Outcome of External Beam Radiation in Differentiated Thyroid Cancer: A 10-year Experience

Objective: Role of external beam radiation (EBRT) in differentiated thyroid cancer (DTC) is controversial. Outcomes of EBRT are also not uniform among studies due to variation in practices. Therefore, this study was elicited to evaluate the outcome of EBRT in DTC in context of our institutional practice. Methods: Medical records of DTC patients who received EBRT to neck with or without mediastinum from January 2004 to December 2013 were retrospectively reviewed. All patients underwent total thyroidectomy (TT) or completion of thyroidectomy. EBRT could be given immediate after TT as adjuvant treatment or given at time of recurrence or RAI refractory as salvage treatment. Radioactive iodine (RAI) treatment could be given before or after EBRT or even be omitted. The primary end-points were locoregional failure-free survival (LRFS) and overall survival (OS). Results: Among 47 patients, most of them were female (70%), age 45 years or over (83%), papillary thyroid cancer (75%) and stage III-IV (62%). There were adjuvant EBRT in 8 patients and salvage EBRT in 39 patients. At time of EBRT, there were high risk histology, gross residual tumor, positive surgical margin, lymph node metastasis, distant metastasis and RAI refractory in 21%, 62%, 72%, 66%, 47% and 59% of patients, respectively. Radiation techniques were conventional radiotherapy, three-dimensional conformal radiotherapy (3D-CRT) and intensity modulated radiotherapy (IMRT) in 14, 19 and 14 patients with median EBRT dose of 50, 60 and 66 Gy (30-70 Gy), respectively. At median follow-up time of 26.6 months (1-82), LRFS at 2 and 4 year were 74% and 63%, respectively. The 2- and 4-year OS were 62% and 42%, respectively. On multivariate analysis, age ≥ 45 years tended to associate with worse OS (p=0.058). EBRT dose ≤ 50 Gy also had a trend to be related with both worse LRFS (p=0.069) and OS (p=0.079). Conclusion: EBRT might be given either as adjuvant or salvage treatment, particularly in case of gross residual tumor and RAI refractory. Escalation of EBRT dose to over 50 Gy with advanced EBRT technique such as IMRT might improve the LRFS and OS

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

AimIn 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.BackgroundIt 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 methodsAn 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.ResultsThe 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%/3mm criterion) and 96.72±0.84% (for the 2%/2mm criterion).ConclusionsThe 8 participating RT centers achieved a satisfactory quality level of IMRT/VMAT clinical implementation