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Howard Amols

Publications and source records attributed to Howard Amols.

At least 19 recordsLinked to original sources
PubMed2006

Long-term outcome of high dose intensity modulated radiation therapy for patients with clinically localized prostate cancer.

PURPOSE: We report on the long-term results and late toxicity outcomes of high dose intensity modulated radiation therapy for patients with clinically localized prostate cancer. MATERIALS AND METHODS: Between 1996 and 2000 a total of 561 patients with clinically localized prostate cancer were treated with intensity modulated radiation therapy. All patients were treated to a dose of 81 Gy prescribed to the planning target volume. Prostate specific antigen relapse was defined according to the American Society for Therapeutic Radiology and Oncology consensus and Houston definitions (absolute nadir plus 2 ng/ml dated at the call). Median followup was 7 years (range 5 to 9). RESULTS: The 8-year actuarial PSA relapse-free survival rates for patients in favorable, intermediate and unfavorable risk groups according to the American Society for Therapeutic Radiology and Oncology definition were 85%, 76% and 72%, respectively (p <0.025). The 8-year actuarial prostate specific antigen relapse-free survival rates for patients in favorable, intermediate and unfavorable risk groups according to the Houston definition were 89%, 78% and 67%, respectively (p = 0.0004). The 8-year actuarial likelihood of grade 2 rectal bleeding was 1.6%. Three patients (0.1%) experienced grade 3 rectal toxicity requiring either 1 or more transfusions or a laser cauterization procedure. No grade 4 rectal complications have been observed. The 8-year likelihood of late grade 2 and 3 (urethral strictures) urinary toxicities were 9% and 3%, respectively. Among patients who were potent before intensity modulated radiation therapy, erectile dysfunction developed in 49%. The cause specific survival outcomes for favorable, intermediate and unfavorable risk cases were 100%, 96% and 84%, respectively. CONCLUSIONS: These long-term results confirm our previous observations regarding the safety of high dose intensity modulated radiation therapy for clinically localized prostate cancer. Despite the application of high radiation doses, the incidence of rectal bleeding at 8 years was less than 2%. Despite the increased conformality of the dose distribution associated with intensity modulated radiation therapy, excellent long-term tumor control outcomes were achieved.

Aged↗
PubMed2006

Image-fusion of MR spectroscopic images for treatment planning of gliomas.

1H magnetic resonance spectroscopic imaging (MRSI) can improve the accuracy of target delineation for gliomas, but it lacks the anatomic resolution needed for image fusion. This paper presents a simple protocol for fusing simulation computer tomography (CT) and MRSI images for glioma intensity-modulated radiotherapy (IMRT), including a retrospective study of 12 patients. Each patient first underwent whole-brain axial fluid-attenuated-inversion-recovery (FLAIR) MRI (3 mm slice thickness, no spacing), followed by three-dimensional (3D) MRSI measurements (TE/TR: 144/1000 ms) of a user-specified volume encompassing the extent of the tumor. The nominal voxel size of MRSI ranged from 8 x 8 x 10 mm3 to 12 x 12 x 10 mm3. A system was developed to grade the tumor using the choline-to-creatine (Cho/Cr) ratios from each MRSI voxel. The merged MRSI images were then generated by replacing the Cho/Cr value of each MRSI voxel with intensities according to the Cho/Cr grades, and resampling the poorer-resolution Cho/Cr map into the higher-resolution FLAIR image space. The FUNCTOOL processing software was also used to create the screen-dumped MRSI images in which these data were overlaid with each FLAIR MRI image. The screen-dumped MRSI images were manually translated and fused with the FLAIR MRI images. Since the merged MRSI images were intrinsically fused with the FLAIR MRI images, they were also registered with the screen-dumped MRSI images. The position of the MRSI volume on the merged MRSI images was compared with that of the screen-dumped MRSI images and was shifted until agreement was within a predetermined tolerance. Three clinical target volumes (CTVs) were then contoured on the FLAIR MRI images corresponding to the Cho/Cr grades. Finally, the FLAIR MRI images were fused with the simulation CT images using a mutual-information algorithm, yielding an IMRT plan that simultaneously delivers three different dose levels to the three CTVs. The image-fusion protocol was tested on 12 (six high-grade and six low-grade) glioma patients. The average agreement of the MRSI volume position on the screen-dumped MRSI images and the merged MRSI images was 0.29 mm with a standard deviation of 0.07 mm. Of all the voxels with Cho/Cr grade one or above, the distribution of Cho/Cr grade was found to correlate with the glioma grade from pathologic finding and is consistent with literature results indicating Cho/Cr elevation as a marker for malignancy. In conclusion, an image-fusion protocol was developed that successfully incorporates MRSI information into the IMRT treatment plan for glioma.

Brain Neoplasms↗
PubMed2006

Integrating respiratory gating into a megavoltage cone-beam CT system.

We have previously described a low-dose megavoltage cone beam computed tomography (MV CBCT) system capable of producing projection image using one beam pulse. In this study, we report on its integration with respiratory gating for gated radiotherapy. The respiratory gating system tracks a reflective marker on the patient's abdomen midway between the xiphoid and umbilicus, and disables radiation delivery when the marker position is outside predefined thresholds. We investigate two strategies for acquiring gated scans. In the continuous rotation-gated acquisition, the linear accelerator (LINAC) is set to the fixed x-ray mode and the gantry makes a 5 min, 360 degree continuous rotation, during which the gating system turns the radiation beam on and off, resulting in projection images with an uneven distribution of projection angles (e.g., in 70 arcs each covering 2 degrees). In the gated rotation-continuous acquisition, the LINAC is set to the dynamic arc mode, which suspends the gantry rotation when the gating system inhibits the beam, leading to a slightly longer (6-7 min) scan time, but yielding projection images with more evenly distributed projection angles (e.g., approximately 0.8 degrees between two consecutive projection angles). We have tested both data acquisition schemes on stationary (a contrast detail and a thoracic) phantoms and protocol lung patients. For stationary phantoms, a separate motion phantom not visible in the images is used to trigger the RPM system. Frame rate is adjusted so that approximately 450 images (13 MU) are acquired for each scan and three-dimensional tomographic images reconstructed using a Feldkamp filtered backprojection algorithm. The gated rotation-continuous acquisition yield reconstructions free of breathing artifacts. The tumor in parenchymal lung and normal tissues are easily discernible and the boundary between the diaphragm and the lung sharply defined. Contrast-to-noise ratio (CNR) is not degraded relative to nongated scans of stationary phantoms. The continuous rotation-gated acquisition scan also yields tomographic images with discernible anatomic features; however, streak artifacts are observed and CNR is reduced by approximately a factor of 4. In conclusion, we have successfully developed a gated MV CBCT system to verify the patient positioning for gated radiotherapy.

Electrons↗
PubMed2006

Low-dose megavoltage cone-beam computed tomography for lung tumors using a high-efficiency image receptor.

We report on the capabilities of a low-dose megavoltage cone-beam computed tomography (MV CBCT) system. The high-efficiency image receptor consists of a photodiode array coupled to a scintillator composed of individual CsI crystals. The CBCT system uses the 6 MV beam from a linear accelerator. A synchronization circuit allows us to limit the exposure to one beam pulse [0.028 monitor units (MU)] per projection image. 150-500 images (4.2-13.9 MU total) are collected during a one-minute scan and reconstructed using a filtered backprojection algorithm. Anthropomorphic and contrast phantoms are imaged and the contrast-to-noise ratio of the reconstruction is studied as a function of the number of projections and the error in the projection angles. The detector dose response is linear (R2 value 0.9989). A 2% electron density difference is discernible using 460 projection images and a total exposure of 13 MU (corresponding to a maximum absorbed dose of about 12 cGy in a patient). We present first patient images acquired with this system. Tumors in lung are clearly visible and skeletal anatomy is observed in sufficient detail to allow reproducible registration with the planning kV CT images. The MV CBCT system is shown to be capable of obtaining good quality three-dimensional reconstructions at relatively low dose and to be clinically usable for improving the accuracy of radiotherapy patient positioning.

Equipment Design↗
PubMed2005

Reduction of organ motion in lung tumors with respiratory gating.

We evaluated the ability of a commercial respiratory gating system to assure the reproducibility of internal anatomy in respiration synchronized CT (RS-CT) scans. This passive system uses an infrared sensitive camera to track the motion of reflective markers mounted on the abdomen. Eighteen patients, nine with lung tumors and nine with liver tumors, were selected for evaluation of the Varian Real-Time Position Monitor respiratory gating system. Liver tumors were chosen as surrogate for lower lobe tumors. Each patient underwent at least two identical RS-CT scans, at end-inspiration (EI) or end-expiration (EE), to assess intra-fraction reproducibility. Twelve patients also underwent a free breathing scan and an opposed-respiration phase synchronized scan (EI if the two first were an EE and vice versa). On each CT, a physician contoured the liver, the kidneys, the spleen, and the diaphragms for the liver patients; and similarly, the lungs, the gross tumor volume (GTV), the trachea, the heart and the diaphragms for the lung patients. After registering the different CT images using bony anatomy, the changes of each structure between the respective data sets were quantified in terms of its volume, the displacement of its center of mass (COM), and an "index" coefficient of reproducibility. An analysis of the CT scans obtained at EI and EE phases yielded an average superior-inferior (SI) difference of the diaphragm position of 14.4 mm (range: 45.9-0.9). A similar analysis of CT scans acquired at the same breathing phase yielded 0.7 mm (range: 3.1-0, p=0.0001). Similar conclusions were derived in analysis of COM positions of the following structures: lungs, heart, lung's GTV, liver, spleen and kidneys. Evaluation of volume changes for lungs, liver, and spleen confirmed reproducibility of RS-CT while the "index" coefficient confirmed reproducibility of RS-CT of all organs. A commercial gating system using external markers for RS-CT significantly improves the positional reproducibility of thoracic and upper abdominal structures. This reproducible decrease in organ motion will allow a reduction of the margin of expansion facilitating increase in target dose beyond that allowed by conventional radiation treatments.

Adult↗
PubMed2005

Results of a phase I dose-escalation study using three-dimensional conformal radiotherapy in the treatment of inoperable nonsmall cell lung carcinoma.

BACKGROUND: The objective of this study was to report the results of a Phase I dose-escalation study using three-dimensional conformal radiation therapy (3D-CRT) for the treatment of patients with nonsmall cell lung carcinoma (NSCLC). METHODS: Between 1991 and 2003, 104 patients were enrolled for 3D-CRT at Memorial Sloan-Kettering Cancer Center. The median patient age was 69 years. Twenty-eight percent of patients had Stage I-II NSCLC, 33% of patients had Stage IIIA NSCLC, 32% of patients had Stage IIIB NSCLC, and 6% of patients had recurrent NSCLC. Induction chemotherapy was received by 16% of patients. Radiation was delivered in daily fractions of 1.8 grays (Gy) for doses < or = 81.0 Gy and in daily fractions of 2.0 Gy for higher doses. Accrual at a dose level was complete when 10 patients received the intended dose without unacceptable acute morbidity. RESULTS: After an incident of fatal acute radiation pneumonitis at the starting dose of 70.2 Gy, the protocol was modified to limit normal tissue complication probabilities (NTCP) to < 25%. The dose was then escalated from 70.2 Gy, to 75.6 Gy, 81.0 Gy, and 84.0 Gy, with at least 10 patients treated at each dose level. Unacceptable pulmonary toxicity occurred at 90.0 Gy. Subsequently, another 10 patients were accrued at the 84.0 Gy level with acceptable toxicity. Thus, 84.0 Gy was the maximum tolerated dose (MTD). The crude late pulmonary toxicity rate was 7%, the 2-year local control rate was 52%, the disease-free survival rate was 33%, and the overall survival rate was 40%. The median survival was 21.1 months. Overall survival was improved significantly in patients who received > or = 80.0 Gy. CONCLUSIONS: The MTD of 3D-CRT for NSCLC with an NTCP constraint of 25% was 84.0 Gy in the current study. There was a suggestion of improved survival in patients who received 80.0 Gy.

Adult↗
PubMed2005

Comparison of end normal inspiration and expiration for gated intensity modulated radiation therapy (IMRT) of lung cancer.

BACKGROUND AND PURPOSE: Gated delivery of radiation during part of the respiration cycle may improve the treatment of lung cancer with intensity modulated radiation therapy (IMRT). In terms of the respiration phase for gated treatment, normal end-expiration (EE) is more stable but normal end-inspiration (EI) increases lung volume. We compare the relative merit of using EI and EE in gated IMRT for sparing normal lung tissue. PATIENTS AND METHODS: Ten patients received EI and EE respiration-triggered CT scans in the treatment position. An IMRT plan for a prescription dose of 70 Gy was generated for each patient and at each respiration phase. The optimization constraints included target dose uniformity, less than 35% of the total lung receiving 20 Gy or more and maximum cord dose <or=45 Gy. We compared planning target volume (PTV) coverage, mean lung dose, percentage of total lung receiving 20 Gy or more (V(20)) and lung normal tissue complication probability (NTCP). RESULTS: For 9 of the 10 patients, cord and lung doses were acceptable and PTV coverage was similar for EE and EI, with lung sparing was equal to or slightly better at EI than at EE. For the 10th patient, lung sparing at EI was significantly better. Patient averaged mean lung dose was 15.4 Gy (range: 7.1-20.4) at EI and 16.3 Gy (range: 6.9-21.9) at EE. The average V(20) was 23.8% (range: 13-36.4) at EI and 25.3% (range: 13-37.3) at EE. The average NTCP at EI was 8 versus 12% at EE. CONCLUSIONS: Dosimetric indices of lung protection for IMRT plans at EI are better than at EE. For 9 out of the 10 patients in our study, this difference is small. Thus other factors such as reproducibility, reliability and duty cycle at normal end expiration may be more critical for selecting treatment breathing phase.

Aged↗
PubMed2005

Accurate setup of paraspinal patients using a noninvasive patient immobilization cradle and portal imaging.

Because of the proximity of the spinal cord, effective radiotherapy of paraspinal tumors to high doses requires highly conformal dose distributions, accurate patient setup, setup verification, and patient immobilization. An immobilization cradle has been designed to facilitate the rapid setup and radiation treatment of patients with paraspinal disease. For all treatments, patients were set up to within 2.5 mm of the design using an amorphous silicon portal imager. Setup reproducibility of the target using the cradle and associated clinical procedures was assessed by measuring the setup error prior to any correction. From 350 anterior/posterior images, and 303 lateral images, the standard deviations, as determined by the imaging procedure, were 1.3 m, 1.6 m, and 2.1 in the ant/post, right/left, and superior/inferior directions. Immobilization was assessed by measuring patient shifts between localization images taken before and after treatment. From 67 ant/post image pairs and 49 lateral image pairs, the standard deviations were found to be less than 1 mm in all directions. Careful patient positioning and immobilization has enabled us to develop a successful clinical program of high dose, conformal radiotherapy of paraspinal disease using a conventional Linac equipped with dynamic multileaf collimation and an amorphous silicon portal imager.

Equipment Design↗
PubMed2005

Tumor motion control in the treatment of non small cell lung cancer.

Tumor motion due to respiration during radiation therapy for non-small cell lung cancer is a significant problem. This article reports on two techniques used to control tumor motion: respiratory gating and the deep inspiration breath hold technique. This technique was implemented in 40 patients without significant difficulties and there are encouraging clinical outcomes.

Carcinoma, Non-Small-Cell Lung↗
PubMed2004

Improved local control with higher doses of radiation in large-volume stage III non-small-cell lung cancer.

PURPOSE: It has been suggested that larger tumor volume is associated with poor survival in patients with non-small-cell lung cancer (NSCLC). We investigated whether high-dose radiation improved local control in patients with large-volume Stage III NSCLC. METHODS AND MATERIALS: Seventy-two patients with Stage III NSCLC and gross tumor volumes (GTV) of greater than 100 cc were treated with three-dimensional conformal radiotherapy (3D-CRT). Patients were divided into two groups: those treated to less than 64 Gy (37 patients) and those treated to 64 Gy or higher (35 patients). RESULTS: The 1-year and 2-year local failure rates were 27% and 47%, respectively, for Stage III patients treated to 64 Gy or higher, and 61% and 76%, respectively, for those treated to less than 64 Gy (p = 0.024). The median survival time for patients treated to 64 Gy or higher was 20 months vs. 15 months for those treated to less than 64 Gy (p = 0.068). Multivariate analysis revealed that dose and GTV are predictors of local failure-free survival. A 10 Gy increase in dose resulted in a 36.4% decreased risk of local failure. CONCLUSIONS: Our data suggest that administration of higher doses using 3D-CRT improves local control in Stage III NSCLC patients with large GTVs.

Adult↗
PubMed2004

A practical approach to prevent gantry-couch collision for linac-based radiosurgery.

Gantry-couch collision is a serious concern for treatment planning of the linear accelerator (linac) based stereotactic radiosurgery (SRS). The ability to detect collision at the time of planning eliminates the need for backup plans and preserves the useful beam angles that would be deemed unsafe and discarded otherwise. Most collision-detection schemes embedded in commercial planning software guard only against the most apparent collisions. On the other hand, a fool-proof collision-map or lookup table often requires detailed measurement of machine geometry and complex graphic operations. In this study, we have developed a simple analytical method for collision detection with the use of quick machine-specific measurements. The collision detection is mathematically solved by determining whether two facets in three-dimensional space, representing gantry and couch surfaces, intersect with each other. A computer code was implemented and tested on a Varian Clinac 600C linac equipped with a BrainLab micromultileaf collimator (MLC) device. To measure machine-specific parameters, the lesion isocenter was set to the origin of the stereotactic coordinate system. The reference coordinates of couch bracket corners and micro-MLC to the linac isocenter were measured only once in the treatment room before they were incorporated into the computer program. Couch, gantry, and collimator were subsequently translated and rotated to study the clearance of various beam arrangements and lesion locations. Predicted results were verified at the machine. Our method correctly confirmed clearance for a retrospective study of 54 previously treated SRS plans (76 isocenters). It also accurately predicted the collisions for all ten artificially created cases. In conclusion, we have developed an analytical method for SRS collision detection that is accurate, easy to implement, and computationally inexpensive.

Algorithms↗
PubMed2003

Optimization of conformal thoracic radiotherapy using cone-beam CT imaging for treatment verification.

PURPOSE: Megavoltage cone-beam computed tomography (MVCBCT) has been proposed for treatment verification in conformal radiotherapy. However, the doses required for such imaging may compromise the quality of the delivered dose distribution. The present paper explores the effect of cone-beam imaging on dose homogeneity and critical organ dose and the use of our new tool, adapted intensity-modulated radiation therapy (AIMRT). METHODS AND MATERIALS: Three types of treatment plans were devised (3D-CRT [three-dimensional conformal radiotherapy], IMRT [intensity-modulated radiotherapy], and AIMRT) based on 4 patients with thoracic malignancies. MVCBCT fields were then integrated into the plans. The MVCBCT technique used 21 imaging portals at 10 degrees intervals. The MVCBCT apertures were shaped to conform to the planning target volume with a 6-mm margin. In a second set of plans, the field size was expanded by a further 2 cm. The unoptimized MVCBCT dose distribution was incorporated into the IMRT plan using AIMRT. RESULTS: Normal-tissue complication probability with MVCBCT is acceptable for all plans at the 66.6 Gy level, but exceeds tolerance for both 3D-CRT alone and 3D-CRT with MVCBCT at higher doses. In contrast, the use of AIMRT planning with MVCBCT allowed safe dose escalation to 85 Gy. Expanding the MVCBCT aperture provided better anatomic visibility with an acceptable lung dose. The results using IMRT with MVCBCT fell between the values measured for 3D-CRT and AIMRT with MVCBCT. CONCLUSION: The present study is the first to demonstrate that MVCBCT can be incorporated into 3D-CRT and IMRT planning with minimal effect on planning target volume homogeneity and dose to critical structures. This paves the way for highly conformal radiotherapy at greater doses delivered with increased confidence and safety.

Computer Graphics↗
PubMed2003

New radiotherapy technologies.

Conventional radiation therapy has had limited success in curing inoperable lung cancer due to poor local control. There is evidence to suggest that higher doses of radiation will improve local control. In order to safely deliver higher doses of thoracic radiation, advanced treatment techniques are required. Different biologic indices have been utilized to determine whether dose escalation can be safely accomplished, and the results have been reported from many institutions. Tumor motion control aids in treatment since it allows radiation oncologists to more accurately target tumors and therefore to spare more normal tissue from the radiation field. The imaging information from 18-FDG-PET scans also improves target delineation. Advanced treatment delivery techniques, such as three-dimensional conformal radiation therapy, intensity modulated radiation therapy, and stereotactic radiosurgery are also being used to safely escalate the radiation dose. This article explores the current literature on these issues and other advanced radiation therapy techniques.

Dose-Response Relationship, Radiation↗
PubMed2002

IMRT of large fields: whole-abdomen irradiation.

PURPOSE: To assess the feasibility of inverse planning for whole-abdomen intensity-modulated radiation therapy (IMRT) with bone marrow and kidney sparing and to develop approaches to circumventing field size restrictions in the application of whole-abdomen IMRT using dynamic multileaf collimators (DMLC). METHODS AND MATERIALS: The entire peritoneal cavity as derived from serial computerized tomography scans was defined as the gross target volume, whereas the planning target volume (PTV) was defined as the gross target volume plus a 5-mm margin extending 1 cm superiorly and inferiorly. In 10 randomly selected patients, the PTV ranged from 5629 to 12578 cc (median 7935 cc), and the superior-inferior, lateral, and anterior-posterior dimensions of the PTV ranged from 37 to 46 cm (median 42.5 cm), 27 to 33 cm (median 29 cm), and 18 to 23 cm (median 20 cm), respectively. A single isocenter was defined for patients with field length <40 cm. For patients with fields >40 cm, two isocenters were defined: one in the abdominal region, and the other in the pelvis. For IMRT planning, five 15-MV intensity-modulated beams at gantry angles of 180 degrees, 105 degrees, 35 degrees, 325 degrees, and 255 degrees were used. Optimization was designed to spare kidneys and bones. To fully account for the significant scattered dose contributions, an iterative process for dose calculations was implemented in the optimization. To overcome the 15-cm field width limit of our DMLC delivery system, fields with a width >15 cm were split into two or more subfields. To minimize field match errors, adjacent subfields overlapped by at least 2 cm, with intensity "feathering" in the overlap region. For patients with two isocenters, fields were overlapped and feathered in the cephalad-caudad direction by at least 3 cm. For comparison, conventional anterior-posterior/posterior-anterior 6-MV photon beams with posterior kidney blocks at extended distance were also generated for each patient. RESULTS: Treatment plan optimization calculations required 20-80 min on a 500-MHz DEC alpha workstation. Including beam splitting, an average of 16 DMLC beams was used per patient. Delivery of 150 cGy required, on average, 1442 monitor units. For the same dose constraints on the kidneys, whole-abdomen IMRT resulted in significant dose reduction to the bones and improved PTV coverage as compared to conventional treatment. For a prescription dose of 30 Gy, the volume of the pelvic bones receiving more than 21 Gy was reduced on average by almost 60% with IMRT, and the mean dose to all bones was reduced from 24.0 +/- 1.5 Gy to 18.5 +/- 1.0 Gy (p = 0.002). PTV coverage, as measured by V95 (the volume receiving 95% of the prescription dose), improved from 71.7 +/- 4.8% with conventional treatment to 83.5 +/- 3.9% with IMRT (p = 0.002), although small regions of underdose in areas near the kidneys could not be avoided completely. The high-dose regions within the PTV, as measured by D05 (the dose covering 5% of PTV volume), increased slightly from 31.2 +/- 0.6 Gy with conventional treatment to 32.8 +/- 0.2 Gy with IMRT. CONCLUSION: We have developed a process to plan and deliver whole-abdomen IMRT using standard linear accelerators and DMLC. IMRT can achieve better PTV coverage with the same level of kidney sparing and improved sparing of the bone marrow. These methods may be applicable also to other sites requiring large-field irradiation.

Abdomen↗