Biomedical subjects

Rajat J Kudchadker

Publications and source records attributed to Rajat J Kudchadker.

4 recordsLinked to original sources

PubMed2006

Dosimetric comparison of four target alignment methods for prostate cancer radiotherapy.

PURPOSE: The aim of this study was to compare the dosimetric consequences of 4 treatment delivery techniques for prostate cancer patients treated with intensity-modulated radiotherapy (IMRT). METHODS AND MATERIALS: During an 8-week course of radiotherapy, 10 patients underwent computed tomography (CT) scans 3 times per week (243 total) before daily treatment with a CT-linear accelerator. Treatment delivery was simulated by realigning a fixed-margin treatment plan on each CT scan and calculating doses. The alignment methods were those based on the following: skin marks, bony registration, ultrasonography (US), and in-room CT. For the last two methods, prostate was the alignment target. The dosimetric effects of these alignment methods on the prostate, seminal vesicles, rectum, and bladder were compared. The average daily minimum dose to 0.1 cm3 was used as the metric for target coverage. RESULTS: Skin and bone alignments provided acceptable prostate coverage for only 70% of patients, US alignment for 90%, and CT alignment for 100%. CT-based alignment of the prostate provided seminal vesicle (SV) coverage of > or = 69 Gy for all patients; US and bone alignments provided SV coverage of > or = 60 Gy. This SV coverage may be acceptable for early-stage cancer (equivalent SV dose = 55.8 Gy at 1.8 Gy per fraction), but unacceptable for late-stage cancer (SV dose = 75.6 Gy). At 75.6 Gy, the acceptable rate for SV coverage was 40% for skin and bone alignments, 70% for US, and 80% for CT. CONCLUSIONS: Direct target alignment methods (US and CT) provided better target coverage. CT-guided alignment provided the best and most consistent dosimetric coverage. A larger planning target volume margin is needed for SV coverage when the alignment target is the prostate.

Algorithms↗

PubMed2004

An evaluation of radiation exposure from portal films taken during definitive course of pediatric radiotherapy.

PURPOSE: Recently, considerable attention has been directed toward computed tomography radiation doses (estimated 1 to 4 cGy) received by pediatric patients, because of the potential for increasing a pediatric patient's risk for developing a secondary malignancy. However, minimal attention has been given to the radiation exposure outside the treatment field resulting from the use of portal films to visualize surrounding anatomy. The objective of this study was to quantify the radiation dose from portal imaging delivered within and outside the radiation treatment field during a course of radiation therapy. METHODS AND MATERIALS: A retrospective review was conducted of the port film dose for 56 consecutive pediatric patients who underwent definitive radiation therapy between January 2001 and January 2002. Treatment locations were classified as brain, 27 patients; abdomen, 11 patients; extremities, 9 patients; pelvis, 6 patients; and thorax, 3 patients. Using the dose per monitor unit and total number of port films taken, the total port film dose for each patient was calculated. In addition, port film dose was quantified for 5 pediatric patients undergoing intensity modulated radiation therapy. RESULTS: The mean total port dose varied from a maximum of 46 cGy for brain to a minimum of 17 cGy for thorax. The mean total port dose as a percentage of prescribed dose was less than 1.25% for all locations in this study; however, most of the port dose is a result of the open-field dose from the double-exposure technique. CONCLUSIONS: Care should be exercised while exposing port films of pediatric patients to minimize both the number of films and corresponding radiation exposure without compromising the quality of treatment delivery. Specifically, the number of monitor units used to image regions outside the treatment field should be kept to a minimum, because such exposure could lead to an increased risk of development of secondary neoplasms.

Adolescent↗

PubMed2003

Clinical implications of incorporating heterogeneity corrections in mantle field irradiation.

PURPOSE: Patient dose calculations for mantle-field irradiation have traditionally been performed using homogeneous, water phantom data. The advent of computed tomography (CT)-based treatment planning now permits dose calculations to be corrected for actual patient density. Incorporation of full heterogeneity corrections is desirable, because calculations performed in this fashion more closely represent the actual dose delivered to the patient. In preparation for full clinical implementation of heterogeneity corrections in mantle irradiation, an evaluation of possible changes in dosimetry when transitioning from treatment plans generated without heterogeneity corrections to treatment plans that incorporated full heterogeneity corrections is presented. MATERIALS AND METHODS: A retrospective analysis was performed of treatment plans with and without heterogeneity corrections for 15 consecutive patients who had undergone full mantle-field irradiation. Comparisons were made of the absolute delivered doses (in cGy per monitor unit) and the absolute volume (in cubic centimeters) enclosed by the isodose surface of the 30.6 Gy prescription line and the surface representing 90% of the prescribed dose. Dose-volume histograms (DVHs) were generated and studied to evaluate differences in the doses received by the lungs, heart, and spinal cord between corrected and uncorrected plans. Comparisons were made of the volumes of lung receiving at least 20 Gy, the volumes of heart receiving at least 25.2 Gy, and the maximum cord dose. RESULTS: Dosimetric differences between heterogeneity-corrected and heterogeneity-uncorrected calculations were small. The mean total ratio of corrected-to-uncorrected dose per monitor unit was 1.01, with a standard deviation (SD) of 0.02. The mean corrected-to-uncorrected treated volume ratio (30.6 Gy) was 0.97, SD 0.14, and the mean corrected-to-uncorrected volume ratio of the 90% isodose surface was 0.99, SD 0.02. The ratio of the volume of lung receiving at least 20 Gy was 1.03, SD 0.02; the ratio of the volume of heart receiving at least 25.2 Gy was 1.01, SD 0.03; and the maximum spinal cord dose ratio was 1.02, SD 0.02. CONCLUSIONS: In all patient treatment plans evaluated, no significant dosimetric differences were observed between heterogeneity-corrected and heterogeneity-uncorrected treatment plans. However, unpredictable differences in the prescription isodose (30.6 Gy) were observed. The differences in coverage at the 90% isodose volume were negligible. The dose administered to lung in heterogeneity-corrected plans demonstrates a higher dose overall, with the greatest increase occurring at volumes receiving at least 20 Gy. In light of these small dosimetric differences, we believe that heterogeneity corrections can be incorporated into full mantle-field treatment planning.

Dose Fractionation, Radiation↗

PubMed2002

Electron conformal radiotherapy using bolus and intensity modulation.

PURPOSE: Conformal electron beam therapy can be delivered using shaped bolus, which varies the penetration of the electrons across the incident beam so that the 90% isodose surface conforms to the distal surface of the planning target volume (PTV). Previous use of this modality has shown that the irregular proximal surface of the bolus causes the dose heterogeneity in the PTV to increase from 10%, the typical dose spread of a flat-water surface to approximately 20%. The present work evaluates the ability to restore dose homogeneity by varying the incident electron intensity. METHODS AND MATERIALS: Three patients, one each with chest wall, thorax, and head-and-neck cancer, were planned using electron conformal therapy with bolus, with and without intensity modulation. Resulting dose distributions and dose-volume histograms were compared with non-intensity-modulated bolus plans. RESULTS: In all cases, the DeltaD(90%-10%) for the PTV was reduced; for example, for the head-and-neck case, the DeltaD(90%-10%) for the PTV was reduced from 14.9% to 9.2%. This reduction in dose spread is a direct result of intensity modulation. CONCLUSIONS: The results showed that intensity-modulated electron beams could significantly improve the dose homogeneity in the PTV for patients treated with electron conformal therapy using shaped bolus.

Adult↗