Optimization of stereotactic body radiotherapy treatment planning using a multicriteria optimization algorithm

The goal of this study was to evaluate the use of multi-criteria optimization (MCO) in the planning and optimization of intensity-modulated radiotherapy (IMRT). Twenty (20) IMRT patients (ten (10) with prostate cancer and ten (10) with lung cancer) were randomly selected. The treatment plans for these patients were designed using direct machine parameter optimization (DMPO). Based on these plans, new plans were designed using multi-criteria optimization (MCO), keeping the optimization objectives and constraints unchanged. Comparisons were made between the new plans, which were based on MCO and DMPO, including the dose distribution, dose volume histogram (DVH), the optimization time and the number of monitor units (MUs). The plan designed using both optimization approaches satisfied all clinical requirements. For similar or better target coverage, the rectum, bladder and small bowel were better protected using MCO than when using DMPO. Additionally, MCO reduced the time for optimization by 58% on average, whereas the MUs increased the time for optimization by 32% on average for prostate cancer. For lung cancer cases, the entire lung, heart and spinal cord were better protected using MCO compared to DMPO. Similarly, MCO reduced the time for optimization by 59% on average, whereas the MUs increased the time for optimization by 11% on average. Compared to DMPO, MCO reduces the dose of the organs at risk (OAR) and shortens the time required for optimization.

Functional image-guided stereotactic body radiation therapy planning for patients with hepatocellular carcinoma

Helical Tomotherapy-Based STAT Stereotactic Body Radiation Therapy: Dosimetric Evaluation for a Real-Time SBRT Treatment Planning and Delivery Program

Objective The aim of this study was to evaluate the role of multicriteria optimization (MCO) in planning of intensity-modulated radiotherapy (IMRT).Methods Twenty IMRT patients (ten with prostate and ten with lung cancers) were randomly selected.For these patients,the treatment plans were designed with direct machine parameter optimization (DMPO).Based on these plans,new plans were designed with MCO,while keeping the setting conditions unchanged.Comparison was made between the two plans including the dose distribution,the dose volume histogram,the time of optimization and number of monitor unit (MU),but were play by pairing-t test.Results The plan designed in both optimizations satisfied all clinical requirements.For the same or better target coverage,rectum,bladder and small bowel were better with MCO compared with DMPO,MCO reduced 58％ of the time for optimization by average while MU increased 32％ by average for prostate cancer.For lung cancer,the whole lung,heart and spinal cord were better with MCO compared with DMPO,MCO reduced 59％ of the time for optimization by average while MU increased 11％ by average.Conclusions In comparison with DMPO,MCO reduces the dose of organs at risk,shorten the time of optimization. Key words: Multicriteria optimization; Direct machine parameter optimization; Intensity-modulated radiotherapy planning

PurposeTo investigate the effect of computed tomography (CT) using hepatic arterial phase (HAP) and portal venous phase (PVP) contrast on dose calculation of stereotactic body radiation therapy (SBRT) for liver cancer.MethodsTwenty-one patients with liver cancer were studied. HAP, PVP and non-enhanced CTs were performed on subjects scanned in identical positions under active breathing control (ABC). SBRT plans were generated using seven-field three-dimensional conformal radiotherapy (7 F-3D-CRT), seven-field intensity-modulated radiotherapy (7 F-IMRT) and single-arc volumetric modulated arc therapy (VMAT) based on the PVP CT. Plans were copied to the HAP and non-enhanced CTs. Radiation doses calculated from the three phases of CTs were compared with respect to the planning target volume (PTV) and the organs at risk (OAR) using the Friedman test and the Wilcoxon signed ranks test.ResultsSBRT plans calculated from either PVP or HAP CT, including 3D-CRT, IMRT and VMAT plans, demonstrated significantly lower (p <0.05) minimum absorbed doses covering 98%, 95%, 50% and 2% of PTV (D98%, D95%, D50% and D2%) than those calculated from non-enhanced CT. The mean differences between PVP or HAP CT and non-enhanced CT were less than 2% and 1% respectively. All mean dose differences between the three phases of CTs for OARs were less than 2%.ConclusionsOur data indicate that though the differences in dose calculation between contrast phases are not clinically relevant, dose underestimation (IE, delivery of higher-than-intended doses) resulting from CT using PVP contrast is larger than that resulting from CT using HAP contrast when compared against doses based upon non-contrast CT in SBRT treatment of liver cancer using VMAT, IMRT or 3D-CRT.

Dosimetric Advantages of Proton Beam Stereotactic Body Radiation Therapy for Liver Tumors

Proton Beam Radiotherapy Versus Three-Dimensional Conformal Stereotactic Body Radiotherapy in Primary Peripheral, Early-Stage Non–Small-Cell Lung Carcinoma: A Comparative Dosimetric Analysis

Dosimetric Implication of Neural Planning Organ at Risk Volumes in Stereotactic BodyRadiation Therapy of the Spine

Purpose:The 4π non‐coplanar radiotherapy delivery technique has demonstrated significantly better normal tissue sparing and dose conformality than the clinically used volumetric modulated arc therapy (VMAT). It is unclear whether this is a fundamental limitation of VMAT delivery or the coplanar nature of its typical clinical plans. The non‐coplanar basis of 4π is incorporated into VMAT treatment planning to compare its effect on plan quality.Methods:Clinical stereotactic body radiation therapy plans for 9 liver patients treated with 30–60 Gy using coplanar VMAT (cVMAT) were re‐planned using non‐coplanar VMAT (nVMAT) with 3 arcs and 4 π with 20 intensity‐modulated non‐coplanar fields. All plans were optimized to deliver 100% of the prescribed dose to 95% of the planning target volume (PTV), and nVMAT and 4π plans were tailored to match the maximum and mean PTV dose from the clinical plan. The conformality index (CI), 50% dose spillage volume (R50), normal liver volume receiving &gt;15 Gy (VL&gt;15), and doses to organs at risk (OARs) were compared for all three treatment plans.Results:Compared to cVMAT, the nVMAT and 4π plans reduced VL&gt;15 by an average of 30.6 cm3 and 96.3 cm3, respectively. The average CI was also reduced from 1.22 (cVMAT) to 1.17 (nVMAT) and 1.14 (4π), indicating higher conformality in the same order. Similarly, R50 was reduced from 3.87 (cVMAT) to 3.58 (nVMAT) and 2.74 (4π). With the exception of the mean right kidney dose, which increased by an average of only 0.6 Gy for nVMAT, the dose differences to OARs were not statistically significant between the two VMAT plans. 4π plans either significantly decreased or maintained OAR doses.Conclusion:While the manual selection of intuitive non‐coplanar arcs does show some improvement over coplanar VMAT, the automated beam selection for 4π still results in superior plan quality.This project is supported in part by Varian Medical Systems and NIH R43 CA183390.

Introduction:Radiation Therapy Oncology Group (RTOG) report #0813 and 0915 recommends using D2cm and R50% as plan quality metrics for evaluation of normal tissue sparing in stereotactic body radiation therapy (SBRT) of lung lesion. This study introduces dose falloff gradient (DFG) as a tool for analyzing the dose beyond the planning target volume (PTV) extending into normal tissue structures. In ascertaining the impact of PTV size and SBRT planning techniques in DFG, this study questions the independence of the RTOG recommended metrics.Materials and Methods:In this retrospective study, 41 RapidArc lung SBRT plans with 2 or 3 complete or partial arcs were analyzed. PTV volumes ranged between 5.3 and 113 cm3 and their geographic locations were distributed in both lungs. 6MV, 6 MV-FFF, 10 MV, or 10 MV-FFF energies were used. RTOG-0915 metrics conformity index, homogeneity index, D2cm, R50%, and HDloc were evaluated. DFG was computed from the mean and maximum dose in seven concentric 5 mm wide rings outside the PTV. DFG was investigated against the volume of normal lung irradiated by 50% isodose volume. Treatment plans with alternate energy and couch rotations were generated.Results:The dose falloff beyond PTV was modeled using a double exponential fit and evaluated for relationship with intermediate lung dose. Photon energy and beam configuration had a minimal impact on the dose falloff outside. The product of normalized D2cm and R50% was estimated to have a slowly varying value.Conclusions:Dose falloff outside PTV has been studied as a function of radial distance and ascertained by intermediate dose to normal lung. DFG can serve as a complementary plan quality metric.

Risk of Hepatobiliary Toxicity After SBRT to the Liver for Central Liver Tumors

Dosimetric Comparison of Volumetric Modulated Arc Therapy (VMAT) with and without Flattening Filter for Stereotactic Body Radiation Therapy (SBRT) in Localised Prostate Cancer

Single or few are intensity-modulated arc therapy (IMAT) is intended to be a time saving irradiation method, potentially replacing classical intensity-modulated radiotherapy (IMRT). The aim of this work was to evaluate the quality of different IMAT methods with the potential of fast delivery, which also has the possibility of adapting to the daily shape of the target volume. A planning study was performed. Novel double and triple IMAT techniques based on the geometrical analysis of the target organ at risk geometry (2-step IMAT) were evaluated. They were compared to step and shoot IMRT reference plans generated using direct machine parameter optimization (DMPO). Volumetric arc (VMAT) plans from commercial preclinical software (SMARTARC) were used as an additional benchmark to classify the quality of the novel techniques. Four cases with concave planning target volumes (PTV) with one dominating organ at risk (OAR), viz., the PTV/OAR combination of the ESTRO Quasimodo phantom, breast/lung, spine metastasis/ spinal cord, and prostate/rectum, were used for the study. The composite objective value (COV) and other parameters representing the plan quality were studied. The novel 2-step IMAT techniques with geometry based segment definition were as good as or better than DMPO and were superior to the SMARTARC VMAT techniques. For the spine metastasis, the quality measured by the COV differed only by 3%, whereas the COV of the 2-step IMAT for the other three cases decreased by a factor of 1.4-2.4 with respect to the reference plans. Rotational techniques based on geometrical analysis of the optimization problem (2-step IMAT) provide similar or better plan quality than DMPO or the research version of SMARTARC VMAT variants. The results justify pursuing the goal of fast IMAT adaptation based on 2-step IMAT techniques.

Purpose/objectiveOnline adaptive radiotherapy (ART) with daily MR imaging can improve dosimetric accuracy by accounting for anatomical changes throughout the course of treatment. Existing daily ART prostate studies have diverse conclusions, but most of these studies do not include simultaneous integrated boosts (SIBs) to the dominant intraprostatic lesion, which has shown an increase in biochemical disease-free survival. The purpose of this study is to evaluate the potential dosimetric benefits of daily ART with SIB to the dominant intraprostatic lesion and other targets, as well as the potential sparing of organs-at-risk (OARs) for prostate cancer, and to compare these results with those reported in other published studies.Materials/methodsThirteen patients with prostate cancer treated with MR-guided stereotactic body radiotherapy (SBRT) were included in this study. The prescribed dose to the planning target volume (PTV) was 36.25 Gy in five fractions. The prescription to the intraprostatic boost to the gross tumor volume (GTV) ranged between 40 and 45 Gy. All SBRT fractions employed daily MR-guided setup, and OARs included the bladder, anorectum, bowel, femoral heads, and penile bulb. Daily MRIs and associated contours were used to create adapted treatment plans. For each simulated adapted fraction, the plan was re-optimized based on the contours from the daily setup MRI. Dosimetric metrics for non-adaptive fractions were simulated by re-calculating the dose on each daily setup MRI. PTV and GTV coverage and OAR constraints were used to compare non-adaptive and adaptive approaches.ResultsPTV coverage at the prescription dose level exceeded 90% in 35 out of 64 non-adapted treatment fractions (55%). Conversely, 29 fractions (45%) had less than 90% coverage, with 12 fractions (19%) showing coverage below 85%. The clinical target volume (CTV) coverage was greater than 95% in 52/64 fractions and was below 90% coverage in only 1/64 fractions (1.5%). GTV coverage at the boost dose level ranged from 55% to 100%, with 38 out of 74 fractions (51%) achieving 90% or greater coverage at the prescribed dose. A substantial number of fractions 27/74 (36%) had coverage below 85%, with a handful of fractions exhibiting less than 70% coverage, 5/74 fractions or 7%. All adapted fractions met prescribed coverage for the GTV, CTV, and PTV. Additionally, OAR constraint violations were evaluated and compared for the bladder and anorectum. Very few OAR constraints were exceeded in the non-adaptive setting, and none were exceeded in the adaptive setting. The anorectum dose constraint was exceeded in 22% of the non-adaptive fractions, while all adaptive fractions met the prescribed constraint. All non-adaptive and adaptive fractions met the prescribed bladder dose constraints; however, the adaptive fractions demonstrated some degree of bladder sparing compared to the non-adaptive fractions. Accumulated dose volume histograms were also generated for each patient to evaluate cumulative differences in target coverage and OAR sparing.ConclusionOnline adaptive MR-guided SBRT for prostate cancer, utilizing daily plan re-optimization, resulted in improved target conformality, enhanced coverage, and increased OAR sparing compared to non-adaptive SBRT. The primary benefit observed was improved GTV coverage. Daily adaptive planning enables satisfactory GTV coverage without the need for added margins, while also providing better OAR sparing.

Purpose:The dose difference between three‐dimensional dose (3D dose) and 4D dose which considers motion due to respiratory can be varied according to geometrical relationship between planning target volume (PTV) and organ at risk (OAR). The purpose of the study is to investigate the dose difference between 3D and 4D dose using overlap volume histogram (OVH) which is an indicator that quantify geometrical relationship between a PTV and an OAR.Methods:Five liver cancer patients who previously treated stereotactic body radiotherapy (SBRT) were investigated. Four‐dimensional computed tomography (4DCT) images were acquired for all patients. ITV‐based treatment planning was performed. 3D dose was calculated on the end‐exhale phase image as a reference phase image. 4D dose accumulation was implemented from all phase images using dose warping technique used deformable image registration (DIR) algorithm (Horn and Schunck optical flow) in DIRART. In this study OVH was used to quantify geometrical relationship between a PTV and an OAR. OVH between a PTV and a selected OAR was generated for each patient case and compared for all cases. The dose difference between 3D and 4D dose for normal organ was calculated and compared for all cases according to OVH.Results:The 3D and 4D dose difference for OAR was analyzed using dose‐volume histogram (DVH). On the basis of a specific point which corresponds to 10% of OAR volume overlapped with expanded PTV, mean dose difference was 34.56% in minimum OVH distance case and 13.36% in maximum OVH distance case. As the OVH distance increased, mean dose difference between 4D and 3D dose was decreased.Conclusion:The tendency of dose difference variation was verified according to OVH. OVH is seems to be indicator that has a potential to predict the dose difference between 4D and 3D dose.This work was supported by the Radiation Technology R&amp;D program (No. 2013M2A2A7043498) and the Mid‐career Researcher Program (2014R1A2A1A10050270) through the National Research Foundation of Korea funded by the Ministry of Science, ICT&amp;Future Planning.