Biomedical subjects

Margie A Hunt

Publications and source records attributed to Margie A Hunt.

8 recordsLinked to original sources

PubMed2006

Geometric factors influencing dosimetric sparing of the parotid glands using IMRT.

PURPOSE/OBJECTIVE: To determine the relationship between the parotid volume, parotid-planning target volume (PTV) overlap, and dosimetric sparing of the parotid with intensity-modulated radiation therapy (IMRT). METHODS AND MATERIALS: Parotid data were collected retrospectively for 51 patients treated with simultaneous boost IMRT. Unresectable patients received 54 or 59.4 Gy to subclinical disease, 70 Gy to gross disease. Patients treated postoperatively received 54, 60, and 66 Gy to low-risk, high-risk, and tumor bed regions. Volume and mean dose of each gland and gland segments outside of and overlapping the PTV were collected. Proximity of each gland to each PTV was recorded. RESULTS: Dosimetric sparing (mean dose 21% overlap (p = <0.0001). Among spared glands, the median mean dose in the overlap region was 55.0 Gy in glands with < or =21% overlap, but only 45.4 Gy when overlap >21%. Median mean dose was 25.9 Gy to glands overlapping PTV(54) or PTV(59) alone and 30.0 Gy to those abutting PTV(70) (p < 0.001). Although proximity to PTV(70) was associated with higher parotid dose, satisfactory sparing was achieved in 24 of 43 ipsilateral glands. CONCLUSIONS: Dosimetric sparing of the parotid is feasible when the parotid-PTV overlap is less than approximately 20%. With more overlap, sparing may result in low doses within the overlap region, possibly leading to inadequate PTV coverage. Gland proximity to the high-dose PTV is associated with higher mean dose but does not always preclude dosimetric sparing.

Algorithms↗

PubMed2006

Sensorineural hearing loss in combined modality treatment of nasopharyngeal carcinoma.

BACKGROUND: Combined modality therapy has become the standard of care for nasopharyngeal carcinoma, yet the combined ototoxic effects of radiation and cisplatin are poorly understood. The incidence and severity of sensorineural hearing loss (SNHL) with combined modality therapy was evaluated and the dose-response relation between radiation and hearing loss was investigated. METHODS: Patients with newly diagnosed AJCC Stage II-IVB nasopharynx carcinoma treated from 1994-2003 were identified. The records of 44 ears in 22 patients who received a preirradiation pure tone audiogram and followup audiograms 12+ months postirradiation were included in the analysis. All patients were treated with conformal radiotherapy to 70 Gy and received platinum-based chemotherapy similar to the Intergroup 0099 trial. Composite cochlear dose distributions were calculated. Ototoxicity was measured using intrasubject audiogram comparisons and SNHL was defined as per the American Speech and Hearing Association guidelines, with standard range of speech between 2000-4000 Hz. SNHL was analyzed using Fisher exact test and linear and logistic regression models. RESULTS PATIENT CHARACTERISTICS: median age, 45; 27% Asian; 68% male; 64% WHO III. Median audiologic followup was 29 months (range, 12-76 mos). Mean cochlear dose (Dmean) ranged from 28.4-70.0 Gy (median, 48.5 Gy). SNHL was detected in 25 of the 44 ears (57%) studied. There was an increased risk of SNHL for ears receiving Dmean > 48 Gy compared with those receiving < or = 48 Gy at all frequencies within the range of speech (P = 0.04). Using univariate logistic regression analysis, Dmean to the cochlea, cycles of cisplatin, and time postradiotherapy were independently significant factors in determining the incidence of SNHL (P = 0.02, P = 0.03, and P = 0.04, respectively). In univariate and multivariate linear regression analysis, Dmean was statistically significant at all frequencies in affecting degree of SNHL, whereas the significance of cisplatin and time was variable. CONCLUSIONS: There was a significant increase in risk of SNHL among patients receiving > 48 Gy, suggesting a threshold in cochlear radiation dose-response in the setting of combined modality therapy. This dose should serve as a Dmean constraint maximum for intensity-modulated radiotherapy treatment of nasopharynx carcinoma.

Adolescent↗

PubMed2005

Intensity-modulated radiotherapy as the boost or salvage treatment of nasopharyngeal carcinoma: the appropriate parameters in the inverse planning and the effect of patient's anatomic factors on the planning results.

The current study demonstrates that the large increase in normal tissue penalty often degrades target dose uniformity without a concomitant large improvement in normal tissue dose, especially in anatomically unfavorable patients. The excessively large normal tissue penalties do not improve treatment plans for patients having unfavorable geometry.

Carcinoma↗

PubMed2004

Dosimetric analysis of a simplified intensity modulation technique for prone breast radiotherapy.

PURPOSE: Prone-position breast radiotherapy (RT) has been described as an alternative technique to improve dose homogeneity for women with large, pendulous breasts. We report the feasibility and dosimetric analysis of a simplified intensity-modulated RT (IMRT) technique, previously reported for women in the supine treatment position, to plan prone-position RT to the intact breast. METHODS AND MATERIALS: Twenty patients with clinical Stage TisN0-T1bN1 breast cancer undergoing breast-conserving therapy underwent whole breast RT using a prone position technique. The treatment plans were developed using both conventional tangents and a simplified intensity-modulated tangential beam technique based on optimization of the intensity distributions across the breast. The plans were compared with regard to the dose-volume parameters. RESULTS: Dose heterogeneity within the breast planning target volume was significantly greater for the conventional tangent plans. Of 20 patients, 16 (80%) received maximal doses of > or =110% using the conventional tangents vs. only 1 (5%) using the IMRT plan. The isodose level encompassing 5% of the planning target volume was reduced from an average of 110% with conventional tangents to 105% with IMRT. The maximal dose within the planning target volume was reduced from an average of 114% with conventional tangents to 107% with IMRT. The greatest improvement was seen in the patients with the most pendulous breasts. CONCLUSION: An IMRT planning approach is feasible for prone-position breast RT and improves dose homogeneity, particularly in women with larger, pendulous breasts. Additional follow-up is necessary to determine whether the improvements in dose homogeneity impact acute toxicity and cosmetic outcome in this cohort of women who have historically suffered from poor cosmesis after breast-conserving therapy.

Adult↗

PubMed2003

CT image-guided intensity-modulated therapy for paraspinal tumors using stereotactic immobilization.

PURPOSE: To design and implement a noninvasive stereotactic immobilization technique with daily CT image-guided positioning to treat patients with paraspinal lesions accurately and to quantify the systematic and random patient setup errors occurring with this method. METHODS AND MATERIALS: A stereotactic body frame (SBF) was developed for "rigid" immobilization of paraspinal patients. The inherent accuracy of this system for stereotactic CT-guided treatment was evaluated with phantom studies. Seven patients with thoracic and lumbar spine lesions were immobilized with the SBF and positioned for 33 treatment fractions using daily CT scans. For all 7 patients, the daily setup errors, as assessed from the daily CT scans, were corrected at each treatment fraction. A retrospective analysis was also performed to assess what the impact on patient treatment would have been without the CT-based corrections (i.e., if patient setup had been performed only with the SBF). RESULTS: The average magnitude of systematic and random errors from uncorrected patient setups using the SBF was approximately 2 mm and 1.5 mm (1 SD), respectively. For fixed phantom targets, the system accuracy for the SBF localization and treatment was shown to be within 1 mm (1 SD) in any direction. Dose-volume histograms incorporating these uncertainties for an intensity-modulated radiotherapy plan for lumbar spine lesions were generated, and the effects on the dose-volume histograms were studied. CONCLUSION: We demonstrated a very accurate and precise method of patient immobilization and treatment delivery based on a noninvasive SBF and daily image guidance for paraspinal lesions. The SBF provides excellent immobilization for paraspinal targets, with setup accuracy better than 2 mm (1 SD). However, for highly conformal paraspinal treatments, uncorrected systematic and random errors of 2 mm in magnitude can result in a significantly greater (>100%) dose to the spinal cord than planned, even though the planned target coverage may not change substantially. With daily CT guidance using the SBF, we showed that the maximal spinal cord dose is ensured to be within 10-15% of the planned value.

Humans↗

PubMed2002

Evaluation of concave dose distributions created using an inverse planning system.

PURPOSE: To evaluate and develop optimum inverse treatment planning strategies for the treatment of concave targets adjacent to normal tissue structures. METHODS AND MATERIALS: Optimized dose distributions were designed using an idealized geometry consisting of a cylindrical phantom with a concave kidney-shaped target (PTV) and cylindrical normal tissues (NT) placed 5-13 mm from the target. Targets with radii of curvature from 1 to 2.75 cm were paired with normal tissues with radii between 0.5 and 2.25 cm. The target was constrained to a prescription dose of 100% and minimum and maximum doses of 95% and 105% with relative penalties of 25. Maximum dose constraint parameters for the NT varied from 10% to 70% with penalties from 10 to 1000. Plans were evaluated using the PTV uniformity index (PTV D(max)/PTV D(95)) and maximum normal tissue doses (NT D(max)/PTV D(95)). RESULTS: In nearly all situations, the achievable PTV uniformity index and the maximum NT dose exceeded the corresponding constraints. This was particularly true for small PTV-NT separations (5-8 mm) or strict NT dose constraints (10%-30%), where the achievable doses differed from the requested by 30% or more. The same constraint parameters applied to different PTV-NT separations yielded different dose distributions. For most geometries, a range of constraints could be identified that would lead to acceptable plans. The optimization results were fairly independent of beam energy and radius of curvature, but improved as the number of beams increased, particularly for small PTV-NT separations or strict dose constraints. CONCLUSION: Optimized dose distributions are strongly affected by both the constraint parameters and target-normal tissue geometry. Standard site-specific constraint templates can serve as a starting point for optimization, but the final constraints must be determined iteratively for individual patients. A strategy whereby NT constraints and penalties are modified until the highest acceptable PTV uniformity index is achieved is discussed. This strategy can be used, in simple patient geometries, to ensure the lowest possible normal tissue dose. Strategies for setting the optimum dose constraints and penalties may vary for different optimization algorithms and objective functions. Increasing the number of beams can significantly improve normal tissue dose and target uniformity in situations where the PTV-NT separation is small or the normal tissue dose limits are severe. Setting unrealistically severe constraints in such situations often results in dose distributions that are inferior to plans achieved with more lenient constraints.

Algorithms↗

PubMed2002

Intensity-modulated radiotherapy versus conventional three-dimensional conformal radiotherapy for boost or salvage treatment of nasopharyngeal carcinoma.

PURPOSE: To compare intensity-modulated radiotherapy (IMRT) and conventional three-dimensional conformal radiotherapy (3D-CRT) for the boost treatment of new-onset nasopharyngeal carcinoma (NPC) or the salvage treatment of locally recurrent NPC. METHODS AND MATERIALS: Between January 14 and February 23, 2000, 5-field 3D-CRT treatment plans were generated for 14 consecutive NPC patients using the ADAC Pinnacle planning system in Chang Gung Memorial Hospital, Kaohsiung, Taiwan. The planning data of these patients were later transferred to Memorial Sloan-Kettering Cancer Center, where new IMRT plans, also using 5-7 radiation fields were created for each patient using an inverse treatment planning system. The IMRT and 3D-CRT plans were compared for all 14 patients. The relationship between the anatomic shapes and locations of targets and the results of different plans were studied. RESULTS: Target doses were more homogeneous in IMRT plans. The average maximal brainstem dose (D(05), the dose received by 5% of the brainstem volume) decreased from 30.9% of the prescription dose with 3D-CRT to 15.3% and 14.7% with 5- and 7-field IMRT, respectively (p = 0.004 and 0.003, respectively, compared with 3D-CRT, paired Student's t test). Five anatomic factors were found that predicted greater benefits with IMRT. These factors were (1) vertical length of target >7 cm, (2) minimal distance between target and brainstem <0.1 cm, (3) maximal AP overlap of target and brainstem >0.6 cm, (4) maximal AP overlap of target and spinal cord >1 cm, and (5) vertical overlap of target and eyes >0 cm. For the 7 patients with at least 1 of these 5 anatomic factors, the benefits achieved by IMRT planning would have been greater than the benefits for the other 7 patients (p = 0.005, Fisher's exact test). CONCLUSION: For boost or salvage treatment of NPC, lower normal tissue doses and more homogeneous target doses were achieved with IMRT plans. For NPC patients with at least 1 of the 5 anatomic factors, IMRT is highly recommended.

Algorithms↗

PubMedDate not supplied

Intensity-modulated radiotherapy.

Intensity-modulated radiotherapy represents a recent advancement in conformal radiotherapy. It employs specialized computer-driven technology to generate dose distributions that conform to tumor targets with extremely high precision. Treatment planning is based on inverse planning algorithms and iterative computer-driven optimization to generate treatment fields with varying intensities across the beam section. Combinations of intensity-modulated fields produce custom-tailored conformal dose distributions around the tumor, with steep dose gradients at the transition to adjacent normal tissues. Thus far, data have demonstrated improved precision of tumor targeting in carcinomas of the prostate, head and neck, thyroid, breast, and lung, as well as in gynecologic, brain, and paraspinal tumors and soft tissue sarcomas. In prostate cancer, intensity-modulated radiotherapy has resulted in reduced rectal toxicity and has permitted tumor dose escalation to previously unattainable levels. This experience indicates that intensity-modulated radiotherapy represents a significant advancement in the ability to deliver the high radiation doses that appear to be required to improve the local cure of several types of tumors. The integration of new methods of biologically based imaging into treatment planning is being explored to identify tumor foci with phenotypic expressions of radiation resistance, which would likely require high-dose treatments. Intensity-modulated radiotherapy provides an approach for differential dose painting to selectively increase the dose to specific tumor-bearing regions. The implementation of biologic evaluation of tumor sensitivity, in addition to methods that improve target delineation and dose delivery, represents a new dimension in intensity-modulated radiotherapy research.

Abdominal Neoplasms↗