Biomedical subjects

U Spahn

Publications and source records attributed to U Spahn.

At least 19 recordsLinked to original sources

PubMed2000

[Effect if 3D compared with 2D radiotherapy planning within a conventional treatment schedule of advanced lung cancer].

BACKGROUND: The effect of 3D radiotherapy planning (3D RTP) in comparison to 2D radiotherapy planning (2D RTP) was evaluated in a usually practiced treatment schedule (starting by v./d. opposing portals, continued with computer-planned portals) for non-small-cell lung cancer. PATIENTS AND METHODS: In 20 patients with locally advanced non-small-cell lung cancer the computer-planned part of the treatment schedule was calculated 2- and 3-dimensionally. Target volume were the primary tumor, the involved and the electively irradiated mediastinal lymph nodes. The results of the 2D RTP were recalculated 3-dimensionally and the mean doses to target volume and organs at risk were defined. Further the normal tissue complications were calculated. RESULTS: Under the prerequisite of 44 Gy maximally allowed to the spinal cord and a dose to the reference point of 50 Gy a small, but significant advantage with 2.1 Gy to the target (p = 0.004) and a reduction of 3.6 Gy to the heart (p = 0.05) was achievable for 3D RTP. The dose to the lungs did not differ significantly (19.7 Gy for 2D RTP, 20.3 Gy for 3D RTP). The dose to the heart was not estimated critical by NTCP (normal tissue complication probability). The NTCP for the ipsilateral lung was 16.1 and 18.7% for 2D RTP and 3D RTP, respectively. Regarding the simulator-planned ap/pa fields at the start of the radiotherapy the advantage of 3D RTP was further reduced but remained significant. Favorable with respect to the mean lung dose and the NTCP (18.7% NTCP ipsilateral lung for early onset of 3D planned radiotherapy vs 31.7% for late onset of 3D planned radiotherapy) but not significantly measurable is the early start of the treatment by computerized RTP. CONCLUSION: The main advantage of 3D RTP in treatment of advanced lung cancer is the better coverage of the target volume. A reduction of the mean lung dose cannot be expected. A dose escalation by 3D RTP to target volumes as described here seems not to be possible because of unchanged high lung exposure.

Adult↗

PubMed1998

Radiation pneumonitis as a function of mean lung dose: an analysis of pooled data of 540 patients.

PURPOSE: To determine the relation between the incidence of radiation pneumonitis and the three-dimensional dose distribution in the lung. METHODS AND MATERIALS: In five institutions, the incidence of radiation pneumonitis was evaluated in 540 patients. The patients were divided into two groups: a Lung group, consisting of 399 patients with lung cancer and 1 esophagus cancer patient and a Lymph./Breast group with 78 patients treated for malignant lymphoma, 59 for breast cancer, and 3 for other tumor types. The dose per fraction varied between 1.0 and 2.7 Gy and the prescribed total dose between 20 and 92 Gy. Three-dimensional dose calculations were performed with tissue density inhomogeneity correction. The physical dose distribution was converted into the biologically equivalent dose distribution given in fractions of 2 Gy, the normalized total dose (NTD) distribution, by using the linear quadratic model with an alpha/beta ratio of 2.5 and 3.0 Gy. Dose-volume histograms (DVHs) were calculated considering both lungs as one organ and from these DVHs the mean (biological) lung dose, NTDmean, was obtained. Radiation pneumonitis was scored as a complication when the pneumonitis grade was grade 2 (steroids needed for medical treatment) or higher. For statistical analysis the conventional normal tissue complication probability (NTCP) model of Lyman (with n=1) was applied along with an institutional-dependent offset parameter to account for systematic differences in scoring patients at different institutions. RESULTS: The mean lung dose, NTDmean, ranged from 0 to 34 Gy and 73 of the 540 patients experienced pneumonitis, grade 2 or higher. In all centers, an increasing pneumonitis rate was observed with increasing NTDmean. The data were fitted to the Lyman model with NTD50=31.8 Gy and m=0.43, assuming that for all patients the same parameter values could be used. However, in the low dose range at an NTDmean between 4 and 16 Gy, the observed pneumonitis incidence in the Lung group (10%) was significantly (p=0.02) higher than in the Lymph./Breast group (1.4%). Moreover, between the Lung groups of different institutions, also significant (p=0.04) differences were present: for centers 2, 3, and 4, the pneumonitis incidence was about 13%, whereas for center 5 only 3%. Explicitly accounting for these differences by adding center-dependent offset values for the Lung group, improved the data fit significantly (p < 10(-5)) with NTD50=30.5+/-1.4 Gy and m=0.30+/-0.02 (+/-1 SE) for all patients, and an offset of 0-11% for the Lung group, depending on the center. CONCLUSIONS: The mean lung dose, NTDmean, is relatively easy to calculate, and is a useful predictor of the risk of radiation pneumonitis. The observed dose-effect relation between the NTDmean and the incidence of radiation pneumonitis, based on a large clinical data set, might be of value in dose-escalating studies for lung cancer. The validity of the obtained dose-effect relation will have to be tested in future studies, regarding the influence of confounding factors and dose distributions different from the ones in this study.

Dose-Response Relationship, Radiation↗

PubMed1987