Biomedical subjects

Mohammad Salehpour

Publications and source records attributed to Mohammad Salehpour.

13 recordsLinked to original sources

PubMed2006

Multileaf field-in-field forward-planned intensity-modulated dose compensation for whole-breast irradiation is associated with reduced contralateral breast dose: a phantom model comparison.

PURPOSE: Static multileaf collimated field-in-field forward-planned intensity-modulated radiation treatment (FiF-IMRT) has been shown to improve dose homogeneity compared to conventional wedged fields. However, a direct comparison of the scattered dose to the contralateral breast resulting from wedged and FiF-IMRT plans remains to be documented. METHODS: The contralateral scattered breast dose was measured in a custom-designed anthropomorphic breast phantom in which 108 thermoluminescent dosimeters (TLDs) were volumetrically placed every 1-2cm. The target phantom breast was treated to a dose of 50Gy using three dose compensation techniques: No medial wedge and a 30-degree lateral wedge (M0-L30), 15-degree lateral and medial wedges (M15-L15), and FiF-IMRT. TLD measurements were compared using analysis of variance. RESULTS: For FiF-IMRT, the mean doses to the medial and lateral quadrants of the contralateral breast were 112cGy (range 65-226cGy) and 40cGy (range 18-91 cGy), respectively. The contralateral breast doses with FiF-IMRT were on average 65% and 82% of the doses obtained with the M15-L15 and M0-L30 techniques, respectively (p<0.001). Compared to the M15-L15 technique, the maximum dose reduction obtained with FiF-IMRT was 115cGy (range 13-115cGy). CONCLUSIONS: The dose to the contralateral breast is significantly reduced with FiF-IMRT compared to wedge-compensated techniques. Although long-term follow-up is needed to establish the clinical relevance of this finding, these results, along with the previously reported improvement in ipsilateral dose homogeneity, support the use of FiF-IMRT if resources permit.

Breast Neoplasms↗

PubMed2006

A Monte Carlo model for calculating out-of-field dose from a varian 6 MV beam.

Dose to the patient outside of the treatment field is important when evaluating the outcome of radiotherapy treatments. However, determining out-of-field doses for any particular treatment plan currently requires either time-consuming measurements or calculated estimations that may be highly uncertain. A Monte Carlo model may allow these doses to be determined quickly, accurately, and with a great degree of flexibility. MCNPX was used to create a Monte Carlo model of a Varian Clinac 2100 accelerator head operated at 6 MV. Simulations of the dose out-of-field were made and measurements were taken with thermoluminescent dosimeters in an acrylic phantom and with an ion chamber in a water tank to validate the Monte Carlo model. Although local differences between the out-of-field doses calculated by the model and those measured did exceed 50% at some points far from the treatment field, the average local difference was only 16%. This included a range of doses as low as 0.01% of the central axis dose, and at distances in excess of 50 cm from the central axis of the treatment field. The out-of-field dose was found to vary with field size and distance from the central axis, but was almost independent of the depth in the phantom except where the dose increased substantially at depths less than dmax. The relationship between dose and kerma was also investigated, and kerma was found to be a good estimate of dose (within 3% on average) except near the surface and in the field penumbra. Our Monte Carlo model was found to well represent typical Varian 2100 accelerators operated at 6 MV.

Computer Simulation↗

PubMed2005

Intensity-modulated radiation therapy after hysterectomy: comparison with conventional treatment and sensitivity of the normal-tissue-sparing effect to margin size.

PURPOSE: To determine the influence of target-volume expansion on the reduction in small-bowel dose achieved with use of intensity-modulated radiation therapy (IMRT) vs. standard conformal treatment of the pelvis after hysterectomy, and to investigate the influence of patient body habitus on the normal-tissue sparing achieved with use of IMRT. METHODS AND MATERIALS: A clinical target volume (CTV) was contoured on each of 10 planning computed tomography scans of patients who had been treated for cervical or endometrial cancer after a hysterectomy. Treatment planning was based on vaginal CTVs and regional nodal CTVs. To account for internal motion, margins were added to form an initial planning target volume (PTVA) as follows: 0.0 mm were added to the regional nodal CTV; 10 mm were added anteriorly to the vaginal CTV; and 5 mm were added to the vaginal CTV in all other directions. Two further PTVs (PTVB and PTVC) were produced by a 5-mm expansion of PTVA to give PTVB and a further 5-mm expansion to give PTVC. Treatment plans for all 3 PTVs were produced by use of 2 conformal fields (2FC), 4 conformal fields (4FC), or IMRT to deliver 45 Gy to more than 97% of the PTV. The primary goal of IMRT was to spare small bowel. The change in sparing that accompanied the increase in margin size was assessed by comparison of dose-volume histograms that resulted from PTVA, PTVB, and PTVC. Measured patient dimensions were correlated with bowel sparing. RESULTS: Significantly less small bowel was irradiated by IMRT than by 2FC (p < 0.0001) or 4FC (p < 0.0001) for doses greater than 25 Gy. Significantly less rectum was irradiated by IMRT than by 2FC (p < 0.0001) or 4FC (p < 0.0001). Significantly less bladder was irradiated by IMRT than by 2FC (p < 0.0001). However, the magnitude of the sparing achieved by use of IMRT decreased as margins increased. In particular, the volume of small bowel spared by IMRT vs. 2FC or 4FC decreased as margin size increased (p = 0.0002 and p = 0.008 for 2FC and 4FC, respectively). The amount of normal-tissue sparing achieved by use of IMRT vs. 4FC was inversely correlated with patient body mass index. CONCLUSION: Because the small-bowel sparing achieved with use of IMRT is markedly reduced by relatively small expansions of the target volume, accurate target delineation, highly reproducible patient immobilization, and a clear understanding of internal-organ motion are needed to achieve optimal advantage in the use of IMRT over conventional methods of posthysterectomy pelvic radiation therapy.

Analysis of Variance↗

PubMed2005

Out-of-field photon and neutron dose equivalents from step-and-shoot intensity-modulated radiation therapy.

PURPOSE: To measure the photon and neutron out-of-treatment-field dose equivalents to various organs from different treatment strategies (conventional vs. intensity-modulated radiation therapy [IMRT]) at different treatment energies and delivered by different accelerators. METHODS AND MATERIALS: Independent measurements were made of the photon and neutron out-of-field dose equivalents resulting from one conventional and six IMRT treatments for prostate cancer. The conventional treatment used an 18-MV beam from a Clinac 2100; the IMRT treatments used 6-MV, 10-MV, 15-MV, and 18-MV beams from a Varian Clinac 2100 accelerator and 6-MV and 15-MV beams from a Siemens Primus accelerator. Photon doses were measured with thermoluminescent dosimeters in a Rando phantom, and neutron fluence was measured with gold foils. Dose equivalents to the colon, liver, stomach, lung, esophagus, thyroid, and active bone marrow were determined for each treatment approach. RESULTS: For each treatment approach, the relationship between dose equivalent per MU, distance from the treatment field, and depth in the patient was examined. Photon dose equivalents decreased approximately exponentially with distance from the treatment field. Neutron dose equivalents were independent of distance from the treatment field and decreased with increasing tissue depth. Neutrons were a significant contributor to the out-of field dose equivalent for beam energies > or =15 MV. CONCLUSIONS: Out-of-field photon and neutron dose equivalents can be estimated to any point in a patient undergoing a similar treatment approach from the distance of that point to the central axis and from the tissue depth. This information is useful in determining the dose to critical structures and in evaluating the risk of associated carcinogenesis.

Algorithms↗

PubMed2005

The calculated risk of fatal secondary malignancies from intensity-modulated radiation therapy.

PURPOSE: Out-of-field radiation doses to normal tissues may be associated with an increased risk of secondary malignancies, particularly in long-term survivors. Step-and-shoot intensity-modulated radiation therapy (IMRT), an increasingly popular treatment modality, yields higher out-of-field doses than do conventional treatments, because of an increase in required monitor units (beam-on time). METHODS: We used published risk coefficients (NRCP Report 116) and out-of-field dose equivalents to multiple organ sites to estimate a conservative maximal risk of fatal secondary malignancy associated with 6 IMRT approaches and 1 conventional external-beam approach for prostate cancer. RESULTS: Depending on treatment energy, the IMRT treatments required 3.5-4.9 times as many monitor units to deliver as did the conventional treatment. The conservative maximum risk of fatal second malignancy was 1.7% for conventional radiation, 2.1% for IMRT using 10-MV X-rays, and 5.1% for IMRT using 18-MV X-rays. Intermediate risks were associated with IMRT using 6-MV X-rays: 2.9% for treatment with the Varian accelerator and 3.7% for treatment with the Siemens accelerator, as well as using 15-MV X-rays: 3.4% (Varian) and 4.0% (Siemens). CONCLUSION: The risk of fatal secondary malignancy differed substantially between IMRT and conventional radiation therapy for prostate cancer, as well as between different IMRT approaches. Perhaps this risk should be considered when choosing the optimal treatment technique and delivery system for patients who will undergo prostate radiation.

Dose-Response Relationship, Radiation↗

PubMed2005

Detection of IMRT delivery errors using a quantitative 2D dosimetric verification system.

We investigated the feasibility of detecting intensity modulated radiotherapy delivery errors automatically using a scalar evaluation of two-dimensional (2D) transverse dose measurement of the complete treatment delivery. Techniques using the gamma index and the normalized agreement test (NAT) index were used to parametrize the agreement between measured and computed dose distributions to seven different scalar metrics. Simulated verifications with delivery errors calculated using a commercially available treatment planning system for 9 prostate and 7 paranasal sinus cases were compared to 433 clinical verifications. The NAT index with 5% and 3 mm criteria that included cold areas outside the planning target volume detected the largest percent of delivery errors. Assuming a false positive rate of 5%, it was able to detect 88% of beam energy changes, 94% of a different patient's plan being delivered, 25% of plans with one beam's collimator rotated by 90 degrees, 81% of rotating one beam's gantry angle by 10 degrees, and 100% of omitting the delivery of one beam. However, no instances of changing one beam's monitor unit setting by 10% or shifting the isocenter by 5 mm were detected. Although the phantom shift could not be detected by the small change it made in the dose distribution, our autopositioning algorithm clearly identified the spatial anomaly. Using tighter 3 %/2 mm criteria or combining dose and distance disagreements in an either/or fashion resulted in poorer delivery error detection. The mean value of the 2D gamma index distribution was less sensitive to delivery errors than the other scalar metrics studied. Although we found that scalar metrics do not have sufficient delivery error detection rates to be used as the sole clinical analysis technique, manually examining 2D dose comparison images would result in a near 100% detection rate while performing an ion chamber measurement alone would only detect 54% of these errors.

Algorithms↗

PubMed2005

Dosimetric accuracy of Kodak EDR2 film for IMRT verifications.

Patient-specific intensity-modulated radiotherapy (IMRT) verifications require an accurate two-dimensional dosimeter that is not labor-intensive. We assessed the precision and reproducibility of film calibrations over time, measured the elemental composition of the film, measured the intermittency effect, and measured the dosimetric accuracy and reproducibility of calibrated Kodak EDR2 film for single-beam verifications in a solid water phantom and for full-plan verifications in a Rexolite phantom. Repeated measurements of the film sensitometric curve in a single experiment yielded overall uncertainties in dose of 2.1% local and 0.8% relative to 300 cGy. 547 film calibrations over an 18-month period, exposed to a range of doses from 0 to a maximum of 240 MU or 360 MU and using 6 MV or 18 MV energies, had optical density (OD) standard deviations that were 7%-15% of their average values. This indicates that daily film calibrations are essential when EDR2 film is used to obtain absolute dose results. An elemental analysis of EDR2 film revealed that it contains 60% as much silver and 20% as much bromine as Kodak XV2 film. EDR2 film also has an unusual 1.69:1 silver:halide molar ratio, compared with the XV2 film's 1.02:1 ratio, which may affect its chemical reactions. To test EDR2's intermittency effect, the OD generated by a single 300 MU exposure was compared to the ODs generated by exposing the film 1 MU, 2 MU, and 4 MU at a time to a total of 300 MU. An ion chamber recorded the relative dose of all intermittency measurements to account for machine output variations. Using small MU bursts to expose the film resulted in delivery times of 4 to 14 minutes and lowered the film's OD by approximately 2% for both 6 and 18 MV beams. This effect may result in EDR2 film underestimating absolute doses for patient verifications that require long delivery times. After using a calibration to convert EDR2 film's OD to dose values, film measurements agreed within 2% relative difference and 2 mm criteria to ion chamber measurements for both sliding window and step-and-shoot fluence map verifications. Calibrated film results agreed with ion chamber measurements to within 5 % /2 mm criteria for transverse-plane full-plan verifications, but were consistently low. When properly calibrated, EDR2 film can be an adequate two-dimensional dosimeter for IMRT verifications, although it may underestimate doses in regions with long exposure times.

Dose-Response Relationship, Radiation↗

PubMed2005

Retrospective analysis of 2D patient-specific IMRT verifications.

We performed 858 two-dimensional (2D) patient-specific intensity modulated radiotherapy verifications over a period of 18 months. Multifield, composite treatment plans were measured in phantom using calibrated Kodak EDR2 film and compared with the calculated dose extracted from two treatment planning systems. This research summarizes our findings using the normalized agreement test (NAT) index and the percent of pixels failing the gamma index as metrics to represent the agreement between measured and computed dose distributions. An in-house dose comparison software package was used to register and compare all verifications. We found it was important to use an automatic positioning algorithm to achieve maximum registration accuracy, and that our automatic algorithm agreed well with anticipated results from known phantom geometries. We also measured absolute dose for each case using an ion chamber. Because the computed distributions agreed with ion chamber measurements better than the EDR2 film doses, we normalized EDR2 data to the computed distributions. The distributions of both the NAT indices and the percentage of pixels failing the gamma index were found to be exponential distributions. We continue to use both the NAT index and percent of pixels failing gamma with 5%/3 mm criteria to evaluate future verifications, as these two metrics were found to be complementary. Our data showed that using 2%/2 mm or 3%/3 mm criteria produces results similar to those using 5%/3 mm criteria. Normalized comparisons that have a NAT index greater than 45 and/or more than 20% of the pixels failing gamma for 5%/3 mm criteria represent outliers from our clinical data set and require further analysis. Because our QA verification results were exponentially distributed, rather than a tight grouping of similar results, we continue to perform patient-specific QA in order to identify and correct outliers in our verifications. The data from this work could be useful as a reference for other clinics to indicate anticipated trends in 2D verifications under various conditions.

Algorithms↗

PubMed2004

Advances in radiation treatments of breast cancer.

During the past decade, improvements in treatment-planning tools, computer and imaging technologies, and new therapeutic modalities have allowed radiation to be delivered in a conformal fashion while minimizing treatment toxicity. It is important that physicians involved in breast cancer treatment recognize the numerous advances that have occurred in the delivery of radiation therapy. Changes in 3 specific areas in treatment planning and delivery have revolutionized the way we approach breast cancer treatment: the design of radiation fields using computed tomography (CT) data sets, the development of 3-dimensional dose-calculation algorithms, and the development of new methods to modulate the delivery of radiation dose. With the advent of CT simulators, individual patient anatomy and pathology can be readily visualized and reconstructed in axial, coronal, and sagittal views. With an improved anatomic delineation between the target volumes and critical organ structures, the treatment fields can be designed to be more congruous to the areas at highest risk. In the past few years, new 3-dimensional dose-calculation algorithms have been generated that more accurately calculate dose distributions throughout the treatment-planning volume. Finally, modern linear accelerators allow for modulation of the dose intensity of the radiation beam, which may lead to improved aesthetics and decreased side effects while ensuring that the volumes at high risk receive the prescribed dose. Radiation therapy can be delivered safely and effectively to patients with breast cancer.

Breast Neoplasms↗

PubMed2003

Patient-specific point dose measurement for IMRT monitor unit verification.

PURPOSE: To review intensity-modulated radiation therapy (IMRT) monitor unit verification in a phantom for 751 clinical cases. METHODS AND MATERIALS: A custom water-filled phantom was used to measure the integral dose with an ion chamber for patient-specific quality assurance. The Corvus IMRT planning system was used for all cases reviewed. The 751 clinical cases were classified into 9 treatment sites: central nervous system (27 cases), gastrointestinal (24 cases), genitourinary (447 cases), gynecologic (18 cases), head and neck (200 cases), hematology (12 cases), pediatric (3 cases), sarcoma (8 cases), and thoracic (12 cases). Between December 1998 and January 2002, 1591 measurements were made for these 751 IMRT quality assurance plans. RESULTS: The mean difference (MD) in percent between the measurements and the calculations was +0.37% (with the measurement being slightly higher). The standard deviation (SD) was 1.7%, and the range of error was from -4.5% to 9.5%. The MD and SD were +0.49% and 1.4% for MIMiC treatments delivered in 2-cm mode (261 cases) and -0.33% and 2.7% for those delivered in 1-cm mode (36 cases). Most treatments (420) were delivered using the step-and-shoot multileaf collimator with a 6-MV photon beam; the MD and SD were +0.31% and 1.8%, respectively. Among the 9 treatment sites, the prostate IMRT (in genitourinary site) was most consistent with the smallest SD (1.5%). There were 23 cases (3.1% of all cases) in which the measurement difference was greater than 3.5%; of those, 6 cases used the MIMiC in 1-cm mode, and 14 of the cases were from the head-and-neck treatment site. CONCLUSION: IMRT monitor unit calculations from the Corvus planning system agreed within 3.5% with the point-dose ion chamber measurement in 97% of 751 cases representing 9 different treatment sites. A good consistency was observed across sites.

Algorithms↗

PubMed2003

Intensity-modulated radiotherapy following extrapleural pneumonectomy for the treatment of malignant mesothelioma: clinical implementation.

PURPOSE: New insight into the extent of the target volume for the postoperative irradiation of malignant pleural mesothelioma as determined during surgery has indicated that standard conformal radiotherapy (IMRT) is not sufficient for curative treatment. We describe a novel technique for implementing intensity-modulated radiotherapy (IMRT) to deliver higher doses to treat the full extent of these complex target volumes. METHODS AND MATERIALS: After extrapleural pneumonectomy, 7 patients underwent simulation, treatment planning, and treatment with IMRT to the involved hemithorax and adjacent abdomen. The target volumes encompassed the entire operative bed, including the ipsilateral mediastinum, anterior pleural reflection, and ipsilateral pericardium and the insertion of the diaphragm and crura. These were extensively marked during surgery with radiopaque markers to facilitate target delineation. RESULTS: Setup uncertainty and respiratory-dependent motion were found to be small. Coverage of the planning target volume was very good, with the crus of the diaphragm the most difficult volume to irradiate. The radiation doses to normal structures were acceptable. CONCLUSION: IMRT for treatment of malignant mesothelioma after extrapleural pneumonectomy results in more potentially curative doses to large, complex target volumes with acceptable doses to normal tissues.

Humans↗

PubMed2002

Preoperative chemotherapy and radiation for advanced esophageal carcinoma: comparison between once a day radiation and hyperfractionation, a single-institution experience.

The purpose of this study was to determine the toxicity and efficacy of single daily fractionation as compared with twice-a-day radiation therapy in combination with chemotherapy for preoperative locally advanced thoracic esophageal carcinoma. A retrospective survey was done of 42 patients undergoing concurrent chemotherapy and radiation for preoperative locally advanced thoracic esophageal carcinoma. Twenty-five patients had 5-fluorouracil ([5-FU]), 1,000 mg/m2/d by continuous infusion, days 1-5, and days 22-26), cisplatin (100 mg/m2 intravenously, days 2 and 22), and radiation to a total dose of 4,500 to 5,040 cGy in 180 cGy/fraction every day. Seventeen patients received 5-FU (300 mg/m2/d by continuous infusion, days 1 and 21), cisplatin (20 mg/m2/d for 1 hour, days 1-5 and days 17-20), vinblastine (1 mg/m2 intravenously, days 1-5 and days 17-21) and accelerated hyperfractionated radiation 150 cGy twice a day to a total dose of 4,500 cGy. Response rate, survival, local regional failure rates, and treatment toxicity of the two groups were compared. Surgery was aborted in one patient and another patient refused surgery in the single daily-fractionation group. All patients underwent surgery in the twice-daily group. Complete response (CR) was noted in 12 patients (52%) in the single daily-fractionation group as compared with 9 patients (52%) in the twice-daily group. The median and 3-year survival were 20 months and 35%, respectively, in the single daily-fractionation group. Corresponding figures were 18 months and 32%, respectively, in the twice-daily group. For the 2 groups combined, a statistically significant improvement in survival was observed among blacks who achieved a CR (31 months) as compared with the ones with residual disease (13.5 months). Local and regional failures were 28% and 17%, respectively, for the single daily-fractionation and twice-daily groups. Distant metastases remained significant in both groups and were 36% (single daily-fractionation) and 41% (twice-daily), respectively. Grades III to IV esophagitis and hematologic toxicity developed in 36% and 64% of patients of the single daily-fractionation and twice-daily groups, respectively. The incidence of late complications was 16% (single daily-fractionation) and 11.7% (twice-daily). Preoperative chemotherapy and radiation is effective to achieve a high pathologic CR. Both radiation therapy fractionation schedules are comparable in efficacy and toxicity. Further investigations should be done to assess whether ethnicity may play a role in the prognosis of esophageal carcinoma.

Adult↗

PubMedDate not supplied

Efficacy of combined radiation, paclitaxel and carboplatin for locally advanced non-small cell lung carcinoma.

Locally advanced non-small cell lung carcinoma (NSCLC) has a poor prognosis when treated with conventional chemotherapy and radiation. New chemotherapy agents like paclitaxel may increase the sensitivity of tumors cells to radiation and potentially improve the outcome. The optimal combination of taxane-based chemotherapy agents and radiation is still unclear. We investigated the feasibility of induction chemotherapy followed by concurrent near systemic dose of chemotherapy with radiation. A prospective survey of 29 previously untreated patients with unresectable stage III (15 IIIA, 14 IIIB) NSCLC treated with paclitaxel and carboplatin in combination with radiation was reviewed. The patients received 2 cycles of paclitaxel 225 mg/m2 intravenously (i.v.) over 3 hours, days 1, 22; carboplatin at area under the curve (AUC) 6 based on Calvert formula days 1, 22 following completion of the paclitaxel infusion. Following induction chemotherapy, radiation therapy started on day 43 until completion to a tumor dose of at least 5960 cGy. Cycles 3 and 4 of chemotherapy were begun on days 43 and 63, respectively, and consisted of paclitaxel 175 mg/m2 i.v. over 3 hours, and carboplatin at AUC 6 following paclitaxel infusion. The response rate, acute toxicity, long-term complications, pattern of failure and survival were evaluated and compared to previous studies in the literature. Two patients were lost to follow-up. The response rate to induction carboplatin/paclitaxel was 52%. An overall response rate (complete and partial responders) of 85% was obtained following chemotherapy and radiation. Grade 3-4 acute side-effects were recorded in 9 patients (31%) and consisted of esophagitis (8 patients) and anemia (1 patient). One patient died from cachexia 3 months following treatment (3.7%). The median survival and 3-year survival were 15 months and 30%, respectively, for the remaining 27 patients at a median follow-up of 11 months. There was no difference in survival between stages IIIA and IIIB at 2 years (IIIA: 22%, IIIB: 31%). Local or regional recurrences and distant metastases developed in 9 patients (33%) and 13 patients (46%), respectively. The combination of paclitaxel, carboplatin and radiation for locally advanced non-small cell carcinoma is feasible with acceptable toxicity. The response rate compares favorably with previously reported studies. The decrease of tumor volume following induction chemotherapy allows sparing of the lungs from the toxicity of radiation. However, grades 3-4 esophagitis remain significant. The addition of amifostine may be beneficial in this setting.

Aged↗