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ABSTRACT: Purpose: To implement energy and intensity modulated electron radiotherapy (MERT) using an existing photon multileaf collimator (pMLC) in a modern medical accelerator. Methods: Both Siemens Artiste and Varian Trilogy accelerators have been investigated for MERT using the existing pMLC in the service mode. The limitations of SSD for Varian linac were examined. A Monte Carlo (MC)-based inverse treatment planning code was used for plan optimization and dose calculation. Water scanning data including PDDs and dose profiles at various depths were acquired for various fields shaped by pMLC for 6, 9, 12 and 15MeV electron energies of both Artiste and Varian linacs and compared with MC calculations. Results: Artiste can treat patient with an SSD down to 61 cm to reduce the field penumbra caused by electron in-air scatters. This is comparable to the Siemens Primus accelerator that has an SSD about 60cm. The electron beam characteristics are acceptable in terms of flatness and penumbra as compared with those collimated by electron applicators. Varian Trilogy has to use a longer SSD (about 85 to 90cm) due to the current restriction of the table height. Comparisons between measured PDDs and dose profiles, and MC calculations for various energies for pMLC shaped fields of 3 × 3 cm(2)and 10 × 10 cm(2) showed agreement to within 2%/2mm. Conclusions: With pMLC shaped fields, MC dose calculations agree with measured PDDs and dose profiles at various depths, which warrant the dose accuracy for MERT delivered by pMLC using MC-based dose calculation planning systems. With large SSD on Trilogy, dose profiles deteriorate to some extent as compared with those on Artiste with SSD = 61cm in terms of penumbral width. However the impact of this penumbra difference on the ultimate MERT plan using energy and intensity modulated electron beams is yet to be investigated.
Medical Physics 06/2012; 39(6):3880. · 2.83 Impact Factor
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ABSTRACT: Purpose: To verify an add-on computer-controlled multileaf collimator (eMLC) device on a Varian linac capable of delivering accurate dose for energy-intensity modulated electron radiotherapy (MERT). Methods: The eMLC has 27 pairs of tungsten leaves (tongue and groove design to reduce intraleaf leakage)with 0.56cm width and 2cm thickness, providing a field size as large as 15 cm × 15 cm defined at 94cm SSD. Measurements were done to determine the appropriate jaw setting for an eMLC shaped field, mainly to reduce the leaf leakage outside the eMLC shaped field. The phase space data were acquired by Monte Carlo (MC) simulations for electron beams of energies 6, 9, 12 and 15 MeV, respectively and used as an input source in MC dose calculations in a phantom. MC calculated PDDs and dose profiles were compared with measurements for large fields (e.g. 10 cm × 10 cm) and small fields (e.g. 3.4 cm × 3.4 cm). The eMLC leakage for various energies was measured both in-air and in phantom (at dmax) as a ratio of doses with the eMLC closed and completely open. Results: With the jaw position at 0.5 cm beyond the edge of the eMLC shaped field, it was showed to best eliminate the interleaf leakage, especially for high energies, e.g. 15 MeV. The average leaf leakage ranged from 0.3% (6 MeV) to 2.3% (15 MeV), which were consistent with lower in-phantom values than in-air values. MC calculated PDDs and dose profiles generally agreed with measurements to within 2mm/2%. Conclusions: This eMLC device is capable of delivering energy and intensity modulated electron beams accurately with acceptable leaf leakage for advanced MERT treatment.
Medical Physics 06/2012; 39(6):3880. · 2.83 Impact Factor
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ABSTRACT: Purpose: There are two collimation systems associated with the CyberKnife system, the fixed cone collimator and the Iris collimator. The Iris collimator is used more frequently because of its superior flexibility. However, sometimes treatments have to be canceled or postponed due to Iris collimator mechanical failures. The purpose of this study is to investigate the feasibility of switching collimation systems without replanning. Methods: We first performed Monte Carlo simulations on 10 clinical cases using the Iris collimator and the fixed cone collimator. The conformality index (CI), target volume coverage and the maximum, minimum and mean doses to the critical structures from the iris and fixed plans were compared to determine the feasibility of switching between collimator types without replanning. Results: Our results showed that the two types of collimators deliver similar dose distributions. The average target doses for the fixed plans were 1% to 6% higher than those for the Iris plans. The average CI for the fixed plans was 1.36 compared to 1.28 for the Iris plans. Thus, we adjusted the Iris sizes with a scale factor of 1.024 to achieve a better dose match with the fixed collimators. Doses for the 10 cases were then recalculated. Once this correction was made, the difference between the average target doses for the two collimator plans was reduced to less than 2% and the CIs became almost identical. Conclusions: Small target dose differences were found between plans using different collimation systems, which may be compensated for by adjusting the Iris collimator sizes to ensure similar dose distributions. The differences in the doses to the critical structures between the collimation systems were insignificant. After adjusting the Iris collimator sizes and re-commissioning the planning system, patients can be safely switched from the Iris collimator to the fixed cone collimator without replanning.
Medical Physics 06/2012; 39(6):3808. · 2.83 Impact Factor
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ABSTRACT: Purpose: To investigate optimal fractionations to achieve high tumor control probabilities (TCPs) while maintaining acceptable normal-tissue complication probability (NTCP) using radiobiological models with new parameters derived from recent clinical data for hypofractionated liver- cancer patients. Methods and Materials: Biological parameters for the Marsden TCP model were derived from reported outcomes of a multi- institutional Phase I/II trial. TCP and NTCP (using the LKB model with Dawson's parameters) were calculated for 8 liver cancer patients treated with different hypofractionation regimens. The correlation between tumor size, the normal liver volume receiving at least 15 Gy and NTCP were examined. Using the BioSuite software, we determined the range of fractionation regimens that achieve high TCP for 5% NTCP. Results: The TCP parameters for liver tumors are: alpha= 0.217 Gy-1, alpha spread is 0.067 Gy-1, assuming alpha/beta = 10 Gy and 107 tumor clonogens cm-3. For any given fractionation we have found that NTCP is not correlated with the absolute liver volume receiving at least 15Gy, nor with the dose received by the hottest 700-cc of the normal liver; these constraints are widely used in liver hypofractionation treatment planning. Instead, the parameter which correlates best with NTCP is the percentage liver volume receiving at least 15Gy. For 5 of the 8 patients, no more than 3 fractions were required to achieve a TCP over 96%; for 2 patients TCP increased gradually with number of fractions (from 3 to 10) to 95.2% and 92.2% respectively. The remaining patient had a small liver and larger target volume which resulted in high NTCP for any fractionation. Conclusions: A range of different hypofractionated regimens from 3×12Gy to 5×12 Gy is found to ensure excellent outcomes. However, the commonly used dose-volume metrics for normal liver do not correlate well with NTCP. A new metric is proposed in this study.
Medical Physics 06/2012; 39(6):3601-3602. · 2.83 Impact Factor
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ABSTRACT: Purpose: Intrafractional tumor motion introduces significant dose uncertainty for radiotherapy. Using EPID imaging during IMRT delivery will provide a beam-eye-view (BEV) tumor motion observation and it also provides a cost-efficient tumor tracking method, avoiding additional imaging system. The purpose of this study is to develop a fiducial detection algorithm for tumor motion monitoring using beam-eye-view (BEV) EPID imaging during external beam IMRT treatment. Methods: A gradient-based fiducial detection algorithm was developed which includes steps: (1) determine IMRT segment; (2) define a search region; (3) Image gradient, grad(I), within the search region was calculated and a threshold was applied to find candidates; (4) the size and orientation (obtained using radon transform) of each candidate was determined, and compared to expected values (from treatment plan) to find the fiducial. To test this algorithm, external beam breast IMRT fields were delivered to a breast phantom (size: ∼13×10cm) with a gold fiducial (1×5 mm) on the Varian Trilogy. Portal images were acquired using Varian aSi1000 EPID system with the following settings: continuous mode, 3 averages per image, image size 1024×768 with resolution 0.392mm per pixel, EPID at 140cm SID (source-imager- distance). Results: Twenty portal images acquired at different time during IMRT delivery, of which 10 images were with couch shift (4mm), have been tested and initial results show that the algorithm is able to detect the fiducial successfully (100%). The gradient-based method, which basically uses the edge information, has the advantage over intensity-based method for MV portal images since generally MV images have lower contrast compared with KV images. Conclusion: A gradient-based fiducial algorithm has been developed and tested on breast IMRT treatment using a breast phantom. Further studies are warranted for other tumor sites such as prostate IMRT treatment.
Medical Physics 06/2012; 39(6):3603-3604. · 2.83 Impact Factor
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ABSTRACT: Purpose: To assess the reliability of soft tissue alignment by comparing pre- and post-treatment cone-beam CT (CBCT) for image guidance in stereotactic body radiotherapy (SBRT) of lung cancers. Methods: Our lung SBRT procedures require all patients undergo 4D CT scan in order to obtain patient-specific target motion information through reconstructed 4D data using the maximum-intensity projection (MIP) algorithm. The internal target volume (ITV) was outlined directly from the MIP images and a 3-5 mm margin expansion was then applied to the ITV to create the PTV. Conformal treatment planning was performed on the helical images, to which the MIP images were fused. Prior to each treatment, CBCT was used for image guidance by comparing with the simulation CT and for patient relocalization based on the bony anatomy. Any displacement of the patient bony structure would be considered as setup errors and would be corrected by couch shifts. Theoretically, as the PTV definition included target internal motion, no further shifts other than setup corrections should be made. However, it is our practice to have treating physicians further check target localization within the PTV. Whenever the shifts based on the soft-tissue alignment (that is, target alignment) exceeded a certain value (e.g. 5 mm), a post-treatment CBCT was carried out to ensure that the tissue alignment is reliable by comparing between pre- and post-treatment CBCT. Results: Pre- and post-CBCT has been performed for 7 patients so far who had shifts beyond 5 mm despite bony alignment. For all patients, post CBCT confirmed that the visualized target position was kept in the same position as before treatment after adjusting for soft-tissue alignment. Conclusions: For the patient population studied, it is shown that soft-tissue alignment is necessary and reliable in the lung SBRT for individual cases.
Medical Physics 06/2012; 39(6):3657. · 2.83 Impact Factor
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ABSTRACT: Purpose: The CyberKnife uses an online prediction model to track moving targets. The system works well if patients can breathe regularly. However, some patients cannot maintain a regular breathing pattern, which means a larger PTV margin is necessary for these patients to ensure sufficient CTV dose coverage. However, it is very difficult to predict a patient's breathing pattern in advance. The purpose of this study is to investigate a quick and easy way to adapt the treatment plan if extra margins are needed. Methods: Multiple algorithms have been developed to calculate the adjustment. Generally, if a larger target region requires coverage by the prescription dose, the size of the beams will be larger and they should move in a peripheral direction for a certain distance to avoid hot spots. Dose is recalculated and renormalized consistently after the adjustment. If the dose distribution of the new plan covers the new PTV with acceptable conformality and coverage, the plan will be used for treatment. Otherwise, more iterations of the adjustment are performed. Dose calculations are limited to a small region surrounding the target to reduce calculation time. Results: 5 clinical cases (3 lungs, 1 liver and 1 adrenal) have been tested in this study. The dose margin can be extended up to 10 mm without changing dose distributions around the target region dramatically. The average PTV coverage is 98.7% compared to 99.1% in the original plans and the average CI is 1.22, which is slightly less than the 1.24 in the original plans. Conclusions: Treatment margins can be sufficiently expanded resulting in satisfactory plan quality for patients with breathing irregularities.
Medical Physics 06/2012; 39(6):3852-3853. · 2.83 Impact Factor
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ABSTRACT: Purpose: To evaluate the safety and efficacy of MR guided focused ultrasound (MRgFUS) treatment for bone metastases. Methods: Six patients with scapula (2), humeral head, sacrum, ilium and pubic ramus bone metastases were treated using ExAblate 2000 under MR guidance. In addition to the monthly and annual quality assurance (QA), pre-treatment machine calibration was performed before each treatment including the functionality of the treatment software and the mechanical motion control systems. The effective ultrasound focal spot was verified with an acoustic phantom using MR thermometry. The patient was positioned on a gel pad. The interface between the treatment table, the gel pad and the patient was immersed in degassed water for acoustic coupling. Caution was taken to remove all gas bubbles between the interfaces. Treatment was performed under conscious sedation. Six to eighteen sonications were delivered for each patient treatment depending on each lesion's size. Patients were treated with a frequency of 1 MHz; 32 ± 4.0 to 96 ±11W acoustic power and 628 ± 78 to1859 ± 338J energy for 20-30s for each sonication. MR phase images were used to monitor the temperature changes in real-time. Based on the temperature feedback, the acoustic power was adjusted to reach designed temperatures (=60 °C) for individual sonications. Pain was assessed using the visual analog scale (VAS). Results: All patients tolerated the MRgFUS treatment well. No skin toxicity or other complications were observed. The VAS pain rating was significantly reduced for all 6 patients from 8.2 ± 0.8 before treatment to 4.7 ± 3, 2.7 ± 1.5 and 1.8 ± 1.1 at one day, one month and three months respectively. Conclusions: A comprehensive QA program has been developed for the MRgFUS system. Our data suggest that MRgFUS is a safe, effective and noninvasive treatment modality for palliation of bone metastases.
Medical Physics 06/2012; 39(6):4012. · 2.83 Impact Factor
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ABSTRACT: Purpose: If the Linac is unavailable during the IMRT treatment schedule, the patient can be switched to a different Linac or prostpond treatment until the origonal Linac is available. The resulting dosimetric difference is estimated and the compromise in the TCP is estimated for both scenarios. This work investigates the feasibility and rationale of switching patients between different accelerators for IMRT in contrast to prostponing the treatment. Methods: We performed Monte Carlo simulations of photon beams from different Linac models and vendors. Prostate and head and neck treatment plans for Siemens Primus, Primart, Artiste and Varian-21Ex/IX accelerators are studied in this work. Dose distributions for given plans are recalculated using different beam data with the same nominal energy from different Linacs. We have compared DVHs, the maximum, the minimum and the mean dose to the target and critical structures due to switching accelerators. In the process of switching a treatment plan to a different accelerator, there are issues, such as optimum penumbra compensation, dose distribution at the boundary of target and critical structures and multileaf collimator (MLC) leaf width effects, needed to be considered and verified with measurements. In making the final decision whether to switch machines, the TCP based on a linear-quadratic model with time factor is considered. Results: Two DVHs of two plans from Varian and Siemens models are delivered on different machines. Slight dose coverage differences have been observed. TCP estimation with both delayed and without delayed treatments is calculated. Undesired drop of TCP is observed with treatment gap. Conclusions: Based on the analyses done in this work, it is therapeutically more beneficial to switch a patient to a different machine than to postpone a treatment until the original machine is available, especially for fast growing tumors such as head and neck cancers.
Medical Physics 06/2012; 39(6):3816. · 2.83 Impact Factor
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ABSTRACT: Purpose: To develop and validate an EPID-based 4D patient dose reconstruction framework accounting for linac delivery uncertainties, interfractional and intrafractional motions, and interplay effect. Methods: Patients with fiducial markers were scanned with 4D-CT for SBRT planning. Before treatment, in-room 4D-CT was performed. Both the MLC and the tumor movements were tracked by continuously acquiring EPID images during treatment. Instead of directly using the heterogeneous transit photon fluence measured by the EPID, this method reconstructed the incident beam fluence based on the MLC apertures measured by the EPID and the delivered MU recorded by the linac. To account for the time-dependent-geometry, the incident fluence distributions were sorted into their corresponding phases based on the tumor motion pattern detected by the EPID and accumulated as the incident fluence map for each phase. Together with 4D-CT, it was then used for Monte Carlo dose calculation. Deformable registration was performed to sum up the phase doses for treatment assessment. The feasibility of using the transit EPID images for incident fluence reconstruction was evaluated against EPID in-air measurements. The accuracy of 3D- and 4D-dose reconstruction was validated by a motordriven cylindrical diode array for six clinical SBRT plans. Results: The average difference between the measured and reconstructed fluence maps is within 0.16%. The reconstructed 3D-dose shows 1.4% agreement in the CAX-dose and >98.5% gamma-passing-rate (2%/2mm) in the peripheral-dose. A distorted dose distribution is observed in the measurement for the moving ArcCheck-phantom. The comparison between the measured and the reconstructed 4D-dose without considering interplay fails the gammaevaluation (59%-88.9% gamma-passing-rate). In contrast, when the interplay is considered, the dose distortion phenomena is successfully represented in the reconstructed dose (>97.6% gamma-passing-rate). Conclusions: The experimental validation demonstrates that the proposed method provides a practical way to reconstruct the fractional 4D-doses received by the patient and enables adaptive SBRT strategy.
Medical Physics 06/2012; 39(6):3909. · 2.83 Impact Factor
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ABSTRACT: Purpose: To evaluate the 3D dose distributions using the PDP technique for VMAT H&N treatments. Methods: The novel PDP algorithm uses the patient structures, TPS dose calculation and plan as a base line, then applies the ARC delivery time dependent ArcCheck (Sun Nuclear, Inc.) measurement with the TPS phantom dose to derive patient dose. Five VMAT H&N plans were generated on a Rando phantom with PTV-to-skin distances of 0,1,2,3, and 5 mm, using the Eclipse TPS (Varian, Inc.). Treatments were then delivered on a Varian iX linear accelerator. We compared the measured to calculated data by using 3D gamma analysis, and examined the mean and maximum dose of the PTV DVH. Results: By using a recommended 2 mm(3) calculation voxel the 3D gamma analysis passed 99.6 to 99.9% for a 3% global dose difference and 3mm DTA with a 5% dose threshold. The PTV organ analysis hot-to-cold dose failing point ratio was about 33.8, 21.7 and 22.2, for the 5, 3, and 2 mm PTV-to-surface distance respectively. For the 1 mm distance case, the ratio was about 0.45 and for the 0 mm distance the ratio was found to be 0.37. With a PTV-to-surface distance decrease, the hot spot was found to increase, and the target coverage and homogeneity were degraded. Conclusions: For the recommended 5 mm PTV-to-surface distance the DVH analysis indicated a lower measured target coverage and homogeneity than the planned. This indication is more pronounced as the PTV-to-surface distance decreases. The failing points grew colder as the PTV moves closer to the skin, indicating a TPS over estimation of the surface dose, which agrees with TLD skin measurement published data.
Medical Physics 06/2012; 39(6):3714. · 2.83 Impact Factor
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ABSTRACT: Purpose: To examine and facilitate the feasibility of the ArcCheck cylindrical diode array system as a patient specific QA device for CyberKnife radiosurgery delivery. Methods: There is an obvious necessity for CyberKnife robotic radiosurgery patient QA procedures for hypofractionated treatment of larger planned treatment volumes (PTV), e.g. prostate. This need will increase when the future CyberKnife MLC is introduced. The small unflattened CyberKnife fields, along with the variation of beam-to-detector spatial angles, pose a significant detection challenge for dosimetric systems. The feasibility of the ArcCheck (Sun Nuclear Inc.) cylindrical diode array system for patient-specific QA on the CyberKnife is demonstrated using a beam-to-diode specific angular correction that was developed and has been applied. For localization and tracking, four gold seed fiducial markers were embedded in the system's central plug. We used a Monte Carlo 1% uncertainty for the dose calculation. Results: By disabling the Linac based corrections and applying the custom CyberKnife correction that we developed, the passing rate increased from 39.6% to 99.8% using a 3%3mm gamma criteria for a given lung case. An additional lung case passed 98.5%. In both cases, a 10% dose threshold was used. In addition, brain, trigeminal nerve and lung cases with synchrony tracking are being investigated. Conclusions: We demonstrated the ArcCheck feasibility for CyberKnife patient specific QA performance. The custom CK angular correction that we developed and applied showed a high passing rate for the lung cases. A verification of the polar angle response should be conducted, in addition to the azimuthal angle that was verified for Linacs. Any data that is being retrieved is additional data to the current chamber point measurement procedures.
Medical Physics 06/2012; 39(6):3968. · 2.83 Impact Factor
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ABSTRACT: Purpose: This study aims to investigate the feasibility of using the images of the treatment fields acquired by an electronic portal imaging device (EPID) for real-time target localization. Methods: Forty one patients treated with IMRT and RapidArc were recruited in this study including 37 prostate patients and 4 lung patients. These patients were grouped as: prostate IMRT with lymph node (n=14), prostate IMRT without lymph node (n=17), prostate RapidArc (n=6), and lung IMRT (n=4). For each patient, two to four fiducial markers were implanted inside the tumor. The DRR, which projects the patient anatomy and the fiducial marker at the EPID location, was reconstructed for each field. The MLC aperture of each control point was overlay on its corresponding DRR to evaluate the fractional time when the fiducial marker was seen on the EPID image. The probability of seeing at least one, two, three, and four fiducial markers during the treatment was recorded. Results: For the prostate IMRT patients without lymph nodes included in the target volume, the average probability of seeing at least one, two, three, and four fiducial markers during the treatment was 50% (35%-59%), 39% (23%-51%), 24% (7%-38%), and 12% (4%-29%), respectively. For the prostate IMRT patients with lymph nodes, the probability was 41% (24%-51%), 29% (12%-42%), 15% (3%-24%), and 7% (4%-15%), respectively. For prostate RapidArc treatments using two arcs, the average probability of seeing at least one fiducial marker was 81% (58%-90%) for the full arc and 74% (53%-94%) for the partial arc. For the lung IMRT treatment, the average probability of seeing at least one fiducial marker was 34% (20%-52%). Conclusions: The continuous image acquisition from the EPID during the treatment provides sufficient target movement information for real-time target localization and intrafractional target motion correction for advanced radiotherapy treatments.
Medical Physics 06/2012; 39(6):3684. · 2.83 Impact Factor
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ABSTRACT: Purpose: Advanced imaging techniques have been developed to facilitate patient setup and target localization for advanced prostate radiotherapy. These techniques work well for translational, interfractional organ motion but may Result in poor target coverage for some cases where the effects of rotational motion and organ deformation are not corrected. This work investigates the feasibility of the use of 3D dose distributions to match the target volume to improve target coverage and critical structure sparing. Methods: Fifteen previously treated prostate patients were selected for this retrospective study. Siemens CT-on-rails scans were performed before and after the IMRT treatment weekly. Ninety-eight post-treatment CT-on-rails scans were used to reconstruct the dose distributions. The isodose distributions and DVH were compared with those of the original plans. Target localization was also performed using the prescription isodose surface from the original plan to match the target volume and a new isocenter shift was applied in the dose reconstruction, which was evaluated against the original plans and the reconstructed dose distributions using the standard contour-based target-localization technique. Results: The results show that for contour/anatomy matching, 7.1% of the 98 treatment fractions exhibit poor target coverage (Dmin<65Gy). For the rectum, 27.6% fractions violated our rectal criterion of V65<17% and 26.5% fractions violated the criterion of V40<35%. After the isocenter realignment based on 3D dose/target volume matching, all the fractions delivered >65Gy to the target, and the percentages of fractions that violated the rectal criteria (V65<17% and V40<35%) were reduced to 14.3% and 18.4%, respectively. Conclusions: The current IGRT procedure for isocenter alignment based on contour/anatomy matching is not ideal due to poor soft-tissue contrast, residual translational/rotational organ motion and organ deformation. Target localization based on 3D dose/target volume matching provides better target dose coverage and critical structure sparing that reduces the need for adaptive re-planning.
Medical Physics 06/2012; 39(6):3653. · 2.83 Impact Factor
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Journal of the Royal Statistical Society, Ser. B. 01/2012; 74:745-771.
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ABSTRACT: In conventional particle accelerators, protons are produced in long pulses, in which the average inter-proton distance is in the order of tens of centimeters or more. Therefore, the radiobiology of conventionally accelerated protons is primarily governed by the interaction of a single proton with the cell. In a laser-plasma interaction scheme, the accelerated protons come as a single bunch of particles (less than 1 ps in duration) with inter particle distances that are many orders of magnitude shorter than those in conventional particle accelerators. As laser-accelerated protons traverse the medium, they not only interact with each other, but also with the host medium. It is shown that when the average distance between protons in a cluster is less than or equal to their velocity divided by the characteristic frequency of the collective excitations supported by the medium, the cluster's linear stopping power increases and can reach several times that of sparsely distributed protons. As a result, the elevated radio biological effectiveness of the proton cluster may take place and conditions for its experimental observation are presented.
Physics in Medicine and Biology 05/2011; 56(10):3123-36. · 2.83 Impact Factor
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ABSTRACT: Purpose: It is usually difficult to obtain all the geometric details of a clinical accelerator necessary for accurate modeling of the treatment head. This work is aimed at designing a program that could provide, based on measurements, possible reasons for the dosimetric discrepancy and possible solutions based on empirical equations that are implemented in the program. Material and Methods: In this work, Monte Carlo simulations were performed for all available electron energies. MCBEAM and MCSIM Monte Carlo codes were used for treatment head simulation and phantom dose calculation. As the incident electron energy is the primary tuning parameter for an electron beam several monoenergies were simulated using Monte Carlo. A series of empirical equations were created that govern several beam parameters (R90%, R80%, R50%, R20%, width at 80% of maximum dose) as a function of energy. The empirical equations were then incorporated in a graphic user interface (GUI) program, which allows for the input of the measured and calculated percentage depth dose curves and profiles. The program could then suggest what should be the next step in the tuning process. By analysis of the measured curve, the program could predict the need for a spectrum to represent the electron beam source. An iterative search was then done to find the best spectrum that would represent the electron source. Results: Applying the equation for a measured 6MeV beam predicted that a spectrum of energies is needed to represent the electron source. The iterative search was able to predict the energy spectrum with great accuracy. Conclusion: Our GUI‐based program can be a helpful tool for Monte Carlo beam modeling to facilitate the clinical implementation of Monte Carlo simulations for radiotherapy treatment planning and dosimetry verification. It can reduce the modeling time significantly for less experienced Monte Carlo users
Medical Physics 05/2010; 37(6):3285-3285. · 2.83 Impact Factor
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ABSTRACT: Recent advances in laser technology have made proton (ion) acceleration possible using laser induced plasmas. In this presentation
we will review the theoretical and experimental results of laser-proton acceleration for radiotherapy applications. We will
report on our work progress in the development of a laser-proton therapy system at Fox Chase Cancer Center. The new proton
therapy system is designed as a compact and cost-effective alternative to conventional accelerator based proton systems capable
of delivering intensity-modulated proton therapy (IMPT). The specific aims of our research are: (1) target design for laser-proton
acceleration, (2) system design for particle/energy selection and beam collimation, and (3) dosimetric studies on the use
of laser-accelerated protons for cancer therapy. We have established a 150 TW laser system for preliminary experimental studies.
We also patented a compact particle selection and beam collimating system for IMPT beam delivery and a new gantry design to
make the whole system compact and easy to operate with adequate shielding considerations. Our Monte Carlo results show that
IMPT using laser protons provided superior target coverage and much reduced critical structure dose and integral dose. IMPT
is more dosimetrically advantageous than photon IMRT or conventional proton beams.
KeywordsLaser plasmas–particle acceleration–proton therapy–radiation oncology
01/2010: pages 66-69;
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ABSTRACT: A simple analytical model is developed that allows efficient absolute dose reconstruction in patients undergoing radiation treatments using proton beams. The model is based on the solution of the inverse problem of dose recovery from the 3D information contained in the PET signal, obtained immediately after the treatment. The core of the proposed model lies in the analytical calculation of the introduced positron emitters' species matrix (PESM) or kernel, facilitated by previously developed theoretical calculations of the proton energy fluence distribution. Once the PESM is known, the absolute dose distribution in a patient can be found from the deconvolution of the 3D activity distribution obtained from the PET scanner with the calculated species matrix. As an example, we have used FLUKA Monte Carlo code to simulate the delivery of the radiation dose to a tissue phantom irradiated by a parallel-opposed beam arrangement and calculated the resultant total activity. Deconvolution of the calculated activity with the PESM leads to the reconstructed dose being within 2% of that delivered.
Physics in Medicine and Biology 07/2009; 54(11):N217-28. · 2.83 Impact Factor
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ABSTRACT: As a clinical application of an exciting scientific breakthrough, a compact and cost-efficient proton therapy unit using high-power laser acceleration is being developed at Fox Chase Cancer Center. The significance of this application depends on whether or not it can yield dosimetric superiority over intensity-modulated radiation therapy (IMRT). The goal of this study is to show how laser-accelerated proton beams with broad energy spreads can be optimally used for proton therapy including intensity-modulated proton therapy (IMPT) and achieve dosimetric superiority over IMRT for prostate cancer. Desired energies and spreads with a varying deltaE/E were selected with the particle selection device and used to generate spread-out Bragg peaks (SOBPs). Proton plans were generated on an in-house Monte Carlo-based inverse-planning system. Fifteen prostate IMRT plans previously used for patient treatment have been included for comparison. Identical dose prescriptions, beam arrangement and consistent dose constrains were used for IMRT and IMPT plans to show the dosimetric differences that were caused only by the different physical characteristics of proton and photon beams. Different optimization constrains and beam arrangements were also used to find optimal IMPT. The results show that conventional proton therapy (CPT) plans without intensity modulation were not superior to IMRT, but IMPT can generate better proton plans if appropriate beam setup and optimization are used. Compared to IMRT, IMPT can reduce the target dose heterogeneity ((D5-D95)/D95) by up to 56%. The volume receiving 65 Gy and higher (V65) for the bladder and the rectum can be reduced by up to 45% and 88%, respectively, while the volume receiving 40 Gy and higher (V40) for the bladder and the rectum can be reduced by up to 49% and 68%, respectively. IMPT can also reduce the whole body non-target tissue dose by up to 61% or a factor 2.5. This study has shown that the laser accelerator under development has a potential to generate high-quality proton beams for cancer treatment. Significant improvement in target dose uniformity and normal tissue sparing as well as in reduction of whole body dose can be achieved by IMPT with appropriate optimization and beam setup.
Physics in Medicine and Biology 12/2008; 53(24):7151-66. · 2.83 Impact Factor
