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F M Waterman

Publications and source records attributed to F M Waterman.

At least 37 records · Page 2Linked to original sources
PubMed1997

Anisotropy of an 192iridium high dose rate source measured with a miniature ionization chamber.

The anisotropy of a high dose rate (HDR) 192Ir source was measured in air and in water using a miniature (0.147 cm3) ionization chamber. Measurements were made at a distance of 5 cm from the source center at polar angles from 10 degrees-170 degrees. The anisotropy was found to be less pronounced in water, and the anisotropy is asymmetric about the transverse axis. The results agree with previous ionization chamber and TLD measurements to within +/- 4%. Mean anisotropy factors were determined at each angle from all existing data at 5 cm distance, and compared to published Monte Carlo calculations, and to the values used in the microSelectron HDR brachytherapy planning system (BPS). The Monte Carlo photon transport code appears to systematically underestimate the anisotropy factor by up to 4% in the forward direction and overestimate it by up to 3% in the backward direction. The mean anisotropy factors also indicate that the BPS systematically underestimates the anisotropy factor by up to 3% in the forward direction, and overestimates it by up to 15% in the backward direction. However, the 15% difference occurs at 180 degrees where it is not likely to be clinically significant.

Air↗
PubMed1996

Limitations of the minimum peripheral dose as a parameter for dose specification in permanent 125I prostate implants.

PURPOSE: The objective of this work is to investigate whether the minimum peripheral dose is a practical parameter for dose specification in permanent 125I implants of the prostate. METHODS AND MATERIALS: The investigation was carried out by use of a computer model of ellipsoidal 125I implants in which the average dimension and elongation factor were varied to provide a wide range of geometries. Both ideal and nonideal implants were investigated. The 125I seeds were confined to the target volume except for a portion of the study in which the effect of placing seeds outside the target volume was investigated. RESULTS: The minimum peripheral dose was found to be very sensitive to the seed placement. The irregularities in the seed spacing that inevitably occur in actual implants tend to lower the minimum peripheral dose. As a result, the minimum peripheral dose is generally significantly less than planned by an amount that is unpredictable, and often exceeds 25%. However, the percentage of the target volume that receives a dose less that the prescribed minimum peripheral dose is generally less than 10%. Implanting seeds outside the target volume improves the dose uniformity, but does not appear to offer any advantage in dose coverage, and increases the volume of normal tissue irradiated. CONCLUSION: If a minimum peripheral dose is prescribed for a permanent 125I prostate implant, and the implant is planned using an idealized implant having precisely spaced seeds, the prescribed dose will rarely, if ever, be achieved. Reasonable agreement with the prescribed dose can be achieved only if the requirement for coverage is relaxed from 100 to 90%, or if the total source strength is increased by 20% to compensate for the anticipated imperfections in seed placement.

Brachytherapy↗
PubMed1995

Cholangiocarcinoma: clinical significance of tumor location along the extrahepatic bile duct.

PURPOSE: To define the criteria for resection and/or radiation therapy (RT) of extrahepatic bile duct cancer. MATERIALS AND METHODS: Of 81 patients with extrahepatic bile duct cancer treated from 1983 to 1992, those with proximal duct lesions (n = 56) underwent RT and/or resection or palliative care, and those with distal lesions (n = 25) underwent resection with or without RT. Follow-up was available 3-114 months (median, 28 months). RESULTS: Patients with distal bile duct cancer lived longer than patients with proximal bile duct cancer (survival with Kaplan-Meier analysis, 53% vs 13% at 5 years, respectively, P < .01). Median survival in patients with proximal cancer after RT was more than double that without RT (17 months vs 6 months, respectively, regardless of stage [P = .01]); survival was not significantly different after resection. In patients with distal cancer, RT after resection made no significant difference in median survival (68 months). CONCLUSION: Patients with proximal cancer should undergo primary RT, and expectations should be limited. Patients with distal cancer should undergo resection, and RT may not be needed.

Aged↗
PubMed1995

Thermoradiotherapy in the management of superficial malignant tumors.

In recent years there have been numerous randomized and nonrandomized studies conducted to assess the efficacy of hyperthermia combined with either radiation therapy or chemotherapy, especially in the treatment of superficially seated malignant tumors. The major impact of hyperthermia is currently on locoregional control of tumor. Heat may be directly cytotoxic to tumor cells or inhibit repair of both sublethal and potentially lethal damage after radiation. These effects are augmented by the physiological conditions in tumors which lead to states of acidosis and hypoxia. Blood flow is often impaired in tumor relative to normal tissue, and hyperthermia may lead to a further decrease in blood flow and augment heat sensitivity. Three major areas of clinical investigation have borne the greatest fruit for hyperthermia as adjunctive therapy to radiation therapy. These include recurrent and primary breast lesions, melanoma, and head and neck neoplasms. The thermal enhancement ratio was increased in all cases and is estimated to be 1.4 for neck nodes, 1.5 for breast, and 2 for malignant melanoma. In general, the most important prognostic factors for complete response are radiation dose, tumor size, and minimal thermal parameters (minimum thermal dose, mean minimum temperature or temperature exceeded by 90% of thermal sensors). The number of heat fractions administered per week appears to have no bearing on the overall response, which may be indicative of the effects of thermotolerance. The total number of heat fractions delivered also appears to be irrelevant provided adequate heat is delivered in one or two sessions. The major prognostic factors for the duration of local control are tumor histology, concurrent radiation therapy dose, tumor depth, and mean minimum temperature.

Animals↗
PubMed1994

Dose distributions produced by a shielded vaginal cylinder using a high-activity iridium-192 source.

Algorithms commonly used to compute the dose distribution around a 192Ir source do not calculate the dose by summing the primary and scatter dose components. Thus if the scatter component is reduced significantly by the insertion of a shield into a vaginal cylinder, the algorithm may overestimate the dose delivered to the tumor volume. This problem was investigated by measuring the relative dose around a 2.5 cm diameter shielded vaginal cylinder in a water phantom by use of a 0.147 cm3 thimble ionization chamber. Measurements were made with the cylinder unshielded and with 0.8 cm thick 90 degrees, 180 degrees, and 270 degrees tungsten shields inserted. A reduction in dose was observed on the unshielded side of the cylinder which increased with distance from the source and with the angle subtended by the shield. This reduction did not exceed 2% within 1 cm from the surface of the cylinder with any shield. However, the reduction in dose increased linearly to 3%, 5%, and 15% at a distance of 10 cm from the source with the 90 degrees, 180 degrees, and 270 degrees shields, respectively. On the shielded side of the cylinder, the dose at the surface is reduced to about 13% of its value without the shield; however, this percentage increases with distance reaching a maximum 2-4 cm from the cylinder. The maximum values obtained with the 90 degrees, 180 degrees, and 270 degrees shields were 23%, 17%, and 16%, respectively.

Algorithms↗
PubMed1993

Thermoradiation therapy for superficial malignant tumors.

BACKGROUND: Between 1980-1990, 126 patients were treated with radiation therapy (RT) and hyperthermia using 915-MHz external microwave applicators. All but 11 patients had failed to respond to previous therapy. METHODS: The mean tumor volume was 73 +/- 13 cm3, and the mean radiation dose delivered was 45 +/- 1 Gy. Hyperthermia was administered biweekly in 83% of the fields in 5.5 +/- 0.2 sessions. Lesions were stratified by depth. The predictive influence of pretreatment or treatment parameters was analyzed for the probability of response by logistic regression and for the duration of local control by proportional hazards. RESULTS: In tumors considered potentially heatable (i.e., < or = 3-cm deep), the complete response (CR) rate was 70%, whereas the CR rate for patients with tumors deeper than 3 cm was 18% (P < 0.0001). Among superficial lesions of less than or equal to 3-cm depth that exhibited a CR, 14 recurred (26%, 8.7 +/- 1.6 months), while 39 lesions were recurrence-free at last follow-up of 17.8 +/- 1.4 months. The 50% tumor-effective dose was 44 Gy. For superficial lesions that received between 30-60 Gy, the CR rate was 55% when the fraction size was less than 3 Gy, whereas it was 77% when the fraction size was 3-4 Gy (P = 0.05). Multivariate logistic regression analysis indicated that the model best correlating with CR included concurrent radiation dose (P = 0.006) and tumor volume (P = 0.02; model P = 0.0001). Multivariate proportional hazard analysis indicated that the model best correlating with duration of local control included tumor histology (P = 0.004; model P = 0.0007). The overall survival rate of patients with lesions of less than or equal to 3-cm depth who were treated with thermoradiation therapy was 16.1 +/- 1.2 months. For patients with lesions more than 3-cm deep, survival was 8.7 +/- 1.1 months (P < 0.001). Forty-two fields were treated without any skin reactions (33%), 59 exhibited erythema (47%), and 25 experienced thermal blistering (20%). CONCLUSIONS: Treatment of superficial malignant tumors can benefit from the adjuvant use of hyperthermia delivered with external 915-MHz applicators provided tumors are less than 3 cm from the surface and the lateral margins are within the 50% specific absorption rate (SAR) on the surface.

Adenocarcinoma↗
PubMed1993

'Patchwork' fields in thermoradiotherapy for extensive chest wall recurrences of breast carcinoma.

Chest wall lesions of advanced breast carcinoma in 23 patients were treated with thermoradiotherapy with clinical intent between January 1987 and March 1992. Treatment consisted of external 915 MHz microwave hyperthermia with commercially available applicators and radiation therapy to doses between 32-58 Gy. Twenty-three large, diffuse lesions were treated with multiple field patchwork hyperthermia. All lesions were diffuse with or without multiple nodules < or = 3 cm depth. All lesions had failed previous therapy. The mean number of hyperthermia fields per patient was 3.2 +/- 0.4 (range of 2-7). The complete response rate was 91% in this group of extensive, diffuse lesions treated by the patchwork technique. Mean total radiation dose administered concurrently with multiple field patchwork hyperthermia was 42 +/- 1 Gy. The recurrence rate was 5%. The mean survival in patients who had a complete response was 9.0 +/- 1.3 months. The reduced survival among patchwork treated patients was due to the extensive tumor burden existing outside of the treated fields in these patients. The skin reactions were minor, causing minimal discomfort. There was no evidence of increased thermal damage to skin, or of tumor recurrence at junctions of hyperthermia field overlap. It is concluded that extensive, diffuse lesions of chest wall recurrence of advanced carcinoma of the breast can be treated effectively with multiple field patchwork thermotherapy.

Adult↗
PubMed1993

Hyperthermia and radiation in advanced malignant melanoma.

Advanced melanoma (48 lesions in 40 patients) was treated with external microwave hyperthermia combined with radiation therapy between 1980-1988. Thirty-three lesions in 28 patients were evaluable for tumor response (mean age 64 years, 19 male, 9 female). Evaluable lesions received 13 to 66 Gy (mean 37 +/- 2 Gy) over 5 to 16 fractions (mean of 10) in 14 to 56 elapsed days (mean of 25). Tumor volume (pi/6*length*width*depth) was 62 +/- 16 cm3 (1-377 cm3). Hyperthermia was administered in 6.6 +/- 0.4 sessions (range 1-14), there were 3.2 +/- 0.4 thermal sensors per tumor (range 1-11) and 27 fields were treated twice-weekly (82%). Of the 33 evaluable lesions, 12 exhibited a complete response (36%), and 17 had a partial response (52%). Among the 12 complete responders four recurrences (33%) were observed at 8.6 +/- 1.4 months (median of 8.2 months). In superficial tumors with depth < or = 3 cm and with lateral dimensions within 2 cm of the boundaries of the microwave applicator, the complete response rate was 50% (11/22); whereas for patients with deeper tumors with depth > 3 cm, the complete response rate was 9% (1/11), p = 0.02. The minimal tumor thermal dose during the first hyperthermia treatment session correlated with response (t43min1 = 20 +/- 7 vs. 6 +/- 3 minEq43 degrees C for complete responders and noncomplete responders, respectively, p = 0.06); and 7 of 10 lesions that had t43min 1 > or = 8 minEq43 degrees C achieved a complete response whereas only 5 of 22 lesions (23%) that had t43min1 < 8 minEq43 degrees C did so (p = 0.01). However, neither the minimum tumor temperature during the first treatment, the median minimum tumor temperature over all treatment sessions nor the sum of minimum thermal dose over all treatment sessions correlated with tumor response. Twenty-three patients with 28 lesions died during follow-up (82%). The survival for complete responding patients with superficial lesions was 21.3 +/- 1.5 months compared to 4.5 +/- 0.5 months for patients with superficial lesions that did not experience a complete response (p = 0.0001). For patients with noncomplete responding lesions deeper than 3 cm survival was 4.4 +/- 0.6 months. Twenty lesions were treated without any skin reaction (42%, 20/48). Of the rest, 23 had erythema (48%, 23/48), seven had blistering (14%, 7/48) and one had ulceration of the skin.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1991

RTOG quality assurance guidelines for clinical trials using hyperthermia administered by ultrasound.

Clinical quality assurance guidelines are established for RTOG hyperthermia protocols in which unfocused planar ultrasound may be used to administer hyperthermia. Measurement of temperature at a few fixed points is no longer considered to be adequate. Thermal mapping is required to obtain profiles of the temperature across the tumor dimensions, including margins of normal tissue. The thermometry strategies established for microwaves are to be adhered to with oblique insertion of the probes recommended. Two types of errors arise which are generally not present with microwaves. A measurement error, commonly referred to as a temperature artifact, arises because of absorption and/or viscous heating of the probe. Another error arises when thermocouples are used due to the conduction of heat along the wire leads, especially the copper wire. Several thermometry systems are evaluated with regard to the expected artifact and conduction errors. Acceptable systems include: a) indexing a polyurethane sheathed single sensor thermocouple in a polyurethane catheter, b) indexing a fiberoptic probe in a steel needle, c) indexing a single sensor thermocouple in a steel needle, and d) use of manganin-constantan multisensor thermocouples. Unacceptable systems include: a) fixed or static probes that do not provide profiles of the temperature across the tumor dimensions, b) copper-constantan multisensor thermocouples, and c) teflon sheathed thermocouples inserted into a teflon catheter.

Clinical Protocols↗
PubMed1991

Blood flow in human tumors during local hyperthermia.

The response of tumor blood flow during local hyperthermia was studied at 40 different points in 15 superficial human tumors. Hyperthermia was administered for 60 minutes by use of 915 MHz microwaves. Blood flow was determined from the rate of thermal clearance by use of the bioheat equation. The rate of thermal clearance was sampled at 10-15 minutes intervals by turning the applied power off for 30 seconds. A correction was made for thermal conduction from orthogonal profiles of the tumor temperature. No measurements were made during the first 10-15 minutes of heating. The response of tumor blood flow was found to be independent of temperature in the range of 40-44 degrees C. The mean blood flow rate increased 10-15% between 15 and 30 minutes, but remained nearly constant thereafter. The coefficient of variation in this pattern is 15-20%. No evidence of a sharp reduction in flow was observed. Furthermore, the mean temperature elevation, net forward power, and rate of thermal conduction all remained nearly constant with time, providing further evidence of stability in the blood flow rate. Data obtained in one tumor suggest that a reduction in flow may occur at temperatures above 44 degrees C. The mean blood flow rates obtained in this study range from 0-34 ml/100g/min with an average value of 15 ml/100g/min.

Adenocarcinoma↗
PubMed1989

Mechanisms of heat removal during local hyperthermia.

Mechanisms of heat removal were studied in five recurrent squamous cell head or neck carcinomas, 50-150 cm3, heated by use of external 915 MHz microwave applicators. Thermal clearance measurements were made at a single point in each tumor. Three profiles of the tissue temperature were also measured in orthogonal directions about this point. The conduction term of the bioheat equation was evaluated from the orthogonal temperature profiles by the method of finite differences. The perfusion term of the bioheat equation was determined from the rate of temperature decay corrected for conduction. The results show that thermal conduction plays a major role in the dissipation of thermal energy during local hyperthermia. The rate of removal thermal energy by conduction ranged between 20 and 150 percent of that by perfusion. The temperature profiles show that conduction is higher than is generally expected due to heterogeneities in the blood flow which produce rapid changes in the temperature gradient. The results of this study demonstrate that the heat transport by thermal conduction in perfused tissue cannot be assumed to be small, or negligible, in comparison to that by perfusion.

Blood Circulation↗
PubMed1987

Response of human tumor blood flow to local hyperthermia.

The effect of heat on blood flow in human tumors was studied as a function of time during 1 hour of local hyperthermia induced by 915 MHz microwaves. Blood flow was determined from the rate of thermal clearance by use of the bio-heat transfer equation. The rate of thermal clearance was measured at intervals of approximately 10 minutes throughout the treatment session by turning off the microwave power for 50 seconds. Tumor blood flow increased by amounts varying from 15 to 250% during the first 20-50 minutes of heating at 41-45 degrees C, after which it remained relatively constant during the remainder of the treatment session. The sharp reduction in blood flow or vascular stasis reported in most transplantable rodent tumors after comparable heating was not observed in human tumors. The maximum blood flow observed in heated human tumors ranged from 10-40 ml/min/100 gm. The systematic error due to thermal conduction was estimated to be equivalent to a blood flow of less than 3 ml/min/100 gm.

Adenocarcinoma↗
PubMed1983

Neutron doses in negative pion radiotherapy.

Absorbed neutron doses in regions outside the treatment volume from negative pion radiotherapy are presented, based on neutron spectral measurements for pions stopping in a tissue-equivalent target. A Monte Carlo neutron transport computer code was developed and used to calculate the absorbed dose as a function of the distance from the centre of the treatment volume. The Monte Carlo code, which is a modification of a neutron detector efficiency code, follows neutrons and gamma rays as they interact with either hydrogen or oxygen nuclei in a phantom. The code includes neutron elastic scattering on both hydrogen and oxygen as well as five inelastic nuclear reactions on oxygen. The recoil charged particles which provide the absorbed dose are considered until the neutron escapes the phantom or its kinetic energy falls below 1 ke V. Calculations of absorbed dose are compared with earlier dose calculations and measurements. Measurements of the neutron spectrum from a tissue-equivalent target indicate that the total kinetic energy carried away by neutrons is about 76 MeV, which is a significantly higher value than that used in earlier estimates of the neutron dose. The calculations presented here suggest that the neutron dose outside large treatment volumes may limit the use of negative pions for some therapeutic applications.

Elementary Particles↗
PubMed1979

Energy dependence of the neutron sensitivity of C--CO2, Mg--Ar and TE--TE ionisation chambers.

The neutron sensitivity relative to 60Co of commercially available C--CO2, Mg--Ar and TE--TE ionisation chambers was measured as a function of energy from 1 to 44 MeV. The sensitivity function was obtained by the method of Kuchnir, Vyborny and Skaggs from differences in measurements made at two angles in mixed fields having an isotropic gamma-ray component. Such fields were produced by bombardment of a thick beryllium target with 16 and 28 MeV deuterons, 44 MeV 3He-ions and 35 and 46 MeV protons. The results show that the relative neutron sensitivity of the C--CO2 and Mg--Ar chambers increases continuously with energy, whereas that of the TE--TE chamber is relatively constant.

Argon↗
PubMed1978

Dosimetric properties of neutron beams from the D--D reaction in the energy range from 6.8 to 11.1 MeV.

The tissue kerma in air, the tissue dose at maximum build-up, the relative depth dose on the central axis and the dose build-up characteristics were measured for neutrons produced by 6.8, 8.9 and 11.1 MeV deuterons on deuterium. The neutron beams were produced by a variable-energy cyclotron with a fully stopping deuterium gas target 20 cm long. Measurements were made in a 11.1cm x 11.1 cm field 126 cm from the target entrance window. The dose rate was found to increase rapidly with energy from 0.07 rad min-1 microamperemeter-1 at 6.8MeV to 0.35 rad min-1 muA-1 at 11.1 MeV. The entrance dose is about 50% of the dose maximum for each bombarding energy. The depth of the 95% dose level in the build-up region increased from 50 mg cm-2 at 6.8 MeV to 90 mg cm-2 at 11.1 MeV. The penetration was independent of the bombarding energy in the region investigated. Attenuation of the total dose to 50% of the maximum occurred at 10.2 +/- 0.1 g cm-2 for all three bombarding energies. The dose at the maximum is typically 14% higher than the tissue kerma in air.

Atmosphere↗
PubMed1978

The use of 10B to enhance the tumour dose in fast-neutron therapy.

Incorporation of 10B in tumours treated by fast-neutron therapy would increase the tumour dose via the reaction 10B(n, alpha)7Li which occurs with partially thermalised neutrons. The extent of the dose enhancement was measured for neutron beams with median energies of 2.4, 3.3, 7.0 and 9.0 MeV by two techniques: with a BF3 proportional counter in three beams and activation of 23Na in the fourth. The results obtained with the two techniques are in good agreement. The magnitude of the dose enhancement depends upon the depth, field size and neutron beam energy. The dose enhancement at a depth of 8 cm varied from 0.32% with the lowest-energy beam to 0.07% with the highest-energy beam for each microgram of 10B uptake per gram of tissue. The products of the reaction in 10B would, however, have an RBE about twice that of the fast-neutron dose in the absence of boron. The method may be useful if drugs providing adequate uptake of 10B can be synthesised.

Beryllium↗
PubMed1977

Comparison of two independent methods for determining the neutron/gamma sensitivity of a dosemeter.

Results obtained with two independent methods for measuring the n/gamma sensitivity of non-hydrogenous dosemeters are compared for the neutron beam produced by 8.3 MeV deuterons on beryllium. In one method, a pure neutron field is simulated by taking the difference between measurements made at diffrent angles in a mixed field with an isotropic gamma-ray component. In the second method, the mixed (n+gamma) beam is purified by lead filtration. An assumption in the lead filtration method is that the background radiation is invariant under three different beam conditions. This assumption was found not be be valid in our experimental arrangement; and caused the values obtained for the n/gamma sensitivity to be systematically high. A modification was made in the lead filtration method so that the dosemeter response to background could be determined for each beam condition. Good agreement was obtained between the results of the spectral difference and modified lead filtration methods.

Air↗