Daily MVCT Research Articles

SU‐F‐J‐62: Assessment of Dose Changes Due to Anterior‐Posterior Patient Separation During Daily MVCT Scans

Purpose:To determine the effects of patient separation on absolute dose and dose distribution in patients undergoing pelvic radiotherapy on TomoTherapy.Methods:An Alderson RANDO phantom with 4cm of bolus was imaged on a CT simulator and the resulting scans were contoured as a whole pelvic case. Using TomoTherapy Planning Station, the plan was designed to give 45 Gy to 95% of the treatment volume in 25 fractions. TomoTherapy MVCT scans were performed on the RANDO phantom with 2cm and 4cm of bolus removed to simulate visible changes in a patient's anatomy. The MVCT images were rigidly registered with planning CT images on TomoTherapy Planned Adaptive. The original fluence was recalculated on the MVCT images and changes in dose distribution due to patient separation were quantified by the changes in DVHs for the target volume and the organs at risk.Results:Patient separation difference equivalent to 2cm and 4cm in anterior‐posterior direction resulted in an increase of the PTV D50 and maximum PTV dose of 5.6%, 6.2% for 2cm and 7.7%, 10.4% for 4cm, respectively. For the 2cm change, D50 and maximum doses to organs at risk increased by 6.5%, 7.1% in the bladder, 4.9%, 4.8% in the rectum, and 5.3%, 6.6% in the bowel. For the 4cm change, D50 and maximum doses increased by 10.7%, 12.2% in the bladder, 5.9%, 6.1% in the rectum, and 7.7%, 10.1% in the bowel.Conclusion:This research indicates that, without any changes to the structures, patient separation in the anterior‐posterior direction can affect the dose distribution for the PTV and organs at risk. These results can assist physicians in determining if obtaining a new CT simulation set and replanning is necessary for pelvic patients on TomoTherapy.

EP-1894: Evaluation of a novel method for automatic segmentation of rectum on daily MVCT prostate images

EP-1894: Evaluation of a novel method for automatic segmentation of rectum on daily MVCT prostate images

SU-E-J-109: Evaluation of Deformable Accumulated Parotid Doses Using Different Registration Algorithms in Adaptive Head and Neck Radiotherapy

Purpose: Three deformable image registration (DIR) algorithms are utilized to perform deformable dose accumulation for head and neck tomotherapy treatment, and the differences of the accumulated doses are evaluated. Methods: Daily MVCT data for 10 patients with pathologically proven nasopharyngeal cancers were analyzed. The data were acquired using tomotherapy (TomoTherapy, Accuray) at the PLA General Hospital. The prescription dose to the primary target was 70Gy in 33 fractions.Three DIR methods (B-spline, Diffeomorphic Demons and MIMvista) were used to propagate parotid structures from planning CTs to the daily CTs and accumulate fractionated dose on the planning CTs. The mean accumulated doses of parotids were quantitatively compared and the uncertainties of the propagated parotid contours were evaluated using Dice similarity index (DSI). Results: The planned mean dose of the ipsilateral parotids (32.42±3.13Gy) was slightly higher than those of the contralateral parotids (31.38±3.19Gy)in 10 patients. The difference between the accumulated mean doses of the ipsilateral parotids in the B-spline, Demons and MIMvista deformation algorithms (36.40±5.78Gy, 34.08±6.72Gy and 33.72±2.63Gy ) were statistically significant (B-spline vs Demons, P<0.0001, B-spline vs MIMvista, p =0.002). And The difference between those of the contralateral parotids in the B-spline, Demons and MIMvista deformation algorithms (34.08±4.82Gy, 32.42±4.80Gy and 33.92±4.65Gy ) were also significant (B-spline vs Demons, p =0.009, B-spline vs MIMvista, p =0.074). For the DSI analysis, the scores of B-spline, Demons and MIMvista DIRs were 0.90, 0.89 and 0.76. Conclusion: Shrinkage of parotid volumes results in the dose increase to the parotid glands in adaptive head and neck radiotherapy. The accumulated doses of parotids show significant difference using the different DIR algorithms between kVCT and MVCT. Therefore, the volume-based criterion (i.e. DSI) as a quantitative evaluation of registration accuracy is essential besides the visual assessment by the treating physician. This work was supported in part by the grant from Chinese Natural Science Foundation (Grant No. 11105225).

Accuracy of manual and automated rectal contours using helical tomotherapy image guidance scans during prostate radiotherapy.

94 Background: Prostate radiotherapy can be delivered using daily image-guided helical tomotherapy. Previous work has shown that contouring the rectum on the kV planning CT scan has a Jaccard conformity index (JCI) of 0.78 for different oncologists (inter-observer variability) and 0.82 for a single oncologist (intra-observer variability) (Lutgendorf-Caucig C et al. Feasibility of CBCT-based target and normal structure delineation in prostate cancer radiotherapy: multi-observer and image multi-modality study. Radiother Oncol. 2011;98(2):154-61.). Using the daily image guidance MV CT scan we have developed automated methods to contour the rectum in order to investigate the dose delivered over a course of treatment. We sought to quantify the accuracy of MV manual and automated contours. Methods: A single oncologist (JES) contoured the rectum on 370 MV scans for 10 participants treated with helical tomotherapy to prostate and pelvic lymph nodes. Accuracy of MV manual contours was tested using a scalar algorithm to enlarge and reduce the contours and intra-observer re-contouring at a 3-month interval. Automated contouring, incorporating the Chan-Vese algorithm, was developed and outputs were compared with manual contours. Results: JES could identify differences in MV manual contour size at the level of ±2.2 mm, equivalent to 1.7 pixels. The median JCI for MV re-contouring was 0.87 with inter-quartile range (IQR) 0.78 to 0.90. When compared with manual contours, automated outputs had a median JCI of 0.79 (IQR 0.74 to 0.79). These results were obtained after 3 iterations, each taking less than 10 seconds. Conclusions: Manual contouring using MV scans was accurate, at a level of approximately 2 mm, and reproducible, with JCI of 0.87. The time taken to contour was approximately 20 minutes per scan. Automated contouring was also reproducible with JCI of 0.79 and, in contrast, took less than a minute per scan. Both manual and automated methods produced results comparable to those for contouring using kV scans. We plan to use auto-contouring to calculate accumulated dose to the rectum in an initial cohort of 100 participants. These doses will be correlated with toxicity as part of the VoxTox Study.

A retrospective tomotherapy image-guidance study: analysis of more than 9,000 MVCT scans for ten different tumor sites.

The purpose of this study was to quantify the systematic and random errors for various disease sites when daily MVCT scans are acquired, and to analyze alternative off‐line verification protocols (OVP) with respect to the patient setup accuracy achieved. Alignment data from 389 patients (9,418 fractions) treated at ten different anatomic sites with daily image‐guidance (IG) on a helical tomotherapy unit were analyzed. Moreover, six OVP were retrospectively evaluated. For each OVP, the frequency of the residual setup errors and additional margins required were calculated for the treatment sessions without image guidance. The magnitude of the three‐dimensional vector displacement and its frequency were evaluated for all OVP. From daily IG, the main global systematic error was in the vertical direction (4.4–9.4 mm), and all rotations were negligible (less than 0.5°) for all anatomic sites. The lowest systematic and random errors were found for H&N and brain patients. All OVP were effective in reducing the mean systematic error to less than 1 mm and 0.2° in all directions and roll corrections for almost all treatment sites. The treatment margins needed to adapt the residual errors should be increased by 2–5 mm for brain and H&N, around 8 mm in the vertical direction for the other anatomic sites, and up to 19 mm in the longitudinal direction for abdomen patients. Almost 70% of the sessions presented a setup error of 3 mm for OVPs with an imaging frequency above 50%. Only for brain patients it would be feasible to apply an OVP because the residual setup error could be compensated for with a slight margin increase. However, daily imaging should be used for anatomic sites of difficult immobilization and/or large interfraction movement.PACS numbers: 87.55.‐x, 87.56.‐v

The Ratio of Weight Loss to Planning Target Volume Significantly Impacts Setup Errors in Nasopharyngeal Cancer Patients Undergoing Helical Tomotherapy With Daily MVCT

The Ratio of Weight Loss to Planning Target Volume Significantly Impacts Setup Errors in Nasopharyngeal Cancer Patients Undergoing Helical Tomotherapy With Daily MVCT

PO-0899: Lymphnodes shrinkage measured during RT by daily MVCT predicts tumour relapses of head-and-neck cancer

PO-0899: Lymphnodes shrinkage measured during RT by daily MVCT predicts tumour relapses of head-and-neck cancer

Intra-fraction motion of the prostate during treatment with helical tomotherapy

Background and purposeTo measure the geometric uncertainty resulting from intra-fraction motion and intra-observer image matching, for patients having image-guided prostate radiotherapy on TomoTherapy. Material and methodsAll patients had already been selected for prostate radiotherapy on TomoTherapy, with daily MV-CT imaging. The study involved performing an additional MV-CT image at the end of treatment, on 5 occasions during the course of 37 treatments. 54 patients were recruited to the study. A new formula was derived to calculate the PTV margin for intra-fraction motion. ResultsThe mean values of the intra-fraction differences were 0.0mm, 0.5mm, 0.5mm and 0.0° for LR, SI, AP and roll, respectively. The corresponding standard deviations were 1.1mm, 0.8mm, 0.8mm and 0.6° for systematic uncertainties (Σ), 1.3mm, 2.0mm, 2.2mm and 0.3° for random uncertainties (σ). This intra-fraction motion requires margins of 2.2mm in LR, 2.1mm in SI and 2.1mm in AP directions. Inclusion of estimates of the effect of rotations and matching errors increases these margins to approximately 4mm in LR and 5mm in SI and AP directions. ConclusionsA new margin recipe has been developed to calculate margins for intra-fraction motion. This recipe is applicable to any measurement technique that is based on the difference between images taken before and after treatment.

Adaptive Radiation Therapy Replanning for Head-and-Neck Cancers and the Dosimetric Benefit to the Parotid Glands

Adaptive Radiation Therapy Replanning for Head-and-Neck Cancers and the Dosimetric Benefit to the Parotid Glands

Assessment of intact cervix motion using implanted fiducials in patients treated with helical tomotherapy with daily MVCT positioning

Objectives This study assesses the relative motion of the cervix during the course of treatment in patients with intact cervical cancers treated with pelvic intensity modulated radiation therapy (IMRT). Methods Nineteen patients with intact cervical cancer were treated definitively with tomotherapy using daily megavoltage (MV) CT positioning to pelvic bony anatomy. Textured gold fiducials were placed in three of four quadrants of the cervix prior to CT simulation. Daily MVCTs were registered to the planning CT based on bony anatomy. The center of mass (COM) of the fiducials was used to assess interfractional cervical motion by comparing the relative positions of the COMs. Tumor regression was indirectly assessed by calculating the contraction in the relative distance between fiducial pairs. Results Fourteen patients were evaluable. Average vector motion of the COM was 7.0 mm (SD=5.7 mm; range of 0 to 34 mm). Ninety-five percent of fiducial excursions were encompassed by 8 mm right–left, 12 mm anterior–posterior, and 11 mm superior–inferior. Ninety-five percent of all measured COM motions were ≤18 mm. Contraction was observed in 9 out of 12 patients that were analyzable. In those nine patients, the average distances between the fiducial pairs were 23 mm (range, 5.8 to 48 mm) and 18 mm (range, 3.8 to 41 mm) intheplanningCTand inthe lastdailyMVCT, respectively. On average, fiducials moved 23 % closer together. Conclusion Quantification of the excursions of the intact cervix using daily imaging of implanted fiducials was feasible and useful to define appropriate clinical target volume–planning target volume (CTV–PTV) margins for IMRT. Nonuniform CTV–PTV margins may be appropriate based on differential directional motion.

Image-guided radiotherapy: Is it necessary to adapt?

Introduction Image guidance usage is growing in clinical practice of radiation therapy aiming to make the necessary corrections in the treatment plan in order to compensate for changes in patient's anatomy. In theory, these changes should improve the treatment, but any modifications of the initial plan require additional time, resources and more QA procedures. Materials and methods Several examples of typical patients with head and neck, prostate, and lung cancer were analyzed by simulations of different scenarios of adaptive radiotherapy. Daily MVCT images were used to construct hybrid MV/kV images using the Planned Adaptive software of TomoTherapy Inc. (Madison, WI). Initial planning contours were modified in the hybrid images in order to take into account anatomical changes of the target and organs of risk. Results Calculations of dose-volume histograms for the adapted structures were used for evaluation of the changes significance. A decision to re-plan is taken by the treating physician based on the extent of the anatomical changes with respect to initial anatomy. Adapted plans were prepared for different moments during treatment course. Conclusion Dose summations for the tumours and main organs at risk were used for evaluation of the plan quality. Action level for a re-planning is proposed.

OC-0070: Comparison of setup accuracy of two immobilization systems for head and neck treatment by daily MVCT in tomotherapy

The Second European Society for Radiotherapy and Oncology Forum, ESTRO Forum, Geneva, Switzerland, 19-23 April 2013

EP-1254: Analysis of inter-fraction bladder motion during prostate treatments by daily MVCT Tomotherapy imaging

EP-1254: Analysis of inter-fraction bladder motion during prostate treatments by daily MVCT Tomotherapy imaging

Do Adaptive Radiation Therapy (ART) Assessments Depend on the Employed ART Workflow?

ART uses repeat images of the patient throughout treatment to assess deviations of the delivered dose from the planned dose. Details of this workflow can differ in imaging type, imaging frequency, and deformable image registration (DIR) algorithm. The purpose of this study is to assess how sensitive the dosimetric end-points are to the employed ART workflow. Ten patients were monitored throughout their course of treatment and the daily and cumulative D50% parotid dose was assessed using two different ART workflows. The first workflow used daily in-room MVCT imaging and an MVCT/kVCT based DIR algorithm to propagate planning contours to the daily MVCT and to accumulate recalculated doses on the planning CT. The second workflow used weekly repeat kVCT images that were acquired in the simulation suite. The repeat kVCT scans were rigidly registered to the plan kVCT and a commercial software package was used to propagate planning contours to the repeat kVCT and to accumulate recalculated doses on the planning CT. The dosimetric difference of interest for ART, i.e., the deviation between the delivered and planned dose, was calculated using both workflows. Averaged over all days the mean delivered daily D50% parotid dose based on kVCT and MVCT workflow was 13% and 15% higher than planned. The ratio between the kVCT based dose difference and the MVCT based dose difference was calculated to be 0.97±0.15. This mean ratio shows that there is no systematic difference in the assessing the dosimetric end-point. However, the standard deviation of the ratio is 15%. Comparing this standard deviation to the dosimetric signal of interest, i.e., a mean 13-15% increase in the delivered dose shows that the signal to noise ratio (SNR) is about 1. The cumulative D50% after three weeks of treatment was 7% and 9% higher than the planned dose according to the kVCT and MVCT based assessment. The ratio between the kVCT to MVCT based dose difference was 0.98±0.07. The cumulative D50% at the end of treatment was 11% and 13% higher than the planned dose according to the kVCT and MVCT based assessment while the ratio between the kVCT to MVCT based dose difference was 0.97±0.09. Similar to the daily dose assessments, both kVCT to MVCT cumulative dose assessment ratios have standard deviations that are similar in magnitude to the dosimetric difference of interest. While the true dosimetric effect on the delivered D50% parotid dose due to systematic and random patient changes is unknown, this data indicates that dosimetric assessments may vary with the employed ART workflow. The observed noise is of the same order of magnitude as the dosimetric difference of interest.

Correlation of Delivery Reproducibility With Anatomical Modifications and Intrafraction Motion During Treatments Using Helical Tomotherapy (HT)-Integrated Detectors

To investigate the correlation of the dose reproducibility acquired during treatment delivered, using integrated HT MVCT detectors, with the patient anatomy modifications that can occur during fractionated treatments. To assess the dosimetric effect of intra-fraction motion on the signal acquired by MVCT detectors during the HT treatment delivery (sinogram). First, the MVCT detector data variations related only to the delivery component were quantified. Ten HT plans, with increased level of complexity, were ranked using an extension of the Webb's Modulation Index (MI) for helical delivery. These plans were delivered several times with a phantom positioned between the radiation source and the detectors. Then, five H&N plans, acquired by MVCT detectors during clinical treatments delivery, were studied and correlated with patient anatomic variations evaluated by daily MVCT imaging. As a last step, an anthropomorphic phantom placed on a respiratory gating platform was used to simulate breathing movement during treatments. Setting different ranges of motion and respiratory amplitudes, a clinical HT plan was delivered several time and acquired with MVCT detectors. Two indices were introduced: the “Reproducibility Index” (RI) based on the definition of M.S. Padro (the RIDELIV was used to evaluate data acquired with the phantom while the RITREAT for patient data) and the SIN_DEV index, that quantify the differences on the acquired sinograms respect to the reference one. This indexes were related to the treatment complexity, the patient's anatomy variation and the intra-fraction motions. A dependence of the RIDELIV with the MI factor was observed (R2 = 0.6367), pointing out higher RIDELIV values for the most complex plan. Our analysis confirm the existence of a correlation between the RITREAT and the patient anatomy reductions in the neck diameter (R2 = 0.687) and parotids shrinkage (R2 = 0.521). The analysis of SIN_DEV index related to the anatomical modifications was assessed by means of Spearman correlation (SC), indicate higher SIN_DEV indexes at the end of the treatment that correspond to a larger parotids shrinkage (SC = -0.78, p<0.0001) and neck diameter reduction (SC = -0.75, p<0.0001). The preliminary results concerning the sinogram variations related to the respiratory amplitude and frequency, have showed SIN_DEV indexes up to 5% respect to no movement MVCT data, with a 5,4% of the sinogram area over 5% of difference. This work indicates the potential of using the HT-MVCT detectors data, acquired during the treatment delivery, to evaluate treatment reproducibility, patient's anatomy modifications and intra -fraction movements.

Dose to the skin in helical tomotherapy: Results of in vivo measurements with radiochromic films

PurposeThe aim of this study is to report results of measurements of dose to the skin in vivo with radiochromic EBT films in treatments with helical tomotherapy. Methods and materialsIn vivo measurements were performed by applying pieces of radiochromic films to the skin or to the inner side of thermoplastic mask before the treatment. The sites of treatment included scalp, brain, head and neck, cranio-spinal axis and lower limbs. Skin dosimetry was performed in a patient who experienced grade 3–4 acute side effects to the skin shortly after the first treatment sessions. For each patient we measured the setup errors using the daily MVCT acquired for image guidance of the treatment. EBT films were read with a flatbed Epson Expression scanner and images were processed with an in-house written routine. ResultsA total of 96 measurements of dose to the skin performed on 14 patients. The mean difference and standard error of the mean difference between measured and TPS-calculated dose was −9.2% ± 2.6% for all treatments, −6.6% ± 2.6% for head and neck treatments. These differences were statistically significant at the 0.05 significance level (t-Student test). Planned dose and dose range in the region of measurements were not correlated with dose discrepancy. ConclusionsRadiochromic EBT films are suitable detectors for surface dose measurements in tomotherapy treatments. Results show that TPS overestimates dose to the skin measured with EBT radiochromic films. In vivo skin measurements with EBT films are a useful tool for quality assurance of tomotherapy treatments, as the treatment planning system may not give accurate dose values at the surface.

A case study for online plan adaptation using helical tomotherapy

Helical tomotherapy's ability to provide daily megavoltage (MV) computed tomography (CT) images for patient set-up verification allows for the creation of adapted plans. As plans become more complex by introducing sharper dose gradients in an effort to spare healthy tissue, inter-fraction changes of organ position with respect to plan become a limiting factor in the correct dose delivery to the target. Tomotherapy's planned adaptive option provides the possibility to evaluate the dose distribution for each fraction and subsequently adapt the original plan to the current anatomy. In this study, 30 adapted plans were created using new contours based on the daily MVCT studies of a bladder cancer patient with considerable anatomical variations. Dose to the rectum and two planning target volumes (PTVs) were compared between the original plan, the dose that was actually delivered to the patient, and the theoretical dose from the 30 adapted plans. The adaptation simulation displayed a lower dose to 35% and 50% of the rectum compared to no adaptation at all, while maintaining an equivalent dose to the PTVs. Although online adaptation is currently too time-consuming, it has the potential to improve the effectiveness of radiotherapy.

How Well Do We Spare Scalp with Image-Guided Rotational IMRT

How Well Do We Spare Scalp with Image-Guided Rotational IMRT

SU‐E‐T‐239: Evaluation of Daily Patient Setup for Various Treatment Sites Using MVCT Image Guidance

Purpose: The accuracy and reproducibility of daily patient setup is crucial, especially for highly conformal delivery techniques like Tomotherapy. We retrospectively analyzed daily setup uncertainties for six treatment sites using Tomotherapy MVCT. Methods and Material: Translational shift data based on daily Tomotherapy MVCT registration has been analyzed for 103 patients and six sites: head/neck(n=32), brain(n=16), lung(n=16), abdomen(n=13), prostate(n=18), and pelvis(n=8). Statistical analysis included calculation of group mean shifts, and population systematic and random errors. Van Herkˈs margin formula was used to calculate rigid setup error margins based on population statistics for each site. To evaluate our clinical data with respect to the community, our setup results were compared with published studies. Results: Group mean for head/neck and brain are 0.1–0.3mm (lateral), 0.5–1.1 mm(longitudinal) and 4.0–4.9mm(vertical). Amongst the different treatment sites, population systematic and random errors are smallest for head/neck and brain patients with a range of 1.4 mm to 3.0 mm, corresponding to rigid margins between 4.5 – 9.2mm. These large vertical shifts are due to couch sag and use of shims to account for thermoplastic mask shrinkage between simulation and treatment. The group mean for all other sites ranged from 0.2–1.3 mm(lateral), 0.5–3.7mm (longitudinal) and 1.9&amp;–4.1mm(vertical). Population systematic and random errors for other treatment sites ranged from 2.1–3.9mm(lateral), 2.2–5.6mm(longitudinal) and 2.6–6.5mm(vertical). This corresponds to rigid margins between 7.4–18.9mm. Comparatively, our data is similar to published data which ranges between 0.7 – 3.3mm for head/neck and brain, and 1.7 – 7.2mm for other sites. Conclusion: Our patient setup error on helical Tomotherapy is consistent with the published literature. ACR‐ASTRO guidelines recommend setting clinical tolerances for IGRT patient shifts. Currently, our institution has a 10 mm shift policy. Further analysis is needed to determine if this tolerance is appropriate for our clinic.

Validation of an elastic registration technique to estimate anatomical lung modification in Non-Small-Cell Lung Cancer Tomotherapy

BackgroundThe study of lung parenchyma anatomical modification is useful to estimate dose discrepancies during the radiation treatment of Non-Small-Cell Lung Cancer (NSCLC) patients. We propose and validate a method, based on free-form deformation and mutual information, to elastically register planning kVCT with daily MVCT images, to estimate lung parenchyma modification during Tomotherapy.MethodsWe analyzed 15 registrations between the planning kVCT and 3 MVCT images for each of the 5 NSCLC patients. Image registration accuracy was evaluated by visual inspection and, quantitatively, by Correlation Coefficients (CC) and Target Registration Errors (TRE). Finally, a lung volume correspondence analysis was performed to specifically evaluate registration accuracy in lungs.ResultsResults showed that elastic registration was always satisfactory, both qualitatively and quantitatively: TRE after elastic registration (average value of 3.6 mm) remained comparable and often smaller than voxel resolution. Lung volume variations were well estimated by elastic registration (average volume and centroid errors of 1.78% and 0.87 mm, respectively).ConclusionsOur results demonstrate that this method is able to estimate lung deformations in thorax MVCT, with an accuracy within 3.6 mm comparable or smaller than the voxel dimension of the kVCT and MVCT images. It could be used to estimate lung parenchyma dose variations in thoracic Tomotherapy.