Purpose: To compare proton dose distributions generated with double‐scattering to uniform‐scanning for different clinical sites. Method and Materials: The ‘universal nozzle’ developed by IBA incorporates several delivery modes. In double‐scattering (DS) a flattening filter scatters the proton beam into a flat circular profile. In uniform‐scanning (US) two dipole magnets scan the beam into a rectangular profile. US covers larger volumes both laterally and in depth, and has dosimetric characteristics that are different from US. This study deals with cases that can be treated with either US or DS. Eclipse (Varian) treatment planning is commissioned for both delivery modes. Comparison of water‐phantom calculations to measurements validates the treatment‐planning algorithm. We compare the dose for the following sites: prostate (2 cases), head‐and‐neck (4 cases), cranio‐spinal (3 cases). Dose‐volume‐histograms are used to evaluate target coverage and dose to critical structures. Results: The US in‐air penumbra is typically smaller because of less scattering material in the beam path. For a range of 15.0g/cm 2 , modulation of 8.0g/cm 2 , and air gap of 12.0cm, the 80%–20% penumbra at 11.0cm depth is 4.4mm in US and 6.9mm in DS. In addition, the US distal fall‐off is sharper because of reduced energy straggling in the treatment head. For a range of 5.0 (28.0) cm in water the 80%–20% fall‐off is 2.7mm (5.5mm) in US, compared to 4.0mm (6.0mm) in DS. For deep seated tumors (prostate) the sharper in‐air dose distribution in US is washed out by in‐patient scatter, resulting in no significant benefit. For targets at shallow and intermediate depth, located next to a critical structure, the sharper fall‐off in US allows for better target coverage and less dose to the critical structure. Conclusion: The sharper lateral and distal penumbra in uniform scanning are beneficial when the target volume abuts a critical structure. For deep‐seated tumors this advantage diminishes.
Purpose : To evaluate intra‐fractional prostate motion by post‐treatment PET/CT imaging in in‐vivo verification. Methods : A total of 50 PET/CT imaging studies were performed immediately after daily proton therapy treatment through a single lateral portal. The PET/CT and planning CT were registered by matching the pelvic bones, and the beam path of delivered protons was defined in‐vivo by the positron emission distribution seen only within the pelvic bones. At each fraction treatment, a beam path defined by the fiducial markers seen in the post‐treatment CT is used as a surrogate for the intended beam; it can be different from its planned location at initial treatment planning due to a translational shift during the patient positioning. The discordance between the PET‐defined path and the intended path were derived. The PET‐defined path was compared to the positron‐emission distribution in lipomatous tissues around prostate to determine whether the prostate motion occurred before or after beam delivery. Results : For 30 of the 50 studies with small discordance between the intended and PET‐defined paths, average displacements are 0.6 mm and 1.3 mm along anterior‐posterior (D AP ) and superior‐inferior (D SI ) directions, respectively. For the remaining 20 studies demonstrating a large discordance, 13 studies also show large misalignment while 7 studies show no mismatch between the field edge and the positron emission distribution in lipomatous tissues around the prostate. The standard deviations for D AP and D SI are 5.0 mm and 3.0 mm are for these 13 studies, and 4.6 mm and 3.6 mm for last 7 studies. Conclusion : Systematic analyses of proton‐activated positron emission distributions provide patient‐specific information on prostate motion and patient position variability during daily proton beam delivery. Small fraction of PET/CT studies (approximately 14%) with ∼4‐mm displacement variations may require different margins. Such data are useful in establishing patient‐specific planning target volume (PTV) margins
Purpose: The objective of this study is to evaluate the accuracy from a dosimetry point of view with which proton field matching can be accomplished. Method and Materials: This proton therapy center currently treats patients with a nominal 208 MeV proton beam in a single Fixed Horizontal Beam Line (FHBL) room that employs a double passive beam spreading system with a fixed range modulator. The FHBL room takes advantage of a novel robotic patient positioner system (PPS) providing 6 degrees of freedom with a specified accuracy of 300 microns when transiting up to a 200 kg payload. To investigate field matching doses three methods are used: calculations from a treatment planning system, film dosimetry measurements and scans using a miniature ionization chamber. The field delivery for this study consists of four proton fields matched by the robotic PPS. The measurements are performed in a solid water phantom for the film and a water phantom for the ionization chamber scans Results: The planned dose delivery for the central field is normalized to 100%. The average relative dose values in the field junctions are 128%, 135% and 130% for the ionization chamber scans, film dosimetry and treatment planning calculation, respectively. In this case this was thought to be clinically acceptable as the volume lay entirely within the target. Conclusion:Proton therapy is suitable for treating volumes of relatively large area and shallow depth. In this way the ranged property of the protons can spare underlying structures. The sharp proton penumbra and precision of a robotic patient positioner simplifies field matching. Further study is underway with a half beam block to investigate the range of junction doses that can be expected under a variety of field matching conditions.
Purpose: to investigate the potential of polymer gel dosimeters for concurrent measurements of three‐dimensional positron emission activity and dose distributions; to evaluate the ability of this technique to identify dosimetric errors due to delivery uncertainties, including those due to range modification and target motion.Methods: three BANG3‐Pro2 gel dosimeters irradiated by proton beams were imaged in a PET/CT scanner, starting within 3 minutes after irradiation. The radiation was delivered as a pristine beam under static conditions, as well as an SOBP, with and without phantom motion. The motion trace was defined by a sinusoidal curve with 2 cm peak‐to‐peak amplitude and the frequency of 0.25 Hz. The dose was read out using an established optical CT scanning procedure. PET/CT images of activated gels were validated against analytical calculations of activity and correlated to measured dose. The effects of target motion on activity and dose distributions were evaluated by volumetric gamma analysis against the treatment plan. Results: The profiles of positron emission activity along the central beam axis were found to be consistent with analytical calculations. Temporal dependence of activity decay suggests that the observed PET signal is due mainly to decay of 15O and 11C. Lateral profiles were found to exhibit good spatial correlation throughout the beam range. This allowed using a modified gamma analysis method to compare the signatures of target motion in PET and dose images. Mean gamma for static PET and dose datasets was 0.07 and 0.11, respectively. For the motion delivery, the mean gamma value increased to 0.63 for both datasets. The spatial distributions of the gamma criterion for PET and dose datasets were qualitatively similar. Conclusions: Polymer gels can accurately capture both dosimetric and activation information. Dosimetric errors due to target motion can be quantified by PET/CT using a novel method of analysis. This work was supported by the Bankhead‐Coley Florida Biomedical Research Program under Grant No. 1BD10‐34212.
Scattered neutron dose equivalent to a representative point for a fetus is evaluated in an anthropomorphic phantom of the mother undergoing proton radiotherapy. The effect on scattered neutron dose equivalent to the fetus of changing the incident proton beam energy, aperture size, beam location, and air gap between the beam delivery snout and skin was studied for both a small field snout and a large field snout. Measurements of the fetus scattered neutron dose equivalent were made by placing a neutron bubble detector 10 cm below the umbilicus of an anthropomorphic Rando® phantom enhanced by a wax bolus to simulate a second trimester pregnancy. The neutron dose equivalent in milliSieverts per proton treatment Gray increased with incident proton energy and decreased with aperture size, distance of the fetus representative point from the field edge, and increasing air gap. Neutron dose equivalent to the fetus varied from 0.025 to 0.450 mSv per proton Gray for the small field snout and from 0.097 to 0.871 mSv per proton Gray for the large field snout. There is likely to be no excess risk to the fetus of severe mental retardation for a typical proton treatment of 80 Gray to the mother since the scattered neutron dose to the fetus of 69.7 mSv is well below the estimated radiation absorbed dose threshold of 600 mGy observed for the occurrence of severe mental retardation in prenatally exposed Japanese atomic bomb survivors. However based on the linear no threshold hypothesis and this same typical treatment for the mother, the excess risk to the fetus of radiation induced cancer death in the first 10 years of life is 17.4 per 10,000 children.
Purpose: Positron emission tomography (PET) scanning is a widely used method of proton therapy verification. In this study, a proton radiotherapy accuracy verification process was developed by comparing predicted and measured PET data to verify the correctness of PET prediction and was tested at the Shanghai Proton and Heavy Ion Center. Method: Irradiation was performed on a polymethyl methacrylate (PMMA) phantom. There were two dose groups, to which 2 Gy and 4 Gy doses were delivered, and each dose group had different designed dose depths ranging from 5 cm to 20 cm. The predicted PET results were obtained using a PET prediction calculation module. The measured data were collected with a PET/computed tomography device. The predicted and measured PET data were normalized to similar PET amplitude values before comparison and were compared using depth and lateral profiles for the position error. The error was evaluated at the position corresponding to 50% of the maximum on the PET curves. The mean and standard deviation were calculated based on the data sampled in the scoring area. Results: In the depth comparison, the 2 Gy and 4 Gy dose cases yielded similar mean depth errors between 1 mm and -1 mm, and the deviation was less than 2 mm. In the lateral comparison, the 2 Gy cases had a mean lateral error around 1 mm, and the 4 Gy cases had a mean lateral error less than 1 mm, with a standard deviation less than 1 mm for both the 2 Gy and 4 Gy cases. Conclusion: The comparison of these PMMA phantom cases revealed good agreement between the predicted and measured PET data, with depth and lateral position errors less than 2 mm in total, considering the uncertainty. The comparison results demonstrate that the PET predictions obtained in PMMA phantom tests for single proton beam therapy verification are reliable and that the research can be extended to verification in human body treatment with further investigation.
Purpose: We present a study of dosimetric consequences on doses in water in modeling in‐air proton fluence independently along principle axes for rotated elliptical spots. Methods: Phase‐space parameters for modeling in‐air fluence are the position sigma for the spatial distribution, the angle sigma for the angular distribution, and the correlation between position and angle distributions. Proton spots of the McLaren proton therapy system were measured at five locations near the isocenter for the energies of 180 MeV and 250 MeV. An elongated elliptical spot rotated with respect to the principle axes was observed for the 180 MeV, while a circular‐like spot was observed for the 250 MeV. In the first approach, the phase‐space parameters were derived in the principle axes without rotation. In the second approach, the phase space parameters were derived in the reference frame with axes rotated to coincide with the major axes of the elliptical spot. Monte‐Carlo simulations with derived phase‐space parameters using both approaches to tally doses in water were performed and analyzed. Results: For the rotated elliptical 180 MeV spots, the position sigmas were 3.6 mm and 3.2 mm in principle axes, but were 4.3 mm and 2.0 mm when the reference frame was rotated. Measured spots fitted poorly the uncorrelated 2D Gaussian, but the quality of fit was significantly improved after the reference frame was rotated. As a Result, phase space parameters in the rotated frame were more appropriate for modeling in‐air proton fluence of 180 MeV protons. Considerable differences were observed in Monte Carlo simulated dose distributions in water with phase‐space parameters obtained with the two approaches. Conclusion: For rotated elliptical proton spots, phase‐space parameters obtained in the rotated reference frame are better for modeling in‐air proton fluence, and can be introduced into treatment planning systems.
Large area, shallow fields are well suited to proton therapy. However, due to beam production limitations, such volumes typically require multiple matched fields. This is problematic due to the relatively narrow beam penumbra at shallow depths compared to electron and photon beams. Therefore, highly accurate dose planning and delivery is required. As the dose delivery includes shifting the patient for matched fields, accuracy at the 1–2 millimeter level in patient positioning is also required. This study investigates the dosimetric accuracy of such proton field matching by an innovative robotic patient positioner system (RPPS). The dosimetric comparisons were made between treatment planning system calculations, radiographic film and ionization chamber measurements. The results indicated good agreement amongst the methods and suggest that proton field matching by a RPPS is accurate and efficient. PACS number: 87.55.km
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='translate(0 -400)'/%3e%3cuse xlink:href='%23a' transform='translate(0 -600)'/%3e%3cuse xlink:href='%23a' transform='translate(0 -800)'/%3e%3cuse xlink:href='%23a' transform='translate(0 -1000)'/%3e%3cuse xlink:href='%23a' transform='translate(0 -1200)'/%3e%3cpath d='M0 0h1400v800H0z' style='fill:%23010066'/%3e%3cpath d='M576 100c-166.146 0-301 134.406-301 300s134.854 300 301 300c60.027 0 115.955-17.564 162.927-47.783-27.353 9.44-56.71 14.602-87.271 14.602-147.327 0-266.897-119.172-266.897-266.01 0-146.837 119.57-266.01 266.897-266.01 32.558 0 63.746 5.815 92.602 16.468C696.217 118.91 638.305 100 576 100z' style='fill:%23fc0'/%3e%3cpath d='m914.286 471.429-99.538-53.25 29.43 108.982-66.575-91.165-20.77 110.96-20.428-111.024-66.857 90.96L699.314 418l-99.701 52.943 74.065-85.192-112.8 4.441 103.694-44.62-103.555-44.94L673.8 305.42 600 220l99.538 53.25-29.43-108.982 66.575 91.165 20.77-110.96 20.428 111.023 66.857-90.959L814.97 273.43l99.702-52.944-74.065 85.193 112.8-4.441-103.694 44.62 103.555 44.94-112.785-4.79z' style='fill:%23fc0' transform='matrix(1.2738 0 0 1.2423 -89.443 -29.478)'/%3e%3c/svg%3e)