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Biomedical subjects

Suresh Senan

Publications and source records attributed to Suresh Senan.

At least 19 recordsLinked to original sources
PubMed2007

Bronchiolitis obliterans organizing pneumonia (BOOP) after thoracic radiotherapy for breast carcinoma.

Common complications of thoracic radiotherapy include esophagitis and radiation pneumonitis. However, it is important to be aware of uncommon post-radiotherapy complications such as bronchiolitis obliterans organizing pneumonia (BOOP). We report on two patients with carcinoma of the breast who developed an interstitial lung disease consistent with BOOP. BOOP responds to treatment with corticosteroids and the prognosis is generally good despite of the need for long-term administration of corticosteroids as relapses can occur during tapering of steroids. This report provides guidelines for the evaluation and treatment of patients with pulmonary infiltrates after radiotherapy.

Aged, 80 and over↗
PubMed2006

Reproducibility of target volumes generated using uncoached 4-dimensional CT scans for peripheral lung cancer.

BACKGROUND: 4-dimensional CT (4DCT) scans are increasingly used to account for mobility during radiotherapy planning. As variations in respiratory patterns can alter observed motion, with consequent changes in the generated target volumes, we evaluated the reproducibility of 4D target volumes generated during repeat uncoached quiet respiration. METHODS: A retrospective analysis was performed on two successive scans (4DCT1 and 4DCT2) generated at the same scanning session for 26 patients with peripheral lung cancer treated with stereotactic radiotherapy (SRT). The volume and position of planning target volumes (PTV4DCT1 and PTV4DCT2) contoured on both scans were compared, and a dosimetric analysis performed. A SRT plan optimized for each PTV was sequentially applied to the other PTV, and coverage by the 80% isodose was evaluated. Color intensity projections (CIP) were used to evaluate regions of underdosage. RESULTS: No significant volumetric differences were observed between the two PTVs (t-Test p = 0.60). The average displacement of the center of mass between corresponding PTVs was 1.4 +/- 1.0 mm, but differences in position were 2.0 mm or greater in 5 cases (19%). Coverage of both PTVs by the 80% prescription isodose exceeded 90% for all but one patient. For the latter, the prescription isodose covered only 82.5% of PTV4DCT1. CIP analysis revealed that the region of underdosage was an end-inspiratory position occupied by the tumor for only 10-20% of the respiratory cycle. CONCLUSION: In nearly all patients with stage I lung cancer, the PTV derived from a single uncoached 4DCT achieves dosimetric coverage that is similar to that achieved using two such consecutive scans.

Humans↗
PubMed2006

Evaluating mobility for radiotherapy planning of lung tumors: a comparison of virtual fluoroscopy and 4DCT.

PURPOSE: Fluoroscopy is widely used for evaluating tumor mobility in radiotherapy planning. Lung tumor mobility was scored using virtual fluoroscopy, and this was compared to mobility derived from contoured tumors in all phases of a respiration-correlated (or 4D) CT scan. METHODS AND MATERIALS: 4DCT datasets were reviewed and 29 patients were identified in whom tumors were visible on anterior-posterior fluoroscopy views. Mobility in all directions was estimated on fluoroscopy movie loops by four clinicians. These results were compared to mobility measured from contoured tumor volumes in all phases of the same 4DCT. Internal target volumes (ITV) were generated for both approaches. RESULTS: In eight patients, fluoroscopy did not allow for tumor mobility to be assessed in at least one direction. No significant inter-clinician variation was observed with respect to fluoroscopic assessment of mobility. Clinicians systematically overestimated mobility in all three directions (p<0.05). The mean ITVs derived using fluoroscopy were 52.2% larger than those derived using 4DCT contours, but the individual ITVs were smaller in three patients. CONCLUSION: Use of virtual fluoroscopy generally overestimates the mobility of visible lung tumors, and results in irradiation of unnecessarily large target volumes. In contrast, use of 4DCT minimizes the risk of normal tissue toxicity.

Fluoroscopy↗
PubMed2006

A dosimetric analysis of respiration-gated radiotherapy in patients with stage III lung cancer.

BACKGROUND: Respiration-gated radiotherapy can permit the irradiation of smaller target volumes. 4DCT scans performed for routine treatment were retrospectively analyzed to establish the benefits of gating in stage III non-small cell lung cancer (NSCLC). MATERIALS AND METHODS: Gross tumor volumes (GTVs) were contoured in all 10 respiratory phases of a 4DCT scan in 15 patients with stage III NSCLC. Treatment planning was performed using different planning target volumes (PTVs), namely: (i) PTVroutine, derived from a single GTV plus 'conventional' margins; (ii) PTVall phases incorporating all 3D mobility captured by the 4DCT; (iii) PTVgating, incorporating residual 3D mobility in 3-4 phases at end-expiration. Mixed effect models were constructed in order to estimate the reductions in risk of lung toxicity for the different PTVs. RESULTS: Individual GTVs ranged from 41.5 - 235.0 cm3. With patient-specific mobility data (PTVall phases), smaller PTVs were derived than when 'standard' conventional margins were used (p < 0.001). The average residual 3D tumor mobility within the gating window was 4.0 +/- 3.5 mm, which was 5.5 mm less than non-gated tumor mobility (p < 0.001). The reductions in mean lung dose were 9.7% and 4.9%, respectively, for PTVall phases versus PTVroutine, and PTVgating versus PTVall phases. The corresponding reductions in V20 were 9.8% and 7.0%, respectively. Dosimetric gains were smaller for primary tumors of the upper lobe versus other locations (p = 0.02). Respiratory gating also reduced the risks of radiation-induced esophagitis. CONCLUSION: Respiration-gated radiotherapy can reduce the risk of pulmonary toxicity but the benefits are particularly evident for tumors of the middle and lower lobes.

Journal Article↗
PubMed2006

Color intensity projections: a rapid approach for evaluating four-dimensional CT scans in treatment planning.

PURPOSE: Four-dimensional computerized tomography scans (4DCT) enable intrafractional motion to be determined. Because more than 1500 images can be generated with each 4DCT study, tools for efficient data visualization and evaluation are needed. We describe the use of color intensity projections (CIP) for visualizing mobility. METHODS: Four-dimensional computerized tomography images of each patient slice were combined into a CIP composite image. Pixels largely unchanged over the component images appear unchanged in the CIP image. However, pixels whose intensity changes over the phases of the 4DCT appear in the CIP image as colored pixels, and the hue encodes the percentage of time the tissue was in each location. CIPs of 18 patients were used to study tumor and surrogate markers, namely the diaphragm and an abdominal marker block. RESULTS: Color intensity projections permitted mobility of high-contrast features to be quickly visualized and measured. In three selected expiratory phases ("gating phases") that were reviewed in the sagittal plane, gating would have reduced mean tumor mobility from 6.3 +/- 2.0 mm to 1.4 +/- 0.5 mm. Residual tumor mobility in gating phases better correlated with residual mobility of the marker block than that of the diaphragm. CONCLUSION: CIPs permit immediate visualization of mobility in 4DCT images and simplify the selection of appropriate surrogates for gated radiotherapy.

Color↗
PubMed2006

Time trends in target volumes for stage I non-small-cell lung cancer after stereotactic radiotherapy.

PURPOSE: To identify potential time trends in target volumes and tumor mobility after stereotactic radiotherapy (SRT) for Stage I non-small-cell lung cancer. PATIENTS AND METHODS: Repeat planning computed tomography (CT) scans were performed for 40 tumors during fractionated SRT delivered in either three (n = 21), five (n = 14), or eight fractions (n = 5). The planning CT scans used to define internal target volumes (ITVs) consisted of either six multislice CT scans or a single four-dimensional CT scan. All repeat CT scans were coregistered with the initial (D0) scan to determine volumetric or spatial changes in target volume, and tumor mobility vectors were determined from each scan. RESULTS: A significant decrease in target volumes (ITVs and gross tumor volumes) relative to baseline values was observed starting at the fourth week of SRT (p = 0.015). No trends in tumor mobility were detected during SRT. Significant positional shifts in the ITV, of more than 5 mm, were seen in 26-43% of patients at different times during SRT. CONCLUSION: Significant changes in target volumes can occur during SRT for Stage I non-small-cell lung cancer. A failure to account for such changes e.g., by repeat CT planning or verification using on-board volumetric imaging can lead to inadequate target coverage.

Carcinoma, Non-Small-Cell Lung↗
PubMed2006

4D imaging for target definition in stereotactic radiotherapy for lung cancer.

Stereotactic radiotherapy of Stage I lung tumors has been reported to result in high local control rates that are far superior to those obtained with conventional radiotherapy techniques, and which approach those achieved with primary surgery. Breathing-induced motion of tumor and target tissues is an important issue in this technique and careful attention should be paid to the contouring and the generation of individualized margins. We describe our experience with the use of 4DCT scanning for this group of patients, the use of post-processing tools and the potential benefits of respiratory gating.

Carcinoma, Non-Small-Cell Lung↗
PubMed2005

Renal mobility during uncoached quiet respiration: an analysis of 4DCT scans.

PURPOSE: Data on organ mobility is required for optimizing radiotherapy. Renal mobility was studied in four-dimensional computed tomography (4DCT) scans acquired during uncoached respiration. METHODS AND MATERIALS: The 4DCT scans of 54 patients, in whom at least the upper pole of both kidneys were visualized in all 10 respiratory phases, were analyzed. Scans were performed on a 16-slice CT scanner (slice index and reconstruction, 2.5 mm) during quiet, uncoached respiration. Mobility of the renal apex was evaluated in all patients by use of the z-position on CT slices. Reproducibility of mobility was studied in 8 patients who underwent 1 or 2 repeat 4DCT scans. RESULTS: Mobility was predominantly craniocaudal, with a mean of 9.8 mm for the left kidney and 9.0 mm for the right kidney. Large interpatient variations were observed that ranged from 2.5 to 30 mm (left) and 2.5 to 20 mm (right), and mobility of 1 kidney did not predict for mobility of the contralateral organ. Reproducibility of renal mobility and position at end-expiration was poor, with positional variations in repeat scans appearing to correlate with changes in the amplitude of respiratory waveform and total lung volume. CONCLUSIONS: Large interpatient variations in renal movement occur during uncoached respiration, which indicates that respiratory coaching is useful for 4DCT imaging and treatment delivery.

Abdominal Neoplasms↗
PubMed2005

Use of CD-ROM-based tool for analyzing contouring variations in involved-field radiotherapy for Stage III NSCLC.

BACKGROUND: Interclinician variability in defining target volumes is a problem in conformal radiotherapy. A CD-ROM-based contouring tool was used to conduct a dummy run in an international trial of involved-field chemoradiotherapy for Stage III non-small-cell lung cancer. METHODS AND MATERIALS: The CT scan of an eligible patient was installed on an "auto-run" CD-ROM incorporating a contouring program based on ImageJ for Windows, which runs on any personal computer equipped with a CD-ROM drive. This tool was initially piloted at four academic centers and was subsequently mailed, together with all relevant clinical, radiologic, and positron emission tomography findings, to all participating centers in the international trial. Clinicians were instructed to contour separate gross tumor volumes (GTVs) for the tumor and two enlarged nodes and a clinical target volume for the hilus. A reference "consensus" target volume for each target was jointly generated by three other clinicians. RESULTS: The data received from the four academic centers and 16 study participants were suitable for analysis. Data from one center was unsuitable for detailed analysis because the target volumes were contoured at 1.2-cm intervals. GTVs were available for a total of 21 tumors and 19 nodes, and 15 hilar clinical target volumes were available. The mean GTV of the primary tumor was 13.6 cm(3) (SD, 5.2; median, 12.3; range, 8.3-26.9). The variation in the center of the mass relative to the mean center of the mass in the left-right, ventrodorsal, and craniocaudal axes was 1.5, 0.4, and 1.0 mm, respectively. The largest volume variation was observed for the right hilar clinical target volume (mean, 33.7 cm(3); SD, 31.2; median, 20.3; range, 4.8-109.9). Smaller variations were observed for the subcarinal node (mean, GTV, 1.9 cm(3); SD, 1.2; median, 1.7; range, 0.5-5.3), except caudally where the node was difficult to distinguish from the pericardium. The "consensus" volumes for all targets were generally close to the median of the contoured values. CONCLUSION: Most clinicians were able to use this CD-ROM tool to contour target volumes in compliance with the study protocol. The rapid completion of the dummy run indicated the suitability of this approach for quality assurance in multicenter clinical trials. Routine use of similar tools will reduce the risk that new techniques (or study objectives) are misunderstood and/or misapplied in clinical trials.

CD-ROM↗
PubMed2005

Use of maximum intensity projections (MIP) for target volume generation in 4DCT scans for lung cancer.

PURPOSE: Single four-dimensional CT (4DCT) scans reliably capture intrafractional tumor mobility for radiotherapy planning, but generating internal target volumes (ITVs) requires the contouring of gross tumor volumes (GTVs) in up to 10 phases of a 4DCT scan, as is routinely performed in our department. We investigated the use of maximum intensity projection (MIP) protocols for rapid generation of ITVs. METHODS AND MATERIALS: 4DCT data from a mobile phantom and from 12 patients with Stage I lung cancer were analyzed. A single clinician contoured GTVs in all respiratory phases of a 4DCT, as well as in three consecutive phases selected for respiratory gating. MIP images were generated from both phantom and patient data, and ITVs were derived from encompassing volumes of the respective GTVs. RESULTS: In the phantom study, the ratio between ITVs generated from all 10 phases and those from MIP scans was 1.04. The corresponding center of mass of both ITVs differed by less than 1 mm. In scans from patients, good agreement was observed between ITVs derived from 10 and 3 (gating) phases and corresponding MIPs, with ratios of 1.07 +/- 0.05 and 0.98 +/- 0.05, respectively. In addition, the center of mass of the respective ITVs differed by only 0.4 and 0.5 mm. CONCLUSION: MIPs are a reliable clinical tool for generating ITVs from 4DCT data sets, thereby permitting rapid assessment of mobility for both gated and nongated 4D radiotherapy in lung cancer.

Humans↗
PubMed2005

Critical review of PET-CT for radiotherapy planning in lung cancer.

In the last decade, FDG-PET scans have had a major impact on the treatment of patients with NSCLC. The benefits of staging PET scans are well established, with improved selection of patients for curative radiotherapy or aggressive chemo-radiotherapy. The large body of literature correlating FDG-PET with nodal pathology in NSCLC makes it rational to use PET for designing mediastinal radiation fields. However, suboptimal image-fusion and a low spatial resolution for PET scans, makes use of PET for defining target volumes for primary tumours questionable. Data on the role of PET scans for radiotherapy planning for limited stage small-cell lung cancer is limited, although the incorporation of FDG-PET positive regions would appear to be reasonable.

Carcinoma, Non-Small-Cell Lung↗
PubMed2005

Benefit of respiration-gated stereotactic radiotherapy for stage I lung cancer: an analysis of 4DCT datasets.

PURPOSE: High local control rates have been reported with stereotactic radiotherapy (SRT) for Stage I non-small-cell lung cancer. Because high-dose fractions are used, reduction in treatment portals will reduce the risk of toxicity to adjacent structures. Respiratory gating can allow reduced field sizes and planning four-dimensional computed tomography scans were retrospectively analyzed to study the benefits for gated SRT and identify patients who derive significant benefit from this approach. METHODS AND MATERIALS: A total of 31 consecutive patients underwent a four-dimensional computed tomography scan, in which three-dimensional computed tomography datasets for 10 phase bins of the respiratory cycle were acquired during free breathing. For a total of 34 tumors, the three planning target volumes (PTVs) were analyzed, namely (1) PTV(10bins), derived from an internal target volume (ITV) that incorporated all observed mobility (ITV(10bins)), with the addition of a 3-mm isotropic setup margin; (2) PTV(gating), derived from an ITV generated from mobility observed in three consecutive phases ("bins") during tidal-expiration, plus addition of a 3-mm isotropic margin; and (3) PTV(10 mm), derived from the addition of a 10-mm isotropic margin to the most central gross tumor volumes in the three bins selected for gating. RESULTS: The PTV(10bins) and PTV(gating) were, on average, 48.2% and 33.3% of the PTV(10 mm), and respective mean volumes of normal tissue (outside the PTV) receiving the prescribed doses were 57.1% and 39.1%, respectively, of that of PTV(10 mm). A significant correlation was seen between the extent of tumor mobility (i.e., a three-dimensional mobility vector of at least 1 cm) and reduction in normal tissue irradiation achieved with gating. The ratio of the intersecting and the encompassing volumes of GTVs at extreme phases of tidal respiration predicted for the benefits of gated respiration. CONCLUSION: The use of "standard population-based" margins for SRT leads to unnecessary normal tissue irradiation. The risk of toxicity is further reduced if respiration-gated radiotherapy is used to treat mobile tumors. These findings suggest that gated SRT will be of clinical relevance in selected patients with mobile tumors.

Carcinoma, Non-Small-Cell Lung↗
PubMed2004

Four-dimensional CT scans for treatment planning in stereotactic radiotherapy for stage I lung cancer.

PURPOSE: Hypofractionated stereotactic radiotherapy (SRT) for Stage I non-small-cell lung cancer requires that meticulous attention be paid toward ensuring optimal target definition. Two computed tomography (CT) scan techniques for defining internal target volumes (ITV) were evaluated. METHODS AND MATERIALS: Ten consecutive patients treated with SRT underwent six "standard" rapid multislice CT scans to generate an ITV(6 CT) and one four-dimensional CT (4DCT) scan that generated volumetric datasets for 10 phases of the respiratory cycle, all of which were used to generate an ITV(4DCT). Geometric and dosimetric analyses were performed for (1) PTV(4DCT), derived from the ITV(4DCT) with the addition of a 3-mm margin; (2) PTV(6 CT), derived from the ITV(6 CT) with the addition of a 3-mm margin; and (3) 6 PTV(10 mm), derived from each separate GTV(6 CT), to which a three-dimensional margin of 10 mm was added. RESULTS: The ITV(4DCT) was not significantly different from the ITV(6 CT) in 8 patients, but was considerably larger in 2 patients whose tumors exhibited the greatest mobility. On average, the ITV(6 CT) missed on average 22% of the volume encompassing both ITVs, in contrast to a corresponding mean value of only 8.3% for ITV(4DCT). Plans based on PTV(4DCT) resulted in coverage of the PTV(6 CT) by the 80% isodose in all patients. However, plans based on use of PTV(6 CT) led to a mean PTV(4DCT) coverage of only 92.5%, with a minimum of 77.7% and 77.5% for the two most mobile tumors. PTVs derived from a single multislice CT expanded with a margin of 10 mm were on average twice the size of PTVs derived using the other methods, but still led to an underdosing in the two most mobile tumors. CONCLUSIONS: Individualized ITVs can improve target definition for SRT of Stage I non-small-cell lung cancer, and use of only a single CT scan with a 10-mm margin is inappropriate. A single 4D scan generates comparable or larger ITVs than are generated using six unmonitored rapid CT scans, a finding related to the ability to account for all respiration-correlated mobility.

Carcinoma, Non-Small-Cell Lung↗
PubMed2004

A treatment planning study evaluating a 'simultaneous integrated boost' technique for accelerated radiotherapy of stage III non-small cell lung cancer.

PURPOSE: As local tumour control is poor in stage III non-small cell lung cancer (NSCLC), a radiotherapy planning study was performed to evaluate the potential for treatment acceleration by using a simultaneous integrated boost (SIB) technique in patients who had completed induction chemotherapy. METHODS AND MATERIALS: Co-registered pre- and post-chemotherapy planning CT scans from 10 patients who showed tumour regression after induction chemotherapy were used to compare different treatment schedules: (a) a sequential boost plan delivering, in 2 Gy per fraction, 50 Gy to the pre-chemotherapy tumour volume, followed by a sequential boost of 20 Gy to the post-chemotherapy tumour volume; (b) a SIB technique in which the pre- and post-chemotherapy tumour volumes were treated to different dose levels during each treatment fraction using identical total doses and number of fractions as above; (c) progressively more hypofractionated schedules that delivered the SIB technique in 25 and 20 once-daily fractions; (d) the actual clinical treatment plan in which 70 Gy was delivered to the pre-chemotherapy tumour volume in 35 daily fractions. Differences in the fractionation schemes used for these plans were accounted for by using the normalised total dose (NTD) for comparison, thereby assuming an alpha/beta ratio of 10 Gy for tumour and 3 Gy for normal tissues. The risk of normal tissue toxicity was estimated using the average lung NTD, the lung volume receiving NTD > 20 Gy, the oesophageal volume receiving NTD > 50 Gy, and the length of full circumference irradiated to at least 50 Gy. RESULTS: With respect to the sequential boost technique, the SIB technique improved the sparing of the normal tissues in all patients. In most patients, the SIB plan could also be delivered in 25 fractions without increasing the estimated normal tissue toxicity. With SIB25, the mean lung NTD was reduced from 12.1 to 11.7 Gy, and the fraction of healthy lung tissue receiving NTD > 20 Gy by 2% on average. Although the length and volume of oesophagus irradiated to at least 50 Gy increased for some of the patients, the observed values were less than that was the case for the actual delivered treatment. However, special care should be taken to avoid exceeding the spinal cord tolerance in patients whose tumours are located close to the cord. CONCLUSIONS: A SIB technique that delivers at least 50 Gy to the pre-chemotherapy tumour volume permits accelerated radiotherapy in patients with stage III NSCLC without increasing the expected risks of normal tissue toxicity. By reducing the overall treatment time, the SIB technique may improve local tumour control and survival.

Carcinoma, Non-Small-Cell Lung↗
PubMed2004

Considerations for post-operative radiotherapy to the hemithorax following extrapleural pneumonectomy in malignant pleural mesothelioma.

With growing interest in evaluating extrapleural pneumonectomy (EPP) and post-operative in selected patients with early stage malignant pleural mesothelioma, it is essential that clinical trials should be conducted using a clear and reproducible radiotherapy protocol. The considerations which have determined the policy of radiotherapy planning and treatment delivery for patients with mesothelioma in The Netherlands are given. As well as general considerations such as patient selection, target volume and critical organ delineation, a dose-fractionation scheme, constraints relating to normal tissue, treatment planning, the type of external beam equipment, treatment verification and radiation toxicity and scoring are all taken into account.

Dose Fractionation, Radiation↗
PubMed2004

Literature-based recommendations for treatment planning and execution in high-dose radiotherapy for lung cancer.

BACKGROUND AND PURPOSE: To review the literature on techniques used in high-dose radiotherapy of lung cancer in order to develop recommendations for clinical practice and for use in research protocols. PATIENTS AND METHODS: A literature search was performed for articles and abstracts that were considered both clinically relevant and practical to use. The relevant information was arbitrarily categorized under the following headings: patient positioning, CT scanning, incorporating tumour mobility, definition of target volumes, radiotherapy planning, treatment delivery, and scoring of response and toxicity. RESULTS: Recommendations were made for each of the above steps from the published literature. Although most of the recommended techniques have yet to be evaluated in multicenter clinical trials, their use in high-dose radiotherapy to the thorax appears to be rational on the basis of current evidence. CONCLUSIONS: Recommendations for the clinical implementation of high-dose conformal radiotherapy for lung tumours were identified in the literature. Procedures that are still considered to be investigational were also highlighted.

Dose-Response Relationship, Radiation↗
PubMed2004

Defining target volumes for non-small cell lung carcinoma.

The definition of target volumes for non-small cell lung carcinoma (NSCLC) remains a controversial topic as tradition-based approaches of the past are being critically re-evaluated in the light of the advent of three-dimensional treatment techniques, by the awareness of the poor local control achieved using current treatment fields and radiation doses, and by the major improvements in noninvasive staging that enable the gross tumor volume to be established with greater accuracy. This article reviews the current knowledge and remaining uncertainties in defining target volumes for NSCLC. The use of these new approaches may allow for improvements in the therapeutic ratio of radiotherapy in NSCLC.

Carcinoma, Non-Small-Cell Lung↗