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Advances in Radiotherapy
& Nuclear Medicine Comparison of online ATP versus offline ATS plans

Table 6. Comparison of the dosimetric parameters of various Most previous studies on adaptive radiotherapy have
organs at risk in patients undergoing radical radiotherapy been conducted using cone beam CT (CBCT). CBCT
cannot provide an accurate representation of the border
Organ Parameter ATP ATS P‑values
at risk between the tumor and surrounding normal soft tissue.
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Rectum D40 (cGy) 3671.49±467.14 3911.85±519.92 <0.05 Thus, accurate delivery of doses cannot be ensured.
D30 (cGy) 4008.91±455.14 4222.03±431.68 <0.05 MRI enhances soft tissue contrast, facilitating superior
visualization and differentiation between healthy tissues
D20 (cGy) 4302.35±524.10 4532.84±324.36 <0.05 and tumors as well as aiding in detecting nuanced
Dmin (cGy) 579.34±523.64 1114.30±745.25 <0.05 physiological alterations within the tissues. 26,27 Online
Dmean (cGy) 3136.20±416.57 3564.54±476.61 <0.05 MRgRT permits daily MRI and direct monitoring of the
Bladder Dmin (cGy) 1028.33±391.63 1212.14±560.91 <0.05 CTV and OAR throughout the treatment process. The
Notes: The comparisons were conducted using the Wilcoxon MR-guided strategy provides a higher level of accuracy
rank-sum test. Significant values were determined based on a and an acceptable distribution of the real dose over the
threshold of P<0.05. treatment fractions. Real-time adaptive radiotherapy
Abbreviations: ATP: Adapt-to-position; ATS: Adapt-to-shape; D40, D30, is conducted using daily acquired MRIs. Gupta et al.
D20: The dose received by 40%, 30%, and 20% of the corresponding evaluated MR-Linac-guided online adaptive radiotherapy
organ at risk, respectively; Dmin: Minimum dose; Dmean: Mean dose.
in patients with nasopharyngeal carcinoma using ATS-
Lite and ATP workflows. The use of MR-Linac-guided
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Table 7. Comparison of the dosimetric parameters of
various organs at risk in patients undergoing post‑operative radiotherapy for cervical cancer offers several advantages.
radiotherapy Before each treatment, MR images can be used to determine
the patient’s daily bladder filling to ensure that the OAR
Organ Parameter ATP ATS P‑values meets the requirements for radiotherapy. In particular,
at risk MR-guided adaptive radiotherapy has shown promise in
Rectum D40 (cGy) 3339.24±333.24 3034.21±733.41 <0.05 addressing these challenges due to its superior soft tissue
D30 (cGy) 3678.23±274.83 3411.82±620.59 <0.05 contrast, which allows for clear visualization of tumor and
D20 (cGy) 4051.75±222.24 3866.87±501.21 <0.05 organ changes. This imaging capability supports more
Dmin (cGy) 250.77±35.92 362.86±170.64 <0.05 precise adaptation of the treatment plan, thereby reducing
Bladder V20 (cGy) 4158.42±327.08 4017.98±381.26 <0.05 potential dose discrepancies and minimizing radiation
exposure to critical organs, such as the bladder, rectum,
Notes: The comparisons were conducted using the Wilcoxon rank-sum and small bowel.
test. Significant values were determined based on a threshold of P<0.05.
Abbreviations: ATP: Adapt-to-position; ATS: Adapt-to-shape; D40, D30, ATS and ATP are two workflows of adaptive radiotherapy
D20: The dose received by 40%, 30%, and 20% of the corresponding that exhibit distinct characteristics. ATS enables a more
organ at risk, respectively; Dmin: Minimum dose. precise and intuitive delineation of the patient’s anatomy on
the day of treatment, facilitating more accurate contouring
anatomical changes throughout the treatment course. of the CTV and OAR on that day and optimizing the
Therefore, this approach enhances therapeutic accuracy dose delivery. Dassen et al. evaluated the efficacy of ATP
and effectiveness. At the dosimetric level, compared and ATS in contouring the corresponding target areas in
with non-adaptive radiotherapy, adaptive radiotherapy adaptive radiotherapy for prostate cancer. They determined
can enhance the dosimetric distributions of CTV and that ATS demonstrated the best performance for the
PTV in both patient groups (Tables 2 and 5). These prostate, including seminal vesicles (CTVproS+SV).
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findings reveal that adaptive radiotherapy, which tailors Furthermore, ATP has demonstrated clinically acceptable
treatment based on daily anatomical variations, allows processes and treatment times in patients with high-grade
for more precise tumor targeting while better sparing the gliomas. ATP is less time-consuming than ATS, and all
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surrounding healthy tissues. In both groups of patients, plans it generates meet the clinical requirements. Herein,
the implementation of adaptive planning techniques led the ATS workflow took 35.4 ± 2.4 min, and the ATP
to enhanced dose coverage and conformity to the target workflow took 10.3 ± 0.6 min. Although the use of ATS
areas, ensuring that the prescribed dose was delivered can increase the receptor volume in CTV and PTV, the
more accurately to the CTV and PTV. Thus, adaptive increase is not significant and time-consuming. Therefore,
radiotherapy could improve the outcomes in patients we primarily use the ATP workflow in daily practice. The
with cervical cancer patients using a more individualized plans generated by the ATP workflow are sufficient to
approach that adapts to the evolving anatomy throughout meet clinical needs. At our institution, the high volume of
the course of treatment. patients undergoing MR-Linac-guided radiotherapy limits

Volume 2 Issue 4 (2024) 6 doi: 10.36922/arnm.4919