Comparable Planning Target Volume Research Articles

A predicted three-dimensional dose sequence based treatment planning optimization method for gynecologic IMRT.

In knowledge-based treatment planning (KBTP) for intensity-modulated radiation therapy (IMRT), the quality of the plan is dependent on the sophistication of the predicted dosimetric information and its application. In this paper, we propose a KBTP method that based on the effective and reasonable utilization of a three-dimensional (3D) dose prediction on planning optimization. We used an organs-at-risk (OARs) dose distribution prediction model to create a voxel-based dose sequence based optimization objective for OARs doses. This objective was used to reformulate a traditional fluence map optimization model, which involves a tolerable spatial re-assignment of the predicted dose distribution to the OAR voxels based on their current doses' positions at a sorted dose sequencing. The feasibility of this method was evaluated with ten gynecology (GYN) cancer IMRT cases by comparing its generated plan quality with the original clinical plan. Results showed feasible plan by proposed method, with comparable planning target volume (PTV) dose coverage and greater dose sparing of the OARs. Among ten GYN cases, the average V30 and V45 of rectum were decreased by 4%±4% (p=0.02) and 4%±3% (p<0.01), respectively. V30 and V45 of bladder were decreased by 8%±2% (p<0.01) and 3%±2% (p<0.01), respectively. Our predicted dose sequence-based planning optimization method for GYN IMRT offered a flexible use of predicted 3D doses while ensuring the output plan consistency.

Precision radiotherapy by SPECT lung functional imaging in NSCLC

Background: Single Photon Emission Computed Tomography (SPECT) could be used to avoid the non-affected perfusion areas in patients with non-small-cell lung cancer (NSCLC) and to potentially reduce lung toxicity. The aim of this study is to compare dosimetric differences between two different 3D-conformal treatment plans, with and without CT/SPECT contribution. Methods: Simulation Computed tomography (CT) scans were accurately co-registered with SPECT scans and three different areas, based on SPECT intensity perfusion, were contoured: low perfusion (LP), medium perfusion (MP) and high perfusion (HP). Two different 3D-conformal plans, with co-planar and nonco-planar fields, were generated; one without SPECT information (anatomic plan), and one using the perfusion area identified with functional imaging (functional plan). Results: 9 patients were planned and a total of 18 plans were available for analysis. Anatomical and functional plans resulted in comparable planning target volume (PTV) coverage. In the functional plans, a significant reduction of dose in high perfusion areas was reported. The reduction of HP-V20 Gy values ranged from 15% to 8% (p = 0.046), the ipsiHP-V20 Gy from 38% to 22% (p = 0.028) and ipsiHP-Dmean reduction from 16 Gy to 12 Gy (p = 0.039). No significant differences in other organs at risk (OARs) metrics were reported between anatomical and functional plans. Conclusions: Despite the few cases reported, the strength of our study lies in the reported benefit of functional lung information in 3D conformal radiation planning, without compromising target coverage or worsening dose distribution to the OARs. There is an urgent need for prospective clinical and randomized trials in order to define the role of lung functional imaging in reducing toxicity in clinical practice.

Evaluation of sparing organs at risk (OARs) in left-breast irradiation in the supine and prone positions and with deep inspiration breath-hold.

PurposeTo compare doses to organs at risk (OARs) for left‐sided whole‐breast radiation therapy with comparable planning target volume (PTV) coverage using three techniques: free breathing in a supine position (SFB), deep inspirational breath‐hold in a supine position (SDIBH), and free breathing in prone position (PFB).Materials and methodsThirty‐three patients with left‐sided early‐stage breast cancer underwent CT simulation following SFB, SDIBH, and PFB protocols for whole‐breast radiation therapy. One radiation oncologist contoured the breast PTV, heart, left ventricle (LV), and left anterior descending artery (LAD). Treatment plans were optimized using field‐in‐field technique with the AAA algorithm. Each plan was optimized to provide identical coverage to the PTV such that a reasonable comparison for OAR dosimetry could be evaluated. All plans were prescribed 42.56 Gy in 16 fractions to the left‐breast PTV.ResultsThe mean dose in SFB for the heart, LV, and LAD was 1.92, 3.19, and 21.73 Gy, respectively, which were significantly higher than the mean dose in SDIBH for the heart (1.08 Gy, P ≤ 0.0001), LV (1.50 Gy, P ≤ 0.0001), and LAD (6.3 Gy, P ≤ 0.0001) and in PFB for the heart (0.98 Gy, P ≤ 0.0001), LV (1.34 Gy, P ≤ 0.0001), and LAD (6.57 Gy, P ≤ 0.0001). Similar findings were noted for the cardiac components in SFB for V2.5, V5, V10, V20, and V30 compared with values in SDIBH and PFB. The mean dose for the left lung in PFB was 0.61 Gy that was significantly lower than in SFB (5.63 Gy, P ≤ 0.0001) and SDIBH (5.54 Gy, P ≤ 0.0001). Mean dose and dosimetric values for each OAR increased in SFB and SDIBH for patients with a large breast volume compared with values for patients with a small breast volume.Conclusions SFB results in higher heart, LAD, and LV doses than the other techniques. Both PFB and SDIBH are more advantageous for these OARs irrespective of breast volume. PFB results in significantly lower lung doses than SFB and SDIBH. PFB always provided better results than SFB for the heart, LV, LAD, and lung. This conclusion contrasts with some published studies concluding that the prone position has no benefit for heart sparing.

Personalized automated treatment planning for breast plus locoregional lymph nodes using Hybrid RapidArc

PurposeBreast cancer patients who require locoregional lymph node (LLN) irradiation can be treated using a hybrid RapidArc technique combining 2 tangential and 3 RapidArc fields. Because the creation of hybrid RapidArc plans is complex and labor-intensive, we developed an automated treatment planning workflow using the scripting application programming interface of the Eclipse treatment planning system. Methods and materialsFifteen patients (5 right- and 10 left-sided) previously treated with breast + LLN radiation therapy were replanned using the script. The automated workflow included1 optimal placement of the tangential fields based on the planning target volume and organ-at-risk contours, followed by optimization of field weights and beam energy2; positioning of the RapidArc fields; and3 subsequent RapidArc optimization using the RapidPlan knowledge-based planning solution. ResultsAverage total planning times were 163 ± 97 and 33 ± 5 minutes for the manual and automated plans, respectively, with approximately 130 and 5 minutes of user interaction. Dosimetrically, both sets of plans were very similar, with comparable planning target volume dose homogeneity values and organ-at-risk mean dose differences of ≤1.9 Gy. In 14/15 patients, the physician judged that the automated plan was either preferred (n = 4) or equal (n = 10) to the manual plan. ConclusionsThe complex hybrid RapidArc planning process for patients requiring breast + LLN irradiation was automated by optimizing the tangential field setup and integrating RapidPlan. The quality of the automated and manual plans was comparable, whereas automated planning times were substantially shorter. The principles described here could be used to automate other planning workflows.

Non-coplanar Butterfly VMAT and Deep Inspiration Breath Hold for Mediastinal Lymphoma: Do We Need Both?

Reducing doses to organs at risk (OAR) is an important goal when treating mediastinal lymphoma in young individuals. Volumetric modulated arc therapy (VMAT) improves target coverage & heart sparing but at the expense of low-dose bath to lungs and breasts. Butterfly VMAT (B-VMAT) uses non-co-planar partial arc VMAT, limiting doses to lungs and breasts, but heart sparing may be reduced. In addition, deep inspiration breath hold (DIBH) has been shown to reduce lung and heart doses. The aim of this planning study was to assess the dosimetric benefit of B-VMAT compared to full arc VMAT and also to investigate any added benefit of adding DIBH to either technique. Forty plans for 13 consecutive patients (age: 22-59, 6 females) with mediastinal lymphoma were compared. A free-breathing (FB) scan was acquired for all patients. Two VMAT plans were produced: two full arcs and B-VMAT. The B-VMAT used double 600 partial anterior & posterior arcs and 2 craniocaudal 60° anterior arcs. Seven of these patients also had a DIBH scan and additional VMAT and B-VMAT plans were produced. Plans were optimized to achieve comparable planning target volume (PTV) coverage. Dose to lungs, heart, spinal cord, esophagus, and female breasts were reduced as much as possible. Mean PTV coverage and doses to OARs were compared and differences were tested for statistical significance with Wilcoxon signed-rank test. Results are shown in Table 1. For the FB plans, the Mean Lung Dose (MLD) decreased by 11% and lung V5 reduced by 26% when using B-VMAT. V20 did however increase by 13%. No significant difference was seen in the heart dose between the two techniques. Breast V4 was significantly reduced by 62%. DIBH had more effect on reducing MLD than B-VMAT and the combination of the two techniques was additive. The DIBH B-VMAT plans showed significant reduction in both high and low dose to the lung when compared with FB plans, as well as a significant reduction in mean and high dose to the heart and breast V4. B-VMAT reduces low-dose bath to lungs and female breast with minimal effect on heart sparing and a small increase in lung V20. The benefits of DIBH and B-VMAT are additive and result in maximum sparing of lungs, heart and breasts.Tabled 1Abstract 132; Table 1 *Superscript indicates techniques with which a comparison provides a statistically significant differenceAll patients (13)FB + DIBH cohort (7)*VMATB-VMATP value1:VMAT & FB2:BVMAT & FB3:VMAT & DIBH4:BVMAT & DIBHPTV V95% (%)97.897.90.38298.298.098.198.1MLD (Gy)7.66.80.0056.92,3,46.21,3,44.91,2,44.41,2,3Lung V20 (%)12.714.40.04612.22,3,413.41,3,46.11,2,47.71,2,3Lung V5 (%)43.331.90.00138.42,428.51,431.8421.31,2,3Heart mean dose (Gy)5.65.90.0554.03,44.23,42.81,23.01,2Heart V30 (%)5.65.20.2353.53,43.33,41.61,21.91,2Heart V15 (%)15.115.70.1249.8310.536.51,2,47.13Breast V10 (%)3.33.54.34.43.32.7Breast V4 (%)20.07.718.68.419.26.9 Open table in a new tab

SU‐F‐T‐418: Evaluation of Organs at Risk (OAR) Sparing in Left Breast Irradiation Techniques

Purpose:To compare dose to organs at risk (OAR) for left sided breast radiation therapy with comparable planning target volume (PTV) coverage in three techniques; free breathing in supine position (FB), deep inspirational breath hold in supine (DIBH) and free breathing in prone position (PP).Methods:Ten left sided breast cancer patients suitable for this study underwent a CT scan in three techniques e.g. supine, FB and DIBH and prone position (PP). One radiation oncologist contoured the PTV and OAR (cardiac components) based on RTOG guidelines. Treatment plans were optimized using field‐in‐field technique with AAA algorithm. Each plan was optimized to provide identical coverage to PTV such that a reasonable comparison in OAR dosimetry can be evaluated. The prescribed dose to PTV were 42.56 Gy; 2.66 Gy in 16 fractions.Results:Average lung dose parameters; Dmean, V10, V20 and V30 were 0.5 Gy, 0.6%, 0.2%, and 0.1% respectively in PP which is significantly lower than FB (5.9 Gy, 14.2%, 10.7 %, and 8.4%) and DIBH (5.8 Gy, 14.3%, 10.2%, 7.8%). Similarly average heart Dmean, V2.5, V5, V10, and V20 were much lower in PP (1.2Gy, 9.1%, 2.1%, 0.8%, and 0.4%), and in DIBH (1.2 Gy, 10.6%, 1.7%, 0.5%, and 0.1%) compared to FB (2.6 Gy, 21%, 7.2%, 4.4% and 3.3%) respectively. Similar findings were also noted in the heart component left anterior descending artery (LAD) and Left ventricle (LV) which are correlated to radiation related toxicity.Conclusion:Based on the calculated dose, FB technique provides highest heart and lung dose. Prone has lowest lung dose, and DIBH has lowest LAD dose. It is found that PP is always superior for heart, LV, LAD and lung as compared to FB. This conclusion is in contrast to some published study concluding that prone position has no benefit for heart sparing.

Volumetric modulated arc therapy (VMAT) and simultaneous integrated boost in head-and-neck cancer: is there a place for critical swallowing structures dose sparing?

To explore the potential of volumetric-modulated arc therapy (VMAT) to reduce the risk of swallowing problems after curative chemoradiotherapy. 20 patients with head and neck cancer who previously underwent radiotherapy were selected. Radiotherapy was prescribed according to simultaneous integrated boost technique with all targets irradiated simultaneously over 30 daily fractions. Doses of 70.5 (67.5), 60.0 and 55.5 Gy were prescribed to primary tumour, high-risk nodal regions and low-risk nodal regions, respectively. Pharyngeal constrictor muscles (PCM) and glottic and supraglottic larynx (SGL) were considered organs at risk related to swallowing dysfunction (SW-OARs). Upper pharyngeal constrictor muscles (uPCM), middle pharyngeal constrictor muscles (mPCM) and lower pharyngeal constrictor muscles (lPCM) part of PCM were also outlined separately. Clinical standard plans (standard-VMAT) and plans aiming to spare SW-OARs (swallowing dysfunction-VMAT) were also created. Normal tissue complication probabilities (NTCP) for physician-rated swallowing dysfunction were calculated using a recently predictive model developed by Christianen et al. Planning with two strategies demonstrated comparable planning target volume coverage and no differences in sparing of parotid glands and other non-swallowing organs at risk. SW-VMAT plans provided mean dose reduction for uPCM and SGL by 3.9 and 4.5 Gy, respectively. NTCP values for Radiation Therapy Oncology Group grade 2-4 swallowing dysfunction was decreased by 9.2%. Dose reductions with SW-VMAT depended on tumour location and overlap with SW-OARs. VMAT plans aiming at sparing swallowing structures are feasible, providing a significant reduction in NTCP swallowing dysfunction with respect to conventional VMAT. Dysphagia is today considered one of the dose-limiting toxicities of chemoradiotherapy. The dose sparing of swallowing structures represents a major challenge in radiotherapy. VMAT is a complex new technology having the potential to significantly reduce the risk of dysphagia after curative chemoradiotherapy.

Implementation of spot scanning dose optimization and dose calculation for helium ions in Hyperion.

Helium ions ((4)He) may supplement current particle beam therapy strategies as they possess advantages in physical dose distribution over protons. To assess potential clinical advantages, a dose calculation module accounting for relative biological effectiveness (RBE) was developed and integrated into the treatment planning system Hyperion. Current knowledge on RBE of (4)He together with linear energy transfer considerations motivated an empirical depth-dependent "zonal" RBE model. In the plateau region, a RBE of 1.0 was assumed, followed by an increasing RBE up to 2.8 at the Bragg-peak region, which was then kept constant over the fragmentation tail. To account for a variable proton RBE, the same model concept was also applied to protons with a maximum RBE of 1.6. Both RBE models were added to a previously developed pencil beam algorithm for physical dose calculation and included into the treatment planning system Hyperion. The implementation was validated against Monte Carlo simulations within a water phantom using γ-index evaluation. The potential benefits of (4)He based treatment plans were explored in a preliminary treatment planning comparison (against protons) for four treatment sites, i.e., a prostate, a base-of-skull, a pediatric, and a head-and-neck tumor case. Separate treatment plans taking into account physical dose calculation only or using biological modeling were created for protons and (4)He. Comparison of Monte Carlo and Hyperion calculated doses resulted in a γ mean of 0.3, with 3.4% of the values above 1 and γ 1% of 1.5 and better. Treatment plan evaluation showed comparable planning target volume coverage for both particles, with slightly increased coverage for (4)He. Organ at risk (OAR) doses were generally reduced using (4)He, some by more than to 30%. Improvements of (4)He over protons were more pronounced for treatment plans taking biological effects into account. All OAR doses were within tolerances specified in the QUANTEC report. The biological (4)He model proposed above is a first approach matching biological data published so far. The advantage of (4)He seems to lie in the reduction of dose to surrounding tissue and to OARs. Nevertheless, additional biological experiments and treatment planning studies with larger patient numbers and more tumor indications are necessary to study the possible benefits of helium ion beam therapy in detail.

SU‐E‐T‐735: The Feasibility of Using A Knowledge Base of Prior Treatment Plans in Cervical Cancer: A Dosimetric Comparision with Original Plans

Purpose:To demonstrate the feasibility of using a knowledge base of prior treatment plans to generate new cervical intensity modulated radiation therapy (IMRT) plans. Dosimetric diffeerences were investigated between knowledge‐based IMRT rapidplans and original plans.Methods:A database of 20 cervical IMRT treatment plans were assembled to create a knowledge‐based IMRT rapidplan model. Another 19 clinical cases were randomly selected to test the model. A comparision of the difference in the dose‐volume histograms(DVH) between the semiautomated treatment plans and the original treatment plans were analyzed.Results:On average, the new knowledge‐based rapidplans are capable of achieving very comparable planning target volume coverage as the original plan, to within 1% as evaluated for D98, D95, and D1. For the rectum, the mean and standard deviation of the dose percentage differences for D20, D30, and D50 are3.79%±8.31%, 4.00%±9.87%, and 1.52±10.89%, respectively. For the bladder, the mean and standard deviation of the dose percentage differences for D20, D30, and D50 are −2.43%±9.40%, −2.03%±10.17% and −2.94%±12.30%, respectively. For the femoral heads, the mean and standard deviation of the dose percentage differences for the left and right are 3.15%±18.29% and −3.18%±13.79%. A negative percentage difference indicates that the new plan has greater dose sparing as compared to the original plan.Conclusion:We demonstrate a knowledge‐based IMRT model in cervical cancer can generate clinically acceptable treatment plans of high quality. This semiautomated approach can improve the efficiency of the treatment planning process while ensuring that high quality plans are developed.

Knowledge-based IMRT treatment planning for prostate cancer

To demonstrate the feasibility of using a knowledge base of prior treatment plans to generate new prostate intensity modulated radiation therapy (IMRT) plans. Each new case would be matched against others in the knowledge base. Once the best match is identified, that clinically approved plan is used to generate the new plan. A database of 100 prostate IMRT treatment plans was assembled into an information-theoretic system. An algorithm based on mutual information was implemented to identify similar patient cases by matching 2D beam's eye view projections of contours. Ten randomly selected query cases were each matched with the most similar case from the database of prior clinically approved plans. Treatment parameters from the matched case were used to develop new treatment plans. A comparison of the differences in the dose-volume histograms between the new and the original treatment plans were analyzed. On average, the new knowledge-based plan is capable of achieving very comparable planning target volume coverage as the original plan, to within 2% as evaluated for D98, D95, and D1. Similarly, the dose to the rectum and dose to the bladder are also comparable to the original plan. For the rectum, the mean and standard deviation of the dose percentage differences for D20, D30, and D50 are 1.8% +/- 8.5%, -2.5% +/- 13.9%, and -13.9% +/- 23.6%, respectively. For the bladder, the mean and standard deviation of the dose percentage differences for D20, D30, and D50 are -5.9% +/- 10.8%, -12.2% +/- 14.6%, and -24.9% +/- 21.2%, respectively. A negative percentage difference indicates that the new plan has greater dose sparing as compared to the original plan. The authors demonstrate a knowledge-based approach of using prior clinically approved treatment plans to generate clinically acceptable treatment plans of high quality. This semiautomated approach has the potential to improve the efficiency of the treatment planning process while ensuring that high quality plans are developed.

Giving oligometastases the best shot using stereotactic body radiosurgery with image guidance. How far is the cat out of the bag?

Oligometastatic disease is hypothesized to be a state of limited metastases in which frank widespread metastasis has not yet evolved. Milano et al. reported on patients with oligometastases undergoing two or more curative-intent stereotactic body radiation treatment (SBRT). In these selected patients, the 4-year overall survival and progression-free survival rates were 33% and 28%, respectively (1). Oligometastases should be limited in number and extent while amendable to targeted local therapies for ablation with potential cure. For example, liver resection of oncologic lesions can be associated with long-term survival in selected patients (2). High dose and focal external beam radiation in the form of SBRT may be an alternative to invasive procedures in dealing with certain sites of disease. In this issue of Journal of GI Oncology, Perkins and colleagues focused on the treatment of oligometastases in patients with abdomino-pelvic recurrence or inoperable diseases. As the authors rightfully pointed out, these patients often have received heavy prior treatment of surgery, local radiotherapy, and chemotherapy, which precludes standard local treatment for the oligometastases (3). Perkins et al. review the application of SBRT and early gastrointestinal (GI) toxicities and radiographic responses based on computed tomography (CT) and positron emission tomography (PET). In this cohort of patients, a median SBRT dose of 18 Gy was used. Majority or 87% of patients received single-fraction SBRT, and authors reported a local control rate of 74% with a metabolic response rate of 85%. Of interest, 13% of sites showed a transient increase in the uptake of SUV which subsided in follow-up PET scanning, indicating a potential “flare” response to the SBRT (4). In addition to the encouraging results, the rates of early toxicity profiles at 1 month post-SBRT were limited to grade 1 and grade 2 effects at 61% combining both upper and lower GI sites. A Radiation Therapy Oncology Group (RTOG) – sponsored phase I trial of dose escalation of study of liver metastasis reached the dose level “IV” of 50 Gy given over 10 fractions, and the protocol was closed for accrual (5). The median dose of 18 Gy as reported here by Perkins et al. is biologically less intense, and there is potential for dose study for these GI sites in the future. This report of initial experience is limited to its retrospective nature and short follow-up. A minor portion of all sites, 13%, were treated in a fractionated fashion with the number of fractions limiting to 2 to 3 fractions. The rates of response and toxicity reporting may be affected in such a small cohort of patients. Image guidance was used in 78% of sites with placement of fiducials without significant adverse events according to the authors. Using PET scanning in pre- and post-treatment evaluation may add another dimension in gauging treatment response although the PET data were available only in 39% of the treated sites. The significance and meaning of SUV in PET imaging may be affected by the high dose nature of SBRT on tumor and surrounding normal tissues. In reference to experience of SBRT in lungs, post-treatment PET may have persistent and moderate SUV elevation for 1 to 2 years (6),(7). Therefore, interpretation of PET information in SBRT in GI sites will require further study and follow up. This report adds as building blocks for technical and clinical feasibility of targeted radiotherapy for these difficult-to-treat cases. Studies will be needed to identify patients with oligometastases who will benefit the most from targeted treatment. In the mean time, radiation oncologists will continue to fine tune techniques of delivering precise radiotherapy with cancer-controlling dose with great protection of normal organs. In a dosimetric study by MacDonald et al, proton beam-based targeted treatment produced comparable planning target volume dose with generally less dose to normal tissues than three-dimensional photon-based SBRT in lung cancer patients. The authors qualified that the clinical significance of their study remained to be determined (8). In patients with metastatic diseases, we often consider “the cat to be out of the bag.” With continuous progress in systemic treatments such as chemotherapy and biologics along with advancement in radiation techniques, it is hopeful that oncologists can differentiate subsets of patients with metastatic diseases and be able to restrain or even recapture the cat using multi-modality approaches.