Effects of multiple beam arrangements on the tumor control probability (TCP) and normal tissue complication probability (NTCP) (original) (raw)
Related papers
Optimal Radiation Beam Profiles Considering Uncertainties in Beam Patient Alignment
Acta Oncologica, 1993
The often large uncertainties that exist in beam patient alignment during radiation therapy may require modification of the incident beams to ensure an optimal delivered dose distribution to the target volume. This problem becomes increasingly severe when the required dose distribution of the incident beams becomes more heterogeneous. A simple analytical formula is derived for the case when the fraction number is high, and the desired relative dose variations are small. This formula adjusts the fluence distribution of the incident beam so that the resultant dose distribution will be as close as possible to the desired one considering the uncertainties in beam patient alignment. When sharp dose gradients are important, for instance at the border of the target volume, the problem is much more difficult. It is shown here that, if the tumor is surrounded by organs at risk, it is generally best to open up the field by about one standard deviation of the positional uncertainty-that is a/2 on each side of the target volume. In principle it is simultaneously desirable to increase the prescribed dose by a few per cent compared to the case where the positional uncertainty is negligible, in order to compensate for the rounded shoulders of the delivered dose distribution. When the tissues surrounding the tumor no longer are dose limiting even larger increases in field size may be advantageous. For more critical clinical situations the positional uncertainty may even limit the success of radiotherapy. In such cases one generally wants to create a steeper dose distribution than the underlying random Gaussian displacement process allows. The problem is then best handled by quantifying the treatment outcome under the influence of the stochastic process of patient misalignment. Either the coincidence with the desired dose distribution, or the expectation value of the probability of achieving complication-free tumor control is maximized under the influence of this stochastic process. It is shown that the most advantageous treatment is to apply beams that are either considerably widened or slightly widened and over flattened near the field edges for small and large fraction numbers respectively.
British Journal of Radiology, 2012
Objective: The aim of this study was to investigate the effect of 6 and 15-MV photon energies on intensity-modulated radiation therapy (IMRT) prostate cancer treatment plan outcome and to compare the theoretical risks of secondary induced malignancies. Methods: Separate prostate cancer IMRT plans were prepared for 6 and 15-MV beams. Organ-equivalent doses were obtained through thermoluminescent dosemeter measurements in an anthropomorphic Aldersen radiation therapy human phantom. The neutron dose contribution at 15 MV was measured using polyallyl-diglycolcarbonate neutron track etch detectors. Risk coefficients from the International Commission on Radiological Protection Report 103 were used to compare the risk of fatal secondary induced malignancies in out-of-field organs and tissues for 6 and 15 MV. For the bladder and the rectum, a comparative evaluation of the risk using three separate models was carried out. Dose-volume parameters for the rectum, bladder and prostate planning target volume were evaluated, as well as normal tissue complication probability (NTCP) and tumour control probability calculations. Results: There is a small increased theoretical risk of developing a fatal cancer from 6 MV compared with 15 MV, taking into account all the organs. Dose-volume parameters for the rectum and bladder show that 15 MV results in better volume sparing in the regions below 70 Gy, but the volume exposed increases slightly beyond this in comparison with 6 MV, resulting in a higher NTCP for the rectum of 3.6% vs 3.0% (p50.166). Conclusion: The choice to treat using IMRT at 15 MV should not be excluded, but should be based on risk vs benefit while considering the age and life expectancy of the patient together with the relative risk of radiation-induced cancer and NTCPs.
Archives of Breast Cancer, 2021
Background: Nowadays, radiation therapy plays an important role in the treatment of breast cancer. The important point is the optimal control of the tumor along with the protection of organs at risk. This study aims to investigate and compare the radiobiological factors of the tumor and organs at risk in two different radiation therapy techniques of breast cancer. Methods: Ten left-sided breast cancer patients with breast-conservative surgery were selected for this study. Three-dimensional treatment planning was performed using CT scan images of the patients using PCRT 3D software. Two different tangential external beam techniques were compared: first, dual-isocentric technique (DIT) with two isocentre, one on the breast tissue, and the other one on the supraclavicular lymph nodes and second, a mono-isocentric technique (MIT) with one isocentre at the intersection of the tangential and the supraclavicular field. The total prescribed dose was 5000 cGy per 25 fractions. Dose-volume histograms (DVHs), Tumor control probability (TCP), and normal tissue complication probability (NTCP) curves were used to compare the dosimetric and radiobiological parameters of the tissues in the prementioned techniques. Results: The results showed that the maximum doses in planning target volume (PTV) with mean values of 109% and 110% in the SI and DIT were not significantly different in both techniques and that they were indeed at the optimum level based on the RTOG 1005 protocol. The dose homogeneity index in MMIT was more than that in DIT, while the conformity index and the mean TCP did not show a significant difference in the two techniques. Furthermore, minimum, mean, and maximum dose in the lung and the probability of pneumonitis decreased in MIT. On the other hand, the maximum dose, the dose of 33%, 66%, and 100% of the heart, and the probability of pericarditis in MIT were lower than the figure in DIT. Conclusion: Due to the absence of hot spots at the intersection of tangential and supraclavicular fields and the reduction of mechanical movements of the coach and collimator in MIT, the superiority of this method was confirmed.
An algorithm for maximizing the probability of complication-free tumour control in radiation therapy
Physics in Medicine and Biology, 1992
New radiobiological models are used to describe tumour and normal tissue reactions and to account for their dependence on the irradiated volume and inhomogeneities o f the delivered dose distribution and cell sensitivity. The probability of accomplishing complication-free tumour control is maximized by an iterative algorithm. The algorithm is demonstrated by applying it to a one-dimensional (ID) tumour model but also to a more clinically relevant 2 0 case. The new algorithm is n-dimensional 50 it could simultaneously optimize the dose delivery in a 3 0 volume and io principle also select the ideal beam orientations, beam modalities (photons, electrons, neutrons, etc) and optimal spectral distributions of the corresponding modalities. To make calculation time reasonable, 2 0-3 0 problems are most practical, and suitable beam orientations are preselected by the choice of irradiation kernel. The energy deposition kernel should therefore be selected in order to avoid irradiation through organs at risk. Clinically established dose response parameters for the tissues of interest are used to make the optimization as relevant as possible to the clinical problems at hand. The algorithm can be used even with a poorly selected kernel because it will always, as far as passible, avoid irradiating organs at risk. The generated dose distribution will be optimal with respect to the spatial distribution and assumed radiobiological properties of the tumour and normal tisues at risk for the kernel chosen. More specifically the probability of achieving tumour control without fatal complications in normal tissues is maximized. In the clinical examples a reduced tumour dose is seen at the border to sensitive organs at risk, but instead an increased dose just inside the tumour border is generated. The increased tumour dose has the effect that the dose fall-off is as steep as possible at the border to organs at risk.
Medical Physics, 2010
A physician's decision regarding an ideal treatment approach ͑i.e., radiation, surgery, and/or hormonal͒ for prostate carcinoma is traditionally based on a variety of metrics. One of these metrics is the risk of radiation-induced second primary cancer following radiation treatments. The aim of this study was to investigate the significance of second cancer risks in out-of-field organs from 3D-CRT and IMRT treatments of prostate carcinoma compared to baseline cancer risks in these organs. Methods: Monte Carlo simulations were performed using a detailed medical linear accelerator model and an anatomically realistic adult male whole-body phantom. A four-field box treatment, a four-field box treatment plus a six-field boost, and a seven-field IMRT treatment were simulated. Using BEIR VII risk models, the age-dependent lifetime attributable risks to various organs outside the primary beam with a known predilection for cancer were calculated using organ-averaged equivalent doses. Results: The four-field box treatment had the lowest treatment-related second primary cancer risks to organs outside the primary beam ranging from 7.3ϫ 10 −9 to 2.54ϫ 10 −5 % / MU depending on the patients age at exposure and second primary cancer site. The risks to organs outside the primary beam from the four-field box and six-field boost and the seven-field IMRT were nearly equivalent. The risks from the four-field box and six-field boost ranged from 1.39ϫ 10 −8 to 1.80 ϫ 10 −5 % / MU, and from the seven-field IMRT ranged from 1.60ϫ 10 −9 to 1.35ϫ 10 −5 % / MU. The second cancer risks in all organs considered from each plan were below the baseline risks. Conclusions: The treatment-related second cancer risks in organs outside the primary beam due to 3D-CRT and IMRT is small. New risk assessment techniques need to be investigated to address the concern of radiation-induced second cancers from prostate treatments, particularly focusing on risks to organs inside the primary beam.
Physics in medicine and …, 2008
It has been long known that patients treated with ionizing radiation carry a risk of developing a second cancer in their lifetimes. Factors contributing to the recently renewed concern about the second cancer include improved cancer survival rate, younger patient population as well as emerging treatment modalities such as intensity-modulated radiation treatment (IMRT) and proton therapy that can potentially elevate secondary exposures to healthy tissues distant from the target volume. In the past 30 years, external-beam treatment technologies have evolved significantly, and a large amount of data exist but appear to be difficult to comprehend and compare. This review article aims to provide readers with an understanding of the principles and methods related to scattered doses in radiation therapy by summarizing a large collection of dosimetry and clinical studies. Basic concepts and terminology are introduced at the beginning. That is followed by a comprehensive review of dosimetry studies for external-beam treatment modalities including classical radiation therapy, 3D-conformal x-ray therapy, intensity-modulated x-ray therapy (IMRT and tomotherapy) and proton therapy. Selected clinical data on second cancer induction among radiotherapy patients are also covered. Problems in past studies and controversial issues are discussed. The needs for future studies are presented at the end. Contents
Purpose: To evaluate the biologic differences in treatment plans with different number of beams on 3D conformal radiotherapy for breast cancer patients, and compute the percent of probability to tumor control and complication of normal tissue probability using matlap program. Then determine the optimum plan through these values. Materials and Methods The study potentially included 13 of the female patients diagnosed with breast cancer who were treated after surgery in the Elkhir Hospital and Mansoura University (radiotherapy unit). All patient applied to a standard dose of 40 Gy/15 per fractions to both breast and supraclavicular. Two treatment plans were done by Prowess Panther TPS (Treatment Planning System) and changing the number of beams for each patient then dose-volume histogram (DVH) for each patient was imported to MATLAB program. Results All the results showed that the average TCP% of PTV of the plans that contains more numbers of beams is 54.2 %, while in other plans, 54.6%, meaning that in more numbers of beams the tumor control is nearly the same as less numbers of beams. While the average NTCP of heart (normal tissue) is 23.5% with more number of beams and 25.4 % with less number meaning that complication of some normal tissue such as heart is slight decrease with increasing the number of beams (less damage), but no significance value, also increasing the number of beams of the other OAR such as lung result in slight decrease in damage to normal tissue, but no significance also. Conclusion The numbers of beams are less important to verify control tumor and complications to normal tissue probabilities with planning proposed because the damage to normal tissue and the tumor control probability has nearly the same effect with changing the number of beams. Radio oncologist and medical physicist must make a decision about treatment though the accurate values of TCP and NTCP, and this achieved by test the accurate plan based on these values. MATLAB program is a tool to compute these values. This study avoids the trials and errors that medical physicists counteract by increasing or decreasing the number of beams, and this
Computational and Mathematical Methods in Medicine, 2016
An overview of radiotherapy (RT) induced normal tissue complication probability (NTCP) models is presented. NTCP models based on empirical and mechanistic approaches that describe a specific radiation induced late effect proposed over time for conventional RT are reviewed with particular emphasis on their basic assumptions and related mathematical translation and their weak and strong points.
Radiotherapy and Oncology, 2009
Purpose: To evaluate the photon and neutron out-of-field dose equivalents from 6-and 18-MV intensitymodulated radiation therapy (IMRT) and to investigate the impact of the differences on the associated risk of induced second malignancy using a Monte Carlo model. Methods and materials: A Monte Carlo model created with MCNPX was used to calculate the out-of-field photon dose and neutron dose equivalent from simulated IMRT of the prostate conducted at beam energies of 6 and 18 MV. The out-of-field dose equivalent was calculated at the locations of sensitive organs in an anthropomorphic phantom. Based on these doses, the risk of secondary malignancy was calculated based on organ-, gender-, and age-specific risk coefficients for a 50-year-old man. Results: The Monte Carlo model predicted much lower neutron dose equivalents than had been determined previously. Further analysis illuminated the large uncertainties in the neutron dose equivalent and demonstrated the need for better determination of this value, which plays a large role in estimating the risk of secondary malignancies. The Monte Carlo calculations found that the differences in the risk of secondary malignancies conferred by high-energy IMRT versus low-energy IMRT are minimal and insignificant, contrary to prior findings. Conclusions: The risk of secondary malignancy associated with high-energy radiation therapy may not be as large as previously reported, and likely should not deter the use of high-energy beams. However, the large uncertainties in neutron dose equivalents at specific locations within the patient warrant further study so that the risk of secondary cancers can be estimated with greater accuracy.
The normal tissue sparing potential of adaptive strategies in radiotherapy of bladder cancer
Acta Oncologica, 2008
Background and purpose. To improve the outcome in bladder radiotherapy by improving treatment conformation, we have investigated various adaptive treatment strategies involving on-board tumour/target visualisation for the bladder. The strategies are compared in terms of the amount of normal tissue enclosed within the PTV and the percentage volume overlap between the CTVs (i.e. bladders) on planning and repeat CT scans. Materials and methods. Five male bladder cancer patients having a planning and either 7 or 8 repeat scans during treatment were included in this study. Tumour positions were simulated on the sup/inf/ant/post/left/right wall and were identified in the repeat scans based on a reference coordinate system. The reference origin was positioned on an axis joining the centres of mass of the prostate and the bladder at a point mid way between the centre of mass of the bladder and the inferior bladder wall. Tumour positions on the repeat CTVs were overlapped using translation with corresponding positions on the planning CTV, after which the required isotropic and anisotropic margins were determined using a previously published margin calculation algorithm. Calculations were performed to find the margins required to enclose the envelope covering all repeat CTVs and those enclosing the repeat CTVs one by one, i.e. simulating adaptation on daily basis. These results were compared to optimising the margins for all repeat scans, firstly without any positional correction of the CTV and secondly after applying the optimum translation for the whole bladder. Results. Compared with optimisation of all scans, daily adaptation increased the average percentage volume overlap by 20% to 79Á82% for the various tumour positions. The volume overlap achieved was similar for no translation of the isocentre (average 79%), and slightly higher with optimal translation (average 85%). Conclusion. Translation of the isocentre according to tumour position did not compromise the normal tissue irradiation compared with no translation of the isocentre. Optimal translation of the isocentre is superior in terms of normal tissue sparing.