PO-0912: The risk of radiation-induced cancer following VMAT vs. IMPT of prostate cancer (original) (raw)
Related papers
Radiation treatment dose optimisation using Poisson tumour control probability parameters
Journal of Physics: Conference Series, 2014
This study examines the Poisson tumour control probability (TCP) γ 37 and D 37 parameters of a uniformly irradiated numerical tumour model using changes in tumour burden as a surrogate for treatment response information. An optimum dose D i for a tumour subvolume element V i is described that maximizes TCP as a function of fixed tumour integral dose ξ. TCP was calculated for spatially-varying clonogen density for a total 10 8 cells and radiosensitivity α with mean radiosensitivity in the range 0.4 -1.0 Gy -1 . A bivariate normal distribution is used to describe the radiosensitivity α and the linear term of the linear-quadratic (LQ) cell kill governed the changes in the regional tumour burden within sub-volumes V i . The optimum dose distribution, D i , for V i is obtained as a function of fixed tumour integral dose ξ. For a uniform dose delivery and for TCP = 37%, γ 37 and D 37 are described by the effective radiosensitivity α eff and the effective clonogen number N 0,eff , respectively. α eff is equivalent to differential dose changes in the number of clonogenic cells (tumour burden). The γ 37 values were found to be inversely correlated with variance of the probability density function of the α distribution. For the biologically optimum dose distribution, γ 37 was found to converge to the theoretical maximum limit and D 37 was found to reduce relative to that obtained for the uniform dose case. The TCP parameters γ 37 and D 37 could thus be useful in optimising individual radiation treatment doses even when tumour heterogeneity is taken into account.
Physical and biological aspects of modern radiation therapy planning
Nowotwory, 2003
Over the last 20 years radiation oncology has been exposed to exciting biological and technical developments that have a potential to significantly improve the outcomes of cancer treatment. These developments present new opportunities but also create new challenges for the practitioners of radiation oncology. New tools, methods and techniques are required to fully utilize these developments to create, evaluate and optimize the process of radiation treatment. Here a number of tools for planning modern radiation therapy are presented and discussed. In particular, the need for biological considerations in the treatment planning process is emphasized and a concept of Equivalent Uniform Dose (EUD) based on modeling of cell survival and tissue architecture is described. Examples of IMRT dose distributions for a head and neck cancer developed using purely dosimetric (that is, dose and dose-volume) considerations and using EUD-based considerations are shown. Nowoczesna radioterapia - wp∏yw ...
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.
Optimization and Comparison of Normal Tissue Complication Probability Models in Radiotherapy
In the context of cancer radiotherapy, toxicity prediction is of the major importance to evaluate and compare dose plans. Normal tissue complication probability (NTCP) models are the major methods to predict and prevent the presentation of toxicities, but they have to be optimized and their predictive capacities have to be evaluated. In this investigation, the six main NTCP models were studied and their parameters were fitted on prostate cancer. The results argue that rectum toxicity within 2 years shows some characteristics of a serial organ (n=0.35). Poisson EUD and Logit EUD models have the better predictive abilities and their use in clinical routine should be studied in further works.
Radiotherapy and Oncology, 2013
Most new radiation techniques, have been introduced primarily to reduce the dose to normal tissues in order to prevent radiation-induced side effects. Radiotherapy with protons is such a radiation technique that due to its superior beam properties compared to photons enables better sparing of normal tissues. This paper describes a stepwise methodology to select patients for proton therapy when the primary aim is to reduce side effects. This method has been accepted by the Dutch health authorities to select patients for proton therapy. In addition, an alternative method is described in case randomised controlled trials are considered not appropriate.
Radiotherapy and Oncology, 2009
Purpose: Retrospective study of 3D clinical treatment plans based on radiobiological considerations in the choice of the reference dose level from tumor dose-volume histograms. Methods and materials: When a radiation oncologist evaluates the 3D dose distribution calculated by a treatment planning system, a decision must be made on the percentage dose level at which the prescribed dose should be delivered. Much effort is dedicated to deliver a dose as uniform as possible to the tumor volume. However due to the presence of critical organs, the result may be a rather inhomogeneous dose distribution throughout the tumor volume. In this study we use a formulation of tumor control probability (TCP) based on the linear quadratic model and on a parameter, the F factor. The F factor allows one to write TCP, from the heterogeneous dose distribution (TCP{(e j ,D j )}), as a function of TCP under condition of homogeneous irradiation of tumor volume (V) with dose D (TCP(V,D)). We used the expression of the F factor to calculate the ''ideal" percentage dose level (iDL r ) to be used as reference level for the prescribed dose D delivery, so as to render TCP{(e j ,D j )} equal to TCP(V,D).Methods and materials: The 3D dose distributions of 53 clinical treatment plans were re-evaluated to derive the iDL r and to compare it with the one (D tp L) to which the dose was actually administered. Results: For the majority of prostate treatments, we observed a low overdosing following the choice of a D tp L lower than the iDL r. While for the breast and head-and-neck treatments, the method showed that in many cases we underdosed choosing a D tp L greater than the iDL r . The maximum difference between the iDL r and the D tp L was À3.24% for one of the head-and-neck treatments. Conclusions: Using the TCP model, the probability of tumor control is compromised following an incorrect choice of D tp L; so we conclude that the application of the F factor is an effective tool and clinical aid to derive the optimal reference dose level from the dose-volume histogram (DVH) of each treatment plan.
2013
Stereotactic body radiotherapy Non-small cell lung cancer Dose-response modeling Linear-quadratic formalism Biologically effective dose a b s t r a c t Background and purpose: To compare the linear-quadratic (LQ) and the LQ-L formalism (linear cell survival curve beyond a threshold dose d T ) for modeling local tumor control probability (TCP) in stereotactic body radiotherapy (SBRT) for stage I non-small cell lung cancer (NSCLC). Materials and methods: This study is based on 395 patients from 13 German and Austrian centers treated with SBRT for stage I NSCLC. The median number of SBRT fractions was 3 (range 1-8) and median single fraction dose was 12.5 Gy (2.9-33 Gy); dose was prescribed to the median 65% PTV encompassing isodose (60-100%). Assuming an a/b-value of 10 Gy, we modeled TCP as a sigmoid-shaped function of the biologically effective dose (BED). Models were compared using maximum likelihood ratio tests as well as Bayes factors (BFs). Results: There was strong evidence for a dose-response relationship in the total patient cohort (BFs > 20), which was lacking in single-fraction SBRT (BFs < 3). Using the PTV encompassing dose or maximum (isocentric) dose, our data indicated a LQ-L transition dose (d T ) at 11 Gy (68% CI 8-14 Gy) or 22 Gy (14-42 Gy), respectively. However, the fit of the LQ-L models was not significantly better than a fit without the d T parameter (p = 0.07, BF = 2.1 and p = 0.86, BF = 0.8, respectively). Generally, isocentric doses resulted in much better dose-response relationships than PTV encompassing doses (BFs > 20). Conclusion: Our data suggest accurate modeling of local tumor control in fractionated SBRT for stage I NSCLC with the traditional LQ formalism. (M. Guckenberger). Radiotherapy and Oncology xxx (2013) xxx-xxx Contents lists available at ScienceDirect Radiotherapy and Oncology j o u r n a l h o m e p a g e : w w w . t h e g r e e n j o u r n a l . c o m Please cite this article in press as: Guckenberger M et al. Applicability of the linear-quadratic formalism for modeling local tumor control probability in high dose per fraction stereotactic body radiotherapy for early stage non-small cell lung cancer. Radiother Oncol (2013), http://dx.