scholarly journals How Does the Gradient Measure of the Lung SBRT Treatment Plan Depend on the Tumor Volume and Shape?

2021 ◽  
Vol 11 ◽  
Author(s):  
Yanhua Duan ◽  
Yang Lin ◽  
Hao Wang ◽  
Bodong Kang ◽  
Aihui Feng ◽  
...  

PurposeGradient measure (GM) is a critical index related to normal tissue sparing in radiosurgery. This study aims to describe the dependence of GM on target volume and target shape for lung stereotactic body radiation therapy (SBRT) treatment plans.MethodsA total of 307 peripheral and 119 central lung SBRT treatment plans were enrolled for this study. A least-squares regression was used for data analysis. First, the equations with different functional forms were established to determine the dependence of GM on a univariaty (VP or Sp) and bivariaty (VP and Sp), respectively. Then, the correlation coefficients and p-values of variables for all equations were compared and analyzed to determine the dependence of GM on PTV volume (VP) and sphericity (Sp).ResultsThe power equations had the highest coefficient of determination (R2) in the dependence results of GM on univariate VP. The equations were GM=0.674VP0.178 and GM=0.660VP0.185 for peripheral and central lesions, respectively. On the other hand, the R2 of all functional forms were less than 0.25 when the relationship of GM versus univariate Sp was analyzed. Similarly, the power equation also obtained the highest R2 in bivariaty VP and Sp analysis, whether for central or peripheral. However, the R2 of the bivariate equations were not improved compared with those of univariate equations. Moreover, the p-values of the variable Sp were greater than 0.05.ConclusionsThe GM of the lung SBRT plan is shape-independent and volume-dependent. The dependence of GM on PTV volume for peripheral and central lung cancer can be described by two different power equations. The results of this study can be used as a potential tool to assist dosimetric quality control during the radiosurgery process.

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Margherita Casiraghi ◽  
Reinhard W. Schulte

Treatment planning for particle therapy is currently an active field of research due uncertainty in how to modify physical dose in order to create a uniform biological dose response in the target. A novel treatment plan optimization strategy based on measurable nanodosimetric quantities rather than biophysical models is proposed in this work. Simplified proton and carbon treatment plans were simulated in a water phantom to investigate the optimization feasibility. Track structures of the mixed radiation field produced at different depths in the target volume were simulated with Geant4-DNA and nanodosimetric descriptors were calculated. The fluences of the treatment field pencil beams were optimized in order to create a mixed field with equal nanodosimetric descriptors at each of the multiple positions in spread-out particle Bragg peaks. For both proton and carbon ion plans, a uniform spatial distribution of nanodosimetric descriptors could be obtained by optimizing opposing-field but not single-field plans. The results obtained indicate that uniform nanodosimetrically weighted plans, which may also be radiobiologically uniform, can be obtained with this approach. Future investigations need to demonstrate that this approach is also feasible for more complicated beam arrangements and that it leads to biologically uniform response in tumor cells and tissues.


2022 ◽  
Author(s):  
Jing Shen ◽  
Yinjie TAO ◽  
Hui GUAN ◽  
Hongnan ZHEN ◽  
Lei HE ◽  
...  

Abstract Purpose Clinical target volumes (CTV) and organs at risk (OAR) could be auto-contoured to save workload. The goal of this study was to assess a convolutional neural network (CNN) for totally automatic and accurate CTV and OAR in prostate cancer, while also comparing anticipated treatment plans based on auto-contouring CTV to clinical plans. Methods From January 2013 to January 2019, 217 computed tomography (CT) scans of patients with locally advanced prostate cancer treated at our hospital were collected and analyzed. CTV and OAR were delineated with a deep learning based method, which named CUNet. The performance of this strategy was evaluated using the mean Dice similarity coefficient (DSC), 95th percentile Hausdorff distance (95HD), and subjective evaluation. Treatment plans were graded using predetermined evaluation criteria, and % errors for clinical doses to the planned target volume (PTV) and organs at risk(OARs) were calculated. Results The defined CTVs had mean DSC and 95HD values of 0.84 and 5.04 mm, respectively. For one patient's CT scans, the average delineation time was less than 15 seconds. When CTV outlines from CUNetwere blindly chosen and compared to GT, the overall positive rate in clinicians A and B was 53.15% vs 46.85%, and 54.05% vs 45.95%, respectively (P>0.05), demonstrating that our deep machine learning model performed as good as or better than human demarcation Furthermore, 8 testing patients were chosen at random to design the predicted plan based on the auto-courtoring CTV and OAR, demonstrating acceptable agreement with the clinical plan: average absolute dose differences of D2, D50, D98, Dmean for PTV are within 0.74%, and average absolute volume differences of V45, V50 for OARs are within 3.4%. Without statistical significance (p>0.05), the projected findings are comparable to clinical truth. Conclusion The experimental results show that the CTV and OARs defined by CUNet for prostate cancer were quite close to the ground reality.CUNet has the potential to cut radiation oncologists' contouring time in half. When compared to clinical plans, the differences between estimated doses to CTV and OAR based on auto-courtoring were small, with no statistical significance, indicating that treatment planning for prostate cancer based on auto-courtoring has potential.


2004 ◽  
pp. 334-340
Author(s):  
Gunnar Surber ◽  
Klaus Hamm ◽  
Gabriele Kleinert

Object. There are various kinds of conformity parameters currently in use, although several of them are limited and reflect only target volume coverage or normal tissue overdosage. Indices are reviewed with the goal of determining those that are most significant for the evaluation of radiosurgery treatment plans for patients with vestibular schwannoma, based on the authors' experience at the Novalis Shaped Beam Surgery Center. Methods. Fifty-five radiosurgery plans for patients with vestibular schwannomas (VSs) have been evaluated. In this paper the conformation number (CN) and dose-related CN (dCN) are evaluated, and a penalty for underdosed target volumes and overdosed normal tissue is incorporated. A strategy is discussed to apply these indices (CN and dCN) to define the optimal prescription isodose (PI). For a given radiosurgery treatment plan, permitting partial target underdosage may offer an improvement of the CN. Variations of different conformation indices have been calculated for varying prescription levels—for example, an isodose plan. The resulting graph for the CN is discussed in detail to illustrate its use in defining the optimal PI level. For the 55 cases of VSs reported on, the median CNmax result was 0.78. Conclusions. It is possible to achieve highly conformal dose distributions with Novalis radiosurgical system. The CN is the parameter of choice when evaluating radiosurgery treatment plans and scoring possible treatment plans. It takes into account both target underdosage and normal tissue overdosage and offers a valuable scoring parameter while avoiding false-perfect scores.


Author(s):  
M. Ruschin ◽  
A. Sahgal ◽  
H. Soliman ◽  
B. Chugh ◽  
S. Myrehaug ◽  
...  

Predictive modeling of dose fall-off in radiosurgery could assist in clinical decision-making when prescribing a treatment plan with minimized toxicity risk. The purpose of this study is to develop a predictive dose fall-off model. Materials/Methods: We retrospectively reviewed treatment plans from 257 patients (365 lesions) with total doses ranging from 20 to 35Gy in 5 fractions. For each plan, we measured both total volume of the external contour (EXT) and BrainMinusPTV (BMP) receiving P=20% to P=80% of the prescription dose. The model has form y=Fa(PTV)b+/-delta. y=volume of EXT or BMP (cc’s); a and b are curve-fitting coefficients; PTV=total planning target volume (cc’s); F is an adjustment factor (>1) to account for number of targets; delta is the 95% prediction band. F, a, b, and delta were modeled such that dose-fall can be forecast for any PTV and dose level. Results: The model coefficients were as follows: Coefficient EXT BMP a 19927(100×P)exp(-2) 17122(100×P)exp(-2) b 0.42(100×P)exp(0.17) 0.63 F -0.0156×(100×P)+2.5517 delta 384467×(100×P)exp(-2.3159) The table can be used to determine the model for any P from 20% to 80%. Example: the EXT receiving 50%, P=0.5, a=8.0, b=0.82, F=1.8, delta=45. Thus, EXT-50=8(PTV0.82) or 1.8×8(PTV0.82) for 1-3 or >3 targets, respectively,+/-45cc’s. The model was verified against published values of dose fall-off from linacs. Conclusion: A predictive dose fall-off model was generated for linac-based radiosurgery. The model can be used for quality assurance or for inter-institutional comparisons. Ongoing work is being conducted to extend the model to a SRS cones system.


Author(s):  
Ernest Osei ◽  
Johnson Darko ◽  
Steph Swanson ◽  
Katrina Fleming ◽  
Ronald Snelgrove ◽  
...  

Abstract Objectives: Lung cancer is the most commonly diagnosed cancer in Canada and the leading cause of cancer-related mortality in both men and women in North America. Surgery is usually the primary treatment option for early-stage non-small cell lung cancer (NSCLC). However, for patients who may not be suitable candidates for surgery, stereotactic body radiation therapy (SBRT) is an alternative method of treatment. SBRT has proven to be an effective technique for treating NSCLC patients by focally administering high radiation dose to the tumour with acceptable risk of toxicity to surrounding healthy tissues. The goal of this comprehensive retrospective dosimetric study is to compare the dosimetric parameters between three-dimensional conformal radiation therapy (3DCRT) and volumetric-modulated arc therapy (VMAT) lung SBRT treatment plans for two prescription doses. Methods: We retrospectively analysed and compared lung SBRT treatment plans of 263 patients treated with either a 3DCRT non-coplanar or with 2–3 VMAT arcs technique at 48 Gy in 4 fractions (48 Gy/4) or 50 Gy in 5 fractions (50 Gy/5) prescribed to the planning target volume (PTV), typically encompassing the 80% isodose volume. All patients were treated on either a Varian 21EX or TrueBeam linear accelerator using 6-MV or 10-MV photon beams. Results: The mean PTV V95% and V100% for treatment plans at 48 Gy/4 are 99·4 ± 0·6% and 96·0 ± 1·0%, respectively, for 3DCRT and 99·7 ± 0·4% and 96·4 ± 3·4%, respectively, for VMAT. The corresponding mean PTV V95% and V100% at 50 Gy/5 are 99·0 ± 1·4% and 95·5 ± 2·5% for 3DCRT and 99·5 ± 0·8% and 96·1 ± 1·6% for VMAT. The CIRI and HI5/95 for the PTV at 48 Gy/4 are 1·1 ± 0·1 and 1·2 ± 0·0 for 3DCRT and 1·0 ± 0·1 and 1·2 ± 0·0 for VMAT. The corresponding CIRI and HI5/95 at 50 Gy/5 are 1·1 ± 0·1 and 1·3 ± 0·1 for 3DCRT and 1·0 ± 0·1 and 1·2 ± 0·0 for VMAT. The mean R50% and D2cm at 48 Gy/4 are 5·0 ± 0·8 and 61·2 ± 7·0% for 3DCRT and 4·9 ± 0·8 and 57·8 ± 7·9% for VMAT. The corresponding R50% and D2cm at 50 Gy/5 are 4·7 ± 0·5 and 65·5 ± 9·4% for 3DCRT and 4·7 ± 0·7 and 60·0 ± 7·2% for VMAT. Conclusion: The use of 3DCRT or VMAT technique for lung SBRT is an efficient and reliable method for achieving dose conformity, rapid dose fall-off and minimising doses to the organs at risk. The VMAT technique resulted in improved dose conformity, rapid dose fall-off from the PTV compared to 3DCRT, although the magnitude may not be clinically significant.


2021 ◽  
Vol 27 (3) ◽  
pp. 207-212
Author(s):  
Marcin Szymański ◽  
Maria Piziorska ◽  
Oskar Madetko ◽  
Wioletta Ślusarczyk-Kacprzyk ◽  
Wojciech Bulski

Abstract Introduction: The aim of this study was to propose a dosimetric audit of the CyberKnife system. Dosimetry audit is an important part of the quality assurance process in radiotherapy. Most of the proposed dosimetric audits are dedicated to classical medical accelerators. Currently, there is no commonly implemented scheme for conducting a dosimetric audit of the CyberKnife accelerator. Material and methods: To verify the dosimetric and geometric parameters of the entire radiotherapy process, as is required in E2E test procedure, the CIRS SHANE anthropomorphic phantom was used. A tomography with a resolution of 1.5 mm was prepared, five PTVs (Planning Target Volume) of different volumes were drawn; approximately: 88 cm3, 44 cm3, 15 cm3, 7 cm3, 1.5 cm3. Five treatment plans were made using the 6D Skull tracking method, FIXED collimators, RayTracing algorithm. Each treatment plan was verified in a slab Phantom, with a PinPoint chamber. The dose was measured by an ionization chamber type TM31010 Semiflex, placed in the center area of the target. Results: The result of the QA verification in slab phantom was up to 5,0%. The percentage difference for the measurement in the SHANE phantom was: 4.29%, -1.42%, -0.70%, 1.37%, -1.88% respectively for the targets: 88 cm3, 44 cm3, 15 cm3, 7 cm3, 1.5 cm3. Conclusions: By analyzing various approaches to small-field dosimetry audits in the literature, it can be assumed that the proposed CyberKnife dosimetric audit using the SHANE phantom is an appropriate method of verification of the radiotherapy process. Particular attention should be paid to the target volume, adjusting it to the system capabilities.


2004 ◽  
Vol 101 (Supplement3) ◽  
pp. 334-340 ◽  
Author(s):  
Gunnar Surber ◽  
Klaus Hamm ◽  
Gabriele Kleinert

Object. There are various kinds of conformity parameters currently in use, although several of them are limited and reflect only target volume coverage or normal tissue overdosage. Indices are reviewed with the goal of determining those that are most significant for the evaluation of radiosurgery treatment plans for patients with vestibular schwannoma, based on the authors' experience at the Novalis Shaped Beam Surgery Center. Methods. Fifty-five radiosurgery plans for patients with vestibular schwannomas (VSs) have been evaluated. In this paper the conformation number (CN) and dose-related CN (dCN) are evaluated, and a penalty for underdosed target volumes and overdosed normal tissue is incorporated. A strategy is discussed to apply these indices (CN and dCN) to define the optimal prescription isodose (PI). For a given radiosurgery treatment plan, permitting partial target underdosage may offer an improvement of the CN. Variations of different conformation indices have been calculated for varying prescription levels—for example, an isodose plan. The resulting graph for the CN is discussed in detail to illustrate its use in defining the optimal PI level. For the 55 cases of VSs reported on, the median CNmax result was 0.78. Conclusions. It is possible to achieve highly conformal dose distributions with Novalis radiosurgical system. The CN is the parameter of choice when evaluating radiosurgery treatment plans and scoring possible treatment plans. It takes into account both target underdosage and normal tissue overdosage and offers a valuable scoring parameter while avoiding false-perfect scores.


Author(s):  
Idajet Selmani ◽  
Partizan Malkaj

One of the most important issues in the field of radiotherapy is the correct distribution of the dose around the volume of interest or planning target volume (PTV). For making this possible the exact isodose in a treatment plan has to cover the PTV, so it is used the wedge which is a part of the linear accelerator head. Wedge plays the role of a filter and usually it is called wedge filter. The wedge filter is in use almost in all treatment plans, for all the parts of the body. In this paper it is consider the use of the wedge filter for treatment of rectum tumors. The process starts with the scanning of the patient and the deliantion of the interest’s volums in the Monaco system. In the following the imagins have been sent in the treatment planning system for making the nesessary plans for treatment of the rectum. Two plans were done, one with the use of the wedge and the other without using it. The dose volume histogram helps for compering the results of the plans. The best conformity of the isodoses it was for the plan with the use of wedge through volume of interest, which is planning target volume (PTV).


2022 ◽  
Vol 17 (1) ◽  
Author(s):  
Pierre Trémolières ◽  
Ana Gonzalez-Moya ◽  
Amaury Paumier ◽  
Martine Mege ◽  
Julien Blanchecotte ◽  
...  

Abstract Objectives To characterise the motion of pulmonary tumours during stereotactic body radiation therapy (SBRT) and to evaluate different margins when creating the planning target volume (PTV) on a single 4D CT scan (4DCT). Methods We conducted a retrospective single-site analysis on 30 patients undergoing lung SBRT. Two 4DCTs (4DCT1 and 4DCT2) were performed on all patients. First, motion was recorded for each 4DCT in anterior–posterior (AP), superior-inferior (SI) and rightleft (RL) directions. Then, we used 3 different margins (3,4 and 5 mm) to create the PTV, from the internal target volume (ITV) of 4DCT1 only (PTV D1 + 3, PTV D1 + 4, PTV D1 + 5). We compared, using the Dice coefficient, the volumes of these 3 PTVs, to the PTV actually used for the treatment (PTVttt). Finally, new treatment plans were calculated using only these 3 PTVs. We studied the ratio of the D2%, D50% and D98% between each new plan and the plan actually used for the treatment (D2% PTVttt, D50% PTVttt, D50% ITVttt D98% PTVttt). Results 30 lesions were studied. The greatest motion was observed in the SI axis (8.8 ± 6.6 [0.4–25.8] mm). The Dice index was higher when comparing PTVttt to PTV D1 + 4 mm (0.89 ± 0.04 [0.82–0.98]). Large differences were observed when comparing plans relative to PTVttt and PTV D1 + 3 for D98% PTVttt (0.85 ± 0.24 [0.19–1.00]). and also for D98% ITVttt (0.93 ± 0.12 [0.4–1.0]).D98% PTVttt (0.85 ± 0.24 [0.19–1.00], p value = 0.003) was statistically different when comparing plans relative to PTVttt and PTV D1 + 3. No stastistically differences were observed when comparing plans relative to PTVttt and PTV D1 + 4. A difference greater than 10% relative to D98% PTVttt was found for only in one UL lesion, located under the carina. Conclusion A single 4DCT appears feasible for upper lobe lesions located above the carina, using a 4-mm margin to generate the PTV. Advance in knowledge Propostion of a personalized SBRT treatment (number of 4DCT, margins) according to tumor location (above or under the carina).


2020 ◽  
Vol 93 (1110) ◽  
pp. 20190897
Author(s):  
Jennifer Cannon ◽  
Peter Bownes ◽  
Joshua Mason ◽  
Rachel Cooper

Objective: Assessment of the extent of variation in delineations and dose optimisation performed at multiple UK centres as a result of interobserver variation and protocol differences. Methods: CT/MR images of 2 cervical cancer patients previously treated with external beam radiotherapy (EBRT) and Brachytherapy were distributed to 11 UK centres. Centres delineated structures and produced treatment plans following their local protocol. Organ at risk delineations were assessed dosimetrically through application of the original treatment plan and target volume delineations were assessed in terms of variation in absolute volume and length, width and height. Treatment plan variation was assessed across all centres and across centres that followed EMBRACE II. Treatment plans were assessed using total EQD2 delivered and were compared to EMBRACE II dose aims. Variation in combined intracavitary/interstitial brachytherapy treatments was also assessed. Results: Brachytherapy target volume delineations contained variation due to differences in protocol used, window/level technique and differences in interpretations of grey zones. Planning target volume delineations were varied due to protocol differences and extended parametrial tissue inclusion. All centres met EMBRACE II plan aims for PTV V95 and high-riskclinical target volume D90 EQD2, despite variation in prescription dose, fractionation and treatment technique. Conclusion: Brachytherapy target volume delineations are varied due to differences in contouring guidelines and protocols used. Planning target volume delineations are varied due to the uncertainties surrounding the extent of parametrial involvement. Dosimetric optimisation is sufficient across all centres to satisfy EMBRACE II planning aims despite significant variation in protocols used. Advances in knowledge: Previous multi-institutional audits of cervical cancer radiotherapy practices have been performed in Europe and the USA. This study is the first of its kind to be performed in the UK.


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