Pattern and predictors of volumetric change of parotid glands during intensity modulated radiotherapy (original) (raw)
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Head and neck intensity modulated radiotherapy parotid glands: time of re-planning
La radiologia medica, 2013
Purpose To investigate the correct time point for replanning by evaluating dosimetric changes in the parotid glands (PGs) during intensity-modulated radiotherapy (IMRT) in head and neck cancer patients. Materials and methods Patients with head and neck cancer treated with IMRT were enrolled. During treatment all patients underwent cone-beam computed tomography (CBCT) scans to verify the set-up. CBCT scans at treatment days 10, 15, 20 and 25 were used to transfer the original plan (CBCT plan I, II, III, IV, respectively) using rigid registration between the two. The PGs were retrospectively contoured and evaluated with the dose-volume histogram. The mean dose, the dose to 50 % of volume, and the percentage of volume receiving 30 and 50 Gy were evaluated for each PG. The Wilcoxon sign ranked test was used to evaluate the effects of dosimetric variations and values \0.05 were taken to be significant. Results From February to June 2011, ten patients were enrolled and five IMRT plans were evaluated for each patient. All the dosimetric parameters increased throughout the treatment course. However, this increase was statistically significant at treatment days 10 and 15 (CBCT plan I, II; p = 0.02, p = 0.03, respectively). Conclusion CBCT is a feasible method to assess the dosimetric changes in the PGs. Our data showed that checking the PG volume and dose could be indicated during the third week of treatment.
International Journal of Radiation Oncology*Biology*Physics, 2008
Purpose: To compare parotid gland dose-volume response relationships in a large cohort of patients treated with intensity-modulated (IMRT) and conventional radiotherapy (CRT). Methods and materials: A total of 221 patients (64 treated with IMRT, 157 with CRT) with various head-and-neck malignancies were prospectively evaluated. The distribution of tumor subsites in both groups was unbalanced. Stimulated parotid flow rates were measured before and 6 weeks, 6 months, and 1 year after radiotherapy. Parotid gland dose-volume histograms were derived from computed tomography-based treatment planning. The normal tissue complication probability (NTCP) model proposed by Lyman was fit to the data. A complication was defined as stimulated parotid flow ratio <25% of the pretreatment flow rate. The relative risk of complications was determined for IMRT vs. CRT and adjusted for the mean parotid gland dose using Poisson regression modeling. Results: One year after radiotherapy, NTCP curves for IMRT and CRT were comparable with a TD 50 (uniform dose leading to a 50% complication probability) of 38 and 40 Gy, respectively. Until 6 months after RT, corrected for mean dose, different complication probabilities existed for IMRT vs. CRT. The relative risk of a complication for IMRT vs. CRT after 6 weeks was 1.42 (95% CI 1.21-1.67), after 6 months 1.41 (95% CI; 1.12-1.77), and at 1 year 1.21 (95% CI 0.87-1.68), after correcting for mean dose. Conclusions: One year after radiotherapy, no difference existed in the mean dose-based NTCP curves for IMRT and CRT. Early after radiotherapy (up to 6 months) mean dose based (Lyman) models failed to fully describe the effects of radiotherapy on the parotid glands. Ó
Heterogeneous radiotherapy dose-outcomes response in parotid glands
Convergent Science Physical Oncology
Parotid glands are treated clinically as though the distribution of functional burden were homogeneous. Radiotherapy treatments are planned using whole parotid mean dose to predict risk of salivary dysfunction. Recent progress has identified specific parotid non-homogeneities by demonstrating the existence of regional, bath-and-shower, and dose-volume effects. In this work, parotid regional effects and their impact on salivary function are quantified using a nonparametric (model-free) approach. Regional effects have implications for clinical sparing practices. Radiotherapy planning contours, dose profiles, and late clinical outcomes from a single cohort consisting of N = 332 patients was used. Pre-radiotherapy and one year post-radiotherapy whole mouth stimulated saliva were collected for assessment of salivary dysfunction. Organ-at-risk parotid glands were segmented into 2, 3, 4, 18, and 96 equal-volume sub-segments. Sub-segment relative importance was derived from mean dose regressors using random forests and conditional inference trees. Regressor multicollinearity, cohort homogeneity, and overfitting were addressed. Linear and exponential whole parotid mean dose models were also implemented for comparison purposes. Exclusion of caudal-anterior sub-segments negatively impacted prediction the most. The most important sub-segments had importances 2.4× (on average over all segmentation methods) or >4× (at the finest level of segmentation) that of an equivalent sub-segment in a theoretical homogeneous parotid. In contrast, the least important sub-segments held virtually no importance for prediction. Both random forests and conditional inference trees outperformed parametric (model-based) techniques. Both improved prediction as segmentation was refined. Radiation dose to caudalanterior aspects of the parotid are the strongest predictors of radiotherapy-induced late stimulated whole mouth saliva, and are thus the most clinically-relevant regions for controlling dysfunction. Cranial and posterior aspects are less important. Shifting dose from regions of high importance to low importance may therefore improve patient outcomes.
Early classification of parotid glands shrinkage in radiotherapy patients: A comparative study
Biosystems Engineering, 2015
Parotid gland shrinkage CT based features Radiotherapy During radiotherapy treatment of patients with head-and-neck cancer, the possibility that parotid glands shrink was evidenced, connected with increasing risk of acute toxicity. In this ambit, the early identification of patients in danger is of primary importance, in order to treat them with adaptive therapy. This work studies different approaches for classifying parotid gland samples, taking into account textural features extracted from computed tomography (CT) images of monitored patients. A real dataset is used, and accuracy, sensitivity and specificity are counted as classification performances. Therefore, firstly, different procedures to define classes are compared in terms of their physical meaning and classification performances. Then, different methods for extracting knowledge from the dataset are implemented and compared in terms of performances and model interpretability. First-rate performance was obtained by using Likelihood-Fuzzy Analysis (LFA), which is a recently developing method based on the use of statistical information by means of Fuzzy Logic. The interpretable models extracted with LFA also allow identifying among textural features those able to predict parotid shrinkage. Some of these features are already known and are confirmed here, others are new, and some of them are very early predictors. Finally, an example of textural feature monitoring and classification of a patient is presented, through a reasoning scheme similar to human reasoning, based on the interpretation of simple rule-based models using linguistic variables.
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%).
South Asian journal of cancer
During course of radiation therapy, anatomical variations occur risking overdose of parotid gland. We tried to quantify volume of parotid gland and mean dose to parotid gland after every 10 fractions (#). We conducted the prospective study from July 2016 to May 2017 in 25 patients of early-stage oropharyngeal carcinoma. Patients had Karnofsy Performance Score of 80-100, median age was 54 years, and 18 patients were males. Patients were planned with intensity-modulated radiation therapy planning with dose as 66 Gy/30# to planning target volume (PTV) including primary and 54 Gy/30# to PTV-nodal including elective neck irradiation. After each 10#, replanning was done, and variations in parotid volume were studied including D (mean dose to parotids) and D (the dose delivered to 50% of volume). Other tumor characteristic like PTV of primary was also assessed and minimum PTV volume covered by 95% isodose line was kept as 95%. Average parotid volumes decreased by the mean value of 10% and ...
The British Journal of Radiology, 2012
Objectives: This study evaluates the interobserver variation in parotid gland delineation and its impact on intensity-modulated radiotherapy (IMRT) solutions. Methods: The CT volumetric data sets of 10 patients with oropharyngeal squamous cell carcinoma who had been treated with parotid-sparing IMRT were used. Four radiation oncologists and three radiologists delineated the parotid gland that had been spared using IMRT. The dose-volume histogram (DVH) for each study contour was calculated using the IMRT plan actually delivered for that patient. This was compared with the original DVH obtained when the plan was used clinically. Results: 70 study contours were analysed. The mean parotid dose achieved during the actual treatment was within 10% of 24 Gy for all cases. Using the study contours, the mean parotid dose obtained was within 10% of 24 Gy for only 53% of volumes by radiation oncologists and 55% of volumes by radiologists. The parotid DVHs of 46% of the study contours were sufficiently different from those used clinically, such that a different IMRT plan would have been produced. Conclusion: Interobserver variation in parotid gland delineation is significant. Further studies are required to determine ways of improving the interobserver consistency in parotid gland definition.
International Journal of Radiation Oncology*Biology*Physics, 2013
Purpose-Doses actually delivered to the parotid glands during radiotherapy often exceed planned doses. We hypothesized that the delivered doses correlate better with parotid salivary output than the planned doses, used in all previous studies, and that determining these correlations will help decisions regarding adaptive re-planning (ART) aimed at reducing the delivered doses. Methods and Materials-Prospective study: oropharyngeal cancer patients treated definitively with chemo-irradiation underwent daily cone beam CT (CBCT) with clinical setup alignment based on C2 posterior edge. Parotid glands in the CBCTs were aligned by deformable registration to calculate cumulative delivered doses. Stimulated salivary flow rates were measured separately from each parotid gland pretherapy and periodically posttherapy. Results-36 parotid glands of 18 patients were analyzed. Average mean planned doses was 32 Gy and differences from planned to delivered mean gland doses were −4.9 to +8.4 Gy, median difference +2.2 Gy in glands whose delivered doses increased relative to planned. Both planned and delivered mean doses were significantly correlated with post-treatment salivary outputs at almost all post-therapy time points, without statistically significant differences in the correlations. Large dispersions [on average, standard deviation (SD) 3.6 Gy] characterized the dose/effect relationships for both. The differences between the cumulative delivered doses and planned doses were evident already at first fraction (r=0.92, p<0.0001) due to complex setup deviations, e.g. rotations and neck articulations, uncorrected by the translational clinical alignments. Conclusions-After daily translational setup corrections, differences between planned and delivered doses in most glands were small relative to the SDs of the dose/saliva data, suggesting that ART is not likely to gain measurable salivary output improvement in most cases. These differences were observed already at first treatment, indicating potential benefit for more complex
Radiation Oncology
Background: Functional magnetic resonance imaging may provide several quantitative indices strictly related to distinctive tissue signatures with radiobiological relevance, such as tissue cellular density and vascular perfusion. The role of Intravoxel Incoherent Motion Diffusion Weighted Imaging (IVIM-DWI) and Dynamic Contrast-Enhanced (DCE) MRI in detecting/predicting radiation-induced volumetric changes of parotids both during and shortly after (chemo) radiotherapy of oropharyngeal squamous cell carcinoma (SCC) was explored. Methods: Patients with locally advanced oropharyngeal SCC were accrued within a prospective study offering both IVIM-DWI and DCE-MRI at baseline; IVIM-DWI was repeated at the 10th fraction of treatment. Apparent diffusion coefficient (ADC), tissue diffusion coefficient D t , perfusion fraction f and perfusion-related diffusion coefficient D * were estimated both at baseline and during RT. Semi-quantitative and quantitative parameters, including the transfer constant K trans , were calculated from DCE-MRI. Parotids were contoured on T2-weighted images at baseline, 10th fraction and 8th weeks after treatment end and the percent change of parotid volume between baseline/10th fr (ΔVol 10fr) and baseline/8th wk. (ΔVol post) computed. Correlations among volumetric changes and patient-, treatment-and imaging-related features were investigated at univariate analysis (Spearman's Rho). Results: Eighty parotids (40 patients) were analyzed. Percent changes were 18.2 ± 10.7% and 31.3 ± 15.8% for ΔVol 10fr and ΔVol post , respectively. Among baseline characteristics, ΔVol 10fr was correlated to body mass index, patient weight as well as the initial parotid volume. A weak correlation was present between parotid shrinkage after the first 2 weeks of treatment and dosimetric variables, while no association was found after radiotherapy. Percent changes of both ADC and D t at the 10th fraction were also correlated to ΔVol 10fr. Significant relationships were found between ΔVol post and baseline DCE-MRI parameters. Conclusions: Both IVIM-DWI and DCE-MRI can help to detect/predict early (during treatment) and shortly after treatment completion the parotid shrinkage. They may contribute to clarify the correlations between volumetric changes of parotid glands and patient−/treatment-related variables by assessing individual microcapillary perfusion and tissue diffusivity.
Dose–response relationships within the parotid gland after radiotherapy for head and neck cancer
2004
Background and purpose: To determine the salivary function, after parotid-sparing radiotherapy (RT), of different regions within the parotid gland and to evaluate dose-function relationships within the parotid glands and between patients. Patients and methods: Sixteen head and neck cancer patients, irradiated between September 1999 and November 2000 using a conformal parotid-sparing technique, were included in this study. Before RT and 7 months after RT (range 6-10 months), a salivary gland scintigraphy was performed in all patients combined with a single photon emission computed tomography (SPECT). The salivary excretion fraction (SEF) was measured, after stimulation, in 8-12 transverse 5 mm SPECT slices of each parotid. Loss of salivary excretion fraction (dSEF %) of these slices was calculated as the proportion of SEF after RT as compared to SEF before RT. Since the planning CT-scan and the SPECT-scintigraphy were performed in the same treatment position, the dose to a transverse slice within the parotid gland could be matched to the loss of salivary excretion fraction of that respective slice. A non-linear model was fitted to the dose-loss of function data and the dose resulting in 50% loss of salivary excretion fraction (D 50) was calculated. Results: Before RT, all but one patient presented with normal salivary excretion fractions (SEF) of both parotid glands. Within the same parotid gland, the SEF's of the different slices were almost equal. Seven months after RT, the reduction in SEF was statistically significant (P-value !0.0001). A significant difference in loss of salivary excretion fraction (dSEF) was also observed between both parotid glands (P!0.0001) as a result of the parotid-sparing technique. When plotting the dSEF of a slice versus the dose given to that slice, doses as low as 10-15 Gy could result in a serious loss of function (dSEF O50%). After fitting a non-linear model to these plots, the mean dose resulting in 50% loss of salivary excretion fraction (D 50) 7 months after RT was 22.5 Gy. A large inter-patient variability was found in D 50. Conclusions: Salivary SPECT is a useful tool for the evaluation of the salivary function of different slices within the parotid gland. Before irradiation, the different slices within one parotid gland act as functional sub-units contributing equally to the function of the entire gland. Seven months after an average dose of 22.5 Gy (D 50) the functional sub-unit has lost 50% of its excretion fraction. The high inter-patient variability in D 50 and the observation that low doses (10-15 Gy) can induce serious loss of function should prompt us in the clinic to reduce the dose to the parotids even lower than the threshold of 22.5 Gy.