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Biomedical subjects

B Movsas

Publications and source records attributed to B Movsas.

At least 19 recordsLinked to original sources
PubMed2005

A method for repositioning of stereotactic brain patients with the aid of real-time CT image guidance.

This note presents a method that recalculates the coordinates of the isocentre for patients undergoing stereotactic radiotherapy to the brain with a relocatable head frame based on a pre-treatment CT scan. The method was evaluated by comparing initial stereotactic coordinates of the isocentre with the recalculated coordinates for eight single-fraction patients. These patients had the Brown-Roberts-Wells (BRW) frame fixed to the outer table of the skull, and therefore the coordinates of any anatomical point should be identical between the initial scan and the pre-treatment scan. The differences between the two sets of coordinates were attributed to errors in the method. The results showed that the systematic errors in the recalculated coordinates were less than 0.05 mm, and they were not statistically significant. The random errors (one standard deviation) were from 0.35 mm (lateral) to 0.58 mm (vertical). The average value of the combined 3D difference was 0.75 mm.

Algorithms↗
PubMed2004

Stereotactic IMRT for prostate cancer: dosimetric impact of multileaf collimator leaf width in the treatment of prostate cancer with IMRT.

The focus of this work is the dosimetric impact of multileaf collimator (MLC) leaf width on the treatment of prostate cancer with intensity-modulated radiation therapy (IMRT). Ten patients with prostate cancer were planned for IMRT delivery using two different MLC leaf widths--4mm and 10mm--representing the Radionics micro-multileaf collimator (mMLC) and Siemens MLC, respectively. Treatment planning was performed on the XKnifeRT2 treatment-planning system (Radionics, Burlington, MA). All beams and optimization parameters were identical for the mMLC and MLC plans. All the plans were normalized to ensure that 95% of the planning target volume (PTV) received 100% of the prescribed dose. The differences in dose distribution between the two different plans were assessed by dose-volume histogram (DVH) analysis of the target and critical organs. We specifically compared the volume of rectum receiving 40 Gy (V40), 50 Gy (V50), 60 Gy (V60), the dose received by 17% and 35% of rectum (D17 and D35), and the maximum dose to 1 cm3 of the rectum for a prescription dose of 74 Gy. For the urinary bladder, the dose received by 25% of bladder (D25), V40, and the maximum dose to 1 cm3 of the organ were recorded. For PTV we compared the maximum dose to the "hottest" 1 cm3 (Dmax1 cm3) and the dose to 99% of the PTV (D99). The dose inhomogeneity in the target, defined as the ratio of the difference in Dmax1 cm3 and D99 to the prescribed dose, was also compared between the two plans. In all cases studied, significant reductions in the volume of rectum receiving doses less than 65 Gy were seen using the mMLC. The average decrease in the volume of the rectum receiving 40 Gy, 50 Gy, and 60 Gy using the mMLC plans was 40.2%, 33.4%, and 17.7%, respectively, with p < 0.0001 for V40 and V50 and p < 0.012 for V60. The mean dose reductions for D17 and D35 for the rectum using the mMLC were 20.4% (p < 0.0001) and 18.3% (p < 0.0002), respectively. There were consistent reductions in all dose indices studied for the bladder. The target dose inhomogeneity was improved in the mMLC plans by an average of 29%. In the high-dose range, there was no significant difference in the dose deposited in the "hottest" 1 cm3 of the rectum between the two plans for all cases (p > 0.78). In conclusion, the use of the mMLC for IMRT of the prostate resulted in significant improvement in the DVH parameters of the prostate and critical organs, which may improve the therapeutic ratio.

Equipment Design↗
PubMed2004

Daily target localization for prostate patients based on 3D image correlation.

There are several localization techniques that have been used for prostate treatment. Recently, the potential use of a variety of CT-based equipment in the treatment room has been discussed. The goal of our study was to develop an automated procedure for daily treatment table shift calculation based on two CT data sets: simulation CT data and localization CT data. The method suggested in this study is a 3D image cross-correlation of small regions of interest (ROI) within the two data sets. The relative position of the two ROIs with respect to each other is determined by the maximum value of the normalized cross-correlation function, calculated for all possible relative locations of the two ROIs. After the best match is found the shifts are given by the vector connecting the treatment isocentre and the planning isocentre (both determined by the radio opaque fiducial markers on the patient's skin). The results have been compared with shifts calculated through manual fusion. The shift differences, averaged over 17 statistically independent shift calculations, are less then 1 mm in the lateral and longitudinal directions, and about 1 mm in the AP direction. The impact of image noise on the performance of the algorithm has been tested. The results show that the algorithm accurately adjusts for target positional changes even with Gaussian noise levels as high as 20% inserted.

Algorithms↗
PubMed2004

Outcomes research in cancer clinical trial cooperative groups: the RTOG model.

BACKGROUND: The Radiation Therapy Oncology Group (RTOG), a National Cancer Institute sponsored cancer clinical trials research cooperative, has recently formed an Outcomes Committee to assess a comprehensive array of clinical trial endpoints and factors impacting the net effect of therapy. METHODS: To study outcomes in a consistent, comprehensive and coordinated manner, the RTOG Outcomes Committee developed a model to assess clinical, humanistic, and economic outcomes important in clinical trials. RESULTS: This paper reviews how the RTOG incorporates outcomes research into cancer clinical trials, and demonstrates utilization of the RTOG Outcomes Model to test hypotheses related to non-small-cell lung cancer (NSCLC). In this example, the clinical component of the model indicates that the addition of chemotherapy to radiotherapy (RT) improves survival but increases the risk of toxicity. The humanistic component indicates that esophagitis is the symptom impacting quality of life the greatest and may outweigh the benefits in elderly (> or =70 years) patients. The economic component of the model indicates that accounting for quality-adjusted survival, concurrent chemoRT for the treatment of NSCLC is within the range of economically acceptable recommendations. CONCLUSION: The RTOG Outcomes Model guides a comprehensive program of research that systematically measures a triad of endpoints considered important to clinical trials research.

Carcinoma, Non-Small-Cell Lung↗
PubMed2003

Radiotherapy patterns of care study in lung carcinoma.

PURPOSE: For the first time, a lung Patterns of Care Study was conducted to determine the national patterns of radiation (RT) practice in patients treated for nonmetastatic lung cancer in 1998 to 1999. MATERIALS AND METHODS: A national survey of randomly selected RT institutions in the United States was conducted using two-stage cluster sampling, stratified by practice type. Patients with nonmetastatic lung cancer (Karnofsky performance score [KPS] > or = 60), who received RT as definitive or adjuvant therapy, were randomly selected. To determine national estimates, sample size was weighted by the relative number of institutions per strata and the number of patient records reviewed per the number of patients eligible. Accordingly, 42,335 patient records from 58 institutions were reviewed by trained research associates. The unweighted sample size (or number of patients) was 541. RESULTS: The histologies were small-cell lung cancer (SCLC) in 14.5% of patients versus non-small-cell lung cancer (NSCLC) in 85.5% of patients. The median age was 67 years (range, 29 to 92 years); 61% of patients were male, and 38% were current smokers. Bone scans and brain imaging were not obtained in 34% and 52% of clinical stage (CS) III NSCLC patients, respectively. Regarding treatment strategies, for SCLC and CS III NSCLC, chemotherapy plus RT was used significantly more than RT alone (P <.05); in CS I NSCLC, RT alone was the primary treatment (P <.05). Overall, 58% of patients received systemic therapy. On multivariate analysis, factors correlating with increased use of chemotherapy included younger age, histology (SCLC > NSCLC), increasing CS, increasing KPS, and lack of comorbidities. Only 3% of all patients were treated on prospective clinical trials. CONCLUSION: This study establishes the general patterns of care for lung carcinoma in RT facilities within the United States. As supported by clinical trials, patients with limited-stage SCLC and CS III NSCLC received chemotherapy plus RT more than they received RT alone. Further improvements in staging, smoking cessation, and increased accrual to clinical trials must be encouraged.

Adult↗
PubMed2002

Randomized phase II chemotherapy and radiotherapy trial for patients with locally advanced inoperable non-small-cell lung cancer: long-term follow-up of RTOG 92-04.

PURPOSE: The standard treatment for patients with locally advanced inoperable non-small-cell lung cancer and good prognostic factors has become combined chemotherapy (ChT) and radiotherapy (RT). However, the sequencing of the two modalities, as well as fractionation of RT, has been controversial. The Radiation Therapy Oncology Group (RTOG) Study 92-04 was a randomized Phase II study designed to evaluate further the toxicity and efficacy of 2 different strategies of chemoradiation evaluated in 2 prior RTOG Phase II studies. METHODS: Patients with Stage II or III medically inoperable or unresectable non-small-cell lung cancer, good performance status, and minimal weight loss were enrolled into a prospective randomized Phase II RTOG study. Arm 1 consisted of induction ChT (vinblastine 5 mg/m(2) i.v. bolus weekly for the first 5 weeks, and cisplatin, 100 mg/m(2) i.v. on Days 1 and 29) followed by concurrent ChT/RT (cisplatin 75 mg/m(2) i.v. on Days 50, 71, and 92) during thoracic radiotherapy (63 Gy in 34 fractions during 7 weeks starting on Day 50). Arm 2 was concurrent ChT and hyperfractionated RT starting on Day 1 with a total dose of 69.6 Gy in 58 fractions during 6 weeks, 1.2 Gy/fraction b.i.d. ChT consisted of cisplatin, 50 mg/m(2) i.v. on Days 1 and 8, and oral VP-16, 50 mg b.i.d. for 10 days only on the days of thoracic radiotherapy repeated on Day 29. RESULTS: A total of 168 patients were entered between 1992 and 1994, and 163 patients were eligible for analysis. Eighty-one patients were treated in Arm 1 and 82 patients in Arm 2. Pretreatment characteristics, including age, gender, Karnofsky performance status, histologic features, and stage, were similar. The incidence of acute esophagitis was significantly higher among patients treated in Arm 2 than among those treated in Arm 1 (p <0.0001). The incidence of acute hematologic toxicity was significantly higher among patients treated in Arm 1 (p = 0.01 for anemia and p = 0.03 for other hematologic toxicities) than among those treated in Arm 2. Analysis of late toxicity showed that chronic esophageal toxicity was significantly more frequent in Arm 2 than in Arm 1 (p = 0.003). The time to in-field progression was significantly different (p = 0.009), favoring Arm 2 compared with Arm 1 (26% vs. 45% with failure in 2 years and 30% vs. 49% with failure in 4 years, respectively). The median 2-year and overall 5-year survival rates were similar between the two arms. CONCLUSION: Concurrent ChT and hyperfractionated RT resulted in a significant prolongation of the time to in-field progression, but with higher acute and chronic esophagitis. No other significant differences were observed between the two groups. Investigation with a chemoradio-protector is under way.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2001

Phase II radiation therapy oncology group trial of weekly paclitaxel and conventional external beam radiation therapy for supratentorial glioblastoma multiforme.

PURPOSE: Fractionated external beam radiotherapy (EBRT) +/- carmustine (BCNU) is the standard of care for patients with glioblastoma multiforme (GBM), but survival results remain poor. Preclinical studies indicate synergy between RT and paclitaxel (TAX) in astrocytoma cell lines. Phase I studies in GBM have demonstrated a maximum tolerated dose for TAX of 225 mg/m(2)/3 h/week x 6, during EBRT, with no exacerbation of typical RT-induced toxicities. The Radiation Therapy Oncology Group (RTOG) therefore mounted a Phase II study to determine the feasibility and efficacy of conventional EBRT and concurrent weekly TAX at its MTD. PATIENTS AND METHODS: Sixty-two patients with histologic diagnosis of GBM were enrolled from 8/16/96 through 3/21/97 in a multi-institutional Phase II trial of EBRT and TAX 225 mg/m(2)/3 h (1-3 h before EBRT), administered the first treatment day of each RT week. Total EBRT dose was 60 Gy (200 cGy/fraction), 5 days per week. A smaller treatment field, to include gross disease plus a margin only, was used after 46 Gy. RESULTS: Sixty-one patients (98%) were evaluable. Median age was 55 years (range, 28-78). Seventy-four percent were > or = 50 years. Recursive partitioning analysis (RPA) Classes III, IV, V, VI included 10 (17%), 21 (34%), 25 (41%), and 5 (8%) patients, respectively. Gross total resection was performed in only 16%. There was no Grade 3 or 4 neutropenia or thrombocytopenia. Hypersensitivity reactions precluding further use of TAX occurred in 4 patients. There were 2 instances of late neurotoxicity (4% Grade 3 or 4). Ninety-one percent of patients received treatment per protocol. Seventy-seven percent completed prescribed treatment (6 weeks). Of 35 patients with measurable disease, CR/PR was observed in 23%, MR in 17%, and SD in 43%. Seventeen percent demonstrated progression at first follow-up. Median potential follow-up time is 20 months. Median survival is 9.7 months, with median survivals for RPA classes III, IV, V, and VI of 16.3, 10.2, 9.5, 2.5 months, respectively. Ten patients remain alive. CONCLUSION: Concurrent full-dose EBRT and weekly high-dose TAX is feasible in the majority of GBM patients. Acute toxicity is acceptable; myelosuppression and peripheral sensory neuropathy are surprisingly modest, despite considerably higher overall dose intensity, compared to that achievable in other disease sites. Median survival by RPA class without prolonged adjuvant therapy is comparable to RTOG controls treated with standard EBRT and BCNU (1 year of BCNU).

Adult↗
PubMed2001

To move or not to move: measurements of prostate motion by urethrography using MRI.

PURPOSE: Urethrography is commonly used to aid in definition of the prostate apex during CT simulation for prostate cancer. If the position of the prostate were altered by the urethrogram itself, then systematic error could be introduced into the patient's treatment. Sagittal MRI scans were acquired immediately before and after a localization urethrogram to determine the extent of displacement. METHODS AND MATERIALS: Thirteen patients underwent sagittal T2-weighted fast spin echo MRI scans. Patients were scanned supine in an alpha cradle cast in the treatment position. The prostate was contoured by 3 different observers to determine the apex location on the central sagittal MRI section and the center of mass relative to an immobile bony landmark. Statistical multivariate analysis was performed to establish if there was a net displacement of the prostate (systematic error), and to determine the margin required to cover the random prostate position within a 95% confidence interval. RESULTS: There was no significant systematic motion of either the prostate nor its apex in either the anterior-posterior or superior-inferior directions. The average motion of the prostate center of mass was 0.04 +/- 0.40 cm (1 SD) and 0.01 +/- 0.33 cm in the anterior-posterior and superior-inferior direction, respectively. The corresponding figures for location of the apex were 0.05 +/- 0.30 cm and 0.01 +/- 0.33 cm, respectively. The statistical analysis revealed that a margin of 2 mm is sufficient to cover any random motion of the prostate that could occur as a result of the urethrogram 95% of the time. CONCLUSION: Urethrography during CT simulation for prostate cancer does not cause significant prostate displacement or systematic error in planning and delivering external-beam radiation.

Adenocarcinoma↗
PubMed2001

Can costs be measured and predicted by modeling within a cooperative clinical trials group? Economic methodologic pilot studies of the radiation therapy oncology group (RTOG) studies 90-03 and 91-04.

PURPOSE: To (1) measure radiation therapy costs for patients in randomized controlled clinical trials, (2) compare measured costs to modeling predictions, (3) examine cost distributions, and (4) assess feasibility of collecting economic data within a cooperative group. METHODS: The Radiation Therapy Oncology Group conducted economic pilot studies for two Phase III studies that compared fractionation patterns. Expected quantities of Current Procedural Terminology (CPT) codes and relative value units (RVU) were modeled. Institutions retrospectively provided procedure codes, quantities, and components, which were converted to RVUs used for Medicare payments. Cases were included if the radiation therapy quality control review judged them to have been treated per protocol or with minor variation. Cases were excluded if economic quality review found incomplete economic data. RESULTS: The median and mean RVUs were within the range predicted by the model for all arms of one study and above the predicted range for the other study. CONCLUSION: The model predicted resource use well for patients who completed treatment per protocol. Actual economic data can be collected for critical cost items. Some institutions experienced difficulty collecting retrospective data, and prospective collection of data is likely to allow wider participation in future Radiation Therapy Oncology Group economic studies.

Brain Neoplasms↗
PubMed2001

Increased hypoxia correlates with increased expression of the angiogenesis marker vascular endothelial growth factor in human prostate cancer.

OBJECTIVES: To test the hypothesis that increasing levels of hypoxia are associated with increased expression of vascular endothelial growth factor (VEGF) in prostate cancer by correlating the level of median tissue oxygenation in human prostate tumors with the immunohistochemically determined level of VEGF expression. METHODS: Custom-made Eppendorf oxygen microelectrodes were used to quantitate the pO(2) levels in prostate tumors of 13 men undergoing radical prostatectomy. All pO(2) measurements were performed under fluorine-based general anesthesia. Paraffin-embedded tumor tissue from these men was analyzed to measure the level of VEGF expression by immunohistochemical staining. The significance of the associations between the pO(2) levels and VEGF staining were determined by the Pearson correlations. RESULTS: The range of the median pO(2) levels (based on between 97 and 129 individual measurements) among 13 prostate tumors was 0.5 to 44.9 mm Hg. The blinded comparison of pO(2) levels and VEGF staining intensity demonstrated a significant correlation between increasing hypoxia and the percentage of cells staining positive for VEGF (r = -0.721, P = 0.005). This correlation was also significant when pO(2) levels were compared with the overall immunoreactive score, which takes into account staining intensity (r = -0.642, P = 0.018). CONCLUSIONS: To our knowledge, this is the first study demonstrating a significant association between increasing levels of hypoxia and increased expression of the angiogenesis marker VEGF in human prostate carcinoma. The results of our study further support the exploration of antiangiogenesis strategies for the treatment of human prostate cancer.

Adult↗
PubMed2001

Hypoxia in human prostate carcinoma: an Eppendorf PO2 study.

The purpose of this study was to characterize the extent of hypoxia in human prostate carcinoma using the Eppendorf PO2 microelectrode. Custom-made Eppendorf PO2 microelectrodes were used to obtain PO2 measurements from the pathologically involved region of the prostate (as determined by the pretreatment sextant biopsies), as well as from a region of normal muscle for comparison. Fifty-nine patients with localized prostate cancer were studied, all of whom received brachytherapy implants under spinal anesthesia. A multivariate mixed effects analysis for prediction of tumor oxygenation was performed including the following covariates: type of tissue (prostate versus muscle), prostatic-specific antigen, disease stage, patient age and race, tumor grade, volume, perineural invasion, and hormonal therapy. Because of differences in patient characteristics, control measurements were obtained from normal muscle in all patients. This internal comparison showed that the oxygen measurements from the pathologically involved portion of the prostate were significantly lower (average median PO2 = 2.4 mm Hg) compared with the measurements from normal muscle (average median PO2 = 30.0 mm Hg), p < 0.0001. A multivariate, linear, mixed analysis demonstrated that the only significant predictor of oxygenation was the type of tissue (prostate versus muscle). This study, using in vivo electrode oxygen measurements, suggests that hypoxia exists in human prostate carcinoma. More patients will be accrued to this study to ultimately correlate the oxygenation status in prostate carcinoma tumors with treatment outcome.

Aged↗
PubMed2001

Metastatic meningioma to the lung with multiple pleural metastases.

Meningiomas with both malignant clinical behavior and cytology are rare. Meningiomas comprise approximately 15% of the primary brain tumors. The majority are benign; less than 1% metastasize, most commonly to the lung (61%) followed by liver, lymph node, and bone. Approximately 130 cases of extracranial metastatic meningiomas have been described. Only 13% had more than three metastases, with few cases reported with extensive pleural involvement. We report an interesting case of a malignant meningioma that invaded through the skull in the frontal sinus that later metastasized to the left lung with multiple pulmonary and pleural nodules.

Aged↗
PubMed2001

Quantifying radiation therapy-induced brain injury with whole-brain proton MR spectroscopy: initial observations.

PURPOSE: To quantify the extent of neuronal cell loss imparted to the brain by means of radiation therapy through the decline of the amino acid derivative N-acetylaspartate (NAA) by using proton (hydrogen 1) magnetic resonance (MR) spectroscopy. MATERIALS AND METHODS: Proton MR spectroscopy in a clinical MR imager was used to ascertain the amount of whole-brain NAA before and immediately after whole-brain radiation therapy 3-4 weeks later. Eight patients (four women, four men; median age, 55 years; age range, 39-70 years) were studied. All subjects had lung cancer (non-small cell lung cancer [n = 5], small-cell lung cancer [n = 3]) and received either palliative or prophylactic whole-brain radiation therapy. Six of them also underwent a Mini-Mental Status Examination (MMSE) for correlation with the whole-brain NAA. Two-tailed Student t tests were used to evaluate the data. RESULTS: A significant (P = .042) average decline in whole-brain NAA of -0.91 mmol per person was observed in the cohort. No corresponding changes occurred in MMSE scores. There was no significant difference in whole-brain NAA decline between prophylactic and therapeutic whole-brain radiation therapy. CONCLUSION: Since whole-brain NAA loss was detected even when MMSE scores were unchanged, the former seems to be a more sensitive measure of radiation therapy injury than is the latter.

Adult↗
PubMed2001

Induction and concurrent paclitaxel/carboplatin every 3 weeks with thoracic radiotherapy in locally advanced non-small-cell lung cancer: an interim report.

The paclitaxel/carboplatin combination has demonstrated promising activity in metastatic non-small-cell lung cancer (NSCLC); therefore, we mounted an exploratory study of these agents with thoracic radiation (TRT) in locally advanced NSCLC. Eligibility stipulated a Karnofsky performance status >or= 70%, weight loss or= 2 esophagitis has corresponded to length (> 16 cm) of esophagus in the radiation treatment field (Fisher's exact test, P = 0.006). The partial response rate to induction therapy was 40% and to the combined modality therapy was 60%. The median survival for all 49 patients is 15.3 months, with a median disease-free survival (DFS) of 7.8 months. In the subset of 22 patients treated on the phase I portion of the study, the median survival and DFS were 18.5 months and 13.5 months, respectively. Induction therapy with paclitaxel and carboplatin followed by concurrent chemoradiotherapy with the same agents is an active and well-tolerated treatment approach in locally advanced NSCLC. To date, paclitaxel 175 mg/m2 plus carboplatin AUC 5 administered at 3-week intervals for 2 cycles is safe in combination with TRT.

Journal Article↗
PubMed2001

Marking hypoxia in rat prostate carcinomas with beta-D-[125I]azomycin galactopyranoside and.

UNLABELLED: The purpose of this study was to determine, with a rodent tumor model, if microelectrode measurements of unmodulated tumor oxygenation predict for the avidity of hypoxic markers to tumor tissue. METHODS: The rapidly growing, anaplastic variant of the Dunning rat prostate carcinoma cell line (R3327-AT) was implanted subcutaneously on the upper backs of Fischer X Copenhagen rats. Approximately 100 measurements of PO2 were obtained from tumors of 5-10 g in animals that were restrained and then subjected to different anesthetic procedures. Values of median PO2 (in mm Hg) and percentage of measurements <5 mm Hg obtained from individual tumors were used to define tumor oxygenation status. The radiodiagnostic hypoxic markers beta-D-iodinated azomycin galactopyranoside (IAZGP) and [99mTc]HL-91 were simultaneously administered to 26 animals whose tumor oxygen levels had been measured. Six hours after marker administration, the animals were killed; tumor, blood, and muscle tissues were sampled; and percentage injected dose per gram (%ID/g*), tumor/blood ratio (T/B), and tumor/muscle ratio (T/M) parameters were determined. Parameters of marker avidity to individual tumors were linearly correlated with microelectrode measurements of tumor oxygenation to determine the significance of inverse associations. RESULTS: The median PO2 of 41 tumors varied from 2.0 to 20.9 mm Hg, with an average value of 7.5 +/- 1.4 mm Hg. Six tumors had unusually high values; that is, >10 mm Hg, and when these were excluded from the analysis, the average median PO2 of the remaining 35 was 4.3 +/- 0.7 mm Hg. When electrode measurements of tumor oxygenation were obtained under conditions of halothane anesthesia with the animals breathing O2, carbogen, or air, median PO2 values increased significantly (P = 0.001). When animals were deeply anesthetized by intraperitoneal injection of ketamine-xylazine, median PO2 values were not significantly different (P = 0.13) from those obtained while the animals were restrained and breathing air. There was no inverse correlation of significance between the electrode measurements of median PO2 and the avidity of beta-D-IAZGP nor [99mTc]HL-91 in this tumor model. The range of median PO2 values in these tumors was at least 3 mm Hg, and the range of hypoxic marker avidity was less than twofold. CONCLUSION: These data demonstrate that microelectrode measurements of rat tumor oxygenation did not correlate with the avidity of the two hypoxic markers, at least in this tumor model. The larger dynamic range of tumor oxygen measurements obtained with microelectrodes might be biased to low values by their necrotic fractions, the zones within solid tumors that contain dead cells and debris that will not be labeled by bioreducible hypoxic markers. Hypoxic marker avidity to individual tumors will have to be validated by other assays that can predict for their radiosensitivity.

Anesthesia↗