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| 2. |
- Flejmer, Anna M., et al.
(författare)
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Analytical Anisotropic Algorithm versus Pencil Beam Convolution for treatment planning of breast cancer: implications for target coverage and radiation burden of normal tissue
- 2015
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Ingår i: Anticancer Research. - : International Institute of Anticancer Research. - 0250-7005 .- 1791-7530. ; 35:5, s. 2841-2848
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Tidskriftsartikel (refereegranskat)abstract
- Aim: The present study aimed to investigate the implications of using the analytical anisotropic algorithm (AAA) for calculation of target coverage and radiation burden of normal tissues. Most model parameters, recommendations and planning guidelines associated with a certain outcome are from the era of pencil beam convolution (PBC) calculations on relatively simple assumptions of energy transport in media. Their relevance for AAA calculations that predict more realistic dose distributions needs to be evaluated. Patients and Methods: Forty patients with left-sided breast cancer receiving 3D conformal radiation therapy were planned using PBC with a standard protocol with 50 Gy in 25 fractions according to existing re-commendations. The plans were subsequently recalculated with the AAA and relevant dose parameters were determined and compared to their PBC equivalents. Results: The majority of the AAA-based plans had a significantly worse coverage of the planning target volume and also a higher maximum dose in hotspots near sensitive structures, suggesting that these criteria could be relaxed for AAA-calculated plans. Furthermore, the AAA predicts higher volumes of the ipsilateral lung will receive doses below 25 Gy and smaller volume doses above 25 Gy. These results indicate that lung tolerance criteria might also have to be relaxed for AAA planning in order to maintain the level of normal tissue toxicity. The AAA also predicts lower doses to the heart, thus indicating that this organ might be more sensitive to radiation than thought from PBC-based calculations. Conclusion: The AAA should be preferred over the PBC algorithm for breast cancer radiotherapy as it gives more realistic dose distributions. Guidelines for plan acceptance might have to be re-evaluated to account for differences in dose predictions in order to maintain the current levels of control and complication rates. The results also suggest an increased radiosensitivity of the heart, thus indicating that a revision of the current models for cardiovascular complications may be needed.
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- Flejmer, Anna M., et al.
(författare)
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Clinical implications of the ISC technique for breast cancer radiotherapy and comparison with clinical recommendations
- 2014
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Ingår i: Anticancer Research. - : International Institute of Anticancer Research. - 0250-7005 .- 1791-7530. ; 34:7, s. 3563-3568
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The project studied the implications of using the irregular surface compensator (ISC) technique in comparison to three-dimensional conformal radiation therapy (3D-CRT) for breast cancer treatment. ISC is an electronic compensation algorithm that modulates the fluence across the radiation fields to compensate for irregularly shaped surfaces and deliver a homogeneous dose to a compensation plane. Methods: Ten breast cancer patients (five left- and five right-sided) were planned with both techniques. The planning was done for 50 Gy in 25 fractions with 2 Gy per fraction in all patients. Physical parameters such as doses to the clinical target volume (CTV-T) and the planned target volume (PTV), heterogeneity index and doses to lung and heart were determined and compared for the treatment plans. Results: The ISC technique led to significantly better coverage of the CTV-T and PTV in almost all patients with statistically significant better homogeneity of the dose distribution. The contralateral lung and the heart receive the same doses with both ISC and 3D-CRT plans. However, ISC showed a trend towards decreasing the volumes of the ipsilateral lung irradiated with high doses. Consequently this led to better compliance with the national recommendations for breast radiotherapy. Conclusion: The ISC technique leads to an improvement of the target coverage and the radiation burden of the ipsilateral lung thus allowing better compliance with the national recommendations and increasing the potential for improved quality of life for breast cancer patients. It should therefore be preferred over 3D-CRT for breast cases with difficult dose homogeneity to the PTV or CTV-T.
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- Fowler, Jack F., et al.
(författare)
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Is the α/β ratio for prostate tumours really low and does it vary with the level of risk at diagnosis?
- 2013
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Ingår i: Anticancer Research. - : International Institute of Anticancer Research (IIAR). - 0250-7005 .- 1791-7530. ; 33:3, s. 1009-1011
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Tidskriftsartikel (refereegranskat)abstract
- Aim: To answer the questions: Is the α/β ratio (radiosensitivity to size of dose-per-fraction) really low enough to justify using a few large dose fractions instead of the traditional many small doses? Does this parameter vary with prognostic risk factors? Methods and Materials: Three large statistical overviews are critiqued, with results for 5,000, 6,000 and 14,000 patients with prostate carcinoma, respectively. Results: These major analyses agree in finding the average α/β ratio to be less than 2 Gy: 1.55, (95% confidence interval=0.46-4.52), 1.4 (0.9-2.2), and the third analysis 1.7 (1.4-2.2) by ASTRO and 1.6 (1.2-2.2) by Phoenix criteria. All agree that α/β values do not vary significantly with the low, intermediate, high and “all included” risk factors. Conclusion: The high sensitivity to dose-per-fraction is an intrinsic property of prostate carcinomas and this supports the use of hypofractionation to increase the therapeutic gain for these tumours with dose-volume modelling to reduce the risk of late complications in rectum and bladder.
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| 8. |
- Kjellsson Lindblom, Emely, et al.
(författare)
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Hypoxia Induced by Vascular Damage at High Doses Could Compromise the Outcome of Radiotherapy
- 2019
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Ingår i: Anticancer Research. - : Anticancer Research USA Inc.. - 0250-7005 .- 1791-7530. ; 39:5, s. 2337-2340
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Tidskriftsartikel (refereegranskat)abstract
- Background/Aim: This study investigated the impact of temporary vascular collapse on tumour control probability (TCP) in stereotactic body radiotherapy (SBRT), taking into account different radiosensitivities of chronically and acutely hypoxic cells. Materials and Methods: Three-dimensional tumours with heterogeneous oxygenation were simulated assuming different fractions of collapsed vessels at every treatment fraction. The modelled tumours contained a chronically hypoxic subvolume of 30-60% of the tumour diameter, and a hypoxic fraction ≤5 mm Hg of 30-50%. The rest of the tumours were well-oxygenated at the start of the simulated treatment. Results: For all simulated cases, the largest reduction in TCP from 97% to 2% was found in a tumour with a small chronically hypoxic core treated with 60 Gy in eight fractions and assuming a treatment-induced vascular collapse of 35% in the well-oxygenated region. Conclusion: The timing of SBRT fractions should be considered together with the tumour oxygenation to avoid loss of TCP in SBRT.
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| 9. |
- Kjellsson Lindblom, Emely, et al.
(författare)
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Radiation-induced vascular damage and the impact on the treatment outcome of stereotactic body radiotherapy
- 2019
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Ingår i: Anticancer Research. - : Anticancer Research USA Inc.. - 0250-7005 .- 1791-7530. ; 39:6, s. 2721-2727
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Tidskriftsartikel (refereegranskat)abstract
- Background/Aim: The aim of this study was to investigate radiation-induced tumour vascular damage and its impact thereof on the outcome of stereotactic body radiotherapy (SBRT). Materials and Methods: Vessel densities in animal tumours before and after a single dose of 20 Gy were quantified and used as input for simulations of three-dimensional tumours with heterogeneous oxygenation. SBRT treatments of the modelled tumours in 1-8 fractions were simulated. The impact of vessel collapse on the outcome of SBRT was investigated by calculating tumour control probability (TCP) and the dose required to obtain a TCP of 50% (D50). Results: A radiation-induced increase of acute hypoxia in tumours during SBRT treatment could be simulated based on the experimental data. The D50 values for these tumours were higher than for the simulated tumours without vessel collapse. Conclusion: The vascular changes after high doses of radiation could compromise the outcome of SBRT by increasing tumour hypoxia.
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| 10. |
- Sandström, Helena, et al.
(författare)
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Simultaneous truth and performance level estimation method for evaluation of target contouring in radiosurgery
- 2021
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Ingår i: Anticancer Research. - : Anticancer Research USA Inc.. - 0250-7005 .- 1791-7530. ; 41:1, s. 279-288
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Tidskriftsartikel (refereegranskat)abstract
- Background/Aim: The problem of lack of standardisation in target delineation and herewith the variability of target contours in Gamma Knife radiosurgery is as severe as in linac-based radiotherapy in general. The first aim of this study was to quantify the contouring variability for a group of five radiosurgery targets and estimate their true-volume based on multiple delineations using the Simultaneous Truth and Performance Level Estimation (STAPLE) algorithm. The second aim was to assess the robustness of the STAPLE method for the assessment of the true-volume, with respect to the number of contours available as input. Patients and Methods: A multicentre analysis of the variability in contouring of five cases was performed. Twelve contours were provided for each case by experienced planners for Gamma Knife. To assess the robustness of the STAPLE method with respect to the number of contours used as input, sets of contours were randomly selected in the analysis. Results: A high similarity was observed between the STAPLE generated true-volume and the 50%-agreement volume when all 12 available contours were used as input (90-100%). Lower similarity was observed with smaller sets of contours (10-70%). Conclusion: If a high number of input contours is available, the STAPLE method provides a valuable tool in the estimation of the true volume of a target based on multiple contours as well as the sensitivity and specificity for each input contour relative to the true volume of that structure. The robustness of the STAPLE method for rendering the true target volume depends on the number of contours provided as input and their variability with respect to shape, size and position.
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