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Biomedical subjects

M Wollin

Publications and source records attributed to M Wollin.

At least 19 recordsLinked to original sources
PubMed1998

Range spectra in electron penetration problems.

The theory of electron penetration as predicted by the Fokker-Planck equation is first reviewed within a restricted context that considers the multiple scattering and transport of charged particles. We then broaden the context and show that range straggling effects also fit successfully into this framework, which completes an electron model initiated by Yang. We introduce those effects with a superposition of Fokker-Planck solutions, i.e., by using an incident beam that contains a spectrum of initial energies, or equivalently, a set of csda ranges. Straggling effects appear to be a beam property in this approach but are returned to the material when we use it. All the information needed to construct the spectrum is obtained from a measurement of the electron rest charge distribution in polystyrene. To illustrate the correctness of this procedure, we consider the case of a 20 MeV electron beam incident on water. We predict the absorbed dose distribution as a function of depth and also measure it with an ionization chamber in a water tank. We find nearly perfect agreement between calculation and experiment in this case where all the results derive and apply to a clinically operational machine.

Electrons↗
PubMed1997

The need for individualized dosimetry for tangential breast treatment.

We have examined the isodose distributions of 119 intact breast patients treated on a 6 MV linac to determine if a library of treatment plans could be used instead of individualized computer plans for patient treatments without compromising the quality of those treatments. The parameters studied were: field width, baseline separation, central axis separation, wedge angle, and isodose coverage. At least two wedges were used in the computer plans for each patient and the best plan was then chosen. In order to construct a library of plans, the choice of wedge, treatment isodose, and dose uniformity should be predictable. Our results show that for 90 out of 119 plans (76%), the 30 degrees wedge was best. In the other 29 cases, either the 15 degrees or the 45 degrees wedge yielded better plans. On average, the improvement in dose homogeneity due to choice of wedge was about 2% (range 0-7%) for these cases. Although grouping like-patient parameters generally restricted the isodose variation to +/- 2.5%, there were five patients for which up to a 7% underdosage would not have been predicted. For the set of plans using a 30 degrees wedge, a significant correlation was found for the ratio of the baseline to central axis separation vs. treatment isodose. The average isodose which covered the target area was 97% (range 90-100%) and 102 out of 107 patient plans using the 30 degrees wedge fell between 94 and 100%. We conclude from these results that the variation in dose distribution found with seemingly similar sized breasts is due to the variation in breast shape and symmetry. The use of a library plan with a single wedge and a standardized isodose line for tangential field treatment of intact breast could cause up to a 7% dose difference compared to the actual dosimetry for that patient.

Breast Neoplasms↗
PubMed1994

Feminization as a result of both peripheral conversion of androgens and direct estrogen production from an adrenocortical carcinoma.

A 45-year-old man presented with gynecomastia, hypertension and a large left adrenal mass. Further evaluation revealed elevated serum concentrations of estrogen, estrone sulfate, androstenedione, dehydroepiandrosterone, dehydroepiandrosterone sulfate, deoxycorticosterone, and aldosterone and increased 24-hour urinary 17-ketosteroid and free cortisol excretion. Removal of a 10 kg adrenocortical carcinoma led to normalization of the hormone concentrations and partial resolution of the gynecomastia. There was no clinical evidence of metastases. Incubation of tumor slices demonstrated that the tumor had an active aromatase and sulfotransferase. We estimated that about half the serum estrone arose from peripheral conversion of androstenedione. Feminizing adrenocortical carcinomas are rare and this case is unusual given the lack of clinical metastases and the probable dual source of estrogen from tumor as well as from the peripheral conversion of tumor-derived androgens.

Adrenal Cortex Neoplasms↗
PubMed1994

Splenosis presenting as a left renal mass: a report of two cases.

The development of splenosis is a recognized consequence of splenic trauma. We present 2 cases of splenosis that were initially diagnosed as left renal cell carcinomas. The diagnosis of splenosis was made by technetium sulfur colloid scans. The clinical presentation and diagnosis of these 2 cases of splenosis masquerading as renal cell carcinoma are reviewed.

Adult↗
PubMed1993

Application of the ICRU Report 38 reference volume concept to the radiotherapeutic management of recurrent endometrial and cervical carcinoma.

Radiation therapy was given to 25 patients presenting with pelvic recurrence of endometrial (14) and cervical (11) cancer. Of these patients, all but one had undergone hysterectomy following their original diagnosis. Two endometrial patients received preoperative intracavitary irradiation. The recurrence-free interval ranged from 5 to 71 months (mean = 21 months). External beam radiation therapy for pelvic recurrence ranged from 3000 to 5000 cGy. Additional central radiation was given to 18 patients with either external beam, intracavitary, interstitial, or transvaginal technique. Dose and dose rates from brachytherapy are documented with maximum values, along with the location of these dose points. Such specification is essential in obtaining a more accurate impression of the total dose delivered to the patient, especially when different techniques are employed to increase the dose to the center of the pelvis. Reference volume dimensions, similar to those specified by ICRU Report 38 for intracavitary treatments, are presented. Mean follow-up from completion to radiotherapy is 22 months; 16 patients are dead, 2 are alive with disease, and 7 are alive with no evidence of disease.

Adult↗
PubMed1993

An evaluation of the efficacy of postoperative irradiation in rectal adenocarcinoma.

Cancer of the colon and rectum is the second most common form of cancer in the United States. Although surgery is the primary treatment for rectal cancer, the overall 5-year survival approximates 50%. Pelvic failure rates and their associated morbidity have led to the use of postoperative irradiation, either alone or combined with chemotherapy. We reviewed 77 consecutive patients treated with postoperative irradiation to the pelvis following curative surgery. The prognosis is dependent on surgical stage and histologic grade. The minimal decrease in local recurrence in this study is offset by treatment-related small bowel injury. A subset of patients who may benefit from adjuvant treatment is yet to be defined.

Adenocarcinoma↗
PubMed1992

Iodine125 interstitial brachytherapy in the treatment of carcinoma of the lung.

In a prospective study, 14 patients with primary non-oat cell lung carcinoma were treated with intraoperative Iodine125 (I125) implantation of the lung tumor via lateral thoracotomy or median sternotomy. Staging mediastinal node dissection was performed in each case. Patients were selected when wedge or segmental resections were not technically feasible, such that lobectomy or completion pneumonectomy would have been required or pulmonary function studies were poor. Doses ranged from 8,000 cGy at the periphery to 20,000 cGy at the center. With a minimum 12 month follow-up, mean and median survivals were 16.7 and 15.1 months, respectively. Local control was achieved in 10 of 14 patients (71%) with all local failures occurring in pathologic stage III patients. When separated according to tumor size, local control was obtained in six of seven tumors of less than 3 cm and four of five tumors of 3-5 cm. Both cases with masses greater than 5 cm failed locally. There was one operative mortality and two postoperative complications. All other patients were discharged within one week of surgery. There was no radiation pneumonitis. I125 lung brachytherapy is an excellent alternative treatment for T1 and T2 tumors when medical conditions preclude curative resection.

Aged↗
PubMed1991

Predicting normal tissue injury in radiation therapy.

We tested three radiobiologic models, the nominal standard dose (NSD), the biologic index of reaction (BIR), and the linear quadratic (LQ) models to determine which best predicts normal tissue injury in radiation therapy. Clinical data for radiation myelopathy, rib fracture and pericardial effusion were used for all three models to predict injury. We assumed that on the average injuries occurred at higher equivalent doses of radiation than were received by patients who were not injured. We used a t-test to determine whether there were in fact significant differences in the mean values of the equivalent doses among the injured and non-injured. The means were calculated for the four sets of injury by the three models. For the LQ model it was necessary to choose a value for the parameter alpha/beta; the results were not sensitive to the choice over the range of 1/2 to 12 Gy. None of these models showed a significant difference between injured and non-injured patients for all four sets of data. The BIR model showed significant differences in three sets, the LQ model was significant in two and marginally significant in one set, and the NSD was significant in two sets. This analysis illustrates therefore, that the linear quadratic model can be adopted for analysis of clinical data with results that are no worse and possibly better than the NSD model.

Humans↗
PubMed1990

The CT scanner as a therapy machine.

Many tumors in the brain and in other tissues can be delineated precisely in images obtained with a CT scanner. After the scan is obtained the patient is taken to another room for radiation therapy and is positioned in the beam with the aid of external markers, simulators or stereotactic devices. This procedure is time consuming and subject to error when precise localization of the beam is desired. The CT scanner itself, with the addition of a collimator, is capable of delivering radiation therapy with great precision without the need for external markers. The patient can be scanned and treated on the same table, the isocenter of the beam can be placed precisely in the center of the lesion, the beam can be restricted to just those planes in which the lesion appears several arcs can be obtained by simply tilting the gantry, and the position of the patient in the beam can be monitored continuously during therapy. We describe here the properties of the CTX, the CT scanner modified for therapy.

Animals↗
PubMed1990

Optimization of arc angles in rotational therapy.

Data is presented that will aid in optimizing the arc angles used for rotational therapy for a 6 Mv x-ray beam. Computer calculations of isodose distributions were carried out and the Ap and Lateral dimensions of the 95 and 100% isodose line were tabularized as a function of the field width (6-14 cm), distance between isocenter and patient midline (0-3 cm), and bilateral 120 or 100 degrees arc angle. The 300 degrees rotation cases we studied were generally found to be inferior to 120 degrees or 100 degrees bilateral arc rotations. 120 degrees arcs are best when the target center is within 2 cm of the patient's Ap center. As that separation increases, the bilateral arc angle should be decreased or wedges should be rotated through 300 degrees to avoid maximum doses greater than 105%. The data tables can be used as a starting point for computer calculations to select the field width and the arc angle for a particular target location and size. Of note is the degree to which the dimensions of the 100% isodose line decreases for small field widths and large isocenter to patient midline distances.

Humans↗
PubMed1990

Buried penis. A novel approach.

Buried penis is a congenital abnormality in which the phallus is concealed within the subcutaneous tissue. The corporal bodies and glans have developed normally. A deficiency of penile shaft skin in association with abnormal mobility of the skin gives rise to the phenotypic appearance. The skin defect may be related to an abnormal attachment of dartos muscle during embryogenesis. Correction of this condition requires separation of these abnormal muscular attachments and provision of skin coverage of the penile shaft. It is imperative not to circumcise the patient as this will worsen the skin deficiency. We describe a novel technique for correcting buried penis performed on 12 patients at the Great Ormond Street Hospital for Sick Children. A satisfactory cosmetic result was obtained in all patients.

Humans↗
PubMed1989

Treatment selection for base of tongue carcinoma.

Sixty-two previously untreated patients with squamous cell carcinoma of the base of tongue were retrospectively analyzed. The American Joint Committee on Cancer (AJCC) Stage distribution was I-3, II-7, III-24, and IV-28. The choice of treatment was nonrandomized. The local control was 10/18 with high-dose preoperative radiation, 17/30 with external beam radiation only, and 4/14 with external beam plus interstitial implantation. The median survival for the three treatment regimens were 63, 51, and 13 months, respectively. Preoperative radiation is suggested for tumors with inferior (laryngeal) spread or those with extensive superior extension (to tonsillar fossa and beyond). For centrally placed lesions in the base of the tongue (with or without lateral hypopharyngeal wall spread), radiation alone is recommended. An interstitial implantation should be restricted to lesions equal to or less than 4 x 3 x 2.5 cm3. Since this insertion is technically more demanding than for tumors of the mobile tongue, they should be performed by the more experienced brachytherapist.

Brachytherapy↗
PubMed1989

Radiosensitivity of human prostate cancer and malignant melanoma cell lines.

The relative radioresponsiveness of human prostate cancer compared to malignant melanoma is well known. The effects of beta-estradiol or testosterone on the X-irradiation survival of several human cell lines were studied, including: human prostate carcinoma cell lines PC3 and DU145 and human malignant melanoma cell lines A375 and A875. Lines PC3 and DU145 demonstrated 55-61 fmol per 10(6) cells of androgen receptor with no detectable estrogen or progesterone receptor. Cells were irradiated at 120 cGy/min dose rate. There was no detectable toxicity of up to 10(-4) M testosterone or beta-estradiol on PC3 or DU145 cells in the absence of X-irradiation. At plating efficiencies from 11-13%, and plating densities of 1 x 10(4) cells per 60 cm2 flask, cell lines PC3 and DU145 demonstrated a Do of 108.5 +/- 6.5, n 2.1 +/- 0.7 cGy, and Do of 143.5 +/- 1.5 cGy, n 2.4 +/- 0.5, respectively. The addition of testosterone or beta-estradiol at 10(-4) to 10(-10) M prior to or after, X-irradiation did not alter radiosensitivity. At the same dose rate of 120 cGy/min, malignant melanoma cell lines A375 and A875 had a Do of 125 +/- 2.5 cGy, n 1.56 +/- 0.8 SF2 0.65 +/- 0.03 and line A875 demonstrated a Do of 129 +/- 4.5 cGy, n 1.58 +/- 0.4 SF2 0.55 +/- 0.04, respectively. The radiosensitivity of melanoma cell lines did not decrease at low dose rate 5 cGy/min. Thus, the in vitro radiosensitivity of androgen receptor positive prostate cancer cell lines is not necessarily altered by the presence of androgen before or after irradiation. The data support the concept that all malignant melanoma cell lines do not show a broad-shouldered cell survival curve in vitro and intrinsic cellular radioresistance.

Cell Survival↗
PubMed1989

Priorities in urinary diversion following pyeloplasty.

Debate continues regarding optimal drainage following pyeloplasty. We reviewed the method of drainage in 100 consecutive dismembered pyeloplasties performed from 1983 to 1987. Of the children 20 per cent underwent pyeloplasty with placement of a nephrostomy tube and transanastomotic stent (group 1), while 80 per cent underwent pyeloplasty performed in a nonintubated fashion (group 2). A urethral bladder catheter was used in 20 per cent of the patients in group 1 and in 90 per cent in group 2. While the over-all complication rates and long-term results were similar for both groups, the nature of complications for each group differed. The intubated group had a 10.5 per cent incidence of urinary tract infection, while the nonintubated group demonstrated an 8.6 per cent incidence of postoperative anastomotic leakage. A nephrostomy tube and stent appear to be unnecessary in the routine pyeloplasty and may prolong hospitalization. Selective use of upper tract drainage may help to decrease the incidence of postoperative leakage in specific cases.

Child↗