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George Rodrigues

Publications and source records attributed to George Rodrigues.

13 recordsLinked to original sources
PubMed2006

A comparison of prostate IMRT and helical tomotherapy class solutions.

The purpose of this study was to assess a variety of potential IMRT class solutions as compared to a helical tomotherapy (HT) class solution for localized prostate cancer. Target and critical structures were contoured on 10 prostate cancer patient CT datasets. HT treatment plans were compared to four different IMRT approaches by paired t-tests. HT prostate planning generally provided treatment plans with excellent target homogeneity and favorable critical structure sparing when compared to conventional IMRT.

Humans↗
PubMed2006

Prostate contouring uncertainty in megavoltage computed tomography images acquired with a helical tomotherapy unit during image-guided radiation therapy.

PURPOSE: To evaluate the image-guidance capabilities of megavoltage computed tomography (MVCT), this article compares the interobserver and intraobserver contouring uncertainty in kilovoltage computed tomography (KVCT) used for radiotherapy planning with MVCT acquired with helical tomotherapy. METHODS AND MATERIALS: Five prostate-cancer patients were evaluated. Each patient underwent a KVCT and an MVCT study, a total of 10 CT studies. For interobserver variability analysis, four radiation oncologists, one physicist, and two radiation therapists (seven observers in total) contoured the prostate and seminal vesicles (SV) in the 10 studies. The intraobserver variability was assessed by asking all observers to repeat the contouring of 1 patient's KVCT and MVCT studies. Quantitative analysis of contour variations was performed by use of volumes and radial distances. RESULTS: The interobserver and intraobserver contouring uncertainty was larger in MVCT compared with KVCT. Observers consistently segmented larger volumes on MVCT where the ratio of average prostate and SV volumes was 1.1 and 1.2, respectively. On average (interobserver and intraobserver), the local delineation variability, in terms of standard deviations [Deltasigma = radical(sigma2MVCT-sigma2KVCT)], increased by 0.32 cm from KVCT to MVCT. CONCLUSIONS: Although MVCT was inferior to KVCT for prostate delineation, the application of MVCT in prostate radiotherapy remains useful.

Humans↗
PubMed2006

Comparative planning evaluation of intensity-modulated radiotherapy techniques for complex lung cancer cases.

BACKGROUND AND PURPOSE: Lung cancer treatment can be one of the most challenging fields in radiotherapy. The aim of the present study was to compare different modalities of radiation delivery based on a balanced scoring scheme for target coverage and normal tissue avoidance. PATIENTS AND METHODS: Treatment plans were developed for 15 patients with stage III inoperable non-small cell lung cancer using 3D conformal technique and intensity-modulated radiotherapy (IMRT). Elective nodal irradiation was included for all cases to create the most challenging scenarios with large target volumes. A 2 cm margin was used around the gross tumour volume (GTV) to generate PTV2 and 1cm margin around elective nodes for PTV1 resulting in PTV1 volumes larger than 1000 cm(3) in 13 of the 15 patients. 3D conformal and IMRT plans were generated on a commercial treatment planning system (TheraPlan Plus, Nucletron) with various combinations of beam energies and gantry angles. A 'dose quality factor' (DQF) was introduced to correlate the plan quality with patient specific parameters. RESULTS: A good correlation was found between the quality of the plans and the overlap between PTV1 and lungs. The patient feature factor (PFF), which is a product of several pertinent characteristics, was introduced to facilitate the choice of a particular technique for a particular patient. CONCLUSIONS: This approach may allow the evaluation of different treatment options prior to actual planning, subject to validation in larger prospective data sets.

Carcinoma, Non-Small-Cell Lung↗
PubMed2006

Pelvic chemoradiotherapy after chemotherapy for metastatic bladder cancer.

OBJECTIVE: Consolidative radiotherapy has improved local control in other tumors with high local recurrence rates but has not been well studied in urothelial cancer. We hypothesized that pelvic chemoradiotherapy (PCRT) given after systemic chemotherapy for metastatic bladder cancer (MTCC) might alter the pattern of disease recurrence, and reduce the complications and morbidity of intrapelvic disease relapse. A 74% locoregional relapse rate has been observed in MTCC patients with intrapelvic nodal disease after response to chemotherapy. To explore this hypothesis further, we performed a retrospective analysis and report the efficacy, toxicity and pattern of failure with this approach. MATERIALS AND METHODS: Patients treated for MTCC who received consolidative PCRT following at least a partial response to systemic chemotherapy were identified and their charts reviewed for pelvic relapse, disease progression, survival, and toxicity. RESULTS: Twelve patients were identified and median follow-up was 15.6 months. Nine patients developed progressive disease and died, and median survival was 15.6 months. Three patients had pelvic progression (pelvic failure rate 25%). Median time to pelvic failure was 12.8 months. At last follow-up, three patients were alive and disease-free. No life-threatening toxicities were observed. The most common acute non-hematological toxicities were diarrhea and nausea. CONCLUSIONS: These data support a hypothesis that consolidative PCRT following chemotherapy in MTCC patients with systemic disease control may be feasible and efficacious for improving pelvic disease control. This intervention should be considered for further study in prospective controlled clinical trials.

Aged↗
PubMed2006

Changing management of localized prostate cancer: a comparison survey of Ontario radiation oncologists.

BACKGROUND AND PURPOSE: Annual genitourinary radiation oncology meetings aim to assist in the dissemination of knowledge that may affect current practice. We aim to measure changes in practice approaches that have occurred while these meetings have been conducted. MATERIALS AND METHODS: A previously published survey from 2002 was sent to all genitourinary radiation oncologists in Ontario. Six prostate cancer patient scenarios were used: three definitive (low risk, intermediate risk, high risk), and three post-operative (extracapsular extension, margin positive, slowly rising PSA). There were 21 responders from seven cancer centers. RESULTS: Using biological equivalent dose (BED), there is significant dose escalation in 2005, particularly for intermediate risk patients (mean BED 73.0 Gy2 in 2002 versus 76.1 Gy2 in 2005, p=0.0003). There has been a corresponding move away from the use of neoadjuvant hormones in these patients (2002: 62% versus 2005: 24%, p=0.0097). More accurate prostate localization using fiducials is more common, leading to less use of rectal barium and urethrograms in the simulation process. In the definitive settings there is more utilization of rigid immobilization and more complex treatment delivery including intensity modulated radiotherapy. There is also greater use of multileaf collimation, electronic portal imaging and dose volume histograms in 2005 compared with 2002. CONCLUSIONS: There have been significant changes in the way that prostate cancer is managed with radiotherapy in Ontario between 2002 and 2005. Dose escalation and more complex treatment planning is widely evident.

Humans↗
PubMed2006

Controversies in prostate cancer staging implementation at a tertiary cancer center.

OBJECTIVE: To assess accuracy of recorded prostate cancer stage after implementation of a quality assurance staging improvement plan. METHODS AND MATERIALS: Genitourinary multidisciplinary TNM staging guidelines were prospectively implemented. Educational programs for health records technicians (HRT) and clinicians preceded implementation of the new guidelines. Patient stage information was entered into the Oncology Patient Information System (OPIS) as part of the usual operations of the cancer center by an HRT. Physician and HRT auditors performed a subsequent quality assurance audit on 97 prostate cancer patients seen over a 2-month period. Assessment of staging accuracy and reasons for discrepancies between the OPIS stage and auditor stage were analyzed and reported. RESULTS: Fifty-four (52%) charts showed discrepancies between auditors. Of the fifty-four, twelve (22%) had discrepancies between OPIS and auditor, thirty (56%) showed discrepancies between auditors, and twelve (22%) had discrepancies between OPIS, physician auditor, and HRT auditor. Forty-three (41%) cases had no discrepancies. Reasons for discrepancies included: misinterpretation of the digital rectal examination (16/54), inappropriate use of TRUS/MRI (9/54) in staging, stage not assigned at initial diagnosis (9/54), misinterpretation of pathology (7/54), TNM staging confusion (4/54), OPIS update not performed (3/54), inappropriate use of biopsy data (3/54), disagreement between consultants (2/54), and misinterpretation of TURP result (1/54). Overall staging accuracy was 76% for OPIS, 65% for the physician auditor and 62% for the HRT auditor. CONCLUSIONS: Despite guidelines and educational interventions, computer registry staging accuracy remains an issue. On-going audit procedures are proposed to identify and correct both published and institutional staging guidelines.

Canada↗
PubMed2005

Intensity-modulated arc therapy for treatment of high-risk endometrial malignancies.

PURPOSE: We developed an intensity-modulated arc therapy (IMAT) technique for the treatment of women with high-risk endometrial malignancies. In the context of multimodality therapy, nodal and tumor bed irradiation was delivered while respecting tolerance doses for critical structures. METHODS AND MATERIALS: Five patients were planned and treated with the IMAT technique after hysterectomy. Computed tomographic (CT) scans for treatment planning were acquired with the tumor bed contoured as the clinical target volume (CTV(tumor_bed)) and the iliac and presacral vessels contoured as the gross tumor volume (GTV). In 2 patients the lower para-aortic nodes were included into the GTV. The small bowel, iliac crests, femoral heads, bladder, and rectum were contoured as critical organs. For the nodes, a CTV(nodes) was generated with a 7-10-mm margin around the vessels, and the planning target volume (PTV(nodes)) was generated by a further 5-mm expansion. For the tumor bed, the PTV(tumor_bed) was generated with a margin of 7-10 mm around CTV(tumor_bed). Planning constraints included adequate coverage of the tumor bed (>95% receiving > or =45 Gy) and nodes (> or =95% receiving > or =40 Gy). Arc combinations with different extents were tested, and the final plan was generated based on the balance between complexity (number of arcs), PTV coverage, and critical structure sparing. Conventional and 8-field intensity-modulated radiation therapy (IMRT) plans were generated for each patient for comparison purposes. All patients were treated with IMAT. RESULTS: We found that two anterior intensity-modulated arcs (300 degrees to 30 degrees and 330 degrees to 60 degrees ) adequately treated the PTVs. Furthermore, this IMAT technique allowed sparing of small bowel and the iliac crests (marrow space) to a similar degree as the 8-field IMRT. The 8-field IMRT yielded better dose uniformity than IMAT in the target volumes; however, neither technique was as uniform as the conventional plan. In the 5 patients, IMAT treatment was well tolerated and completed as planned. CONCLUSIONS: We successfully piloted an optimized intensity-modulated arc technique to treat 5 high-risk endometrial cancer patients undergoing multimodality treatment. This allowed a significant reduction in dose to bone marrow and small bowel compared with conventional techniques and was simpler to deliver than multifield IMRT.

Bone Marrow↗
PubMed2004

Planning evaluation of radiotherapy for complex lung cancer cases using helical tomotherapy.

Lung cancer treatment is one of the most challenging fields in radiotherapy. The aim of the present study was to investigate what role helical tomotherapy (HT), a novel approach to the delivery of highly conformal dose distributions using intensity-modulated radiation fan beams, can play in difficult cases with large target volumes typical for many of these patients. Tomotherapy plans were developed for 15 patients with stage III inoperable non-small-cell lung cancer. While not necessarily clinically indicated, elective nodal irradiation was included for all cases to create the most challenging scenarios with large target volumes. A 2 cm margin was used around the gross tumour volume (GTV) to generate primary planning target volume (PTV2) and 1 cm margin around elective nodes for secondary planning target volume (PTV1) resulting in PTV1 volumes larger than 1000 cm3 in 13 of the 15 patients. Tomotherapy plans were created using an inverse treatment planning system (TomoTherapy Inc.) based on superposition/convolution dose calculation for a fan beam thickness of 25 mm and a pitch factor between 0.3 and 0.8. For comparison, plans were created using an intensity-modulated radiation therapy (IMRT) approach planned on a commercial treatment planning system (TheraplanPlus, Nucletron). Tomotherapy delivery times for the large target volumes were estimated to be between 4 and 19 min. Using a prescribed dose of 60 Gy to PTV2 and 46 Gy to PTV1, the mean lung dose was 23.8+/-4.6 Gy. A 'dose quality factor' was introduced to correlate the plan outcome with patient specific parameters. A good correlation was found between the quality of the HT plans and the IMRT plans with HT being slightly better in most cases. The overlap between lung and PTV was found to be a good indicator of plan quality for HT. The mean lung dose was found to increase by approximately 0.9 Gy per percent overlap volume. Helical tomotherapy planning resulted in highly conformal dose distributions. It allowed easy achievement of two different dose levels in the target simultaneously. As the overlap between PTV and lung volume is a major predictor of mean lung dose, future work will be directed to control of margins. Work is underway to investigate the possibility of breath-hold techniques for tomotherapy delivery to facilitate this aim.

Carcinoma, Non-Small-Cell Lung↗
PubMed2004

Prediction of radiation pneumonitis by dose - volume histogram parameters in lung cancer--a systematic review.

BACKGROUND AND PURPOSE: To perform a systematic review of the predictive ability of various dose-volume histogram (DVH) parameters (V(dose), mean lung dose (MLD), and normal tissue complication probability (NTCP)) in the incidence of radiation pneumonitis (RP) caused by external-beam radiation therapy. METHODS AND MATERIALS: Studies assessing the relationship between CT-based DVH reduction parameters and RP rate in radically treated lung cancer were eligible for the review. Synonyms for RP, lung cancer, DVH and its associated parameters (NTCP, V(20), V(30), MLD) were combined in a search strategy involving electronic databases, secondary reference searching, and consultation with experts. Individual or group data were abstracted from the various reports to calculate operating characteristics and odds ratios for the different DVH metrics. RESULTS: A total of 12 published studies and two abstracts were identified. Eleven studies assessed V(dose), seven assessed MLD, and eight assessed NTCP. Nine studies exclusively analyzed the association between various DVH metrics and RP risk. Five studies also analyzed other patient, tumor, and treatment variables in conjunction with standard DVH metrics. A direct comparison between studies and the generation of summary statistics (i.e. meta-analysis) could not be achieved due to significant predictive and outcome variable heterogeneity. Most studies did show an association between DVH parameters and RP risk. However, overall accuracy, sensitivity, specificity, and positive predictive value were generally poor to fair for all three classes of DVH metrics. CONCLUSIONS: An association between DVH parameters and RP risk has been demonstrated in the literature. However, the ideal DVH metric with excellent operating characteristics, either alone or in a model with other predictive variables, for RP risk prediction has not yet been identified. Several recommendations for reporting and conduct of future research into the association between DVH metrics and RP risk are provided.

Carcinoma, Non-Small-Cell Lung↗
PubMed2003

Contemporary management of prostate cancer: a practice survey of Ontario genitourinary radiation oncologists.

OBJECTIVE: To survey radiation oncology practice in the utilization of hormonal and radiation therapy in the primary, adjuvant and salvage treatment of localized prostate cancer. MATERIALS AND METHODS: Genitourinary radiation oncologists practicing in Ontario were invited to participate in a practice survey examining staging, hormonal and radiation management, and radiation technique for a variety of common clinical scenarios. Background demographic information was collected on all respondents. The survey consisted of three cases relating to the hormonal/radiation management of low-, intermediate-, and high-risk prostate cancer as well as two adjuvant and one salvage post-prostatectomy scenarios. The survey response rate was 70% (26/37). RESULTS: Clinicians were more likely to utilize laboratory and imaging studies for staging as the risk categorization increased. Low-risk disease was managed with radiation alone in 26/26 (70 Gy in 65%, 74-79.8 Gy in 35%). Intermediate-risk disease was managed with radiation (70 Gy in 46%, 74-79.8 Gy in 54%) with neoadjuvant hormones in 58%. All respondents managed high-risk disease with adjuvant hormones in addition to radiation therapy (70-71 Gy in 85%, and 76 Gy in 15%). In the pT3a, margin negative (PSA undetectable) scenario, most individuals would not recommend adjuvant radiation (73%). If margins were positive, 30% would still not recommend adjuvant radiation. In the salvage scenario (slowly rising PSA 4 years post-prostatectomy for pT2a close margin disease), all respondents would manage with radiation therapy. Hormones were not routinely recommended in the initial management of the adjuvant and salvage scenarios. Radiation doses utilized for both adjuvant and salvage treatment ranged from 60-70 Gy (median 66 Gy). CONCLUSIONS: General agreement exists for the management of low- and high-risk disease and in the post-prostatectomy salvage setting. Use of dose-escalation and neoadjuvant hormones in the intermediate-risk setting and use of post-prostatectomy adjuvant radiation in the pT3a scenarios varied among radiation oncologists. Current clinical practice in localized prostate cancer reflects the evolving information in the published medical literature.

Antineoplastic Agents, Hormonal↗