Tsair-Fwu Lee

Dosimetric comparisons of helical tomotherapy and step-and-shoot intensity-modulated radiotherapy in nasopharyngeal carcinoma

PURPOSE The study evaluates and quantifies the potential dosimetric gains of helical tomotherapy (HT) versus step-and-shoot intensity-modulated radiotherapy (SaS-IMRT) for nasopharyngeal carcinoma (NPC). MATERIALS AND METHODS Twenty consecutive NPC patients curatively treated by HT were examined. Each case was planned by HT and SaS-IMRT (ADAC Pinnacle(3)) planning system, respectively. Dose plans were compared using dose volume histograms (DVH), conformity index (CI), homogeneity index (HI), and minimal dose to 1cc (D(min_1cc)) of the planned target volume (PTV) and a comprehensive quality index (CQI) of ten organs at risk (OARs). The prescribed dose/fractionation was 72Gy to the PTV, 64.8Gy to the elective PTV, and 54Gy to the clinically negative neck region. The plan of 54Gy to the PTV (PTV(54)) was used to evaluate the CI and HI in the target. The cumulative doses of the three PTV plans to the OARs were calculated. RESULTS We observed the HT plans significantly improved the CI (improvement ratio: 11.9+/-5.5%) and HI (improvement ratio: 8.8+/-1.5%) of the PTV(54) compared with SaS-IMRT plans. In addition, the mean/maximal dose of most of the OARs except chiasm was significantly reduced in HT plans, with the CQI of 0.92+/-0.08. A negative result of HT in chiasm was observed but only significantly revealed in cases without skull base infiltration. CONCLUSIONS A dosimetric gain in CI and HI of PTV and sparing of OARs was significantly obtained in HT versus SaS-IMRT plans in NPC patients. Whether such dosimetric superiority in HT could transfer into clinical advantages needs further investigation.

Health-related quality of life in 640 head and neck cancer survivors after radiotherapy using EORTC QLQ-C30 and QLQ-H&N35 questionnaires.

BackgroundWith the advances in modern radiotherapy (RT), many patients with head and neck cancer (HNC) can be effectively cured, and their health-related quality of life (HR-QoL) has become an important issue. In this study, we evaluated the prognosticators of HR-QoL in a large cohort of HNC patients, with a focus on the result from technological advances in RT.MethodsA cross-sectional investigation was conducted to assess the HR-QoL of 640 HNC patients with cancer-free survival of more than 2 years. Among them, 371 patients were treated by two-dimensional RT (2DRT), 127 by three-dimensional conformal RT (3DCRT), and 142 by intensity-modulated RT (IMRT). The EORTC QLQ-C30 questionnaire and QLQ-H&N35 module were used. A general linear model multivariate analysis of variance was used to analyze the prognosticators of HR-QoL.ResultsBy multivariate analysis, the variables of gender, annual family income, tumor site, AJCC stage, treatment methods, and RT technique were prognosticators for QLQ-C30 results, so were tumor site and RT technique for H&N35. Significant difference (p < 0.05) of HR-QoL outcome by different RT techniques was observed at 2 of the 15 scales in QLQ-C30 and 10 of the 13 scales in H&N35. Compared with 2DRT, IMRT had significant better outcome in the scales of global QoL, physical functioning, swallowing, senses (taste/smell), speech, social eating, social contact, teeth, opening mouth, dry mouth, sticky saliva, and feeling ill.ConclusionsThe technological advance of RT substantially improves the head-and-neck related symptoms and broad aspects of HR-QoL for HNC survivors.

Dual Arc Volumetric-modulated Arc Radiotherapy (VMAT) of Nasopharyngeal Carcinomas: A Simultaneous Integrated Boost Treatment Plan Comparison with Intensity-modulated Radiotherapies and Single Arc VMAT

AIMS To compare the performance of volumetric-modulated arc radiotherapy (VMAT) by dual arc with fixed beam intensity-modulated radiotherapies (IMRTs) and single arc VMAT on nasopharyngeal carcinomas (NPC). MATERIALS AND METHODS Twenty NPC cases were re-planned using the planning system of the Pinnacle(3®)SmartArc (SA) module to compare the performance of the following four techniques: seven-field (7F) and 18-field (18F) fixed beam IMRT, and single (SA(1)) and dual arc VMAT (SA(2)). The plan was delivered on an Elekta Synergy™ Linac equipped with an 80-leaf 1cm multileaf collimator. Three dose levels of planning target volumes (PTVs) with 70/59.4/54.0Gy in 33 fractions were prescribed and delivered as a simultaneous integrated boost. The conformity index and homogeneity index of the PTVs, the comprehensive quality index (CQI), the normal tissue complication probability for the organs at risk (OARs), and the planning time, delivery efficiency and accuracy were analysed. RESULTS A significantly inferior conformity index at the three dose levels of PTV and homogeneity index of PTV(70) were observed in SA(1) compared with the other techniques. Comparable conformity index and homogeneity index of the PTV were observed among 7F/18F IMRT and SA(2). Based on the CQI of the 11 OARs, the most efficient dose reduction was observed in 18F IMRT followed in order by SA(2), 7F IMRT and SA(1). The planning time was on average 13.2/24.9/40.1/42.8min for 7F/18F IMRT/SA(1)/SA(2), respectively. With regards to the delivery efficiency compared with 7F IMRT, a 51 and 41% reduction in delivery time was achieved by SA(1) and SA(2), respectively. All techniques presented a high quality assurance pass rate (>98%) of the Γ(3mm,3%) criterion. CONCLUSION In NPC cases, SA(2) gave superior results in terms of PTV coverage and OAR sparing compared with SA(1) and approached the performance achieved by 18F IMRT, but without sacrificing the delivery efficiency.

Optimization and Implementation of a Load Control Scheduler Using Relaxed Dynamic Programming for Large Air Conditioner Loads

This paper presents the optimization and implementation of a relaxed dynamic programming (RDP) algorithm to generate a daily control scheduling for optimal or near-optimal air conditioner loads (ACLs). The conventional control mode for ACL includes demand control, cycling control, and timer control, to assist customers for saving electricity costs. The proposed load control scheduler (LCS) scheme supports any combination of these three control types to save costs optimally during the dispatch period. Microprocessor hardware techniques were applied to carry out the proposed strategy for realistic application. The Visual C++ language was adopted as the developing tool to carry out the proposed work. Field tests of controlling air conditioners located in the campus of National Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan, were tested on-site to demonstrate the effectiveness of the proposed load control strategy. The results show that interruptible load scheduling can reduce the system load effectively, and the load capacity reduced by the proposed load control strategy follows closely the trajectory of the peak load.

Multivariate analysis of quality of life outcome for nasopharyngeal carcinoma patients after treatment

PURPOSE The study analyzed the prognostic factors of quality of life (QoL) for patients with nasopharyngeal carcinoma (NPC) after treatment, with focusing on the therapeutic benefits of the technological advances in radiotherapy (RT). MATERIALS AND METHODS A cross-sectional investigation was conducted to assess the QoL of 356 NPC patients with cancer-free survival of more than 2 years. Among them, 106 patients were treated by two-dimensional RT (2DRT), 108 by 2DRT plus three-dimensional conformal RT (3DCRT) boost, 58 by 3DCRT alone, and 84 by intensity-modulated RT (IMRT). The QoL was assessed by the EORTC QLQ-C30 questionnaire and QLQ-H&N35 module. The clinical difference of QoL scores between groups was calculated using Cohens D coefficient. RESULTS We found NPC survivors who had a higher education level or annual family income and who had received more advanced RT treatments had better QoL outcomes. Compared with 2DRT, the impact of 3DCRT was small on most scales and moderate (Cohens D: 0.53-0.67) on emotional functioning, pain, and mouth opening; the impact of IMRT was moderate on nine scales and large (Cohens D: 0.80-0.88) on swallowing, social eating, teeth, and mouth opening. CONCLUSIONS In addition to socioeconomic levels, advances in RT technique played a significant role in improving QoL of NPC patients.

Comparative analysis of SmartArc‐based dual arc volumetric‐modulated arc radiotherapy (VMAT) versus intensity‐modulated radiotherapy (IMRT) for nasopharyngeal carcinoma

The purpose of this study was to evaluate and quantify the planning performance of SmartArc‐based volumetric‐modulated arc radiotherapy (VMAT) versus fixed‐beam intensity‐modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) using a sequential mode treatment plan. The plan quality and performance of dual arc‐VMAT (DA‐VMAT) using the Pinnacle3 Smart‐Arc system (clinical version 9.0; Philips, Fitchburg, WI, USA) were evaluated and compared with those of seven‐field (7F)‐IMRT in 18 consecutive NPC patients. Analysis parameters included the conformity index (CI) and homogeneity index (HI) for the planning target volume (PTV), maximum and mean dose, normal tissue complication probability (NTCP) for the specified organs at risk (OARs), and comprehensive quality index (CQI) for an overall evaluation in the 11 OARs. Treatment delivery time, monitor units per fraction (MU/fr), and gamma (Γ3mm,3%) evaluations were also analyzed. DA‐VMAT achieved similar target coverage and slightly better homogeneity than conventional 7F‐IMRT with a similar CI and HI. NTCP values were only significantly lower in the left parotid gland (for xerostomia) for DA‐VMAT plans. The mean value of CQI at 0.98±0.02 indicated a 2% benefit in sparing OARs by DA‐VMAT. The MU/fr used and average delivery times appeared to show improved efficiencies in DA‐VMAT. Each technique demonstrated high accuracy in dose delivery in terms of a high‐quality assurance (QA) passing rate (>98%) of the (Γ3mm,3%) criterion. The major difference between DA‐VMAT and 7F‐IMRT using a sequential mode for treating NPC cases appears to be improved efficiency, resulting in a faster delivery time and the use of fewer MU/fr. PACS number: 87.53.Tf, 87.55.x, 87.55.D, 87.55.dk

Using Multivariate Regression Model with Least Absolute Shrinkage and Selection Operator (LASSO) to Predict the Incidence of Xerostomia after Intensity-Modulated Radiotherapy for Head and Neck Cancer

Purpose The aim of this study was to develop a multivariate logistic regression model with least absolute shrinkage and selection operator (LASSO) to make valid predictions about the incidence of moderate-to-severe patient-rated xerostomia among head and neck cancer (HNC) patients treated with IMRT. Methods and Materials Quality of life questionnaire datasets from 206 patients with HNC were analyzed. The European Organization for Research and Treatment of Cancer QLQ-H&N35 and QLQ-C30 questionnaires were used as the endpoint evaluation. The primary endpoint (grade 3+ xerostomia) was defined as moderate-to-severe xerostomia at 3 (XER3m) and 12 months (XER12m) after the completion of IMRT. Normal tissue complication probability (NTCP) models were developed. The optimal and suboptimal numbers of prognostic factors for a multivariate logistic regression model were determined using the LASSO with bootstrapping technique. Statistical analysis was performed using the scaled Brier score, Nagelkerke R2, chi-squared test, Omnibus, Hosmer-Lemeshow test, and the AUC. Results Eight prognostic factors were selected by LASSO for the 3-month time point: Dmean-c, Dmean-i, age, financial status, T stage, AJCC stage, smoking, and education. Nine prognostic factors were selected for the 12-month time point: Dmean-i, education, Dmean-c, smoking, T stage, baseline xerostomia, alcohol abuse, family history, and node classification. In the selection of the suboptimal number of prognostic factors by LASSO, three suboptimal prognostic factors were fine-tuned by Hosmer-Lemeshow test and AUC, i.e., Dmean-c, Dmean-i, and age for the 3-month time point. Five suboptimal prognostic factors were also selected for the 12-month time point, i.e., Dmean-i, education, Dmean-c, smoking, and T stage. The overall performance for both time points of the NTCP model in terms of scaled Brier score, Omnibus, and Nagelkerke R2 was satisfactory and corresponded well with the expected values. Conclusions Multivariate NTCP models with LASSO can be used to predict patient-rated xerostomia after IMRT.

Pretreatment Quality of Life As a Predictor of Distant Metastasis and Survival for Patients With Nasopharyngeal Carcinoma

PURPOSE The purpose of this study was to examine the prognostic value of pretreatment quality of life (QoL) data on locoregional control (LRC), distant metastasis-free survival (DMFS), and overall survival (OS) in patients with nasopharyngeal carcinoma (NPC). PATIENTS AND METHODS A total of 347 new patients with NPC, who were curatively treated by conformal radiotherapy from March 2003 to December 2007, were recruited. The Taiwan Chinese version of the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire C30 was completed before treatment. Multivariate Coxs proportional hazards models were used to analyze the impact of clinical and QoL variables on the treatment results. RESULTS The 5-year LRC, DMFS, and OS rates were 72.9%, 79.1%, and 68.4%, respectively. After adjusting the clinical variables, 10 QoL variables were observed to be significantly (P < .05) related to OS, and four QoL variables were related to DMFS. No QoL variable was predictive of LRC. Among the QoL variables that significantly predicted OS and DMFS, physical functioning was the most powerful predictor. A 10-point increase in the physical functioning score was associated with a 23% (95% CI, 12% to 34%) reduction in the likelihood of death and a 22% (95% CI, 9% to 36%) reduction in the likelihood of distant metastasis. CONCLUSION Our findings indicate that pretreatment QoL variables, especially physical functioning, provide easily available prognostic value for distant metastasis and survival in patients with NPC.

Quantitative analysis of normal tissue effects in the clinic (QUANTEC) guideline validation using quality of life questionnaire datasets for parotid gland constraints to avoid causing xerostomia during head-and-neck radiotherapy

PURPOSE To perform a validation test of the quantitative analysis of normal tissue effects in the clinic (QUANTEC) guidelines against quality of life (QoL) questionnaire datasets collected prospectively from patients with head and neck (HN) cancers, including HN squamous cell carcinoma (HNSCC) and nasopharyngeal carcinoma (NPC). METHODS AND MATERIALS QoL questionnaire datasets from 95 patients with NPC and 142 with HNSCC were analyzed separately. The European Organization for Research and Treatment of Cancer H&N35 QoL questionnaire was used as the endpoint evaluation. The primary endpoint (grade 3(+) xerostomia) was defined as moderate to severe xerostomia 3 and 12 months after the completion of RT, and excluded patients with grade 3(+) xerostomia at the baseline. The Lyman-Kutcher-Burman normal tissue complication probability (NTCP) model was used to describe the incidence of xerostomia. Negative predictive values (NPVs) were used to determine the rate of correctly predicting the lack of complications. RESULTS NTCP fitted parameters were TD₅₀=37.8 Gy (CI: 29.1-46.9 Gy), m=0.59 (CI: 0.48-0.80) and TD50=43.9 Gy (CI: 33.2-52.8 Gy), m=0.48 (CI: 0.37-0.76) at the 3-month and 12-month time points, respectively. For QUANTEC validation, HN and HNSCC data validation gave similar results at 3 months; at mean doses to the spared parotid of ≤20 and ≤25 Gy, the QoL dataset showed approximately 22% and 28% rates of xerostomia, respectively. At 12 months, the rates of xerostomia were approximately 13% and 19%, respectively. For NPC cases, the dataset showed approximately 0% and 33% (∼67% NPV) rates of xerostomia at 3 months. At 12 months, both rates of xerostomia were approximately 0% (∼100% NPV), which differed significantly from the results for the HNSCC cohort. CONCLUSION The QoL datasets validated the QUANTEC guidelines and suggested that the modified QUANTEC 20/20-Gy spared-gland guideline is suitable for clinical use in HNSCC cohorts to effectively avoid xerostomia, and the QUANTEC 25-Gy guideline is justified for NPC cohorts.

Dosimetric Comparison of Helical Tomotherapy and Dynamic Conformal Arc Therapy in Stereotactic Radiosurgery for Vestibular Schwannomas

The dosimetric results of stereotactic radiosurgery (SRS) for vestibular schwannoma (VS) performed using dynamic conformal arc therapy (DCAT) with the Novalis system and helical TomoTherapy (HT) were compared using plan quality indices. The HT plans were created for 10 consecutive patients with VS previously treated with SRS using the Novalis system. The dosimetric indices used to compare the techniques included the conformity index (CI) and homogeneity index (HI) for the planned target volume (PTV), the comprehensive quality index (CQI) for nine organs at risk (OARs), gradient score index (GSI) for the dose drop-off outside the PTV, and plan quality index (PQI), which was verified using the plan quality discerning power (PQDP) to incorporate 3 plan indices, to evaluate the rival plans. The PTV ranged from 0.27-19.99 cm(3) (median 3.39 cm(3)), with minimum required PTV prescribed doses of 10-16 Gy (median 12 Gy). Both systems satisfied the minimum required PTV prescription doses. HT conformed better to the PTV (CI: 1.51 ± 0.23 vs. 1.94 ± 0.34; p < 0.01), but had a worse drop-off outside the PTV (GSI: 40.3 ± 10.9 vs. 64.9 ± 13.6; p < 0.01) compared with DCAT. No significant difference in PTV homogeneity was observed (HI: 1.08 ± 0.03 vs. 1.09 ± 0.02; p = 0.20). HT had a significantly lower maximum dose in 4 OARs and significant lower mean dose in 1 OAR; by contrast, DCAT had a significantly lower maximum dose in 1 OAR and significant lower mean dose in 2 OARs, with the CQI of the 9 OARs = 0.92 ± 0.45. Plan analysis using PQI (HT 0.37 ± 0.12 vs. DCAT 0.65 ± 0.08; p < 0.01), and verified using the PQDP, confirmed the dosimetric advantage of HT. However, the HT system had a longer beam-on time (33.2 ± 7.4 vs. 4.6 ± 0.9 min; p < 0.01) and consumed more monitor units (16772 ± 3803 vs. 1776 ± 356.3; p < 0.01). HT had a better dose conformity and similar dose homogeneity but worse dose gradient than DCAT. Plan analysis confirmed the dosimetric advantage of HT, although not all indices revealed a better outcome for HT. Whether this dosimetric advantage translates into a clinical benefit deserves further investigation.