Molecular Imaging for Integrated Medical Therapy and Drug Development, 2010
Tumor hypoxia, or the condition of low oxygen, is a key factor for tumor progression and treatmen... more Tumor hypoxia, or the condition of low oxygen, is a key factor for tumor progression and treatment resistance. Because hypoxic tumor cells are more resistant to ionizing radiation, hypoxia has been a focus of clinical research in radiation therapy for half a century. During this period, interest in targeting tumor hypoxia has waxed and waned as promising treatments emerged from
International Journal of Radiation Oncology Biology Physics, 2000
Purpose: To evaluate the incidence and prognostic significance of lymph node metastasis in maxill... more Purpose: To evaluate the incidence and prognostic significance of lymph node metastasis in maxillary sinus carcinoma.Methods and Materials: We reviewed the records of 97 patients treated for maxillary sinus carcinoma with radiotherapy at Stanford University and at the University of California, San Francisco between 1959 and 1996. Fifty-eight patients had squamous cell carcinoma (SCC), 4 had adenocarcinoma (ADE), 16 had undifferentiated carcinoma (UC), and 19 had adenoid cystic carcinoma (AC). Eight patients had T2, 36 had T3, and 53 had T4 tumors according to the 1997 AJCC staging system. Eleven patients had nodal involvement at diagnosis: 9 with SCC, 1 with UC, and 1 with AC. The most common sites of nodal involvement were ipsilateral level 1 and 2 lymph nodes. Thirty-six patients were treated with definitive radiotherapy alone, and 61 received a combination of surgical and radiation treatment. Thirty-six patients had neck irradiation, 25 of whom received elective neck irradiation (ENI) for N0 necks. The median follow-up for alive patients was 78 months.Results: The median survival for all patients was 22 months (range: 2.4–356 months). The 5- and 10-year actuarial survivals were 34% and 31%, respectively. Ten patients relapsed in the neck, with a 5-year actuarial risk of nodal relapse of 12%. The 5-year risk of neck relapse was 14% for SCC, 25% for ADE, and 7% for both UC and ACC. The overall risk of nodal involvement at either diagnosis or on follow-up was 28% for SCC, 25% for ADE, 12% for UC, and 10% for AC. All patients with nodal involvement had T3–4, and none had T2 tumors. ENI effectively prevented nodal relapse in patients with SCC and N0 neck; the 5-year actuarial risk of nodal relapse was 20% for patients without ENI and 0% for those with elective neck therapy. There was no correlation between neck relapse and primary tumor control or tumor extension into areas containing a rich lymphatic network. The most common sites of nodal relapse were in the ipsilateral level 1–2 nodal regions (11/13). Patients with nodal relapse had a significantly higher risk of distant metastasis on both univariate (p = 0.02) and multivariate analysis (hazard ratio = 4.5, p = 0.006). The 5-year actuarial risk of distant relapse was 29% for patients with neck control versus 81% for patients with neck failure. There was also a trend for decreased survival with nodal relapse. The 5-year actuarial survival was 37% for patients with neck control and 0% for patients with neck relapse.Conclusion: The overall incidence of lymph node involvement at diagnosis in patients with maxillary sinus carcinoma was 9%. Following treatment, the 5-year risk of nodal relapse was 12%. SCC histology was associated with a high incidence of initial nodal involvement and nodal relapse. None of the patients presenting with SCC histology and N0 necks had nodal relapse after elective neck irradiation. Patients who had nodal relapse had a higher risk of distant metastasis and poorer survival. Therefore, our present policy is to consider elective neck irradiation in patients with T3–4 SCC of the maxillary sinus.
To determine the diagnostic accuracy and the ideal timing of fluoro-fluorodeoxyglucose positron-e... more To determine the diagnostic accuracy and the ideal timing of fluoro-fluorodeoxyglucose positron-emission tomography (PET) in the posttreatment surveillance of head and neck mucosal squamous cell carcinoma (HNSCC). Retrospective chart review. Our sample includes 103 adult patients with 118 posttreatment PET scans who had undergone treatment for HNSCC. We correlated PET results with surgical pathology and clinical outcome in the subsequent 6 months. For the detection of locoregional persistent or recurrent HNSCC, PET scans had a sensitivity of 82%, specificity of 92%, positive predictive value (PPV) of 64%, negative predictive value (NPV) of 97%, and overall accuracy of 90%. For the detection of distant metastases, PET scans had a sensitivity of 89%, specificity of 97%, PPV of 85%, NPV of 98%, and overall accuracy of 96%. PET scans of the head and neck region performed greater than 1 month after the completion of radiation compared with scans performed within 1 month had a significantly higher sensitivity of 95% versus 55% (P < .01) and NPV of 99% versus 90% (P < .01). PET is effective in detecting distant metastases in the posttreatment surveillance for HNSCC patients. A negative PET is highly reliable for all sites. However, a positive PET in the head and neck region is unreliable because of a high false-positivity rate. PET of the head and neck region has a statistically significant risk of a false-negative reading when performed within 1 month of radiation.
This article demonstrates the technical feasibility of noninvasive treatment of unresectable spin... more This article demonstrates the technical feasibility of noninvasive treatment of unresectable spinal vascular malformations and primary and metastatic spinal tumors by use of image-guided frameless stereotactic radiosurgery. Stereotactic radiosurgery delivers a high dose of radiation to a tumor volume or vascular malformation in a limited number of fractions and minimizes the dose to adjacent normal structures. Frameless image-guided radiosurgery was developed by coupling an orthogonal pair of x-ray cameras to a dynamically manipulated robot-mounted linear accelerator that guides the therapy beam to treatment sites within the spine or spinal cord, in an outpatient setting, and without the use of frame-based fixation. The system relies on skeletal landmarks or implanted fiducial markers to locate treatment targets. Sixteen patients with spinal lesions (hemangioblastomas, vascular malformations, metastatic carcinomas, schwannomas, a meningioma, and a chordoma) were treated with total treatment doses of 1100 to 2500 cGy in one to five fractions by use of image-guided frameless radiosurgery with the CyberKnife system (Accuray, Inc., Sunnyvale, CA). Thirteen radiosurgery plans were analyzed for compliance with conventional radiation therapy. Tests demonstrated alignment of the treatment dose with the target volume within +/-1 mm by use of spine fiducials and the CyberKnife treatment planning system. Tumor patients with at least 6 months of follow-up have demonstrated no progression of disease. Radiographic follow-up is pending for the remaining patients. To date, no patients have experienced complications as a result of the procedure. This experience demonstrates the feasibility of image-guided robotic radiosurgery for previously untreatable spinal lesions.
... 3. Nordsmark M, Overgaard J: A confirmatory prognostic study on oxygenation status and loco .... more ... 3. Nordsmark M, Overgaard J: A confirmatory prognostic study on oxygenation status and loco ... Lung Cancer, 2005. Cited Here... 14. Le QT, Chen E, Salim A, et al: An evaluation of tumor oxygenation and gene expression in patients with early stage non-small cell lung cancers. ...
International Journal of Radiation Oncology Biology Physics, 2003
To review the combined experiences of University of California, San Francisco, and Stanford Unive... more To review the combined experiences of University of California, San Francisco, and Stanford University Medical Center in the treatment of intracranial germ cell tumors (GCT) and to assess the impact of craniospinal radiation (CSI) on patterns of relapse, progression-free survival (PFS), and overall survival (OS).Ninety-three patients received radiation for newly diagnosed intracranial GCTs, including 49 germinomas, 16 nongerminomatous GCTs (NGGCT), and 28 with no biopsy. Median follow-up for surviving patients was 4.5 years (range 0.25–34). Tests for variables correlating with OS and PFS were conducted using Cox proportional hazards model.Five-year PFS and OS rates were 60% ± 15% and 68% ± 14% for patients with NGGCT and 88% ± 5% and 93% ± 4% for those with germinoma. Of 6 patients with localized NGGCT who did not receive CSI, 1 experienced an isolated spinal recurrence but was salvaged. Of 41 patients with localized germinoma, 6 who received CSI and 35 who did not, no isolated spinal cord relapses occurred. Twenty-one patients with localized germinoma received neither CSI nor whole brain radiation. Of these, none of 18 with ventricular radiation relapsed. One of 3 patients with primary tumor radiation relapsed intracranially but had only received 11 Gy at initial treatment. On multivariate analysis, germinoma histology but not CSI correlated with improved PFS and OS.CSI is not indicated in the treatment of localized germinomas. For patients with localized germinomas treated with radiation alone, we recommend ventricular irradiation followed by primary tumor boost to a total of 45–50 Gy.
International Journal of Radiation Oncology*Biology*Physics, 2002
1. Int J Radiat Oncol Biol Phys. 2002 Dec 1;54(5):1299-301. Tumor hypoxia is important in radioth... more 1. Int J Radiat Oncol Biol Phys. 2002 Dec 1;54(5):1299-301. Tumor hypoxia is important in radiotherapy, but how should we measure it? Brown JM, Le QT. Comment on Int J Radiat Oncol Biol Phys. 2002 Dec 1;54(5):1537-49. PMID: 12459349 [PubMed - indexed for MEDLINE]. ...
International Journal of Radiation Oncology*Biology*Physics, 2010
... (Int J Radiat Oncol Biol Physics 2009;75:1064-1070) Hans Christiansen, Hendrik A. Wolff, Ralp... more ... (Int J Radiat Oncol Biol Physics 2009;75:1064-1070) Hans Christiansen, Hendrik A. Wolff, Ralph MW Rödel, Christoph Matthias, Clemens F. Hess International Journal of Radiation Oncology * Biology * Physics April 2010 (Vol. 76, Issue 5, Pages 1600-1601). ...
International Journal of Radiation Oncology Biology Physics, 2005
Purpose: To determine the efficacy of concurrent 5-fluorouracil (5-FU) and intensity-modulated ra... more Purpose: To determine the efficacy of concurrent 5-fluorouracil (5-FU) and intensity-modulated radiotherapy (IMRT) followed by body stereotactic radiosurgery (SRS) in patients with locally advanced pancreatic cancer. Methods and Materials: In this prospective study, all patients (19) had pathologically confirmed adenocarcinoma and were uniformly staged. Our treatment protocol consisted of 45 Gy IMRT with concurrent 5-FU followed by a 25 Gy SRS boost to the primary tumor. Results: Sixteen patients completed the planned therapy. Two patients experienced Grade 3 toxicity (none had more than Grade 3 toxicity). Fifteen of these 16 patients were free from local progression until death. Median overall survival was 33 weeks. Conclusions: Concurrent IMRT and 5-FU followed by SRS in patients with locally advanced pancreatic cancer results in excellent local control, but does not improve overall survival and is associated with more toxicity than SRS, alone.
Objective: To determine whether obstetric admissions to the intensive care unit (ICU) are useful ... more Objective: To determine whether obstetric admissions to the intensive care unit (ICU) are useful quality-assurance indicators.Methods: We analyzed retrospectively obstetric ICU admissions at two tertiary care centers from 1991 to 1997.Results: The 131 obstetric admissions represented 0.3% of all deliveries. The majority (78%) of women were admitted to the ICU postpartum. Obstetric hemorrhage (26%) and hypertension (21%) were the two most common reasons for admission. Together with cardiac disease, respiratory disorders, and infection, they accounted for more than 80% of all admissions. Preexisting medical conditions were present in 38% of all admissions. The median Acute Physiology and Chronic Health Evaluation II score was 8.5. The predicted mortality rate for the group was 10.0%, and the actual mortality rate was 2.3%.Conclusion: The most common precipitants of ICU admission were obstetric hemorrhage and uncontrolled hypertension. Improved management strategies for these problems may significantly reduce major maternal morbidity.
Purpose and objective: The primary goal of this study was to examine systematically the dosimetri... more Purpose and objective: The primary goal of this study was to examine systematically the dosimetric effect of small patient movements and linear accelerator angular setting misalignments in the delivery of intensity modulated radiation therapy. We will also provide a method for estimating dosimetric errors for an arbitrary combination of these uncertainties.Materials and methods: Sites in two patients (lumbar-vertebra and nasopharynx) were studied. Optimized intensity modulated radiation therapy treatment plans were computed for each patient using a commercially available inverse planning system (CORVUS, NOMOS Corporation, Sewickley, PA). The plans used nine coplanar beams. For each patient the dose distributions and relevant dosimetric quantities were calculated, including the maximum, minimum, and average doses in targets and sensitive structures. The corresponding dose volumetric information was recalculated by purposely varying the collimator angle or gantry angle of an incident beam while keeping other beams unchanged. Similar calculations were carried out by varying the couch indices in either horizontal or vertical directions. The intensity maps of all the beams were kept the same as those in the optimized plan. The change of a dosimetric quantity, Q, for a combination of collimator and gantry angle misalignments and patient displacements was estimated using Δ=Σ(ΔQ/Δxi)Δxi. Here ΔQ is the variation of Q due to Δxi, which is the change of the i-th variable (collimator angle, gantry angle, or couch indices), and ΔQ/Δxi is a quantity equivalent to the partial derivative of the dosimetric quantity Q with respect to xi.Results: While the change in dosimetric quantities was case dependent, it was found that the results were much more sensitive to small changes in the couch indices than to changes in the accelerator angular setting. For instance, in the first example in the paper, a 3-mm movement of the couch in the anterior–posterior direction can cause a 38% decrease in the minimum target dose or a 41% increase in the maximum cord dose, whereas a 5° change in the θ1=20° beam only gave rise to a 1.5% decrease in the target minimum or 5.1% in the cord maximum. The effect of systematic positioning uncertainties of the machine settings was more serious than random uncertainties, which tended to smear out the errors in dose distributions.Conclusions: The dose distribution of an intensity modulated radiation therapy (IMRT) plan changes with patient displacement and angular misalignment in a complex way. A method was proposed to estimate dosimetric errors for an arbitrary combination of uncertainties in these quantities. While it is important to eliminate the angular misalignment, it was found that the couch indices (or patient positioning) played a much more important role. Accurate patient set-up and patient immobilization is crucial in order to take advantage fully of the technological advances of IMRT. In practice, a sensitivity check should be useful to foresee potential IMRT treatment complications and a warning should be given if the sensitivity exceeds an empirical value. Quality assurance action levels for a given plan can be established out of the sensitivity calculation.
Molecular Imaging for Integrated Medical Therapy and Drug Development, 2010
Tumor hypoxia, or the condition of low oxygen, is a key factor for tumor progression and treatmen... more Tumor hypoxia, or the condition of low oxygen, is a key factor for tumor progression and treatment resistance. Because hypoxic tumor cells are more resistant to ionizing radiation, hypoxia has been a focus of clinical research in radiation therapy for half a century. During this period, interest in targeting tumor hypoxia has waxed and waned as promising treatments emerged from
International Journal of Radiation Oncology Biology Physics, 2000
Purpose: To evaluate the incidence and prognostic significance of lymph node metastasis in maxill... more Purpose: To evaluate the incidence and prognostic significance of lymph node metastasis in maxillary sinus carcinoma.Methods and Materials: We reviewed the records of 97 patients treated for maxillary sinus carcinoma with radiotherapy at Stanford University and at the University of California, San Francisco between 1959 and 1996. Fifty-eight patients had squamous cell carcinoma (SCC), 4 had adenocarcinoma (ADE), 16 had undifferentiated carcinoma (UC), and 19 had adenoid cystic carcinoma (AC). Eight patients had T2, 36 had T3, and 53 had T4 tumors according to the 1997 AJCC staging system. Eleven patients had nodal involvement at diagnosis: 9 with SCC, 1 with UC, and 1 with AC. The most common sites of nodal involvement were ipsilateral level 1 and 2 lymph nodes. Thirty-six patients were treated with definitive radiotherapy alone, and 61 received a combination of surgical and radiation treatment. Thirty-six patients had neck irradiation, 25 of whom received elective neck irradiation (ENI) for N0 necks. The median follow-up for alive patients was 78 months.Results: The median survival for all patients was 22 months (range: 2.4–356 months). The 5- and 10-year actuarial survivals were 34% and 31%, respectively. Ten patients relapsed in the neck, with a 5-year actuarial risk of nodal relapse of 12%. The 5-year risk of neck relapse was 14% for SCC, 25% for ADE, and 7% for both UC and ACC. The overall risk of nodal involvement at either diagnosis or on follow-up was 28% for SCC, 25% for ADE, 12% for UC, and 10% for AC. All patients with nodal involvement had T3–4, and none had T2 tumors. ENI effectively prevented nodal relapse in patients with SCC and N0 neck; the 5-year actuarial risk of nodal relapse was 20% for patients without ENI and 0% for those with elective neck therapy. There was no correlation between neck relapse and primary tumor control or tumor extension into areas containing a rich lymphatic network. The most common sites of nodal relapse were in the ipsilateral level 1–2 nodal regions (11/13). Patients with nodal relapse had a significantly higher risk of distant metastasis on both univariate (p = 0.02) and multivariate analysis (hazard ratio = 4.5, p = 0.006). The 5-year actuarial risk of distant relapse was 29% for patients with neck control versus 81% for patients with neck failure. There was also a trend for decreased survival with nodal relapse. The 5-year actuarial survival was 37% for patients with neck control and 0% for patients with neck relapse.Conclusion: The overall incidence of lymph node involvement at diagnosis in patients with maxillary sinus carcinoma was 9%. Following treatment, the 5-year risk of nodal relapse was 12%. SCC histology was associated with a high incidence of initial nodal involvement and nodal relapse. None of the patients presenting with SCC histology and N0 necks had nodal relapse after elective neck irradiation. Patients who had nodal relapse had a higher risk of distant metastasis and poorer survival. Therefore, our present policy is to consider elective neck irradiation in patients with T3–4 SCC of the maxillary sinus.
To determine the diagnostic accuracy and the ideal timing of fluoro-fluorodeoxyglucose positron-e... more To determine the diagnostic accuracy and the ideal timing of fluoro-fluorodeoxyglucose positron-emission tomography (PET) in the posttreatment surveillance of head and neck mucosal squamous cell carcinoma (HNSCC). Retrospective chart review. Our sample includes 103 adult patients with 118 posttreatment PET scans who had undergone treatment for HNSCC. We correlated PET results with surgical pathology and clinical outcome in the subsequent 6 months. For the detection of locoregional persistent or recurrent HNSCC, PET scans had a sensitivity of 82%, specificity of 92%, positive predictive value (PPV) of 64%, negative predictive value (NPV) of 97%, and overall accuracy of 90%. For the detection of distant metastases, PET scans had a sensitivity of 89%, specificity of 97%, PPV of 85%, NPV of 98%, and overall accuracy of 96%. PET scans of the head and neck region performed greater than 1 month after the completion of radiation compared with scans performed within 1 month had a significantly higher sensitivity of 95% versus 55% (P < .01) and NPV of 99% versus 90% (P < .01). PET is effective in detecting distant metastases in the posttreatment surveillance for HNSCC patients. A negative PET is highly reliable for all sites. However, a positive PET in the head and neck region is unreliable because of a high false-positivity rate. PET of the head and neck region has a statistically significant risk of a false-negative reading when performed within 1 month of radiation.
This article demonstrates the technical feasibility of noninvasive treatment of unresectable spin... more This article demonstrates the technical feasibility of noninvasive treatment of unresectable spinal vascular malformations and primary and metastatic spinal tumors by use of image-guided frameless stereotactic radiosurgery. Stereotactic radiosurgery delivers a high dose of radiation to a tumor volume or vascular malformation in a limited number of fractions and minimizes the dose to adjacent normal structures. Frameless image-guided radiosurgery was developed by coupling an orthogonal pair of x-ray cameras to a dynamically manipulated robot-mounted linear accelerator that guides the therapy beam to treatment sites within the spine or spinal cord, in an outpatient setting, and without the use of frame-based fixation. The system relies on skeletal landmarks or implanted fiducial markers to locate treatment targets. Sixteen patients with spinal lesions (hemangioblastomas, vascular malformations, metastatic carcinomas, schwannomas, a meningioma, and a chordoma) were treated with total treatment doses of 1100 to 2500 cGy in one to five fractions by use of image-guided frameless radiosurgery with the CyberKnife system (Accuray, Inc., Sunnyvale, CA). Thirteen radiosurgery plans were analyzed for compliance with conventional radiation therapy. Tests demonstrated alignment of the treatment dose with the target volume within +/-1 mm by use of spine fiducials and the CyberKnife treatment planning system. Tumor patients with at least 6 months of follow-up have demonstrated no progression of disease. Radiographic follow-up is pending for the remaining patients. To date, no patients have experienced complications as a result of the procedure. This experience demonstrates the feasibility of image-guided robotic radiosurgery for previously untreatable spinal lesions.
... 3. Nordsmark M, Overgaard J: A confirmatory prognostic study on oxygenation status and loco .... more ... 3. Nordsmark M, Overgaard J: A confirmatory prognostic study on oxygenation status and loco ... Lung Cancer, 2005. Cited Here... 14. Le QT, Chen E, Salim A, et al: An evaluation of tumor oxygenation and gene expression in patients with early stage non-small cell lung cancers. ...
International Journal of Radiation Oncology Biology Physics, 2003
To review the combined experiences of University of California, San Francisco, and Stanford Unive... more To review the combined experiences of University of California, San Francisco, and Stanford University Medical Center in the treatment of intracranial germ cell tumors (GCT) and to assess the impact of craniospinal radiation (CSI) on patterns of relapse, progression-free survival (PFS), and overall survival (OS).Ninety-three patients received radiation for newly diagnosed intracranial GCTs, including 49 germinomas, 16 nongerminomatous GCTs (NGGCT), and 28 with no biopsy. Median follow-up for surviving patients was 4.5 years (range 0.25–34). Tests for variables correlating with OS and PFS were conducted using Cox proportional hazards model.Five-year PFS and OS rates were 60% ± 15% and 68% ± 14% for patients with NGGCT and 88% ± 5% and 93% ± 4% for those with germinoma. Of 6 patients with localized NGGCT who did not receive CSI, 1 experienced an isolated spinal recurrence but was salvaged. Of 41 patients with localized germinoma, 6 who received CSI and 35 who did not, no isolated spinal cord relapses occurred. Twenty-one patients with localized germinoma received neither CSI nor whole brain radiation. Of these, none of 18 with ventricular radiation relapsed. One of 3 patients with primary tumor radiation relapsed intracranially but had only received 11 Gy at initial treatment. On multivariate analysis, germinoma histology but not CSI correlated with improved PFS and OS.CSI is not indicated in the treatment of localized germinomas. For patients with localized germinomas treated with radiation alone, we recommend ventricular irradiation followed by primary tumor boost to a total of 45–50 Gy.
International Journal of Radiation Oncology*Biology*Physics, 2002
1. Int J Radiat Oncol Biol Phys. 2002 Dec 1;54(5):1299-301. Tumor hypoxia is important in radioth... more 1. Int J Radiat Oncol Biol Phys. 2002 Dec 1;54(5):1299-301. Tumor hypoxia is important in radiotherapy, but how should we measure it? Brown JM, Le QT. Comment on Int J Radiat Oncol Biol Phys. 2002 Dec 1;54(5):1537-49. PMID: 12459349 [PubMed - indexed for MEDLINE]. ...
International Journal of Radiation Oncology*Biology*Physics, 2010
... (Int J Radiat Oncol Biol Physics 2009;75:1064-1070) Hans Christiansen, Hendrik A. Wolff, Ralp... more ... (Int J Radiat Oncol Biol Physics 2009;75:1064-1070) Hans Christiansen, Hendrik A. Wolff, Ralph MW Rödel, Christoph Matthias, Clemens F. Hess International Journal of Radiation Oncology * Biology * Physics April 2010 (Vol. 76, Issue 5, Pages 1600-1601). ...
International Journal of Radiation Oncology Biology Physics, 2005
Purpose: To determine the efficacy of concurrent 5-fluorouracil (5-FU) and intensity-modulated ra... more Purpose: To determine the efficacy of concurrent 5-fluorouracil (5-FU) and intensity-modulated radiotherapy (IMRT) followed by body stereotactic radiosurgery (SRS) in patients with locally advanced pancreatic cancer. Methods and Materials: In this prospective study, all patients (19) had pathologically confirmed adenocarcinoma and were uniformly staged. Our treatment protocol consisted of 45 Gy IMRT with concurrent 5-FU followed by a 25 Gy SRS boost to the primary tumor. Results: Sixteen patients completed the planned therapy. Two patients experienced Grade 3 toxicity (none had more than Grade 3 toxicity). Fifteen of these 16 patients were free from local progression until death. Median overall survival was 33 weeks. Conclusions: Concurrent IMRT and 5-FU followed by SRS in patients with locally advanced pancreatic cancer results in excellent local control, but does not improve overall survival and is associated with more toxicity than SRS, alone.
Objective: To determine whether obstetric admissions to the intensive care unit (ICU) are useful ... more Objective: To determine whether obstetric admissions to the intensive care unit (ICU) are useful quality-assurance indicators.Methods: We analyzed retrospectively obstetric ICU admissions at two tertiary care centers from 1991 to 1997.Results: The 131 obstetric admissions represented 0.3% of all deliveries. The majority (78%) of women were admitted to the ICU postpartum. Obstetric hemorrhage (26%) and hypertension (21%) were the two most common reasons for admission. Together with cardiac disease, respiratory disorders, and infection, they accounted for more than 80% of all admissions. Preexisting medical conditions were present in 38% of all admissions. The median Acute Physiology and Chronic Health Evaluation II score was 8.5. The predicted mortality rate for the group was 10.0%, and the actual mortality rate was 2.3%.Conclusion: The most common precipitants of ICU admission were obstetric hemorrhage and uncontrolled hypertension. Improved management strategies for these problems may significantly reduce major maternal morbidity.
Purpose and objective: The primary goal of this study was to examine systematically the dosimetri... more Purpose and objective: The primary goal of this study was to examine systematically the dosimetric effect of small patient movements and linear accelerator angular setting misalignments in the delivery of intensity modulated radiation therapy. We will also provide a method for estimating dosimetric errors for an arbitrary combination of these uncertainties.Materials and methods: Sites in two patients (lumbar-vertebra and nasopharynx) were studied. Optimized intensity modulated radiation therapy treatment plans were computed for each patient using a commercially available inverse planning system (CORVUS, NOMOS Corporation, Sewickley, PA). The plans used nine coplanar beams. For each patient the dose distributions and relevant dosimetric quantities were calculated, including the maximum, minimum, and average doses in targets and sensitive structures. The corresponding dose volumetric information was recalculated by purposely varying the collimator angle or gantry angle of an incident beam while keeping other beams unchanged. Similar calculations were carried out by varying the couch indices in either horizontal or vertical directions. The intensity maps of all the beams were kept the same as those in the optimized plan. The change of a dosimetric quantity, Q, for a combination of collimator and gantry angle misalignments and patient displacements was estimated using Δ=Σ(ΔQ/Δxi)Δxi. Here ΔQ is the variation of Q due to Δxi, which is the change of the i-th variable (collimator angle, gantry angle, or couch indices), and ΔQ/Δxi is a quantity equivalent to the partial derivative of the dosimetric quantity Q with respect to xi.Results: While the change in dosimetric quantities was case dependent, it was found that the results were much more sensitive to small changes in the couch indices than to changes in the accelerator angular setting. For instance, in the first example in the paper, a 3-mm movement of the couch in the anterior–posterior direction can cause a 38% decrease in the minimum target dose or a 41% increase in the maximum cord dose, whereas a 5° change in the θ1=20° beam only gave rise to a 1.5% decrease in the target minimum or 5.1% in the cord maximum. The effect of systematic positioning uncertainties of the machine settings was more serious than random uncertainties, which tended to smear out the errors in dose distributions.Conclusions: The dose distribution of an intensity modulated radiation therapy (IMRT) plan changes with patient displacement and angular misalignment in a complex way. A method was proposed to estimate dosimetric errors for an arbitrary combination of uncertainties in these quantities. While it is important to eliminate the angular misalignment, it was found that the couch indices (or patient positioning) played a much more important role. Accurate patient set-up and patient immobilization is crucial in order to take advantage fully of the technological advances of IMRT. In practice, a sensitivity check should be useful to foresee potential IMRT treatment complications and a warning should be given if the sensitivity exceeds an empirical value. Quality assurance action levels for a given plan can be established out of the sensitivity calculation.
Uploads
Papers by Quynh Le