K Li

Longitudinal Changes in Tumor Perfusion Pattern during the Radiation Therapy Course and its Clinical Impact in Cervical Cancer

PURPOSE To study the temporal changes of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) perfusion patterns during the radiation therapy (RT) course and their influence on local control and survival in cervical cancer. METHODS AND MATERIALS DCE-MRI was performed in 98 patients with Stage IB(2)-IVA cervical cancer before RT (pre-RT) and during early RT (20-25 Gy) and mid-RT (45-50 Gy). Signal intensity (SI) from the DCE-MRI time-SI curve was derived for each tumor voxel. The poorly perfused low-DCE tumor subregions were quantified as lower 10th percentiles of SI (SI10). Local control, disease-specific survival, and overall survival were correlated with DCE parameters at pre-RT, early RT, and mid-RT. Median follow-up was 4.9 (range, 0.2-9.0) years. RESULTS Patients (16/98) with initial pre-RT high DCE (SI10 >or=2.1) had 100% 5-year local control, 81% disease-specific survival, and 81% overall survival, compared with only 79%, 61%, and 55%, respectively, in patients with pre-RT low DCE. Conversion from pre-RT low DCE to high DCE in early RT (28/82 patients) was associated with higher local control, disease-specific survival, and overall survival (93%, 74%, and 67%, respectively). In comparison with all other groups, outcome was worst in patients with persistently low DCE from pre-RT throughout the mid-RT phase (66%, 44%, and 43%; p = 0.003, 0.003, and 0.020; respectively). CONCLUSION Longitudinal tumor perfusion changes during RT correlate with treatment outcome. Persistently low perfusion in pre-RT, early RT, and mid-RT indicates a high risk of treatment failure, whereas outcome is favorable in patients with initially high perfusion or subsequent improvements of initially low perfusion. These findings likely reflect reoxygenation and may have potential for noninvasive monitoring of intra-treatment radio-responsiveness and for guiding adaptive therapy.

Predicting outcomes in cervical cancer: a kinetic model of tumor regression during radiation therapy.

Applications of mathematical modeling can improve outcome predictions of cancer therapy. Here we present a kinetic model incorporating effects of radiosensitivity, tumor repopulation, and dead-cell resolving on the analysis of tumor volume regression data of 80 cervical cancer patients (stages 1B2-IVA) who underwent radiation therapy. Regression rates and derived model parameters correlated significantly with clinical outcome (P < 0.001; median follow-up: 6.2 years). The 6-year local tumor control rate was 87% versus 54% using radiosensitivity (2-Gy surviving fraction S(2) < 0.70 vs. S(2) > or = 0.70) as a predictor (P = 0.001) and 89% vs. 57% using dead-cell resolving time (T(1/2) < 22 days versus T(1/2) > or = 22 days, P < 0.001). The 6-year disease-specific survival was 73% versus 41% with S(2) < 0.70 versus S(2) > or = 0.70 (P = 0.025), and 87% vs. 52% with T(1/2) < 22 days versus T(1/2) > or = 22 days (P = 0.002). Our approach illustrates the promise of volume-based tumor response modeling to improve early outcome predictions that can be used to enable personalized adaptive therapy.

Stereotactic radiosurgery with or without whole brain radiotherapy for patients with a single radioresistant brain metastasis.

Purpose:To examine the outcomes of patients with a single brain metastasis from radioresistant histologies (renal cell carcinoma and melanoma) treated with stereotactic radiosurgery (SRS) with or without whole brain radiotherapy (WBRT). Methods and Materials:We reviewed the medical records of 27 patients treated at our institution between 2000 and 2007 with a single radioresistant brain metastasis. Patients were treated with Gamma Knife based SRS. Tumor histologies included renal cell carcinoma and melanoma. Results:Patients were treated to a median marginal dose was 20 Gy (range, 15–22 Gy). At follow-up intervals ranging from 1.8 to 23.2 months, the radiographic responses were as follows: progression in 7 patients; stable in 5 patients; and shrinkage in 15 patients. Fifteen patients (56%) developed distant brain failure. Seven of the 27 patients were alive at last follow-up. The 3-, 6-, 9-, 12-, and 18-months after SRS local control rates were 82.8%, 77.9%, 69.3%, 69.3%, and 55.4%, respectively. None of the 5 patients who received WBRT developed distant brain failure although the follow-up intervals were short (range, 3.5–13.7 months; median, 5.1 months). WBRT did not appear to affect local control, progression free survival, and overall survival (P = 0.32, 0.87, 0.69). One patient developed worsening of symptoms attributable to SRS. Conclusions:Gamma Knife SRS is a safe and feasible strategy for treatment of patients with a single radioresistant brain metastasis. Radiosurgery alone is a reasonable treatment option, but may carry a greater likelihood of distant brain recurrence.

Sequential magnetic resonance imaging of cervical cancer: the predictive value of absolute tumor volume and regression ratio measured before, during, and after radiation therapy.

The objectives of this study were to investigate outcome prediction by measuring absolute tumor volume and regression ratios using serial magnetic resonance imaging (MRI) during radiation therapy (RT) for cervical cancer and to develop algorithms capable of identifying patients at risk of a poor therapeutic outcome.

Sequential magnetic resonance imaging of cervical cancer

The objectives of this study were to investigate outcome prediction by measuring absolute tumor volume and regression ratios using serial magnetic resonance imaging (MRI) during radiation therapy (RT) for cervical cancer and to develop algorithms capable of identifying patients at risk of a poor therapeutic outcome.

Stereotactic body radiation therapy for nonpulmonary primary tumors

Stereotactic body radiation therapy (SBRT) represents a novel treatment modality for cancer and has been used to treat various types of primary cancer with curative intent. Data on the use of SBRT for various primary sites are emerging. While the largest body of data is concerned with early-stage lung cancer, there is also a fair amount of experience in the treatment of nonpulmonary primary sites with SBRT. This article will provide an overview of radiobiologic, technical and clinical aspects of the use of this emerging treatment modality for various nonpulmonary primary tumors.

Outcome Prediction of Cervical Cancer: Kinetic Model of Tumor Regression during Radiation Therapy

Applications of mathematical modeling can improve outcome predictions of cancer therapy. Here we present a kinetic model incorporating effects of radiosensitivity, tumor repopulation, and dead-cell resolving on the analysis of tumor volume regression data of 80 cervical cancer patients (stages 1B2-IVA) who underwent radiation therapy. Regression rates and derived model parameters correlated significantly with clinical outcome (P < 0.001; median follow-up: 6.2 years). The 6-year local tumor control rate was 87% versus 54% using radiosensitivity (2-Gy surviving fraction S(2) < 0.70 vs. S(2) > or = 0.70) as a predictor (P = 0.001) and 89% vs. 57% using dead-cell resolving time (T(1/2) < 22 days versus T(1/2) > or = 22 days, P < 0.001). The 6-year disease-specific survival was 73% versus 41% with S(2) < 0.70 versus S(2) > or = 0.70 (P = 0.025), and 87% vs. 52% with T(1/2) < 22 days versus T(1/2) > or = 22 days (P = 0.002). Our approach illustrates the promise of volume-based tumor response modeling to improve early outcome predictions that can be used to enable personalized adaptive therapy.

Sequential MR Imaging of Cervical Cancer: Predictive Value of Absolute Tumor Volume and Regression Ratio Measured before, during and after Radiation Therapy

The objectives of this study were to investigate outcome prediction by measuring absolute tumor volume and regression ratios using serial magnetic resonance imaging (MRI) during radiation therapy (RT) for cervical cancer and to develop algorithms capable of identifying patients at risk of a poor therapeutic outcome.

SU-E-T-547: A Method to Correlate Treatment Planning Issue with Clinical Analysis for Prostate Stereotactic Body Radiotherapy (SBRT)

PURPOSE In this study, the algorithms and calculation setting effect and contribution weighing on prostate Volumetric Modulated Arc Therapy (VMAT) based SBRT were evaluated for clinical analysis. METHODS A low risk prostate patient under SBRT was selected for the treatment planning evaluation. The treatment target was divided into low dose prescription target volume (PTV) and high Dose PTV. Normal tissue constraints include urethra and femur head, and rectum was separated into anterior, lateral and posterior parts. By varying the constraint limit of treatment plan calculation setting and algorithms, the effect on dose coverage and normal tissue dose constraint parameter carried effective comparison for the nominal prescription and constraint. For each setting, their percentage differences to the nominal value were calculated with geometric mean and harmonic mean. RESULTS In the arbitrary prostate SBRT case, 14 variables were selected for this evaluation by using nominal prescription and constraint. Six VMAT planning settings were anisotropic analytic algorithm stereotactic beam with and without couch structure in grid size of 1mm and 2mm, non stereotactic beam, Acuros algorithm . Their geometry means of the variable sets for these plans were 112.3%, 111.9%, 112.09%, 111.75%, 111.28%, and 112.05%. And the corresponding harmonic means were 2.02%, 2.16%, 3.15%, 4.74%, 5.47% and 5.55%. CONCLUSIONS In this study, the algorithm difference shows relatively larger harmonic mean between prostate SBRT VMAT plans. This study provides a methodology to find sensitive combined variables related to clinical analysis, and similar approach could be applied to the whole treatment procedure from simulation to treatment in radiotherapy for big clinical data analysis.

SU-E-T-194: Evaluation and Simulation of Shallow Depth Skin Dose from Couch Top in Radiotherapy

PURPOSE When the treatment couch-top contacts the patient, the skin dose to the patient also generates clinical significance as the radiation beam passes through the couch. In this study, the effect on entrance shallow depth dose was investigated for the carbon fiber exact couch-top from Varian Medical System. METHODS An Accredited Dosimetry Calibration Laboratory (ADCL) calibrated PTW parallel-plate thin-window chamber was used to measure the doses in the build-up region. Firstly, the shallow depth doses at different field sizes, depths and incident angle beams were measured for 6MV and 18MV photon beams. To test the couch top contribution to the dose distribution, the depth of measurement went down to 10cm. The couch was simulated in the Eclipse treatment planning system and the related point dose was calculated with different depths. The CT number of the couch top was adjusted to generate agreement between measurement and simulation. RESULTS At a 2mm depth, the surface dose increased with the decrease of the field size. Comparing with and without the couch top, as field sizes vary from 20cm×20cm to 2cm×2cm, the dose increased from 35% to 53% of for 6MV, and from 50% to 113% for 18MV. At 0mm depth, the dose difference was most significant and is at the level of 300%. Angle incident beam dose increase due to couch top varied with complicated dose distribution. Extended Depth Dose measurement shows that couch top effect on dose in build-up region extends to depths of 1cm for 6MV and 2cm for 18MV. An appropriate CT number setting of the couch top is between -200HU to -300HU. CONCLUSIONS The couch simulation in Eclipse displays better dosimetric accuracy in couch contacted skin dose. However, calculation factors such as surface definition, heterogeneity, calculation resolution and algorithm also need extra consideration.