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Biomedical subjects

B Paliwal

Publications and source records attributed to B Paliwal.

14 recordsLinked to original sources
PubMed2001

A new approach to dose escalation in non-small-cell lung cancer.

PURPOSE: To describe the radiobiological rationale for dose-per-fraction escalation in non-small-cell lung cancer (NSCLC) and to devise a novel Phase I scheme to implement this strategy using advanced radiotherapy delivery technologies. METHODS AND MATERIALS: The data from previous dose escalation trials in NSCLC are reanalyzed to establish a dose-response relationship in this disease. We also use data relating prolongation in treatment time to survival to compute the potential doubling time for lung tumors. On the basis of these results, and using a Bayesian model to determine the probability of pneumonitis as a function of mean normalized lung dose, a dose-per-fraction escalation strategy is developed. RESULTS: Standard approaches to dose escalation using 2 Gy per fraction, five fractions per week, require doses in excess of 85 Gy to achieve 50% long-term control rate. This is partly because NSCLCs repopulate rapidly, with a 1.6% per day loss in survival from prolongation in overall treatment time beyond 6 weeks, and a cell doubling time of only 2.5 to 3.3 days. A dose-per-fraction escalation strategy, with a constant number of fractions, 25, and overall time, 5 weeks, is projected to produce tumor control rates predicted to be 10%-15% better than 2 Gy per fraction dose escalation, with equivalent late effects. This Phase I clinical study is divided into three parts. Step 1 examines the feasibility of the maximum breath-holding technique and junctioning of tomotherapy slices. Step 2 treats 10 patients with 30 fractions of 2 Gy over 6 weeks and then reduces duration to 5 weeks using fewer but larger fractions in 10 patients. Step 3 will consist of a dose-per-fraction escalation study on roughly 50 patients, maintaining 25 fractions in 5 weeks. Bayesian methodology (a modification of the Continual Reassessment Method) will be used in Step 3 to allow consistent and efficient escalation within five volume bins. CONCLUSION: A dose-per-fraction escalation approach in NSCLC should yield superior outcomes, compared to standard dose escalation approaches using a fixed dose per fraction, for a given level of pneumonitis and late toxicity. Highly conformal radiotherapy techniques, such as intensity modulated radiotherapy (IMRT) and helical tomotherapy with its adaptive capabilities, will be necessary to achieve significant dose-per-fraction escalation without unacceptable lung and esophageal morbidity.

Carcinoma, Non-Small-Cell Lung↗
PubMed2000

A spiral phantom for IMRT and tomotherapy treatment delivery verification.

A solid water/cylindrical phantom is machined to create a spiral cavity for placing radiographic or radiochromatic film in a spiral configuration. This spiral phantom is used to sample, predict, and measure data in three-dimension subspace. The predicted data are obtained by projecting the patient plan data on the spiral phantom in the treatment planning software. The measured data are obtained by irradiating the spiral phantom (with film in the spiral cavity) as per the treatment plan. The predicted and measured data are converted to a two-dimensional matrix and plotted as a spiralogram. Comparison of these predicted and measured spiralograms provides a quantitative comparison and thus validation of treatment delivered as planned. The spiral phantom is a simple, cost-effective approach to sample 3D data from complexly shaped, intensity modulated or compensated multiple beams. A software script is being written to automate the entire process of projection, data sampling, and comparison. Design aspects and some examples of dose verification are presented. The usefulness of the spiral phantom for intensity modulated radiation therapy and dynamic field shaping are discussed.

Computer Simulation↗
PubMed1995

A study of the effect of cone shielding in intraoperative radiotherapy.

The primary goal of intraoperative radiation therapy is to irradiate the intraoperatively determined tumor target volume with a single fraction of tumoroidal dose while minimizing the dose to all adjacent healthy tissues. To reduce dose outside the treatment volume, lead sheets are often used to cover the external surface of the cone tip thus providing a shielding for the tissues outside the field. In this paper, the effect of the shielding on the depth dose distributions and dose profiles at different depths is studied based on experimental data. The results were also compared against an EGS4 Monte Carlo code for the same geometry as the measurements. The cones varied in size having diameters of 5 cm, 7 cm, and 9 cm, and the electron energies ranged from 6 MeV to 22 MeV. The depth dose curves and dose profiles (at two different depths in the phantom) were measured and computed with and without the lead shielding for the various combinations of cone sizes and electron energies using a water phantom to simulate the patient. It was found that the presence of lead increases on average across the treatment area the dose to the tumor from 2% up to 5%, while the dose outside the cone was reduced by as much as 75%. Both measurements and calculations were found to be in agreement.

Combined Modality Therapy↗
PubMed1993

Resource utilization. High dose rate versus low dose rate brachytherapy for gynecologic cancer.

A comparative analysis of anesthesia use, perioperative morbidity and mortality, capital, and treatment cost of high dose rate versus low dose rate intracavitary brachytherapy for gynecologic malignancy is presented. To assess current anesthesia utilization, application location, and high dose rate afterloader availability for gynecologic brachytherapy in private and academic practices, a nine-question survey was sent to 150 radiotherapy centers in the United States, of which 95 (63%) responded. Of these 95 respondents, 95% used low dose rate brachytherapy, and 18% possessed high dose rate capability. General anesthesia was used in 95% of programs for tandem + ovoid and in 31% for ovoids-only placement. Differences among private and academic practice respondents were minimal. In our institution, a cost comparison for low dose rate therapy (two applications with 3 hospital days per application, operating and recovery room use, spinal anesthesia, radiotherapy) versus high dose rate treatment (five outpatient departmental applications, intravenous anesthesia without an anesthesiologist, radiotherapy) revealed a 244% higher overall charge for low dose rate treatment, primarily due to hospital and operating room expenses. In addition to its ability to save thousands of dollars per intracavitary patient, high dose rate therapy generated a "cost-shift," increasing radiotherapy departmental billings by 438%. More importantly, perioperative morbidity and mortality in our experience of 500+ high dose rate applications compared favorably with recently reported data using low dose rate intracavitary treatment. Capital investment, maintenance requirements, and depreciation costs for high dose rate capability are reviewed. Application of the defined "revenue-cost ratio" formula demonstrates the importance of high application numbers and consistent reimbursement for parity in high dose rate operation. Logically, inadequate third-party reimbursement (e.g., Medicare) reduces high dose rate parity and threatens the future availability of high dose rate technology.

Anesthesia↗
PubMed1992

Weight consideration in the use of cerrobend beam blocks.

The technique of using customized field blocking to protect sensitive normal tissue during megavoltage radiation treatment is common practice in modern radiation therapy. The introduction of CT-based treatment planning has revolutionized customized field shaping. We carried out a prospective evaluation of 54 cerrobend blocks during a one-month time period. The goals of this study were to analyze the specific block patterns and correlate these with field size, block weight, and field setup. Factors contributing to excessively large and heavy cerrobend blocks defined as > or = 20 lbs. were identified. Twenty-two percent of blocks were found to be excessively large and one-third of these were a consequence of planning decisions. A review of these situations suggests that alternative methods would have avoided the excessive weight. Concerns have been raised regarding the safety of large and heavy cerrobend blocks. These blocks were therefore analyzed in terms of tray sag and tray break-point. Our data suggest that within this clinical range of block weight, neither tray sag nor tray break-point are of significant concern.

Humans↗
PubMed1989

Hyperthermia quality assurance guidelines.

These Hyperthermia Quality Assurance guidelines are a result of a joint workshop of the Hyperthermia Committee of the American College of Radiology and the Hyperthermia Physics Center, which is the national quality assurance program under Contract No. N01-CM-37512 with the National Cancer Institute. Hyperthermia technology presently lacks the kind of standardization in equipment, treatment procedures, patient monitoring, and treatment documentation available in radiotherapy. Therefore, preventing unacceptable variability in treatment data demands a strong commitment to in-house quality control procedures and to centralized quality assurance reviews in cooperative multi-institutional trials. This paper presents a set of test procedures necessary to ensure proper operation of equipment, suggests a frequency for such tests, and also includes guidelines on quality control procedures to be used during treatment to improve the safety, effectiveness, and reproducibility of hyperthermia treatments. A set of forms are presented to indicate the minimum data, albeit incomplete, that must be collected for acceptable documentation of treatment. These guidelines should be valuable not only to the new entrants in the field but also to those participating in multi-institutional cooperative hyperthermia trials. They have been approved by the Hyperthermia Committees of American College of Radiology, American Society for Therapeutic Radiology and Oncology, Radiation Therapy Oncology Group and the American Association of Physicists in Medicine.

Forms and Records Control↗
PubMed1983

Fortification of existing rooms used for brachytherapy patients.

Often, the radiation exposure levels around brachytherapy patient rooms exceed the limits allowed by Nuclear Regulatory Commission (NRC) regulations and National Council on Radiation Protection (NCRP) recommendations. Since a neighboring patient may be present in the radiation field from a brachytherapy patient, or patients, continuously for 7 days, the dose equivalent rate must not exceed 6 muSv/hr (0.6 mrem/hr). Several boundary conditions constrain solutions to the problem of excessive radiation levels: (1) the cost should not be recurring, (2) the rooms used for brachytherapy patients must be compatible with use for nonbrachytherapy patients, (3) free access through halls must be maintained, (4) all brachytherapy rooms must be compatible with independent use, (5) shielding must not eliminate space required for a resuscitation cart, (6) shielding should not require storage, (7) the weight of shielding must remain within the tolerance of the floor, and (8) the location of beds must match utility outlets in the wall. Possible solutions to the problem include leaving rooms empty around the patient, use of portable shields, or the addition of substantial amounts of shielding material in the walls of the brachytherapy rooms, as well as changing the radionuclides routinely used. The optimum solution for a given institution depends on the frequency of brachytherapy procedures, bed occupancy rate, and available empty space.

Brachytherapy↗
PubMedDate not supplied

Whole body hyperthermia (41-42 degrees C): a simple technique for unanesthetized mice.

A technique for accomplishing 41-42 degrees C whole body hyperthermia (WBH) in unrestrained, unanesthetized mice using a simple apparatus is reported. This method combines a radiant heat technology with monitoring of individual rectal temperatures at 10-min intervals. In 66 heating sessions, involving 116 AKR mice and a total of 619 WBH treatments, the mortality rate was less than 1%. Treatment at 41-42 degrees C for periods of up to 120 min were accomplished. Relationships of several variables of mouse temperature-time profiles were studied including (1) initial core temperature, (2) rate of heating, (3) whole body irradiation, and (4) the presence of tumor (transplanted AKR leukemia). Sham treatments produce a consistent temperature-time profile showing about a 1 degree C rise. Between-mouse variability, as well as between-treatment variability in individual animals was estimated. Thermal mapping of the device demonstrates a range from 32-38 degrees C of the air temperature in the zone with the mice to a high of 47 degrees C near to the radiant heating surface at the top of the apparatus.

Animals↗
PubMedDate not supplied

Tomotherapy: a new concept for the delivery of dynamic conformal radiotherapy.

Tomotherapy, literally "slice therapy," is a proposal for the delivery of radiation therapy with intensity-modulated strips of radiation. The proposed method employs a linear accelerator, or another radiation-emitting device, which would be mounted on a ring gantry like a CT scanner. The patient would move through the bore of the gantry simultaneously with gantry rotation. The intensity modulation would be performed by temporally modulated multiple independent leaves that open and close across the slit opening. At any given time, any leaf would be (1) closed, covering a portion of the slit, (2) open, allowing radiation through, or (3) changing between these states. This method would result in the delivery of highly conformal radiation. Overall treatment times should be comparable with contemporary treatment delivery times. The ring gantry would make it convenient to mount a narrow multisegmented megavoltage detector system for beam verification and a CT scanner on the treatment unit. Such a treatment unit could become a powerful tool for treatment planning, conformal treatment, and verification using tomographic images. The physical properties of this treatment delivery are evaluated and the fundamental design specifications are justified.

Humans↗