Biomedical subjects

D Spelbring

Publications and source records attributed to D Spelbring.

8 recordsLinked to original sources

PubMed1998

Fast iterative algorithms for three-dimensional inverse treatment planning.

Three types of iterative algorithms, algebraic inverse treatment planning (AITP), simultaneous iterative inverse treatment planning (SIITP), and iterative least-square inverse treatment planning (ILSITP), differentiated according to their updating sequences, were generalized to three dimension with true beam geometry and dose model. A rapid ray-tracing approach was developed to optimize the primary beam components. Instead of recalculating the dose matrix at each iteration, the dose distribution was generated by scaling up or down the dose matrix elements of the previous iteration. This significantly increased the calculation speed. The iterative algorithms started with an initial intensity profile for each beam, specified by a two-dimensional pixel beam map of M elements. The calculation volume was divided into N voxels, and the calculation was done by repeatedly comparing the calculated and desired doses and adjusting the values of the beam map elements to minimize an objective function. In AITP, the iteration is performed voxel by voxel. For each voxel, the dose discrepancy was evaluated and the contributing pencil beams were updated. In ILSITP and SIITP, the iteration proceeded pencil beam by pencil beam instead of voxel by voxel. In all cases, the iteration procedure was repeated until the best possible dose distribution was achieved. The algorithms were applied to two examples and the results showed that the iterative techniques were able to produce superior isodose distributions.

Algorithms↗

PubMed1996

A comparison of four patient immobilization devices in the treatment of prostate cancer patients with three dimensional conformal radiotherapy.

PURPOSE: To determine the variability of patient positioning during three-dimensional conformal radiotherapy (3D-CRT) for prostate cancer treated with no immobilization or one of four immunobilization devices, and to determine the effects of patient body habitus and pelvic circumference on patient movement with each individual inmobilization technique. METHODS AND MATERIALS: To see whether our immobilization techniques have improved day-to-day patient movement, a retrospective analysis was carried out. A total of 62 patients treated at one facility on a single machine with 3D-CRT via a four-field box technique (anterior-posterior and opposed laterals) in the supine position with either no immobilization or one of four immobilization devices. Five groups of patients were compared: (a) group 1-no immobilization; (b) group 2-alpha cradle from the waist to upper thigh; (c) group 3-alpha cradle from waist to below the knees; (d) group 4-styrofoam leg immobilizer (below knees); and (e) group 5-aquaplast cast encompassing the entire abdomen and pelvis to midthigh with alpha cradle immobilization to their lower legs and feet. Prior to starting radiotherapy, portal films of all four treatment fields were obtained 1 day before treatment. Subsequently, portal films were then obtained at least once a week. Portal films were compared with the simulation films and appropriate changes were made and verified on the next day prior to treatment. A deviation of greater than 0.5 cm or greater was considered to be clincally significant in our analysis. We studied the difference among the types of immobilization and no immobilization by looking at the frequency of movements (overall, and on each of the three axes) that a patient had during the course of his treatment. Using a logistic regression model, the probability of overall and individual directional movement for each group was obtained. In addition, the effects of patient body habitus and pelvic circumference on movement were analyzed. RESULTS: The maximum deviation was 2 cm and the median deviation was 1.2 cm. For each patient, the probability of movement ranged from 0 to 76%, with a mean of 39%. There was no significant difference seen in overall movement with any of the immobilzation devices compared to no immobilization, but there was less vertical (9 vs. 18%; p = 0.03) and AP (6 vs. 15%; p = 0.14) movement with the aquaplast than any other group. However, when examining the lateral direction, the aquaplast had significantly more movement (32 vs. 9%; p < 0.001). When accounting for body habitus and pelvic circumference, no immobilization device was effective in reducing movement in obese patients or in patients with pelvic circumference greater than 105 cm. The aquaplast group had a significantly increased amount of lateral movement with obesity (42 vs. 23%; p < 0.05), and with pelvic circumference >105 cm (33 vs. 29%; p < 0.05). CONCLUSIONS: There was no significant reduction in overall patient movement noted with any of the immobilization devices compared to no immobilization. The aquaplast group had reduced vertical and AP movement of greater than 0.5 cm. There was significantly more lateral movement with aquaplast appreciated in obese patients or patients with pelvic circumferences greater than 105 cm. The aquaplast immobilization appears to be useful in reducing movement in two very clinicaly important dimensions (AP and vertical). Despite our findings, other immobilization may still be useful especially in the treatment of nonobese patients. It is clear that the optimal immobilization technique and patient positioning are yet to be determined.

Body Constitution↗

PubMed1995

The potential for normal tissue dose reduction with neoadjuvant hormonal therapy in conformal treatment planning for stage C prostate cancer.

PURPOSE: Preirradiation hormonal cytoreduction of prostate cancer has been proven to reduce exposure of normal structures by decreasing the size of the target volume. Dose-volume histogram (DVH) analysis, however, does not always appear to demonstrate a strong positive benefit with the use of neoadjuvant hormone therapy. This study analyzes various other factors influencing dose to normal organs, which may determine the success or failure of neoadjuvant hormonal therapy in achieving its goals. METHODS AND MATERIALS: Patients with bulky clinical Stage C adenocarcinoma of the prostate were given 3 months of hormone treatment consisting of oral Flutamide and monthly Zoladex injections prior to irradiation. Computerized tomography (CT) scans of the pelvis were obtained both prior to and following hormonal treatment. Treatment plans were generated by three-dimensional (3D) conformal treatment planning. The change in the volume of the prostate was assessed along with the percentage of prescribed dose delivered to the rectum and bladder. Various factors such as prostate size, bladder/rectum size, and organ shape were studied. Both dose-volume histograms (DVH) and dose-surface area histograms (DSH) were used for analysis. RESULTS: Six of seven patients had reduction in the size of their prostates. The mean volumes of the prostate before and after hormonal manipulation were 129.1 +/- 32.9 standard deviation (SD) cm3 and 73.0 +/- 29.5 SD cm3, respectively (p = 0.0059). The volume of rectum receiving 80% of the prescribed dose was reduced in five of seven patients from a mean of 83.2 to 59.9 cm3 (p = 0.045). The volume of bladder receiving 80% of the prescribed dose was also reduced in five out of seven patients from a mean of 74.5 to 40.2 cm3 (p = 0.098). Correlation between the size of the prostate and volume of rectum and bladder treated was not always consistent: greater reduction in prostate size did not necessarily result in large decreases in dose to bladder or rectum. The total size of the bladder and rectum were found to be important factors in normal tissue radiation exposure; the benefits of hormone therapy may be lost if the bladder and rectum are allowed to decrease in size. Also, the bladder may be prone to sagging into the pelvis of some patients following hormone therapy, resulting in a less optimal therapeutic ratio. CONCLUSION: Reduction in prostate size by neoadjuvant hormonal manipulation does decrease the amount of normal tissue irradiated in most patients. However, the correlation between the reduction in prostate size and amount of rectum or bladder treated is not linear if other variables are not controlled. Factors such as the shape of the organs, as well as the distensible nature of the bladder and rectum, play major roles in dose to normal tissues. These facts may mask the benefits of cytoreduction and could be obstacles in realizing consistent benefits from preirradiation hormonal treatment in the clinical setting if they are ignored.

Adenocarcinoma↗

PubMed1995

Dose-surface histograms as treatment planning tool for prostate conformal therapy.

Dose-surface histograms are studied and compared with dose-volume histograms, as an evaluation tool for prostate treatment planning. For thin walled hollow organs, such as the rectum and bladder, the surface area irradiated is a more appropriate measure of the biological effect than the full volume. It is also more accurate and efficient to define the surface for a hollow structure and compute the surface area histograms. Application of the dose-surface histograms provide new insights into prostate treatment planning. A simple idealized geometry model demonstrates that the percentage surface area intersected by the geometric beam edge differs from the percentage volume intersected. For a group of prostate patients, it is shown that the dose-surface histograms yield substantially different results from the dose-volume histograms in ranking four-, six-, and, eight-field treatment plans and in calculating the fraction of the rectum irradiated to high dose. The difference in terms of surface area between these plans in the high-dose region is usually less than that in terms of the volume, and a reverse of plan ranking order can consequently occur. The percentage of organ surface irradiated to high dose is typically greater than the percentage volume by 5% to 10%. The use of the dose-surface histograms in analysis of organ motion and/or patient setup uncertainty, and analysis of rectal complications, is also discussed.

Biophysical Phenomena↗

PubMed1992

Quantification of doses to mediastinal lymph nodes in Hodgkin's disease.

Hodgkin's disease is highly curable today. Radiotherapy (RT) is the treatment of choice in the early stages. A mantle field is often used in the RT of Hodgkin's disease, and the technique and dosimetry are quite complex. We used computerized tomography (CT)-based dosimetry to determine doses delivered to different mediastinal nodes with the commonly used technique in Hodgkin's disease that was originally described by Kaplan. We used dose-volume histograms to determine doses to various groups of nodes in nine patients. Significant inhomogeneity (30%, 30%, 35%, 35%, 30%, 40%, 35%, 35%, and 30% in the nine patients) in dose distribution was found within the mediastinum. With the advent of 3-dimensional CT-based treatment planning, we are able to quantify such inhomogeneities. The question arises whether a homogeneous, lesser dose can achieve equal results. Average doses and "effective doses" were also calculated. The "effective doses" in eight patients (for a prescribed dose of 44 Gy) with a midline posterior spinal cord block added at 20 Gy were 37.3 Gy, 34.3 Gy, 36.0 Gy, 38.4 Gy, 35.8 Gy, 38.1 Gy, 36.7 Gy, and 36.7 Gy, respectively. A homogeneous dose equivalent to effective dose may achieve the same control as an inhomogeneous dose delivery. Prospective 3-D dosimetric studies are required to confirm this concept.

Hodgkin Disease↗

PubMed1991

Beams eye view-based photon radiotherapy I.

Geographic miss, dosimetric miss (underdosing), and proximity of the tumor to sensitive normal tissues are some of the causes of inadequate radiation dose delivery; this is one of many causes of failure after radiotherapy. In the past decade, computerized tomography (CT)-based treatment planning has helped to overcome some of these problems. Beam's eye view (BEV)-based radiotherapy planning is an improvement over CT-based treatment planning that may further increase the therapeutic ratio. Since January 1988, we have treated 198 patients with BEV-based photon radiotherapy. About 40% of our patients treated with radical radiotherapy undergo BEV-based treatment, and about 70% of patients who undergo planning CT in the treatment position receive BEV-based radiotherapy. Our findings are as follows: (a) routine use of BEV-based RT (BEVRT) is possible in a busy radiation oncology department; (b) BEVRT improves geometric coverage of tumors; (c) BEVRT is extremely useful in the design of oblique portals; (d) time commitments for various members of the RT treatment-planning team are reasonable; (e) BEVRT helps individualize RT technique; (f) preliminary data suggest decreased acute toxicity with the use of BEVRT for prostate cancer patients. Whether these advantages will help to improve the outcome (i.e., improve local control and survival) and/or decrease the long-term toxicity is not yet known.

Breast Neoplasms↗

PubMed1991

The use of a negative beam to simulate a midline block.

The physics behind the use of a negatively weighted beam to calculate the dose distribution under a midline block in computerized treatment planning systems is reviewed. To correctly reproduce the dose under the block, it is necessary and sufficient to know the relative dose at one reference depth on the central axis under the block. If the relative weight of the negative beam is then adjusted to produce agreement at that depth, good agreement can be obtained throughout. Comparisons between calculated and measured dose distributions under a midline block are presented for two therapy beams with 4MV and 6MV nominal energies.

Computer Simulation↗

PubMed1991

Estimation of doses to heart, coronary arteries, and spinal cord in mediastinal irradiation for Hodgkin's disease.

Early-stage Hodgkin's disease is highly curable with radiotherapy. However, radiotherapy for Hodgkin's disease is not without complications, particularly those related to irradiation of the mediastinum. In attempts to decrease complications, it is important not to compromise the results. To plan such a strategy, one needs to know the doses delivered to various volumes of normal tissues with present techniques. However, such dose-volume data do not exist. Here we demonstrate, with computerized tomography-based dosimetric techniques, such a dose-volume relationship for the heart, coronary arteries, and spinal cord. The doses were determined retrospectively in eight patients. With a prescribed dose of 44 Gy, the volumes of the heart receiving at least 22, 26, 31, 35, 40, or 44 Gy were: 77%, 75%, 70%, 57%, 33%, and 2%, respectively. The average modal doses to the coronary arteries were: anterior interventricular artery, 18.48 Gy; circumflex arterial branch, 37.84 Gy; left coronary artery, 34.76 Gy; and right coronary artery, 36.96 Gy. The average maximum spinal cord dose was 37.25 Gy. A similar prospective documentation of dose-volume relationships and correlation with (functional) long-term complications may be helpful in the development of new strategies for decreasing complications.

Coronary Vessels↗