as the possibility of applying intensity modulated irradiation fields within the whole 40 cm × 40 cm usable field size is now possible for the first time. In this work we analyzed dose profiles of small off‐axis fields generated with the SIEMENS MLC160. Method and Materials: Measurements have been performed for 6 MeV nominal photon energy at a linear accelerator equipped with a 160MLC (Artiste, SIEMENS, Kemnath, Germany). Dose profiles are measured with a diode PTW‐60012 (PTW‐Freiburg, Germany) in water. Results: Larger deviations from symmetrical dose distributions have been found for fields which are generated at the maximum diagonal off‐axis positions. Two different methods for an analytical description of the dose distribution generated by these fields are presented, based on the convolution of a rectangular linear‐function with a kernel. A sum of two Gaussian distributions as well as a Lorentz‐type function are used as such kernels. While the Gaussian method leads to known field parameterization parameters, the Lorentz type kernel offers a larger data reduction and a full analytical description of the profile. Conclusion: Both methods offer the possibility of analyzing the underlying fluence profiles. Characteristic parameters of the kernel functions are serving to represent the dose drop off at the field edges. While for the Gaussian method the slope can be expressed in terms of a regular wedge‐angle, a linear fluence profile can be applied for the Lorentz method. With this approach an analytical representation of the dose profile is possible which may act as further input for treatment planning systems or data reduction.

Conflict of Interest: The work was performed in cooperation with SIEMENS Health Care (Kemnath, Germany).
SU‐FF‐T‐343: Analysis of Chest Wall In‐Vivo Dosimetry for Post Mastectomy Radiotherapy Using Helical TomoTherapy
Authors: Ito S , Parker B , Gibbons J , Levine R , Hogstrom K
Published: April 2010

Purpose: To analyze clinical in‐vivo skin dose data from post‐mastectomy radiation therapy (PMRT) patients who received chest wall (CW) irradiation from the TomoTherapy Hi‐Art system. Method and Materials: In‐vivo CW skin dose measurements were compared with calculated dose for 5 patients. For each of the 5 patients, the in‐vivo data consisted of TLD‐measured CW skin doses at 4 locations near the mastectomy scar for 15 fractions. Doses were calculated at each measurement point using patient planning CT data. The location of each in‐vivo TLD was defined on the CT by a radiopaque pellet. A permanent mark on the CW at each pellet location had been used to place TLDs prior to treatment. Calculated doses were determined by transferring the TomoTherapy dose distributions to the Pinnacle treatment planning system (TPS) where a Region of Interest (ROI) was defined at each TLD location. The percent difference between the measured (in‐vivo) and calculated (TPS) doses for each dose point and patient were determined and analyzed (mean ± σ). Results: Combining doses for all 4 TLD points over the 15 fractions, percent dose differences for the 5 patients were −0.1±3.8, −4.1±3.1, 0.7±3.2, −0.8±3.9, and −2.1±3.7%, respectively. 28% of the measured fraction point doses differed from the calculated dose by more than 5%; 2% differed by more than 10%. Possible factors for the dose differences are inaccuracies in the TPS dose calculation, intra/interfraction motion of the patients, and air cavity between the bolus and patient. Conclusions: Results showed all average doses to be within the limits of clinical acceptability (5%). However, understanding the reasons for point dose differences greater than 5% for a single fraction might allow improvement to our existing technique. Conflict of Interest: This work funded in part by a research grant with TomoTherapy, Inc.
SU‐FF‐T‐348: Beam Attenuation and Beam Spoiling Properties of An Electromagnetic Array Used for Patient Localization and Tumor Tracking
Authors: Kassaee A , Lin L , Garver E , Metz J , Vapiwala N
Published: April 2010

Purpose: To investigate the beam attenuation and beam spoiling properties of the Calypso electromagnetic array used for patient localization and tumor tracking during the radiation delivery Method and Materials: One of the main components of the Calypso 4D system is an electromagnetic array placed above patients who are implanted with transponders. We measured both the narrow and board beam attenuation properties of the array including the effect of beam angle (0 to 90 degree). A photon diode placed in cylindrical graphite buildup cap was used for narrow geometry, field size of 1 cm ×1 cm, and a 0.6 cc cylindrical farmer chamber placed in a polystyrene buildup cap for broad geometry, field size of 10 cm × 10 cm. For broad beam geometry, distances of 2, 5, and 10 cm between the chamber and the array were used. Measurements were performed using a Varian Clinac IX linear accelerator with 6 MV and 15 MV photon beams. Beam spoiling properties of the array was studied by placing the array above a water equivalent phantom with an imbedded Markus parallel plate chamber and measuring depth doses. Depth doses were measured for both 6 MV and 15 MV photon beams with 10 cm × 10 cm field size for distances of 2, 5, and 10 cm between array and phantom surface. Results: Narrow beam geometry attenuation is 1.5 % and 1.3% for 6 MV and 15 MV beam respectively. Beam angle dependence is more pronounced at angles greater than 70 degrees with attenuation greater than 5%. Broad beam attenuation, in clinical cases, is nonexistent due to scatter contribution. Spoiling properties could be appreciable. Conclusion: Attenuation properties of the array may be ignored for treatment delivery for most clinical cases. Spoiling effect could be appreciable depending on array distance to patient surface.
SU‐FF‐T‐349: Small Field Dosimetry in Non‐Homogeneous Phantom
Authors: Wagter C De , Srivastava R
Published: April 2010

Purpose: Small fields has been used in radiotherapy due to development of new technology in tomotherapy, radiosurgery (SRS), intensity modulated radiotherapy (IMRT), Gamma Knife, and Cyber Knife. We study the dosimetry of small fields like output factor, profiles in homogenous and non‐homogeneous phantom. Material and Methods: Field sizes of 0.8, 1.6, 2.4, 3.2, 4.8 and 9.6 cm square (defined at isocenter level) were used for this experiment from Elekta Synergy accelerator (Elekta, Crawley, UK). Two phantoms were used in this study: polystyrene (Polystyrol 495F, BASF, Germany) 30 × 30 × 20 cm3 phantom of 1‐cm thick slabs and a sandwiched (non‐homogeneous) lung equivalent phantom, which is further described. The sandwiched phantom is a combination of nine polystyrene slabs (1‐cm thick each) of density 1.02 ± 0.02 g/cm3 positioned above and below two slabs (1.2‐cm thick each) of lung equivalent density 0.3 ± 0.02g/cm3. EBT film (International Specialty Products, NJ, USA) has been applied in this study and results were compared with diamond detector (Type 60003‐9‐0002 — PTW‐Freiburg). Results: A 4.3% and 1.1%output difference was measured in homogeneous polystyrene phantom between EBT film and diamond measurement at 0.8cm and 1.6cm square field sizes respectively for 6 MV. This value is 2.4% and 1.4% in higher photon energy of 18 MV because lateral range of electrons is the critical parameter that influences the charge particle equilibrium rather than forward range of the electrons. Due to electronic disequilibrium, this value is high (33.6%) in non‐homogeneous phantom. The profile showed that 18MV has lower response for small field than 6MV photon beam in both phantom materials. Conclusion: EBT film can be used for output factor measurements and relative dosimetry for small fields. This uncertainty in non homogeneous medium between two detectors has activated us to continue this study.
SU‐FF‐T‐362: Dosimetric Evaluation of the OneDose MOSFET for Measuring Kilovoltage Imaging Dose From Image‐Guided Radiotherapy
Authors: Ding G , Coffey C
Published: April 2010

Purpose: There is a growing interest to determine and to manage the additional image dose to radiotherapy patients. An easy‐to‐use in vivo dosimeter would be very useful for kilovoltage (kV) x‐rays used in IGRT. This study aims to provide the dosimetric characteristics of the commercially available OneDose™ for measuring dose from kV x‐rays with energy ranging from 60 to 125 kVp used in IGRT procedures with respect to reproducibility and energy correction factors. Method and Materials: The OneDoseTM system consists of a small MOSFET dosimeter with overall physical dimensions of 6 mm wide, 33 mm long, and < 1 mm thick and a portable handheld battery‐powered reader. The dosimeter is wireless with adhesive backing to stick to patient's skin. This single‐use dosimeter was pre‐calibrated by the manufacturer using Co‐60 beams. The energy response for kV x‐rays produced by a Varian OBI system was determined by using an ionization chamber in which the air‐kerma calibration factors were obtained from an Accredited Dosimetry Calibration Laboratory (ADCL). Results: The dosimeters have reproducible readings with a deviation of 1–4% for imaging dose of only a few cGy. The energy correction factors were found to be 0.27 – 0.32 for kV x‐rays from the OBI system ranging from 60 to 125 kVp including beams from cone‐beam CT. Conclusion: OneDose™ dosimeter has a similar reproducibility when used for measuring dose from kV photon beams as that when used for measuring dose from MV photon beams. A correction factor that is energy dependent must be applied because of the over‐responds to x‐rays in the diagnostic energy range. The ease‐to‐use allows the OneDose™ dosimeter to be suitable for in vivo dosimetry of measuring doses resulting from imaging guidance.

Conflict of Interest: Research sponsored by Sicel Technologies, Inc. Morrisville NC.
SU‐FF‐T‐370: Evaluation of An Anthropomorphic Pelvis Phantom for Proton Therapy
Authors: Grant R , Ibbott G , Sahoo N , Tucker S , Zhu X , Followill D
Published: April 2010

Purpose: To design and implement an anthropomorphic pelvis phantom to audit proton therapy treatment procedures. Method and Materials: A pelvis phantom already in use for independent audits of photon IMRT treatments was retrofitted for use with protons. The relative stopping power of each material used to construct the phantom was measured. Hounsfield Units were determined for each material with a clinical CT scanner. The tissue equivalence of the materials was determined by comparing with the CT calibration curve used clinically for human tissues. A CT simulation of the phantom was then performed and a proton treatment plan was devised. TLD and radiochromic film were inserted in the phantom and the treatment plan was delivered. The measurements from the TLD and film were compared to calculations made with the treatment planning system. Profile plots through the coronal and sagittal planes were compared to confirm agreement between the treatment plan and delivery. Results: Measured relative stopping powers differed by as much as 10% from values used by the planning system. The comparison between the plan and the TLD showed a difference in dose of less than 3%. The film showed a 2 mm shift in the anterior‐posterior profile and a 6 mm shift in the superior‐inferior profile. The width of the delivered high‐dose region shown by the right‐left film profile differed by as much as 8 mm compared to the plan profile. Conclusion: Preliminary results show the phantom will be able to confirm agreement between measured and calculated dose within 5%/3mm. Stopping power differences between tissue and phantom materials might account for discrepancies between the treatment plan and delivery in the left‐right direction, as lateral fields were used. Conflict of Interest: Work supported by PHS CA010953 and CA081647, awarded by NCI, DHHS, and funds from the RTOG.
SU‐FF‐T‐373: Investigation of Humidity Effects On Beam Monitor Performance in a Proton Clinical Gantry
Authors: Nichiporov D , Solberg K , Klyachko A , Das I , Zhao Q
Published: April 2010

Purpose: To investigate the effect of ambient humidity on performance characteristics of ionization chambers used as beam monitors in two clinical proton gantry systems, and to choose optimal electrode materials. Method and Materials: Dose calibration results for two identical, vented beam monitors, with electrodes constructed of Mylar film with graphite coating, and each installed in a gantry nozzle, were analyzed for stability over a period of 1 year. Additionally, two ion chambers of similar design, but constructed using Kapton for base layer and either i) gold‐plated copper or ii) graphite paint for electrodes, were fabricated for testing purposes. The test chambers were placed in a controlled humidity environment and their performance was evaluated in a proton beam under various humidity conditions. Results: Mylar‐based electrodes of the gantry beam monitors provide a dose calibration that varied within ±2% (maximum deviation from mean), over a period of 1 year while room's relative humidity (RH) varied from 20% to 70%, with brief excursions to 15% and 80%. Kapton‐based copper gold‐plated electrodes provided linear (±1%) response in dose rates up to 180 Gy/min, and were stable within ±1% in terms of measured charge per monitor unit, in the range of 10%–90% RH. The response of Kapton‐based carbon paint electrodes was linear (±1%) in dose rate up to 8 Gy/min and showed a slight rising trend (about 3% increase) in the 50% – 80% RH range. Conclusion: Treatment room humidity may affect the performance of Mylar‐based electrodes in a beam monitor with open‐to‐atmosphere design. When humidity of 70% RH or higher is possible, copper gold‐plated electrodes on Kapton show superior performance compared with graphite paint electrodes.
SU‐FF‐T‐375: Radiotherapy Dose Reconstruction Using a Compton Camera Imaging System
Authors: Mundy DW
Published: April 2010

Purpose: To reconstruct three‐dimensional dose delivered during radiation therapy treatments by using a Compton camera imaging (CCI) system to detect and image photons scattered from the patient. Method and Materials: MCNPX was used to simulate a CCI detector system and a monoenergetic photon beam incident on a simplified head phantom. Each of two CCI detectors was modeled with parallel planar ideal scatter and absorption detectors separated by 5‐cm. The two systems were positioned parallel to one another and perpendicular to the photon beam on opposite sides of the phantom. Relevant detector event data was extracted from the MCNPX output and passed to an image reconstruction algorithm. The reconstruction algorithm solved the intersection of the cone defined by the detector event information (and describing all possible points of origin of the detected photon) with each plane (slice) of the image space, producing a 3D rendering of the source spatial distribution. Voxel intensity of the reconstructed image is proportional to energy deposition at the corresponding physical location. Results: Detector event data from 3 × 108 source photons was used to reconstruct the scattered photon spatial distribution in the (20 cm)3 space between the two CCI systems with voxel dimensions of (1 mm)3. A comparison of the reconstructed image with the actual energy deposition at each voxel location as tallied by MCNPX showed good qualitative agreement. The reconstructed image accurately depicted high dose regions in the tumor and in the skull at beam entry and exit points. Conclusion: This work indicates the potential for a CCI system to reconstruct the dose distribution delivered to a patient during radiotherapy treatment without the need for implanted devices or secondary dose calculations. Research is ongoing to improve reconstructed image quality and to assess the performance of the proposed system under treatment‐room conditions.
SU‐FF‐T‐378: Accurate Water Calorimetry Without Corrections for Heat Transport?
Authors: Tosh R , Chen‐Mayer H
Published: April 2010

Purpose: To use the phase transform of the output‐time waveform from a water calorimeter subject to periodic radiation exposure for purposes of identifying shutter periods at which corrections for heat transport are unnecessary. Method and Materials: The response of a Domen‐type calorimeter of cylindrical geometry to radiation exposure in a 60Co beam is studied analytically, numerically and experimentally under conditions in which the beam is chopped by a shutter. Previous studies in our laboratory have shown an oscillatory dependence of the apparent dose rate upon shutter period which is the signature in the frequency domain of the effects of heat conduction and convection. However, because the apparent dose rate oscillates about the actual dose rate, it should be possible to identify one or more shutter periods at which the effects cancel and the resultant Fourier amplitude provides an accurate measure of the dose rate despite the presence of distortions in the time waveform. Identifying these nodes in the magnitude frequency response of the calorimeter is possible with accurate analytical and numerical models, but we are also exploring the relationship between real and imaginary components of the calorimeter frequency response to identify such points from the phase transform. Using COMSOL Multiphysics, models of our calorimeter have been run with heat sources that mimic a 10 cm × 10 cm 60Co beam. Output of these models is compared to series solutions of the heat transport equations and experimental data. Results: Computational and experimental data exhibit correlated oscillations in the phase and magnitude transforms that suggest a simple analytical relationship between them that would allow the identification of shutter periods at which the effects of heat transport are negligible. Conclusion: The existence of distinct shutter periods where heat transport distortions cancel is demonstrated, suggesting that water calorimetry might be done without such corrections.
SU‐FF‐T‐380: The Application of MRI Pulse Sequences for In‐Vivo Verification of the Proton Beam Radiotherapy
Authors: Seco J , Seethamraju R , Bussiere M , Kooy H , Sharp GC , Harisinghani M
Published: April 2010

Purpose: The purpose of this study is to assess the clinical feasibility and effectiveness of magnetic resonance imaging (MRI) for quality assurance and dosimetry in proton beam therapy. The hypothesis is that as MRI relies on the relaxation times of protons within chemical compounds present in the tumor that are affected by proton beam therapy. Therefore, the biochemical response of the tumor site to proton therapy should be visible on the MRI machine after 1 or more days post‐treatment. Materials & Methods: A 1.5 Tesla MRI machine was used in the present study. Several gel and animal tissue phantoms were made to assess the feasibility of the MRI to quantitatively and qualitatively capture the additional therapeutic protons. The protons have a finite range in the gel/tissue, where the majority of the protons accumulate at the end of the range. The gel phantoms were composed of either gelatin (high content of water) or mayonnaise (high content of fatty compounds). The tissue phantom was composed of bovine tissue with muscle and fat. The proton beams used had a range of 16cm in water (160 MeV kinetic energy) and modulation of 6cm. A total dose of 50 cGray was delivered, which took a total of 5 minutes. Each phantom was imaged with dedicated T1, T2 and T2* weighted MR sequences post‐proton irradiation. Results: A T1 (3D VIBE) image (TE=2.45ms, TR=5.27ms) of the gelatin and bovine tissue produced a bright oval region representing the end‐of‐range to within 3mm of the proton treatment. While a T2* image (TE=48ms and TR=2200ms) for the mayonnaise phantom indicated a large bright area in the phantom representing the broad proton beam irradiating the phantom. Conclusions: Preliminary results obtained with gelatin, mayonnaise and bovine tissue indicates that MRI is an excellent tool for quality assurance proton range.
SU‐FF‐T‐396: A Novel Approach for Determining Radiation‐Induced Second Cancer Risks From Selected Prostate Treatments Using Monte Carlo Simulations and An Anatomically‐Realistic Computational Phantom
Authors: Bednarz B , Xu XG
Published: April 2010

Purpose: There is an important and growing concern about the potential elevated risk of radiation‐induced second cancers associated new forms of radiation treatments. Concurrently with the recently formed AAPM Task Group 158 we have developed a framework to calculate volume‐averaged organ doses to patients using the Monte Carlo method. Using previously calculated organ doses from selected 3D‐CRT and IMRT treatments of prostate cancer, this study calculates radiation‐induced second cancer risks from these treatments utilizing the BIER VII report methodology. Method and Materials: A detailed model of a Varian Clinac 2100C was combined with the RPI Adult male computational phantom to calculate volume‐averaged organ doses from a 3D‐CRT 4‐field box treatment, a box treatment plus a 6‐field boost treatment, as well as a 7‐field IMRT treatment. Based on these organ doses, organ‐specific excess relative risks (ERR) and lifetime attributable risks (LAR) were determined using the methodology outlined in the recently published BEIR VII report. The total whole‐body LAR was determined for each treatment using arbitrary but clinically relevant monitor unit (MU) values of 10,000 and 40,000 for the 3D‐CRT and IMRT treatments. Results: For organs closest to the primary beam the ERR/MU is higher for the IMRT treatment compared to the 3D‐CRT treatments, resulting from an increase in the number of fields needed for IMRT treatments. For organs further away from the treatment volume the ERR/MU appears slightly higher for the 3D‐CRT treatments, as a consequence of the added neutron component of the 18‐MV primary beam. The total whole‐body LAR for the IMRT treatment was 2%, compared to about 0.4% from the box treatment and 0.9% from the box plus boost treatment. Conclusion: The tools presented in this study improve upon previous methodologies by using the most accurate dosimetry methods as well as the most practical second cancer risk models.
SU‐FF‐T‐398: Monte Carlo Simulations to Configure a Treatment Planning System for Modulated Scanning Proton Delivery
Authors: Dolney D , McDonough J
Published: April 2010

Purpose: To generate a library of data in order to configure our treatment planning system for modulated, scanned proton delivery. Method and Materials: We use Monte Carlo simulations to generate modulated scanning data for our treatment planning system. A simplified model of the treatment delivery nozzle was implemented as our simulation geometry. Primary protons were generated in the nozzle just downbeam of the last pair of focusing quadrupole magnets. The phase space for these primary protons is taken to be double‐Gaussian in both spatial and angular distribution. Given the specifications of spot‐size at isocenter, the beam emittance, and that the beam be focused at isocenter, the phase space for primaries was derived by back‐transporting the spot‐size at isocenter using Fermi‐Eyges theory. Results: We find good agreement between Fermi‐Eyges theory and Monte Carlo for pencil beams propagating through vacuum and air. The difference in spot size between Fermi‐Eyges and Monte Carlo at isocenter is less than 100 um. We generate profiles and depth‐dose curves that were used to configure our treatment planning system. Conclusions: Fermi‐Eyges theory can be used to find initial phase spaces for pencils beams focused at isocenter. This work was supported by the US Army Medical Research and Materiel Command under Contract Agreement No. DAMD17‐W81XWH‐04‐2‐0022. Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the US Army.
SU‐FF‐T‐403: Comparison of Calculated RBE Between Actively Scanned and Passively Scattered Carbon Beams Based On GEANT4 Monte Carlo Simulations
Authors: Remmes NB , Herman MG , Kruse JJ
Published: April 2010

Purpose: To compare calculations of the relative biological effectiveness (RBE) for a passively scattered carbon beam to that for a scanned beam with the same physical dose distribution in the spread out Bragg peak (SOBP). It is possible that differences in the spectrum of the fragments between the two beams could significantly affect the RBE, making it difficult to compare clinical doses from scattered and scanned carbon beams. Method and Materials: A simulation program based on the GEANT4 toolkit was developed to mimic measurements and other simulations from a passively scattering carbon beam at the NIRS in Japan. Closely spaced pristine Bragg peaks in water were simulated for both a scanned beam — where depth was adjusted by adjusting energy directly — and for a passively scattered beam — where depth was adjusted by changing the thickness of an aluminum degrader. Pristine peaks were then weighted to fit a pre‐defined SOBP dose distribution. RBEs for both beams were calculated using the linear‐quadratic survival model in use at NIRS. The depth dose, calculated RBE, and effective doses were then compared between the scanned beam simulation and the passive beam simulation. Results: No significant difference was found in the calculated RBE between the scanned carbon beam and the scattered carbon beam. After fitting to the SOBP region of previously published data, no significant difference was found in the dose, RBE, or effective dose between the scanned beams and the scattered beam. Conclusion: This work indicates that it should be possible to equate the biological effective doses between scattered and scanned carbon beams in so much as the LQ RBE model used can predict differences in the beams.