Dosimetric validation of two different radiobiological models for parotid gland functionality of tongue cancer (original) (raw)
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International Journal of Radiation Oncology*Biology*Physics, 2010
The dose-response relationship of the parotid gland has been described most frequently using the Lyman-Kutcher-Burman model. However, various other normal tissue complication probability (NTCP) models exist. We evaluated in a large group of patients the value of six NTCP models that describe the parotid gland dose response 1 year after radiotherapy. A total of 347 patients with head-and-neck tumors were included in this prospective parotid gland dose-response study. The patients were treated with either conventional radiotherapy or intensity-modulated radiotherapy. Dose-volume histograms for the parotid glands were derived from three-dimensional dose calculations using computed tomography scans. Stimulated salivary flow rates were measured before and 1 year after radiotherapy. A threshold of 25% of the pretreatment flow rate was used to define a complication. The evaluated models included the Lyman-Kutcher-Burman model, the mean dose model, the relative seriality model, the critical volume model, the parallel functional subunit model, and the dose-threshold model. The goodness of fit (GOF) was determined by the deviance and a Monte Carlo hypothesis test. Ranking of the models was based on Akaike's information criterion (AIC). None of the models was rejected based on the evaluation of the GOF. The mean dose model was ranked as the best model based on the AIC. The TD(50) in these models was approximately 39 Gy. The mean dose model was preferred for describing the dose-response relationship of the parotid gland.
Validation of a new method for dose determination in radiosurgery: "The Sosa Model" (Atena Editora)
Validation of a new method for dose determination in radiosurgery: "The Sosa Model" (Atena Editora), 2023
Objectives: to compare and validate the doses determined according to the novel method for calculating doses in radiosurgery called the Sosa Model (MS) with the dose protocols of national and international institutions. Material and Method: retrospective study on 403 tumor lesions of different histology found in 172 patients treated by radiosurgery at the Gamma Knife Dominican Center (CGKD), using MRI images of 1.5 and 3.0 Tesla with protocol for neuronavigation. In MS, the Sosa Score (SS) is obtained by adding 3 scores to a constant of 10Gy: Volume Score (VS), Radioresistance Score (RS), Eloquence Score (ES) of the lesion, complying with the formula that supports it. : SS= VS+RS+ES+10. Using the Wilcoxon Signed-Rank Test, it was compared with the conventional doses used in the CGKD, which are similar to those used internationally. Results: most lesions received between 12 and 24 Gy, calculated by both methods. Of the meningiomas treated in the CGKD, 65% received a dose of 12 to 14 Gy. Most of the doses suggested by the MS were between 15 and 18 Gy. On average, metastases treated in CGKD received between 16 and 24 Gy (220 of 247, 89%). The doses recommended by the MS were very close, ranging between 15 and 21 Gy (232 of 247, 93.9%). In Non-Functional Pituitary Adenomas, the MS (17-18 Gy) yields doses above those of the CGKD (12-16 Gy) since it does not include adaptations to protect the visual pathway. In Functional Pituitary Adenomas, MS falls below the particularly high doses (25 to 35 Gy) internationally recommended. The Acoustic Neuromas all received between 12 and 13 Gy in the CGKD and most of the doses recommended by the MS were between 14 and 15 Gy. Conclusions: Comparing the doses used by CGKD and those recommended by MS, there is a close proximity when it comes to Acoustic Neuromas and Metastases, but an important difference when it comes to Adenomas and Meningiomas. When applying the Wilcoxon Signed Rank Test to the 403 lesions studied, the mean difference between the two dose calculation systems was 0.23 Gy (95% CI: -0.127-0.60).
Journal of Radiation Research, 2012
Stereotactic irradiation/IMRT/Intermittent irradiation/Sublethal damage repair/Reoxygenation/ LQ model. Since the dose delivery pattern in high-precision radiotherapy is different from that in conventional radiation, radiobiological assessment of the physical dose used in stereotactic irradiation and intensitymodulated radiotherapy has become necessary. In these treatments, the daily dose is usually given intermittently over a time longer than that used in conventional radiotherapy. During prolonged radiation delivery, sublethal damage repair takes place, leading to the decreased effect of radiation. This phenomenon is almost universarily observed in vitro. In in vivo tumors, however, this decrease in effect can be counterbalanced by rapid reoxygenation, which has been demonstrated in a laboratory study. Studies on reoxygenation in human tumors are warranted to better evaluate the influence of prolonged radiation delivery. Another issue related to radiosurgery and hypofractionated stereotactic radiotherapy is the mathematical model for dose evaluation and conversion. Many clinicians use the linear-quadratic (LQ) model and biologically effective dose (BED) to estimate the effects of various radiation schedules, but it has been suggested that the LQ model is not applicable to high doses per fraction. Recent experimental studies verified the inadequacy of the LQ model in converting hypofractionated doses into single doses. The LQ model overestimates the effect of high fractional doses of radiation. BED is particularly incorrect when it is used for tumor responses in vivo, since it does not take reoxygenation into account. For normal tissue responses, improved models have been proposed, but, for in vivo tumor responses, the currently available models are not satisfactory, and better ones should be proposed in future studies.
International Journal of Radiation Oncology*Biology*Physics, 2001
Purpose: To study the radiation tolerance of the parotid glands as a function of dose and volume irradiated. Methods and Materials: One hundred eight patients treated with primary or postoperative radiotherapy for various malignancies in the head-and-neck region were prospectively evaluated. Stimulated parotid flow rate was measured before radiotherapy and 6 weeks, 6 months, and 1 year after radiotherapy. Parotid gland dose-volume histograms were derived from CT-based treatment planning. The normal tissue complication probability model proposed by Lyman was fit to the data. A complication was defined as stimulated parotid flow rate <25% of the preradiotherapy flow rate. Results: The mean stimulated preradiotherapy flow rate of 174 parotid glands was 0.34 mL/min. The mean flow rate reduced to 0.12 mL/min 6 weeks postradiotherapy, but recovered to a mean flow rate of 0.20 mL/min at 1 year after radiotherapy. Reduction in postradiotherapy flow rate correlated significantly with mean parotid dose. No threshold dose was found. Increasing the irradiated volume of parotid glands from 0%-40% to 90-100% in patients with a mean parotid dose of 35-45 Gy resulted in a decrease in flow ratio from, respectively, approximately 100% to less than 10% 6 weeks after radiation. The flow ratio of the 90%-100% group partially recovered to 15% at 6 months and to 30% at 1 year after radiotherapy. The normal tissue complication probability model parameter TD 50 (the dose to the whole organ leading to a complication probability of 50%) was found to be 31, 35, and 39 Gy at 6 weeks, 6 months, and 1 year postradiotherapy, respectively. The volume dependency parameter n was around 1, which means that the mean parotid dose correlates best with the observed complications. There was no steep dose-response curve (m ؍ 0.45 at 1 year postradiotherapy). Conclusions: This study on dose/volume/parotid gland function relationships revealed a linear correlation between postradiotherapy flow ratio and parotid gland dose and a strong volume dependency. No threshold dose was found. Recovery of parotid gland function was shown at 6 months and 1 year after radiotherapy. In radiation planning, attempts should be made to achieve a mean parotid gland dose at least below 39 Gy (leading to a complication probability of 50%).
Australasian Physics & Engineering Sciences in Medicine, 2009
A Clinician's discrimination between radiation therapy treatment plans is traditionally a subjective process, based on experience and existing protocols. A more objective and quantitative approach to distinguish between treatment plans is to use radiobiological or dosimetric objective functions, based on radiobiological or dosimetric models. The efficacy of models is not well understood, nor is the correlation of the rank of plans resulting from the use of models compared to the traditional subjective approach. One such radiobiological model is the Normal Tissue Complication Probability (NTCP). Dosimetric models or indicators are more accepted in clinical practice. In this study, three radiobiological models, Lyman NTCP, critical volume NTCP and relative seriality NTCP, and three dosimetric models, Mean Lung Dose (MLD) and the Lung volumes irradiated at 10Gy (V 10 ) and 20Gy (V 20 ), were used to rank a series of treatment plans using, harm to normal (Lung) tissue as the objective criterion. None of the models considered in this study showed consistent correlation with the Radiation Oncologists plan ranking. If radiobiological or dosimetric models are to be used in objective functions for lung treatments, based on this study it is recommended that the Lyman NTCP model be used because it will provide most consistency with traditional clinician ranking.
Progress in Medical Physics, 2021
This study was designed to investigate the dosimetric difference between intensitymodulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) in head and neck cancer (HNC). The study primarily focuses on low-dose spillage evaluation between these two techniques. Methods: This retrospective study involved 45 patients with HNC. The treatment plans were generated using the IMRT and VMAT techniques for all patients. Dosimetric comparisons were performed in terms of target coverage, organ-at-risk (OAR) sparing, and various parameters, including conformity index, uniformity index, homogeneity index, conformation number, low-dose volumes, and normal tissue integral dose (NTID). Results: No significant (P>0.05) difference in planning target volume coverage (D 95%) was observed between IMRT and VMAT plans for supraglottic larynx, hard palate, and tongue cancers. A decrease in dose volumes ranging from 1 Gy to 30 Gy was observed for VMAT plans compared with those for IMRT plans, except for V 1Gy and V 30Gy for supraglottic larynx cancer and V 1Gy for tongue cancer. Moreover, decreases (P<0.05) in NTID were observed for VMAT plans compared with that for IMRT plans in supraglottic larynx (4.50%), hard palate (12.80%), and tongue (7.76%) cancers. In contrast, a slight increase in monitor units for VMAT compared with those for IMRT in supraglottic larynx (0.46%), hard palate (2.54%), and tongue (7.56%) cancers. Conclusions: For advanced-stage HNC, both IMRT and VMAT offer satisfactory clinical plans. VMAT offers a conformal and homogeneous dose distribution with comparable OAR sparing and higher dose falloff outside the target volume than IMRT, which provides an edge to reduce the risk of secondary malignancies for HNC over IMRT.
Volume and Heterogeneity Dependence of the Dose-Response Relationship for Head And Neck Tumours
Acta Oncologica, 1995
Based on the Poisson statistics of cell kill a model for the response of heterogeneous tumours to non-uniform dose delivery have been developed. The five parameters required to characterize the response are the 50% response dose, Ds0, the normalized dose-response gradient, y, the tumour heterogeneity factor, A, the relative volume, u and the extra daily dose required to counteract the tumour cell proliferation, 6. The model has been fitted to data from a number of clinical investigations to allow the derivation of clinically relevant radiation response parameters for head and neck tumours. The D,, value for T2 larynx cancers is 59.9 Gy in 41 days with a relative standard deviation of 2.1 Gy and the y value is 2.9 with a relative standard deviation of 0.3. The value of S, which is most consistent with the clinical data for laryngeal turnours, is 0.35Gy/day and this value should be used if the treatment time is changed from the 41 days normalization. The heterogeneity factor, 6, is dose to zero for laryngeal tumours which indicates that their response is basically governed by Poisson statistics. Nasopharyngeal tumours, on the other hand, exhibit h values around 0.2 which indicates that these tumours are more heterogeneous in their internal organization and so are their responses to radiation.
Radiotherapy and Oncology, 2010
Background and purpose: Adaptive strategies in radiotherapy (RT) require the knowledge of the total dose given to every organ of the body. Because of anatomical changes and setup errors non-rigid registration is necessary to map the different dose fractions to a common reference. This study evaluates practically if the accumulation of all of these registered dose fractions must take radiobiology into account in a classical clinical setting. Materials and methods: Ten patients with head and neck tumors treated by chemo-RT were used. Contrast-enhanced CT scans were acquired prior and during RT following delivery of mean doses of 14.2, 24.5, 35.0 and 44.9 Gy and the planned pre-treatment helical tomotherapy sinograms were applied on the per-treatment CTs to create a series of per-treatment dose distributions corresponding to each pertreatment CT image. In order to calculate the cumulative dose distribution, the per-treatment dose maps were non-rigidly deformed by using the deformation map computed by a non-rigid registration. The deformed dose maps were then summed in two ways: one while taking radiobiology into account and one without. These two strategies were compared using clinical surrogates in the target volumes (TV) and in surrounding organs at risk (OAR). Results: The differences between the strategies, while statistically significant (p < 0.05), are clinically irrelevant. In the OARs, the mean differences stay in the 0.01-0.07 Gy range for the total dose. In the targets, all mean differences stay in the 0.001-0.012 Gy range. However, some local high difference spots appear leading to punctual errors as high as 2.5 Gy. Conclusion: If using current radiotherapy practices and clinical recommendations based on dose surrogates computed globally on OARs and TVs, one does not need to take radiobiological effects into account while accumulating total dose as these lead to very small differences compared to a simple accumulation technique consisting of a linear sum of the dose fractions. However, care must be taken if other adaptive strategies, based on local rather than global information, are used.
2022
Die Kohlenstoffionentherapie (CIRT) bietet neben einer vorteilhaften Dosisverteilung auch eine höhere relative biologische Wirksamkeit (RBE) als Photonen oder Protonen. Die RBE von Kohlenstoffionen variiert je nach Position innerhalb der Teilchenspur erheblich, sodass komplexe mathematische Modelle für die Bestrahlungsplanung benötigt werden, um eine gleichmäßige biologische Wirkung im Zielvolumen zu erzielen. Aus historischen Grünnden werden in CIRT-Zentren weltweit zwei verschiedene Modelle, MKM und LEM, verwendet.Während japanische Einrichtungen einen Großteil der klinischen Erfahrungen für die CIRT mit MKM eingebracht haben, ist LEM das fuhrende RBE-Modell in Europa und China.Um von den japanischen Erfahrungen zu proftieren, wenden viele europäische Zentren japanische Behandlungsschemata an, obwohl deren Bestrahlungsplanung auf LEM basiert.Dies erfordert Anpassungen der geplanten Dosiswerte für das Tumorvolumen sowie der maximalen Grenzwerte für die Risikoorgane (OAR). Da davon ...
RADIOTHERAPY DOSE–VOLUME EFFECTS ON SALIVARY GLAND FUNCTION
Publications relating parotid dose-volume characteristics to radiotherapy-induced salivary toxicity were reviewed. Late salivary dysfunction has been correlated to the mean parotid gland dose, with recovery occurring with time. Severe xerostomia (defined as long-term salivary function of <25% of baseline) is usually avoided if at least one parotid gland is spared to a mean dose of less than z20 Gy or if both glands are spared to less than z25 Gy (mean dose). For complex, partial-volume RT patterns (e.g., intensity-modulated radiotherapy), each parotid mean dose should be kept as low as possible, consistent with the desired clinical target volume coverage. A lower parotid mean dose usually results in better function. Submandibular gland sparing also significantly decreases the risk of xerostomia. The currently available predictive models are imprecise, and additional study is required to identify more accurate models of xerostomia risk. Ó 2010 Elsevier Inc.