Biomedical subjects

David Mansur

Publications and source records attributed to David Mansur.

5 recordsLinked to original sources

PubMed2006

Peripheral doses from pediatric IMRT.

Peripheral dose (PD) data exist for conventional fields (> or = 10 cm) and intensity-modulated radiotherapy (IMRT) delivery to standard adult-sized phantoms. Pediatric peripheral dose reports are limited to conventional therapy and are model based. Our goal was to ascertain whether data acquired from full phantom studies and/or pediatric models, with IMRT treatment times, could predict Organ at Risk (OAR) dose for pediatric IMRT. As monitor units (MUs) are greater for IMRT, it is expected IMRT PD will be higher; potentially compounded by decreased patient size (absorption). Baseline slab phantom peripheral dose measurements were conducted for very small field sizes (from 2 to 10 cm). Data were collected at distances ranging from 5 to 72 cm away from the field edges. Collimation was either with the collimating jaws or the multileaf collimator (MLC) oriented either perpendicular or along the peripheral dose measurement plane. For the clinical tests, five patients with intracranial or base of skull lesions were chosen. IMRT and conventional three-dimensional (3D) plans for the same patient/target/dose (180 cGy), were optimized without limitation to the number of fields or wedge use. Six MV, 120-leaf MLC Varian axial beams were used. A phantom mimicking a 3-year-old was configured per Center for Disease Control data. Micro (0.125 cc) and cylindrical (0.6 cc) ionization chambers were appropriated for the thyroid, breast, ovaries, and testes. The PD was recorded by electrometers set to the 10(-10) scale. Each system set was uniquely calibrated. For the slab phantom studies, close peripheral points were found to have a higher dose for low energy and larger field size and when MLC was not deployed. For points more distant from the field edge, the PD was higher for high-energy beams. MLC orientation was found to be inconsequential for the small fields tested. The thyroid dose was lower for IMRT delivery than that predicted for conventional (ratio of IMRT/conventional ranged from 0.47-0.94) doses approximately [0.4-1.8 cGy]/[0.9-2.9 cGy]/fraction, respectively. Prior phantom reports are for fields 10 cm or greater, while pediatric central nervous system fields range from 4 to 7 cm, and effectively much smaller for IMRT (2-6 cm). Peripheral dose in close proximity (< 10 cm from the field edge) is dominated by internal scatter; therefore, field-size differences overwhelm phantom size affects and increased MU. Distant peripheral dose, dominated by head leakage, was higher than predicted, even when accounting for MUs (approximtely factor of 3) likely due to the pediatric phantom size. The ratio of the testes dose ranged from 3.3-5.3 for IMRT/conventional. PD to OAR for pediatric IMRT cannot be predicted from large-field full phantom studies. For regional OAR, doses are likely lower than predicted by existing "large field" data, while the distant PD is higher.

Brain Neoplasms↗

PubMed2002

Three-dimensional conformal therapy versus standard radiation therapy in localized carcinoma of prostate: an update.

This study updates technical principles and results of 3-dimensional conformal radiation therapy (3D-CRT) in localized carcinoma of the prostate. Between January 1992 and December 1999, 312 patients were treated with 3D-CRT and 135 patients were treated with bilateral arcs standard radiation therapy (SRT) alone for clinical stage T1b-c or T2 histologically confirmed prostate cancer. None of these patients received hormonal therapy. Mean follow-up for patients in the 3D-CRT group was 3.2 years (range, 2-5.9 years) and for SRT patients, 4.7 years (range, 4-7 years). For 3D-CRT, 7 intersecting fields were used (cerrobend blocking or multileaf collimation) to deliver 68-74 Gy to the prostate. Standard radiation therapy consisted of bilateral 120 degree rotational arcs, with portals using 2-cm margins around the prostate to deliver 68-70 Gy to the prostate. The criterion for chemical disease-free survival was a postirradiation prostate-specific antigen (PSA) value following the American Society for Therapeutic Radiology and Oncology guidelines. Symptoms during treatment were quantitated weekly, and late effects were assessed every 4-6 months. Dose-volume histograms showed a two-thirds reduction with 3D-CRT in normal bladder or rectum receiving > or = 70 Gy with 3D-CRT. Higher 5-year chemical disease-free survival was observed with 3D-CRT (75%; for T1b-c and 79%; for T2 tumors) compared with SRT (61% and 65%, P = 0.01 and P = 0.12, respectively). There was no statistically significant difference in chemical disease-free survival in patients with Gleason score of < or = 4 (P = 0.85), but, with Gleason score of 5-7, the 5-year survival rates were 83% with 3D-CRT and 59% with SRT (P < or = 0.01). In 245 patients with pretreatment PSA of < or = 10 ng/mL treated with 3D-CRT, the chemical disease-free rate was 80% versus 72% in 98 patients treated with SRT (P = 0.21). In patients with PSA of 10.1-20 ng/mL, the chemical disease-free survival rate for 50 patients treated with 3D-CRT was 71% compared with 43% for 20 patients treated with SRT (P = 0.02). The corresponding values were 59% and 16%, respectively, for patients with PSA levels > 20 ng/mL (P = 0.09). On multivariate analysis, the most important prognostic factors for chemical failure were pretreatment PSA (P = 0.004), nadir PSA (P = 0.001), and 3D-CRT technique (P = 0.012). Moderate dysuria was reported by 2%-5% of patients treated with 3D-CRT in contrast to 6%-9% of patients treated with SRT. The incidence of moderate loose stools or diarrhea, usually after the fourth week of treatment, was 3%-5% in the 3D-CRT patients and 8%-19% in the SRT group. Late intestinal grade 2 morbidity (proctitis or rectal bleeding) was 1% in the 3D-CRT group in contrast to 7% in SRT patients. The 3D-CRT spares more normal tissues, yields higher chemical disease-free survival, and results in less treatment morbidity than SRT in treatment of stage T1-T2 prostate cancer. Follow-up at > or = 10 years is needed to confirm these observations.

Adenocarcinoma↗

PubMedDate not supplied

Impact of elapsed treatment time on outcome of external-beam radiation therapy for localized carcinoma of the prostate.

PURPOSE: The purpose of this study was to evaluate the impact of elapsed treatment time in external-beam radiation therapy for localized prostate carcinoma. MATERIALS AND METHODS: The medical records of 1083 patients with localized prostate carcinoma treated between 1970 and December 1999 with external irradiation alone were reviewed. Median follow-up was 6 years (range, 4-24 years). Since 1987, prostate-specific antigen levels were obtained in 687 patients before the initiation of radiation therapy, and all patients seen in follow-up had prostate-specific antigen determinations. There were 344 patients with T1c, 496 with T2, and 243 with T3 tumors. The elapsed treatment time was divided into < or = 7, 7.1-9, or > 9 weeks. Local tumor control was determined by rectal examination and cause-specific survival or prostate-specific antigen failure according to American Society of Therapeutic Radiology and Oncology consensus criteria. Because of dose-escalation studies, tumor dose levels ranged from 66-73.8 Gy, given in 1.8- to 2-Gy fractions. RESULTS: In patients with stage T1c, local failure ranged from 0% to 10% with doses < or = 72 Gy with; elapsed treatment time had no impact. No pelvic failures were detected in 88 patients receiving doses > 72 Gy. In patients with T2 who received < or = 70 Gy, overall pelvic failure rate was 4% (12/306) in those with an elapsed treatment time of < or = 9 weeks, in contrast to 27% (12/44) for those with an elapsed treatment time > 9 weeks; at 10 years, patients with T2 tumors treated in > 9 weeks had a higher actuarial pelvic failure rate (35%), in contrast to 5% to 18% with shorter treatment times. For patients with T2 tumors who received 70-72 Gy, pelvic failure rate ranged from 0% to 32%, and there were no failures in 37 patients treated to higher doses. In patients with prostate-specific antigen values whose tumors were stage T1c, the chemical failure rate was 41% (60/147) with a tumor dose < 70 Gy, compared with 17% (4/24) in those who received higher doses. In patients with stage 2 disease who were treated with < 70 Gy, the chemical failure rate was 31%, and the rate was 12%-18% in those who received higher doses. In stage T3, the clinical pelvic failure rate ranged from 25% to 32% in the three elapsed time groups, and the chemical failure rate ranged from 48% to 69%, and there was no significant correlation with elapsed time or total irradiation dose. Cause-specific survival without chemical failure in patients with stage T1c disease at 10 years was 85%-90% in the three elapsed treatment time groups. In patients with stage T2 disease, the corresponding values were 80% and 90% for elapsed treatment times < 9 weeks, in contrast to 65% for patients treated > 9 weeks. In patients with stage T3 disease, cause-specific survival was about 60% in all elapsed treatment groups. There was no significant correlation of elapsed treatment time with urinary or rectal morbidity. CONCLUSIONS: Patients treated with radiation therapy for stage T2 localized prostate carcinoma showed a greater incidence of pelvic and chemical failures and a lower cause-specific survival when elapsed treatment time was > 9 weeks in comparison with the failure and survival rates occurring with shorter times. Higher doses of irradiation (> 72 Gy) eliminate the influence of prolongation of treatment time on outcome.

Aged↗

PubMedDate not supplied

Uncertainties in radiation therapy: target volume definition in prostate cancer.

Accurate definition of target volumes and pelvic organs at risk is critical to improve the outcome in patients treated with irradiation for localized carcinoma of the prostate. Precise delineation of these structures will assist in more rational therapeutic decisions and optimized radiation therapy treatment planning and delivery. Increased conformity in radiation dose distribution allows delivery of higher doses of irradiation and dose escalation studies and results in improved tumor control, lower incidence of distant metastasis, improved survival and better quality of life. Multiple imaging methods are available and significant advances have been made in image fusion to enhance target volume definition. An exhaustive review of the literature is presented.

Dose Fractionation, Radiation↗

PubMedDate not supplied

Clinical assessment of outcome of prostate cancer (TCP, NTCP).

In the recent past there have been major advances in the management of patients with prostate cancer. New imaging procedures as 3-D CRT and IMRT have played a major role in the tretament of patients with localized prostate cancer. 3-D CRT allows higher doses to be delivered more precisely to the target volume with acceptable organs at risk morbidity. Improved tumor control results in lower incidence of distant metastases and better survival with an enhanced quality of life. This outcome yields a lower cost per treatment of patients over their life time.

Clinical Trials as Topic↗