Parotid Dose Research Articles

A comparison of the gamma index and dose volume histogram of patient for IMRT/VMAT with different QA systems

Radiotherapy has a vital part in the treatment of prostate tumor. Three-dimensional conformal radiotherapy (3D-CRT), intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques are currently used. In this concern, the present study is a trial to shed further light on the mean differences and to note the similarity or dissimilarity between the proposed three techniques of radiotherapy for head & neck (H & N) cancer. Measurements were carried out based on two dimensional (2D) array PTW and portal dosimetry in patient with head and neck canceras tool for evaluation. Specifically, the aim of the first part was to demonstrate that quality assurance (QA) tool for IMRT and its passing rate criteria might not expect dose errors in patient. This study examines the effect of systematic positional multi-leaf collimator (MLC) bank errorson gamma (Γ) examination results used for QA of treatment technique and to assess the result of dose changes presented in dynamic multi-leaf collimator (DMLC) modeling and delivery methods on metrics for IMRT. Twenty head and neck IMRT plans were selected for current study using the same group of dose–volume constraints. Treatment plans were created using 3D-CRT, VMAT and IMRT techniques. Homogeneity index (HI), Conformity index (CI), max. spinal cord dose, max. brainstem dose, mean parotid dose, larynx dose, oral cavity dose, and monitor units (MUs) were compared. For every patient, a group of data analysis was done for each technique and then imported to the DVH (PTW 2D array) for processing. A measured dose volume histogram metrics (DVH) was created in QA system and note the similarity to the calculated DVH from the treatment plan. Their variations due to errors related to the treatment planning system (TPS) (its algorithm for dose calculation) in addition to beam delivery. It is clearly shown that VMAT has a little better CI whereas the volume of small doses was higher.VMAT had lesser MUs than IMRT. 3D-CRT had the lowest common MU, CI and HI. IMRT would be preferred to VMAT in head and neck radiotherapy. Also, the current study showed even if the whole of IMRT QA had high Gamma passing rates 98.3 ± 1.3% (96.7-99.7%) for “3%/3 mm” criteria, there were located significant errors in some of the calculated clinical dose metrics. This study approves that conventional IMRT QA are not a prescient warning of errors in PTV dose and OAR dose (organs at risk). The dose QA has to allow us to expect and evaluate the relation of results of gamma test and DVH for treatment technique plan.

Pattern of geometric changes of parotid gland in conventional and intensity-modulated radiotherapy in nasopharyngeal cancer patients

AbstractIntroductionThis study compared the pattern of radiation induced parotid changes between conventional (ConRT) and intensity modulated radiotherapy (IMRT) in nasopharyngeal carcinoma patients.Methods56 adult NPC patients treated with IMRT (n=28) and conventional radiotherapy (n=28) were recruited. CT scans were acquired before radiotherapy, at 10th, 20th and 30th fractions, and 3 months after treatment. Parotid gland was delineated in the corresponding CT slices and its mean dose was calculated. The volumetric and geometric changes of the parotid gland at various time intervals were compared against the pre-treatment structure set. The pattern of changes was compared between the two techniques.ResultsThe mean parotid dose of IMRT (37.5±9.5 Gy) was significantly lower than ConRT (49.1±7.4 Gy). The parotid gland volume, DICE similarity coefficient and lateral dimension of patient head gradually decreased during the radiotherapy course and partially recovered in 3 months post-treatment. The differences between two groups were not significant until at 3 month after treatment, where IMRT showed significantly better volume recovery.ConclusionSimilar parotid gland size and location changes were observed during the treatment course in both ConRT and IMRT. However IMRT demonstrated better parotid volume recovery after treatment.

PO-1066: Delineation uncertainty and parotid gland doses and estimated NTCPs in head and neck proton therapy

PO-1066: Delineation uncertainty and parotid gland doses and estimated NTCPs in head and neck proton therapy

Dosimetric Impact of Metal Artifacts From Dental Implants and Clinical Implications for Head And Neck IMRT Treatment Planning

Dental implants are increasingly prevalent in the head and neck cancer patient population and result in the creation of artifacts on CT imaging for treatment planning. In our practice, we have noticed more mucosal toxicity adjacent to dental implants and hypothesized that this observation may be due to errors in dose calculation. The purpose of this study was to retrospectively evaluate dosimetric differences in target coverage and organ at risk (OAR) sparing when adjusting for spurious CT measurements attributed to dental metal artifact. Nine patients with dental implants who were previously treated at our institution with definitive radiation for oropharyngeal cancer were selected for this retrospective study. All patients were treated with 6 MV photons using intensity modulated radiation therapy (IMRT). Dose calculation was performed using an algorithm with heterogeneity corrections. Dental implant and streak artifact volumes were contoured and new IMRT plans were generated with identical beam geometry and monitor units using the uncorrected reference CT data set and a corrected CT data set. Artifacts were assigned a soft tissue electron density value with a Hounsfield unit (HU) of zero. Using descriptive statistics, target volumes and OAR dosimetry were reported and compared between the clinical treatment plans and re-calculated plans. Target volumes analyzed were GTV (D95, D98, D99), intermediate-risk PTV (D95, D98, D99), and high-risk PTV (D95, D98, D99, D2cc). The maximum dose, Dmax, was also collected for each plan. OARs analyzed included the bilateral parotids (mean), oral uninvolved (mean), OAR pharynx (mean), mandible (max), and cord (max). The median artifact volume was 41.6 cc (range, 22.5 to 56.8 cc). When accounting for artifact error, there were small but statistically significant relative increases in Dmax (0.24%, P=.0273), mean oral uninvolved dose (0.24%, P=.0234), and mean left parotid dose (0.20%, P=.0469). On average, the hot spot (Dmax) increased by 181 cGy when accounting for artifact. There were no significant dosimetric differences between plans in terms of GTV, intermediate-risk PTV, and high-risk PTV coverage. There were no significant differences for the mandible max dose, cord max dose, OAR pharynx mean dose, or the right parotid mean dose. In this retrospective study, there was minimal dose variation to target volumes and OAR structures when substituting artifact with soft tissue density HUs. There were significant differences in terms of maximum dose and dose to the uninvolved oral cavity, which suggests that ignoring artifacts in CT images during planning may result in greater hot spots. While small, these differences are worthy of further study as they may at least partially contribute to increased rates of empirically observed mucosal toxicity in the vicinity of dental artifacts.

A study on the impact of patient-related parameters in the ability to spare parotid glands by intensity-modulated radiotherapy for head and neck squamous cell carcinomas.

This study aims to study the effect of geometric- and patient-related variables in achieving the desired dose-volume constraints to parotid for patients undergoing definitive/adjuvant intensity-modulated radiotherapy (IMRT) for head and neck squamous cell carcinomas (HNSCC). This retrospective study considered HNSCC patients who underwent IMRT at our center between 2009 and 2014. Patients' details and dose-volume parameters were collected, and correlated with dose to parotids using Pearson's correlation test. Sixty-seven patients were found to be eligible. Oral primary predominated (37.3%) and 53 (79%) had locally advanced disease. The parotid volume (PV) had no impact on mean dose. There was a negative linear correlation between the ratio (Parotid-planning target volume [PTV] overlap)/PV and mean dose to the whole parotid (y = 1.14-0.011×; R2 = 0.509; P = 0.001), suggesting that a ratio of 0.7 resulted in mean dose ≥ 40 Gy and potentially irreversible xerostomia. No association was found between site of primary and parotid dose, but node-positive (N+) patients received significantly higher dose compared to N0 patients (34.5 Gy vs. 29.5 Gy; P = 0.001). N + patients persisted to receive higher dose even when T stage was accounted for (32.5 Gy vs. 28.9 Gy for </= T2, 35.4 Gy vs. 30.1 Gy for > T2; P = 0.003). On the last follow-up, 35 patients (52%) had >/=Grade II xerostomia. Average mean dose to combined PV was higher in patients with > grade I xerostomia compared to patients with </=Grade I (35 Gy vs. 29 Gy; P = 0.01). The degree of PTV overlap with parotid (≥30%) and N + disease are the strongest predictors of poor parotid sparing by IMRT.

43. CBCT dose calculation: accuracy assessment of four different methods

Introduction Cone Beam CT (CBCT) images aim at target volume repositioning before treatment fraction. These images may be used for dose calculation in order to dosimetrically quantify anatomical variations that occurs during treatment. The main limits are image quality, Hounsfield numbers (HU) consistency and CBCT reconstruction size. This study aims to assess accuracy of several CBCT dose calculation methods. Methods This study deals with four CBCT (XVI, Elekta) and CT image sets acquired on the same day in context of weekly dose planning of one H&N patient treated with VMAT technique. CT-CBCT sets were used to quantify CBCT dose calculation accuracy by investigating four methods: (i) use of a density to HU relation from phantom CBCT image (phantom HU-D relation), (ii) use of a density to HU relation from patient CBCT image (patient HU-D relation), (iii) density override by three classes threshold (air, soft tissues, bone) and (iv) elastic deformation (Admire, Elekta) between planning CT and CBCT image, by creating a pseudo-CT. After rigid registration, plan characteristics are projected on CBCT images (or pseudo-CT) with Pinnacle v.9.10 (Philips). Dose distribution comparison between CT-based (reference) and CBCT-based calculation was performed by a gamma analysis in 2D and 3D ( γ 2D and γ 3D, criteria: 2%/2 mm, 30% threshold). Then, dose differences were reported in terms of 95% target coverage, parotid glands mean dose (Dmean) and PRV spinal cord maximum dose (D2%). Results On average, γ 3D (percentage of points with gamma The gamma analysis showed location of discrepancy areas: near body contour, regarding shoulders and in presence of heterogeneities ( Fig. 1 ). These differences can be explained by the poor image quality and the HU inconsistency of CBCT images in some areas. The method with pseudo-CT seems to be the best to pass over these issues because densities come from planning CT. Conclusions The four evaluated methods show that dose differences can reach 5% for parotid glands and are lower than 2% for spinal cord and target volumes. The 3D gamma analysis results (2%/2 mm) are higher than 95% for three among four methods. However, additional uncertainties have to be taken into consideration in case of CBCT image delineation and/or calculation on truncated images. This preliminary study shows CBCT dose calculation feasibility to quantify impact of patient anatomical variations during treatment and trigger a new plan based on CT if necessary. The future work is real delivered dose monitoring, based on CBCT image, in perspective of dose guided adaptive radiotherapy.

Scintigraphic Evaluation of Salivary Function after Intensity Modulated Radiotherapy for Head and Neck Cancer

Xerostomia is a common complication in patients treated for head and neck cancers (HNC). Highly conformal radiotherapy (RT) techniques, such as intensity modulated radiotherapy (IMRT), result in better normal tissue sparing in comparison to 3-dimensional conformal radiotherapy. We investigated salivary function using quantitative scintigraphy and aimed to identify associations between dosimetric parameters of the parotid glands and quality of life (QoL) for HNC patients receiving IMRT. Thirty patients treated for HNC were prospectively recruited. Salivary excretion function (SEF) was measured by 99mTc pertechnetate scintigraphy prior to RT and then 1 and 12 months after its completion. The recovery of parotid gland excretion function was expressed as the ratio of post- and pre-treatment SEF. Patient-reported QoL was evaluated by the EORTC QLQ-C30 and H&N35 questionnaires. The mean SEF before RT was 49.2±14.8%. In the univariate analysis we found that older age (r=-0.29, p=0.049) and localization of tumour in oral cavity or oropharynx (comparing to larynx/hypopharynx, p=0.030) affected recovery of salivary flow 12 months after RT. Mean parotid dose was significantly correlated with recovery of salivary flow 12 months after RT (r=-0.46, p=0.001). In the multivariate analysis all aforementioned factors were found to be significantly associated with salivary flow 12 months after RT - age (β=-0.39, p=0.002), tumour localized in oral cavity or oropharynx (β =-0.36, p=0.004), mean parotid dose (β=-0.44, p<0.001). Self-reported grade ≥3 xerostomia was more often in patients with tumour localized in oral cavity or oropharynx (p=0.027). It was also more common in patients who received higher mean dose for both parotids and in patients with worse recovery of salivary flow 12 months after RT. However these results were not statistically significant (p=0.104 and p=0.089, respectively). The results of scintigraphic evaluation of salivary function are strongly correlated with the mean parotid dose. However, this objective method is only partially associated with patients’ self-reported outcomes. The possible reason for that phenomenon is the fact that xerostomia is highly subjective and several factors, not just simply salivary flow, may be involved in its perception. This may be particularly important in older patients who were found to have the worst recovery of salivary flow.

Decoding Dysgeusia: Taste Dysfunction in Head and Neck Cancer Patients Receiving Radiation Therapy

Taste dysfunction (dysguesia) in patients receiving radiotherapy (RT) leads to decline in numerous quality of life outcomes. How to measure this robustly remains a challenge that needs to be addressed to enable effective approaches to prevent or to treat this complication. This study seeks to characterize the ability to measure and characterize radiation-induced dysgeusia with a patient reported outcome measure of asking patients to provide a relative percentage of their taste function. Utilizing prospectively collected data at the point of care in our institutional Oncospace database, patients treated for head and neck cancers reported percent of preserved taste function data for time points at baseline, weekly through radiotherapy, and at every three months through 24 months. The average assessment of percent taste function at each time point was plotted from baseline to 24 months. A multivariate analysis was conducted to assess for patient, tumor, or treatment factors with respect to taste function. From 2010-2016, 164 patients with taste function assessments and who had bilateral neck and pharyngeal RT were identified with a mean age of 59 years, male (77%) of Caucasian (71%), African-American (20%) and Other (9%) ethnicities. 46% had an advanced T stage (T3-T4); 55% had an advanced N stage (N2b, N3), and 4% had nasopharynx, 76% oropharynx, 1% oral cavity, and 19% had hypopharynx/larynx primaries. 51% of patients had no surgical intervention. 74% had chemotherapy as part of their regimen. Taste function declined rapidly from baseline to the end of RT, with the lowest measure (<14 points of 100) at the end-of-treatment measure. Taste function slowly recovered after RT, at a rate of 0.8 points improvement for every 10 days (p<.001). Patients who had surgery prior to RT had the least change in taste function. The mean dose to the parotid and advanced nodal stage significantly affected taste function. (P=0.01) Higher dose was associated with slower recovery: for every additional 1 Gy increase in dose, taste function recovered 0.4 points lower. None of the following factors affected taste function: age, gender, race, primary tumor site, or use of chemotherapy. Patient-reported percent in taste function follows a characterizable pattern of loss and recovery during and following radiotherapy. Advanced nodal stage and mean parotid dose significantly affected patient-reported taste function. This study identifies a simple patient reported question that may be a promising method to evaluate radiation-related dysgeusia that warrants further evaluation.

Decision Support for the Design of Clinical Trials: Dose De-escalation in HPV+ Oropharyngeal Cancer

HPV+ oropharyngeal cancer patients have substantially higher survival rates than HPV- patients, leading clinicians to question whether the current policy of 70 Gy provides an optimal balance between toxicity and survival rates. However, uncertainty in the variation of tumor control probability (TCP) for HPV+ patients with dose makes trial design difficult. In addition, to consider changing clinical practice, the expected effects on normal tissue complications must be taken into account. The goal of the study was to understand the effects that these considerations have on changing the current policy of a prescription dose of 70 Gy. We modeled the decision process with a Bayesian Network and used a Markov Model to calculate QALYs. A Monte Carlo cohort analysis was performed that included the effects of patient heterogeneity and treatment outcome uncertainty. Patient heterogeneity was accounted for in some cases by taking variable distributions from our clinical database (e.g. mean parotid dose) and in others by using distributions from the literature (e.g. TCP model parameters and health state utilities). Nested Monte Carlo sampling was used to examine the effects of different groups of variables separately. We explored the effects of 1) outcome model parameters, 2) doses to critical structures, and 3) patient utilities for health states. The modeled cohort reproduced toxicity and cure rates published in the literature for a prescription dose of 70 Gy. Different subsets in the modeled cohort achieved higher QALYs for different prescription doses. Under the assumption that dose de-escalation to 55 Gy reduces overall survival by less than 7%, we find that a lower prescription dose increases QALYs for 80% of the cohort, with achievable mean doses to critical structures and patient preferences determining which Rx dose is optimal for each individual. Under the assumption that dose de-escalation to 55 Gy reduces OS by up to 10%, we find that a lower prescription dose still increases QALYs for half of the population. We used this model to identify which parameters have the most influence in the decision process, and in particular to examine how limiting uncertainty in these parameters leads to a reduction in decision uncertainty. For this case we find that a clinical trial must be powered to see an overall survival reduction of 7% or less in order for clinicians to definitively choose a lower Rx dose. Furthermore, a personalized approach by choosing an Rx dose based upon achievable doses to critical structures and/or assessing patient preferences has the potential to increase QALYs for a greater proportion of the population. This model-based technique can be used more generally to guide the design of clinical trials to reduce uncertainty in key parameters so that clinicians may confidently identify which groups of patients have the highest possibility to benefit.

Redistributed versus homogenous radiotherapy dose for head and neck cancer; a treatment planning study

Abstract Dose redistribution, where radio-resistant parts of the tumour are boosted while the border of the planning target volume receives a lower dose has the potential to increase local control in advanced head and neck squamous cell carcinoma (HNSCC). In this treatment planning study for 20 patients, standard radiotherapy (RT) of 70 Gy, was compared to redistributed RT following the ARTFORCE trial protocol (NCT01504815), i.e., a fluorodeoxyglucose-positron emission tomography (FDG-PET) based heterogeneous simultaneous-integrated-boost to a total dose of 64–84 Gy. Redistribution marginally increased the mean ipsilateral ⧹contralateral parotid dose by 1.55⧹0.55 Gy but not dose to other organs at risk.

Elective nodal dose of 60 Gy or 50 Gy in head and neck cancers: A matched pair analysis of outcomes and toxicity

PurposeThe main objective of this study was to evaluate appropriate doses for elective nodal irradiation (ENI) in head and neck squamous cell carcinoma (HNSCC) patients to optimize the therapeutic ratio. Methods and materialsA matched pair analysis of 2 similar cohorts of HNSCC treated with intensity modulated radiation therapy with different dose prescriptions to the elective nodal regions was conducted. One group received 60 Gy, whereas the other received 50 Gy (ENI60 and ENI50 groups, respectively). Isolated regional recurrences (IRR) and locoregional control were evaluated. Doses received by the parotid and thyroid glands were compared among both groups and were clinically correlated with the trend of salivary function recovery and incidence of hypothyroidism. ResultsOf the 110 patients studied, 97 were eligible for analysis after matching based on propensity scores. The 3-year locoregional control rate was similar in ENI60 and ENI50 (78.7% and 77%, respectively; P = .93). There were no IRR in ENI regions in either group. The mean ipsilateral parotid dose in ENI60 was significantly higher compared with ENI50 (42 vs 35.7 Gy, P = .03). There was no significant difference in the mean contralateral parotid doses (32.5 vs 31.7 Gy, P = .6). The mean thyroid doses were high in ENI60 compared with ENI50 (54.7 vs 43.3 Gy, P < .001). A significant difference in ipsilateral parotid salivary excretory fraction ratio at 1 year (P = .03) was observed with quicker recovery of salivary function. The salivary excretory fractions were poorer in the ENI60 group with higher mean parotid doses (P = .009). At 2 years, 26 patients (54%) in the ENI60 group and 13 patients (26.5%) in the ENI50 group developed biochemical hypothyroidism (P = .007). ConclusionsDoses of 50 Gy equivalent are sufficient to sterilize the uninvolved nodal regions because the rates of IRR are extremely low. Using ENI50 results in clinically meaningful reduction in salivary and thyroid toxicity in HNSCC.

Differences in Parotid Dosimetry and Expected Normal Tissue Complication Probabilities in Whole Brain Radiation Plans Covering C1 Versus C2.

ObjectivesThere is no consensus standard regarding the placement of the inferior field border in whole brain radiation therapy (WBRT) plans, with most providers choosing to cover the first versus (vs.) second cervical vertebrae (C1 vs. C2). We hypothesize that extending coverage to C2 may increase predicted rates of xerostomia.MethodsFifteen patients underwent computed tomography (CT) simulation; two WBRT plans were then produced, one covering C2 and the other covering C1. The plans were otherwise standard, and patients were prescribed doses of 25, 30 and 37.5 gray (Gy). Dose-volume statistics were obtained and normal tissue complication probabilities (NTCPs) were estimated using the Lyman-Burman-Kutcher model. Mean parotid dose and predicted xerostomia rates were compared for plans covering C2 vs. C1 using a two-sided patient-matched t-test. Plans were also evaluated to determine whether extending the lower field border to cover C2 would result in a violation of commonly accepted dosimetric planning constraints.ResultsThe mean dose to both parotid glands was significantly higher in WBRT plans covering C2 compared to plans covering C1 for all dose prescriptions (p<0.01). Normal tissue complication probabilities were also significantly higher when covering C2 vs. C1, for all prescribed doses (p<0.01). Predicted median rates of xerostomia ranged from <0.03%-21% for plans covering C2 vs. <0.001%-12% for patients treated with plans covering C1 (p<0.01), dependent on the treatment dose and NTCP model. Plans covering C2 were unable to constrain at least one parotid to <20 Gy in 31% of plans vs. 9% of plans when C1 was covered. A total parotid dose constraint of <25 Gy was violated in 13% of plans covering C2 vs. 0% of plans covering C1.ConclusionsCoverage of C2 significantly increases the mean parotid dose and predicted NTCPs and results in more frequent violation of commonly accepted dosimetric planning constraints.

Whole-brain Irradiation Field Design: A Comparison of Parotid Dose

Whole-brain radiation therapy (WBRT) plays an important role in patients with diffusely metastatic intracranial disease. Whether the extent of the radiation field design to C1 or C2 affects parotid dose and risk for developing xerostomia is unknown. The goal of this study is to examine the parotid dose based off of the inferior extent of WBRT field to either C1 or C2. Patients treated with WBRT with either 30 Gy or 37.5 Gy from 2011 to 2014 at a single institution were examined. Parotid dose constraints were compared with Radiation Therapy Oncology Group (RTOG) 0615 nasopharyngeal carcinoma for a 33-fraction treatment: mean <26 Gy, volume constraint at 20 Gy (V20) < 20 cc, and dose at 50% of the parotid volume (D50) < 30 Gy. Biologically effective dose (BED) conversions with an α/β of 3 for normal parotid were performed to compare with 10-fraction and 15-fraction treatments of WBRT. The constraints are as follows: mean < BED 32.83 Gy, V15.76 (for 10-fraction WBRT) or V17.35 (for 15-fraction WBRT) < 20 cc, and D50 < BED 39.09 Gy. Nineteen patients treated to C1 and 26 patients treated to C2 were analyzed. Comparing WBRT to C1 with WBRT to C2, the mean left, right, and both parotids' doses were lower when treated to C1. Converting mean dose to BED3, the parotid doses were lower than BED3 constraint of 32.83 Gy: left (30.12 Gy), right (30.69 Gy), and both parotids (30.32 Gy). V20 to combined parotids was lower in patients treated to C1. When accounting for fractionation of WBRT received, the mean corrected V20 volume was less than 20 cc when treating to C1. D50 for C1 was lower than C2 for the left parotid, right parotid, and both parotids. BED3 conversion for the mean D50 of the left, right, and both parotids was less than 39.09 Gy. In conclusion, WBRT to C1 limits parotid dose, and parotid dose constraints are achievable compared with inferior border at C2. A possible mean parotid dose constraint with BED3 should be less than 32.83 Gy.

Clinical significance of treatment delivery errors for helical TomoTherapy nasopharyngeal plans – A dosimetric simulation study

PurposeDevelop a framework to characterize helical TomoTherapy (HT) machine delivery errors and their clinical significance. Method and materialsTen nasopharynx HT plans were edited to introduce errors in Jaw width (JW), couch speed (CS), gantry period (GP), gantry start position (GSP), multi leaf collimator leaf open times (MLC LOT). In case of MLC LOT only, both systematic and random delivery errors were investigated. Each error type was simulated independently for a range of magnitudes. Dose distributions for the clinical reference plans and the error simulated plans were compared to establish the magnitude for each error type which resulted in a change in clinical tolerance, defined as 5% variation in D95 of PTV70, D0.1cc of spinal cord, D0.1cc of brainstem and the smallest value of either a 10% or 3.6Gy dose variation in mean parotid dose. ResultsDose variation from systematic delivery errors in JW ±0.5mm, CS ranges between −1% to 1.5%, GP ±1s, GSP ranges between −20 to 2.50 and MLC LOT random error up to 2% from the planned value relative to the clinical reference plan was within the set tolerance values for all the patient cohorts. GSP errors and the random MLC LOT errors with up to 10% standard deviation were found to be relatively insensitive compared to other delivery errors. ConclusionThis work has established a framework to characterize HT machine delivery errors. This framework could be applied to any patient dataset to determine clinically relevant HT QA tolerances.

Comprehensive assessment of xerostomia in patients receiving radiation for head and neck cancer

Purpose: Xerostomia is a well known complication of radiation for head and neck cancer. It causes significant impairment of Quality Of Life (QOL).Comprehensive assessment is possible with the help of scintigraphy, Dose-volume histogram (DVH) parameters as well as QOL questionnaire. Methods: Thirty patients of head and neck cancer undergoing radiation were assessed for xerostomia. Scintigraphic assessment of parotid gland function was done before and at six weeks after radiation. QOL questionnaire was administered before, during, and at six weeks after radiation as well as at two years of follow up. Dose received by parotids were correlated with scintigraphic and QOL outcomes. Results: Mean parotid gland volume and dose received were 24.9 cc and 45.3 Gy respectively. Mean Salivary Excretion Factor (SEF) decreased from 54.1 to 12 at six weeks after radiation. QOL scores worsened from first week (mean value: 2.37) of radiotherapy (RT) to fourth week (mean value: 15.50, p < 0.0000) , remained same till completion of RT (mean value: 17.57, p = 0.1063) and at six weeks after radiation (mean value:16.10, p = 0.2519 ). There was a significant decrease in QOL scores between post RT six weeks versus two years follow up (p < 0.0000). Mean parotid dose and QOL scores correlated at six weeks (p < 0.0000), whereas no correlation was found between SEF and QOL. Conclusion: Comprehensive assessment of parotid gland function with Scintigraphy, QOL questionnaire and its correlation with dose volume parameters is helpful in quantifying xerostomia. Even though radiation induced xerostomia persisted for a long time after radiation, it did not translate to decreased QOL.

Outcomes of intensity-modulated radiotherapy as primary treatment for oropharyngeal squamous cell carcinoma - a European singleinstitution analysis.

To analyse survival and toxicity outcomes in patients treated with primary intensity-modulated radiotherapy (IMRT) for oropharyngeal squamous cell carcinoma (OPSCC) in the era of routine human papilloma virus (HPV) testing. Single-institution case series. Tertiary Head and Neck Cancer Unit. A total of 186 patients received IMRT (+/- chemotherapy) for radical primary treatment of OPSCC between March 2010 and December 2013. HPV status was available for 88% of cases. Median radiation dose was 65 Gy in 30 daily fractions. 90% of stage III/IV patients received concurrent chemotherapy or cetuximab. Overall, disease-free and disease-specific survival; rates of late xerostomia and dysphagia. A total of 177 patients completed treatment (Stage I/II: 23; Stage III/IV: 154), with median follow-up of 26 months. Estimated 3-year overall survival (OS), disease-free survival (DFS) and disease-specific survival (DSS) rates were 77.2% (70.5-83.9), 72.3% (65.4-79.2) and 80.2% (74.1-86.3). Estimated 3-year OS, DFS and DSS for HPV-positive patients were 90.9% (85.2-96.6), 87.9% (81.4-94.4) and 91.8% (86.3-97.3). A previously identified risk stratification method was validated, showing improved OS for low-risk over high-risk patients (HR 0.09, P < 0.001). The 2-year feeding tube retention rate was 6%, and 2-year grade ≥2 xerostomia rate was 38% (23% if mean contralateral parotid dose <24 Gy). Outcomes with IMRT are favourable, particularly in the HPV-positive patient group. This data further supports the use of a previously described prognostication model that can be used to select patients for escalation/de-escalation clinical trials.

SU-G-BRC-02: A Novel Multi-Criteria Optimization Approach to Generate Deliverable Intensity-Modulated Radiation Therapy (IMRT) Treatment Plans

Purpose: To present a novel multi-criteria optimization (MCO) solution approach that generates treatment plans with deliverable apertures using column generation. Methods: We demonstrate our method with 10 locally advanced head-and-neck cancer cases retrospectively. In our MCO formulation, we defined an objective function for each structure in the treatment volume. This resulted in 9 objective functions, including 3 distinct objectives for primary target volume, high-risk and low-risk target volumes, 5 objectives for each of the organs-at-risk (OARs) (two parotid glands, spinal cord, brain stem and oral cavity), and one for the non-target non-OAR normal tissue. Conditional value-at-risk (CVaR) constraints were utilized to ensure at least certain fraction of the target volumes receiving the prescription doses. To directly generate deliverable plans, column generation algorithm was embedded within our MCO approach for aperture shape generation. Final dose distributions for all plans were generated using a Monte Carlo kernel-superposition dose calculation. We compared the MCO plans with the clinical plans, which were created by clinicians. Results: At least 95% target coverage was achieved by both MCO plans and clinical plans. However, the average conformity indices of clinical plans and the MCO plans were 1.95 and 1.35, respectively (31% reduction, p<0.01). Compared to the conventional clinical plan, the proposed MCO method achieved average reductions in left parotid mean dose of 5% (p=0.06), right parotid mean dose of 18% (p<0.01), oral cavity mean dose of 21% (p=0.03), spinal cord maximum dose of 20% (p<0.01), brain stem maximum dose of 61% (p<0.01), and normal tissue maximum dose of 5% (p<0.01), respectively. Conclusion: We demonstrated that the proposed MCO method was able to obtain deliverable IMRT treatment plans while achieving significant improvements in dosimetric plan quality.

SU‐F‐J‐17: Patient Localization Using MRI‐Guided Soft Tissue for Head‐And‐Neck Radiotherapy: Indication for Margin Reduction and Its Feasibility

Purpose:On‐board MRI provides superior soft‐tissue contrast, allowing patient alignment using tumor or nearby critical structures. This study aims to study H&amp;N MRI‐guided IGRT to analyze inter‐fraction patient setup variations using soft‐tissue targets and design appropriate CTV‐to‐PTV margin and clinical implication.Methods:282 MR images for 10 H&amp;N IMRT patients treated on a ViewRay system were retrospectively analyzed. Patients were immobilized using a thermoplastic mask on a customized headrest fitted in a radiofrequency coil and positioned to soft‐tissue targets. The inter‐fraction patient displacements were recorded to compute the PTV margins using the recipe: 2.5∑+0.7σ. New IMRT plans optimized on the revised PTVs were generated to evaluate the delivered dose distributions. An in‐house dose deformation registration tool was used to assess the resulting dosimetric consequences when margin adaption is performed based on weekly MR images. The cumulative doses were compared to the reduced margin plans for targets and critical structures.Results:The inter‐fraction displacements (and standard deviations), ∑ and σ were tabulated for MRI and compared to kVCBCT. The computed CTV‐to‐PTV margin was 3.5mm for soft‐tissue based registration. There were minimal differences between the planned and delivered doses when comparing clinical and the PTV reduced margin plans: the paired t‐tests yielded p=0.38 and 0.66 between the planned and delivered doses for the adapted margin plans for the maximum cord and mean parotid dose, respectively. Target V95 received comparable doses as planned for the reduced margin plans.Conclusion:The 0.35T MRI offers acceptable soft‐tissue contrast and good spatial resolution for patient alignment and target visualization. Better tumor conspicuity from MRI allows soft‐tissue based alignments with potentially improved accuracy, suggesting a benefit of margin reduction for H&amp;N radiotherapy. The reduced margin plans (i.e., 2 mm) resulted in improved normal structure sparing and accurate dose delivery to achieve intended treatment goal under MR guidance.

SU‐F‐J‐86: Method to Include Tissue Dose Response Effect in Deformable Image Registration

Purpose:Organ changes shape and size during radiation treatment due to both mechanical stress and radiation dose response. However, the dose response induced deformation has not been considered in conventional deformable image registration (DIR). A novel DIR approach is proposed to include both tissue elasticity and radiation dose induced organ deformation.Methods:Assuming that organ sub‐volume shrinkage was proportional to the radiation dose induced cell killing/absorption, the dose induced organ volume change was simulated applying virtual temperature on each sub‐volume. Hence, both stress and heterogeneity temperature induced organ deformation. Thermal stress finite element method with organ surface boundary condition was used to solve deformation. Initial boundary correspondence on organ surface was created from conventional DIR. Boundary condition was updated by an iterative optimization scheme to minimize elastic deformation energy. The registration was validated on a numerical phantom. Treatment dose was constructed applying both the conventional DIR and the proposed method using daily CBCT image obtained from HN treatment.Results:Phantom study showed 2.7% maximal discrepancy with respect to the actual displacement. Compared with conventional DIR, subvolume displacement difference in a right parotid had the mean±SD (Min, Max) to be 1.1±0.9(−0.4∼4.8), −0.1±0.9(−2.9∼2.4) and −0.1±0.9(−3.4∼1.9)mm in RL/PA/SI directions respectively. Mean parotid dose and V30 constructed including the dose response induced shrinkage were 6.3% and 12.0% higher than those from the conventional DIR.Conclusion:Heterogeneous dose distribution in normal organ causes non‐uniform sub‐volume shrinkage. Sub‐volume in high dose region has a larger shrinkage than the one in low dose region, therefore causing more sub‐volumes to move into the high dose area during the treatment course. This leads to an unfavorable dose‐volume relationship for the normal organ. Without including this effect in DIR, treatment dose in normal organ could be underestimated affecting treatment evaluation and planning modification.Acknowledgement: Partially Supported by Elekta Research Grant

SU‐F‐T‐168: Development and Implementation of An Anthropomorphic Head &amp; Neck Phantom for the Assessment of Proton Therapy Treatment Procedures

Purpose:To design a Head and Neck (H&amp;N) anthropomorphic QA phantom that the Imaging and Radiation Oncology Core Houston (IROC‐H) can use to verify the quality of intensity modulated proton therapy (IMPT) H&amp;N treatments for institutions participating in NCI clinical trials.Methods:The phantom was created to serve as a remote auditing tool for IROC‐H to evaluate an institution's IMPT planning and delivery abilities. The design was based on the composition, size, and geometry of a generalized oropharyngeal tumor and contains critical structures (parotids and spinal cord). Radiochromic film in the axial and sagittal planes and thermoluminescent dosimeters (TLD)‐100 capsules were embedded in the phantom and used to perform the dose delivery evaluation. A CT simulation was used to create a passive scatter and a spot scanning treatment plan with typical clinical constraints for H&amp;N cancer. The IMPT plan was approved by a radiation oncologist and the phantom was irradiated multiple times. The measured dose distribution using a 7%/4mm gamma analysis (85% of pixels passing) and point doses were compared with the treatment planning system calculations.Results:The designed phantom could not achieve the target dose prescription and organ at risk dose constraints with the passive scatter treatment plan. The target prescription dose could be met but not the parotid dose constraint. The average TLD point dose ratio in the target was 0.975, well within the 5% acceptance criterion. The dose distribution analysis using various acceptance criteria, 5%/4mm, 5%/3mm, 7%/4mm and 7%/5mm, had average pixel passing rates of 85.9%, 81.8%, 89.6% and 91.6%, and respectively.Conclusion:An anthropomorphic IMPT H&amp;N phantom was designed that can assess the dose delivery of proton sites wishing to participate in clinical trials using a 5% TLD dose and 7%/4mm gamma analysis acceptance criteria.