Spot Scanning Proton Therapy Research Articles

Robust Optimization for Spot Scanning Proton Therapy based on Dose-Linear Energy Transfer (LET) Volume Constraints

Robust Optimization for Spot Scanning Proton Therapy based on Dose-Linear Energy Transfer (LET) Volume Constraints

Dosimetric Evaluation of Beam-specific PTV and Worst-case Optimization Methods for Liver Proton Therapy.

In spot-scanning proton therapy, intra-fractional anatomical changes by organ movement can lead to deterioration in dose distribution due to beam range variation. To explore a more robust treatment planning method, this study evaluated the dosimetric characteristics and robustness of two proton therapy planning methods for liver cancer. Two- or three-field treatment plans were created for 11 patients with hepatocellular carcinoma or metastatic liver cancer using a single-field uniform dose (SFUD) technique. The plans were optimized using either beam-specific planning target volume (BSPTV) or worst-case optimization (WCO). The target coverage for the gross tumor volume (GTV), planning target volume (PTV), and organs at risk (OAR) parameters related to toxicity were calculated from the perturbed dose distributions, considering setup and range uncertainties. Statistical analyses of the BSPTV and WCO plans were performed using the Wilcoxon signed-rank sum test (p<0.05). The calculation times for a single optimization process were also recorded and compared. The robustness of the WCO plans in the worst-case scenario was significantly higher than that of the BSPTV plan in terms of GTV target coverage, prevention of maximum dose increase to the gastrointestinal tract, and the dose received by normal liver regions. However, there were no significant differences in PTV, and the calculation time required to create the WCO plan was considerably longer. In SFUD proton therapy for liver cancer, the WCO plans required a longer optimization time but exhibited superior robustness in GTV coverage and sparing of OARs.

Evaluation of a prototype array for daily quality assurance in spot scanning proton therapy.

Quality assurance (QA) on a daily basis is an essential task in radiotherapy. In pencil beam scanning proton therapy (PBS), there is a lack of available practical QA devices for routine daily QA in comparison to conventional radiotherapy. The aim was to characterize and evaluate a prototype for the task of daily QA routine for PBS with parameters recommended by the AAPM TG 224, that is, the dose output constancy, the spot position and the distal range verification. Furthermore, a time efficient calibration method for fast and reliable daily QA routine was established for theprototype. First, a calibration routine was designed and evaluated, which characterizes the array response and allows for a conversion of the measured signal to clinically needed QA parameters. Finally, a time and resource efficient daily QA routine was developed andtested. The prototype array can distinguish spot position deviations with sub-millimeter accuracy, as well as changes in the spot size in terms of FWHM with a 2 sensitivity. The range and thus the energy can be evaluated at different depths also with sub-millimeter precision. After some training, the setup of the prototype device took roughly two minutes and the total beamtime was about one minuteon cyclotron site and five minutesfor synchrotrons. A prototype for daily QA in spot scanning proton therapy was evaluated, which features a fast and easy setup and allows for measuring relevant beam parameters, typically within less than a minute of beam time. All QA parameters as recommended by the AAPM TG 224 report can be analyzed with sufficientaccuracy.

Interplay Effect in Spot-Scanning Proton Therapy with Rescanning, Breath Holding, and Gating: A Phantom Study

Interplay Effect in Spot-Scanning Proton Therapy with Rescanning, Breath Holding, and Gating: A Phantom Study

Five-Year Prostate-Specific Membrane Antigen Positron Emission Tomography-Based Outcomes of Spot-Scanning Proton Radiation Therapy for Localized Prostate Cancer: A Single Institution Experience

PURPOSE: We report 5-year oncologic outcomes of a prospective series of patients with prostate cancer treated with spot-scanning proton therapy (SSPT).METHODS AND MATERIALS: A prospective registry identified patients with prostate cancer treated with SSPT between January 2016 and December 2018. Five-year overall survival (OS), local control (LC), biochemical failure (BF), regional and distant failures, and adverse events (AEs) were assessed. Biochemical failure was defined as rise in PSA ≥ 2.0 ng/mL above nadir PSA. Baseline-adjusted toxicities were assigned using CTCAE v5.0.RESULTS: With a median follow up of 4.4 years, 284 prostate cancer patients were treated with SSPT. Median total radiation dose was 79.2 Gy over 44 fractions, 70 Gy over 28 fractions, and 38 Gy over 5 fractions for conventional fractionation (CF), hypofractionation (HF), and stereotactic body radiation therapy (SBRT), respectively. Biochemical failure rate for all patients was 6.7%. Five-year LC rates for CF, HF, and SBRT were 100%, 100%, and 97.3%, respectively (p = 0.07). Regional recurrences occurred in 12 (4.2%) patients: 8 treated with CF, 2 with HF, and 2 with SBRT (p = 0.62). Distant failures occurred in 12 patients (4.2%): 5 treated with CF, 7 with HF, and none with SBRT (p = 0.05). Five-year OS for patients treated with CF, HF, and SBRT SSPT were 88.1%, 86.1%, and 97.2%, respectively (p = 0.1). Acute and chronic grade 2+ GI AEs occurred in 8 (2.8%) and 51 (18.0%) patients, respectively. Acute and chronic grade 3+ GI AEs occurred in 3 (1.1%) and 4 (1.4%) patients, respectively. Acute and chronic grade 2+ GU-related AEs were observed in 71 (25%) and 63 (22.2%) patients, respectively. Acute and chronic grade 3+ GU toxicity were observed in 3 (1.1%) and 6 (2.1%) patients, respectively.CONCLUSIONS: SSPT provides high local control rates and excellent oncologic outcomes across different fractionation schedules with low long-term AE rates.

Impact of interplay effects on spot scanning proton therapy with motion mitigation techniques for lung cancer: SFUD versus robustly optimized IMPT plans utilizing a four-dimensional dynamic dose simulation tool

BackgroundThe interaction between breathing motion and scanning beams causes interplay effects in spot-scanning proton therapy for lung cancer, resulting in compromised treatment quality. This study investigated the effects and clinical robustness of two types of spot-scanning proton therapy with motion-mitigation techniques for locally advanced non-small cell lung cancer (NSCLC) using a new simulation tool (4DCT-based dose reconstruction).MethodsThree-field single-field uniform dose (SFUD) and robustly optimized intensity-modulated proton therapy (IMPT) plans combined with gating and re-scanning techniques were created using a VQA treatment planning system for 15 patients with locally advanced NSCLC (70 GyRBE/35 fractions). In addition, gating windows of three or five phases around the end-of-expiration phase and two internal gross tumor volumes (iGTVs) were created, and a re-scanning number of four was used. First, the static dose (SD) was calculated using the end-of-expiration computed tomography (CT) images. The four-dimensional dynamic dose (4DDD) was then calculated using the SD plans, 4D-CT images, and the deformable image registration technique on end-of-expiration CT. The target coverage (V98%, V100%), homogeneity index (HI), and conformation number (CN) for the iGTVs and organ-at-risk (OAR) doses were calculated for the SD and 4DDD groups and statistically compared between the SD, 4DDD, SFUD, and IMPT treatment plans using paired t-test.ResultsIn the 3- and 5-phase SFUD, statistically significant differences between the SD and 4DDD groups were observed for V100%, HI, and CN. In addition, statistically significant differences were observed for V98%, V100%, and HI in phases 3 and 5 of IMPT. The mean V98% and V100% in both 3-phase plans were within clinical limits (> 95%) when interplay effects were considered; however, V100% decreased to 89.3% and 94.0% for the 5-phase SFUD and IMPT, respectively. Regarding the significant differences in the deterioration rates of the dose volume histogram (DVH) indices, the 3-phase SFUD plans had lower V98% and CN values and higher V100% values than the IMPT plans. In the 5-phase plans, SFUD had higher deterioration rates for V100% and HI than IMPT.ConclusionsInterplay effects minimally impacted target coverage and OAR doses in SFUD and robustly optimized IMPT with 3-phase gating and re-scanning for locally advanced NSCLC. However, target coverage significantly declined with an increased gating window. Robustly optimized IMPT showed superior resilience to interplay effects, ensuring better target coverage, prescription dose adherence, and homogeneity than SFUD.Trial registration: None.

Three-dimensional dosimetry of dose degradations around gold markers in spot-scanning proton therapy

Three-dimensional dosimetry of dose degradations around gold markers in spot-scanning proton therapy

Simultaneous reduction of number of spots and energy layers in intensity modulated proton therapy for rapid spot scanning delivery.

Reducing proton treatment time improves patient comfort and decreases the risk of error from intrafractional motion, but must be balanced against clinical goals and treatment planquality. To improve the delivery efficiency of spot scanning proton therapy by simultaneously reducing the number of spots and energy layers using the reweighted regularizationmethod. We formulated the proton treatment planning problem as a convex optimization problem with a cost function consisting of a dosimetric plan quality term plus a weighted regularization term. We iteratively solved this problem and adaptively updated the regularization weights to promote the sparsity of both the spots and energy layers. The proposed algorithm was tested on four head-and-neck cancer patients, and its performance, in terms of reducing the number of spots and energy layers, was compared with existing standard and group regularization methods. We also compared the effectiveness of the three methods ( , group , and reweighted ) at improving plan delivery efficiency without compromising dosimetric plan quality by constructing each of their Pareto surfaces charting the trade-off between plan delivery and planquality. The reweighted regularization method reduced the number of spots and energy layers by an average over all patients of and , respectively, with an insignificant cost to dosimetric plan quality. From the Pareto surfaces, it is clear that reweighted provided a better trade-off between plan delivery efficiency and dosimetric plan quality than standard or group regularization, requiring the lowest cost to quality to achieve any given level of deliveryefficiency. Reweighted regularization is a powerful method for simultaneously promoting the sparsity of spots and energy layers at a small cost to dosimetric plan quality. This sparsity reduces the time required for spot scanning and energy layer switching, thereby improving the delivery efficiency of protonplans.

Spot scanning proton therapy for unresectable bulky retroperitoneal dedifferentiated liposarcoma: a case report.

The development of effective treatment strategies for unresectable retroperitoneal sarcoma is desirable. Herein, we suggest that definitive proton therapy (PT) could be a promising treatment option, regardless of the large size of the tumor. A 52-year-old man presented with a discomfort of the lower abdomen. Computed tomography revealed a retroperitoneal tumor, measuring over 20cm in the largest dimensions, which was surrounded by the gastrointestinal (GI) tract. Biopsy revealed dedifferentiated liposarcoma. Neoadjuvant chemotherapy was ineffective, and the tumor was ultimately deemed unresectable. The patient opted to receive PT instead of continuation of chemotherapy. Spot scanning PT (SSPT) at a total dose of 60.8Gy (relative biological effectiveness) in 16 fractions was employed. SSPT administered a dose to the tumor while successfully sparing the surrounding GI tract. He did not receive any maintenance systemic therapy after PT. The tumor gradually shrunk over more than 7 years, with no evidence of recurrence outside the irradiation field. The initial measurable tumor volume of 2925cc decreased to 214cc at the final follow-up, seven and a half years after PT. The patient is alive without any severe complications.

Dosimetric Evaluation of Target Motion Effects in Spot-Scanning Proton Therapy: A Phantom Study

PurposeTo evaluate intrafractional motion effects as a function of peak-to-peak motion and period during single-field, single-fraction and single-field, multifraction irradiation of the moving target in spot-scanning proton therapy. Materials and MethodsAn in-house dynamic phantom was used to simulate peak-to-peak motion of 5, 10, and 20 mm with periods of 2, 4, and 8 seconds. The dose distribution in the moving target was measured using radiochromic films. During the perpendicular motion, the film was fixed and moved perpendicular to the beam direction without changing the water equivalent thickness (WET). During longitudinal motion, the film was fixed and moved along the beam direction, causing a change in WET. Gamma index analysis was used with criteria of 3%/3 mm and 3%/2 mm to analyze the dose distributions. ResultsFor single-fraction irradiation, varying the period did not result in a significant difference in any of the metrics used (P > .05), except for the local dose within the planning target volume (P < .001). In contrast, varying peak-to-peak motion was significant (P < .001) for all metrics except for the mean planning target volume dose (P ≈ .88) and the local dose (P ≈ .47). The perpendicular motion caused a greater decrease in gamma passing rate (3%/3 mm) than WET variations (65% ± 5% vs 85% ± 4%) at 20 mm peak-to-peak motion. ConclusionThe implementation of multifraction irradiation allowed to reduce hot and cold spots but did not reduce dose blurring. The motion threshold varied from 7 to 11 mm and depended on the number of fractions, the type of motion, the acceptance criteria, and the calculation method used.

Spot-scanning proton therapy for early breast cancer in free breathing versus deep inspiration breath-hold.

Proton therapy for breast cancer is usually given in free breathing (FB). With the use of deep inspiration breath-hold (DIBH) technique, the location of the heart is displaced inferiorly, away from the internal mammary nodes and, thus, the dose to the heart can potentially be reduced. The aim of this study was to explore the potential benefit of proton therapy in DIBH compared to FB for highly selected patients to reduce exposure of the heart and other organs at risk. We aimed at creating proton plans with delivery times feasible with treatment in DIBH. Sixteen patients with left-sided breast cancer receiving loco-regional proton therapy were included. The FB and DIBH plans were created for each patient using spot-scanning proton therapy with 2-3 fields, robust and single field optimization. For the DIBH plans, minimum monitor unit per spot and spot spacing were increased to reduce treatment delivery time. All plans complied with target coverage constraints. The median mean heart dose was statistically significant reduced from 1.1 to 0.6 Gy relative biological effectiveness (RBE) by applying DIBH. No statistical significant difference was seen for mean dose and V17Gy RBE to the ipsilateral lung. The median treatment delivery time for the DIBH plans was reduced by 27% compared to the FB plans without compromising the plan quality. The median absolute reduction in dose to the heart was limited. Proton treatment in DIBH may only be relevant for a subset of these patients with the largest reduction in heart exposure.

A Single-Institution Prospective Study To Evaluate the Safety and Efficacy of Real- Time Image-Gated Spot-Scanning Proton Therapy (RGPT) for Prostate Cancer

BackgroundIn Real-time-image Gated spot-scanning Proton Therapy (RGPT), the dose distribution is distorted by gold fiducial markers placed in the prostate. Distortion can be suppressed by using small markers and more than two fields, but additional fields may increase the dose to organs at risk. Therefore, we conducted a prospective study to evaluate the safety and short-term clinical outcome of RGPT for prostate cancer. MethodsBased on the previously reported frequency of early adverse events (AE) and the non-inferiority margin of 10%, the required number of cases was calculated to be 43 using the one-sample binomial test by the SWOG statistical tools with the one-sided significance level of 2.5% and the power 80%. Patients with localized prostate cancer were enrolled and 3-4 pure gold fiducial markers of 1.5 mm diameter were inserted in the prostate. The prescribed dose was 70 Gy(RBE) in 30 fractions, and treatment was performed with three fields from the left, right, and the back, or four fields from either side of slightly anterior and posterior oblique fields. The primary endpoint was the frequency of early AE (≥ Grade 2) and the secondary endpoint was the biochemical relapse-free survival rate (BRFS) and the frequency of late AE. ResultsForty-five cases were enrolled between 2015 and 2017 and all patients completed the treatment protocol. The median follow-up period was 63.0 months. The frequency of early AE (≥ Grade 2) was observed in 4 cases (8.9%), therefore the non-inferiority was verified. The overall 5-year BRFS was 88.9%. As late AE, Grade 2 rectal bleeding were observed in 8 cases (17.8%). ConclusionsThe RGPT for prostate cancer with 1.5 mm markers and 3- or 4- fields was as safe as conventional proton therapy in early AE, and its efficacy was suggested comparable with previous studies.

Optimization of a YAP(Ce) prompt X-ray camera for imaging with spot scanning proton beams at clinical dose levels

Prompt secondary electron bremsstrahlung X-ray (prompt X-ray) imaging using a low-energy X-ray camera is a promising method for observing the beam shape from outside a subject. However, it has sometimes been necessary to conduct such imaging at a higher dose than the clinical level to acquire images with acceptable quality. To solve this problem, we optimized a prompt X-ray imaging system to use for spot scanning proton therapy system. The new camera had more than one order higher sensitivity to image several types of beams, including those at the clinical dose level. The optimized prompt X-ray imaging system uses a 4 mm diameter pinhole collimator to increase sensitivity, and it is combined with a larger YAP(Ce) scintillator to increase the magnification ratio and thus improve spatial resolution. We used a list-mode data-acquisition system with high count rate capability. Prompt X-ray images were acquired by irradiating a water phantom with proton beams from the spot scanning proton therapy system. Measurements were taken for pencil beams, spread-out Bragg peak (SOBP) beams, and a beam utilized in actual clinical therapy. For all of the beams, we could measure scanning spot images within a spill and evaluate the ranges for the accumulated images at the clinical dose level. From the list-mode data, we measured the temporarily altered positions of the scanning beams as well as the accumulations of the prompt X-ray images. The optimized prompt X-ray imaging system could improve sensitivity while maintaining better spatial resolution. The new system realized prompt X-ray imaging at the clinical dose level and holds promise for future clinical imaging of prompt X-rays.

Comparative dosimetric study of spot-scanning proton therapy versus volumetric-modulated radiation therapy for extrahepatic bile duct cancer

This study aimed to compare the dose distributions and clarify the dosimetric characteristics of spot-scanning proton therapy (SSPT) and photon volumetric modulated arc therapy (VMAT) for extrahepatic bile duct cancer (EBDC). This retrospective study included 10 patients with EBDC treated with real-time image-gated SSPT. Using the simultaneous integrated boost technique, the 2 prescription dose levels for planning target volumes were 72.6 and 44 Gy, delivered in 22 fractions. Plan quality comparisons were conducted by analyzing various parameters, including homogeneity, conformity, dose to organs at risk, and normal tissue complication probability (NTCP) for radiation-induced liver damage (RILD). The target dose distributions using SSPT were almost equivalent to those achieved using photon VMAT. There was a significant reduction in all liver dose parameters, the NTCP value for RILD, and kidney dose (mean, V12 Gy, and V18 Gy) in SSPT than in photon VMAT. No significant differences were observed in the intestinal doses in the high-dose area. Thus, compared with photon VMAT, SSPT for EBDC significantly reduced radiation doses to the liver and kidneys and has shown potential clinical benefits of reduced radiation-induced toxicity.

Oncologic Outcomes of Conventionally Fractionated, Hypofractionated, and Stereotactic Body Spot-Scanned Proton Radiation Therapy for Prostate Cancer: The Mayo Clinic Experience.

Spot/pencil beam scanned proton therapy is a relatively new technology with fundamental differences from double scattered or IMRT. We aimed to report the long-term oncologic outcomes of a contemporary prospective series of patients treated with spot-scanned proton therapy (SSPT). An IRB-approved prospective registry identified patients with prostate cancer treated with proton therapy between January 2016 and December 2018. Descriptive statistics were calculated for all patients. Clinical, demographic, and treatment characteristics were gathered and analyzed. Kaplan-Meier curves were generated to estimate survival and recurrence rates. Outcomes assessed included 5-year overall survival (OS), 5-year local control (LC), biochemical failure (BF), regional and distant failures, and physician-reported adverse events (AEs). Biochemical failure was defined as rise in PSA ≥ 2.0 ng/mL above nadir PSA. Acute and chronic gastrointestinal (GI) and genitourinary (GU) grade 2+ and grade 3+ baseline-adjusted AEs were assigned using CTCAE v5.0. All failures were re-staged with PET C-11 or PSMA. With a median follow up of 4.4 years (IQR 3.7 - 5), two hundred and eighty-six prostate cancer patients with a median age of 72 (IQR 67.5 - 77) were treated with spot-scanned proton radiation. The median Gleason grade group was 3 (IQR 2 - 4). The median pre-RT PSA was 6.9 ng/mL (IQR 4.3 - 10.5). Median T-stage was T1c. Nearly 64% of all patients were on androgen deprivation therapy at the time of initiating radiation treatment. The median total radiation dose was 79.2 Gy delivered over 44 fractions, 70 Gy over 28 fractions, and 38 Gy over 5 fractions for CF, HF, and SBRT regimens, respectively. The BF rate for all patients was 8.4%. The 5-year LC rates for CF, HF, and SBRT were 100% (95% CI: 100 - 100), 100% (95% CI: 100 - 100), and 97.3% (95% CI: 92.2 - 100), respectively (p = 0.07). Regional recurrences occurred in 12 (4.2%) patients: 8 (5.6%) treated with CF, 2 (2.1%) with HF, and 2 (4.3%) with SBRT (p = 0.62). Distant metastatic failures occurred in 12 patients (4.2%): 5 (3.5%) treated with CF, 7 (7.4%) with HF, and none with SBRT (0%) (p = 0.052). The 5-year OS for patients treated with CF, HF, and SBRT SSPT were 88.2% (95% CI: 81.8 - 95), 86.2% (95% CI: 77.6 - 95.6), and 97.2% (95% CI: 92 - 100), respectively (p = 0.1). Acute and chronic grade 2+ GI baseline-adjusted AEs occurred in 8 (2.8%) and 51 (17.8%) patients, respectively. Acute and chronic grade 3+ GI baseline-adjusted AEs occurred in 3 (1%) and 4 (1.4%) patients, respectively. Acute and chronic grade 2+ GU-related AEs were observed in 72 (25.2%) and 63 (22%) patients, respectively. Acute and chronic grade 3+ GU toxicity was observed in 3 (1%) and 6 (2.1%) patients, respectively. Spot-scanned proton radiation therapy provides high local control rates and excellent oncologic outcomes across different fractionation schedules with low long-term AE rates.

Spot Scanning Proton Therapy for Pregnant Patients with Brain and Head and Neck Tumors

When radiotherapy is medically necessary, x-ray based treatments (XRT) have traditionally been used to treat pregnant patients. Treatment planning and delivery techniques may be modified to minimize dose to the fetus but results in less optimal plans due to avoiding posterior beams or arcs. Monte Carlo calculations and published case studies suggest spot scanning proton therapy (PRT) reduces the equivalent dose to the fetus by a factor of 10 compared to XRT and does not require modified treatment planning techniques. However, due to concern for dose uncertainties and neutron scatter with PRT, few centers have adopted PRT over XRT for pregnant patients. The purpose of this work is to perform a retrospective study on the pregnant patients previously treated at our institution with XRT to measure the equivalent dose that would be delivered to the fetus with spot scanning PRT compared to XRT. PRT plans were made for seven pregnant patients, 4 brain tumors and 3 head and neck tumors, who had received XRT. Due to the finite range of protons, the fetal exposure is dominated by neutrons and not the primary beam. Thus, no beam arrangement modifications were required to minimize fetal dose for PRT plans. Fetal dose measurements were performed with the patient plans using a Rando phantom and Wendi-2 (Thermo Scientific) meter placed at the phantom's abdomen. The Wendi-2 measures ambient dose equivalent, which accounts for the biological effect of the neutron energies. Measurements were made at various distances from isocenter to the center of the detector. The total dose equivalent from PRT at several out of field distances was compared to that from XRT. Patient specific measurements were used to determine the total fetal dose from each modality, accounting for the changing position of the fetus each week of the mother's treatment. The imaging dose for standard of practice imaging, including verification CT scans and daily alignment imaging, was also evaluated using a similar setup with a Fluke 451 dose meter. The average measured fetal equivalent dose for the brain plans was 0.4 mSv for PRT and 7 mSv for XRT. For the head and neck plans, it was 6 mSv for PRT and 90 mSv for XRT. The dose from PRT was consistently at least a factor of 10 less than the XRT plans. In addition, the PRT plans were preferred by the physicians when considering tumor coverage and other normal tissue sparing. Daily imaging added between 0.05 and 1.5 mSv to the total dose in the PRT treatments. This retrospective study showed that when treating brain or head and neck tumors in pregnant patients, the equivalent dose a fetus would receive with PRT is approximately a factor of 10 less than XRT without making any compromises in treatment planning. These results support changing the standard of practice to utilizing spot scanning PRT as the preferred method for treating pregnant patients with brain or head and neck tumors when available instead of XRT. We have brought this process to clinic at our center.

High-speed low-noise optical respiratory monitoring for spot scanning proton therapy

PurposeTo investigate a novel optical markerless respiratory sensor for surface guided spot scanning proton therapy and to measure its main technical characteristics. MethodsThe main characteristics of the respiratory sensor including sensitivity, linearity, noise, signal-to-noise, and time delay were measured using a dynamic phantom and electrical measuring equipment on a laboratory stand. The respiratory signals of free breathing and deep-inspiration breath-hold patterns were acquired for various distances with a volunteer. A comparative analysis of this sensor with existing commercially available and experimental respiratory monitoring systems was carried out based on several criteria including principle of operation, patient contact, application to proton therapy, distance range, accuracy (noise, signal-to-noise ratio), and time delay (sampling rate). ResultsThe sensor provides optical respiratory monitoring of the chest surface over a distance range of 0.4–1.2 m with the RMS noise of 0.03–0.60 mm, SNR of 40–15 dB (for motion with peak-to-peak of 10 mm), and time delay of 1.2 ± 0.2 ms. ConclusionsThe investigated optical respiratory sensor was found to be appropriate to use in surface guided spot scanning proton therapy. This sensor combined with a fast respiratory signal processing algorithm may provide accurate beam control and a fast response in patients’ irregular breathing movements. A careful study of correlation between the respiratory signal and 4DCT data of tumor position will be required before clinical implementation.

PD-0250 Intrafraction tumor motion monitoring and dose reconstruction for liver spot scanning proton therapy

PD-0250 Intrafraction tumor motion monitoring and dose reconstruction for liver spot scanning proton therapy

Erratum to: Experimental Study of the Target Motion Effect on the Dose Distribution in Spot-Scanning Beam Proton Therapy

Erratum to: Experimental Study of the Target Motion Effect on the Dose Distribution in Spot-Scanning Beam Proton Therapy

Prostatic urinary tract visualization with super-resolution deep learning models.

In urethra-sparing radiation therapy, prostatic urinary tract visualization is important in decreasing the urinary side effect. A methodology has been developed to visualize the prostatic urinary tract using post-urination magnetic resonance imaging (PU-MRI) without a urethral catheter. This study investigated whether the combination of PU-MRI and super-resolution (SR) deep learning models improves the visibility of the prostatic urinary tract. We enrolled 30 patients who had previously undergone real-time-image-gated spot scanning proton therapy by insertion of fiducial markers. PU-MRI was performed using a non-contrast high-resolution two-dimensional T2-weighted turbo spin-echo imaging sequence. Four different SR deep learning models were used: the enhanced deep SR network (EDSR), widely activated SR network (WDSR), SR generative adversarial network (SRGAN), and residual dense network (RDN). The complex wavelet structural similarity index measure (CW-SSIM) was used to quantitatively assess the performance of the proposed SR images compared to PU-MRI. Two radiation oncologists used a 1-to-5 scale to subjectively evaluate the visibility of the prostatic urinary tract. Cohen's weighted kappa (k) was used as a measure of agreement of inter-operator reliability. The mean CW-SSIM in EDSR, WDSR, SRGAN, and RDN was 99.86%, 99.89%, 99.30%, and 99.67%, respectively. The mean prostatic urinary tract visibility scores of the radiation oncologists were 3.70 and 3.53 for PU-MRI (k = 0.93), 3.67 and 2.70 for EDSR (k = 0.89), 3.70 and 2.73 for WDSR (k = 0.88), 3.67 and 2.73 for SRGAN (k = 0.88), and 4.37 and 3.73 for RDN (k = 0.93), respectively. The results suggest that SR images using RDN are similar to the original images, and the SR deep learning models subjectively improve the visibility of the prostatic urinary tract.