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B R Murray

Publications and source records attributed to B R Murray.

5 recordsLinked to original sources
PubMed2001

Dosimetric evaluation of lung tumor immobilization using breath hold at deep inspiration.

PURPOSE: To examine the dosimetric benefit of self-gated radiotherapy at deep-inspiration breath hold (DIBH) in the treatment of patients with non-small-cell lung cancer (NSCLC). The relative contributions of tumor immobilization at breath hold (BH) and increased lung volume at deep inspiration (DI) in sparing high-dose lung irradiation (> or = 20 Gy) were examined. METHODS AND MATERIALS: Ten consecutive patients undergoing radiotherapy for Stage I-IIIB NSCLC who met the screening criteria were entered on this study. Patients were instructed to BH at DI without the use of external monitors or breath-holding devices (self-gating). Computed tomography (CT) scans of the thorax were performed during free breathing (FB) and DIBH. Fluoroscopy screened for reproducible tumor position throughout DIBH, and determined the maximum superior-inferior (SI) tumor motion during both FB and DIBH. Margins used to define the planning target volume (PTV) from the clinical target volume included 1 cm for setup error and organ motion, plus an additional SI margin for tumor motion, as determined from fluoroscopy. Three conformal treatment plans were then generated for each patient, one from the FB scan with FB PTV margins, a second from the DIBH scan with FB PTV margins, and a third from the DIBH scan with DIBH PTV margins. The percent of total lung volume receiving > or = 20 Gy (using a prescription dose of 70.9 Gy to isocenter) was determined for each plan. RESULTS: Self-gating at DIBH was possible for 8 of the 10 patients; 2 patients were excluded, because they were not able to perform a reproducible DIBH. For these 8 patients, the median BH time was 23 (range, 19-52) s. The mean percent of total lung volume receiving > or = 20 Gy under FB conditions (FB scan with FB PTV margins) was 12.8%. With increased lung volume alone (DIBH scan with FB PTV margins), this was reduced to 11.0%, tending toward a significant decrease in lung irradiation over FB (p = 0.086). With both increased lung volume and tumor immobilization (DIBH scan with DIBH PTV margins), the mean percent lung volume receiving > or = 20 Gy was further reduced to 8.8%, a significant decrease in lung irradiation compared to FB (p = 0.011). Furthermore, at DIBH, the additional benefit provided by tumor immobilization (i.e., using DIBH instead of FB PTV margins) was also significant (p = 0.006). The relative contributions of tumor immobilization and increased lung volume toward reducing the percent total lung volume receiving > or = 20 Gy were patient specific; however, all 8 of the patients analyzed showed a dosimetric benefit with this DIBH technique. CONCLUSION: Compared to FB conditions, at DIBH the mean reduction in percent lung volume receiving > or = 20 Gy was 14.3% with the increase in lung volume alone, 22.1% with tumor immobilization alone, and 32.5% with the combined effect. The dosimetric benefit seen at DIBH was patient specific, and due to both the increased lung volume seen at DI and the PTV margin reduction seen with tumor immobilization.

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PubMed2001

Held-breath self-gating technique for radiotherapy of non-small-cell lung cancer: a feasibility study.

PURPOSE: To examine the feasibility of a held-breath self-gating (HBSG) technique in the radiotherapy of lung cancer. MATERIAL AND METHODS: Sixteen consecutive eligible and consenting patients undergoing radiotherapy for non-small-cell lung cancer were accrued for this study. The patients underwent a standardized training session and were then asked to breath hold at four points in the breathing cycle (maximal and end tidal, inspiration and expiration) while under fluoroscopic visualization. Plain films and video imaging with digital image analysis were used to record and measure the movement of the diaphragm, a tumor surrogate, in the superior-inferior axis. These measurements were obtained during and between multiple separate breath holds within one session and between breath holds in sessions held at least one day apart. RESULTS: Maximal inspiration and expiration tend to provide the best positional reliability, and the standard deviation of diaphragmatic position ranged from 0.13 to 2.57 mm, with an average of 0.97 mm. During a single breath hold, the diaphragmatic movement averaged 2.62 mm with a standard deviation of 1.28 mm. The day-to-day variation of diaphragmatic positions was less than 5 mm. The held-breath self-gating technique resulted in a reduction of diaphragmatic movement by an average of 11.9 mm when compared to that seen during tidal breathing. CONCLUSION: In the radiotherapeutic management of non-small-cell lung cancer, this HBSG technique offers a simple method that provides superior immobilization of the diaphragm compared to tidal breathing. Clinical implementation of this technique should allow for a reduction of treatment margins, thus sparing more normal tissues and facilitating dose escalation.

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PubMed1998

Evaluation of optimized compensators on a 3D planning system.

A commercially available treatment planning system contains several functions that allow for the automation of missing tissue and optimized compensators, where the former retracts the bolus toward the source, and the latter attempts, by iteration, to establish a uniform dose at some user defined depth. The intent of this paper is to report on the compensators designed by the system and to compare them to those devised through conventional techniques. It is demonstrated that the system can model the dosimetric effects of compensators with a high degree of accuracy; measured and predicted doses agree to within 3%. Optimized compensators show slightly improved dose uniformity over thickness reduced compensators. Both show significantly improved uniformity over compensators that simply retract the bolus geometry. In cases where internal inhomogeneities exist, however, the dose uniformity from the optimized compensators vary by as much as 6% at the target depth. These deviations are comparable to the errors of the inhomogeneity algorithm itself. The pathlength reduction technique has been applied to both missing tissue and inhomogeneity compensation, and it has been found that for inhomogeneity compensation, the pathlength reduced compensators produce more uniform distributions than those generated by the optimization algorithm.

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