S. Chaudhari

University of Washington Seattle, Seattle, WA, United States

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Publications (19)56.73 Total impact

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    ABSTRACT: 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.
    Physics in Medicine and Biology 10/2009; 54(19):5663-74. · 2.70 Impact Factor
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    ABSTRACT: 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. 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. 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. Tomotherapy's 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.
    Radiotherapy and Oncology 10/2009; 93(1):64-70. · 4.52 Impact Factor
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    ABSTRACT: 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 patient's 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.
    Pattern Recognition 06/2009; 42(6):1162-1171. · 2.58 Impact Factor
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    ABSTRACT: In their classic paper, Yu et al (1998 Phys. Med. Biol. 43 91) investigated the interplay between tumor motion caused by breathing and dynamically collimated, intensity-modulated radiation delivery. The paper's analytic model assumed an idealized, sinusoidal pattern of motion. In this work, we investigate the effect of tumor motion based on patients' breathing patterns for typical tomotherapy treatments with field widths of 1.0 and 2.5 cm. The measured breathing patterns of 52 lung- and upper-abdominal-cancer patients were used to model a one-dimensional motion. A convolution of the measured beam-dose profiles with the motion model was used to compute the dose-distribution errors, and the positive and negative dose errors were recorded for each simulation. The dose errors increased with increasing motion magnitude, until the motion was similar in magnitude to the field width. For the 1.0 cm and 2.5 cm field widths, the maximum dose-error magnitude exceeded 10% in some simulations, even with breathing-motion magnitudes as small as 5 mm and 10 mm, respectively. Dose errors also increased slightly with increasing couch speed. We propose that the errors were due to subtle drifts in the amplitude and frequency of breathing motion, as well as changes in baseline (exhalation) position, causing both over- and under-dosing of the target. The results of this study highlight potential breathing-motion-induced dose delivery errors in tomotherapy. However, for conventionally fractionated treatments, the dose delivery errors may not be co-located and may average out over many fractions, although this may not be true for hypofractionated treatments.
    Physics in Medicine and Biology 05/2009; 54(8):2541-55. · 2.70 Impact Factor
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    ABSTRACT: 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.
    Physics in Medicine and Biology 05/2009; 54(8):2315-22. · 2.70 Impact Factor
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    ABSTRACT: To evaluate the feasibility of using helical tomotherapy for locally advanced left-sided breast cancer. 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. 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. 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.
    International journal of radiation oncology, biology, physics 03/2009; 73(4):1243-51. · 4.59 Impact Factor
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    ABSTRACT: 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%.
    Medical Physics 03/2009; 36(2):329-38. · 2.91 Impact Factor
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    ABSTRACT: 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. 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. 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. 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.
    International Journal of Radiation OncologyBiologyPhysics 09/2008; 71(5):1511-7. · 4.52 Impact Factor
  • Kl Moore, Sm Goddu, S. Chaudhari, Ej Kintzel, Da Low
    International Journal of Radiation OncologyBiologyPhysics 09/2008; 35(6). · 4.52 Impact Factor
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    ABSTRACT: 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. 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. 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. 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.
    International journal of radiation oncology, biology, physics 06/2008; 72(4):1134-9. · 4.59 Impact Factor
  • Medical Physics - MED PHYS. 01/2008; 35(6).
  • Medical Physics 01/2008; 35(6). · 2.91 Impact Factor
  • S Chaudhari, S Goddu, S Mutic, J Grigsby, D Low
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    ABSTRACT: Purpose: To verify the patient‐specific dosimetric accuracy of the helical tomotherapy system. Methods and Materials: Tomotherapy is a new and complex delivery system. Varying parameters such as pitch and modulating the beam at various angles during fan‐beam delivery can produce highly conformal dose distributions. Patient‐specific dosimetric verification is thus critical. This study uses a custom‐designed 18×18×18 cm3 phantom made from water‐equivalent plastic and Exradin A1SL ionization chambers to perform patient‐specific quality assurance (QA) procedures. During treatment, proper positioning of the patient is critical to avoid compromising treatment delivery. Tomotherapy allows roll correction to compensate for patient positioning errors. The roll correction was tested for 5°, 10°, 20°, and 30° using radiographic film dosimetry, the “cheese” phantom and the custom‐designed cuboid phantom. Results: Average ionization chamber correction factors for all patients treated on Tomotherapy were within 1.2%. Film dosimetry for every patient was also performed prior to treatment. Gamma and isodose overlay profiles were analyzed using commercial film analysis software. Results showed no significant dose delivery errors, and all patients passed within 5%. Gamma analysis was performed and showed excellent agreement by comparison with plans without phantom rotation.. Gamma values were within 3.3% at 3mm and 5% distance to agreement. A custom leaf‐control file, or sinogram, is created for each patient's plan, and replicated each time the patient plan is to be delivered. Dosimetric verification for three patient plans was performed to verify the integrity of the sinogram replication process. Results for each tested plan agreement within 1% for each patient fraction. Conclusion: Tomotherapy allows for accurate delivery, and accurately applies the roll correction as shown by direct dose distribution measurements. Conflict of Interest: This work supported in part by a grant from Tomotherapy, Inc.
    Medical Physics 05/2007; 34(6):2498-2499. · 2.91 Impact Factor
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    ABSTRACT: 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.
    Medical Physics 05/2007; 34(6):2336-2336. · 2.91 Impact Factor
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    ABSTRACT: Purpose: To quantitate shallow‐depth dose calculation accuracy for IMRT breast treatment plans created with Tomotherapy system and to estimate the dose errors caused by setup errors. Methods: A cylindrical solid water phantom with radiochromic film was used for this purpose. The split phantom can hold a film in coronal or sagittal planes. A 5cm thick PTV was contoured by extending it to the surface of the phantom. A plan was optimized to treat the superficial PTV while limiting the dose to the surrounding critical structures. To evaluate the setup uncertainties multiple phantom plans were generated by shifting the phantom 5, 10 and 20 mm to right and up (7, 14, and 28mm distance) and simulated doses were compared against the measured doses. The 3D dose matrices from TPS for no‐shift and shifted phantom plans were exported in DICOM and were analyzed in MatLab. Doses from eleven transverse slices were analyzed to estimate the dose differences in the shifted phantom plans. Shifted phantom plan dose distributions were transposed back onto the patient PTV and computed dose difference histograms (DDHs) in the PTV volume. Results: The planning system overestimated the shallow‐depth dose by as much as 14%, but was smaller than 3% at depths greater than 5mm. PTV DDHs for no and 7 mm shifts showed <5% dose differences, while for 14 mm, the dose differences were ⩽10% and were very large for the 28 mm shift. Conclusion: Tomotherapy planning system computes the shallow‐depth dose within 14% accuracy at 1.0 mm and better than 3% for depths greater than 5mm. Setup errors ⩽7mm showed negligible dose errors, consistent with the use of image‐guided therapy. Large shifts were required to induce large dose errors in the PTV. Conflict of Interest: This work supported in part by Tomotherapy, Inc.
    Medical Physics 05/2007; 34(6):2501-2501. · 2.91 Impact Factor
  • D. Rangaraj, S. Chaudhari, S. Goddu, D. Low
    Medical Physics 01/2007; 34(6):2469-. · 2.91 Impact Factor
  • Medical Physics - MED PHYS. 01/2007; 34(6).
  • Medical Physics 01/2007; 34(6). · 2.91 Impact Factor
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    ABSTRACT: Purpose: Helical Tomotherapy is a relatively new treatment modality that is being used to treat lesions that lie within and near low‐density organs. Accurate dose calculations are critical to the effective use of this modality. This study quantified the Tomotherapy treatment planning system (TPS) convolution‐superposition‐based dose calculation accuracy in heterogeneous media. Method and Materials: This evaluation required a custom fabricated dosimetry phantom with lung‐equivalent and water‐equivalent media. The phantom consisted of an 18×18×18 cm3 cuboid constructed from slabs of water‐equivalent and lung‐equivalent materials (LN300 Gammex RMI, Middleton, WI (ρ ∼0.3g/cc), and Balsa wood (ρ ∼0.1g/cc) and imaged on a CT scanner. Dose measurements were conducted using both film and ionization chambers using the same phantom geometry. Evaluations were conducted using an esophageal treatment plan, delivering 1.8 Gy/fraction, was superimposed onto the phantom CT‐datasets and computed the dose distributions using the Tomotherapy treatment planning system. Radiochromic film (EBT, International specialty Products, Wayne, NJ) sheets were inserted between slabs of virtual water and lung equivalent material LN‐300. Experiments were repeated with radiographic film (Kodak EDR2, Eastman Kodak, Rochester, NY) with balsa wood. Calibration curves for absolute dosimetry for both types of film were generated from additional film exposures and ion chamber measurements on the Tomotherapy unit. Ionization‐chamber measurements were performed to confirm the film dosimetry. Results: Doses measured inside the water‐equivalent plastic were within 2% of the computed doses by the Tomotherapy planning system. Measurements with radiochromic film in LN‐300 material verified that the planning system computed the doses within 5%. Similar results were observed with EDR2 film in Balsa wood. Conclusions: The dose calculation accuracy of TPS was measured to be within 5% in lung material and within 2% in water‐equivalent plastic. This work supported in part by Tomotherapy, Inc.
    Medical Physics 01/2006; 33(6). · 2.91 Impact Factor