Impact of Breast Size on Dosimetric Indices in Proton Versus X-ray Radiotherapy for Breast Cancer

Deep inspiration breath hold (DIBH) radiotherapy is a technique used to manage early stage left-sided breast cancer. This study compared dosimetric indices of patient-specific X-ray versus proton therapy DIBH plans to explore differences in target coverage, radiation doses to organs at risk, and the impact of breast size. Radiotherapy plans of sixteen breast cancer patients previously treated with DIBH radiotherapy were re-planned with hybrid inverse-planned intensity modulated X-ray radiotherapy (h-IMRT) and intensity modulated proton therapy (IMPT). The total prescribed dose was 40.05 Gy in 15 fractions for all cases. Comparisons between the clinical, h-IMRT, and IMPT evaluated doses to target volumes, organs at risk, and correlations between doses and breast size. Although no differences were observed in target volume coverage between techniques, the h-IMRT and IMPT were able to produce more even dose distributions and IMPT delivered significantly less dose to all organs at risk than both X-ray techniques. A moderate negative correlation was observed between breast size and dose to the target in X-ray techniques, but not IMPT. Both h-IMRT and IMPT produced plans with more homogeneous dose distribution than forward-planned IMRT and IMPT achieved significantly lower doses to organs at risk compared to X-ray techniques.

Clinically Oriented Target Contour Evaluation Using Geometric and Dosimetric Indices Based on Simple Geometric Transformations

Purpose: In radiotherapy, geometric indices are often used to evaluate the accuracy of contouring. However, the ability of geometric indices to identify the error of contouring results is limited primarily because they do not consider the clinical background. The purpose of this study is to investigate the relationship between geometric and clinical dosimetric indices. Methods: Four different types of targets were selected (C-shaped target, oropharyngeal cancer, metastatic spine cancer, and prostate cancer), and the translation, scaling, rotation, and sine function transformation were performed with the software Python to introduce systematic and random errors. The transformed contours were regarded as reference contours. Dosimetric indices were obtained from the original dose distribution of the radiotherapy plan. The correlations between geometric and dosimetric indices were quantified by linear regression. Results: The correlations between the geometric and dosimetric indices were inconsistent. For systematic errors, and with the exception of the sine function transformation (R2: 0.023-0.04, P > 0.05), the geometric transformations of the C-shaped target were correlated with the D98% and Dmean (R2: 0.689-0.988), 80% of which were P < 0.001. For the random errors, the correlations obtained by the all targets were R2 > 0.384, P < 0.05. The Wilcoxon signed-rank test was used to compare the spatial direction resolution capability of geometric indices in different directions of the C-shaped target (with systematic errors), and the results showed only the volumetric geometric indices with P < 0.05. Conclusions: Clinically, an assessment of the contour accuracy of the region-of-interest is not feasible based on geometric indices alone. Dosimetric indices should be added to the evaluations of the accuracy of the delineation results, which can be helpful for explaining the clinical dose response relationship of delineation more comprehensively and accurately.

Clinically oriented contour evaluation using geometric and dosimetric indices based on simple geometric transformations

Background: In radiotherapy, geometric indices are often used to evaluate the accuracy of contouring; however, the ability of geometric indices to identify the error of contouring results is limited, mainly because it does not consider any clinical background. To study the relationship between geometric indices and dosimetric indices, four different types of targets were selected to introduce the systematic and random geometric errors in the delineation process. Materials and Methods: The C-shaped target outlined in the American Association of Physicists in Medicine (AAPM) TG-119 report (The report of Task Group 119 of the AAPM) and the targets of three actual cases of oropharyngeal cancer, metastatic spine cancer, and prostate cancer were selected as the test contours that needed to be modified. Python software was used to perform translation, scaling, rotating and sine function transformation to introduce systematic and random errors into the above contours. These geometrically transformed contours were regarded as reference contours corrected by systematic and random errors. The corresponding dosimetric indices were obtained from the original dose distribution of the radiotherapy plan, and correlations (R²) between geometric and dosimetric indices were quantified through linear regression. The Wilcoxon signed rank test was used to compare the ability of spatial-direction discrimination between the geometric indices of different directions of transformations. Results: The correlations between the geometric and dosimetric indices were inconsistent for the targets. For systematic errors, except for the sine function transformation (R²: 0.023–0.04, p＞0.05), the geometric transformations of the C-shaped target’s planning target volume (C-PTV) had correlations with the dosimetric indices D98% and Dmean (R²: 0.689–0.988), 80% of which were strongly correlated (R² > 0.8). For the random errors, the correlation coefficients of the actual cases were also high, R2 > 0.384, p < 0.05. The results of Wilcoxon signed rank test showed that only the p-values of volumetric geometric indices of C-PTV were less than 0.05. Conclusions: Clinically, an assessment of the contour accuracy of the region of interest is not feasible based on geometric indices alone, and should be combined with dosimetric indices. Keywords: Contour evaluation, Geometric indices, Dosimetric indices, Geometric transformation

Clinically oriented contour evaluation using geometric and dosimetric indices based on simple geometric transformations

Background: In radiotherapy, geometric indices are often used to evaluate the accuracy of contouring; however, the ability of geometric indices to identify the error of contouring results is limited, and they do not consider any clinical background. Based on the reference contouring, we systematically introduced the known geometric errors to study the relationship between geometric indices and dosimetric indices and evaluated the clinical feasibility of assessing the accuracy of contouring based on geometric indices alone.Materials and Methods: A C-shaped target, organ at risk (Core), and intensity-modulated radiotherapy (IMRT) plan outlined in the American Association of Physicists in Medicine (AAPM) TG-119 report (The report of Task Group 119 of the AAPM) were used as references. Translation, scaling, rotation (except for the Core), and sine function transformation were performed to simulate the test contours. The corresponding dosimetric indices were obtained from the original dose distribution of the radiotherapy plan, and correlations (R²) between geometric and dosimetric indices were quantified through linear regression. The Wilcoxon signed rank test was used to compare the differences between the geometric indices of three different directions of translation transformations.Results: The correlations between the geometric and dosimetric indices were inconsistent for the contouring of the target and Core after the geometric transformation. Except for the sine function transformation (R²: 0.04–0.023, P > 0.05), the other geometric transformations of the planning target volume (PTV) had correlations with the dosimetric indices D98% and Dmean (R²: 0.689–0.988), 80% of which were strongly correlated. The correlation results for the other geometric transformations in the Core were similar to those in the PTV except for the posterior direction transformation. The results of Wilcoxon signed rank test showed that only the P-values of volumetric geometric indices of PTV were less than 0.05.Conclusions: The dosimetric indices are heavily influenced by the contour differences, thus highlighting their importance in the evaluation process. Clinically, an assessment of the contour accuracy of the region of interest is not feasible based on geometric indices alone, and should be combined with dosimetric indices.

Dosimetric comparison of fixed field dynamic IMRT and VMAT techniques in simultaneous integrated boost radiotherapy of Prostate Cancer

Background: As the high risk prostate cancer can be benefited from the combination of hypo-fractionated radiotherapy and pelvic conventional fraction radiotherapy, the comparison between fixed field dynamic IMRT and VMAT techniques can provide suggestion for clinical treatment. Methods: We selected 10 patients with high risk prostate cancer who received radiotherapy at Sun Yat-sen University Cancer Center from 2013 January to 2013 December. The target including the prostate, seminal vesicle and pelvic lymph nodes. With the same prescription and optimized parameters, 9 field IMRT, single arc and double arc VMAT treatment plans were designed, which are expressed by 9F, 1ARC and 2ARC respectively. The dose distribution of the targets, organs at risk (OAR), monitor units (MUs), treatment time and gamma pass ratios of dose verification were compared. Results: The D2%(69.37±0.89)Gy,D50%(66.92±0.63)Gy, HI(0.09±0.02) and CI(0.83±0.05) of PTV1 in 9F were slightly better than those of 1ARC which were (71.13±1.21) Gy, (68.50±0.76)Gy, (0.12±0.02), (0.74±0.07), except D98% , the difference were significant(p<0.05). All dosimetric indices of PTV1 in 9F and 2ARC were close and has no significant differences (p>0.05). The V95 %(99.45±0.78)% of PTV2 in 9F was slightly better than that in 1ARC (99.35±1.28)%, the difference was significant (p<0.05). All dosimetric indices of PTV2in 9F and 2ARC were close and the difference were no significant (p>0.05). The Dmean of bladder and the V67.5Gyof rectum between all three plans were similarity The Dmean of left and right femoral in 1ARC and 2ARC were lower than that in 9F, and the difference was significant (p<0.05). Other dosimetric indices of OARs in 9F were lower than those in 1ARC and 2ARC, and much lower than 1ARC, the difference were significant (p<0.05). The mean monitor units in 1ARC and 2ARC were fewer by 70.0% and 67.2% in comparison with 9F. The treatment mean time in 1ARC and 2ARC were shorter by 81.7% and 61% in comparison with 9F. The verification pass ratios of γ(3%/3mm)were 97.8% (9F), 98.9% (1ARC) and 99.4% (2ARC) respectively, the difference were significant(p<0.05). Conclusion: Compared with IMRT, VMAT improved delivery efficiency noticeably. Two arcs provided comparable tumor dosimetric coverage, but performed worse in dose sparing for bladder, rectum and small bowel. IMRT plan was better than VMAT in prostate cancer simultaneous integrated boost radiotherapy.

Clinically oriented contour evaluation using geometric and dosimetric indices based on geometric transformation

Background : In radiotherapy, geometric indices are often used to evaluate the accuracy of contouring; However, the ability of geometric indices to identify the error of contouring results is limited, and there is lack of clinical background. Based on the reference contouring, we systematically introduced geometric errors to study the relationship between geometric and dosimetric indices and evaluated the clinical feasibility of assessing the accuracy of contouring based on geometric indices alone. Materials and Methods: A C-shaped target, organ at risk (Core), and intensity-modulated radiotherapy (IMRT) plan outlined in the American Association of Physicists in Medicine (AAPM) TG-119 report (The report of Task Group 119 of the AAPM) were used as references. Translation, scaling, rotation (except for the Core), and sine function transformation were performed to simulate the contouring results. The corresponding dosimetric indices were obtained from the original dose distribution of the radiotherapy plan, and correlations (R²) between geometric indices and dosimetric indices were quantified through linear regression. The clinical applicability of the threshold for geometric indices was analyzed by combining the geometric indices and dose difference diagram. Results: The correlations between the geometric and dosimetric indices were different and inconsistent for the contouring of the target and Core after the geometric transformation simulation. Except for the sine function transformation (R²: 0.04–0.023, p > 0.05), the other three geometric indices of the planning target volume (PTV) had strong correlations with the dosimetric indices D98% and D mean (R²: 0.689–0.988), 80% of which were strongly correlated with a p < 0.001. The correlation results for the other geometric transformations in the Core were similar to those in the PTV except for the down shift transformation. Conclusions: The dosimetric indices are heavily influenced by the contour differences, thus highlighting their importance in the evaluation process. Clinically, an assessment of the contour accuracy of the region of interest is not feasible based on geometric indices alone, and should be combined with dosimetric indices. Keywords: Contour evaluation, Geometric indices, Dosimetric indices, Geometric transformation simulation