S Chaudhari

Exploring feature-based approaches in PET images for predicting cancer treatment outcomes

Accumulating evidence suggests that characteristics of pre-treatment FDG-PET could be used as prognostic factors to predict outcomes in different cancer sites. Current risk analyses are limited to visual assessment or direct uptake value measurements. We are investigating intensity-volume histogram metrics and shape and texture features extracted from PET images to predict patients response to treatment. These approaches were demonstrated using datasets from cervix and head and neck cancers, where AUC of 0.76 and 1.0 were achieved, respectively. The preliminary results suggest that the proposed approaches could potentially provide better tools and discriminant power for utilizing functional imaging in clinical prognosis.

Helical Tomotherapy Planning for Left-Sided Breast Cancer Patients With Positive Lymph Nodes: Comparison to Conventional Multiport Breast Technique

PURPOSE To evaluate the feasibility of using helical tomotherapy for locally advanced left-sided breast cancer. METHODS AND MATERIALS Treatment plans were generated for 10 left-sided breast cancer patients with positive lymph nodes comparing a multiport breast (three-dimensional) technique with the tomotherapy treatment planning system. The planning target volumes, including the chest wall/breast, supraclavicular, axillary, and internal mammary lymph nodes, were contoured. The treatment plans were generated on the tomotherapy treatment planning system to deliver 50.4 Gy to the planning target volume. To spare the contralateral tissues, directional blocking was applied to the right breast and right lung. The optimization goals were to protect the lungs, heart, and right breast. RESULTS The tomotherapy plans increased the minimal dose to the planning target volume (minimal dose received by 99% of target volume = 46.2 +/- 1.3 Gy vs. 27.9 +/- 17.1 Gy) while improving the dose homogeneity (dose difference between the minimal dose received by 5% and 95% of the planning target volume = 7.5 +/- 1.8 Gy vs. 37.5 +/- 26.9 Gy). The mean percentage of the left lung volume receiving >or=20 Gy in the tomotherapy plans decreased from 32.6% +/- 4.1% to 17.6% +/- 3.5%, while restricting the right-lung mean dose to <5 Gy. However, the mean percentage of volume receiving >or=5 Gy for the total lung increased from 25.2% +/- 4.2% for the three-dimensional technique to 46.9% +/- 8.4% for the tomotherapy plan. The mean volume receiving >or=35 Gy for the heart decreased from 5.6% +/- 4.8% to 2.2% +/- 1.5% in the tomotherapy plans. However, the mean heart dose for tomotherapy delivery increased from 7.5 +/- 3.4 Gy to 12.2 +/- 1.8 Gy. CONCLUSION The tomotherapy plans provided better dose conformity and homogeneity than did the three-dimensional plans for treatment of left-sided breast tumors with regional lymph node involvement, while allowing greater sparing of the heart and left lung from doses associated with increased complications.

Prospective Clinical Trial of Positron Emission Tomography/Computed Tomography Image-Guided Intensity-Modulated Radiation Therapy for Cervical Carcinoma With Positive Para-Aortic Lymph Nodes

PURPOSE To describe a more aggressive treatment technique allowing dose escalation to positive para-aortic lymph nodes (PALN) in patients with cervical cancer, by means of positron emission tomography (PET)/computed tomography (CT)-guided intensity-modulated radiation therapy (IMRT). Here, we describe methods for simulation and planning of these treatments and provide objectives for target coverage as well as normal tissue sparing to guide treatment plan evaluation. METHODS AND MATERIALS Patients underwent simulation on a PET/CT scanner. Treatment plans were generated to deliver 60.0 Gy to the PET-positive PALN and 50.0 Gy to the PALN and pelvic lymph node beds. Treatment plans were optimized to deliver at least 95% of the prescribed doses to at least 95% of each target volume. Dose-volume histograms were calculated for normal structures. RESULTS The plans of 10 patients were reviewed. Target coverage goals were satisfied in all plans. Analysis of dose-volume histograms indicated that treatment plans involved irradiation of approximately 50% of the bowel volume to at least 25.0 Gy, with less than 10% receiving at least 50.0 Gy and less than 1% receiving at least 60.0. With regard to kidney sparing, approximately 50% of the kidney volume received at least 16.0 Gy, less than 5% received at least 50.0 Gy, and less than 1% received at least 60.0 Gy. CONCLUSIONS We have provided treatment simulation and planning methods as well as guidelines for the evaluation of target coverage and normal tissue sparing that should facilitate the more aggressive treatment of cervical cancer.

Deformable registration of abdominal kilovoltage treatment planning CT and tomotherapy daily megavoltage CT for treatment adaptation

In adaptive radiation therapy the treatment planning kilovoltage CT (kVCT) images need to be registered with daily CT images. Daily megavoltage CT (MVCT) images are generally noisier than the kVCT images. In addition, in the abdomen, low image contrast, differences in bladder filling, differences in bowel, and rectum filling degrade image usefulness and make deformable image registration very difficult. The authors have developed a procedure to overcome these difficulties for better deformable registration between the abdominal kVCT and MVCT images. The procedure includes multiple image preprocessing steps and a two deformable registration steps. The image preprocessing steps include MVCT noise reduction, bowel gas pockets detection and painting, contrast enhancement, and intensity manipulation for critical organs. The first registration step is carried out in the local region of the critical organs (bladder, prostate, and rectum). It requires structure contours of these critical organs on both kVCT and MVCT to obtain good registration accuracy on these critical organs. The second registration step uses the first step results and registers the entire image with less intensive computational requirement. The two-step approach improves the overall computation speed and works together with these image preprocessing steps to achieve better registration accuracy than a regular single step registration. The authors evaluated the procedure on multiple image datasets from prostate cancer patients and gynecological cancer patients. Compared to rigid alignment, the proposed method improves volume matching by over 60% for the critical organs and reduces the prostate landmark registration errors by 50%.

Dosimetric consequences of uncorrected setup errors in helical Tomotherapy treatments of breast-cancer patients

BACKGROUND AND PURPOSE The Tomotherapy Hi-Art II system allows acquisition of pre-treatment MVCT images to correct patient position. This work evaluates the dosimetric impact of uncorrected setup errors in breast-cancer radiation therapy. MATERIALS AND METHODS Breast-cancer patient-positioning errors were simulated by shifting the patient computed-tomography (CT) dataset relative to the planned photon fluence and re-computing the dose distributions. To properly evaluate the superficial region, film measurements were compared against the Tomotherapy treatment planning system (TPS) calculations. A simulation of the integrated dose distribution was performed to evaluate the setup error impact over the course of treatment. RESULTS Significant dose differences were observed for 11-mm shifts in the anterolateral and 3-mm shifts in the posteromedial directions. The results of film measurements in the superficial region showed that the TPS overestimated the dose by 14% at a 1-mm depth, improving to 3% at depths >or=5mm. Significant dose reductions in PTV were observed in the dose distributions simulated over the course of treatment. CONCLUSIONS Tomotherapys rotational delivery provides sufficient photon fluence extending beyond the skin surface to allow an up to 7-mm uncorrected setup error in the anterolateral direction. However, the steep dose falloff that conforms to the lung surface leads to compromised dose distributions with uncorrected posteromedial shifts. Therefore, daily image guidance and consequent patient repositioning is warranted for breast-cancer patients.

Estimation of Setup Uncertainty Using Planar and MVCT Imaging for Gynecologic Malignancies

PURPOSE This prospective study investigates gynecologic malignancy online treatment setup error corrections using planar kilovoltage/megavoltage (KV/MV) imaging and helical MV computed tomography (MVCT) imaging. METHODS AND MATERIALS Twenty patients were divided into two groups. The first group (10 patients) was imaged and treated using a conventional linear accelerator (LINAC) with image-guidance capabilities, whereas the second group (10 patients) was treated using tomotherapy with MVCT capabilities. Patients treated on the LINAC underwent planar KV and portal MV imaging and a two-dimensional image registration algorithm was used to match these images to digitally reconstructed radiographs (DRRs). Patients that were treated using tomotherapy underwent MVCT imaging, and a three-dimensional image registration algorithm was used to match planning CT to MVCT images. Subsequent repositioning shifts were applied before each treatment and recorded for further analysis. To assess intrafraction motion, 5 of the 10 patients treated on the LINAC underwent posttreatment planar imaging and DRR matching. Based on these data, patient position uncertainties along with estimated margins based on well-known recipes were determined. RESULTS The errors associated with patient positioning ranged from 0.13 cm to 0.38 cm, for patients imaged on LINAC and 0.13 cm to 0.48 cm for patients imaged on tomotherapy. Our institutional clinical target volume-PTV margin value of 0.7 cm lies inside the confidence interval of the margins established using both planar and MVCT imaging. CONCLUSION Use of high-quality daily planar imaging, volumetric MVCT imaging, and setup corrections yields excellent setup accuracy and can help reduce margins for the external beam treatment of gynecologic malignancies.

The validation of tomotherapy dose calculations in low-density lung media

The dose-calculation accuracy of the tomotherapy Hi-Art II(R) (Tomotherapy, Inc., Madison, WI) treatment planning system (TPS) in the presence of low-density lung media was investigated. In this evaluation, a custom-designed heterogeneous phantom mimicking the mediastinum geometry was used. Gammex LN300 and balsa wood were selected as two lung-equivalent materials with different densities. Film analysis and ionization chamber measurements were performed. Treatment plans for esophageal cancers were used in the evaluation. The agreement between the dose calculated by the TPS and the dose measured via ionization chambers was, in most cases, within 0.8%. Gamma analysis using 3% and 3 mm criteria for radiochromic film dosimetry showed that 98% and 95% of the measured dose distribution had passing gamma values < or =1 for LN300 and balsa wood, respectively. For a homogeneous water-equivalent phantom, 95% of the points passed the gamma test. It was found that for the interface between the low-density medium and water-equivalent medium, the TPS calculated the dose distribution within acceptable limits. The phantom developed for this work enabled detailed quality-assurance testing under realistic conditions with heterogeneous media.

Enhanced efficiency in helical tomotherapy quality assurance using a custom-designed water-equivalent phantom

Tomotherapy is an image-guided, intensity-modulated radiation therapy system that delivers highly conformal dose distributions in a helical fashion. This system is also capable of acquiring megavoltage computed-tomography images and registering them to the planning kVCT images for accurate target localization. Quality assurance (QA) of this device is time intensive, but can be expedited by improved QA tools and procedures. A custom-designed phantom was fabricated to improve the efficiency of daily QA of our Tomotherapy machine. The phantom incorporates ionization chamber measurement points, plugs of different densities and slide-out film cartridges. The QA procedure was designed to verify in less than 30 min the vital components of the tomotherapy system: static beam quality and output, image quality, correctness of image registration and energy of the helical dose delivery. Machine output, percent depth dose and off-axis factors are simultaneously evaluated using a static 5 x 40 cm(2) open field. A single phantom scan is used to evaluate image quality and registration accuracy. The phantom can also be used for patient plan-specific QA. The QA results over a period of 6 months are reported in this paper. The QA process was found to be simple, efficient and capable of simultaneously verifying several important parameters.

TU-D-M100F-09: Breathing Motion-Induced Dose Delivery Error Evaluations as Applied to Tomotherapy Dose Delivery

Purpose: To develop a method for evaluating breathing motion‐induced dose delivery errors in Tomotherapy dose delivery. Methods and Materials: Dosimetric inaccuracy can result from breathing‐induced tumor motion in Tomotherapy treatment delivery. Patient breathing motion patterns were simulated using quantitative spirometry‐measured patient tidal volumes and converting the tidal volume to tumor motion by varying the ratio of tumor motion to tidal volume for 34 patients. Simulations of Tomotherapy deliveries were conducted modifying the previously published techniques by using measured beam profiles instead of step‐function fluences, and couch speeds typical of Tomotherapy treatments. Radiochromic film and our in‐house 4D phantom were used to verify the algorithm. Results: As expected, the breathing motion blurred the dose distributions, but slow drifts in the average tissue position caused detectable dose errors. The dose errors were expectedly largest with the smallest (1.0cm) field size, and could be >10% for motion amplitudes comparable to the field size. As the field width increased relative to the motion amplitude, and as couch‐speed (pitch) decreased, the error also decreased, and as such these settings may be preferable for patient treatments. These slow drifts occurred over time periods that were coincident with the amount of time required for the field to pass a stationary point. Measurements agreed with the simulation. Conclusions: Previous breathing motion studies did not use real patient breathing patterns and therefore did not consider the impact of slow, relatively small drifts in those patterns. The drifts change direction during the breathing measurement, causing dose errors that are both positive and negative. While the individual dose fraction errors can be >10%, they are unlikely to occur in the same place each day, so the average dose is likely to be consistent with earlier studies. Conflict of Interest: This work supported in part by a grant from Tomotherapy, Inc.

SU‐EE‐A1‐06: Helical Tomotherapy Planning for Left‐Sided Breast Cancer Patients with Positive Lymph Nodes: Compared to Conventional Multi‐Port‐Breast Technique

Purpose: The objective of this study was to evaluate the feasibility of using helical tomotherapy for left‐sided breast cancer patients with involved lymph nodes. Method and Materials: Four left‐sided breast cancer patients treated using conventional multi‐port‐breast technique were retrospectively planned on Tomotherapy planning system. PTVs including chest‐wall/breast, supraclavicular, axillary and internal‐ mammary lymphnodes were contoured. Optimized treatment plans were generated on Tomotherapy TPS using 25mm field‐width with pitch of 0.42. The modulation factors varied from 1.5–2.6. All plans had a prescription of 50.4Gy to 93% and 46.9Gy to 98% of the PTV. Directional blocking was used on the right side to limit the dose to the contra‐lateral‐breast and lung. The optimization goals for planning were to protect the heart and lungs from receiving excessive doses. Resulting plans were compared against a conventional multi‐port breast technique. Lung toxicities using the Lymann‐Kutcher‐Burman model were estimated for tomotherapy plans. The parameters used for these calculations are TD50%=30.8Gy, slope(m)=0.37 and the exponent(a)=1. Results: Tomotherapy increased the minimum dose to the PTV (D99% = 44.6Gy for tomotherapy versus 30.5Gy for 3D) while improving the homogeneity index (HI = 1.16 for tomotherapy and 1.52 for 3D). The mean V20Gy for the left lung decreased from 32.6% (3D) to 16.4% (tomotherapy) while keeping the mean right lung dose well under 4Gy. However, the mean V5Gy volume increased from 26.4% (3D) to 42.6% (tomotherapy). The mean V35Gy for the heart decreased from 6.5%–2.5%, while the mean heart dose increased from 9.5Gy–11.3Gy for conventional and tomotherapy, respectively. The estimated NTCP for lung range from 1.4% to 2.4% for tomotherapy plans. Conclusion: Tomotherapy plans have better conformity and dose homogeneity than the 3D‐ plans. Tomotherapy provided improved sparing for the heart and lungs.Conflict of Interest: This work supported in part by Tomotherapy, Inc.