Uniform Scanning Proton Therapy Research Articles

Feasibility study of utilizing Sphinx Compact for quality assurance in uniform scanning proton therapy

PurposeTo investigate the feasibility of utilizing the Sphinx Compact detector for quality assurance in a uniform scanning proton therapy system. MethodThe Sphinx Compact detector was used to measure various dosimetric parameters of uniform scanning proton beam at the Oklahoma Proton Center: distal range, distal-fall-off, collinearity, field symmetry, flatness, and field size for four different beams. A specially designed brass aperture was used to perform the required measurements. The Sphinx Compact measurement results were validated against the measurement results from the well-established detectors in proton therapy: IBA Zebra, IBA MatriXX-PT, EBT3 films, and Logos XRV-124. The data collected using the Sphinx Compact was analyzed in myQA software. ResultsBased on the data analysis performed, the Sphinx Compact measurements were within acceptable accuracy to the results from the detectors mentioned in the Method section. Specifically, the lateral penumbra was within ±0.4 mm, collinearity was within ± 0.5 mm, flatness was within ±0.6 %, symmetry within ±1.6 %, distal range was within ±0.5 mm, distal-fall-off was <0.9 mm, and field size was within ±1 mm. The reproducibility of the Sphinx Compact was tested for range and collinearity, and the results were within ±0.1 mm. ConclusionThe sphinx Compact detector could potentially replace multiple detectors utilized for monthly QA in uniform scanning proton therapy. In a multi-room center, performing the QA with one detector compared to using multiple detectors dramatically reduces total QA time and the complexity of the QA process.

Prediction of the output factor using machine and deep learning approach in uniform scanning proton therapy.

PurposeThe purpose of this work is to develop machine and deep learning‐based models to predict output and MU based on measured patient quality assurance (QA) data in uniform scanning proton therapy (USPT).MethodsThis study involves 4,231 patient QA measurements conducted over the last 6 years. In the current approach, output and MU are predicted by an empirical model (EM) based on patient treatment plan parameters. In this study, two MATLAB‐based machine and deep learning algorithms — Gaussian process regression (GPR) and shallow neural network (SNN) — were developed. The four parameters from patient QA (range, modulation, field size, and measured output factor) were used to train these algorithms. The data were randomized with a training set containing 90% and a testing set containing remaining 10% of the data. The model performance during training was accessed using root mean square error (RMSE) and R‐squared values. The trained model was used to predict output based on the three input parameters: range, modulation, and field size. The percent difference was calculated between the predicted and measured output factors. The number of data sets required to make prediction accuracy of GPR and SNN models' invariable was also evaluated.ResultsThe prediction accuracy of machine and deep learning algorithms is higher than the EM. The output predictions with [GPR, SNN, and EM] within ± 2% and ± 3% difference were [97.16%, 97.64%, and 92.95%] and [99.76%, 99.29%, and 97.18%], respectively. The GPR model outperformed the SNN with a smaller number of training data sets.ConclusionThe GPR and SNN models outperformed the EM in terms of prediction accuracy. Machine and deep learning algorithms predicted the output factor and MU for USPT with higher predictive accuracy than EM. In our clinic, these models have been adopted as a secondary check of MU or output factors.

Proceedings to the 6th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA): 14-16 October 2019, Hosted by Miami Cancer Institute, part of Baptist Health South Florida, Miami, FL, USA.

Proceedings to the 6th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA): 14-16 October 2019, Hosted by Miami Cancer Institute, part of Baptist Health South Florida, Miami, FL, USA.

Early outcomes of breast cancer patients treated with post-mastectomy uniform scanning proton therapy

BackgroundPostmastectomy proton radiotherapy improves normal tissue sparing in comparison to photon-based approaches. Several studies have reported dosimetry comparison and tolerable acute toxicity profile with limited follow-up. We report our institutional experience of postmastectomy proton radiation including clinical efficacy and toxicities. MethodsFrom December 2013 to February 2015, 42 consecutive patients who received mastectomy for non-metastatic breast cancer were treated with adjuvant chest wall and regional nodal proton therapy at a single proton center. 3D conformal uniform scanning with en face matching fields was used. ResultsThe median follow-up among patients was 35 months (range 1–55 months). There was one local failure, zero regional nodal failure, and six distant failures. The 3-year rate of locoregional disease-free survival was 96.3%, metastasis-free survival was 84.1%, and overall survival was 97.2%. The only local failure event occurred on the chest wall within the radiation field, approximately 2.5 years after the completion of radiation. Skin dermatitis, fatigue, and esophagitis were the most common acute toxicity. All patients developed grade 1 or 2 acute skin toxicity and there was no grade 3 or 4 acute skin toxicity. Proton radiation is able to achieve excellent target coverage with median PTV V95 over 95% and heart sparing with median mean heart dose less than 1 Gy (RBE). ConclusionWith close to three years of median follow-up, post-mastectomy proton radiation has shown excellent locoregional control rates and favorable toxicity profile. Long-term adverse effect of heart-sparing radiation will require longer follow-up time and randomized clinical trials.

Adaptive planning and toxicities of uniform scanning proton therapy for lung cancer patients

Adaptive planning and toxicities of uniform scanning proton therapy for lung cancer patients

Acute and Late Toxicity of Uniform Scanning Proton Therapy for Breast Cancer Patients

Acute and Late Toxicity of Uniform Scanning Proton Therapy for Breast Cancer Patients

SU‐F‐T‐133: Uniform Scanning Proton Therapy for Lung Cancer: Toxicity and Its Correlation with Dosimetry

Purpose:To analyze the toxicity of uniform scanning proton therapy for lung cancer patients and its correlation with dose distribution.Methods:In this study, we analyzed the toxicity of 128 lung cancer patients, including 18 small cell lung cancer and 110 non small cell lung cancer patients. Each patient was treated with uniform scanning proton beams at our center using typically 2–4 fields. The prescription was typically 74 Cobalt gray equivalent (CGE) at 2 CGE per fraction. 4D Computerized Tomography (CT) scans were used to evaluate the target motion and contour the internal target volume, and repeated 3 times during the course of treatment to evaluate the need for plan adaptation. Toxicity data for these patients were obtained from the proton collaborative group (PCG) database. For cases of grade 3 toxicities or toxicities of interest such as esophagitis and radiation dermatitis, dose distributions were reviewed and analyzed in attempt to correlate the toxicity with radiation dose.Results:At a median follow up time of about 21 months, none of the patients had experienced Grade 4 or 5 toxicity. The most common adverse effect was dermatitis (81%: 52%‐Grade 1, 28%‐Grade 2, and 1% Grade 3), followed by fatigue (48%), Cough (46%), and Esophagitis (45%), as shown in Figure 1. Severe toxicities, such as Grade 3 dermatitis or pain of skin, had a clear correlation with high radiation dose.Conclusion:Uniform scanning proton therapy is well tolerated by lung cancer patients. Preliminary analysis indicates there is correlation between severe toxicity and high radiation dose. Understanding of radiation resulted toxicities and careful choice of beam arrangement are critical in minimizing toxicity of skin and other organs.

Impact of grid size on uniform scanning and IMPT plans in XiO treatment planning system for brain cancer.

The main purposes of this study are to: 1) evaluate the accuracy of XiO treatment planning system (TPS) for different dose calculation grid size based on head phantom measurements in uniform scanning proton therapy (USPT); and 2) compare the dosimetric results for various dose calculation grid sizes based on real computed tomography (CT) dataset of pediatric brain cancer treatment plans generated by USPT and intensity‐modulated proton therapy (IMPT) techniques. For phantom study, we have utilized the anthropomorphic head proton phantom provided by Imaging and Radiation Oncology Core (IROC). The imaging, treatment planning, and beam delivery were carried out following the guidelines provided by the IROC. The USPT proton plan was generated in the XiO TPS, and dose calculations were performed for grid size ranged from 1 to 3 mm. The phantom containing thermoluminescent dosimeter (TLDs) and films was irradiated using uniform scanning proton beam. The irradiated TLDs were read by the IROC. The calculated doses from the XiO for different grid sizes were compared to the measured TLD doses provided by the IROC. Gamma evaluation was done by comparing calculated planar dose distribution of 3 mm grid size with measured planar dose distribution. Additionally, IMPT plan was generated based on the same CT dataset of the IROC phantom, and IMPT dose calculations were performed for grid size ranged from 1 to 3 mm. For comparative purpose, additional gamma analysis was done by comparing the planar dose distributions of standard grid size (3 mm) with that of other grid sizes (1, 1.5, 2, and 2.5 mm) for both the USPT and IMPT plans. For patient study, USPT plans of three pediatric brain cancer cases were selected. IMPT plans were generated for each of three pediatric cases. All patient treatment plans (USPT and IMPT) were generated in the XiO TPS for a total dose of 54 Gy (relative biological effectiveness [RBE]). Treatment plans (USPT and IMPT) of each case was recalculated for grid sizes of 1, 1.5, 2, and 2.5 mm; these dosimetric results were then compared with that of 3 mm grid size. Phantom study results: There was no distinct trend exhibiting the dependence of grid size on dose calculation accuracy when calculated point dose of different grid sizes were compared to the measured point (TLD) doses. On average, the calculated point dose was higher than the measured dose by 1.49% and 2.63% for the right and left TLDs, respectively. The gamma analysis showed very minimal differences among planar dose distributions of various grid sizes, with percentage of points meeting gamma index criteria 1% and 1 mm to be from 97.92% to 99.97%. The gamma evaluation using 2% and 2 mm criteria showed both the IMPT and USPT plans have 100% points meeting the criteria. Patient study results: In USPT, there was no very distinct relationship between the absolute difference in mean planning target volume (PTV) dose and grid size, whereas in IMPT, it was found that the decrease in grid size slightly increased the PTV maximum dose and decreased the PTV mean dose and PTV D50%. For the PTV doses, the average differences were up to 0.35 Gy (RBE) and 1.47 Gy (RBE) in the USPT and IMPT plans, respectively. Dependency on grid size was not very clear for the organs at risk (OARs), with average difference ranged from −0.61 Gy (RBE) to 0.53 Gy (RBE) in the USPT plans and from −0.83 Gy (RBE) to 1.39 Gy (RBE) in the IMPT plans. In conclusion, the difference in the calculated point dose between the smallest grid size (1 mm) and the largest grid size (3 mm) in phantom for USPT was typically less than 0.1%. Patient study results showed that the decrease in grid size slightly increased the PTV maximum dose in both the USPT and IMPT plans. However, no distinct trend was obtained between the absolute difference in dosimetric parameter and dose calculation grid size for the OARs. Grid size has a large effect on dose calculation efficiency, and use of 2 mm or less grid size can increase the dose calculation time significantly. It is recommended to use grid size either 2.5 or 3 mm for dose calculations of pediatric brain cancer plans generated by USPT and IMPT techniques in XiO TPS.PACS numbers: 87.55.D‐, 87.55.ne, 87.55.dk

SU‐E‐T‐595: Output Factor Calculation for a Uniform Scanning Proton Therapy System

Purpose:To develop an analytical model that predicts dose output factors for patient treatment fields in a uniform scanning proton therapy system.Methods:A model to predict output factors for patient specific treatment fields was produced based on the methods developed by Kooy et al. (2003). The Kooy model predicts the output factor based on the ratio of the entrance dose under calibration conditions to that for a given range and modulation corrected for the inverse square effect. Field specific output factors were plotted as a function of a single parameter r, where r = (Range‐Modulation)/Modulation. The model targeted user range 1 sub‐span 3 through user range 2 sup‐span 2 of the IBA uniform scanning proton therapy system. The data set included points measured using the 10 cm and 18 cm snout sizes to eliminate stem effects on the monitor unit chambers. The data was fit using equation 15 from Kooy et al. (2003), and the resulting model was tested against measurements that were not included in the original data set.Results:For the range and sub span investigated, 120 data points were tested against the model prediction. The model predicted the output factor within 2% for 96% of the points tested and within 2.5% for 99% of the points tested. All points were within 3% of the predicted values.Conclusion:Monitor units for patient treatment fields with proton ranges that fall within the tested interval can be predicted using a model based on the methods developed at MGH. With further evaluation, it will be possible to model all user ranges and sub‐spans of the IBA system. Further testing is also needed to predict output factors using a 25 cm snout which introduces variable scanning pattern sizes and stem effects on the monitor unit chambers.

Intensity modulated proton therapy versus uniform scanning proton therapy: Treatment planning study of the prostate cancer in patients with a unilateral metallic hip prosthesis

The purpose of this study is to compare the dosimetric results between the uniform scanning proton therapy (USPT) and intensity modulated proton therapy (IMPT) plans for the prostate cancer in patients with a unilateral metallic hip prosthesis. Five prostate cancer cases with left (n = 3) and right (n = 2) metallic hip prostheses were included in this retrospective study. For each case, the USPT and IMPT plans were generated using two anterior-oblique beams and one lateral beam for a total dose of 79.2 Gy(RBE) to be delivered in 44 fractions. For a given case, the beam parameters, dose prescription, and delivery schema in the IMPT plan were kept identical to the ones in the USPT plan. The IMPT and USPT plans were compared for various dosimetric parameters. The mean dose to the target volume was comparable. Both the IMPT and USPT techniques achieved the target coverage goals. Dose homogeneity was found to be similar in the IMPT and USPT plans. For both the rectum and bladder, the IMPT plans produced favorable dosimetric results in the low-, medium-, and high-dose regions when compared to the USPT plans. For the high dose regions, the rectal V 70 was lower in the IMPT plans by about 3.89 cc when compared to the one in the USPT plans. The rectal V 80 in the IMPT plans (1.10 cc) was almost half than the one in the USPT plans (2.39 cc). In comparison to the USPT plans, the mean dose to the rectum, bladder, and femoral head were lower in the IMPT plans by about 8.91%, 4.15%, and 41.09%, respectively. Based on the preliminary results of five cases presented in this study, the IMPT plans provided slightly better dosimetric results compared to the USPT plans, especially in sparing the rectum and bladder in the low-, medium-, and high-dose regions, for the treatment of the prostate cancer in patients with a unilateral metallic hip prosthesis. Future studies need to address the impact of the setup uncertainties and intra-fraction prostate motion in the IMPT planning of the prostate cancer patients with prosthetic hip replacements.

Daily QA in proton therapy using a single commercially available detector.

We present here a novel method for using a single device in the daily quality assurance (QA) of pencil beam scanning (PBS) proton beams and an improved method for uniform scanning (US). The device can be used to measure the spot position, spot sigma, range, output, collinearity of the X‐ray system and proton beam, and to QA the first scatterers and a number of other imaging and mechanical checks. We have performed the daily QA according to this procedure for more than six months in both a PBS gantry and a US gantry. All of the tests were found to be sensitive and accurate enough to determine if the property being tested is within the tolerance. The output has remained within the ±2% tolerance, with the majority of measurements within ±1%, and the range was within ±0.5mm. The collinearity of the proton beam in both gantries is within the ±1mm tolerance in both X and Y directions for all measurements. A novel procedure to measure the functionality of the first scatterers in the US gantry is included in the QA procedure. It was found to be sensitive enough to pick up the thinnest scatterer of 0.6 mm in both possible failure methods — when it always remains in the beam or in the case when it never goes into the beam. The daily QA procedure presented here can be implemented at PBS or US proton therapy centers with a minimal outlay for equipment and setup time. The procedure can be performed in less than 30 min, and has been found to be accurate and reliable enough for the QA of a proton therapy gantry before patient treatment every day.PACS number: 87.55.Qr

Hypofractionated Preoperative Radiation Therapy to a Partial Tumor Volume in Retroperitoneal Sarcomas (RPS): A Dosimetric Comparison Between Intensity Modulated Radiation Therapy (IMRT) and Uniform Scanning Proton Therapy (PT)

Hypofractionated Preoperative Radiation Therapy to a Partial Tumor Volume in Retroperitoneal Sarcomas (RPS): A Dosimetric Comparison Between Intensity Modulated Radiation Therapy (IMRT) and Uniform Scanning Proton Therapy (PT)

SU-E-T-170: Evaluation of Rotational Errors in Proton Therapy Planning of Lung Cancer

Purpose: To investigate the impact of rotational (roll, yaw, and pitch) errors in proton therapy planning of lung cancer. Methods: A lung cancer case treated at our center was used in this retrospective study. The original plan was generated using two proton fields (posterior-anterior and left-lateral) with XiO treatment planning system (TPS) and delivered using uniform scanning proton therapy system. First, the computed tomography (CT) set of original lung treatment plan was re-sampled for rotational (roll, yaw, and pitch) angles ranged from −5° to +5°, with an increment of 2.5°. Second, 12 new proton plans were generated in XiO using the 12 re-sampled CT datasets. The same beam conditions, isocenter, and devices were used in new treatment plans as in the original plan. All 12 new proton plans were compared with original plan for planning target volume (PTV) coverage and maximum dose to spinal cord (cord Dmax). Results: PTV coverage was reduced in all 12 new proton plans when compared to that of original plan. Specifically, PTV coverage was reduced by 0.03% to 1.22% for roll, by 0.05% to 1.14% for yaw, and by 0.10% to 3.22% for pitch errors. In comparison to original plan, the cord Dmax in new proton plans was reduced by 8.21% to 25.81% for +2.5° to +5° pitch, by 5.28% to 20.71% for +2.5° to +5° yaw, and by 5.28% to 14.47% for −2.5° to −5° roll. In contrast, cord Dmax was increased by 3.80% to 3.86% for −2.5° to −5° pitch, by 0.63% to 3.25% for −2.5° to −5° yaw, and by 3.75% to 4.54% for +2.5° to +5° roll. Conclusion: PTV coverage was reduced by up to 3.22% for rotational error of 5°. The cord Dmax could increase or decrease depending on the direction of rotational error, beam angles, and the location of lung tumor.

Treatment planning study comparing proton therapy, RapidArc and IMRT for a synchronous bilateral lung cancer case

Purpose: The main purpose of this study is to perform a treatment planning study on a synchronous bilateral non-small cell lung cancer case using three treatment modalities: uniform scanning proton therapy, RapidArc, and intensity modulated radiation therapy (IMRT). Methods : The maximum intensity projection (MIP) images obtained from the 4 dimensional-computed tomography (4DCT) scans were used for delineation of tumor volumes in the left and right lungs. The average 4D-CT was used for the treatment planning among all three modalities with identical patient contouring and treatment planning goal. A proton therapy plan was generated in XiO treatment planning system (TPS) using 2 fields for each target. For a comparative purpose, IMRT and RapidArc plans were generated in Eclipse TPS. Treatment plans were generated for a total dose of 74 CGE or Gy prescribed to each planning target volume (PTV) (left and right) with 2 CGE or Gy per fraction. In IMRT and RapidArc plans, normalization was done based on PTV coverage values in proton plans. Results: The mean PTV dose deviation from the prescription dose was lower in proton plan (within 3.4%), but higher in IMRT (6.5% to 11.3%) and RapidArc (3.8% to 11.5%) plans. Proton therapy produced lower mean dose to the total lung, heart, and esophagus when compared to IMRT and RapidArc. The relative volume of the total lung receiving 20, 10, and 5 CGE or Gy (V20, V10, and V5, respectively) were lower using proton therapy than using IMRT, with absolute differences of 9.71%, 22.88%, and 39.04%, respectively. The absolute differences in the V20, V10, and V5 between proton and RapidArc plans were 4.84%, 19.16%, and 36.8%, respectively, with proton therapy producing lower dosimetric values. Conclusion : Based on the results presented in this case study, uniform scanning proton therapy has a dosimetric advantage over both IMRT and RapidArc for a synchronous bi-lateral NSCLC, especially for the normal lung tissue, heart, and esophagus sparing. Further studies on a large group of patients with bi-lateral lung cancer are required to validate the dosimetric superiority of proton therapy over the IMRT and RapidArc. ------------------------------- Cite this article as: Rana S, Pokharel S, Zheng Y, Zhao L, Risalvato D, Vargas C, Cersonsky N. Treatment planning study comparing proton therapy, RapidArc and intensity modulated radiation therapy for a synchronous bilateral lung cancer case. Int J Cancer Ther Oncol 2014; 2 (2):020216. DOI: 10.14319/ijcto.0202.16

Proton Therapy vs. VMAT for Prostate Cancer: A Treatment Planning Study

Abstract Purpose: The main objective of this study was to compare the dosimetric quality of volumetric modulated arc therapy (VMAT) with that of proton therapy for high-risk prostate cancer. Patients and Materials: Twelve patients with high-risk prostate cancer previously treated with uniform scanning proton therapy (USPT) were included in this study. Proton planning was done using the XiO treatment planning system (TPS) with two 1800 parallel-opposed lateral fields. The VMAT planning was done using the RapidArc technique with two arcs in the Eclipse TPS. The VMAT and proton plans were calculated using the anisotropic analytical algorithm and pencil-beam algorithm, respectively. The calculated VMAT and proton plans were then normalized so that at least 95% of the planning target volume (PTV) received the prescription dose. The dosimetric evaluation was performed by comparing the physical dose-volume parameters, which were obtained from the VMAT and proton plans. Results: The average difference in the PTV ...

An anthropomorphic spine phantom for proton beam approval in NCI-funded trials.

As part of the approval process for the use of scattered or uniform scanning proton therapy in National Cancer Institute (NCI)‐sponsored clinical trials, the Radiological Physics Center (RPC) mandates irradiation of two RPC anthropomorphic proton phantoms (prostate and spine). The RPC evaluates these irradiations to ensure that they agree with the institutions' treatment plans within criteria of the NCI‐funded cooperative study groups. The purpose of this study was to evaluate the use of an anthropomorphic spine phantom for proton matched‐field irradiation, and to assess its use as a credentialing tool for proton therapy beams. We used an anthropomorphic spine phantom made of human vertebral bodies embedded in a tissue substitute material called Muscle Substitute/Solid Rigid Number 4 (MS/SR4) comprising three sections: a posterior section containing the posterior surface and the spinous processes, and left and right (L/R) sections containing the vertebral bodies and the transverse processes. After feasibility studies at three institutions, the phantom, containing two thermoluminescent dosimeters (TLDs) for absolute dose measurements and two sheets of radiochromic film for relative dosimetry, was shipped consecutively to eight proton therapy centers participating in the approval study. At each center, the phantom was placed in a supine or prone position (according to the institution's spine treatment protocol) and imaged with computed tomography (CT). The images then were used with the institution's treatment planning system (TPS) to generate two matched fields, and the phantom was irradiated accordingly. The irradiated phantom was shipped to the RPC for analysis, and the measured values were compared with the institution's TPS dose and profiles using criteria of ± 7% for dose agreement and 5 mm for profile distance to agreement. All proton centers passed the dose criterion with a mean agreement of 3% (maximum observed agreement, 7%). One center failed the profile distance‐to‐agreement criterion on its initial irradiation, but its second irradiation passed the criterion. Another center failed the profile distance‐to‐agreement criterion, but no repeat irradiation was performed. Thus, seven of the eight institutions passed the film profile distance‐to‐agreement criterion with a mean agreement of 1.2 mm (maximum observed agreement 5 mm). We conclude that an anthropomorphic spine phantom using TLD and radiochromic film adequately verified dose delivery and field placement for matched‐field treatments.PACS number: 87.55.‐x, 87.55.N‐

A Brief Note on the Limitation of Treatment Planning in Proton Therapy

Currently, proton therapy is being used for the cancer treatment at 11 centers in the United States of America [1], and there is an increasing interest in using proton therapy at many other institutions, which have proton centers either at the planning stage or under construction. [1] The primary reasons of using protons over photons for the cancer treatment is because of proton's physical properties such as finite beam range, near-zero exit dose, and sharp lateral penumbra. [2,3] Treatment planning in proton therapy is done with an aim of depositing the majority of the dose in the tumor, which is typically covered by the spread-out Bragg peak (SOBP) and avoiding the proton beam ranging into the critical structure. In uniform scanning proton therapy, the beam delivery system deposits an uniform dose for a near rectangular scanning area after the degraded proton beam is scanned laterally. [4] One of the commercially available treatment planning systems (TPS) for the uniform scanning proton therapy is XiO (CMS Inc., St. Louis, MO). The commissioning data in the XiO TPS are generally based on the measurements performed in water medium. Recently, it was reported that the XiO TPS could overestimate the lateral penumbra in uniform scanning proton therapy planning, and this study was based on the measurements done in the homogeneous (water) medium. [5] In real clinical situations, however, proton beams may pass through the inhomogeneous media consisting of tissues with different electron densities. Although the impact of heterogeneities on the measured lateral penumbra may be minimal [6], it is necessary to investigate the accuracy of TPS in predicting lateral penumbra in the presence of low-and high-density heterogeneities for various beam conditions. Additionally, it is imperative to investigate the limitation of TPS in predicting proton range for different clinical situations. The dependency of range uncertainties on the tumor location also needs further investigation since same range uncertainty value may not be applicable for all the proton beams. At present, commercially available TPS in proton therapy do not incorporate dose contribution due to secondary neutrons. [7] The results from different studies on neutron dose in proton therapy may not agree with each other due to dependency of neutron production on the treatment conditions and beam shaping components. [7] Hence, it is recommended to carry out an independent neutron study at the proton center before treating cancer patients using proton therapy technique.

Dosimetric impact of number of treatment fields in uniform scanning proton therapy planning of lung cancer.

The main purpose of this study was to perform a treatment planning study for lung cancer comparing 2-field (2F) versus 3-field (3F) techniques in uniform scanning proton therapy (USPT). Ten clinically approved lung cancer treatment plans delivered using USPT at our proton center were included in this retrospective study. All 10 lung cases included 4D computed tomography (CT) simulation. The delineation of target volumes was done based on the maximum intensity projection (MIP) images. Both the 3F and 2F treatment plans were generated for the total dose of 74 cobalt-gray-equivalent (CGE) with a daily dose of 2 CGE. 3F plan was generated by adding an extra beam in the 2F plan. Various dosimetric parameters between 2F and 3F plans were evaluated. 3F plans produced better target coverage and conformality as well as lower mean dose to the lung, with absolute difference between 3F and 2F plans within 2%. In contrast, the addition of third beam led to increase of low-dose regions (V20 and V5) in the lung in 3F plans compared to the ones in 2F plans with absolute difference within 2%. Maximum dose to the spinal cord was lower in 2F plans. Mean dose to the heart and esophagus were comparable in both 3F and 2F plans. In conclusion, the 3F technique in USPT produced better target coverage and conformality, but increased the low-dose regions in the lung when compared to 2F technique.

Impact of heterogeneities on lateral penumbra in uniform scanning proton therapy

Purpose : In the treatment planning of uniform scanning proton therapy, an aperture block is designed for each beam with a margin, which typically includes the lateral penumbra measured in water (homogenous) medium. However, during real proton therapy treatment, protons may pass through tissues of different densities within the patient's body before they are stopped. The main aim of this study was to investigate the dependency of lateral penumbra on low- and high-density heterogeneities placed in the plateau and spread-out Bragg peak (SOBP) regions. Method: The measurements were performed by placing radiographic films at the isocenter (center of SOBP), and each proton beam was delivered with 150 monitor units using standard beam conditions of the institution. Results and Conclusion: The preliminary results from this study showed that the lateral penumbra of uniform scanning proton beams was less sensitive to the inhomogeneities introduced in the protons beam path. The low-density heterogeneity in the plateau region had more impact on the lateral penumbra when compared to the low-density in the SOBP region. In contrast, the placement of high-density heterogeneity (whether in the plateau or SOBP region) produced a very minimal difference. The overall difference in lateral penumbra among different phantoms was within ±1 mm. ---------------------- Cite this article as: Rana S, Singh H. Impact of heterogeneities on lateral penumbra in uniform scanning proton therapy. Int J Cancer Ther Oncol 2013; 1 (2):01026. DOI : http://dx.doi.org/10.14319/ijcto.0102.6

SU‐E‐T‐667: Accuracy of XiO Treatment Planning System in Predicting Lateral Penumbra for Different Air Gap and Compensator Thickness in Uniform Scanning Proton Therapy

Purpose: The purpose of this study is to investigate the accuracy of XiO treatment planning system (TPS) in predicting lateral penumbra (80%‐20% distance) for different air gap (AG) and compensator thickness (COMP) in uniform scanning proton therapy. Methods: First, the dependency of lateral penumbra on AG was investigated for AG 0, 5, 10, 15, 20, 25, 30, and 35 cm using beam parameters of range (R)=16cm, modulation (M)=10cm, COMP=5cm, snout (SNT)=10, and aperture diameter(AP)=10 cm. Second, the dependency of lateral penumbra on COMP was investigated for COMP 0, 5, 10, 15, and 20 cm using beam parameters of R=30cm, M=10cm, AG=5cm, SNT=10, and AP=10cm. Dose calculations were performed in a virtual water phantom using XiO TPS with pencil beam algorithm, whereas measurements were done using solid‐water plates and EDR‐2 films. Furthermore, depth for all dose calculations and measurements was selected at the center of Spread Out Bragg Peak (SOBP), which coincided with the isocenter of the beam. The OmniPro‐I' mRT software was used to analyze the films. The lateral penumbra from the dose computations and measurements were compared for the horizontal and vertical scanning magnets. Results: Both the TPS and measurements showed an almost linear increase in lateral penumbra with increasing AG. The lateral penumbra results of TPS were larger than measurements, with difference ranged from 0.5 to 1.6 mm for horizontal scanning magnet and from 0.5 to 2.6 mm for vertical scanning magnet. The dependency of lateral penumbra on COMP was less sensitive compared to lateral penumbra versus AG. The discrepancy between lateral penumbra results of TPS and measurements for different COMP ranged from 0.2 to 0.8 mm for horizontal scanning magnet and from 0.9 to 1.7 mm for vertical scanning magnet. Conclusion: The XiO TPS over‐predicted the lateral penumbra compared with the measurements.