Stereotactic Body Radiotherapy Plans Research Articles

Predicting Survival after Liver SBRT by Deep Learning-Based Analysis of Treatment Dose Plans

Optimizing dose delivery during liver radiation therapy (RT) is critical for the success of the treatment. Modern high-dose stereotactic body RT (SBRT) has shown an increase of 3-year survival to 73% from 38% for standard RT. In practice, finding the optimal SBRT plan with all patient specific factors considered is challenging, as optimization is based on population-averaged dose-volume histograms (DVHs). In this work, we, for the first time, harness the power of deep learning to learn the relationships between 3D dosimetric treatment plans of liver patients and their survival data and then use the deep neural networks-based model to predict post-SBRT survival for new patients. A database of 125 liver SBRTs with complete follow-ups was collected at our institution. Among 125 patients, 58 were treated for liver metastases, 36 for hepatocellular carcinoma, 27 for cholangiocarcinoma, and 4 for other primary cancers. The aim was to study SBRT dose plans over liver volumes and predict which patients will be alive 2 years after the treatments. All dose plans were rescaled to 1.5 cm3 resolution and superimposed with liver mask so that only doses delivered to the livers remain. To analyze the resulting 3D dose images, we utilized the concept from deep learning – convolutional neural networks – specially developed to discover the consistent patterns in digital images. Individually for primary and metastatic cancers, the SBRTs were separated into 20 folders, and CNN performance was validated following 20-folder cross validation experiment. The deep learning model was able to discover consistent patterns in dose plans associated with negative survival prognosis. The model performance was of 0.738 and 0.660 measured in terms of area under the receiving operator characteristic curves (AUC of ROC) for primary and metastatic cases, respectively. When separated by deep learning, 58% and 27% of patients with positive and negative survival prognosis, respectively, were alive 2 years after SBRT for primary liver cancer. Similarly, 55% and 30% of patients with positive and negative survival prognosis, respectively, were alive 2 years after SBRT for metastatic liver cancer. The most negative survival prognosis for primary liver cancer is associated with irradiation of the liver segments II (risk score (RS): 0.57), V (RS: 0.68) and VIII (RS: 0.70). The most negative survival prognosis for metastatic liver cancer is associated with irradiation of the liver segments IV (RS: 0.73), V (RS: 0.64) and VI (RS: 0.61). A novel framework pioneering the concept of deep analysis of dose plans has been developed for predicting liver post-SBRT survival. The obtained results are very promising and opens a new avenue towards highly personalized RT planning.

Stereotactic body proton therapy for liver tumors: Dosimetric advantages and their radiobiological and clinical implications.

Background and PurposePhoton Stereotactic Body Radiotherapy (SBRT) for primary and metastatic tumors of the liver is challenging for larger lesions. An in silico comparison of paired SBRT and Stereotactic Body Proton Therapy (SBPT) plans was performed to understand the potential advantages of SBPT as a function of tumor size and location.Methods and materialsTheoretical tumor volumes with maximum diameter of 1–10 cm were contoured in the dome, right inferior, left medial, and central locations. SBRT and SBPT plans were generated to deliver 50 Gy in 5 fractions, max dose <135%. When organs-at-risk (OAR) constraints were exceeded, hypothetical plans (not clinically acceptable) were generated for comparison. Liver normal tissue complication probability (NTCP) models were applied to evaluate differences between treatment modalities.ResultsSBRT and SBPT were able to meet target goals and OAR constraints for lesions up to 7 cm and 9 cm diameter, respectively. SBPT plans resulted in a higher integral gross target dose for all lesions up to 7 cm (mean dose 57.8 ± 2.3 Gy to 64.1 ± 2.2 Gy, p < 0.01). Simultaneously, SBPT spared dose to the uninvolved liver in all locations (from 11.5 ± 5.3 Gy to 8.6 ± 4.4 Gy, p < 0.01), resulting in lower NTCP particularly for larger targets in the dome and central locations. SBPT also spared duodenal dose across all sizes and positions (from 7.3 ± 1.1 Gy to 1.1 ± 0.3 Gy, p < 0.05).ConclusionThe main advantages of SBPT over SBRT is meeting plan goals and constrains for larger targets, particularly dome and central locations, and sparing dose to uninvolved liver. For such patients, SBPT may allow improvements in tumor control and treatment safety.

Convex Probe EBUS-guided Fiducial Placement for Malignant Central Lung Lesions.

Stereotactic body radiotherapy (SBRT) had become a therapeutic modality in patients with primary tumors, locally recurrent as well as oligometastasis involving the lung. Some modalities of SBRT require fiducial marker (FM) for dynamic tumor tracking. Previous studies have focused on evaluating bronchoscopic-guided FM placement for peripheral lung nodules. We describe the safety and feasibility of placing FM using real-time convex probe endobronchial ultrasound (CP-EBUS) for SBRT in patients with centrally located hilar/mediastinal masses or lymph nodes. This is a retrospective review of patients who were referred to Beth Israel Deaconess Medical Center's multidisciplinary thoracic oncology program for FM placement to pursue SBRT. Thirty-seven patients who underwent real-time CP-EBUS were included. Patients had a median age of 71 years [interquartile range (IQR), 59.5 to 80.5]. The median size of the lesion was 2.2 cm (IQR, 1.4 to 3.3 cm). The median distance from the central airway was 2.4 cm (IQR, 0 to 3.4 cm). A total of 51 FMs (median of 1 per patient) were deployed in 37 patients. At the time of SBRT planning, 46 (90.2%) were confirmed radiologically in 32 patients. Patients with unsuccessful fiducial deployment (n=5) underwent a second procedure using the same technique. Of those, 3 patients had a successful fiducial placement via bronchoscopy, 1 patient required FM placement by percutaneous computed tomography-guided approach and 1 patient required FM placement through EUS by gastroenterology. CP-EBUS-guided FM placement for patients with malignant lymph nodes and central parenchymal lung lesions appears to be safe and feasible.

주요간문맥종양혈전을 동반한 간세포암에 대한 다기관 체부정위방사선치료계획 비교연구(KROG 16-17)

Background/Aims: To evaluate the technical feasibility of stereotactic body radiotherapy (SBRT) for hepatocellular carcinoma (HCC) with the major portal vein tumor thrombosis (PVTT). Methods: Ten institutions affiliated with the Korean Stereotactic Radiosurgery Group were provided the contours of four cases: the first case was the first branch PVTT with sufficient normal liver volume (NLV), the second was the first branch PVTT with insufficient NLV, the third was the main trunk PVTT at confluence level, and the fourth was the main trunk PVTT with entire length. The institutions were asked to make SBRT plans according to their current treatment protocols and to complete facility questionnaires. Results: Based on institutional protocols, SBRT was feasible in nine institutions for the first case (32-60 Gy in 3-5 fractions), in eight institutions for the second case (32-50 Gy in 3-5 fractions), in seven institutions for the third case (35-60 Gy in 3-5 fractions), and in four institutions for the fourth case (35-42 Gy in 4-5 fractions). The other institutions recommended hypo- or conventional fractionation due to insufficient NLV or gastrointestinal organ proximity. With analysis of the SBRT dose to the central hepatobiliary tract, the major PVTT could theoretically be associated with a high risk of hepatobiliary toxicity. Conclusions: Although SBRT is a technically feasible option for HCC with the major PVTT, there was a variability among the participating institutions. Therefore, further studies will be necessary to standardize the practice of SBRT for the major PVTT. (J Liver Cancer 2018;18:130-141)

ITV-Based Robust Optimization for VMAT Planning of Stereotactic Body Radiation Therapy of Lung Cancer

PurposeUsing planning target volume (PTV) to account for setup uncertainties in stereotactic body radiation therapy (SBRT) of lung cancer has been questioned because a significant portion of the PTV contains low-density lung tissue. The purpose of this study is to (1) investigate the feasibility of using robust optimization to account for setup uncertainties in volumetric modulated arc therapy plan for lung SBRT and (2) evaluate the potential normal tissue–sparing benefit of a robust optimized plan compared with a conventional PTV-based optimized plan. Methods and materialsThe study was conducted with both phantom and patient cases. For each patient or phantom, 2 SBRT lung volumetric modulated arc therapy plans were generated, including an optimized plan based on the PTV (PTV-based plan) with a 5-mm internal target volume (ITV)-to-PTV margin and a second plan based on robust optimization of ITV (ITV-based plan) with ±5-mm setup uncertainties. The target coverage was evaluated on ITV D99 in 15 scenarios that simulated a 5-mm setup error. Dose-volume information on normal lung tissue, intermediate-to-high dose spillage, and integral dose was evaluated. ResultsCompared with PTV-based plans, ITV-based robust optimized plans resulted in lower normal lung tissue dose, lower intermediate-to-high dose spillage to the body, and lower integral dose, while preserving the dose coverage under setup error scenarios for both phantom and patient cases. ConclusionsUsing ITV-based robust optimization, we have shown that accounting for setup uncertainty in SBRT planning is feasible. Further clinical studies are warranted to confirm the clinical effectiveness of this novel approach.

The dosimetric differences in calculating lung SBRT plans on different image data sets: Comparison of the free breathing scan to both the average intensity projection scan and to the sum of calculations on each respiratory phase of the 4DCT scan

The purpose of this study is to evaluate the dosimetric differences to the lung internal target volume (ITV) in stereotactic body radiation therapy (SBRT) when calculated on the free breathing (FB) scan in comparison to calculations on the average intensity projection (AIP) scan as well as the sum of dose calculated on each of the treated respiratory phases. The clinical treatment plan data for 16 SBRT lung patients were retrospectively chosen for this study, 5 of which were 30% to 70% respiratory phase gated. All patients had ITV contours and fixed monitor units from the treatment approved plan copied over to each scan on which calculations were to be made. The results of this study yielded 6 out of 16 patients with greater than or equal to 2% difference in ITV maximum dose (D0) and 2 of 16 patients with greater than or equal to 2% difference in ITV minimum dose (D100). The range of ITV dose differences for these 8 patients was 2% to 4.7% with no patients exceeding a 5% difference in D0 or D100. None of the patients had greater than or equal to 2% difference in ITV mean dose (Dmean). Sixty-three percent of patients with greater than 2% ITV dose difference in any of the categories reviewed were those patients with greater than 1 cm gross tumor motion. This study concluded that in order to reduce uncertainty in dose to the ITV, tumor motion should be assessed at simulation and limited to below 1 cm in any direction if possible.

P280] Comparison of two stereotactic body radiotherapy techniques for the treatment of prostate cancer

Purpose In this study, it has been compared the Planning Target Volume (PTV) and critical organs dose in Stereotactic Body Radiotherapy (SBRT) plans created by CyberKnife (CK) and volumetric arc radiotherapy (VMAT) techniques for patients with prostate cancer. Methods The computed tomography images of 8 patients with low or intermediate risk prostate cancer were acquired in 1 mm thickness and transferred to the MultiPlan v4.5.3 treatment planning system (TPS). The PTV and critical structures were contoured. The Clinical Target Volume (CTV) was generated by encompassing the prostate plus the 1 cm proximal part of seminal vesicles. To create the PTV, a margin of 3 mm was added in the posterior direction and 5 mm in the other directions to the CTV. The treatment plans were created with CK technique. To create the SBRT plans with the VMAT technique, the volumes were transferred to the Aria v15.1 system. The double arc VMAT plans were prepared. The prescribed dose for PTV was 33.50 Gy/5fr in both techniques. Conformity Index (CI), Homogeneity Index (HI) of PTV, critical organs doses, the integral dose (ID) to the patient body and monitor unit (MU) values were assessed using the Wilcoxon test. Results For plans created with CK and VMAT technique, CI was 1.11 ± 0.06 and 1.04 ± 0.01, HI was 1.20 ± 0.04 and 1.08 ± 0.01, respectively; there was a statistically significant difference between them. The differences between all critical organ doses except D1cc of the rectum were significant statistically in favor of VMAT. The mean of the difference of the mean right testicular dose was 137.1 cGy. It was 113.8 cGy for left testicular. MU value and the ID were found significantly to be higher in the CK technique. Conclusions The VMAT technique compared with the CK technique provides better sparing of the critical structures, and the irradiation time is shorter as the MU value is less. The less irradiation time is to be advantageous in minimizing uncertainties due to patient movement. In conclusion, the VMAT technique may be preferred, especially in young patients. This work was supported by Scientific Research Projects Coordination Unit of Istanbul University (Project Number: I.U. BAP-23057).

Dose Prediction Model for Duodenum Sparing With a Biodegradable Hydrogel Spacer for Pancreatic Cancer Radiation Therapy

We previously have shown the feasibility of duodenum sparing using a biodegradable hydrogel spacer in pancreatic cancer radiation therapy. In this study, we propose an overlap volume histogram (OVH) prediction model to select patients who might benefit from hydrogel placement and to predict the hydrogel spacing required to achieve clinical constraints. OVH metrics for the duodenum were collected from the stereotactic body radiation therapy plans of 232 patients with unresectable pancreatic cancer (33Gy in 5 fractions). OVH metrics L9cc and L3cc were defined as the tumor volume expansion distance at which 9cm3 and 3cm3 volumes of the duodenum overlap with tumor. D9cc and D3cc of the duodenum were defined as the dose-volume histogram dose to 9cm3 and 3cm3, respectively, of the duodenum. Prediction models were established by linear regression between Lx and Dx, where x=3cm3 and 9cm3. OVH thresholds were obtained for predicting the target spacer thickness. The accuracy of the prediction model was then evaluated using treatment plans on pre-and post-hydrogel injection computed tomography scans from 2 cadaver specimens and 6 patients with previously treated locally advanced pancreatic cancer with simulated spacer. Linear regression analysis showed a significant correlation between Lx and Dx (r2=0.51 and 0.51 for L3cc-D3cc and L9cc-D9cc, respectively; both P<.01). The OVH thresholds were Lˆ3cc=7mm and Lˆ9cc=13mm. The observed planning doses D3cc and D9cc of duodenum from pre-and post-hydrogel injection computed tomography scans of cadaver specimens and clinical patients with simulated spacer using predicted target spacer thickness were within the OVH model prediction range. Our model may predict which patients require placement of a hydrogel spacer before stereotactic body radiation therapy to meet predefined dose constraints. Furthermore, by predicting the required target hydrogel thickness, the spacer injection can be better guided to improve efficacy.

Mo1301 NOVEL PLATINUM FIDUCIAL SEEDS MADE IN HOUSE AND WIRE PUSH DELIVERY METHOD

Endoscopic Ultrasound (EUS) guided techniques have largely replaced percutaneous and surgical methods for fiducial implantation into deep abdominal lesions. Precise fiducial placement and detection is essential for modern stereotactic body radiation therapy (SBRT), and can be used in computed tomography (CT) and magnetic resonance imaging (MRI) for pre-treatment planning for guided radiation therapy. Gold fiducials have been used for their inertness and visibility on CT, however, platinum fiducials have recently emerged as a viable alternative. New accessories are also emerging to facilitate fiducial delivery including pre-loaded EUS fine needle implantation (FNI) needles. In this case series, we present our experience with implantation of platinum fiducials made in-house with a modified wire push technique and review the quality of pre-treatment imaging of gold coil (GC), solid gold (SG), and solid platinum seed (PS) fiducials. This single center observational case series included subjects undergoing EUS-guided fiducial implantation between January 1, 2011 and April 1, 2016 from a prospectively collected EUS database at The Ottawa Hospital (Canada). Patient demographics (age, sex), procedure details (type of fiducial), and radiologist interpretation of pre-treatment MRI/CT data (signal voids created by fiducials) was assessed using hospital records. During the study period, 17 patients underwent EUS implantation of a total of 48 fiducials with 12 patients (71%) proceeding to pre-treatment MRI/CT imaging. Pre-treatment CT scans were successful in locating the signal void in all 17 patients. Follow-up MRI showed variable results, depending on type of fiducials implanted. In the 14 patients with PS fiducials alone, 37 of 38 [98% (95% CI 92-100%)] fiducial signal voids were confirmed. For the 2 patients with only GC fiducials, a signal void was not delineated from any of the fiducials [0% (95% CI 0-39%)]. One patient received a mix, 2 PS and 2 GC fiducials, and only 2 signal voids [50% (95% CI 15-85%)] were identified. Cost analysis revealed a 20-fold decrease in price of in house made fiducials compared to commercial fiducial purchase. PS fiducials and non-preloaded fiducials were deployed by loading into the FNA needle handle and pushing fiducials through the needle using an ERCP wire. Implantation was performed by pulling the needle back while using fluoroscopy to confirm fiducial deposition. PS fiducials provide superior visibility compared to GC and SG fiducials when fused CT-MRI imaging is used for pre-treatment planning of SBRT. For SBRT in centers using fused CT-MRI imaging, PS fiducials should be the preferred choice, especially if cost-saving can be achieved with PS fiducials produced in-house. Additionally, our ERCP wire push technique is effective and less cumbersome than front-loading techniques.

Functional liver image guided hepatic therapy (FLIGHT) with hepatobiliary iminodiacetic acid (HIDA) scans

PurposeHepatobiliary iminodiacetic acid (HIDA) scans provide global and regional assessments of liver function that can serve as a road map for functional avoidance in stereotactic body radiation therapy (SBRT) planning. Functional liver image guided hepatic therapy (FLIGHT), an innovative planning technique, is described and compared with standard planning using functional dose-volume histograms. Thresholds predicting for decompensation during follow up are evaluated. Methods and materialsWe studied 17 patients who underwent HIDA scans before SBRT. All SBRT cases were replanned using FLIGHT. The following dosimetric endpoints were compared for FLIGHT versus standard SBRT planning: functional residual capacity <15 Gy (FRC15HIDA), mean liver dose (MLD), equivalent uniform dose (EUD), and functional EUD (FEUD). Receiver operating characteristics curves were used to evaluate whether baseline HIDA values, standard cirrhosis scoring, and/or dosimetric data predicted clinical decompensation. ResultsCompared with standard planning, FLIGHT significantly improved FRC15HIDA (mean improvement: 5.3%) as well as MLD, EUD, and FEUD (P < .05). Considerable interindividual variations in the extent of benefit were noted. Decompensation during follow-up was associated with baseline global HIDA <2.915%/min/m2, FRC15HIDA <2.11%/min/m2, and MELD ≥11 (P < .05). ConclusionsFLIGHT with HIDA-based parameters may complement blood chemistry-based assessments of liver function and facilitate individualized, adaptive liver SBRT planning.

Dosimetric Implications of Computerised Tomography-Only versus Magnetic Resonance-Fusion Contouring in Stereotactic Body Radiotherapy for Prostate Cancer.

Background: Magnetic resonance (MR)-fusion contouring is the standard of care in prostate stereotactic body radiotherapy (SBRT) for target volume localisation. However, the planning computerised tomography (CT) scan continues to be used for dose calculation and treatment planning and verification. Discrepancies between the planning MR and CT scans may negate the benefits of MR-fusion contouring and it adds a significant resource burden. We aimed to determine whether CT-only contouring resulted in a dosimetric detriment compared with MR-fusion contouring in prostate SBRT planning. Methods: We retrospectively compared target volumes and SBRT plans for 20 patients treated clinically with MR-fusion contouring (standard of care) with those produced by re-contouring using CT data only. Dose was 36.25 Gy in 5 fractions. CT-only contouring was done on two occasions blind to MR data and reviewed by a separate observer. Primary outcome was the difference in rectal volume receiving 36 Gy or above. Results: Absolute target volumes were similar: 63.5 cc (SD ± 27.9) versus 63.2 (SD ± 26.5), Dice coefficient 0.86 (SD ± 0.04). Mean difference in apex superior-inferior position was 1.1 (SD ± 3.5; CI: −0.4–2.6). Small dosimetric differences in favour of CT-only contours were seen, with the mean rectal V36 Gy 0.3 cc (95% CI: 0.1–0.5) lower for CT-only contouring. Conclusions: Prostate SBRT can be successfully planned without MR-fusion contouring. Consideration can be given to omitting MR-fusion from the prostate SBRT workflow, provided reference to diagnostic MR imaging is available. Development of MR-only work flow is a key research priority to gain access to the anatomical fidelity of MR imaging.

Technical Note: A planning technique to lower normal tissue toxicity in lung SBRT plans based on two likely dependent RTOG metrics.

Intermediate- and low-dose falloff in stereotactic body radiotherapy (SBRT) of lung tumor is known to relate to normal tissue toxicity. The purpose is twofold to analyze the relation between RTOG parameters (namely, R50%, D2cm) in lung SBRT plans and to explore planning methods that correlate with higher than acceptable dose to normal tissue. RTOG recommended target dose coverage, conformity index, homogeneity index, R50%, and D2cm were evaluated retrospectively in 105 lung tumor SBRT plans. Deviations in R50% and D2cm were correlated with parameters including prescription dose, tumor location, number of beams or arcs, beam configuration (coplanar or noncoplanar), type of treatment plan (3D-CRT, IMRT or volumetric arc therapy), and shortest distance to the chest wall. All plans met the target coverage, conformity index, homogeneity index, and critical organ dose tolerance objectives. Dose falloff product (DFP) of R50% and D2cm has a small variance and small dependence on PTV. Low correlation between DFP and PTV suggests that R50% and D2cm are not independent. Coplanar beam placement was found to be prevalent among plans with large deviations in R50%, D2cm. This study questions the independence of the two RTOG recommended metrics, R50% and D2cm in lung SBRT plans, and suggests that noncoplanar beams may provide better normal tissue sparing by reducing the intermediate dose falloff.

A Dose Falloff Gradient Study in RapidArc Planning of Lung Stereotactic Body Radiation Therapy.

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.

Single fraction computed tomography-guided high-dose-rate brachytherapy or stereotactic body radiotherapy for primary and metastatic lung tumors?

PurposeTo provide a pilot dosimetric study of computed tomography (CT)-guided high-dose-rate (HDR) brachytherapy (BRT) and stereotactic body radiotherapy (SBRT) for primary and metastatic lung lesions.Material and methodsFor nine lung primary and metastasis patients, 3D image-based BRT plan using a single virtual catheter was planned for 34 Gy in single fraction to the gross tumor volume (GTV) + 3 mm margin to account for tumor deformation. These plans were compared to margin-based (MB-) and robustness optimized (RO-) SBRT, assuming the same tumor deformation under real-time tumor tracking. Consistent dose calculation was ensured for both BRT and SBRT plans using the same class of collapsed cone convolution superposition algorithm. Plan quality metrics were compared by Friedman tests and Wilcoxon t-tests.Results and ConclusionsBrachytherapy plans showed significant higher GTV mean dose compared to MB- and RO-SBRT (122.2 Gy vs. 50.4 and 44.7 Gy, p < 0.05), and better dose gradient index (R50) = 2.9 vs. 4.3 and 8.4 for MB- and RO-SBRT, respectively. Dose constraints per the RTOG 0915 protocol were achieved for all critical organs except chest wall in BRT. All other dose-volume histograms (DVH) metrics are comparable between BRT and SBRT. Treatment delivery time of BRT and SBRT plans significantly increased and decreased with increasing GTV size, respectively. SBRT using advanced MLC tracking technique and non-coplanar VMAT can achieve comparable dosimetric quality to HDR BRT. Whether or not, the significantly higher GTV dose can increase killing of radioresistant tumor cells and offset the effect of tumor reoxygenation in single fraction BRT, requires further clinical investigation.

Evaluating which plan quality metrics are appropriate for use in lung SBRT.

Several dose metrics in the categories-homogeneity, coverage, conformity and gradient have been proposed in literature for evaluating treatment plan quality. In this study, we applied these metrics to characterize and identify the plan quality metrics that would merit plan quality assessment in lung stereotactic body radiation therapy (SBRT) dose distributions. Treatment plans of 90 lung SBRT patients, comprising 91 targets, treated in our institution were retrospectively reviewed. Dose calculations were performed using anisotropic analytical algorithm (AAA) with heterogeneity correction. A literature review on published plan quality metrics in the categories-coverage, homogeneity, conformity and gradient was performed. For each patient, using dose-volume histogram data, plan quality metric values were quantified and analysed. For the study, the radiation therapy oncology group (RTOG) defined plan quality metrics were: coverage (0.90 ± 0.08); homogeneity (1.27 ± 0.07); conformity (1.03 ± 0.07) and gradient (4.40 ± 0.80). Geometric conformity strongly correlated with conformity index (p < 0.0001). Gradient measures strongly correlated with target volume (p < 0.0001). The RTOG lung SBRT protocol advocated conformity guidelines for prescribed dose in all categories were met in ≥94% of cases. The proportion of total lung volume receiving doses of 20 Gy and 5 Gy (V20 and V5) were mean 4.8% (±3.2) and 16.4% (±9.2), respectively. Based on our study analyses, we recommend the following metrics as appropriate surrogates for establishing SBRT lung plan quality guidelines-coverage % (ICRU 62), conformity (CN or CIPaddick) and gradient (R50%). Furthermore, we strongly recommend that RTOG lung SBRT protocols adopt either CN or CIPadddick in place of prescription isodose to target volume ratio for conformity index evaluation. Advances in knowledge: Our study metrics are valuable tools for establishing lung SBRT plan quality guidelines.

Investigation the impact of maximum control point on dose calculation in Eclipse treatment planning system for lung SBRT

Purpose: Choosing an appropriate parameter on the computerized treatment planning systems (TPSs) influences on the accuracy of dose calculation. Several dosimetric parameters have been studied to achieve a more accurate dose and qualitative plan. The purpose of this study was to determine the impact of maximum control point on the dose calculation on Eclipse TPSs for lung Stereotactic Body Radiation Therapy (SBRT) considering the plan quality, the computation time and the treatment file size. Methods: Dose distributions for the 8 lung SBRT plans with varying maximum control point of 64, 166, and 320 were calculated by Eclipse TPSs with flattening filter free (FFF) beam. The treatment dose was prescribed at 85% isodose level of 54 Gy to the planning target volume (PTV). The dosimetric impact can be evaluated from target coverage, conformity index (CI), homogeneity index (HI), and organ at risk (OAR) doses, while the computation time and the file storage space were compared with the recommended number of control point. Results: The use of 64 control points per subfields tended to increase the dose at PTV and OARs comparing with the 166 and 320 control point plans, while the HI and CI values were similar. The average increases of OARs doses including the spinal cord, heart, esophagus and total lung depended on the photon beam energy. The higher average control point (AVG) number leaded to increase the computation time and the file size for both 6X-FFF and 10X-FFF photon beams. The correlations between AVG and plan storaage space were observed in the same ratio as the computation time. Conclusion: Using the minimal number of control point, the quantitative analysis in the PTV and OARs showed no clinically significant variation in dose, therefore choosing an optimal number of fixed control points leaded to balance the plan quality, the computation time and the file size.

Noninvasive Cardiac Radiation for Ablation of Ventricular Tachycardia

BackgroundRecent advances have enabled noninvasive mapping of cardiac arrhythmias with electrocardiographic imaging and noninvasive delivery of precise ablative radiation with stereotactic body radiation therapy (SBRT). We combined these techniques to perform catheter-free, electrophysiology-guided, noninvasive cardiac radioablation for ventricular tachycardia.MethodsWe targeted arrhythmogenic scar regions by combining anatomical imaging with noninvasive electrocardiographic imaging during ventricular tachycardia that was induced by means of an implantable cardioverter–defibrillator (ICD). SBRT simulation, planning, and treatments were performed with the use of standard techniques. Patients were treated with a single fraction of 25 Gy while awake. Efficacy was assessed by counting episodes of ventricular tachycardia, as recorded by ICDs. Safety was assessed by means of serial cardiac and thoracic imaging.ResultsFrom April through November 2015, five patients with high-risk, refractory ventricular tachycardia underwent treatment. The mean noninvasive ablation time was 14 minutes (range, 11 to 18). During the 3 months before treatment, the patients had a combined history of 6577 episodes of ventricular tachycardia. During a 6-week postablation “blanking period” (when arrhythmias may occur owing to postablation inflammation), there were 680 episodes of ventricular tachycardia. After the 6-week blanking period, there were 4 episodes of ventricular tachycardia over the next 46 patient-months, for a reduction from baseline of 99.9%. A reduction in episodes of ventricular tachycardia occurred in all five patients. The mean left ventricular ejection fraction did not decrease with treatment. At 3 months, adjacent lung showed opacities consistent with mild inflammatory changes, which had resolved by 1 year.ConclusionsIn five patients with refractory ventricular tachycardia, noninvasive treatment with electrophysiology-guided cardiac radioablation markedly reduced the burden of ventricular tachycardia. (Funded by Barnes–Jewish Hospital Foundation and others.)

Modeling the target dose fall-off in IMRT and VMAT planning techniques for cervical SBRT

There has been growing interest in the use of stereotactic body radiotherapy (SBRT) technique for the treatment of cervical cancer. The purpose of this study was to characterize dose distributions as well as model the target dose fall-off for intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) delivery techniques using 6 and 10 MV photon beam energies. Fifteen (n = 15) patients with non-bulky cervical tumors were planned in Pinnacle3 with a Varian Novalis Tx (HD120 MLC) using 6 and 10 MV photons with the following techniques: (1) IMRT with 10 non-coplanar beams (2) dual, coplanar 358° VMAT arcs (4° spacing), and (3) triple, non-coplanar VMAT arcs. Treatment volumes and dose prescriptions were segmented according to University of Texas Southwestern (UTSW) Phase II study. All plans were normalized such that 98% of the planning target volume (PTV) received 28 Gy (4 fractions). For the PTV, the following metrics were evaluated: homogeneity index, conformity index, D2cc, Dmean, Dmax, and dose fall-off parameters. For the organs at risk (OARs), D2cc, D15cc, D0.01cc, V20, V40, V50, V60, and V80 were evaluated for the bladder, bowel, femoral heads, rectum, and sigmoid. Statistical differences were evaluated using a Friedman test with a significance level of 0.05. To model dose fall-off, expanding 2-mm-thick concentric rings were created around the PTV, and doses were recorded. Statistically significant differences (p < 0.05) were noted in the dose fall-off when using 10 MV and VMAT3-arc, as compared with IMRT. VMAT3-arc improved the bladder V40, V50, and V60, and the bowel V20 and V50. All fitted regressions had an R2 ≥ 0.98. For cervical SBRT plans, a VMAT3-arc approach offers a steeper dose fall-off outside of the target volume. Faster dose fall-off was observed in smaller targets as opposed to medium and large targets, denoting that OAR sparing is dependent on target size. These improvements are further pronounced with the use of 10-MV photons.

Compass model-based quality assurance for stereotactic VMAT treatment plans

PurposeTo use Compass as a model-based quality assurance (QA) tool for stereotactic body radiation therapy (SBRT) and stereotactic radiation therapy (SRT) volumetric modulated arc therapy (VMAT) treatment plans calculated with Eclipse treatment planning system (TPS). Materials and methodsTwenty clinical stereotactic VMAT SBRT and SRT treatment plans were blindly selected for evaluation. Those plans included four different treatment sites: prostate, brain, lung and body. The plans were evaluated against dose-volume histogram (DVH) parameters and 2D and 3D gamma analysis. The dose calculated with Eclipse treatment planning system (TPS) was compared to Compass calculated dose (CCD) and Compass reconstructed dose (CRD). ResultsThe maximum differences in mean dose of planning target volume (PTV) were 2.7 ± 1.0% between AAA and Acuros XB calculation algorithm TPS dose, −7.6 ± 3.5% between Eclipse TPS dose and CCD dose and −5.9 ± 3.7% between Eclipse TPS dose and CRD dose for both Eclipse calculation algorithms, respectively. 2D gamma analysis was not able to identify all the cases that 3D gamma analysis specified for further verification. ConclusionsCompass is suitable for QA of SBRT and SRT treatment plans. However, the QA process should include wide set of DVH-based dose parameters and 3D gamma analysis should be the preferred method when performing clinical patient QA. The results suggest that the Compass should not be used for smaller field sizes than 3 × 3 cm2 or the beam model should be adjusted separately for both small (FS ≤ 3 cm) and large (FS > 3 cm) field sizes.

Helical Therapy is Safe for Lung Stereotactic Body Radiation Therapy Despite Limitations in Achieving Sharp Dose Gradients.

Purpose:We observed that many of our helical therapy lung stereotactic body radiation therapy plans did not meet the Radiation Therapy Oncology Group (RTOG) recommended R50% (volume of 50% of the prescription dose/planning target volume), which characterizes the steepness of dose fall off. We hypothesized that despite not meeting R50%, helical therapy lung stereotactic body radiation therapy plans would confer similar local control and minimal side effects as previously reported using nonhelical treatment platforms.Materials and Methods:We report a retrospective review of all consecutive patients treated off-protocol with stereotactic body radiation therapy for peripheral lung lesions from 2008 to 2013 utilizing helical therapy. Seventy-four patients (81 lesions and 79 plans) were treated with doses ranging from 48 to 60 Gy in 3 to 5 fractions prescribed to the edge of the planning target volume.Results:Forty-eight (61%) plans had major deviation from R50%. Only 1 (<1%) plan had a major deviation from the R100%. All plans had > 95% planning target volume coverage by prescription dose, 7(8.6%) plans with 121% to 133% maximum dose, and lung V20 Gy <10% in 70 (89%) plans. With a median follow-up of 4.7 years (95% confidence interval: 4.1-5.3), local control for all patients at 1, 2, and 5 years was 94.6%, 83.4%, and 74%, respectively. For patients with primary stage I-II lung cancer (n = 46), the 1, 2, and 5-year local control: 97.2%, 94.2%, and 86.9%; RC: 97.6%, 82.5%, and 69.5%; and DM: 3%, 16%, and 33.4%, respectively. Patients treated for lung metastases (n = 26) had worse local control at 1, 2, and 5 years: 94.4%, 69.3%, and 55.5%, respectively. Side effects were rare with 2 (3%) patients reporting chest wall pain and 6 (8%) patients experiencing radiation pneumonitis, including 1 patient who had grade 5 radiation pneumonitis.Conclusions:Helical therapy delivers a safe and effective lung stereotactic body radiation therapy plan, despite not being able to meet RTOG’s recommended R50 conformality constraint.