Streamlining the image-guided radiotherapy process for proton beam therapy (original) (raw)
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Tomographic images by proton Computed Tomography system for proton therapy applications
IEEE Nuclear Science Symposium Conference Record, 2012
Proton therapy is a highly precise form of cancer treatment, which requires accurate knowledge of the dose delivered to the patient and verification of the correct patient position to avoid damage to critical normal tissues. The development of pCT (proton Computed Tomography) system represents an important feature for precise proton radiation treatment planning because it could permit the direct measurement of the proton stopping power distribution, improving the accuracy in dose calculus, and the patient's position. A pCT prototype was manufactured in order to demonstrate the capability to acquire, during treatments in proton therapy centers, radiographic and tomographic images according to clinical demands.
A novel dose-based positioning method for CT image-guided proton therapy
Medical Physics, 2013
Proton dose distributions can potentially be altered by anatomical changes in the beam path despite perfect target alignment using traditional image guidance methods. In this simulation study, the authors explored the use of dosimetric factors instead of only anatomy to set up patients for proton therapy using in-room volumetric computed tomographic (CT) images. Methods: To simulate patient anatomy in a free-breathing treatment condition, weekly time-averaged four-dimensional CT data near the end of treatment for 15 lung cancer patients were used in this study for a dose-based isocenter shift method to correct dosimetric deviations without replanning. The isocenter shift was obtained using the traditional anatomy-based image guidance method as the starting position. Subsequent isocenter shifts were established based on dosimetric criteria using a fast dose approximation method. For each isocenter shift, doses were calculated every 2 mm up to ±8 mm in each direction. The optimal dose alignment was obtained by imposing a target coverage constraint that at least 99% of the target would receive at least 95% of the prescribed dose and by minimizing the mean dose to the ipsilateral lung. Results: The authors found that 7 of 15 plans did not meet the target coverage constraint when using only the anatomy-based alignment. After the authors applied dose-based alignment, all met the target coverage constraint. For all but one case in which the target dose was met using both anatomy-based and dose-based alignment, the latter method was able to improve normal tissue sparing. Conclusions: The authors demonstrated that a dose-based adjustment to the isocenter can improve target coverage and/or reduce dose to nearby normal tissue.
Analysis of the Rate of Re-planning in Spot-Scanning Proton Therapy
International Journal of Particle Therapy
Purpose Finite proton range affords improved dose conformality of radiation therapy when patient regions-of-interest geometries are well characterized. Substantial changes in patient anatomy necessitate re-planning (RP) to maintain effective, safe treatment. Regularly planned verification scanning (VS) is performed to ensure consistent treatment quality. Substantial resources, however, are required to conduct an effective proton plan verification program, which includes but is not limited to, additional computed tomography (CT) scanner time and dedicated personnel: radiation therapists, medical physicists, physicians, and medical dosimetrists. Materials and Methods Verification scans (VSs) and re-plans (RPs) of 711 patients treated with proton therapy between June 2015 and June 2018 were studied. All treatment RP was performed with the intent to maintain original plan integrity and coverage. The treatments were classified by anatomic site: brain, craniospinal, bone, spine, head and ...
International journal of radiation oncology, biology, physics, 2016
This study aimed to assess the clinical impact of spot size and the addition of apertures and range compensators on the treatment quality of pencil beam scanning (PBS) proton therapy and to define when PBS could improve on passive scattering proton therapy (PSPT). The patient cohort included 14 pediatric patients treated with PSPT. Six PBS plans were created and optimized for each patient using 3 spot sizes (∼12-, 5.4-, and 2.5-mm median sigma at isocenter for 90- to 230-MeV range) and adding apertures and compensators to plans with the 2 larger spots. Conformity and homogeneity indices, dose-volume histogram parameters, equivalent uniform dose (EUD), normal tissue complication probability (NTCP), and integral dose were quantified and compared with the respective PSPT plans. The results clearly indicated that PBS with the largest spots does not necessarily offer a dosimetric or clinical advantage over PSPT. With comparable target coverage, the mean dose (Dmean) to healthy organs was...
Journal of Radiation Oncology, 2020
Objective Pretreatment imaging plays a crucial role in determining geometric positional uncertainty of the patient during radiotherapy. Our purpose is to investigate the effect of frequent pretreatment imaging protocol (scenario) on actual dose delivery in radiotherapy. This paper presents a critical analysis of frequent imaging protocol with respect to Idealized daily imaging protocol (IDIP). Methods and materials Retrospective patients of Ca-carcinoma cervix, Ca-buccal mucosa, Ca-tongue treated with intensity-modulated radiation therapy (IMRT) undergoing daily cone beam computed tomography (CBCT) imaging protocol was selected for this study. Every treated fraction of these patients was simulated considering its daily geometrical setup uncertainties occurred. Indirect evaluation of virtual treatment plans was conducted in the treatment planning system (TPS) for 3 days a week, 2 days a week, and 1 day a week frequency imaging protocols. Results obtained from these frequent imaging protocols were compared with IDIP. Result Deviation between predicted and delivered dose found increasing with decreasing frequency of imaging. Significant deviations were observed in all the estimated plan quality parameters for patients treated with frequent imaging protocols and IDIP. Deviations were found more in case of pelvis sites than head and neck sites. Conclusion This study plays a vital role in establishing optimum pretreatment imaging protocols in busy clinics. Three days a week imaging protocol is the best suit protocol found with minimal deviation and ample implementation feasibility. This study proposed an opinion pertaining to the revision of setup margin formula in order to accommodate variation due to imaging techniques and frequency of imaging attempted during radiotherapy.
Analysis of characteristics of images acquired with a prototype clinical proton radiography system
Medical Physics, 2021
PurposeVerification of patient‐specific proton stopping powers obtained in the patient’s treatment position can be used to reduce the distal and proximal margins needed in particle beam planning. Proton radiography can be used as a pretreatment instrument to verify integrated stopping power consistency with the treatment planning CT. Although a proton radiograph is a pixel by pixel representation of integrated stopping powers, the image may also be of high enough quality and contrast to be used for patient alignment. This investigation quantifies the accuracy and image quality of a prototype proton radiography system on a clinical proton delivery system.MethodsWe have developed a clinical prototype proton radiography system designed for integration into efficient clinical workflows. We tested the images obtained by this system for water‐equivalent thickness (WET) accuracy, image noise, and spatial resolution. We evaluated the WET accuracy by comparing the average WET and rms error i...
In vivo verification of proton beam path by using post-treatment PET/CT imaging
Medical Physics, 2009
The purpose of this study is to establish the in vivo verification of proton beam path by using proton-activated positron emission distributions. Methods: A total of 50 PET/CT imaging studies were performed on ten prostate cancer patients 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, referred to as the PET-defined beam path. Because of the patient position correction at each fraction, the marker-defined beam path, determined by the centroid of implanted markers seen in the posttreatment ͑post-Tx͒ CT, is used for the planned beam path. The angular variation and discordance between the PET-and marker-defined paths were derived to investigate the intrafraction prostate motion. For studies with large discordance, the relative location between the centroid and pelvic bones seen in the post-Tx CT was examined. The PET/CT studies are categorized for distinguishing the prostate motion that occurred before or after beam delivery. The post-PET CT was acquired after PET imaging to investigate prostate motion due to physiological changes during the extended PET acquisition. Results: The less than 2°of angular variation indicates that the patient roll was minimal within the immobilization device. Thirty of the 50 studies with small discordance, referred as good cases, show a consistent alignment between the field edges and the positron emission distributions from the entrance to the distal edge. For those good cases, average displacements are 0.6 and 1.3 mm along the anterior-posterior ͑D AP ͒ and superior-inferior ͑D SI ͒ directions, respectively, with 1.6 mm standard deviations in both directions. For the remaining 20 studies demonstrating a large discordance ͑more than 6 mm in either D AP or D SI ͒, 13 studies, referred as motion-after-Tx cases, also show large misalignment between the field edge and the positron emission distribution in lipomatous tissues around the prostate. These motion-after-Tx cases correspond to patients with large changes in volume of rectal gas between the post-Tx and the post-PET CTs. The standard deviations for D AP and D SI are 5.0 and 3.0 mm, respectively, for these motion-after-Tx cases. The final seven studies, referred to as position-error cases, which had a large discordance but no misalignment, were found to have deviations of 4.6 and 3.6 mm in D AP and D SI , respectively. The positionerror cases correspond to a large discrepancy on the relative location between the centroid and pelvic bones seen in post-Tx CT and recorded x-ray radiographs. Conclusions: Systematic analyses of proton-activated positron emission distributions provide patient-specific information on prostate motion ͑ M ͒ and patient position variability ͚͑ p ͒ during daily proton beam delivery. The less than 2 mm of displacement variations in the good cases indicates that population-based values of ͚ p and M used in margin algorithms for treatment planning at the authors' institution are valid for the majority of cases. However, a small fraction of PET/CT studies ͑approximately 14%͒ with ϳ4 mm displacement variations may require different margins. Such data are useful in establishing patient-specific planning target volume margins.