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Advances in Radiotherapy
& Nuclear Medicine Advancements and challenges in radioactive iodine-125

continuous radiation release to kill tumor cells, was first heterogeneity to surrounding tissue can enhance the effect
proposed by Pierre Curie in 1901 . Radiation therapy is of immunotherapy (Figure 1).
[1]
categorized into different dose rates, including high dose
rate (HDR) (>12 Gy/h), medium dose rate (2 – 12 Gy/h), 2. Technological development
low dose rate (LDR) (0.4 – 2 Gy/h), and ultra-LDR For many years, ultrasound has been the preferred image
(<0.4 Gy/h) . Among these categories, iodine-125 (I-125) guidance method for I-125 seeds brachytherapy in prostate
[2]
is the most widely used radioactive sealed source for cancer. However, for other types of tumors, ultrasound
permanent interstitial brachytherapy. I-125 seeds have a imaging suffers from low resolution. Consequently, over
half-life of 60 days and emit photons with an energy level the past two decades, there has been a growing shift
of 27 keV . In 1983, Professor Holm of Denmark invented toward the use of computed tomography (CT)-guided
[3]
transperineal I-125 seed implantation, developing a and magnetic resonance imaging (MRI)-guided imaging
standardized procedure for treating prostate cancer with modalities for I-125 brachytherapy. CT-guided I-125
transrectal ultrasound guidance. This innovative approach brachytherapy offers three advantages, including enhanced
ultimately demonstrated therapeutic efficacy comparable target visualization, real-time monitoring of needle
to external radiation therapy and surgery, earning its arrangements, and 3D digital image reconstruction. For
[4]
inclusion in the NCCN Guidelines for prostate cancer . cases of recurrent head-and-neck cancer, a previous study
In the past two decades, in addition to its established use has shown promising results, with 1- and 2-year local
in prostate cancer, studies have demonstrated the feasibility control (LC) rates of 47.8% and 36.4% (median LC time
and safety of I-125 brachytherapy in the treatment of head of 10 months) and 1- and 2-year overall survival (OS)
and neck, thoracic, abdominal, pelvic, and spinal tumors, rates of 41.3% and 32.2% (median OS time of 8 months).
including both primary and metastatic tumors [5-9] . Recent Notably, the absence of adverse events was associated
[10]
years have witnessed significant changes in the application with improved LC . In the context of portal vein tumor
of brachytherapy, driven by technological advancements. embolism in hepatocellular carcinoma (HCC), CT-guided
However, our understanding of the radiation biology I-125 brachytherapy achieved an LC rate of 78.9% and a
mechanisms underlying brachytherapy remains limited, median OS time of 14.5 months, with no reported serious
[11]
with existing data primarily focused on dose rate effects. adverse events .
I-125 brachytherapy stands out for its capacity to provide The safety and efficacy of CT-guided I-125 seed
extremely high doses within the treatment area, a feat brachytherapy have been well-established for treating
unattainable with external beam radiation therapy (EBRT). recurrent head-and-neck cancer and portal vein tumor
Moreover, it offers the additional benefit of minimizing embolism in HCC. Due to the superior visibility of the
irradiation to surrounding healthy tissue by rapidly prostate gland and capsule in MRI compared to CT and
reducing the dose outside the target lesion. To ensure the ultrasound, MRI has been implemented into the prostate
effectiveness of radiation therapy, precise dose delivery I-125 brachytherapy [12,13] . Moreover, MRI offers excellent
is crucial. The introduction of 3D-printed individualized visualization of normal tissue, and its incorporation
templates, treatment planning systems, and robot-assisted into prostate I-125 brachytherapy holds the potential to
systems has greatly enhanced the accuracy of dose delivery. enhance dose assessment and limit radiation exposure to
At present, with the assistance of 3D-printed organs at risk [12,14] . A study on MRI-guided I-125 interstitial
individualized templates, CT-guided brachytherapy has brachytherapy for HCC reported complete response in 22
achieved a good match of dose verification between lesions (33.8%), partial response in 24 lesions (36.9%),
post-operative and preoperative planning. There is no stable disease in 9 lesions (13.8%), and progressive disease
[15]
significant difference in multiple dosimetric indicators (PD) in 10 lesions (15.4%) . MRI-guided I-125 interstitial
between pre-operative planning and post-operative dose brachytherapy for HCC is technically feasible and effective.
verification, demonstrating an accuracy improvement The introduction of 3D-printed personalized templates
exceeding 90%. Post-operative seed migration poses a has significantly improved the accuracy of I-125 interstitial
potential risk, leading to adverse clinical outcomes and brachytherapy. In 2012, Huang et al. innovatively
complications, such as pulmonary or cardiac particle introduced 3D printing into I-125 brachytherapy for head
embolism. The use of stranded I-125 seeds can also reduce and neck tumors, effectively reducing needle layout errors.
the occurrence of seed migration following implantation. Subsequently, this innovative technique was extended to
In tumor treatment, immunotherapy is gaining increasing treat chest, abdominal, and pelvic tumors in 2015 . These
[16]
importance, and brachytherapy’s unique ability to 3D-printed templates contain essential information, such
deliver concentrated radiation with limited low-dose as body surface characteristics, localization markers, and

Volume 1 Issue 2 (2023) 2 https://doi.org/10.36922/arnm.0914