Prognostic significance of pretreatment 18F-fluorodeoxyglucose positron emission tomography evaluation using metabolic tumor volume of the primary tumor and lymph nodes in advanced hypopharyngeal cancer.

BACKGROUND: The purpose of this study was to retrospectively evaluate the usefulness of pretreatment positron emission tomography (PET) using metabolic tumor volume (MTV) of the primary tumor and lymph nodes in advanced hypopharyngeal cancer. METHODS: From June 2007 to December 2015, consecutive patients with advanced hypopharyngeal cancer who underwent PET and were treated with definitive radiation therapy were retrospectively reviewed. RESULTS: A total of 61 patients were eligible for this study. On multivariate analysis, MTV of the primary tumor (MTV-T) was significantly related to the local control rate and overall survival (OS) (P = .036 and .012, respectively). In patients with lower MTV-T, MTV of metastatic lymph nodes (MTV-N) was significantly related to disease-specific survival and OS (P = .012 and .017, respectively). CONCLUSION: MTV-T is a significant predictor in patients with advanced hypopharyngeal cancer, and MTV-N is also significant in patients with lower MTV-T.

Neoadjuvant Radiotherapy with Capecitabine Plus Bevacizumab for Locally Advanced Lower Rectal Cancer: Results of a Single-institute Phase II Study.

BACKGROUND/AIM: A single-arm phase II clinical trial was conducted to evaluate the safety and efficacy of adding bevacizumab to standard capecitabine-based neoadjuvant chemoradiotherapy (CRT) for the treatment of locally advanced rectal cancer (LARC). PATIENTS AND METHODS: Twenty-five patients were enrolled. Patients received capecitabine-based CRT for 5 weeks and 3 days. Bevacizumab was administered every 2 weeks during CRT. Within 6-10 weeks after completion of CRT, surgery was performed. RESULTS: With regard to CRT-related acute toxicities, most of the adverse events were limited to grade 1. A pathological complete response was obtained in four (16%) patients. In total, six patients (24%) developed postoperative complications. Six out of five (83%) patients healed without the need for surgical intervention. CONCLUSION: Although acute toxicity during CRT with bevacizumab was minimal and postoperative complications do not seem to increase, the addition of bevacizumab apparently offers no clinically-significant benefit for patients with LARC.

Dose Escalation Study of Concurrent Chemoradiotherapy With the Use of Involved-field Conformal Radiotherapy and Accelerated Hyperfractionation in Combination With Cisplatin and Vinorelbine Chemotherapy for Stage III Non-small Cell Lung Cancer: The Final Report.

OBJECTIVES: A phase I study to determine a recommended dose of thoracic radiotherapy using accelerated hyperfractionation for unresectable non-small cell lung cancer was conducted. MATERIALS AND METHODS: We used chemotherapy of a cisplatin doublet and 2 dose levels of radiation with accelerated hyperfractionation. The radiation dose levels were: a total dose of 60 Gy in 40 fractions at level 1, and 66 Gy in 44 fractions at level 2. Eligible patients with unresectable stage III non-small cell lung cancer received cisplatin and vinorelbine. Radiation therapy started on day 2 of chemotherapy and was delivered twice daily for 5 days a week. RESULTS: Total 12 patients were enrolled, with 6 patients each at dose levels 1 and 2. Dose-limiting toxicity was noted in 2 patients at level 1; one patient had grade 3 febrile neutropenia and the other patient had grade 3 esophagitis. No dose-limiting toxicity was noted in the 6 patients at level 2. Grade 3 to 4 leukopenia, neutropenia, and anemia were noted in 11 (92%), 9 (75%), and 8 (67%) of the total 12 patients, respectively. Grade 3 anorexia and infection were noted in 2 patients (17%) at each level. Grade 3 nausea, fatigue, esophagitis, and febrile neutropenia were noted in 1 patient (8%) at each level. The response rate in the total 12 patients was 83.3%. The median progression-free survival time and the median overall survival time were 10.7 and 24.2 months, respectively. CONCLUSIONS: Sixty-six gray in 44 fractions is the recommended dose for the following phase II study.

Treatment results of neoadjuvant chemoradiotherapy followed by radical esophagectomy in patients with initially inoperable thoracic esophageal cancer.

PURPOSE: We evaluated the effectiveness of neoadjuvant chemoradiotherapy (CRT) followed by esophagectomy for cT4 esophageal cancer or lymph node metastases (LNM) invading adjacent structures. MATERIALS AND METHODS: We retrospectively evaluated 42 consecutive patients with thoracic esophageal cancer who underwent CRT followed by esophagectomy between 2008 and 2013. All were initially considered to be unresectable because of cT4 (n = 32) disease or LN invasion (n = 10). Radiotherapy was administered at 41.4 Gy/23 fr with concurrent chemotherapy. At completion of CRT, restaging was performed using computed tomography (CT). RESULTS: All cT4 tumors were downstaged, LNM invading to adjacent structures were considered to be released, and subtotal esophagectomy was performed. The median follow-up period was 42 months. The curative resection (R0) rate was 94% in cT4 group and 70% in LN invasion group. The 3-year overall survival (OS) and 3-year locoregional control (LRC) rates were 65-80% in the cT4 group and 50-67% in LN invasion group, respectively. CONCLUSIONS: The cT4 group showed good rates of R0, OS, and LRC. Surgical resection should be an effective option when downstaging is achieved by CRT for patients with initially inoperable thoracic esophageal cancer.

Efficacy and toxicity profiles of two chemoradiotherapies for stage II laryngeal cancer - a comparison between late course accelerated hyperfractionation (LCAHF) and conventional fractionation (CF).

OBJECTIVE: To evaluate the treatment results of late course accelerated hyperfractionation (LCAHF) compared with conventional fractionation (CF) for stage II laryngeal cancer. METHODS: Fifty-nine consecutive patients treated for stage II laryngeal cancer were retrospectively reviewed. Thirty-two patients underwent LCAHF, twice-daily fractions during the latter half with a total dose of 69 Gy. Twenty-seven patients received CF of 70 Gy. RESULTS: The local control rates (LCRs), overall survival (OS), and disease-specific survival (DSS) at 5 years were 80.6%, 74.0%, and 90.4%, respectively, after LCAHF and 64.7%, 68.2%, and 90.5%, respectively, after CF. There were no significant differences in LCR, OS, and DSS (p = .11, 0.68, and 0.69, respectively). In a small number of patients with supraglottic cancer, LCAHF was associated with a significantly higher LCR at 5 years compared with CF (100% vs. 41.7%; p = .02). CONCLUSIONS: This is the first report that compared the results of LCAHF and CF for stage II laryngeal cancer. We could not find significant differences in LCR, DSS, and OS rates between LCAHF and CF groups. Although in a small number of patients with supraglottic cancer, LCAHF may improve the LCR compared with CF.

Correlations of post-implant regional dosimetric parameters at 24 hours and one month, with clinical results of low-dose-rate brachytherapy for localized prostate cancer.

PURPOSE: To evaluate the correlations of post-implant regional dosimetrics at 24 hours (24 h) and 1 month after implant procedures, with clinical outcomes of low-dose-rate (LDR) brachytherapy for localized prostate cancer. MATERIAL AND METHODS: Between January 2008 and December 2014, 130 consecutive patients treated for localized prostate cancer, receiving definitive iodine-125 (125I) brachytherapy treatment were retrospectively analyzed. All patients underwent post-implant CT imaging for dosimetric analysis at 24 h and 1 month after implantation procedure. Prostate contours were divided into quadrants: anterior-superior (ASQ), posterior-superior (PSQ), anterior-inferior (AIQ), and posterior-inferior (PIQ). Predictive factors and cut-off values of biochemical failure-free survival (BFFS) and toxicities of LDR brachytherapy were analyzed. RESULTS: The median follow-up time was 69.5 months. Seven patients (5.4%) had biochemical failure. The 3-year and 5-year BFFS rates were 96.7% and 93.1%, respectively. On multivariate analysis, prostate-specific antigen and Gleason score were significant prognostic factors for biochemical failure. D90 (the minimal dose received by 90% of the volume) of PSQ and PIQ at 24 h, and D90 of PSQ at 1 month were also significant factors. The cut-off values of PSQ D90 were 145 Gy at 24 h and 160 Gy at 1 month. D90 of the whole prostate was not significant at 24 h and at 1 month. D90 of PSQ at 1 month was a significant factor for rectal hemorrhage. CONCLUSIONS: Post-implant D90 of PSQ is significantly associated with BFFS for localized prostate cancer not only at 1 month, but also at 24 hours. D90 of PSQ at 1 month is also a significant factor for rectal hemorrhage.

Three-dimensional conformal radiotherapy for locally advanced hepatocellular carcinoma with portal vein tumour thrombosis: evaluating effectiveness of the model for end-stage liver disease (MELD) score compared with the Child-Pugh classification.

OBJECTIVE: The purpose of this study was to retrospectively evaluate the effectiveness of the model for end-stage liver disease (MELD) score compared with the Child-Pugh classification in patients who received three-dimensional conformal radiotherapy (3D CRT) for hepatocellular carcinoma (HCC) with portal vein tumour thrombosis (PVTT) by analyzing toxicity and prognostic factors. METHODS: 56 consecutive patients who had locally advanced HCC with PVTT treated by 3D CRT between September 2007 and April 2013 were retrospectively reviewed. RESULTS: The median survival time of all patients was 6.4 months. Receiver-operating characteristic (ROC) analysis identified MELD score = 7.5 [area under the curve (AUC) 0.81] and Child-Pugh score = 6.5 (AUC 0.86) as the best cut-off values for predicting the incidence of complications over Common Terminology Criteria for Adverse Events grade 2. There was no significant difference in the discrimination power between the MELD score and the Child-Pugh score on comparison of the two ROC curves (p = 0.17). On multivariate analysis, age, MELD score and radiotherapy dose were significant prognostic factors for overall survival (p = 0.021, 0.038 and 0.006, respectively). In contrast, the Child-Pugh classification, tumour response, PVTT response and the number of prior interventional radiologic treatments were not significant on multivariate analysis. CONCLUSION: This study showed that the best MELD score cut-off value is 7.5 and that the MELD score is a better prognostic factor than the Child-Pugh classification in 3D CRT for HCC with PVTT. ADVANCES IN KNOWLEDGE: The MELD score is useful for predicting the risk of severe toxicities and the prognosis of patients treated with 3D CRT for PVTT.

Results of surgery plus postoperative radiotherapy for patients with malignant parotid tumor.

PURPOSE: The latest version of the World Health Organization (WHO) histologic classification of salivary gland malignancies was published in 2005. To contribute to data accumulation on the basis of this latest version, a retrospective study was performed. MATERIALS AND METHODS: Participants comprised 27 patients who underwent postoperative radiotherapy between 2000 and 2013. Two, eight, and 17 patients were allocated to low, intermediate, and high-grade groups, respectively, in accordance with the latest WHO classification. The radiation field included the tumor bed and ipsilateral regional lymph nodes for 25 patients. The radiation dose was 46-60 Gy (median 56 Gy). RESULTS: Median duration of follow-up was 41 months. Five-year locoregional control was 89 %. Two patients experienced local recurrence and 7 patients developed distant metastases. No patients in the low or intermediate-grade groups developed distant metastases. Overall 3 and 5-year survival for all patients were 81 and 75 %, respectively. Five-year overall survival for patients in the low and intermediate-grade groups was 100 %, compared with 59 % for patients in the high-grade group (p = 0.03). CONCLUSION: Favorable locoregional control was achieved for patients with malignant parotid tumors who underwent surgery plus postoperative radiotherapy. Patients with high-grade tumors frequently experienced distant metastases and prognosis was poor.

Neoadjuvant capecitabine, bevacizumab and radiotherapy for locally advanced rectal cancer: results of a single-institute Phase I study.

The aim of this Phase I clinical trial was to assess the feasibility and safety of capecitabine-based preoperative chemoradiotherapy (CRT) combined with bevacizumab and to determine the optimal capecitabine dose for Japanese patients with locally advanced rectal cancer. Patients with cT3/T4 rectal cancer were eligible. Bevacizumab was administered at 5 mg/kg intravenously on Days 1, 15 and 29. Capecitabine was administered on weekdays concurrently with pelvic radiotherapy at a daily dose of 1.8 Gy, totally to 50.4 Gy. Capecitabine was initiated at 825 mg/m(2) twice daily at Dose Level 1, with a planned escalation to 900 mg/m(2) twice daily at Dose Level 2. Within 6.1-10.3 (median, 9.4) weeks after the completion of the CRT, surgery was performed. Three patients were enrolled at each dose level. Regarding the CRT-related acute toxicities, all of the adverse events were limited to Grade 1. There was no Grade 2 or greater toxicity. No patient needed attenuation or interruption of bevacizumab, capecitabine or radiation. All of the patients received the scheduled dose of CRT. All of the patients underwent R0 resection. Two (33.3%) of the six patients had a pathological complete response, and five (83.3%) patients experienced downstaging. In total, three patients (50%) developed postoperative complications. One patient developed an intrapelvic abscess and healed with incisional drainage. The other two patients healed following conservative treatment. This regimen was safely performed as preoperative CRT for Japanese patients with locally advanced rectal cancer. The recommended capecitabine dose is 900 mg/m(2) twice daily.

Lung cancer: a 6-field technique using lateral beams in conformal radiotherapy for bilateral supraclavicular lymph node metastases.

A 6-field technique using lateral beams in conformal radiotherapy was developed for patients with bilateral supraclavicular lymph node metastasis of lung cancer. The possibility of using this technique in practice was evaluated. Six fields with the same isocenter point (IP) were arranged. Two fields using anterior-posterior opposed beams involved all of the planning target volume (PTV). The next 2 fields using off-cord oblique beams involved the PTV inferior to the IP. The remaining 2 fields using lateral opposed beams, that shielded the spinal cord, involved the PTV superior to the IP. The oblique 2 fields and lateral 2 fields were connected using a half-beam technique. In 6 patients with non-small-cell lung cancer (NSCLC, n = 4) or small-cell lung cancer (SCLC, n = 2), treatment re-planning based on this technique was performed. This technique was applicable in 4 patients with NSCLC, in whom the general criteria of radiotherapy for lung cancer were met. In 2 patients with SCLC, the cumulative volume of lung that received more than 20 Gy exceeded 37% of the total lung volume. This technique was usable in 67% of the patients and was not necessarily contraindicated in the other 33%.

Delivery parameter variations and early clinical outcomes of volumetric modulated arc therapy for 31 prostate cancer patients: an intercomparison of three treatment planning systems.

We created volumetric modulated arc therapy (VMAT) plans for 31 prostate cancer patients using one of three treatment planning systems (TPSs)--ERGO++, Monaco, or Pinnacle--and then treated those patients. A dose of 74 Gy was prescribed to the planning target volume (PTV). The rectum, bladder, and femur were chosen as organs at risk (OARs) with specified dose-volume constraints. Dose volume histograms (DVHs), the mean dose rate, the beam-on time, and early treatment outcomes were evaluated and compared. The DVHs calculated for the three TPSs were comparable. The mean dose rates and beam-on times for Ergo++, Monaco, and SmartArc were, respectively, 174.3 ± 17.7, 149.7 ± 8.4, and 185.8 ± 15.6 MU/min and 132.7 ± 8.4, 217.6 ± 13.1, and 127.5 ± 27.1 sec. During a follow-up period of 486.2 ± 289.9 days, local recurrence was not observed, but distant metastasis was observed in a single patient. Adverse events of grade 3 to grade 4 were not observed. The mean dose rate for Monaco was significantly lower than that for ERGO++ and SmartArc (P < 0.0001), and the beam-on time for Monaco was significantly longer than that for ERGO++ and SmartArc (P < 0.0001). Each TPS was successfully used for prostate VMAT planning without significant differences in early clinical outcomes despite significant TPS-specific delivery parameter variations.

A dose-volume intercomparison of volumetric-modulated arc therapy, 3D static conformal, and rotational conformal techniques for portal vein tumor thrombus in hepatocellular carcinoma.

We created volumetric-modulated arc therapy (VMAT) plans for portal vein tumor thrombus (PVTT) in hepatocellular carcinoma, and compared the results with those from three-dimensional conformal radiotherapy (3D-CRT) and rotational conformal radiotherapy (R-CRT) plans. CT scan data from 10 consecutive patients with PVTT treated with 3D-CRT between January 2008 and January 2010 were utilized in the analysis. We analyzed the dosimetric properties of the plans for the 10 patients using the three different techniques with three different isocenter doses of 50, 56 and 60 Gy in 2-Gy fractions. The D95, Dmean, homogeneity index and conformity index were compared for the planning target volume (PTV). The Dmean, V20 and V30 were also compared for normal livers. The monitor units (MUs) and the treatment time were also evaluated. The normal liver V30 for VMAT was significantly less than that for 3D-CRT for the prescribed doses of 56 and 60 Gy (P < 0.05). It was also found that the normal liver V30 resulting from 3D-CRT was prohibitively increased when the prescribed dose was increased in two steps. For PTV D95, we found no significant differences between the three techniques for the 50- and 56-Gy prescriptions, or between VMAT and the other techniques for the 60-Gy prescription. The differences in the MUs and treatment times were not statistically significant between VMAT and 3D-CRT. We have demonstrated that VMAT may be a more advantageous technique for dose escalation reaching 60 Gy in the treatment of PVTT due to the reduced normal liver V30.

[Electronic portal image device dosimetry for volumetric modulated arc therapy].

Recently electronic portal image devices (EPIDs) have been widely used for quality assurance and dose verification. However there are no reports describing EPID dosimetry for Elekta volumetric modulated arc therapy (VMAT). We have investigated EPID dosimetry during VMAT delivery using a commercial software EPIDose with an Elekta Synergy linac. Dose rate dependence and the linac system sag during gantry rotation were measured. Gamma indices were calculated between measured doses using an EPID and calculation made by a treatment planning system for prostate VMAT test plans. The results were also compared to gamma indices using films and a two-dimensional detector array, MapCHECK2. The pass rates of the gamma analysis with a criterion of 3% and 2 mm for the three methods were over 96% with good consistency. Our results have showed that EPID dosimetry is feasible for Elekta VMAT.

Minimum requirements for commissioning and long-term quality assurance of Elekta multi-leaf collimator for volumetric modulated arc therapy.

We have proposed minimum requirements for commissioning and long-term quality assurance (QA) of an Elekta multi-leaf collimator (MLC) for volumetric modulated arc therapy (VMAT). The MLC leaf position accuracy during VMAT delivery was evaluated with the use of three different QA test plans: (1) a leaf gap-width test between opposing leaves by measurement of the isocenter dose during constant-gap sliding-window delivery with varied dose rates, MLC leaf speeds, and gantry angles; (2) a leaf position test by picket-fence delivery with and without gantry rotation; and (3) a leaf-bank symmetry test by measurement of the field geometry with different collimator angles at a fixed gantry position. All the QA test plans were created using an ERGO++ treatment-planning system. The leaf gap-width deviation was within 0.2 mm, the leaf position deviation was within 0.5 mm, and the leaf-bank symmetry error was within 0.5 mm under all the test conditions. MLC leaf position accuracy and long-term stability were confirmed by the proposed procedures.

[Positional accuracy and quality assurance of Backup JAWs required for volumetric modulated arc therapy].

The tolerance of the Backup diaphragm (Backup JAW) setting in Elekta linac was specified as 2 mm according to the AAPM TG-142 report. However, the tolerance and the quality assurance procedure for volumetric modulated arc therapy (VMAT) was not provided. This paper describes positional accuracy and quality assurance procedure of the Backup JAWs required for VMAT. It was found that a gap-width error of the Backup JAW by a sliding window test needed to be less than 1.5 mm for prostate VMAT delivery. It was also confirmed that the gap-widths had been maintained with an error of 0.2 mm during the past one year.

[Quality assurance procedure for assessing mechanical accuracy of a radiation field center in stereotactic radiotherapy].

Stereotactic radiotherapy requires a quality assurance (QA) program that ensures the mechanical accuracy of a radiation field center. We have proposed a QA method for achieving the above requirement by conducting the Winston Lutz test using an electronic portal image device (EPID). An action limit was defined as three times the standard deviation. Then, the action limits for mean deviations of the radiation field center during collimator rotation, gantry rotation, and couch rotation in clockwise and counterclockwise resulted in 0.11 mm, 0.52 mm, 0.37 mm, and 0.41 mm respectively. Two years after the QA program was launched, the mean deviation of the radiation field center during gantry rotation exceeded the above action limit. Consequently, a mechanical adjustment for the gantry was performed, thereby restoring the accuracy of the radiation field center. A field center shift of 0.5 mm was also observed after a micro multi-leaf collimator was unmounted.

[Mechanical accuracy of a stereotactic irradiation system using a micro multi-leaf collimator].

Mechanical accuracy of a stereotactic irradiation system using a micro multi-leaf collimator (mMLC), Elekta DMLC, has been evaluated. Measurements were made to obtain transmission, leakage, penumbra, and positioning accuracy of the DMLC leaf for a 6 MV photon beam. Mechanical accuracy and long term stability of a linac isocenter was also evaluated. The resulting transmission, along a line perpendicular to the leaf movement, was 0.31±0.01%, and the leakage from the closed opposing leaf pairs was 0.39±0.01%. The measured penumbra, at a depth incurring maximum dose, was 2.37±0.16 mm toward the leaf end and 2.14±0.18 mm toward the leaf side for various field sizes. The leaf gap width error, of 0.10±0.08 mm, was obtained by analyzing picket fence test results. The maximum leaf positioning error, of 0.14±0.06 mm, was obtained by analyzing the log file for a various gantry angles during an arc delivery. The isocenter accuracy was within a radius of 1 mm, without any recalibration for two years. In conclusion, our stereotactic irradiation system using DMLC was capable of providing accurate stereotactic treatment.

Limited-stage small cell lung cancer: local failure after concurrent chemoradiotherapy with use of accelerated hyperfractionation.

PURPOSE: The aim of this study was to update data of radiation therapy regimens for improvement in local control in patients with limited-stage small cell lung cancer, a retrospective study was conducted. MATERIALS AND METHODS: Results of early concurrent chemoradiotherapy with accelerated hyperfractionation in 30 patients between 1998 and 2005 were retrospectively reviewed. The prescribed dose was 45 Gy in 30 fractions in all patients. RESULTS: All patients received a full dose of radiation therapy; however, interruptions for >or=5 days, mainly due to hematologic toxicity, were required in 18 patients (60%). The 5-year Kaplan-Meier survival rate and the median survival time were 26% and 26 months, respectively. The 4-year in-field control rate was 56%. Sites of relapse were local relapse in 9 patients (6 for in-field relapse, 3 for marginal relapse) and distant metastases in 16 patients (11 for distant metastases only, 5 for distant metastases with local relapse). The sites of marginal relapse were the upper margin in two patients and the peripheral margin in one patient. Grade 3 radiation esophagitis was observed in only three patients. CONCLUSION: Because in-field control was insufficient, a more effective approach should be sought to provide better local control.

Primary central nervous system lymphoma in Japan: changes in clinical features, treatment, and prognosis during 1985-2004.

We have conducted nationwide surveys of primary central nervous system lymphoma (PCNSL) treated since 1985. In the present study, we newly collected data between 2000 and 2004 and investigated changes in clinical features and outcome over time. A total of 739 patients with histologically proven PCNSL under going radiotherapy were analyzed. Seventeen institutions were surveyed, and data on 131 patients were collected. These data were compared with updated data that were previously obtained for 466 patients treated during 1985-1994 and 142 patients treated during 1995-1999. Recent trends toward decrease in male/female ratio, increase in aged patients, and increase in patients with multiple lesions were seen. Regarding treatment, decrease in attempts at surgical tumor removal and increases in use of systemic chemotherapy and methotrexate (MTX)-containing regimens were observed. The median survival time was 18, 29, and 24 months for patients seen during 1985-1994, 1995-1999, and 2000-2004, respectively, and the respective 5-year survival rates were 15%, 30%, and 30%. In groups seen during 1995-1999 and during 2000-2004, patients who received systemic or MTX-containing chemotherapy had better prognosis than those who did not. Multivariate analysis of all patients seen during 1985-2004 suggested the usefulness of MTX-containing chemotherapy as well as the importance of age, lactate dehydrogenase level, and tumor multiplicity as prognostic factors. Thus, this study revealed several notable changes in clinical features of PCNSL patients. The prognosis improved during the last 10 years. Advantage of radiation plus chemotherapy, especially MTX-containing chemotherapy, over radiation alone was suggested.

Usefulness of FDG-microPET for early evaluation of therapeutic effects on VX2 rabbit carcinoma.

PURPOSE: The aim of this study was to determine the potential use of high-resolution FDG-microPET for predicting the primary effects of radiotherapy and/or hyperthermia on tumor-bearing rabbits. METHODS: Twenty-eight VX2 xenografts in the thighs of rabbits were divided into the following 5 treatment groups: radiotherapy at a single dose of 10, 20 or 30 Gy, hyperthermia (43 degrees Celsius, 1 hour), and the combination of radiotherapy and hyperthermia (10 Gy + 43 degrees Celsius, 1 hour). FDG-microPET images were obtained by using a microPET P4 system at pretreatment and at 24 hours and 7 days after treatment. For the evaluation by FDG-microPET, tumor/muscle (T/M) ratios, retention index [RI = (T/M ratio at 120 min - T/M ratio at 60 min) / T/M ratio at 60 min], and time activity curve (TAC) were acquired. RESULTS: We divided the xenografts into a responder group (partial response + stable disease, n=14) and a non-responder group (progressive disease, n = 14). The T/M ratio at 24 hours after the treatment in the responder group was decreased remarkably with that at pre-treatment (p < 0.05), while in the non-responder group it showed no significant change between the time points. The RI and TAC patterns were comparable to T/M ratios in each treatment group. T/M ratios, RI, and TAC indicated marked changes at the time point of 24 hours in the responder group, although the tumors did not show any significant hange in volume at that time. Photomicrographs of sections showed that the number of viable tumor cells in the responder group decreased at 24 hours after treatment and that inflammatory cell infiltration was marked and almost all viable tumor cells had disappeared by day 7 after treatment. CONCLUSION: These results suggest that early evaluation by FDG-microPET, especially 24 hours after treatment, is useful to predict the primary effects of the treatment. Histological analysis showed that inflammatory cell infiltration at 7 days after treatment was considered to be a cause of accumulation of FDG in the tumors that showed a significant decrease in tumor cell number. This false-positive should be noted when predicting tumor response by FDG accumulation.