Various techniques of contouring the rectum and their impact on rectal dose-volume histograms (original) (raw)
Related papers
Physics in medicine and biology, 2014
When pooling retrospective data from different cohorts, slice thicknesses of acquired computed tomography (CT) images used for treatment planning may vary between cohorts. It is, however, not known if varying slice thickness influences derived dose-response relationships. We investigated this for rectal bleeding using dose-volume histograms (DVHs) of the rectum and rectal wall for dose distributions superimposed on images with varying CT slice thicknesses. We used dose and endpoint data from two prostate cancer cohorts treated with three-dimensional conformal radiotherapy to either 74 Gy (N = 159) or 78 Gy (N = 159) at 2 Gy per fraction. The rectum was defined as the whole organ with content, and the morbidity cut-off was Grade ≥2 late rectal bleeding. Rectal walls were defined as 3 mm inner margins added to the rectum. DVHs for simulated slice thicknesses from 3 to 13 mm were compared to DVHs for the originally acquired slice thicknesses at 3 and 5 mm. Volumes, mean, and maximum do...
Strahlentherapie und Onkologie, 2006
To evaluate rectal dose-volume relations during three-dimensional conformal radiotherapy of patients with prostate cancer by means of different rectal volume contours. Patients and Methods: 55 patients with prostate cancer underwent three-dimensional conformal external-beam radiotherapy. Rectal dose-volume histograms were calculated for four separately contoured rectal volumes in all patients resulting in four groups. In group 1 the outer rectal wall was contoured two CT slices above and below the planning target volume. The rectal contour of group 2 was drawn from the anal verge up to the sigmoid. Furthermore, the posterior half of the rectum was contoured for both volumes mentioned above (groups 1a and 2a). Statistical analysis was then performed using nonparametric Wilcoxon tests. Results: The mean target dose was 72.9 Gy (standard deviation [SD] ± 2.1 Gy). The minimum target dose was 70.2 Gy. Mean rectum dose (± SD) over all patients was 50.7 Gy (± 4.6 Gy), 45.2 Gy (± 5.4 Gy), 43.2 Gy (± 4.2 Gy), and 38.7 Gy (± 5.5 Gy) for group 1, 2, 1a, and 2a, respectively. The corresponding volumes receiving ≥ 70 Gy for groups 1 and 2 were 14.0% (± 5.3%) and 11.9% (± 4.5%). These differences were statistically significant. Comparison of minimum and mean rectal dose also revealed a statistically significant difference toward higher doses in groups 1 and 1a (p < 0.001). Maximum rectal doses for groups 1 and 2 as well as for groups 1a and 2a revealed no statistically significant difference (p = 1.0). Conclusion: Data from the literature on normal-tissue complication probability (rectal bleeding) refer to different rectal contours. When applying dose restrictions to the rectum, contouring becomes a significant factor that determines the risk of rectal toxicity. The results of this study show that different ways of rectal contouring significantly influence doses to the rectum. The influence of organ at risk contouring should be considered thoroughly in conformal radiotherapy of prostate cancer patients, especially in dose escalation studies. It is recommended to calculate the doses for absolute rectal volumes and correlate these data with toxicity in order to be able to achieve comparable results among different institutions.
International Journal of Radiation Oncology*Biology*Physics, 2007
Purpose: The purpose of this article was to investigate how exceeding specified rectal wall dose-volume constraints impacts on the risk of late rectal bleeding by using radiobiologic calculations. Methods and Materials: Dose-volume histograms (DVH) of the rectal wall of 250 patients with prostate cancer were analyzed. All patients were treated by three-dimensional conformal radiation therapy, receiving mean target doses of 80 Gy. To study the main features of the patient population, the average and the standard deviation of the distribution of DVHs were generated. The mean dose , generalized equivalent uniform dose formulation (gEUD), modified equivalent uniform dose formulation (mEUD) 0 , and normal tissue complication probability (NTCP) distributions were also produced. The DVHs set was then binned into eight classes on the basis of the exceeding or the fulfilling of three dose-volume constraints: V 40 ؍ 60%, V 50 ؍ 50%, and V 70 ؍ 25%. Comparisons were made between them by , gEUD, mEUD 0 , and NTCP. Results: The radiobiologic calculations suggest that late rectal toxicity is mostly influenced by V 70 . The gEUD and mEUD 0 are risk factors of toxicity always concordant with NTCP, inside each DVH class. The mean dose, although a reliable index, may be misleading in critical situations. Conclusions: Both in three-dimensional conformal radiation therapy and particularly in intensity-modulated radiation therapy, it should be known what the relative importance of each specified dose-volume constraint is for each organ at risk. This requires a greater awareness of radiobiologic properties of tissues and radiobiologic indices may help to gradually become aware of this issue. © 2007 Elsevier Inc.
Journal of Cancer Therapy, 2014
Purpose: To evaluate the performance of a rectum model in predicting late rectal toxicity of prostate patients undergoing 3D conformal radiation therapy while following a dietary protocol combined with image guidance. Methods: A linear accelerator equipped with a Cone Beam Computed Tomography (CBCT) system was used to treat 20 patients who were following a dietary protocol. The setup was verified by co-registering CBCT scans with the planning CT scan (pCT). A mean dose volume histogram () as the arithmetical mean of the rectum DVHs from each CBCT scan was obtained. A suitably defined 3D rectum model (Average Rectum, AR) was defined and its DVH (DVHAR) was calculated. DVHs were also evaluated for the first five CBCT scans using both methods ( and DVHAR5). The Lyman-Kutcher-Burman NTCP model with QUANTEC parameters was used to compare the calculated DVHs. The QUANTEC dose values were used to describe the time behaviour of the relative volumes using the Gamma Distribution for the frequency of the relative rectum volumes at each QUANTEC dose value. Results: No statistically significant differences between NTCPAR5 and NTCPAR and between NTCP and NTCP were found. The best agreement with the observed toxicity rate (0%) was obtained form DVHAR. The Gamma Distributions of the rectum volumes at the QUANTEC dose levels were found to be highly variable among the patients. Conclusions: Both dietary protocol and image guidance were found effective in limiting late rectal toxicity. AR was a better predictor for late rectal toxicity and better described the * Corresponding author. M. D'Andrea et al. 1040 rectum volume during the treatment course. Finally, from the Gamma distributions, and from our toxicity data, we can suggest V75 as the best predictor of late rectal toxicity.
Iranian Journal of Radiation Research, 2019
Background: In prostate radiotherapy, changes in the volume of the bladder and rectum can influence dose delivery. In this study, cone-beam computerised tomography (CBCT) imaging was used to assess volumetric, and corresponding radiation dosimetric changes, for the bladder and rectum in patients with prostate cancer treated using VMAT. Materials and Methods: Treatment planning computed tomography (simCT) and CBCT images were retrospectively evaluated in 22 patients with prostate cancer. Bladder and rectal volumes were recontoured in 176 CBCT images. CBCT images were used for VMAT treatment plan recalculation and to obtain bladder and rectum radiation doses. Results: Mean rectal volumes measured by CBCT were significantly larger than those estimated by simCT (P=0.001). A 14% increase in rectum volume resulted in a 9% increase in mean rectum doses. The percent volumes (Vx) of the rectum receiving 40, 50, 60 and 70 Gy doses based on CBCT results were significantly larger than those bas...