A qualitative study of improving megavoltage computed tomography image quality and maintaining dose accuracy using cycleGAN-based image synthesis.

BACKGROUND: Due to inconsistent positioning, tumor shrinking, and weight loss during fractionated treatment, the initial plan was no longer appropriate after a few fractional treatments, and the patient will require adaptive helical tomotherapy (HT) to overcome the issue. Patients are scanned with megavoltage computed tomography (MVCT) before each fractional treatment, which is utilized for patient setup and provides information for dose reconstruction. However, the low contrast and high noise of MVCT make it challenging to delineate treatment targets and organs at risk (OAR). PURPOSE: This study developed a deep-learning-based approach to generate high-quality synthetic kilovoltage computed tomography (skVCT) from MVCT and meet clinical dose requirements. METHODS: Data from 41 head and neck cancer patients were collected; 25 (2995 slices) were used for training, and 16 (1898 slices) for testing. A cycle generative adversarial network (cycleGAN) based on attention gate and residual blocks was used to generate MVCT-based skVCT. For the 16 patients, kVCT-based plans were transferred to skVCT images and electron density profile-corrected MVCT images to recalculate the dose. The quantitative indices and clinically relevant dosimetric metrics, including the mean absolute error (MAE), structural similarity index measure (SSIM), peak signal-to-noise ratio (PSNR), gamma passing rates, and dose-volume-histogram (DVH) parameters (Dmax , Dmean , Dmin ), were used to assess the skVCT images. RESULTS: The MAE, PSNR, and SSIM of MVCT were 109.6 ± 12.3 HU, 27.5 ± 1.1 dB, and 91.9% ± 1.7%, respectively, while those of skVCT were 60.6 ± 9.0 HU, 34.0 ± 1.9 dB, and 96.5% ± 1.1%. The image quality and contrast were enhanced, and the noise was reduced. The gamma passing rates improved from 98.31% ± 1.11% to 99.71% ± 0.20% (2 mm/2%) and 99.77% ± 0.18% to 99.98% ± 0.02% (3 mm/3%). No significant differences (p > 0.05) were observed in DVH parameters between kVCT and skVCT. CONCLUSION: With training on a small data set (2995 slices), the model successfully generated skVCT with improved image quality, and the dose calculation accuracy was similar to that of MVCT. MVCT-based skVCT can increase treatment accuracy and offer the possibility of implementing adaptive radiotherapy.

Evaluation of Dose Calculation Based on Cone-Beam CT Using Different Measuring Correction Methods for Head and Neck Cancer Patients.

Purpose: To investigate and compare 2 cone-beam computed tomography (CBCT) correction methods for CBCT-based dose calculation. Materials and Methods: Routine CBCT image sets of 12 head and neck cancer patients who received volumetric modulated arc therapy (VMAT) treatment were retrospectively analyzed. The CBCT images obtained using an on-board imager (OBI) at the first treatment fraction were firstly deformable registered and padded with the kVCT images to provide enough anatomical information about the tissues for dose calculation. Then, 2 CBCT correction methods were developed and applied to correct CBCT Hounsfield unit (HU) values. One method (HD method) is based on protocol-specific CBCT HU to physical density (HD) curve, and the other method (HM method) is based on histogram matching (HM) of HU value. The corrected CBCT images (CBCTHD and CBCTHM for HD and HM methods) were imported into the original planning system for dose calculation based on the HD curve of kVCT (the planning CT). The dose computation result was analyzed and discussed to compare these 2 CBCT-correction methods. Results: Dosimetric parameters, such as the Dmean, Dmax and D5% of the target volume in CBCT plan doses, were higher than those in the kVCT plan doses; however, the deviations were less than 2%. The D2%, in parallel organs such as the parotid glands, the deviations from the CBCTHM plan dose were less than those of the CBCTHD plan dose. The differences were statistically significant (P < .05). Meanwhile, the V30 value based on the HM method was better than that based on the HD method in the oral cavity region (P = .016). In addition, we also compared the γ passing rates of kVCT plan doses with the 2 CBCT plan doses, and negligible differences were found. Conclusion: The HM method was more suitable for head and neck cancer patients than the HD one. Furthermore, with the CBCTHM-based method, the dose calculation result better matches the kVCT-based dose calculation.

[Study on Automatic Plan Method for Radiotherapy after Breast-conserving Surgery Based on TiGRT System].

To study an automatic plan(AP) method for radiotherapy after breast-conserving surgery based on TiGRT system and and compare with manual plan (MP). The dosimetry parameters of 10 patients and the evaluation of scoring table were analyzed, it was found that the targets dose of AP were better than that of MP, but there was no statistical difference except for CI, The V5, V20 and V30 of affected lungs and whole lungs in AP were lower than all that in MP, the Dmean of hearts was slightly higher than that of MP, but the difference was not statistically significant, the MU of AP was increase by 16.1% compared with MP, the score of AP evaluation was increase by 6.1% compared with MP. So the AP could be programmed and automated while ensuring the quality of the plan, and can be used to design the plans for radiotherapy after breast-conserving surgery.

Long-term outcomes of nasopharyngeal carcinoma treated with helical tomotherapy using simultaneous integrated boost technique: A 10-year result.

Background: To evaluate the long-term survival and treatment-related toxicities of helical tomotherapy (HT) in nasopharyngeal carcinoma (NPC) patients. Methods: One hundred and ninety newly diagnosed non-metastatic NPC patients treated with HT from September 2007 to August 2012 were analyzed retrospectively. The dose at D95 prescribed was 70-74Gy, 60-62.7Gy and 52-56Gy delivered in 33 fractions to the primary gross tumor volume (pGTVnx) and positive lymph nodes (pGTVnd), the high risk planning target volume (PTV1), and the low risk planning target volume (PTV2), respectively, using simultaneous integrated boost technique. The statistical analyses were performed and late toxicities were evaluated and scored according to the Common Terminology Criteria for Adverse Events (version 3.0). Results: The median follow-up time was 145 months. The 10-year local relapse-free survival (LRFS), nodal relapse-free survival (NRFS), distant metastasis-free survival (DMFS) and overall survival (OS) were 94%, 95%, 86%, and 77.8%; respectively. Fifty (26.3%) patients had treatment-related failures at the last follow-up visit. Distant metastasis, occurred in 25 patients, was the major failure pattern. Multivariate analysis showed that age and T stage were independent predictors of DMFS and OS, Concomitant chemotherapy improved overall survival, but anti-EGFR monoclonal antibody therapy failed. The most common late toxicities were mainly graded as 1 or 2. Conclusions: Helical tomotherapy with simultaneous integrated boost technique offered excellent long-term outcomes for NPC patients, with mild late treatment-related toxicities. Age and clinical stage were independent predictors of DMFS and OS. And, concurrent chemotherapy means better OS. Further prospective study is needed to confirm the superiority of this technology and to evaluate the roles of anti-EGFR monoclonal antibody treatment.

GSTP1 Ile105Val polymorphism might be associated with the risk of radiation pneumonitis among lung cancer patients in Chinese population: A prospective study.

Background: Growing data suggest that DNA damage repair and detoxification pathways play crucial roles in radiation-induced toxicities. To determine whether common functional single-nucleotide polymorphisms (SNPs) in candidate genes from these pathways can be used as predictors of radiation pneumonitis (RP), we conducted a prospective study to evaluate the associations between functional SNPs and risk of RP. Methods: We recruited a total of 149 lung cancer patients who had received intensity modulated radiation therapy (IMRT). GSTP1 and XRCC1 were genotyped using the SurPlexTM-xTAG method in all patients. RP events were prospectively scored using the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE), version 4.0. Kaplan-Meier analysis was used to determine the cumulative probability of RP of grade ≥ 2. Cox proportional hazard regression was performed to identify clinical variables and SNPs associated with risk of RP grade ≥ 2, using univariate and multivariate analysis, respectively. Results: With a median follow-up of 9 months, the incidence of RP of grade ≥ 2 was 38.3%. A predicting role in RP was observed for the GSTP1 SNP (adjusted hazard ratio 3.543; 95% CI 1.770-7.092; adjusted P< 0.001 for the Ile/Val and Val/Val genotypes versus Ile/Ile genotype). Whereas, we found that patients with XRCC1 399Arg/Gln and Gln/Gln genotypes had a lower risk of RP compares with those carrying Arg/Arg genotype (adjusted HR 0.653; 95% CI 0.342-1.245), but with no statistical significance observed (adjusted P = 0.195). Conclusions: Our results suggested a novel association between GSTP1 SNP 105Ile/Val and risk of RP development, which suggests the potential use of this genetic polymorphism as a predictor of RP. In addition, genetic polymorphisms of XRCC1 399Arg/Gln may also be associated with RP.

Association of DNA repair gene polymorphisms with the risk of radiation pneumonitis in lung cancer patients.

A total of 149 lung cancer patients were recruited to receive intensity modulated radiation therapy (IMRT). The association of developing radiation pneumonitis (RP) with genetic polymorphism was evaluated. The risks of four polymorphic sites in three DNA repair related genes (ERCC1, rs116615:T354C and rs3212986:C1516A; ERCC2, rs13181:A2251C; XRCC1, rs25487:A1196G) for developing grade ≥ 2 RP were assessed respectively. It was observed that ERCC1 T354C SNP had a significant effect on the development of grade ≥ 2 RP (CT/TT vs. CC, adjusted HR = 0.517, 95% CI, 0.285-0.939; adjusted P = 0.030). It is the first time demonstrating that CT/TT genotype of ERCC1 354 was significantly associated with lower RP risk after radio therapy.

Propensity score matching analysis of a phase II study on simultaneous modulated accelerated radiation therapy using helical tomotherapy for nasopharyngeal carcinomas.

BACKGROUND: Using propensity score matching method (PSM) to evaluate the feasibility and clinical outcomes of simultaneous modulated accelerated radiation therapy (SMART) using helical tomotherapy (HT) in patients with nasopharyngeal carcinoma (NPC). METHODS: Between August 2007 and January 2016, 381 newly diagnosed NPC patients using HT were enrolled in pre-PSM cohort, including 161 cases in a prospective phase II study (P67.5 study, with a prescription dose of 67.5Gy in 30 fractions to the primary tumour and positive lymph nodes) and 220 cases in a retrospective study (P70 study, with a prescription dose of 70Gy in 33 fractions to the primary tumour and positive lymph nodes). Acute and late toxicities were assessed according to the established RTOG/EORTC criteria and Common Terminology Criteria for Adverse Events (CTCAE) V 3.0. Survival rate were assessed with Kaplan-Meier method, log-rank test and Cox regression. RESULTS: After matching, 148 sub-pairs of 296 patients were generated in post-PSM cohort. The incidence of grade 3-4 leukopenia, thrombocytopenia and anemia in the P67.5 group was significantly higher than in the P70 study, but no significant different was found in other acute toxicities or late toxicities between the two groups. The median follow-up was 33 months in the P67.5 and P70 group, ranging 12-54 months and 6-58 months, respectively. No significant differences in 3-year local-regional recurrence free survival (LRRFS), distant metastasis-free survival (DMFS), disease free survival (DFS) and overall survival (OS) were observed between the 2 groups. Univariate analysis showed that age, T stage, clinical stage were the main factors effecting survival. Cox proportional hazards model showed that 67.5Gy/30F pattern seemed superior in 3-year OS (HR = 0.476, 95% CI: 0.236-0.957). CONCLUSIONS: Through increasing fraction dose and shortening treatment time, the P67.5 study achieved excellent short-term outcomes and potential clinical benefits, with acceptable acute and late toxicities. TRIAL REGISTRATION: The trial was registered at Chinese Clinical Trial Registry on 5 July 2014 with a registration code of ChiCTRONC-14,004,895.

[Accuracy of Dose Calculation with CBCT Images under Different Scanning Conditions].

The treatment plans were designed based on planning CT of Catphan phantom's homogenic and heterogenetical module, respectively. With the OBI system, Catphan phantom was scanned under different scanning conditions. The dose was recalculated by applying treatment plans based on planning CT to the CBCT images with its individual hounsfield unit-electron density calibration curve. The dose distributions were compared with those of the original plan, the results of HI showed a good agreement. CIs in the homogenic module were superior to those in the heterogenetical one. There is a good dose distribution for CBCT images under different scanning conditions. It is helpful for CBCT images directly used for dose re-calculation in adaptive radiation therapy (ART).

Hypofractionated Helical Tomotherapy for Older Aged Patients With Prostate Cancer: Preliminary Results of a Phase I-II Trial.

In our center, the feasibility and related acute toxicities of hypofractionated helical tomotherapy have been evaluated in older aged patients with prostate cancer . Between February 2009 and February 2014, 67 patients (older than 65 years) were enrolled in a prospective phase I-II study (registered number, ChiCTR-ONC-13004037). Patients in cohort 1 (n = 33) and cohort 2 (n = 34) received 76 Gy in 34 fractions (2.25 Gy/F) and 71.6 Gy in 28 fractions (2.65 Gy/F), respectively, to the prostate and seminal vesicles, while 25 patients in cohort 2 also received integrated elective lymph node irradiation (50.4 Gy). All patients were treated with helical tomotherapy, and daily image guidance was performed before each treatment. Acute toxicities were assessed with Radiation Therapy Oncology Group (RTOG)/European Organization for Research on Treatment of Cancer (EORTC) criteria. No significant difference was detected between the 2 cohorts in the incidence of acute toxicities. In cohort 1, the incidences of grade 1 and 2 genitourinary and gastrointestinal toxicities were 45.5% and 45.4%, respectively, and without grade 3 and 4 toxicities. In cohort 2, the incidences of acute grade 1 and 2 genitourinary and gastrointestinal toxicities were 47.1% and 55.9%, respectively, and grade 3 genitourinary toxicity (hematuria) was noted only in 1 patient. No significant difference was detected in the incidence of acute toxicities between the patients receiving integrated elective lymph node irradiation and those receiving irradiation to prostate and seminal vesicle in cohort 2. Univariate and multivariate analyses were performed with clinical parameters. Only the baseline weight was found negatively correlated with genitourinary toxicities at a weak level (relative risk = 0.946, 95% confidence interval 0.896-0.998], P = .043). This study shows that 2 hypofractionation regimens (76 Gy/34F and 71.6 Gy/28F) delivered with HT are well tolerated in older aged patients having prostate cancer without significant difference for acute toxicities between the 2 cohorts. Late toxicities and treatment outcomes for these patients are under investigation.

[Evaluation of Cone Beam CT Image Quality and Analysis of Its Long-term Stability on HU Values under Different Conditions].

Objective: To evaluate the cone beam CT (CBCT) image quality and its long-term stability for HUs under different scanning conditions. Methods: With the OBI system, Catphan 504 phantom using the different modes was scanned through one year. Analysis of variance (ANOVA) was used to evaluate the CBCT images. Results: The results of contrast resolution under different scanning conditions met the requirements of acceptance test procedure. Spatial contrast resolution(≥5 lp/cm) of half-fan scanning conditions were inferior to those (≥7 lp/cm) of ful-fan mode. The accuracies of spatial linear distance and angle were within±1%. HUs in air density plug were constant, but HUs of other plugs with different conditions had the signifi cant difference (F=660.84,P=0). Under different conditions in a year, the mean HUs showed a good agreement. Conclusions: HUs of CBCT image under different scanning conditions exist a little difference, but there is a good consistency for the long term stability analysis. It is helpful for CBCT images directly used for dose re-calculation in adaptive radiation therapy (ART).

[RapidArc Delivery Performance Using EDR2 Film and EPID Measurement].

This study describes the development and implementation of EDR2 film and electronic portal imaging device (EPID) during RapidArc QA. The tests were designed to evaluate RapidArc performance using EDR2 film and EPID tools. The accuracy of MLC position during gantry rotation, the ability to vary and control the dose-rate and gantry speed, the synchronization of variable MLC speed and dose-rate were examined. The picket fence test of MLC in stationary gantry and RapidArc modes were implemented. The film and EPID showed a good consistency. During the evaluation of MLC speed, gantry speed and dose-rates, the dose of different parts in a field showed a good agreement, with the mean deviation of 0.24%vs 0.19%. The analysis of dose value was less than 2%. This study demonstrated that EDR2 film and EPID system can be used as reliable and efficient quality assurance tools for RapidArc delivery performance. Of course, the use of VMAT QA with EPID increases the efficiency of routine QA.

[Results of Five-year Quality Control Program and the Change of QA Mode for Helical Tomotherapy Machine].

Helical tomotherapy (HT), as a new IMRT technology, utilizes a fan beam of radiation for treatment. It combines the main characteristics of a modern CT scanner and a linear accelerator to achieve the function of helical tomotherapy. Due to the complexity of the system with a highly integrated and automated features, monitoring its operation, continuing to improve the stability and reliability, and simplifying its quality control procedures has become an important part of quality assurance (QA) for HT. Based on the results of afi ve-year quality control (QC) program, and the initial application of new QA equipment, this study wil summarize the standardization mode of its QA and explore the changes of QA mode.

[The Dose Effect of Isocenter Selection during IMRT Dose Verification with the 2D Chamber Array].

To investigate the dose effect of isocenter difference during IMRT dose verification with the 2D chamber array. The samples collected from 10 patients were respectively designed for IMRT plans, the isocenter of which was independently defined as P(o), P(x) and P(y). P(o) was fixed on the target center and the other points shifted 8cm from the target center in the orientation of x/y. The PTW729 was used for 2D dose verification in the 3 groups which beams of plans were set to 0 degrees. The γ-analysis passing rates for the whole plan and each beam were gotten using the different standards in the 3 groups, The results showed the mean passing rate of γ-analysis was highest in the P(o) group, and the mean passing rate of the whole plan was better than that of each beam. In addition, it became worse with the increase of dose leakage between the leaves in P(y) group. Therefore, the determination of isocenter has a visible effect for IMRT dose verification of the 2D chamber array, The isocenter of the planning design should be close to the geometric center of target.

[Patient-specific dose verification method using ArcCHECK for total marrow irradiation with intensity modulated arc therapy].

To investigate the patient-specific dose verification method using ArcCHECK for total marrow irradiation (TMI) with Volumetric Modulated Arc Therapy (VMAT) and Helical Tomotherapy (HT). The kVCT images collected from 8 patients were respectively designed for RapidArc and Tomotherapy plans in total marrow irradiation. ArcCHECK was used for dose verification for the head-neck, chest-abdomen and pelvic. The merging function of ArcCHECK was used in VMAT and the method of double plans (reference and delivery plans) were used in HT. The γ-analysis passing rates for the head-neck, chest-abdomen, pelvic were 98.9% ± 1.9%, 98.4% ± 1.8%, 97.4% ± 2.1% for VMAT plans and 94.3% ± 1.5%, 96.5 ± 1.2%, 94.1% ± 1.9% for HT plans. The results show that using the merging function of ArcCHECK can achieve the dose verification well for VMAT plans with TMI. The method of double plans was done for the dose verification of HT plans with TMI as well as the plans with the targets keeping away from the set-up center.

Actual anatomical and dosimetric changes of parotid glands in nasopharyngeal carcinoma patients during intensity modulated radiation therapy.

The goal of this study was to evaluate the actual anatomical and dosimetric changes of parotid glands in nasopharyngeal carcinoma patients during intensity modulated radiation therapy. With helical tomotherapy, its planning system, and adaptive software, weekly anatomical and dosimetric changes of parotid glands in 35 NPC patients were evaluated. Interweekly parotid volume varied significantly (P < 0.03). The rate of volume change reached the highest level at the 16th fraction. The average V 1 increased by 32.2 (left) and 28.6 (right), and the average D 50 increased by 33.9 (left) and 24.93 (right), respectively. Repeat data comparison indicated that the V 1 and D 50 varied significantly among different fractions (both with P = 0.000). The variation of parotid volume was inversely correlated with that of the V 1 and D 50 (both with P = 0.000). In conclusion, parotid volume and actual dose vary significantly in NPC patients during IMRT. Replanning at the end of the fourth week of IMRT may have clinical benefits.

Replanning Criteria and Timing Definition for Parotid Protection-Based Adaptive Radiation Therapy in Nasopharyngeal Carcinoma.

The goal of this study was to evaluate real-time volumetric and dosimetric changes of the parotid gland so as to determine replanning criteria and timing for parotid protection-based adaptive radiation therapy in nasopharyngeal carcinoma. Fifty NPC patients were treated with helical tomotherapy; volumetric and dosimetric (D mean, V 1, and D 50) changes of the parotid gland at the 1st, 6th, 11th, 16th, 21st, 26th, 31st, and 33rd fractions were evaluated. The clinical parameters affecting these changes were studied by analyses of variance methods for repeated measures. Factors influencing the actual parotid dose were analyzed by a multivariate logistic regression model. The cut-off values predicting parotid overdose were developed from receiver operating characteristic curves and judged by combining them with a diagnostic test consistency check. The median absolute value and percentage of parotid volume reduction were 19.51 cm(3) and 35%, respectively. The interweekly parotid volume varied significantly (p < 0.05). The parotid D mean, V 1, and D 50 increased by 22.13%, 39.42%, and 48.45%, respectively. The actual parotid dose increased by an average of 11.38% at the end of radiation therapy. Initial parotid volume, initial parotid D mean, and weight loss rate are valuable indicators for parotid protection-based replanning.

A Dosimetric Analysis of Preoperative Intensity-modulated and Image-guided Radiation Therapy with and without Simultaneous Integrated Boost for Locally Advanced Rectal Cancer.

Preoperative concurrent chemoradiation, total mesorectal excision and adjuvant chemotherapy have become the standard of care for patients with locally advanced rectal cancer (LARC). Several studies have reported increased pathologic complete response rates and improved locoregional control with escalating doses of preoperative radiotherapy. In this study, we assess the dosimetric feasibility and impact of intensity-modulated and image-guided radiation therapy (IMRT-IGRT) with a simultaneous integrated boost (SIB) in preoperative chemoradiation for LARC. Ten rectal cancer patients treated with preoperative chemoradiation were enrolled in this study, and IMRT56.25Gy and IMRT50Gy plans were made for each patient with a CTV-PTV50Gy margin of 5 mm and a GTV-PTV56.25Gy margin of 10 mm adapted to daily KV cone-beam computed tomography (CBCT) imaging. In the boost group (IMRT56.25Gy), the prescribed doses were 56.25 Gy to the gross tumor (PTV56.25Gy) and 50 Gy to areas at high risk of harboring microscopic disease (PTV50Gy). Doses were delivered over 25 daily fractions using a SIB technique. In the no-boost group (IMRT50Gy), the prescribed dose was 50 Gy to PTV50Gy without a boost. The goals were to give at least 95% of the prescribed doses to at least 95% of the PTVs while keeping irradiated volumes of the organs at risk dose as low as possible. Differences in dose distributions between the two sets of plans were analyzed using a paired sample t-test. All IMRT56.25Gy plans met the needs of the prescribed doses and organ at risk dose constraints. Compared to IMRT50Gy, the addition of a SIB in IMRT56.25Gy resulted in significant increases in mean dose and V40Gy to the bladder and significant increases of V30Gy and V40Gy to femoral heads (p < 0.05 for all points). There were no significant differences in dose to small bowel or pelvic bone marrow between the two sets of plans. Preoperative IMRT-IGRT with SIB for LARC is feasible dosimetrically with respect to organ at risk dose constraints. A phase II trial to evaluate the clinical safety and efficacy of this approach is being undertaken.

Clinical study of nasopharyngeal carcinoma treated by helical tomotherapy in China: 5-year outcomes.

BACKGROUND: To evaluate the outcomes of nasopharyngeal carcinoma (NPC) patients treated with helical tomotherapy (HT). METHODS: Between September 2007 and August 2012, 190 newly diagnosed NPC patients were treated with HT. Thirty-one patients were treated with radiation therapy as single modality, 129 with additional cisplatin-based chemotherapy with or without anti-EGFR monoclonal antibody therapy, and 30 with concurrent anti-EGFR monoclonal antibody therapy. RESULTS: Acute radiation related side effects were mainly grade 1 or 2. Grade 3 and greater toxicities were rarely noted. The median followup was 32 (3-38) months. The local relapse-free survival (LRFS), nodal relapse-free survival (NRFS), distant metastasis-free survival (DMFS), and overall survival (OS) were 96.1%, 98.2%, 92.0%, and 86.3%, respectively, at 3 years. Cox multivariate regression analysis showed that age and T stage were independent predictors for 3-year OS. CONCLUSIONS: Helical tomotherapy for NPC patients achieved excellent 3-year locoregional control, distant metastasis-free survival, and overall survival, with relatively minor acute and late toxicities. Age and T stage were the main prognosis factors.

[Verification of the couch automatic movement accuracy for Hi-ART tomotherapy].

The QUASAR Penta-guide Phantom with fiducial markers was scanned, and the CT images were transferred to Pinnacle workstation. Skin and target volumes were contoured and transferred to TomoPlan treatment planning system. The phantom was scanned with Megavoltage CT (MVCT). MVCT images were matched to the planning CT. Automatic adjustment of treatment couch was completed. It was found that the green laser coincided with the etched center crosshairs in lateral and longitudinal directions with an error less than 2 mm. However 2 mm vertical tabletop lag was found, but could be eventually corrected. Verifications for specific patients with head and pelvic tumors were also completed, the residual setup error were analyzed. The automatic movement of tabletop after image match is satisfactory.

[Effect of adaptive replanning on adverse reactions and clinical outcome in nasopharyngeal carcinoma treated by helical tomotherapy].

OBJECTIVE: To observe the effect of adaptive replanning on adverse reactions and clinical outcome of nasopharyngeal carcinoma treated by helical tomotherapy. METHODS: Fifty nasopharyngeal carcinoma patients treated by TomoTherapy system were retrospectively analyzed. Among these patients, 25 received repetitive CT simulation and replanning, and another 25 case-matched control patients without replanning were identified by matching age, gender, pathological type, UICC stage, weight loss, etc. Wilcoxon test was used to evaluate the effect of replanning on acute and chronic radiation reactions within individuals. Kaplan-Meier study was used to estimate the survival of patients with or without replanning. RESULTS: There was a significant difference in late salivary grand damage between the replanning and the control group (P=0.046), while no difference was observed in acute or other late side effects between the two groups. The median follow-up of the two groups was 32 months (7-42 months) and 26 months (8-46 months), respectively. The median local relapse-free survival time, 2-year local relapse-free survival and 2-year lymphnode relapse-free survival in the two groups were similar (36 months, 92% and 100%). No significant difference was found in the 2-year metastasis relapsefree survival (80% and 96%) and the 2-year overall survival between the two groups (88% and 92%, P>0.05). CONCLUSION: Adaptive replanning may reduce the severity of late damage of salivary glands after helical tomotherapy in nasopharyngeal carcinoma patients without improvement of 2-year survival rate.