Experienced Radiation Oncologist Research Articles

Evaluating the Feasibility of Applying Deformable Registration Into Adaptive Therapy for NRG Oncology RTOG 1106

Adaptive radiotherapy has been introduced to reduce normal tissue toxicities and escalate tumor dose and is evaluated in clinical trials. The purpose of our study is to evaluate the feasibility and efficacy of deformable registration, as compared with rigid registration, for adaptive planning of RTOG 1106 Randomized Phase II Trial of Individualized Adaptive Radiotherapy Using During-Treatment FDG-PET/CT and Modern Technology in Locally Advanced Non-Small Cell Lung Cancer (NSCLC). Thirteen patients from RTOG 1106 trial with both primary planning CTs and re-scanned CTs were included in this study. An experienced radiation oncologist contoured the tumor volumes (TVs) and organs at risk (OARs) on the re-scanned CTs, and treatment plans were made on these CTs. Backward deformable registration (from adaptive image to initial image) and Forward deformable registration (from initial images to adaptive images) were performed upon these patients. The deformed contours were compared with the original contours for geometry and dosimetry. The geometry comparison was performed using the Dice Similarity Coefficient (DSC) and Mean Distance to Agreement (MDA). The dosimetry differences were evaluated by the deviation of dose between deformed contours and original. Five different contours were studied that included Heart, Lungs-GTV, Esophagus, Spinal Cord, and PTV. The performance of backward deformable registration and forward deformable registration were also compared. The average DSC of all contours for forward deformable registration is 84.83±15.48%, while the average DSC for backward deformable registration is 85.12±16.01%. The DSC for Heart, Lung_L, Lung_R, and GTV are 86.69±5.70%, 95.17±2.06%, 96.17±1.83%, and 61.88±13.24% respectively. The relatively low DSC value for GTV is due to the volume change of GTVs from the primary CTs to the re-scanned CTs. The MDA for Esophagus and Spinal Cord are 1.89±0.56mm and 2.19±1.59mm respectively. For the dosimetric comparison, the average deviation of V30Gy, V40Gy, Dmax, and Dmean of Heart, V5, V20, and Dmean of Lungs, Dmax and Dmean of Esophagus, Dmax of Spinal Cord, and Dmin, Dmax, and D95 of PTV are 7.08±7.97%, 5.86±6.95%, 1.38±2.65Gy, 3.46±4.35Gy, 1.45±1.20%, 0.95±0.76%, 0.55±0.46Gy, 0.62±0.53Gy, 3.22±2.93Gy, 0.72±0.73Gy, 10.39±11.13Gy, 0.59±1.15Gy, 4.30±5.90Gy Respectively. Deformable registration is highly desirable for accurate dosimetry of adaptive planning. Detailed workflow of the implementation needs to be optimized.

An International Radiosurgery Consortium Survey for Gynecological Stereotactic Ablative Radiation Therapy

Stereotactic Ablative Radiotherapy (SABR) has been shown to be a highly effective treatment that improves local control in many disease sites. However, the role of SABR in gynecological cancers (GYN) has not been well-established. We hypothesize that there exists considerable variation in GYN SABR practice and technique among institutions. The goal of this study is to determine clinical and technical factors in utilization of GYN SABR among 11 experienced radiation oncologists. A comprehensive 63 question survey on GYN SABR was sent out to 11 radiation oncologists who have published original research, conducted clinical trials or have an established GYN SABR program at their institutions in 5 different countries. Issues addressed were clinical factors, indications, technique, dose and systemic therapy considered in SABR. Responses were combined and analyzed at a central institution. Most respondents indicated that salvage therapy for nodal (82%) and primary recurrent disease (91%) could be considered standard options for SABR in the setting of inability to administer brachytherapy. All other indications should be considered on clinical trials. Most would not use SABR as a boost in primary treatment unless a patient has absolute contraindications to brachytherapy or on clinical trial. Multi-modality imaging is often (91%) used for planning including PET, CT contrast and MRI. Bladder protocols and fiducial markers are common (82%) in set-up protocols. There is a wide variation for OAR tolerances however small bowel is considered the dose-limiting structure for most experts (91%). Fractionation schedules range from 3-6 fractions for definitive and boost SABR. For boost treatments, total EQD2 range from 64 Gy to 85 Gy, when prescribing to a CTV. 73% of respondents would treat chemotherapy sequentially after SABR with at least a 1 week break. Although SABR has becoming increasingly standard in other oncology disease sites, there remains a wide variation in both clinical and technical factors when treating GYN cancers. Nodal and recurrent disease is considered a potential indication for SABR whereas other indications should be offered on clinical trials. There is interest in incorporating SABR in GYN tumors in combination with sequential chemo especially in the recurrent and salvage setting. Further studies are warranted to establish consensus guidelines for GYN SABR treatment.

Preliminary Investigation of Adaptive Glioblastoma Radiation Therapy Using the Integrated High-Field MRI-LINAC

The MRL has the potential to visualize changes in glioblastoma (GBM) tumor volume over the course of radiotherapy. We hypothesize that the MRL can adapt for tumor volume changes observable with MRI at time of treatment. As part of a prospective ethics-board approved imaging study, MR images of GBM patients receiving 60 Gy in 30 fractions are acquired at 4 time points: Day0 (planning), Day10 (post ten fractions), Day20 and at 1-month follow-up. Using the T1-weighted post-gadolinium injection images, the enhancing volume indicating the gross tumor volume (GTV) was contoured by an experienced radiation oncologist at each time point for 3 of 20 planned patients. Relative and absolute volume changes in GTV were measured. Plan adaptation feasibility was tested in one case by simulating a new planning target volume (PTV) based on the changed GTV and then using the Adapt Plan workflow in the Monaco MRL research planning system version 5.19.02 (Elekta AB, Stockholm, Sweden) to warp the beam apertures to the new PTV. For 2 of the 3 patients analyzed the GTV shrunk by 14% and 20% at Day20 and 51% and 42% at 1 month when compared to the original GTV. For the third patient, an increase in GTV of 37% was observed at Day20. In the case of GTV reduction, the enhancing region tended to shrink in medially from within the brain towards the surgical entry point. The image set containing the 20% GTV shrinkage at Day20 was used to generate the adapted plan with the new PTV being 31% smaller than the original. The resulting beam apertures were correspondingly reduced to the shape of the new PTV by a mean of 22% (18cm2). The reduction in beam aperture area followed by warm-start optimization maintained coverage of the new PTV while reducing the maximum dose to the brainstem and optic chiasm by 37% and 39% respectively for the fractions that would receive the adapted plan. We are continuing to gather novel data related to volumetric changes in GBM tumor volume over the course of radiotherapy. Preliminary observations indicate unidirectional changes over time continuing to occur throughout and after the course of radiotherapy. Preliminary findings also indicate the feasibility of adapting for observed tumor changes and ongoing work is being undertaken to develop an adaptive strategy for the MRL that involves auto-segmentation and planning boost doses with similar or improved safety profile compared to our current standard.

Tangential Field Radiotherapy for Breast Cancer-The Dose to the Heart and Heart Subvolumes: What Structures Must Be Contoured in Future Clinical Trials?

The aim of the present study was to evaluate if it is feasible for experienced radiation oncologists to visually sort out patients with a large dose to the heart. This would facilitate large retrospective data evaluations. And in case of an insufficient visual assessment, to define which structures should be contoured and which structures can be skipped as their dose can be derived from other easily contoured structures for future clinical trials. Planning CTs of left-sided breast cancer patients treated with 3D-conformal radiotherapy by tangential fields were visually divided into two groups: with an estimated high dose (HiD) and with an estimated low dose (LoD) to the heart. For 46 patients (22 HiD and 24 LoD), the heart, the left ventricle, the left anterior descending artery (LAD), the right coronary artery, and the ramus circumflexus were contoured. A helper structure (HS) around the LAD was generated in order to consider if contouring uncertainties of the LAD could be acceptable. We analyzed the mean dose (Dmean), the maximum dose, the V10, V20, V30, V40, and the length of the LAD that received 20 and 40 Gy. The two groups had a significant different Dmean of the heart (p < 0.001). The average Dmean to the heart was 4.0 ± 1.3 Gy (HiD) and 2.3 ± 0.8 Gy (LoD). The average Dmean to the LAD was 26.2 ± 7.4 Gy (HiD) and 13.0 ± 7.5Gy (LoD) with a very strong positive correlation between Dmean LAD and Dmean HS in both groups. The Dmean heart is not a good surrogate parameter for the dose to the LAD since it might underestimate clinically significant doses in 1/3 of the patients in LoD group. A visual assessment of the dose to the heart could be reliable if performed by experienced radiation oncologists. However, the Dmean heart is not always a good surrogate parameter for the dose to the LAD or for the Dmean to the left ventricle. Thus, if specific late toxicities are evaluated, we strongly recommend contouring of the specific heart substructures as a heart Dmean is not highly specific.

Long-term survival in patients with NSCLC treated with single fraction vs multi-fraction palliative radiotherapy in the case of lung tumor, brain metastases, and bone metastases.

e20082 Background: Patients with advanced non-small cell lung cancer (NSCLC) are candidates for different types of treatment, including chemotherapy and radiotherapy or supportive care. Despite the fatal prognosis in advanced disease, many experienced radiation oncologists will apply radiation at low doses with the intention of palliative care. Choosing an effective radiation dose that does not cause significant complications remains under discussion. Methods: We used an extensive database of medical patients diagnosed with NSCLC, treated with palliative radiotherapy at the Oncology Centre in Bydgoszcz, Poland, from June 1998 to December 2013. A group of 3202 patients was divided into subgroups: A) 1762 patients irradiated on the lung tumor (without distant metastases): Total dose: A1) 6 Gy/1 fr.(n = 19); A2) 8 Gy/1 fr.(n = 276); A3) 20 Gy/5 fr.(n = 1349); A4) 30 Gy/10 fr.(n = 118). B) 548 patients irradiated on the central nervous system (CNS) metastases: B1) 20 Gy/5 fr.(n = 476); B2) 30 Gy/10 fr.(n = 72). C) 892 patients irradiated on the bone metastases: C1) 8 Gy/1 fr.(n = 452); C2) 10 Gy/1 fr.(n = 30); C3) 20 Gy/5 fr.(n = 341); C4) 30 Gy/10 fr.(n = 69). Date of death was obtained from medical records. Patients who were alive or whose date of death could not be determined were censored at the date of their last encounter. Survival was calculated from the start of treatment to the date of death or censorship. Results: Overall Survival (in months) for each group was: A1) = 6; A2) = 5; A3) = 7; A4) = 7. B1) = 4; B2) = 4. C1) = 5; C2) = 4; C3) = 4; C4) = 5. There was no significant difference in survival between patients treated with single fraction pRT or multi-fractionation schedules in all groups of patients. Conclusions: The patients who were prescribed single fraction palliative radiotherapy did not have poorer prognoses or experience shorter survival than patients who were prescribed multi-fraction pRT in the case of lung tumor, brain metastases and bone metastases.

Exploratory study of the association of volumetric modulated arc therapy (VMAT) plan robustness with local failure in head and neck cancer

This work is to show which is more relevant to cause local failures (LFs) due to patient setup uncertainty between the planning target volume (PTV) underdosage and the potential target underdosage subject to patient setup uncertainties in head and neck (H&N) cancer treated with volumetric‐modulated arc therapy (VMAT). Thirteen LFs in 10 H&N patients treated by VMAT were analyzed. Measures have been taken to minimize the chances of insufficient target delineation for these patients and the patients were clinically determined to have LF based on the PET/CT scan results by an experienced radiologist and then reviewed by a second experienced radiation oncologist. Two methods were used to identify the possible locations of LF due to underdosage: (a) examining the standard VMAT plan, in which the underdosed volume in the nominal dose distribution (UVN) was generated by subtracting the volumes receiving the prescription doses from PTVs, and (b) plan robustness analysis, in which in addition to the nominal dose distribution, six perturbed dose distributions were created by translating the CT iso‐center in three cardinal directions by the PTV margin. The coldest dose distribution was represented by the minimum of the seven doses in each voxel. The underdosed volume in the coldest dose distribution (UVC) was generated by subtracting the volumes receiving the prescription doses in the coldest dose distribution from the volumes receiving the prescription doses in the nominal dose distribution. UVN and UVC were subsequently examined for spatial association with the locations of LF. The association was tested using the binominal distribution and the Fisher's exact test of independence. We found that of 13 LFs, 11 were associated with UVCs (P = 0.011), while three were associated with UVNs (P = 0.99). We concluded that the possible target underdosage due to patient setup uncertainties appeared to be a more relevant factor associated with LF in VMAT for H&N cancer than the compromised PTV coverage at least for the patients included in this study.

P05.05 Post whole-brain radiotherapy hippocampal volumetry and neuronal changes measured by MR spectroscopy

Abstract Although cognitive impairment after radiotherapy is likely multifactorial, hippocampus (Hipp) is believed to be particularly sensitive to radiation injury due to presented neuronal stem cells involved in memory formation. Biomarkers of radiation injury can help elucidate the mechanism of post WBRT cognitive decline. In our previous prospective study, we demonstrated Hipp MR spectroscopy to be feasible and sensitive method for non-invasive measurement of radiotherapy injury. We observed decline in Hipp concentration of N-acetyl aspartat (NAA), the marker of neuronal viability and density, within left as well as right Hipp 4 months after WBRT. Herein, we present pilot data of Hipp volumetry in this patients cohort. METHODS: Structural MRI of patients involved in our previous study, where we measured Hipp NAA concentrations before and 4 months after WBRT, were retrieved. Left and right Hipp was contoured by experienced radiation oncologist and neuroradiologist. Volumes of Hipp were compared pre and post WBRT and changes were correlated to NAA concentrations. First 15 patients from our previous study were included in this pilot volumetry study (10 mens, median age 58 years, 26% renal cancer, 20% NSCLC, median overall survival 14.6 months). Mean NAA concentration in the right Hipp significantly decreased by 12% from 8.53mM to 7.43mM (0.001). Corresponding concentrations within left Hipp are 8.58mM and 7.69mM leading to significant decrease by 10.5% (0.004). Volume of right Hipp decreased by 9.2% (from median 2.52cc to 2.47cc; not significant) and left Hipp by 5.6% (from median 2.42cc to 2.27cc, not significant). DISCUSSION: We observed non significant decrease in volume of Hipp after WBRT. With no known normative standards, it is not possible to estimate an effect of small sample size to calculated p values. Remarkable difference in Hipp contouring results was observed within this pilot study. Hipp volumetry after WBRT may shed more lights into brain radioinjury, however more robust volumetry approach is needed for valid final results including correlations between volumetric data and concentrations. CONCLUSION: Significant decrease in mean Hipp NAA concentrations and non significant decrease in median Hipp volumes was observed in our patients cohort, four months after WBRT. Although presented pilot data are hypothesis generating, more patients as well as more robust approach in Hipp volumetry is needed for drawing valid conclusions.

The role of delineation education programs for improving interobserver variability in target volume delineation in gastric cancer.

To assess whether delineation courses for radiation oncologists improve interobserver variability in target volume delineation for post-operative gastric cancer radiotherapy planning. 29 radiation oncologists delineated target volumes in a gastric cancer patient. An experienced radiation oncologist lectured about delineation based on contouring atlas and delineation recommendations. After the course, the radiation oncologists, blinded to the previous delineation, provided delineation for the same patient. The difference between delineated volumes and reference volumes for pre- and post-course clinical target volume (CTV) were 19.8% (-42.4 to 70.6%) and 12.3% (-12.0 to 27.3%) (p = 0.26), respectively. The planning target volume (PTV) differences pre- and post-course according to the reference volume were 20.5% (-40.7 to 93.7%) and 13.1% (-10.6 to 29.5%) (p = 0.30), respectively. The concordance volumes between the pre- and post-course CTVs and PTVs were 467.1 ± 89.2 vs 597.7 ± 54.6 cm3 (p < 0.001) and 738.6 ± 135.1 vs 893.2 ± 144.6 cm3 (p < 0.001), respectively. Minimum and maximum observer variations were seen at the cranial part and splenic hilus and at the caudal part of the CTV. The kappa indices compared with the reference contouring at pre- and post-course delineations were 0.68 and 0.82, respectively. The delineation course improved interobserver variability for gastric cancer. However, impact of target volume changes on toxicity and local control should be evaluated for further studies. Advances in knowledge: This study demonstrated that a delineation course based on current recommendations helped physicians delineate smaller and more homogeneous target volumes. Better target volume delineation allows proper target volume irradiation and preventing unnecessary normal tissue irradiation.

SC09.04 Radiotherapy in China

SC09.04 Radiotherapy in China

Interobserver Variability in the Delineation of Gross Tumour Volume and Specified Organs-at-risk During IMRT for Head and Neck Cancers and the Impact of FDG-PET/CT on Such Variability at the Primary Site

PurposeTo assess interobserver variability (IOV) in the delineation of structures during intensity-modulated radiation therapy for head and neck squamous cell carcinoma and the impact of fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) on such variability at the primary site. MethodsThree experienced head-neck radiation oncologists, blinded to each other, delineated the primary site gross tumour volume (GTV) and specified organs-at-risk (OARs) viz parotid gland, spinal cord, and cochlea in 10 patients with pharyngolaryngeal cancers suited for definitive intensity-modulated radiation therapy. IOV was assessed by concordance index (CI), Dice similarity coefficient (DSC), and Fleiss' kappa. Subsequently, the observers refined their corresponding GTVs incorporating information from FDG-PET/CT. The impact of FDG-PET/CT on variability of GTV was assessed by comparing the overlap indices with and without FDG-PET/CT using paired ‘t’ test. ResultsThere was moderate IOV in the delineation of GTV as evidenced by mean CI, DSC, and Fleiss' kappa of 0.41, 0.57, and 0.56, respectively. The use of FDG-PET/CT improved consistency of target volume delineation with resultant improvement in the overlap indices (mean CI, DSC, and Fleiss' kappa of 0.54, 0.69, and 0.69, respectively) that was statistically significant (P < .001). There was good agreement between the three observers for delineation of spinal cord and parotid glands. Concordance was worst for the cochlea. ConclusionThis study demonstrates the presence of moderate IOV between three experienced head and neck radiation oncologists in an academic institutional setting for the delineation of GTV. The use of FDG-PET/CT for target volume delineation results in significant reduction of such variability.

Radiomics based targeted radiotherapy planning (Rad-TRaP): a computational framework for prostate cancer treatment planning with MRI.

BackgroundRadiomics or computer – extracted texture features have been shown to achieve superior performance than multiparametric MRI (mpMRI) signal intensities alone in targeting prostate cancer (PCa) lesions. Radiomics along with deformable co-registration tools can be used to develop a framework to generate targeted focal radiotherapy treatment plans.MethodsThe Rad-TRaP framework comprises three distinct modules. Firstly, a module for radiomics based detection of PCa lesions on mpMRI via a feature enabled machine learning classifier. The second module comprises a multi-modal deformable co-registration scheme to map tissue, organ, and delineated target volumes from MRI onto CT. Finally, the third module involves generation of a radiomics based dose plan on MRI for brachytherapy and on CT for EBRT using the target delineations transferred from the MRI to the CT.ResultsRad-TRaP framework was evaluated using a retrospective cohort of 23 patient studies from two different institutions. 11 patients from the first institution were used to train a radiomics classifier, which was used to detect tumor regions in 12 patients from the second institution. The ground truth cancer delineations for training the machine learning classifier were made by an experienced radiation oncologist using mpMRI, knowledge of biopsy location and radiology reports. The detected tumor regions were used to generate treatment plans for brachytherapy using mpMRI, and tumor regions mapped from MRI to CT to generate corresponding treatment plans for EBRT. For each of EBRT and brachytherapy, 3 dose plans were generated - whole gland homogeneous (mathbb {P}^{text {WH}}) which is the current clinical standard, radiomics based focal (mathbb {P}^{text {RF}}), and whole gland with a radiomics based focal boost (mathbb {P}^{text {WF}}). Comparison of mathbb {P}^{text {RF}} against conventional mathbb {P}^{text {WH}} revealed that targeted focal brachytherapy would result in a marked reduction in dosage to the OARs while ensuring that the prescribed dose is delivered to the lesions. mathbb {P}^{text {WF}} resulted in only a marginal increase in dosage to the OARs compared to mathbb {P}^{text {WH}}. A similar trend was observed in case of EBRT with mathbb {P}^{text {RF}} and mathbb {P}^{text {WF}} compared to mathbb {P}^{text {WH}}.ConclusionsA radiotherapy planning framework to generate targeted focal treatment plans has been presented. The focal treatment plans generated using the framework showed reduction in dosage to the organs at risk and a boosted dose delivered to the cancerous lesions.

Impact of coronal and sagittal views on lung gross tumor volume delineation

Background and purposeTo study the impact of coronal and sagittal views (CSV) on the gross tumor volume (GTV) delineation on CT and matched PET/CT scans in non-small cell lung cancer. Material and methodsGTV delineations were performed by 11 experienced radiation oncologists on CT and PET/CT in 22 patients. Two tumor groups were defined: Group I: Primary tumors surrounded by lung or visceral pleura, without venous invasion, and without large extensions to the chest wall or the mediastinum. Group II: Tumors invading the hilar region, heart, large vessels, pericardium, and the mediastinum and/or associated with atelectasis. Tumor volumes and inter-observers variations (SD) were calculated and compared according to the use of axial view only (AW), axial/coronal/sagittal views (ACSW) and ACSW/PET (ACSWP). ResultsCSV were not frequently used (57.4% out of 242 delineations on CT). For group I, ACSW didn’t improve significantly mean GTVs. SDs were small on CT and on PET (SD=0.3cm). For group II, ACSW had 27–46% smaller observer variation (mean SD=0.7cm) than AW (mean SD=1.1cm). The smaller observer variation of ACSW users was associated with, on average, a 40% smaller delineated volume (p=0.038). Mean GTV of ACSWP was 21% larger than mean GTV of ACSW on CT. ConclusionsFor smaller lung tumors surrounded by healthy lung tissue the effect of multiple axis delineation is limited. However, application of coronal and sagittal windows is highly beneficial for delineation of more complex tumors, with atelectasis and/or pathological lymph nodes even if PET is used.

TU‐H‐CAMPUS‐IeP3‐01: Simultaneous PET Restoration and PET/CT Co‐Segmentation Using a Variational Method

Purpose:PET images are usually blurred due to the finite spatial resolution, while CT images suffer from low contrast. Segment a tumor from either a single PET or CT image is thus challenging. To make full use of the complementary information between PET and CT, we propose a novel variational method for simultaneous PET image restoration and PET/CT images co‐segmentation.Methods:The proposed model was constructed based on the Γ‐convergence approximation of Mumford‐Shah (MS) segmentation model for PET/CT co‐segmentation. Moreover, a PET de‐blur process was integrated into the MS model to improve the segmentation accuracy. An interaction edge constraint term over the two modalities were specially designed to share the complementary information. The energy functional was iteratively optimized using an alternate minimization (AM) algorithm. The performance of the proposed method was validated on ten lung cancer cases and five esophageal cancer cases. The ground truth were manually delineated by an experienced radiation oncologist using the complementary visual features of PET and CT. The segmentation accuracy was evaluated by Dice similarity index (DSI) and volume error (VE).Results:The proposed method achieved an expected restoration result for PET image and satisfactory segmentation results for both PET and CT images. For lung cancer dataset, the average DSI (0.72) increased by 0.17 and 0.40 than single PET and CT segmentation. For esophageal cancer dataset, the average DSI (0.85) increased by 0.07 and 0.43 than single PET and CT segmentation.Conclusion:The proposed method took full advantage of the complementary information from PET and CT images.This work was supported in part by the National Cancer Institute Grants R01CA172638. Shan Tan and Laquan Li were supported in part by the National Natural Science Foundation of China, under Grant Nos. 60971112 and 61375018.

TU‐H‐CAMPUS‐JeP2‐05: Can Automatic Delineation of Cardiac Substructures On Noncontrast CT Be Used for Cardiac Toxicity Analysis?

Purpose:To evaluate the feasibility of using an automatic segmentation tool to delineate cardiac substructures from computed tomography (CT) images for cardiac toxicity analysis for non‐small cell lung cancer (NSCLC) patients after radiotherapy.Methods:A multi‐atlas segmentation tool developed in‐house was used to delineate eleven cardiac substructures including the whole heart, four heart chambers, and six greater vessels automatically from the averaged 4DCT planning images for 49 NSCLC patients. The automatic segmented contours were edited appropriately by two experienced radiation oncologists. The modified contours were compared with the auto‐segmented contours using Dice similarity coefficient (DSC) and mean surface distance (MSD) to evaluate how much modification was needed. In addition, the dose volume histogram (DVH) of the modified contours were compared with that of the auto‐segmented contours to evaluate the dosimetric difference between modified and auto‐segmented contours.Results:Of the eleven structures, the averaged DSC values ranged from 0.73 ± 0.08 to 0.95 ± 0.04 and the averaged MSD values ranged from 1.3 ± 0.6 mm to 2.9 ± 5.1mm for the 49 patients. Overall, the modification is small. The pulmonary vein (PV) and the inferior vena cava required the most modifications. The V30 (volume receiving 30 Gy or above) for the whole heart and the mean dose to the whole heart and four heart chambers did not show statistically significant difference between modified and auto‐segmented contours. The maximum dose to the greater vessels did not show statistically significant difference except for the PV.Conclusion:The automatic segmentation of the cardiac substructures did not require substantial modification. The dosimetric evaluation showed no statistically significant difference between auto‐segmented and modified contours except for the PV, which suggests that auto‐segmented contours for the cardiac dose response study are feasible in the clinical practice with a minor modification to the PV vessel.

SU‐C‐BRA‐05: Delineating High‐Dose Clinical Target Volumes for Head and Neck Tumors Using Machine Learning Algorithms

Purpose:To develop and test population‐based machine learning algorithms for delineating high‐dose clinical target volumes (CTVs) in H&amp;N tumors. Automating and standardizing the contouring of CTVs can reduce both physician contouring time and inter‐physician variability, which is one of the largest sources of uncertainty in H&amp;N radiotherapy.Methods:Twenty‐five node‐negative patients treated with definitive radiotherapy were selected (6 right base of tongue, 11 left and 9 right tonsil). All patients had GTV and CTVs manually contoured by an experienced radiation oncologist prior to treatment. This contouring process, which is driven by anatomical, pathological, and patient specific information, typically results in non‐uniform margin expansions about the GTV. Therefore, we tested two methods to delineate high‐dose CTV given a manually‐contoured GTV: (1) regression‐support vector machines(SVM) and (2) classification‐SVM. These models were trained and tested on each patient group using leave‐one‐out cross‐validation. The volume difference(VD) and Dice similarity coefficient(DSC) between the manual and auto‐contoured CTV were calculated to evaluate the results. Distances from GTV‐to‐CTV were computed about each patient's GTV and these distances, in addition to distances from GTV to surrounding anatomy in the expansion direction, were utilized in the regression‐SVM method. The classification‐SVM method used categorical voxel‐information (GTV, selected anatomical structures, else) from a 3×3×3cm3 ROI centered about the voxel to classify voxels as CTV.Results:Volumes for the auto‐contoured CTVs ranged from 17.1 to 149.1cc and 17.4 to 151.9cc; the average(range) VD between manual and auto‐contoured CTV were 0.93 (0.48–1.59) and 1.16(0.48–1.97); while average(range) DSC values were 0.75(0.59–0.88) and 0.74(0.59–0.81) for the regression‐SVM and classification‐SVM methods, respectively.Conclusion:We developed two novel machine learning methods to delineate high‐dose CTV for H&amp;N patients. Both methods showed promising results that hint to a solution to the standardization of the contouring process of clinical target volumes.Varian Medical Systems grant

SU‐F‐J‐96: Comparison of Frame‐Based and Mutual Information Registration Techniques for CT and MR Image Sets

Purpose:To compare the accuracy of CT‐MR registration using a mutual information method with registration using a frame‐based localizer box.Methods:Ten patients having the Leksell head frame and scanned with a modality specific localizer box were imported into the treatment planning system. The fiducial rods of the localizer box were contoured on both the MR and CT scans. The skull was contoured on the CT images. The MR and CT images were registered by two methods. The frame‐based method used the transformation that minimized the mean square distance of the centroids of the contours of the fiducial rods from a mathematical model of the localizer. The mutual information method used automated image registration tools in the TPS and was restricted to a volume‐of‐interest defined by the skull contours with a 5 mm margin. For each case, the two registrations were adjusted by two evaluation teams, each comprised of an experienced radiation oncologist and neurosurgeon, to optimize alignment in the region of the brainstem. The teams were blinded to the registration method.Results:The mean adjustment was 0.4 mm (range 0 to 2 mm) and 0.2 mm (range 0 to 1 mm) for the frame and mutual information methods, respectively. The median difference between the frame and mutual information registrations was 0.3 mm, but was not statistically significant using the Wilcoxon signed rank test (p=0.37).Conclusion:The difference between frame and mutual information registration techniques was neither statistically significant nor, for most applications, clinically important. These results suggest that mutual information is equivalent to frame‐based image registration for radiosurgery. Work is ongoing to add additional evaluators and to assess the differences between evaluators.

Fully automatic volumetric modulated arc therapy plan generation for rectal cancer

Background and purposeTo develop and evaluate a fully automatic rectal planning optimizer (ARPO) for volumetric modulated arc therapy (VMAT) treatment planning without human interaction. Materials and methodsThe ARPO was developed using inherent Pinnacle3 script language; it was designed to perform the whole planning process including planning structure generation, beam placement, doseline setting and treatment planning. The automatic scheme adjusts the objectives of the objective function simulating the operation of dosimetrists based on our clinical experience. A total of 29 planned rectal cancer patients were retrospectively replanned using the ARPO (VMATauto) under the same constraints. ResultsWith the ARPO, the hands-on time required for the whole planning process was significantly reduced to <1min. All VMATauto plans were recognized as clinically acceptable and 69% as clinically improved; 3% of VMATauto plans were marked equal and 28% inferior to manually generated VMATman plans when reviewed in a single-blind study by one experienced radiation oncologist. Without any planning workload the VMATauto plans had similar planning target volume dose coverage to the VMATman plans and statistically better organ-at-risk sparing, especially regarding lower small intestine irradiation. ConclusionsThe ARPO is robust and dramatically efficient in clinical application and provides improved planning quality.

Evaluation of an automated knowledge based treatment planning system for head and neck.

BackgroundThis study evaluated an automated inverse treatment planning algorithm, Pinnacle Auto-Planning (AP), and compared automatically generated plans with historical plans in a large cohort of head and neck cancer patients.MethodsFifty consecutive patients treated with volumetric modulated arc therapy (Eclipse, Varian Medical System, Palo Alto, CA) for head and neck were re-planned with AP version 9.10. Only one single cycle of plan optimization using one single template was allowed for AP. The dose to the planning target volumes (PTV’s; 3–4 dose levels), the organs at risk (OAR’s) and the effective working time for planning was evaluated. Additionally, two experienced radiation oncologists blind-reviewed and ranked 10 plans.ResultsDose coverage and dose homogeneity of the PTV were significantly improved with AP, however manually optimized plans showed significantly improved dose conformity. The mean dose to the parotid glands, oral mucosa, swallowing muscles, dorsal neck tissue and maximal dose to the spinal cord were significantly reduced with AP. In 64 % of the plans, the mean dose to any OAR (spinal cord excluded) was reduced by >20 % with AP in comparison to the manually optimized plans. In 12 % of the plans, the manually optimized plans showed reduced doses by >20 % in at least one OAR. The experienced radiation oncologists preferred the AP plan and the clinical plan in 80 and 20 % of the cases, respectively. The average effective working time was 3.8 min ± 1.1 min in comparison to 48.5 min ± 6.0 min using AP compared to the manually optimized plans, respectively.ConclusionThe evaluated automated planning algorithm achieved highly consistent and significantly improved treatment plans with potentially clinically relevant OAR sparing by >20 % in 64 % of the cases. The effective working time was substantially reduced with Auto-Planning.

Interobserver variability in clinical target volume delineation for primary mediastinal B-cell lymphoma

PurposeThe purpose of this study was to evaluate interobserver variability among radiation oncologists with experience in the field of lymphoma radiation therapy in the delineation of clinical target volume (CTV) in a challenging case of primary mediastinal B-cell lymphoma. Methods and materialsTen experienced radiation oncologists were invited to a 1-day contouring session. The case of a 56-year-old man with primary mediastinal B-cell lymphoma with complete metabolic response after chemotherapy was chosen as the sample for the study. A brief presentation of his clinical history was given, together with guidelines for contouring. The 10 CTVs obtained were then compared in terms of variation in total volume and in craniocaudal, laterolateral, and anteroposterior diameters. The CTV with the best Dice similarity coefficient (DSC) between the union of all 10 CTVs and the individual CTV was considered the reference CTV, and the DSC and the Hausdorff distance (HD) for each volume compared with the reference CTV were then calculated. ResultsA significant variability was found in total volume (mean, 498.3 cm3; range, 181.8-1003 cm3) and craniocaudal (median, 144.7 mm; range, 80.6-159 mm), laterolateral (median, 133.5 mm; range, 83.7-149.5 mm), and anteroposterior diameters (median, 136.2 mm; range, 84-150.5 mm). Analysis of the DSC and the HD showed a mean DSC of 0.53 (range, 0.31-0.74) and a mean HD of 6.4 cm (range, 1.8-14.8 cm). ConclusionsResults of this study strongly indicate the need to develop and share appropriate contouring guidelines among experts and suggest the promotion of specific educational activities to improve radiation therapy quality in both clinical trials and routine clinical practice.

Implementation and Clinical Evaluation of Automated Planning for IMRT Treatment of Breast Cancer

Implementation and Clinical Evaluation of Automated Planning for IMRT Treatment of Breast Cancer