Beam characterization and monitoring of a high intensity pulsed electron source.
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Electrons↗
Biomedical subjects
C C Ling
Publications and source records attributed to C C Ling.
Overlap detection and contour-tracking algorithms for critical organs--application to kidney.
An auto-contouring technique has been developed for critical structures on transverse Computer Tomographic (CT) images with one or two overlap regions where object and background have similar CT values. In this technique, those regions are identified and skipped during contour tracking. The contours thus obtained are discontinuous which are corrected afterwards by suitable interpolations. The overlap detection criterion is never satisfied in a nonoverlapping environment and the contour, in this case, is essentially tracked on the basis of CT value threshold alone. The entire process can be initiated by minimal operator intervention. The method has been successfully tested for kidneys and several examples are furnished. The success and concomitant limitations of this technique are also discussed.
Algorithms↗
Thermal enhancement of melphalan and oxaliplatin cytotoxicity in vitro.
It has been established that hyperthermia can enhance cytotoxicity of some chemotherapeutic agents. This has led to various clinical trials of thermochemotherapy, although many questions remain unanswered. The effects of various agents have been studied on animal tumours with different histopathology at elevated temperatures. These studies indicated that alkylating agents were most effective to all tumours at a moderately elevated temperature. Cisplatin was also effective to all tumours, but its effectiveness at 41.5 degrees C was less than that of alkylating agents. To quantitatively study these findings, the magnitude of thermal enhancement of melphalan, an alkylating agent, and that of oxaliplatin, a new platinum compound, were studied at 37-44.5 degrees C by the colony formation assay. The dose of each agent was kept constant, and cell survival was determined as a function of treatment time. The cell survival curve was exponentially related with treatment time at all test temperatures, and the T(0) (the time to reduce survival from 1 to 0.37) decreased with an increasing temperature. These results suggested that the cytotoxic effect of these agents occurred with a constant rate at 37 degrees C, and the rate was facilitated with an increasing temperature. This suggests that heat can accelerate the cytotoxic chemical reaction, leading to substantial thermal enhancement. The thermal enhancement ratio (TER, the ratio of the T(0) at 37 degrees C to the T(0) at an elevated temperature) increased with an increase in the temperature. The activation energy for melphalan at moderately elevated temperatures was largest among the agents tested in the laboratory and that for oxaliplatin was approximately half of the melphalan activation energy. This suggests that the thermal enhancement for the cytotoxicity of melphalan or alkylating agents might be the greatest. Potential mechanisms of thermal enhancement of cytotoxicity were discussed.
Animals↗
Electrons as the cause of the observed dmax shift with field size in high energy photon beams.
For megavoltage x-ray beams, it is well known that the percent depth-dose increases considerably with field size in the buildup region, resulting in a significant shift in the apparent position of maximum dose, dmax. The nature of this increase has been investigated using a sweeping magnet placed just below the treatment head of a 25-MV linac. Measurements show that for increasing magnetic fields the dose in the buildup region is continually reduced, until a point is reached beyond which no additional reduction is observed. Here the buildup curve is essentially field size independent. These results clearly show that electrons are the primary cause of dose increase with field size in the buildup region, in contrast to a recent publication claiming that scattered photons are the cause. Further measurements were made by blocking out the primary beam at the level of the jaws and measuring the depth dose of the scattered electrons originating from the jaws. The results show that a thickness of approximately 1 gcm-2, of either polystyrene or lead, reduces the dose by a factor of two, providing further evidence that the scattered component of the beam consists of low energy electrons.
Electrons↗
Improving the buildup and depth-dose characteristics of high energy photon beams by using electron filters.
The attributes of high energy photon beams, i.e., low surface dose, large dmax and improved %DD, are compromised with increase in field size. This is due to the relative increase with field size of the electron component in the beam, as shown by recent experiments done here using a sweeeping magnet. The present study shows that the advantages can be partially regained with the use of foils to remove electrons. Various thicknesses of Al, Cu, Sn, and Pb were placed in a 25-MV linac x-ray beam at several sites in the treatment head. Buildup curves were measured with a "pancake" chamber for various SSD and field sizes. The magnitude of improvement achieved is dependent upon field size, SSD, the atomic number of the foil material, and foil thickness. Pb foil (0.55 gcm-2) provided the best overall improvement. Surface dose reduction of 10%-20% can be achieved along with significant increase in dmax and %DD. These findings suggest a new design feature for the next generation of high energy linacs.
Aluminum↗
Coincidence sum peak assay of 125I activity using solid state detectors.
The use of solid state detectors in the coincidence sum peak technique of 125I activity assay has been studied. The improved energy resolution of these detectors allows distinct resolution of the K a, K beta and gamma peaks, and four sum peaks resulting from the coincident detection of the different X and gamma photons. Theoretical considerations yield three separate equations, each of which can be used, in conjunction with the experimental sum peak spectrum to give the activity of the 125I sample in question. This method is suitable for calibration of 125I activities in the range of 0.01-0.5 muCi with precisions of 2%-3%.
Humans↗
Magnetic analysis of the radiation components of a 10 MV photon beam.
For megavoltage x-ray beams, the percent depth dose increases considerably with field size in the buildup region, with a concomitant shift in the position of the maximum dose (dmax) to a shallower depth. Various authors disagree as to the cause of this effect. The radiation components contributing to absorbed dose in the buildup region of 10-MV photon field were analyzed as a function of field size by placing an electromagnet next to the Clinac 18 treatment head. The percent depth dose curves in the buildup region, obtained with a parallel plate chamber downstream from the magnetic field at 85 cm SSD, exhibited no dmax shift and a much reduced dependence on field size, in clear distinction with similar data taken with zero magnetic field. Confirmatory data were obtained at 100 and 120 cm SSD. These results clearly show that scattered electrons are the primary cause for the dmax shift and the dose increase in the buildup region with increasing field size.
Electrons↗
Measurement of dose distribution around Fletcher-Suit-Delcos colpostats using a Therados radiation field analyzer (RFA-3).
Using a small silicon diode and the Therados RFA-3 automated dosimetry system, the relative dose distribution around Fletcher-Suit-Delcos colpostats was measured. Thermoluminescent dosimeters (LiF) were used for absorbed dose measurements. These data provide the basis for computerized dose calculations which will account for the attenuation effects of the rectal and bladder shieldings. The stainless-steel housing attenuated the radiation of a Cs-137 source by 6%. The tungsten shields caused a further dose reduction of 15%-25%.
Brachytherapy↗
Two-dimensional dose distribution of 125I seeds.
Two-dimensional dose distribution has been measured for the new (model 6711) 125I seeds used in interstitial implants. Two independent methods, using a silicon diode or thermoluminescent dosimeters, yielded identical results. At any given distance r from the seed center, the dose varies with theta, the angle relative to the seed's axis. Similarly, the r dependence of the dose distribution is different at various theta values. These observations can be qualitatively understood in terms of several factors, namely, source encapsulation, geometrical relationship, and attenuation and scatter. Empirical expressions which approximate the measured results have been developed to facilitate clinical dose distribution calculations.
Brachytherapy↗
Interface dosimetry for I-125 sources.
Use of I-125 in breast implants may be therapeutically beneficial due to the 40% higher dose to the tumor relative to the normal adipose tissue. The dose distribution in the interface between adipose and nonadipose tissues is studied with mathematical models and radiobiological measurements. The dose transition zone is narrow, about 10 mu, which is roughly the diameter of a cell. The dimension of the transition zone is weakly sensitive to the geometry of the interface. In most geometries, cells on either side of the interface receive doses that are significantly different (25%-35%). Radiobiological measurements are consistent with calculated results, providing a check on the theoretical model.
Animals↗
Dose distribution of 125I sources in different tissues.
The low-energy photons of 125I deposit energy in tissues primarily by the photoelectric effect, which is strongly dependent on the atomic number Z. Thus dose distributions of 125I sources in media of different Z are not the same. LiF and CaF2 thermoluminescent dosimeters were used for relative dose distribution measurements in materials that are equivalent to muscle, breast, and bone. The experimental data are in good agreement with published results for muscle, and in reasonable agreement with Monte Carlo calculations for all the tissues tested. These measured data provide the basis for dose distribution calculations when 125I seeds are implanted in or near inhomogeneous tissues.
Bone and Bones↗
Clinically relevant optimization of 3-D conformal treatments.
In this paper a method of computer-aided optimization of 3-D conformal treatment plans is presented which incorporates models to predict the clinical consequences of resulting dose distributions. Even though these models are simplistic, it is submitted that their intelligent use leads to treatment plans which indicate lower normal tissue complications and higher tumor control. Dose distribution data, biological models, and observed normal tissue and tumor response data are used to compute tumor control and normal tissue complication probabilities for each of the critical normal structures encountered in a treatment plan. These quantities are combined into a single score using an objective function which incorporates the importance of each end point as assessed by the physician. Using the "simulated annealing" method of optimization, the beam weights are adjusted to maximize the score. Additional constraints are applied to ensure consistency of the results of optimization with the judgment of the physician. These optimization methods have been applied to conformal treatment plans consisting of multiple fixed fields with conformal field shaping. The results indicate that the methods presented have considerable potential.
Aged↗
Final report of the 70.2-Gy and 75.6-Gy dose levels of a phase I dose escalation study using three-dimensional conformal radiotherapy in the treatment of inoperable non-small cell lung cancer.
PURPOSE AND OBJECTIVE: Three-dimensional conformal radiotherapy (3D-CRT) is a mode of high-precision radiotherapy designed to increase the tumor dose and decrease the dose to normal tissues. This study reports the final results of the first two dose levels (70.2 Gy and 75.6 Gy) of a phase I dose-escalation study using 3D-CRT for the treatment of non-small cell lung cancer. PATIENTS AND METHODS: Fifty-two patients were treated with 3D-CRT without chemotherapy. The median age was 67 years (range, 39-82 years). The majority of patients had locally advanced cancer. Tumor was staged as I/II in 10%, IIIA in 40%, and IIIB in 50%. Radiation was delivered in daily fractions of 1.8 Gy, 5 days a week. A radiation dose level was considered complete when 10 patients received the intended dose without unacceptable acute morbidity. Toxicity was scored according to the Radiation Therapy Oncology Group grading scheme. RESULTS: Twenty patients were initially assigned to the 70.2-Gy level; 14 of them received the intended dose. Three patients experienced severe acute toxicity, two with grade 3 (requiring steroids or oxygen) and a third with grade 5 (fatal) acute radiation pneumonitis. Because of the grade 5 pulmonary toxicity, the protocol was modified, and only patients with a calculated risk of normal tissue complication of less than 25% were eligible for dose escalation. Patients who had a normal tissue complication probability (NTCP) of greater than 25% received a lower dose of radiation. An additional 18 patients were entered on the modified study; 11 of them received 70.2 Gy. One patient experienced grade 3 acute pneumonitis. Despite dose reduction in four patients because of an unacceptably high NTCP, two additional patients developed grade 3 pulmonary toxicity. Fourteen patients were accrued to the 75.6-Gy dose level, and 10 received the intended dose. One of the 10 patients experienced grade 3 pulmonary toxicity and one developed grade 3 esophageal toxicity. Three patients were treated to lower doses as a result of their calculated NTCP without toxicity, and one patient refused treatment. The 2-year local control, disease-free survival, and overall survival rates were 37%, 12%, and 24%, respectively. The median survival time was 11 months. DISCUSSION: Treatment to 70.2 Gy and 75.6 Gy using 3D-CRT was delivered with acceptable morbidity when NTCP constraints were observed. Local control was encouraging in these patients with locally advanced disease. Patients are currently being accrued to the 81-Gy level of the study.
Adult↗
Liver abscess concomitant with hemobilia due to rupture of hepatic artery aneurysm: a case report.
Hepatic artery aneurysm is an uncommon lesion, usually extrahepatic and rarely intrahepatic. Rupture of hepatic artery aneurysm into the biliary tract is a rare cause of hemobilia. Angiography is the diagnostic method of choice and surgical intervention is the procedure of choice for extrahepatic rupture. Interventional angiography with embolization is optimal for inaccessible intrahepatic aneurysm and extremely poor risk patients. Reported here is a rare case of left intrahepatic artery aneurysm ruptured into the intrahepatic bile duct in the course of liver abscess. Embolization of the hepatic artery resulted in cessation of bleeding.
Adult↗
The feasibility of dose escalation with three-dimensional conformal radiotherapy in patients with prostatic carcinoma.
PURPOSE: To evaluate the acute morbidity, late toxicity, and response to treatment in patients with prostate cancer treated on a phase I dose-escalation study with three-dimensional conformal radiotherapy. METHODS: A group of 432 patients with stages T1c-T3 prostate cancer were treated with three-dimensional conformal radiotherapy targeting the prostate and seminal vesicles, but effectively excluding the surrounding normal tissue structures from the high-dose volume. A minimum tumor dose of 64.8 to 66.6 Gy was given to 89 patients (20%), 70.2 Gy to 199 patients (46%), 75.6 Gy to 98 patients (23%), and 81.0 Gy to 46 patients (11%). RESULTS: Treatment was well tolerated, and the acute toxicities and long-term complications observed were of minimal severity (grade 1 or 2) regardless of dose. Acute grade 2 rectal symptoms were observed in 15% of patients, whereas 40% developed grade 2 urinary symptoms. Among patients who received from 64.8 to 70.2 Gy, the 2-year actuarial likelihood of grade 2 late toxicity was 2% for rectal and 1% for urinary complications, compared to 11% and 5%, respectively, for those treated with doses ranging from 75.6 to 81 Gy. Only three patients (0.7%) have so far developed severe (grade 3 or 4) late urethral or rectal complications. The rate of prostate-specific antigen normalization from abnormal pretreatment levels to a value of < or = 1.0 ng/mL was used as an endpoint to evaluate the initial response to treatment. When the analysis was restricted to patients with pretreatment prostate-specific antigen levels of < or = 20 ng/mL, patients who received 70.2 Gy had a significantly higher rate of prostate-specific antigen normalization than patients who received 64.8 to 66.6 Gy. Evaluation of the prostate-specific antigen response at 75.6 Gy and 81.0 Gy was not possible because of the short follow-up time in many of these patients. CONCLUSIONS: Three-dimensional conformal radiotherapy technique has made it possible safely to escalate radiation doses to unprecedented levels in patients with prostatic cancer. Preliminary evidence for an improved initial prostate-specific antigen response with higher doses indicates a potential for an improved therapeutic ratio with the three-dimensional conformal radiotherapy approach.
Adenocarcinoma↗