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Biomedical subjects

M Wollin

Publications and source records attributed to M Wollin.

47 records · Page 3Linked to original sources
PubMed1976

Analysis of dose, dose-rate and treatment time in the production of injuries by radium treatment for cancer of the uterine cervix.

A retrospective study has been made of 15 patients who had developed severe complications to the bladder, rectum and ureters after radiation therapy for carcinoma of the cervix. Comprehensive dose distribution in the pelvis were calculated with computer assistance to visualize how the normal organs had been irradiated. The risk of normal tissue injury was analysed graphically with respect to the maximum radium dose, dose-rate and irradiation time. The two groups of data representing the injured and non-injured organs separate much better in a dose-rate versus dose plot than in a conventional Strandqvist type dose-time plot. This implies that in radium therapy, the dose-rate rather than the treatment time, is the important parameter in modifying the risk of normal tissue injury. Our results show a good separation of injured from non-injured cases only when the maximum values of dose and dose-rate were used. This suggests that clinically significant injury may develop from relatively small regions of high dose and dose-rate. Since the dose-rate varies from point to point in the pelvis (unlike treatment time), comprehensive determinations of dose-rate distributions are required in order to locate the sites of potential injuries.

Dose-Response Relationship, Radiation↗
PubMed1976

Modification of the biologic dose to normal tissue by daily fraction. Model for calculating normal tissue tolerance.

A method to predict normal tissue injury is proposed that includes high daily doses and unusual times successfully by calculating a new value called BIR (Biologic Index of Reaction). BIR and NSD were calculated for various normal tissue reactions. With the aid of statistical correlation techniques it is found that the BIR model is better than the NSD model in predicting radiation myelopathy and vocal edema and as good as NSD in predicting rib fracture. Neither model predicts pericardial effusion. In no case were the results of BIR inferior to those of NSD.

Edema↗
PubMedDate not supplied

Local control of T1 vocal cord cancer with radiation therapy: the importance of tumor character vs. treatment parameters.

Ninety-one patients with T1 vocal cord carcinoma received primary irradiation treatment. The 5- and 10-year determinate disease-free survival was 80%; the 5- and 10-year determinate survival including surgical salvage was 92%. Tumors involving more than one-half of a vocal cord or involving the anterior commissure or exhibiting an exophytic growth pattern had numerically, but not statistically, higher local failure rates than tumors without these characteristics. Precise radiation treatment technique appears more important for local control (LC) than tumor character. The crucial treatment factors for high LC with few radiation complications are reproducible daily patient positioning, use of contour-compensating devices (wedges), field size of 5 X 5 cm, and a radiation prescription with a time-dose fractionation value of 101 to 106.

Carcinoma, Squamous Cell↗
PubMedDate not supplied

Unequal weighting of given doses in opposed fields in treatment of cancer of the tonsillar region using 60Co, 4-, 8-, 15-, 24-MVp photons.

Weighting of given doses from parallel opposed fields is a widespread practice in radiation therapy of cancer in the tonsillar region. In order to determine when weighting is useful, dose distributions on the central axis were calculated for various energies (60Co, 4-, 8-, 15-, and MVp photons), weighting factors, and field separations. Criteria for judging the usefulness of weighting were (i) that variation in the dose across the tumor volume not exceed 10%, and (ii) that the dose to critical tissues outside the target volume be at least 20% less than target volume dose. The clinical situation that met these criteria was a lateral lesion that extended to less than one-third of the transverse diameter of the head, treated with either 60Co, 8, or 4 MVp with 4:1 weighting. Under these conditions, weighting was considered to be justified.

Cobalt Radioisotopes↗
PubMedDate not supplied

Single- and double-plane iridium-192 interstitial implants: implantation guidelines and dosimetry.

Computerized dosimetric studies of single- and double-plane iridium-192 (Ir-192) planar implants were performed. With respect to dose homogeneity, we found that the optimal source and ribbon separation for single-plane implants was 1.0 cm. For double-plane implants, the preferred ribbon and plane separation was 1.5 cm, maintaining a 1-cm separation for the sources. Using these separations, standard dose rate curves for single- and double-plane Ir-192 implants were generated by computer calculations. These standard curves are useful for quickly and fairly accurately estimating the dose from any size planar implant, without requiring more time-consuming individual computer dosimetry. We believe that the curves will prove to be of practical clinical value to physicists and radiotherapists.

Brachytherapy↗
PubMedDate not supplied

Conversion from Cs-137 to Ir-192 for high dose rate remote afterloading: practical considerations.

High dose rate (HDR) remote afterloading is increasingly being used to replace many conventional low dose rate (LDR) brachytherapy procedures. Implementation of the microSelectron-HDR with Ir-192 at our facility necessitated this study to obtain equivalent dosimetric distributions with those of our LDR Cs-137 techniques using our current treatment planning system. Three anatomical sites are presented: nasopharynx, esophagus, and uterine cervix. Attention must be given to the anisotropy of Cs-137 tubes when converting to Ir-192; for linear geometries, total equivalent activity may be preserved but the shapes of the resulting isodose curves for Ir-192 are longer than those of Cs-137. In the case of Fletcher-Suit intracavitary treatments of the uterine cervix, the longer contours for Ir-192 in the vaginal ovoids results in higher isodose levels reaching the bladder and rectum. Maintaining the traditional dose levels to these organs is accomplished by modifying the loading of the ovoids to approximately 85% of the corresponding Cs-137 activity. Computerized dosimetry is presented, along with a chart we have devised to easily convert a standard LDR treatment to HDR dwell times. Our results are especially suitable to those users who will continue to make use of their present computer treatment planning system.

Brachytherapy↗