Intensity-modulated Radiotherapy For Nasopharyngeal Carcinoma Research Articles

43 Clinical-dosimetric relationship between lacrimal gland dose and ocular toxicity after intensity-modulated radiotherapy for nasopharyngeal carcinoma

43 Clinical-dosimetric relationship between lacrimal gland dose and ocular toxicity after intensity-modulated radiotherapy for nasopharyngeal carcinoma

Deletion of concurrent chemotherapy on the basis of sequential chemoradiotherapy for non-metastatic stage T4 nasopharyngeal carcinoma in IMRT era.

Intensity-modulated radiotherapy (IMRT) combined with concurrent chemotherapy is deemed as the mainstay treatment in locoregionally advanced nasopharyngeal carcinoma (NPC). Nevertheless, the tolerance of severe acute toxicity of concurrent chemotherapy was unsatisfied. In addition, T4 is the predicting factor of poor prognosis for NPC patients. In this retrospective analysis, the long-term outcomes IMRT combined by induction chemotherapy deleting concurrent chemotherapy with or without adjuvant chemotherapy for T4 non-metastatic NPC were analyzed. From January 2005 to November 2016, a total of 145 biopsy-proven non-metastatic T4 NPC was treated with IMRT combined by induction chemotherapy with or without adjuvant chemotherapy. The survival and side effects of the patients were analyzed. Median follow-up time was 74 months (ranges, 8-186 months). 10.0%, 61.3%, 27.3%, and 1.3% developed grade 1, 2, 3, and 4 mucositis during IMRT, respectively. 5.5% and 2.0% patients experienced grade 1 and 2 nausea and vomiting; no patients developed grade 3 or 4 nausea and vomiting. Of 145 patients enrolled, 5-year and 10-year overall survival(OS) rates were 73.7% and 53.9%, local progression-free survival(LPFS) rates were 86.1% and 71.6%, regional progression-free survival(RPFS) rates were 96.7% and 92.8%, distant metastasis-free survival (DMFS) rates were 86.7%, 78.2%, respectively. At the last follow-up, five patients developed cranial nerve injury, one patient developed mandibular bone necrosis, four patients developed temporal lobe injury, four patients developed nasopharyngeal massive hemorrhage (three cases after recurrence and one case without recurrence), and five patients developed second primary tumor. The survival outcomes of treating T4 NPC IMRT combined by induction chemotherapy deleting concurrent chemotherapy with or without adjuvant chemotherapy are encouraging. Moreover, mucosal reaction, nausea, and vomiting reaction were reduced during IMRT.

Selectively sparing of the supraclavicular area during intensity-modulated radiotherapy in nasopharyngeal carcinoma: A double-center observation study

Background and purposeThis study was aimed at evaluating the feasibility of sparing the supraclavicular area, namely levels IVb and Vc, during intensity-modulated radiotherapy (IMRT) in nasopharyngeal carcinoma (NPC) patients with N1-2 disease[except N1 disease with purely restropharyngeal lymph nodes(RPN) involvement], and providing a basis for the revision of International Guideline for the delineation of the clinical target volume (CTV). Patients and materialsPatients with NPC (stage TanyN1-2M0) diagnosed pathologically in Fujian Cancer Hospital (Center 1, Only Lin SJ‘s attending group) from January 2014 to March 2018 and Jiangxi Cancer Hospital(Center 2) from January 2014 to December 2015 were included. According to our principle, the supraclavicular area (levels IVb and Vc) were excluded from the CTVnd. Survival outcomes focused on regional recurrence-free survival (RRFS) and recurrence rates of levels IVb and Vc were analysed. ResultsA total of 672 eligible patients were recruited (Center 1, n = 362; Center 2, n = 310). There was no significant difference in 5-year RRFS (97.33 % vs. 97.24 %, p = 0.980), overall survival (OS) (89.14 % vs. 88.56 %, p = 0.327), local recurrence-free survival (LRFS) (94.90 % vs. 95.30 %, p = 0.593) and distant metastasis-free survival (DMFS) (89.38 % vs. 86.60 %, p = 0.130) between Center 1 and Center 2. Twenty patients developed regional failure (median: 36 months), among them, only one case (0.15 %) was recorded as levels IVb and Vc recurrence. ConclusionOmitting the supraclavicular area (levels IVb and Vc) during IMRT should be safe and feasible for N1-2 disease (except N1 disease with purely RPN involvement). Well-designed multicenter prospective trials should be conducted to confirm our findings.

Effect of Intensity Level on Dose in Intensity-modulated Radiotherapy for Nasopharyngeal Carcinoma

Effect of Intensity Level on Dose in Intensity-modulated Radiotherapy for Nasopharyngeal Carcinoma

A Neural Network-based Method for Predicting Dose to Organs at Risk in Intensity-modulated Radiotherapy for Nasopharyngeal Carcinoma

ObjectiveA neural network method was used to establish a dose prediction model for organs at risk (OARs) during intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). Materials and methodsIn total, 103 patients with NPC were randomly selected for IMRT. Suborgans were automatically generated for OARs using ring structures based on distance to the target using a MATLAB program and the corresponding volume of each suborgan was determined. The correlation between the volume of each suborgan and the dose to each OAR was analysed and neural network prediction models of the OAR dose were established using the MATLAB Neural Net Fitting application. The R-value and mean square error in the regression analysis were used to evaluate the prediction model. ResultsThe OAR dose was related to the volume of the corresponding sub-OAR. The average R-values for the normalised mean dose (Dnmean) to parallel organs and serial organs and the normalised maximum dose (Dn0) to serial organs in the training set were 0.880, 0.927 and 0.905, respectively. The mean square error for each OAR in the prediction model was low (ranging from 1.72 × 10−4 to 7.06 × 10−3). ConclusionThe neural network-based model for predicting OAR dose during IMRT for NPC is simple, reliable and worth further investigation and application.

Set-up errors of the neck are underestimated using the overall registration frame of head and neck in IMRT for NPC.

There is no standardized registration frame of cone beam CT (CBCT) in intensity modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). The overall registration frame that covers the whole head and neck is the most commonly used CBCT registration frame for NPC patients in IMRT. To compare the set-up errors using different registration frames of CBCT for NPC to assess the set-up errors for different region of the commonly used clinical overall registration frame. 294 CBCT images of 59 NPC patients were collected. Four registration frames were used for matching. The set-up errors were obtained using an automatic matching algorithm and then compared. The expansion margin from the clinical target volume (CTV) to the planned target volume (PTV) in the four groups was also calculated. The average range of the isocenter translation and rotation errors of four registration frames are 0.89∼2.41 mm and 0.49∼1.53°, respectively, which results in a significant difference in the set-up errors (p < 0.05). The set-up errors obtained from the overall frame are smaller than those obtained from the head, upper neck, and lower neck frames. The margin ranges of the overall, head, upper neck, and lower neck frames in three translation directions are 1.49∼2.39 mm, 1.92∼2.45 mm, 1.86∼3.54 mm and 3.02∼4.78 mm, respectively. The expansion margins calculated from the overall frame are not enough, especially for the lower neck. Set-up errors of the neck are underestimated by the overall registration frame. Thus, it is important to improve the position immobilization of the neck, especially the lower neck. The margin of the target volume of the head and neck region should be expanded separately if circumstances permit.

Efficacy and toxicity of three concurrent chemoradiotherapy regimens in treating nasopharyngeal carcinoma: Comparison among cisplatin, nedaplatin, and lobaplatin.

Few studies directly compare efficacy and toxicity among lobaplatin, nedaplatin and cisplatin concurrently with intensity-modulated radiotherapy (IMRT) in nasopharyngeal carcinoma (NPC). Totally 141 treatment-naïve NPC without distant metastasis receiving IMRT concurrent with cisplatin or nedaplatin or lobaplatin were retrospectively enrolled. Their response rate, toxicity and long-term survival were compared. Complete response (CR) rates of concurrent lobaplatin (CR-nasopharynx [CR-nx], 82.7%; CR-cervical lymph node [CR-nd], 94.2%) were lower than those of cisplatin (CR-nx, 89.3%; CR-nd, 98.2%) and nedaplatin (CR-nx, 93.9%; CR-nd, 97.0%), but statistical significance wasn't detected. Estimated five-year overall survival (OS), local relapse-free survival (LRFS), distant metastasis-free survival (DMFS) and progression-free survival (PFS) weren't statistically significant between three groups. Multivariable analysis by COX proportional hazards model showed concurrent chemotherapy regimen wasn't an independent prognostic factor. Gastrointestinal toxicity was prevalent in platinum-based concurrent chemotherapy; cisplatin group suffered heavier (≥grade 2) than other two groups. More nephrotoxicity happened in cisplatin group (17.9%) than nedaplatin (9.1%) and lobaplatin (2.0%) groups. Incidence of dermatitis of ≥grade 2 was higher in cisplatin group (60.7%) than nedaplatin (27.3%) and lobaplatin (9.6%) groups. More patients in lobaplatin and nedaplatin groups suffered from any grade thrombocytopenia (P < .001), but incidence of severe thrombocytopenia (≥grade 3) was similar. Economic cost was significant less in lobaplatin group. Cisplatin, nedaplatin and lobaplatin are equally effective when used concurrently with IMRT in NPC. Lobaplatin and nedaplatin have potential to be alternatives to cisplatin in terms of less severe acute side-effects and economic cost.

Parotid Gland Stem Cell Preservation during Intensity-Modulated Radiotherapy for Nasopharyngeal Carcinoma: Dosimetric Analysis and Feasibility.

Objective Parotid gland (PG) is a radiosensitive organ, and xerostomia (XS) is a key factor affecting patients' life quality after conventional radiotherapy for head and neck tumors. In this study, dosimetry analysis was performed on PG stem cell preservation in intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). Methods All clinical data of 80 NPC patients diagnosed pathologically in the Radiotherapy Department of Taizhou Hospital of Zhejiang Province Affiliated with Wenzhou Medical University from August 2017 to September 2019 were retrospectively analyzed. Patients were assigned to a regular group and a restricted group according to different IMRT plans, in which a dose limitation for the parotid duct was added in the restricted group in addition to the conventional plan used in the regular group to minimize the parotid duct radiation dose. The differences in planning target volume (PTV) dose distribution, organ at risk (OAR) dose, and dose to the PG and its ducts were compared between the two groups. Results Significantly higher mean irradiation doses of the brainstem, mandible, and oral cavity were determined in the restricted group compared with the regular group (P > 0.05), but there was no significant difference in the mean dose of other OARs irradiated (P > 0.05). As compared to the irradiation of bilateral PGs, no statistical differences were found in the mean irradiation dose and V30 between regular and restricted groups (P > 0.05), but lower V20 and higher V45 were determined in the restricted group (P < 0.05). The mean irradiation dose, V15, V20, and V26 of bilateral parotid ducts were lower in the restricted group as compared to the regular group (P < 0.05). Conclusion IMRT for NPC can effectively reduce the mean irradiation dose and play a PG stem cell preservation role by giving specific dose limitation conditions to the parotid duct area without affecting PTV dose distribution and OAR irradiation dose, which has certain feasibility.

Second Primary Lung Adenocarcinoma After Intensity-Modulated Radiotherapy for Nasopharyngeal Carcinoma.

ObjectiveThe improvement of the efficacy of intensity-modulated radiotherapy (IMRT) for nasopharyngeal cancer (NPC) has prolonged the survival of patients, and the incidence of the second tumor has gradually increased. Among them, second primary lung adenocarcinoma (SPLAC) attributes the highest incidence. This study aimed to determine the long-term risk of SPLAC in NPC patients after IMRT.MethodsFrom May 2005 to May 2018, a total of 1,102 non-metastatic NPC patients who received IMRT in our hospital were enrolled, and the incidence and efficacy of SPLAC were followed up in the long term.ResultsOver a median follow-up period of 66 months, a total of 22 cases of SPLAC were observed, with an incidence of 2.0%. The 1-, 2-, 3-, 4-, and 5-year cumulative risks of SPLAC were 0.4%, 0.7%, 0.8%, 1.1%, and 1.7%, respectively. During follow-up, 90.9% (20/22) of the SPLAC detected was in early stage, and the recurrence rate of surgery alone was 5.3% (1/19).ConclusionIn NPC patients, the proportion of SPLAC after IMRT was similar to that of the normal population, and most of them were found in early stage during follow-up, with good surgical efficacy.

Clinical Profile and Treatment Outcomes in Patients Treated with Intensity-Modulated Radiotherapy (IMRT) for Carcinoma Nasopharynx: A Retrospective Analysis.

Objective To retrospectively evaluate the clinical outcome of carcinoma nasopharynx patients treated with the IMRT technique. Methods Eighty-one nasopharyngeal carcinoma patients who were treated with IMRT with or without chemotherapy between the period January 2011 and December 2014 at a comprehensive tertiary cancer center, Kerala, India, were included in the study. The mean age was 43 years (range 13–77 years), and majority of the patients were males (67.9%). The stagewise distribution of disease at presentation was 2 (2.5%) in stage I, 19 in stage II (23.5%), 31 (38.3%) in stage III, and 29 (35.8%) in stage IV. All patients were treated using simultaneous integrated boost (SIB) schedule using IMRT with 6 MV photon to a dose of 66 Gy in 30 fractions, 2.2 Gy per fraction prescribed to high-risk PTV; 60 Gy in 30 fractions, 2 Gy per fraction to intermediate risk PTV; and 54 Gy in 30 fractions, 1.8 Gy per fraction to low-risk PTV. Concurrent chemotherapy with cisplatin was offered to patients with stage II and above disease. Neoadjuvant chemotherapy with cisplatin and 5FU was given to patients with initially advanced disease (T3, T4, N2, and N3). Survival estimates were generated using the Kaplan–Meier method. The univariate analysis was performed using log-rank tests. Results The 5-year locoregional control (LRC), distant metastasis-free survival (DMFS), disease-free survival (DFS), and overall survival (OS) rates were 87.5%, 87%, 61.6%, and 62.5%, respectively. The 5-year OS was 100% for stage I (n = 2), 67% for stage II (n = 19), 70.4% for stage III (n = 31), and 68.1% for stage IV (n = 29). The DFS at 5 years was 100% for stage I, 61.1% for stage II, 56.2% for stage III, and 84.8% for stage IV disease. The univariate analysis showed that age, nodal stage, and use of induction chemotherapy showed an improved trend towards OS, though the results were not statistically significant. The predominant pattern of failure in the present study was distant metastasis. Most patients who developed distant metastasis in our study had either an advanced T stage or N3 disease at presentation. Conclusion The present study shows our initial experience with IMRT for nasopharyngeal carcinoma. The compliance to RT was good in this study. The 5-year LRC and OS rate of nasopharyngeal carcinoma patients treated with IMRT were 87.5% and 62.5%. Distant metastasis was the main pattern of failure.

Multivariate NTCP Model of Hypothyroidism After Intensity-Modulated Radiotherapy for Nasopharyngeal Carcinoma.

ObjectiveTo evaluate the incidence of hypothyroidism in patients with nasopharyngeal carcinoma after intensity-modulated radiotherapy (IMRT), analyze its correlation with multiple influencing factors such as thyroid exposure dose, thyroid volume, and gender, and construct a multivariate-based normal tissue complication probability (NTCP) model for the occurrence of hypothyroidism after IMRT.Materials and MethodsThe thyroid hormone levels of patients at different points in time before and after radiotherapy were tested, and statistics on the incidence of hypothyroidism after treatment were obtained. The dose-volume data of patients’ thyroids were converted into EQD2 equivalent dose values. The correlation between hypothyroidism after radiotherapy and thyroid exposure dose, thyroid volume, gender, and other factors was analyzed, and an NTCP model was constructed.ResultsA total of 69 patients with nasopharyngeal carcinoma were enrolled in this study. Twelve months after radiotherapy, a total of 24 patients (34.8%) developed hypothyroidism. Univariate analysis and multivariate analysis revealed that the average thyroid dose and thyroid volume are the most important factors affecting hypothyroidism after radiotherapy. The NTCP model constructed based on the average dose and thyroid volume has a good degree of fit.ConclusionThe volume and average dose of the thyroid gland are the key factors affecting the occurrence of hypothyroidism in patients with nasopharyngeal carcinoma after radiotherapy. The NTCP model constructed based on multivariate construction suggests that reducing the average dose of the thyroid to the greatest extent is an effective way to protect thyroid functions.

Prognostic analysis of 152 patients with distant metastasis after intensity-modulated radiotherapy for nasopharyngeal carcinoma.

The aim of this study was to analyze the prognostic factors for nasopharyngeal carcinoma (NPC) patients with distant metastasis after intensity-modulated radiotherapy (IMRT), and to provide a further basis for clinical treatment options. One hundred and fifty-two NPC patients with distant metastasis after IMRT from January 2006 to December 2017 were included in this study and reviewed for analysis. The patients were followed up for a median time of 43 months. The survival rate was calculated and compared using the Kaplan-Meier method and log-rank tests, respectively. The Cox risk ratio model was used for univariate and multivariate analyses. Among all patients, the median interval from treatment completion to distant metastasis was 11.3 months. The median post-metastasis survival was 14 months, and the 1-, 2-, and 3-year survival rates were 60.4%, 40.2%, and 27.6%, respectively. Through univariate analysis, we found that overall survival was related to lymph node (N) staging at diagnosis, whether induction chemotherapy was utilized, the interval time from initial radiotherapy completion to distant metastasis, with/without liver metastasis, and whether chemotherapy or palliative radiotherapy were utilized after metastasis discovery. Cox regression results showed that liver metastasis, multi-organ metastasis, chemotherapy after metastasis, and the time from radiotherapy completion to distant metastasis were independent prognostic factors for patient survival. The prognosis of NPC patients with distant metastasis after IMRT was related to the time from radiotherapy completion to distant metastasis, liver and multi-organ metastasis, and whether adjuvant chemotherapy was administered. Both adequate adjuvant chemotherapy and palliative radiotherapy could potentially prolong the patients' survival.

Temporal Lobe Necrosis Following Radiotherapy in Nasopharyngeal Carcinoma: New Insight Into the Management.

Cerebral radiation necrosis (CRN) is one of the most prominent sequelae following radiation therapy for nasopharyngeal carcinoma (NPC), which might have devastating effects on patients’ quality of life (QOL). Advances in histopathology and neuro-radiology have shed light on the management of CRN more comprehensively, yet effective therapeutic interventions are still lacking. CRN was once regarded as progressive and irreversible, however, in the past 20 years, with the application of intensity-modulated radiation therapy (IMRT), both the incidence and severity of CRN have declined. In addition, newly developed medical agents including bevacizumab-a humanized monoclonal antibody against vascular endothelial growth factor (VEGF), nerve growth factor (NGF), monosialotetrahexosylganglioside (GM1), etc., have shown great potency in successfully reversing radiation-induced CRN. As temporal lobes are most frequently compromised in NPC patients, this review will summarize the state-of-the-art progress regarding the incidence, pathophysiology, prevention, treatment, and prognosis of temporal lobe necrosis (TLN) after IMRT in NPC.

Normal tissue complication probability (NTCP) models for predicting temporal lobe injury after intensity-modulated radiotherapy in nasopharyngeal carcinoma: A large registry-based retrospective study from China

PurposeTo develop predictive models with dosimetric and clinical variables for temporal lobe injury (TLI) in nasopharyngeal carcinoma (NPC) after intensity-modulated radiotherapy (IMRT). Materials and methodsData of 8194 NPC patients who received IMRT-based treatment were retrospectively reviewed. TLI was diagnosed by magnetic resonance imaging. Dosimetric factors were selected by penalized regression and machine learning, with area under the receiver operating curve (AUC) calculated. Cox proportional hazards models containing the most predictive dosimetric factor with/without clinical variables were performed. A nomogram was generated as a visualization of Cox regression for predicting TLI-free survival. ResultsDuring median follow-up of 66.8 months (interquartile range [IQR] 54.2–82.2 months), 12.1% of patients (989/8194) developed TLI. Median latency from IMRT to TLI was 36 months (IQR 28–47 months). D0.5cc (dose delivered to 0.5-cm3 temporal-lobe volume) was the most predictive dosimetric factor (AUC: 0.799). Tolerance dose for 5% and 50% probabilities to develop TLI in 5 years were 65.06 Gy (95% confidence interval [CI]: 64.19–65.92) and 89.75 Gy (95% CI: 87.39–92.11), respectively. A nomogram comprising age, T stage, and D0.5cc significantly outperformed the model with only D0.5cc in predicting TLI (C-index: 0.78 vs. 0.737 in train set; 0.775 vs. 0.73 in test set; both P < 0.001). The nomogram-defined high-risk group had worse 5-year TLI-free survival. ConclusionsD0.5cc of 65.06 Gy was the tolerance dose of the temporal lobe. Reducing D0.5cc decreased risk of TLI, especially in older patients with advanced T stage. The nomogram could predict TLI precisely and allow individualized follow-up management.

Dosimetry of Submandibular Glands on Xerostomia for Nasopharyngeal Carcinoma.

PurposeTo investigate dosimetry of submandibular glands on xerostomia after intensity-modulated radiotherapy for nasopharyngeal carcinoma (NPC).MethodsFrom September 2015 to March 2016, 195 NPC patients were investigated. Xerostomia was evaluated at 12 months after treatment via the RTOG/EORTC system. The least absolute shrinkage and selection operator regression model was used to optimize feature selection for grades 2–3 xerostomia. Multivariable logistic regression analysis was applied to build a predicting model incorporating the feature selected in the least absolute shrinkage and selection operator regression model. Discrimination, calibration, and clinical usefulness of the predicting model were assessed using the C-index, calibration plot, and decision curve analysis.ResultsThe V30 of the parotid glands was selected based on the least absolute shrinkage and selection operator regression. The nomogram displayed good discrimination with a C-index of 0.698 (95% confidence interval [CI]: 0.626–0.771) and good calibration (model 1). Addition of the dosimetric parameters including the mean dose to the submandibular glands, V50 of the submandibular glands, and volume of the submandibular glands to the model 1 failed to show incremental prognostic value (model 2). The model 2 showed a C-index of 0.704 (95% CI: 0.632–0.776). Decision curve analysis demonstrated that the model 1 was clinically useful when intervention was decided at the possibility threshold of > 20%. Within this range, net benefit was comparable between the model 1 and model 2.ConclusionPGv30 was a major predictive factor of grades 2–3 xerostomia for NPC. In contrast, the mean dose to the submandibular glands, V50 of the submandibular glands, and volume of the submandibular glands were not independent predictive factors.

Effect of the number of control points on the plan quality of intensity-modulated radiotherapy for nasopharyngeal carcinoma

ABSTRACT This study aimed to investigate the effect of the number of control points (CPs) on the plan quality, plan delivery efficiency, and gamma passing rate (GPR) of intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). Twenty patients with NPC were selected. With all other optimization conditions unchanged, only the number of CPs in each field was changed and optimized to formulate four groups of IMRT plans (CP10, CP15, CP20, and CP25) for each case. An IMRT factor (IF) was used to evaluate the plan complexity, and the plan quality index (PQI) was employed to measure the plan quality. The MatriXX was used to measure each plan, and the plan delivery time (PDT) was recorded. The CP20 group had the lowest PQI (20.2%), while the CP10 group had the highest PQI (51.4%). The monitor unit (MU) values and PDTs gradually increased as the number of control points increased, while the MUs/segment significantly decreased. A negative correlation was observed between GPR and IF at the three commonly used criteria (R2 = 0.39, 0.39, and 0.41, respectively). Considering the IMRT plan quality and the efficiency and accuracy of plan delivery, 20 CPs per field should be used in the IMRT planning for NPC.

Geometric Changes in the Parotid, Submandibular, and Thyroid Glands during Intensity Modulated Radiotherapy for Nasopharyngeal Carcinoma: A Cohort Study

Background: Intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) acts on the tumor and affects surrounding organs at risk (OARs). This study aimed to quantify the geometric changes in the parotid gland, the submandibular gland (SMG), and the thyroid, during the course of treatment. Methods: Twenty patients diagnosed with locally advanced NPC were consecutively enrolled, and received definitive chemoradiotherapy in 33 fractions over 6.5 weeks. Each patient underwent planning computed tomography (pCT) followed by six weekly repeat CTs (rCTs) without contrast enhancement. Each rCT was rigidly registered to its pCT. Changes in terms of volume, position, and shape of the OARs were assessed. Differences in left- and right-sided OARs were compared. Results: Radiation doses to the parotid, SMG, and thyroid were 32.12 ± 11.2 Gy (mean ± standard deviation SD), 25.46 ± 8.62 Gy, and 18.89 ± 10.24 Gy, respectively. Volume reductions of 28.6% ± 14.6% (mean ± SD), 26.6% ± 17.1%, and 12.3% ± 11.3% were observed in the parotid, SMG, and thyroid, respectively. Rate of volume loss for the parotid and SMG decreased from 1.6-1.7% per day in the first week to 0.5%-0.6% in the last week. Contrarily, not all thyroid lobes decreased in volume during treatment. The center of mass of the parotid shifted 2.0-2.6 mm medially; for the SMG and thyroid, a 0.1-0.5 mm medial shift was noted. The displacement in the anterior-posterior and cranial-caudal directions was &lt; 0.6 mm. The 3-dimensional vector displacements of the parotid and SMG were 2.2-2.9 mm, and that of thyroid was 4.0-4.3 mm. The overlapping metrics of all three OARs decreased over time, and the shortest perpendicular distance increased from 1.5-1.8 mm in the first week to 2.4-2.5 mm in the last week. The geometric differences between weeks were statistically significant (P&lt;0.05). Conclusions: The volume, position, and shape of the OARs changed significantly during IMRT for NPC. These geometric changes displayed a time association, suggesting the necessity to re-plan treatment for better sparing of these OARs.

PO-0834: Tumor regression during intensity-modulated radiotherapy of nasopharyngeal carcinoma

PO-0834: Tumor regression during intensity-modulated radiotherapy of nasopharyngeal carcinoma

Hypothyroidism In Nasopharyngeal Carcinoma Patients After IMRT: Update Results Of A 5- Year Longitudinal Study

Hypothyroidism (HT) is a common long-term complication after intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). The aim of this study is to investigate the incidence and risk factors for predicting HT among NPC patients. February 2012 to December 2014, 178 consecutive NPC patients (median 47 years; range 18-72 years) were included in the present study. All patients were treated with IMRT with or without chemotherapy. Serum thyroid function by measuring TSH (thyroid stimulating hormone) and FT4 (free thyroxine) was evaluated before and after IMRT regularly. The cumulative probability of thyroid dysfunction was estimated using Kaplan-Meier method. Cox proportional hazard models with univariate and multivariate analyses were carried out to examine which clinical and dosimetric parameters were associated with the development of HT. The median follow-up was 61.6 months (range: 29.9-89.5 months). Of the 178 patients, 82 (46.1%) developed radiation-induced HT. Of the 82 patients, 76 were diagnosed with primary HT, 4 with central HT and 2 with a mixture of both primary and central HT. The 3- and 5- year actuarial risks of HT were 42.1% and 52.4%, respectively. The cumulative incidence of HT found in our study is generally compatible with a time-dependent effect, but it reached a plateau at 5 years following treatment. The median clinical latency for central HT was much longer than that for primary HT (15.8months vs 26.8months), but it didn’t reach statistical significance (p = 0.096). Smaller thyroid volume was identified to be an independent predictive factor for HT in both univariate and multivariate analyses (p = 0.000). A clear dose-dependent risk of HT was established in all the four multivariate models: Dtmean (p = 0.001), V40 (p = 0.014), V45 (p = 0.000) and V50 (p = 0.002) of the thyroid were all significant variables. The V50 multivariate model revealed that patients with thyroid V50 above 0.3 had a relative risk of HT that was 4.2 times the risk in those with V50 below 0.3. None of the dosimetric parameters related to pituitary gland reach statistical significance. Primary HT occurs fairly commonly after irradiation to the neck, whereas central HT is considered less common following IMRT for NPC. Dtmean and V50 were most predictive of the development of HT. Dtmean<45Gy and V50 < 0.3 should be recommended as the useful dose constraints during plan optimization.

A New Model for Predicting Hypothyroidism After Intensity-Modulated Radiotherapy for Nasopharyngeal Carcinoma.

ObjectivesTo develop a model that can predict the risk of hypothyroidism (HT) after intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC), and to accordingly recommend dose constraints.Materials and MethodsNPC patients treated between 2011 and 2015 were retrospectively reviewed. HT was defined by an abnormally high level of thyrotropin. The dosimetry parameters Vx (percentage of thyroid volume receiving more than x Gy of radiation) and Va,b (percentage of thyroid volume receiving >a Gy, while ≤b Gy radiation) were calculated. The primary endpoint was the development of HT within the first 2 years after IMRT. The least absolute shrinkage and selection operator and multivariate logistic regression were used to identify predictors of HT.ResultsA total of 545 patients were included in the analyses, with a median follow-up of 36 months. Of the 545 patients, 138 developed HT within 2 years, and the 2-year incidence of HT was 25.3%. In patients with thyroid volume >20 cm3, the 2-year incidence of HT was 11.7% (16/137); in patients with thyroid volume ≤20 cm3 and V30,60 ≤ 80%, the 2-year HT incidence was 19.9% (33/166); in patients with thyroid volume ≤20 cm3 and V30,60 > 80%, the 2-year incidence of HT was 36.8% (89/242).ConclusionThyroid volume and V30,60 could be reliable predictors of HT after IMRT for NPC. For patients with thyroid volume ≤20 cm3, thyroid V30,60 ≤ 80% might be a useful dose constraint to adopt during IMRT planning.