Radiobiological mechanisms of stereotactic body radiation therapy and stereotactic radiation surgery

Despite the increasing use of stereotactic body radiation therapy (SBRT) and stereotactic radiation surgery (SRS) in recent years, the biological base of these high-dose hypo-fractionated radiotherapy modalities has been elusive. Given that most human tumors contain radioresistant hypoxic tumor cells, the radiobiological principles for the conventional multiple-fractionated radiotherapy cannot account for the high efficacy of SBRT and SRS. Recent emerging evidence strongly indicates that SBRT and SRS not only directly kill tumor cells, but also destroy the tumor vascular beds, thereby deteriorating intratumor microenvironment leading to indirect tumor cell death. Furthermore, indications are that the massive release of tumor antigens from the tumor cells directly and indirectly killed by SBRT and SRS stimulate anti-tumor immunity, thereby suppressing recurrence and metastatic tumor growth. The reoxygenation, repair, repopulation, and redistribution, which are important components in the response of tumors to conventional fractionated radiotherapy, play relatively little role in SBRT and SRS. The linear-quadratic model, which accounts for only direct cell death has been suggested to overestimate the cell death by high dose per fraction irradiation. However, the model may in some clinical cases incidentally do not overestimate total cell death because high-dose irradiation causes additional cell death through indirect mechanisms. For the improvement of the efficacy of SBRT and SRS, further investigation is warranted to gain detailed insights into the mechanisms underlying the SBRT and SRS.

Analysis on the Calculated Dose in the Lung Radiation Surgery Planning Using TomoTherpay / 의학물리

The applicability and feasibility of TomoTherapy in the lung radiation surgery was analyzed by comparison of the calculated dose distribution in TomoTherapy planning with the results of conventional IMRS (intensity modulated radiation surgery) using LINAC (linear accelerator). The acquired CT (computed tomograph) images of total 10 patients whose tumors' motion were less than 5 mm were used in the radiation surgery planning and the same prescribed dose and the same dose constraints were used between TomoTherapy and LINAC. The results of TomoTherapy planning fulfilled the dose requirement in GTV (gross tumor volume) and OAR (organ at risk) in the same with the conventional IMRS using LINAC. TomoTherapy was superior in the view point of low dose in the normal lung tissue and conventional LINAC was superior in the dose homogeneity in GTV. The calculated time for treatment beam delivery was long more than two times in TomoTherapy compared with the conventional LINAC. Based on the results in this study, TomoTherapy can be evaluated as an effective way of lung radiation surgery for the patients whose tumor motion is little when the optimal planning is produced considering patient's condition and suitability of dose distribution.

Analysis on the Decrease of Planning Target Volume in the Case of Lung Radiation Surgery with the Application of Respiratory Gated Radiotherpy Method / 의학물리

The application of a respiratory gated radiotherpy method to the lung radiation surgery was evaluated compared with the conventional method in which the whole tumor motion range is considered in the delineation of PTV (Planning target volume). The four dimensional CT simulation images were acquired for the five NSCLC (Non-small cell lung cancer) patients for radiation surgery. The respiratory gated plan was prepared with the 50% phase CT images and the conventional method was planned based on the ITV (Internal target volume) which include all the target volumes created in each phase CT images within a whole respiratory period. The DVH (Dose volume histogram) of OAR (Organ at risk) which calculated in each method was compared for the evaluation of the plan properness. The relative decrease of OARs' DVH were verified in the application of respiratory gated method. The average decrease rate were 16.88+/-9.97% in the bronchus, 34.13+/-19.15% in the spinal cord, 28.42+/-18.49% in the chest wall and 32.48+/-16.66% in the lung. Based on these results, we can verified the applicability and the effectiveness of the respiratory gated method in the lung radiation surgery.

On-line Setup for Lung Cancer Patient in Stereotactic Radiation Surgery using CBCT

PURPOSE: On-line setup procedure was performed before treatment for lung cancer patient for stereotactic radiation surgery (SRS) using recently introduced Cone Beam CT. MATERIALS AND METHODS: Cone Beam CT was performed for 10 patients who did SRS during 18 July and 1 September, 2006 using On Board Imager (OPB) system made by Varian, USA. The treatment position of patient was corrected comparing Images obtaining from CBCT and used in treatment planning. RESULTS: Comparing the CBCT images and CT images used in treatment planning, the movement of the couch is 2.3+/-2.3 mm, 1.8+/-2.8 mm, 0.3+/-3.5 mm for vertical, lateral, and longitudinal direction. It took about 1 hr for conventional treatment procedure in image acquisition of CT before treatment and image registration. But it took about 4~7 minute in on-line setup using CBCT (1~2 min for image acquisition using CBCT, 2~3 min for CT reconstruction of 2.5 mm slice thickness, 1~2 min for on-line setup using image registration). CONCLUTION: The accurate treatment could be performed after tumor localization for SRS using CBCT images. And the consumed time for tumor localization was reduced significantly.

THERAPEUTIC MANNERS AND TRENDS OF CERVICAL ESOPHAGEAL CARCINOMA / 中华放射肿瘤学杂志

One hundred seventy of patients with cervical esophageal carcinoma (30 cases were treated by pre-operative radiation and surgery (combined group), 27 cases by surgery alone, 113 cases by radical radiation). The doses of the preoperative radiation and the radiacal radiation were D T40 Gy/4w and above D T 50 Gy/5w, respectively. The 5 year survival rates were 40% in the combined group, 15.3% in surgry alone, and 28% in radical radiation groups. The difference of survival rates in the combined group and surgery alone was significantly different statistically. Factors affecting the survivals were lymphnode metastasis in radical radiation and recurrent larygeal nerve paralysis in the combined group. The main causes of failure were local residual and recurrence (71%) in radical radiation and lymphnode metastasis (81%) in the combined group. The authors believe that pre-operative radiation combined with surgery could improve the survival of cervical esophageal carcinoma. Radical radiation is also one of effective treatment methods for cercical esophageal carcinoma.