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Publications (9)23.81 Total impact

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    ABSTRACT: The reliable prediction of output factors for spread-out proton Bragg peak (SOBP) fields in clinical practice remained unrealized due to a lack of a consistent theoretical framework and the great number of variables introduced by the mechanical devices necessary for the production of such fields. These limitations necessitated an almost exclusive reliance on manual calibration for individual fields and empirical, ad hoc, models. We recently reported on a theoretical framework for the prediction of output factors for such fields. In this work, we describe the implementation of this framework in our clinical practice. In our practice, we use a treatment delivery nozzle that uses a limited, and constant, set of mechanical devices to produce SOBP fields over the full extent of clinical penetration depths, or ranges, and modulation widths. This use of a limited set of mechanical devices allows us to unfold the physical effects that affect the output factor. We describe these effects and their incorporation into the theoretical framework. We describe the calibration and protocol for SOBP fields, the effects of apertures and range-compensators and the use of output factors in the treatment planning process.
    Physics in Medicine and Biology 01/2006; 50(24):5847-56. · 2.70 Impact Factor
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    ABSTRACT: The magnitude of inter- and intrafractional patient motion has been assessed for a broad set of immobilization devices. Data was analyzed for the three ordinal directions--left-right (x), sup-inf (y), and ant-post (z)--and the combined spatial displacement. We have defined "rigid" and "non-rigid" immobilization devices depending on whether they could be rigidly and reproducibly connected to the treatment couch or not. The mean spatial displacement for intrafractional motion for rigid devices is 1.3 mm compared to 1.9 mm for nonrigid devices. The modified Gill-Thomas-Cosman frame performed best at controlling intrafractional patient motion, with a 95% probability of observing a three-dimensional (3D) vector length of motion (v95) of less than 1.8 mm, but could not be evaluated for interfractional motion. All other rigid and nonrigid immobilization devices had a v95 of more than 3 mm for intrafractional patient motion. Interfractional patient motion was only evaluated for the rigid devices. The mean total interfractional displacement was at least 3.0 mm for these devices while v95 was at least 6.0 mm.
    Medical Physics 12/2005; 32(11):3468-74. · 2.91 Impact Factor
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    ABSTRACT: Modern radiotherapy equipment is capable of delivering high precision conformal dose distributions relative to isocentre. One of the barriers to precise treatments is accurate patient re-positioning before each fraction of treatment. At Massachusetts General Hospital, we perform daily patient alignment using radiographs, which are captured by flat panel imaging devices and sent to an analysis program. A trained therapist manually selects anatomically significant features in the skeleton, and couch movement is computed based on the image coordinates of the features. The current procedure takes about 5 to 10 min and significantly affects the efficiency requirement in a busy clinic. This work presents our effort to develop an improved, semi-automatic procedure that uses the manually selected features from the first treatment fraction to automatically locate the same features on the second and subsequent fractions. An implementation of this semi-automatic procedure is currently in clinical use for head and neck tumour sites. Radiographs collected from 510 patient set-ups were used to test this algorithm. A mean difference of 1.5 mm between manual and automatic localization of individual features and a mean difference of 0.8 mm for overall set-up were seen.
    Physics in Medicine and Biology 11/2005; 50(19):4667-79. · 2.70 Impact Factor
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    ABSTRACT: Clinical target volumes of the thorax and abdomen are typically expanded to account for inter- and intrafractional organ motion. Usually, such expansions are based on clinical experience and planar observations of target motion during simulation. More precise, 4-dimensional motion margins for a specific patient may improve dose coverage of mobile targets and yet limit unnecessarily large field expansions. We are studying approaches to targeting moving tumors throughout the entire treatment process, from treatment planning to beam delivery. Radio-opaque markers were implanted under CT guidance in the liver at the gross tumor periphery. Organ motion during light respiration was volumetrically imaged by 4D Computed Tomography. Marker motion was also acquired by fluoroscopy and compared with 4DCT data. During treatment, daily diagnostic x-ray images were captured at end-exhale and -inhale for patient setup and target localization. Based on the time-resolved CT data, target volumes can be designed to account for respiratory motion during treatment. Motion of the tumor as derived from 4DCT was consistent with fluoroscopic motion analysis. Radiographs acquired in the treatment room enabled millimeter-level patient set-up and assessment of target position relative to bony anatomy. Daily positional variations between bony anatomy and implanted markers were observed. Image guided therapy, based on 4DCT imaging, fluoroscopic imaging studies, and daily gated diagonstic energy set-up radiographs is being developed to improve beam delivery precision. Monitoring internal target motion throughout the entire treatment process will ensure adequate dose coverage of the target while sparing the maximum healthy tissue.
    Radiotherapy and Oncology 01/2005; 73 Suppl 2:S68-72. · 4.52 Impact Factor
  • Medical Physics 01/2005; 32(6). · 2.91 Impact Factor
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    J. Flanz, T. Delaney, H. Kooy, S. Rosenthal, U. Titt
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    ABSTRACT: The Northeast Proton Therapy Center (NPTC) at Massachusetts General Hospital has been treating patients with proton beams since November 2001. Over 200 patients were treated in the first year of operation. This facility has replaced the program at the Harvard Cyclotron Laboratory (HCL) where proton treatments had been underway for over three decades. Features such as rotating gantries and deeper proton penetration allow a wider range of clinical applications at this new facility. The requirements of accelerator reproducibility and availability are perhaps at a higher level than those required at an accelerator based physics facility. These requirements and the system performance will be highlighted in this paper. Operation of a proton cyclotron produced by industry (Ion Beam Applications) and the four operating beam lines along with the Gantries and patient-positioning systems will be discussed. Of particular interest in addition to the required availability is the systematic approach to safety and accuracy in the design and implementation.
    Particle Accelerator Conference, 2003. PAC 2003. Proceedings of the; 06/2003
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    ABSTRACT: With proton beam radiation therapy a smaller volume of normal tissues is irradiated at high dose levels for most anatomic sites than is feasible with any photon technique. This is due to the Laws of Physics, which determine the absorption of energy from photons and protons. In other words, the dose from a photon beam decreases exponentially with depth in the irradiated material. In contrast, protons have a finite range and that range is energy dependent. Accordingly, by appropriate distribution of proton energies, the dose can be uniform across the target and essentially zero deep to the target and the atomic composition of the irradiated material. The dose proximal to the target is lower compared with that in photon techniques, for all except superficial targets This resultant closer approximation of the planning treatment volume (PTV) to the CTV/GTV (grossly evident tumor volume/subclinical tumor extensions) constitutes a clinical gain by definition; i.e. a smaller treatment volume that covers the target three dimensionally for the entirety of each treatment session provides a clinical advantage. Several illustrative clinical dose distributions are presented and the clinical outcome results are reviewed briefly. An important technical advance will be the use of intensity modulated proton radiation therapy, which achieves contouring of the proximal edge of the SOBP (spread out Bragg peak) as well as the distal edge. This technique uses pencil beam scanning. To permit further progressive reductions of the PTV, 4-D treatment planning and delivery is required. The fourth dimension is time, as the position and contours of the tumor and the adjacent critical normal tissues are not constant. A potentially valuable new method for assessing the clinical merits of each of a large number of treatment plans is the evaluation of multidimensional plots of the complication probabilities for each of 'n' critical normal tissues/ structures for a specified tumor control probability. The cost of proton therapy compared with that of very high technology photon therapy is estimated and evaluated. The differential is estimated to be approximately 1.5 provided there were to be no charge for the original facility and that there were sufficient patients for operating on an extended schedule (6-7 days of 14-16 h) with > or = two gantries and one fixed horizontal beam.
    Acta Oncologica 01/2003; 42(8):800-8. · 2.87 Impact Factor
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    ABSTRACT: The authors report the results of a prospective study of patients with malignant neuroendocrine tumors of the sinonasal tract who received multimodality treatment incorporating high-dose proton-photon radiotherapy. Nineteen patients with olfactory neuroblastoma (ONB) or neuroendocrine carcinoma (NEC) were treated between 1992 and 1998 on a prospective study. Four patients had Kadish Stage B disease, and 15 patients had Kadish Stage C disease. The median patient age was 44 years. Patients received chemotherapy with 2 courses of cisplatin and etoposide followed by high-dose proton-photon radiotherapy to 69.2 cobalt-Gray equivalents (CGE) using 1.6-1.8 CGE per fraction twice daily in a concomitant boost schedule. Two further courses of chemotherapy were given to responders. Of 19 patients, 15 patients were alive at the time of this report with a median follow-up of 45 months (range, 20-92 months). Four patients died from disseminated disease 8-47 months after their original diagnosis. The 5-year survival rate was 74%. There were two local recurrences, and both patients underwent salvage surgery. The 5-year local control rate of initial treatment was 88%. Acute toxicity of chemotherapy was tolerable, with no patient sustaining more than Grade 3 hematologic toxicity. Thirteen patients showed a partial or complete response to chemotherapy. One patient developed unilateral visual loss after the first course of chemotherapy; otherwise, visual preservation was achieved in all patients. Four patients who were clinically intact developed radiation-induced damage to the frontal or temporal lobe by magnetic resonance imaging criteria. Two patients showed soft tissue and/or bone necrosis, and one of these patients required surgical repair of a cerebrospinal fluid leak. Neoadjuvant chemotherapy and high-dose proton-photon radiotherapy is a successful treatment approach for patients with ONB and NEC. Radical surgery is reserved for nonresponders. Due to the precision of delivery of radiation with stereotactic setup and protons, no radiation-induced visual loss was observed.
    Cancer 06/2002; 94(10):2623-34. · 5.20 Impact Factor
  • International Journal of Radiation Oncology Biology Physics - INT J RADIAT ONCOL BIOL PHYS. 01/1998; 42(1):222-222.