Journal of Thai Association of Radiation Oncology

Comparison of set up error of SBRT technique between Vision RT and Gating (RPM) for lung cancer using Cone-beam computed tomography (CBCT) at Chulalongkorn hospital.

Nongnut Khamta — 2025-09-22

Background: Radiation therapy for lung cancer using Stereotactic Body Radiation Therapy (SBRT) involves delivering high doses of radiation to the cancerous tumor. However, since the lungs are constantly moving due to breathing, the tumor can also move. Therefore, it is necessary to have patient positioning devices to minimize the movement of the tumor and ensure the highest accuracy in patient positioning during radiation treatment.

Objectives: This study aims to compare the effectiveness of DIBH SBRT in lung cancer patients with the Vision RT system and Real-time position management system (RPM, Gating).

Materials and methods: This study is a retrospective study of a total of 30 patients who received treatment from January 2021 to December 2022, divided into 2 groups both receiving a DIBH SBRT at lung lesion treatment. The first one was combined with the Vision RT system, and the second one was with respiratory gating. Compared both groups by using shift value from image-guided radiation therapy (IGRT) which was a Cone-beam computed tomography (CBCT) and analyzed by using percentage, mean, standard deviation, and t-test.

Results: For DIBH SBRT in lung lesions combined with Vision RT, the mean shift values from CBCT in vertical, longitudinal, and lateral were 0.25+0.19 cm, 0.35+0.25 and 0.19+0.19 cm, respectively. For DIBH SBRT combined with respiratory gating, the mean shift values from CBCT in vertical, longitudinal, and lateral were 0.41+0.26 cm, 0.5+0.44 cm. and 0.27+0.23 cm, respectively. A statistically significant difference was observed between the two systems in the vertical direction (p-value = 0.0001), the longitudinal direction (p-value = 0.02), and the lateral direction (p-value = 0.04).

Conclusion: Treating lung cancer patients by using DIBH SBRT techniques combined with Vision RT can lower the shift values in CBCT caused by positioning error compared to the use of respiratory gating. Which can lower the change in re-positioning leading to the unnecessary exposure dose.

Identifying predictive parameters for failure of DQA in patient using helical tomotherapy planning

Wanwisa Bumrungpagdee — 2025-12-01

Background: Radiation therapy using helical tomotherapy requires pre-treatment delivery quality assurance (DQA) to verify treatment accuracy. However, in certain urgent situations such as patients requiring radiation to stop bleeding, those receiving radiation for pain relief, or those with a strictly scheduled treatment course where DQA cannot be performed immediate treatment planning and delivery are necessary without DQA verification.

Objective: To identify predictors associated with DQA failure and to develop a predictive model for pre-treatment DQA in helical tomotherapy.

Materials and Methods: Data were retrospectively collected from treatment plans stored in the Accuray Precision system. The data included the following parameters: treatment sites (Head and Neck, Brain, Chest, Abdomen, and Pelvis), fraction dose, target volume, field width (1 cm, 2.5 cm, 5 cm), pitch, modulation factor (planned and actual), gantry rotations, gantry period, beam-on time, couch travel, couch speed, fraction monitor units (MUs), and leaf open time parameters (maximum, minimum, mean, mode, and standard deviation). All data were obtained from the Radiation Oncology Unit, Department of Radiology, Buddhachinaraj Hospital, Phitsanulok, between January 2020 and December 2023. Predictive factors for delivery quality assurance (DQA) failure prior to treatment delivery were analyzed using odds ratios (ORs) derived from logistic regression analysis with stepwise backward selection.

Results: Predictors significantly associated with DQA failure requiring treatment re-planning included: pelvic treatment sites (OR 2.91, 95% CI 1.52-5.57), field width of 2.5 cm (OR 0.25, 95% CI 0.07-0.91), beam on time (OR 0.99, 95% CI 0.99-0.99), couch speed (mm/sec) (OR 0.14, 95% CI 0.32-0.60), leaf open time (mode) (OR 0.99, 95% CI 0.99-1.00), and leaf open time (std) (OR 1.02, 95% CI 1.01-1.04).

Conclusion: The predictors obtained from this study can be applied to improve the efficiency of treatment planning, reduce the necessity of repeating pre-treatment quality assurance, and shorten the waiting time in cases where re-planning is required, especially in urgent situations where quality assurance cannot be performed. Therefore, they serve as tools to support clinical decision making more rapidly and accurately.

Evaluation of Patient Setup Errors in Pelvic Cancer Radiation Therapy: A Comparative Study Between 3D Surface Imaging (AlignRT) and Conventional Laser Alignment

Kaewalin Phuetpon — 2025-12-01

Background: Radiation therapy plays an important role in treating cancers located in the pelvic region. The patients have to be treated in multiple fractions, therefore, the accuracy of patient setup before each treatment session directly impacts the effective treatment.

Objective: To compare the setup errors in pelvic cancer patients using laser alignment system versus 3D surface imaging system (AlignRT). The study also examined the characteristics of the AlignRT system.

Materials and Methods: The study began with an evaluation of the characteristics of the AlignRT system, including daily quality assurance checks, factors that may affect system performance, and the system’s accuracy in detecting setup errors. Data were then collected from 10 pelvic cancer patients positioned using a laser system and the AlignRT system. Position verification was performed before radiation using Cone Beam Computed Tomography.

Results: The study of AlignRT system characteristics showed that daily setup errors were within 0.4 millimeters. Factors from gantry angle, couch angle, room lighting, and region of interest were within 0.2 mm, 0.1 degrees, 0.1 mm, and 0.2 mm, respectively. Clinically, setup errors in patients positioned with the AlignRT system were smaller than those positioned with the laser system in both the longitudinal and lateral directions. A statistically significant difference was found in the lateral direction, but not in the longitudinal or vertical directions.

Conclusion: The AlignRT system demonstrates high accuracy and precision, and it can be effectively applied for pre-radiation positioning in pelvic cancer patients, serving as a viable alternative to traditional methods such as skin marking or laser systems.

Alternative techniques as a substitute for 4D-CT Simulation in Lung cancer patients

Ploy Dangsamak — 2025-12-11

Background: In radiation therapy for lung cancer, the lung lesions move with respiration. Currently, there is a technique, four-dimensional computed tomography (4D-CT), that acquire images while tracking the respiratory graph during the CT scan, resulting in images with accurate size and position of the lung lesions. However, this method is complex and the cost of purchasing the equipment is quite high.

Objectives: Conduct a study on research data regarding breath-holding techniques and slow CT as a replacement for 4D-CT.

Materials & methods: This study used the Phillips Big Bore RT CT scanner to collect image data, utilizing a moving phantom, specifically the computerized imaging reference systems (CIRS), which is a device that simulates a tumor. The respiratory rate was set to 12 breaths per minute, which is the normal breathing rate for patients. Scans were performed using 4D-CT, inhale/exhale breath-hold CT, 4 sets of slow CT, according to difference of pitch and rotation, and standard CT. The respiratory management device used was the Sentinel 4D-CT (C-RAD AB, Sweden), which is an optical Surface Monitoring Systems (OSMS). Once the image sets for treatment planning were obtained, radiation oncologists contoured the tumor lesion on each CT image set.

Results: The slow CT2 image set and the inhale/exhale breath-hold CT image set acquire tumor volumes of 8.16 and 9.36 cubic centimeters, respectively, which were close to the tumor volume defined using the internal target volume (ITV) obtained from the 4D-CT, 9.93 cubic centimeters. However, the inhale/exhale breath-hold method has the limitation of requiring patients to hold their breath at a normal level.

Conclusion: The appropriate method for performing a Phillips Big Bore RT CT scan to replace 4D-CT is slow CT by setting the parameters with the lowest pitch value of 0.563 and the highest rotation time of 1 second. The results are of a quality comparable to that of 4D-CT.

Break–even point of Radixact® X9 helical tomotherapy machines for cancer treatment

Tharatorn Tungkasamit — 2025-12-11

Background: The Radixact® X9 system is an advanced radiotherapy technique in cancer treatment with high investment costs, necessitating economic evaluation for resource allocation.

Objective: To analyze the break-even point of Radixact® X9 usage at Udon Thani and Lopburi Cancer Hospitals.

Materials & methods: A descriptive study collecting direct and indirect cost data in 2024 to calculate unit costs and break-even points in terms of patient numbers and treatment fractions, including sensitivity analysis.

Results: Udon Thani Cancer Hospital showed a unit cost of 150,737.03 THB and a break-even point of 356.45 patients/year, whereas Lopburi Cancer Hospital had a higher unit cost of 230,355.21 THB and a break-even point of 499.27 patients/year. Sensitivity analysis identified capital costs as the most influential factor with labor costs being less impactful.

Conclusion: Achieving the break-even point for Radixact® X9 services requires a substantial patient volume. Capital cost is the most critical factor affecting economic viability. These findings provide essential data for investment planning, resource management, and radiotherapy policy-making in Thailand.