Secondary cancer risk from modern external-beam radiotherapy of prostate cancer patients: Impact of fractionation and dose distribution.

Modern radiotherapy (RT) uses altered fractionation, long beam-on time and image-guided procedure. This study aimed to compare secondary cancer risk (SCR) associated with primary field, scatter/leakage radiations and image-guided procedure in prostate treatment using intensity-modulated RT (IMRT), CyberKnife stereotactic body RT (CK-SBRT) in relative to 3-dimensional conformal RT (3D-CRT). Prostate plans were generated for 3D-CRT, IMRT (39 fractions of 2 Gy), and CK-SBRT (five fractions of 7.25 Gy). Excess absolute risk (EAR) was calculated for organs in the primary field using Schneider's mechanistic model and concept of organ equivalent dose (OED) to account for dose inhomogeneity. Doses from image-guided procedure and scatter/leakage radiations were determined by phantom measurements. The results showed that hypofractionation relative to conventional fractionation yielded lower SCR for organs in primary field (p ≤ 0.0001). SCR was further modulated by dose-volume distribution. For organs near the field edge, like the rectum and pelvic bone, CK-SBRT plan rendered better risk profiles than IMRT and 3D-CRT because of the absence of volume peak in high dose region (relative risk [RR]: 0.65, 0.22, respectively, p ≤ 0.0004). CK-SBRT and IMRT generated more scatter/leakage and imaging doses than 3D-CRT (p ≤ 0.0002). But primary field was the major contributor to SCR. EAR estimates (risk contributions, primary field: scatter/leakage radiations: imaging procedure) were 7.1 excess cases per 104 person-year (PY; 3.64:2.25:1) for CK-SBRT, 9.93 (7.32:2.33:1) for IMRT and 8.24 (15.99:2.35:1) for 3D-CRT (p ≤ 0.0002). We conclude that modern RT added more but small SCR from scatter/leakage and imaging doses. The primary field is a major contributor of risk which can be mitigated by the use of hypofractionation.

MALAT1 Decreases the Sensitivity of Head and Neck Squamous Cell Carcinoma Cells to Radiation and Cisplatin.

BACKGROUND/AIM: Two-thirds of head and neck squamous cell carcinoma (HNSCC) patients present with locally advanced (LA) stages and have a poor survival rate. The aim of this study was to investigate the roles of the long non-coding RNAs MALAT1 on radiation and cisplatin sensitivity of HNSCC cells. MATERIALS AND METHODS: Clonogenic, cell viability, and apoptosis assays were performed in cells following MALAT1 knockdown using CRISPR/Cas9 system. RESULTS: MALAT1 was overexpressed in HNSCC cell lines as compared to a non-tumorigenic cell line. The number of colonies formed after radiation was significantly reduced in MALAT1 knockdown cells. The IC50 value of cisplatin in MALAT1 knockdown cells was lower than that of the control cells. MALAT1 knockdown resulted in cell cycle arrest at G2/M phase, DNA damage and apoptotic cell death. CONCLUSION: MALAT1 knockdown enhanced the sensitivity of HNSCC cells to radiation and cisplatin partly through the induction of G2/M cell cycle arrest resulting in DNA damage and apoptosis.

Multi-institutional evaluation using the end-to-end test for implementation of dynamic techniques of radiation therapy in Thailand.

AIM: In this study, an accuracy survey of intensity-modulated radiation therapy (IMRT) and volumetric arc radiation therapy (VMAT) implementation in radiotherapy centers in Thailand was conducted. BACKGROUND: It is well recognized that there is a need for radiotherapy centers to evaluate the accuracy levels of their current practices, and use the related information to identify opportunities for future development. MATERIALS AND METHODS: An end-to-end test using a CIRS thorax phantom was carried out at 8 participating centers. Based on each center's protocol for simulation and planning, linac-based IMRT or VMAT plans were generated following the IAEA (CRP E24017) guidelines. Point doses in the region of PTVs and OARs were obtained from 5 ionization chamber readings and the dose distribution from the radiochromic films. The global gamma indices of the measurement doses and the treatment planning system calculation doses were compared. RESULTS: The large majority of the RT centers (6/8) fulfilled the dosimetric goals, with the measured and calculated doses at the specification points agreeing within ±3% for PTV and ±5% for OARS. At 2 centers, TPS underestimated the lung doses by about 6% and spinal cord doses by 8%. The mean percentage gamma pass rates for the 8 centers were 98.29 ± 0.67% (for the 3%/3 mm criterion) and 96.72 ± 0.84% (for the 2%/2 mm criterion). CONCLUSIONS: The 8 participating RT centers achieved a satisfactory quality level of IMRT/VMAT clinical implementation.

In vivo whole body dosimetry measurement technique of total body irradiation: a 12-year retrospective study result from one institute in Thailand.

OBJECTIVE: The main problem of total body irradiation (TBI) is how to maintain radiation dose homogeneity throughout the body during a treatment course. The simple set up treatment with non-complicated in vivo dosimetry measurement technique is the ideal method to solve this problem. For this reason, the authors have reported the results of in vivo dosimetry measurement method to prove the reliability of dose distribution from the authors' TBI technique. MATERIAL AND METHOD: The authors reviewed the data of dose measurement record from 53 patients' treatment files to report the uniformity of absorbed in vivo dose distribution throughout the whole body from TBI with semiconductor detectors and ionization chamber with the accepted homogeneity within +/- 10% of the prescribed dose. The result was reported in the term of mean and standard deviation of absorbed dose difference from the prescribed dose. RESULTS: The uniformity of radiation dose distribution throughout the whole body of all patients calculated from semiconductors was accepted with mean difference value of -3.2 +/- 2.5% from the prescribed dose and the difference of mean absorbed dose value at midline point between semiconductor and ionization chamber was 4 +/- 3.3%. CONCLUSION: This TBI dosimetry measurement technique has been proved to exhibit the reliability of dose homogeneity throughout the whole body within the accepted value. This could be applied for use at any institute that has some limitation in resources and small treatment room.