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L B Marks

Publications and source records attributed to L B Marks.

At least 37 records · Page 2Linked to original sources
PubMed2000

A new three-dimensional dose distribution reduction scheme for tubular organs.

In tubular structures, spatial aspects of the dose distribution may be important in determining the normal tissue response. Conventional dose-volume-histograms (DVHs) and dose-surface-histograms (DSHs) lack spatial information and may not be adequate to represent the three-dimensional (3D) dose data. A new 3D dose distribution data reduction scheme which preserves its longitudinal and circumferential character is presented. Dose distributions were generated at each axial level for esophagus or rectum in 123 patients with lung cancer or prostate cancer. Dose distribution histograms at each axial level were independently analyzed along the esophageal or rectal circumference to generate dose-circumference-histogram (DCH) sheets. Two types of plots were then generated from the DCH sheet. The first considered the percentage of the circumference at each axial level receiving various doses. The second considered the minimum dose delivered to any percentage of the circumference at each axial level. The DCH as a treatment planning tool can be easily implemented in a 3D planing system and is potentially useful for the study of the relationship between the complication risk and the longitudinal and circumferential dose distributions.

Dose-Response Relationship, Radiation↗
PubMed2000

Can angiotensin-converting enzyme inhibitors protect against symptomatic radiation pneumonitis?

This study was designed to determine whether patients taking angiotensin-converting enzyme (ACE) inhibitors while receiving radiation therapy for lung cancer are protected from developing symptomatic radiation pneumonitis. The records of 213 eligible patients receiving thoracic irradiation for lung cancer with curative intent at Duke University Medical Center from 1994-1997 were reviewed. Of the 213 patients, 26 (12.2%) were on ACE inhibitors (usually for the management of hypertension) during radiotherapy (group 1); the remaining 187 patients (group 2) were not. Patients were irradiated, with fields shaped to protect normal tissues, with total doses of 50-80 Gy. After treatment, patients were generally followed every 3 months for 2 years, then every 6 months thereafter. Symptomatic radiation pneumonitis was scored according to modified National Cancer Institute Common Toxicity Criteria (i.e., radiographic changes alone were not sufficient for the diagnosis of pneumonitis). There was no difference in the incidence of pneumonitis between the two groups (P = 0.75). Fifteen percent of the patients on ACE inhibitors (group 1) developed symptomatic radiation-induced lung injury compared to 12% of the patients not receiving these drugs (group 2). Although patients in group 1 tended to develop pneumonitis slightly sooner than did patients in group 2, this difference also was not significant (P = 0. 8). Within the dose range prescribed for treating hypertension, ACE inhibitors do not appear to either decrease the incidence or delay the onset of symptomatic radiation pneumonitis among lung cancer patients receiving thoracic irradiation.

Adult↗
PubMed2000

Routine 3D treatment planning: opportunities, challenges, and hazards.

Three-dimensional (3D) treatment planning refers to the use of software and hardware tools to design and implement more accurate and conformal radiation therapy. This is a major advance in oncology that should lead to the reduction of treatment-associated morbidity and facilitate safe dose escalation for many tumor sites. This technology affords the incorporation of physiologic and anatomic information into the treatment planning process, further enhancing our ability to improve the therapeutic ratio. However, as with any new technology, care must be taken when applying it in the clinic. The introduction of 3D planning presents new challenges to existing quality assurance systems. These need to be addressed to maintain patient safety. Based on our experience with over 1,500 patients treated at Duke University, the benefits, challenges, and hazards of routine 3D treatment planning are discussed.

Dose Fractionation, Radiation↗
PubMed1999

The effect of patient-specific factors on radiation-induced regional lung injury.

PURPOSE: To assess the impact of patient-specific factors on radiation (RT)-induced reductions in regional lung perfusion. METHODS: Fifty patients (32 lung carcinoma, 7 Hodgkin's disease, 9 breast carcinoma and 2 other thoracic tumors) had pre-RT and > or = 24-week post-RT single photon emission computed tomography (SPECT) perfusion images to assess the dose dependence of RT-induced reductions in regional lung perfusion. The SPECT data were analyzed using a normalized and non-normalized approach. Furthermore, two different mathematical methods were used to assess the impact of patient-specific factors on the dose-response curve (DRC). First, DRCs for different patient subgroups were generated and compared. Second, in a more formal statistical approach, individual DRCs for regional lung injury for each patient were fit to a linear-quadratic model (reduction = coefficient 1 x dose + coefficient 2 x dose2). Multiple patient-specific factors including tobacco history, pre-RT diffusion capacity to carbon monoxide (DLCO), transforming growth factor-beta (TGF-beta), chemotherapy exposure, disease type, and mean lung dose were explored in a multivariate analysis to assess their impact on the coefficients. RESULTS: None of the variables tested had a consistent impact on the radiation sensitivity of regional lung (i.e., the slope of the DRC). In the formal statistical analysis, there was a suggestion of a slight increase in radiation sensitivity in the dose range >40 Gy for nonsmokers (vs. smokers) and in those receiving chemotherapy (vs. no chemotherapy). However, this finding was very dependent on the specific statistical and normalization method used. CONCLUSION: Patient-specific factors do not have a dramatic effect on RT-induced reduction in regional lung perfusion. Additional studies are underway to better clarify this issue. We continue to postulate that patient-specific factors will impact on how the summation of regional injury translates into whole organ injury. Refinements in our methods to generate and compare SPECT scans are needed.

Adult↗
PubMed1999

Clinical and dosimetric predictors of radiation-induced esophageal toxicity.

PURPOSE: To evaluate the incidence, severity, and clinical/dosimetric predictors of acute and chronic esophageal toxicities in patients with non-small cell lung cancer (NSCLC) treated with high-dose conformal thoracic radiation. METHODS AND MATERIALS: Ninety-one patients with localized NSCLC treated definitively with high-dose conformal radiation therapy (RT) at Duke University Medical Center (DUMC) were reviewed. Patient characteristics were as follows: 53 males and 38 females; median age 64 yr (range 46-82); stage I--16, II--3, IIIa--40, IIIb--30, X--2; dysphagia pre-RT--6 (7%). Treatment parameters included: median corrected dose-78.8 Gy (range 64.2-85.6); BID fractionation-58 (64%); chemotherapy-43 (47%). Acute and late esophageal toxicities were graded by RTOG criteria. Using 3D treatment planning tools, the esophagus was contoured in a uniform fashion, the 3D dose distribution calculated (with lung density correction), and the dose-volume (DVH) and dose-surface histograms (DSH) generated. At each axial level, the percentage of the esophageal circumference at each dose level was calculated. The length of circumferential esophagus and the maximum circumference treated to doses >50 Gy were assessed. Patient and treatment factors were correlated with acute and chronic esophageal dysfunction using univariate and multivariate logistic regression analyses. RESULTS: There were no acute or late grade 4 or 5 esophageal toxicities. Ten of 91 patients (11%) developed grade 3 acute toxicity. On univariate analysis of clinical parameters, both dysphagia pre-RT (p = 0.10) and BID fractionation (p = 0.11) tended toward significantly predicting grade 3 acute esophagitis. None of the dosimetric parameters analyzed significantly predicted for grade 3 acute esophagitis. Twelve of 66 assessable patients (18%) developed late esophageal toxicity. Of the clinical parameters analyzed, only dysphagia pre-RT (p = 0.06) tended toward significantly predicting late esophageal toxicity. On univariate analyses, the effects of percent organ volume treated >50 Gy (p = 0.05), percent surface area treated >50 Gy (p = 0.05), length of 100% circumference treated >50 Gy (p = 0.04), and maximum percent of circumference treated >80 Gy (p = 0.01) significantly predicted for late toxicity of all grades. On multivariate analysis, percent organ volume treated >50 Gy (p = 0.02) and maximum percent of circumference treated >80 Gy (p = 0.02) predicted for late toxicity. CONCLUSIONS: Late esophageal toxicity following aggressive, high-dose conformal radiotherapy is common but rarely severe. Dosimetric variables addressing the longitudinal and circumferential character of the esophagus have biologic rationale and are predictive of late toxicity. Further studies are needed to assess whether these parameters are better predictors than those derived from traditional DVHs.

Acute Disease↗
PubMed1999

Variability of the location of internal mammary vessels and glandular breast tissue in breast cancer patients undergoing routine CT-based treatment planning.

PURPOSE: To determine the variability of position of internal mammary vessels (IMV) and glandular breast tissue (GBT) in patients undergoing breast-conserving radiation therapy. To assess the frequency and magnitude of tangential field border shifts based on preradiation therapy (RT) computed tomography (CT) imaging in breast cancer patients. METHODS AND MATERIALS: Five hundred and ninety breast cancer patients irradiated between 9/94 and 3/98 underwent routine CT-based treatment planning. Two analyses were performed. First, the position of IMV and GBT, outlined on the central axis CT image, was determined relative to the midsternum in 111 patients irradiated during a 12-month period. In the second analysis, the difference between anticipated (pre-CT) and actual (CT-based) tangential field borders was assessed in 254 patients irradiated during a 2-year period. RESULTS: In the first analysis, the depth of the IMVs varied from 1 to 6 cm (median 2.4 cm). The lateral distance from the midsternum also varied widely (range 1.7 to 3.7 cm, median 2.5 cm). Similar variability was found in the position of the GBT. In the second analysis, CT information led to changes of anticipated field borders in 65% of patients. The lateral border was shifted in 56% of patients (anteriorly 18%, posteriorly 38%). When the patients were segregated based on internal mammary node (IMN) treatment, the medial border was shifted in 49% of patients when the IMNs were treated in the tangential fields and in 24% when the GBT only was treated. The frequency of lateral field border shifts was similar in both groups. CONCLUSIONS: The position of IMVs and GBT varies widely in breast cancer patients. Tangential field borders based on surface anatomy may not be ideal. Among 254 breast cancer patients, the field borders were shifted in 65% of patients when CT information was available. Thus, in most breast cancer patients, field borders are shifted when CT-based treatment planning is used.

Breast Neoplasms↗
PubMed1999

Assessing the cost-effectiveness of postmastectomy radiation therapy.

PURPOSE: To assess the cost-effectiveness of postmastectomy local-regional radiation therapy (RT) for patients with breast cancer with regard to local-regional relapse (LRR) and quality-adjusted life years (QALY). METHODS AND MATERIALS: Data from the literature are used to estimate the risk of LRR, and the impact of RT on the risk of LRR and survival. The risk of LRR is related linearly to the number of positive axillary nodes 1% rate of LRR = 10 + (4 x number of positive nodes)]. RT reduces the risk of LRR by 67%. LRRs are treated with excision or biopsy followed by RT; half being controlled locally and half receiving additional salvage surgery and chemotherapy. Absolute improvements in 10-year overall survival due to RT are assumed to vary between 1 and 12%; and accrue linearly during the initial 10-year follow-up period. Professional and technical charges are used as a surrogate for costs. Money spent and benefits recognized in future years are discounted to 1997 values using a 3% annual rate. Quality factors are used to adjust for treatment, disease, and toxicity status. RESULTS: The cost per LRR prevented with the addition of routine postmastectomy RT is highly dependent upon the number of positive axillary nodes and ranges from $100,000-$200,000 for patients with 0-2 nodes, and $25,000-$75,000 for > or = 4 nodes. The cost per QALY gained at 10 years is $10,000-$110,000 for survival benefits > or = 3%. CONCLUSIONS: The cost per LRR prevented decreases with increasing numbers of positive axillary nodes. There is not a sharp cutoff at the < or = 3 vs. > or = 4 lymph node number, suggesting that using this cutoff for recommending or not recommending RT following mastectomy is not economically logical. The cost per QALY of $10,000-$100,000 compares favorably to that of other accepted medical procedures. Modest changes in the quantitative assumptions do not qualitatively alter the results. Concerns regarding costs should not generally preclude the use of postmastectomy RT.

Breast Neoplasms↗
PubMed1999

Acute and late morbidity of using a breast positioning ring in women with large/pendulous breasts.

PURPOSE: To assess acute and late effects of radiation therapy in women with breast cancer treated with a breast positioning ring. MATERIALS AND METHODS: Fifty-six patients with large and/or pendulous breasts were irradiated using a breast positioning ring. The incidence of acute morbidity was correlated with patient weight and breast 'size'. Cosmesis was scored at > or = 1 year following radiation therapy by the patients. Dose changes in the buildup region under the ring were measured using a computer-controlled scanning system. RESULTS: Moist desquamation (MD) occurred in 60.7% (34/56) of patients treated with the breast ring. The incidence of MD was more common in patients with larger breasts (P = 0.08), the severity necessitating a treatment interruption in 5 out of 56 (9%) patients. Cosmesis at > or = 1 year following radiation therapy was scored as > or = good by all patients. The surface dose under the ring was approximately 85% of the Dmax dose. CONCLUSIONS: The incidence or severity of acute MD in patients treated with a breast positioning ring appears high in patients with large pendulous breasts, and might be related in part, to the increased skin dose due to the positioning ring. To date, there appears to be no significant late normal tissue effects in patients treated with the positioning ring. Additional follow up is needed to assess the long-term consequences of the ring on cosmesis.

Adult↗
PubMed1999

Conformal radiation therapy treatment planning reduces the dose to the optic structures for patients with tumors of the paranasal sinuses.

PURPOSE: Compare dose distributions of traditional versus conformal beam orientations in paranasal sinus malignancies. MATERIALS AND METHODS: Maximum normal tissue doses, dose volume histograms (DVH), normal tissue complication probabilities (NTCP), and the percentage of each normal tissue receiving >80% of the average target dose (V80) were calculated. RESULTS/CONCLUSIONS: Conformal planning reduced the V80 to the optic nerves and chiasm as well as the normal tissue maximum doses to the ipsilateral and contralateral optic nerves and chiasm, and mean NTCPs.

Ethmoid Sinus↗
PubMed1999

Multimodality nuclear medicine imaging in three-dimensional radiation treatment planning for lung cancer: challenges and prospects.

The purpose of this study was to determine the utility of quantitative single photon emission computed tomography (SPECT) lung perfusion scans and F-18 fluorodeoxyglucose positron emission computed tomography (PET) during X-ray computed tomography (CT)-based treatment planning for patients with lung cancer. Pre-radiotherapy SPECT (n = 104) and PET (n = 35) images were available to the clinician to assist in radiation field design for patients with bronchogenic cancer. The SPECT and PET scans were registered with anatomic information derived from CT. The information from SPECT and PET provides the treatment planner with functional data not seen with CT. SPECT yields three-dimensional (3D) lung perfusion maps. PET provides 3D metabolic images that assist in tumor localization. The impact of the nuclear medicine images on the treatment planning process was assessed by determining the frequency, type, and extent of changes to plans. Pre-radiotherapy SPECT scans were used to modify 11 (11%) treatment plans; primarily altering beam angles to avoid highly functioning tissue. Fifty (48%) SPECT datasets were judged to be 'potentially useful' due to the detection of hypoperfused regions of the lungs, but were not used during treatment planning. PET data influenced 34% (12 of 35) of the treatment plans examined, and resulted in enlarging portions of the beam aperture (margins) up to 15 mm. Challenges associated with image quality and registration arise when utilizing nuclear medicine data in the treatment planning process. Initial implementation of advanced SPECT image reconstruction techniques that are not typically used in the clinic suggests that the reconstruction method may influence dose response data derived from the SPECT images and improve image registration with CT. The use of nuclear medicine transmission computed tomography (TCT) for both SPECT and PET is presented as a possible tool to reconstruct more accurate emission images and to aid in the registration of emission data with the planning CT. Nuclear medicine imaging techniques appear to be a potentially valuable tool during radiotherapy treatment planning for patients with lung cancer. The utilization of accurate nuclear medicine image reconstruction techniques and TCT may improve the treatment planning process.

Humans↗
PubMed1999

The effect of beam divergence on target coverage.

The well-known fact that radiation beams diverge is frequently not considered during the treatment planning process. Complacency with respect to beam divergence can, in some situations, lead to inappropriate field design. In this review, the potential problems arising from failure to adequately account for beam divergence in treatment planning are outlined, and commonly encountered clinical examples are illustrated.

Brain Neoplasms↗
PubMed1999

Postmastectomy radiotherapy: toxicities and techniques to reduce them.

The role of locoregional radiation therapy after mastectomy is controversial. It reduces the risk of tumor relapse, improves breast cancer-specific survival and possibly overall survival, but has potential morbidity. This article reviews the technical aspects of postmastectomy radiation therapy and its associations with treatment-related morbidity. We consider common problems that arise in the technical setup of radiation fields. Adverse effects of postmastectomy radiation therapy may be reduced or prevented by careful radiation treatment planning.

Breast Neoplasms↗
PubMed1999

A neural network to predict symptomatic lung injury.

A nonlinear neural network that simultaneously uses pre-radiotherapy (RT) biological and physical data was developed to predict symptomatic lung injury. The input data were pre-RT pulmonary function, three-dimensional treatment plan doses and demographics. The output was a single value between 0 (asymptomatic) and 1 (symptomatic) to predict the likelihood that a particular patient would become symptomatic. The network was trained on data from 97 patients for 400 iterations with the goal to minimize the mean-squared error. Statistical analysis was performed on the resulting network to determine the model's accuracy. Results from the neural network were compared with those given by traditional linear discriminate analysis and the dose-volume histogram reduction (DVHR) scheme of Kutcher. Receiver-operator characteristic (ROC) analysis was performed on the resulting network which had Az = 0.833 +/- 0.04. (Az is the area under the ROC curve.) Linear discriminate multivariate analysis yielded an Az = 0.813 +/- 0.06. The DVHR method had Az = 0.521 +/- 0.08. The network was also used to rank the significance of the input variables. Future studies will be conducted to improve network accuracy and to include functional imaging data.

Adult↗
PubMed1999

Incorporation of functional status into dose-volume analysis.

The dose-volume histogram (DVH) has gained wide acceptance as a mechanism for reducing the voluminous data of a three-dimensional dose distribution into a two-dimensional graph. These graphs are often converted to a single figure of merit. This data reduction technique is used both for clinical treatment plan evaluation and as part of proposed systems for estimating control and complication probabilities. It has long been recognized that a major shortcoming of the DVH as an analysis tool is that all spatial information is discarded. A subtler problem, which is addressed in this work, is that the DVH also implies homogeneity of biological consequence of irradiation in what may be a functionally heterogeneous volume of tissue. An extension to the DVH, the functional dose-volume histogram, or dose-function histogram (DFH), is proposed, that explicitly includes quantitative three-dimensional functional information. The concept is illustrated by the use of SPECT imaging to assess the functional status of irradiated lung.

Humans↗
PubMed1999

Quantitative pulmonary single photon emission computed tomography for radiotherapy applications.

Pulmonary imaging using single photon emission computed tomography (SPECT) is the focus of current radiotherapy research, including dose-response analysis and three-dimensional (3D) radiation treatment planning. Improvement in the quantitative capability of SPECT may help establish its potential role in this application as well as others requiring accurate knowledge of pulmonary blood flow. The purposes of this study were to quantitatively evaluate SPECT filtered backprojection (FBP) and ordered subset-expectation maximization (OS-EM) reconstruction implementations for measuring absolute activity concentration in lung phantom experiments, and to incorporate quantitative SPECT techniques in 3D-RTP for lung cancer. Quantitative FBP (nonuniform iterative Chang attenuation compensation, scatter correction, and 3D postreconstruction Metz filtering) and OS-EM implementations were compared with a "clinical" implementation of FBP (uniform multiplicative Chang attenuation compensation and post-reconstruction von Hann filtering), for their ability to improve quantification of inactive and active spherical defects in the lungs of an anthropomorphic torso phantom. Activity concentration estimates were found to depend on many factors, such as region of interest size, scatter subtraction constant (k), postreconstruction deconvolution filtering and, in the case of OS-EM, total number of iterations. In general, reconstruction implementations incorporating compensation for nonuniform attenuation and scatter provided reduced bias relative to the clinical implementation. Potential applications to lung radiotherapy, including dose-functional histograms and treatment planning are also discussed. SPECT has the potential to provide accurate estimates of lung activity distributions that, together with improved image quality, may be useful for the study and prediction of therapeutic response.

Algorithms↗
PubMed1999

Impact of consolidation radiotherapy in patients with advanced breast cancer treated with high-dose chemotherapy and autologous bone marrow rescue.

PURPOSE: To examine the impact of consolidation radiotherapy (RT) after high-dose chemotherapy with autologous bone marrow rescue (HDC) in patients with advanced breast cancer. PATIENTS AND METHODS: Between 1988 and 1994,425 patients with metastatic or recurrent breast cancer received doxorubicin, fluorouracil, and methotrexate (AFM) induction chemotherapy in a single-institution prospective trial. One hundred patients who achieved a complete response were randomized to receive HDC (cyclophosphamide, cisplatin, carmustine), with autologous bone marrow rescue immediately after AFM, or to observation, with HDC to be administered at next relapse. Seventy-four of the 100 became eligible for RT; 53 received consolidation RT (HDC RT+ and 21 did not (HDC RT-). The assignment of RT was not randomized. The RT+ and RT- groups were similar with regard to number of involved sites, the fraction of patients with only local-regional disease, age, and interval since initial diagnosis. Local control at previously involved sites and distant sites was assessed with extensive radiologic and clinical evaluations at the time of first failure or most recent follow-up. The impact of RT on failure patterns, event-free survival, and overall survival was evaluated. RESULTS: Sites of first failure were located exclusively at previously involved sites in 28% of RT+ patients versus 62% of RT- patients (P < .01). Event-free survival at 4 years was 31% and 21% in the RT+ and RT-groups, respectively (P = .02). Overall survival at 4 years was 30% and 16% in the RT+ and RT- groups, respectively (P = .20). CONCLUSION: Patients with advanced breast cancer who were treated with HDC without RT failed predominantly at the initial sites of disease. The addition of RT appeared to reduce the failure rate at initial disease sites and may improve event-free and overall survival. Our observations await verification in a trial in which assignment to RT is randomized.

Adult↗
PubMed1999

The rationale and use of three-dimensional radiation treatment planning for lung cancer.

Treatment of lung cancer with conventional radiation therapy is associated with suboptimal local tumor control and poor long-term survival. Poor local tumor control may result from inaccurate tumor targeting, failure to satisfactorily conform to dose distribution with the target volume, and/or inadequate radiation doses. Three-dimensional treatment planning is a radiotherapy technique that provides more accurate dose targeting via the direct transfer of three-dimensional anatomic information from diagnostic scans into the planning process. This technology can assist treatment planning by providing dose-volume histograms, an estimation of normal tissue complication probabilities, and facilitate dose escalation. Preliminary clinical studies suggest that this is a feasible approach worthy of additional study. The three-dimensional tools provide new opportunities to better understand radiation-induced changes in pulmonary function.

Carcinoma, Small Cell↗