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Query: UMLS:C0376358 (prostate cancer)
 59,338 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The calculation of the percentage cumulative histogram of the rectal wall (DWH) in prostate cancer radiotherapy may be subject to large uncertainties due to the difficulty of assessing the wall thickness on CT images. For this reason often only the external contour is used to define the rectum and then the percentage cumulative dose-volume histogram (DVH) of the rectum including any filling is calculated as a 'surrogate' for the DWH. More recently, other approaches using only the external contour have been proposed to estimate the DWH such as the percentage normalized dose-surface histograms (NDSH). A similar concept can be used when considering the solid rectum (the percentage normalized DVH, NDVH). The purpose of this investigation was to assess the relationships between rectal DVH, NDVH, DSH, NDSH and DWH in the common case of three- and four-field techniques in prostate cancer irradiation. Analytical relationships between the above parameters have been derived for a cylindrical rectum model in the case of three- and four-field techniques. The model is applied to the case of an empty rectum, a full rectum and to the more realistic mixed full/empty rectum situation for a four-field technique delivering 76 Gy (ICRU dose) with 18 MV x-rays. Different positions of the lateral beam with respect to the rectum axis were simulated. In the case of no lumen variation along the z-axis, the DWH is found to be very close to the DVH and to the DSH for empty and full rectum, respectively. The largest differences (up to 15%) between DVH and DSH were seen in the high-dose region (>70 Gy). In the more realistic case of lumen variation along the z-axis, the DWH always lies between NDVH and NDSH and, excluding the full-rectum situation, the DWH differs from the DVH by less than 7% in the 50-75 Gy range. In the case of significant portions of rectum being completely shielded, the DVH may differ from the NDVH/NDSH/DWH by up to 10-15%. In most clinical situations NDVH is within a few per cent of DWH, whilst NDSH may differ from DWH by up to 15-20%, especially in the high-dose region (V70). In conclusion, for most situations, the DVH is highly correlated with NDVH and DWH. A high degree of consistency between NDVH and DWH was found in most clinical cases whilst largest deviations between NDSH and DWH were evident in the high-dose region (70-75 Gy). In the less common case of a very full rectum a poorer correlation between DVH/NDVH and DWH was found whilst NDSH mimicked the DWH very well. In summary, except for the case of a 'very full' rectum, NDVH may be used as a robust surrogate for DWH. The DVH seems to be sufficiently robust if the rectum is prevalently empty.
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PMID:A cylindrical model of the rectum: comparing dose-volume, dose-surface and dose-wall histograms in the radiotherapy of prostate cancer. 1297 77

The purpose of this study was to quantify the impact of inter-fraction modifications of bladder during RT of prostate cancer on bladder dose surface maps (DSM). Eighteen patients treated with daily image-guided Tomotherapy and moderate hypofractionation (70-72.8Gy at 2.5-2.6Gy/fr in 28 fractions and full bladder) were considered. Bladder contours were delineated on co-registered daily Megavoltage CT (MVCT) by a single observer and copied on the planning CT to generate dose-volume/surface histograms (DVH/DSH) and bladder DSMs. Discrepancies between planned and daily absorbed doses were analyzed through the average of individual systematic errors, the population systematic errors and the population random errors for the DVH/DSHs and DSMs. In total, 477 DVH/DSH and 472 DSM were available. DSH and DVH showed small population systematic errors of absolute surfaces (<3.4cm(2)) and volumes (<8.4cm(3)) at the highest doses. The dose to the posterior bladder base assessed on DSMs showed a mean systematic error below 1Gy, with population systematic and random errors within 4 and 3Gy, respectively. The region surrounding this area shows higher mean systematic errors (1-3Gy), population systematic (8-11Gy) and random (5-7Gy) errors. In conclusion, DVH/DSH and DSMs are quite stable with respect to inter-fraction variations in the high-dose region, within about 2cm from bladder base. Larger systematic variations occur in the anterior portion and cranially 2.5-3.5cm from the base. Results suggest that dose predictors related to the high dose area (including the trigone dose) are likely to be sufficiently reliable with respect to the expected variations due to variable bladder filling.
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PMID:Bladder dose-surface maps and urinary toxicity: Robustness with respect to motion in assessing local dose effects. 2705 49