Page 73 - ARNM-2-4

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

1. Introduction the anatomical configuration. ATP is more commonly
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used for brain tumors, demonstrating clinically acceptable
Cervical cancer is a highly prevalent form of malignant processes and treatment times in high-grade gliomas.
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tumor in females. Radiotherapy is becoming an However, ATS is more commonly used for prostate cancer,
1
increasingly important component in the treatment for which it has demonstrated improved dose delivery.
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of cervical cancer. Advances in multimodal imaging Patients treated for cervical cancer exhibit inter- or
technology have increased the accuracy of contouring intrafraction anatomical changes. The Elekta Unity system
clinical target volume (CTV) and organs at risk (OAR). allows for obtaining an MRI before and during treatment,
Furthermore, image-guidance technology has considerably facilitating daily plan adaptation. This capability enables
reduced the associated errors. For cervical cancer, the the adjustment of treatment plans in response to daily
2
power of magnetic resonance (MR) imaging (MRI)- anatomical variations, ensuring precise dose delivery to
based morphological imaging has driven advancements CTV with each session. Despite these advancements, some
in response assessment and image-guided brachytherapy. limitations exist to the wide clinical application of adaptive
3
The Elekta Unity MR-Linac can perform daily MR imaging radiotherapy.
using a 1.5 T MRI scanner, allowing real-time monitoring
of the patient’s clinical target area and OAR for relevant Herein, offline ATS planning was performed using
contouring adjustments. However, due to the close MR images obtained during treatment. The dosimetric
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anatomical proximity of the cervix to the bladder and outcomes of the two workflows were analyzed by
rectum in addition to the varying physiological states of comparing the delivered doses to the CTV, planning
the patients, daily fluctuations in the filling and positioning target volume (PTV), bladder, rectum, small bowel,
of these organs can cause dose distribution deviations, and femoral head in online ATP and offline ATS plans.
making online adaptive radiotherapy essential Adaptive This comparison allowed for an assessment of the dose
5,6
radiotherapy encompasses the adaptation of radiotherapy distribution across the different anatomical structures in
plans based on patient-specific anatomical variations that each adaptive planning approach. Herein, we aimed to
have been identified through image-guided radiation investigate the dosimetric differences between online ATP
therapy (IGRT), optimization of planning, and dose and offline ATS plans in MR-guided adaptive radiotherapy
delivery to ensure accurate treatment. 7 for cervical cancer. Furthermore, we aimed to evaluate
radiotherapy modalities for treating cervical cancer to
Adaptive radiotherapy can be implemented at 3 time address the clinical requirements and provide guidance on
scales as follows: offline in adjacent fractions, online optimizing ART protocols to improve the precision of dose
immediately before the fraction, and online during delivery, minimize exposure to healthy tissues, and reduce
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treatment. Online and real-time adaptive radiotherapy the risk of radiation-induced complications. Ultimately, we
protocols allow plan modification while the patient is on intend to support the development of adaptable patient-
the couch, thereby allowing the plan to be updated on specific radiotherapy strategies that meet the dynamic
the basis of real-time anatomical changes. This enables requirements of cervical cancer treatment.
the delineation of smaller safer borders due to the
greater certainty of the tumor location. Offline adaptive 2. Methods
radiotherapy aims to correct for systematic changes in
OAR that are identified by imaging during treatment and 2.1. Inclusion criteria
plans are modified offline. Online and offline adaptive Of the 30 patients with cervical cancer who underwent
9,10
radiotherapy play different roles in cancer treatment. radiotherapy at Shandong Cancer Hospital between
Online adaptive radiotherapy is effective for treating September 2020 and June 2023, 25 met the inclusion criteria.
pancreatic and cervical tumors, 11-16 whereas offline adaptive The following were the inclusion criteria: Age between
radiotherapy has been beneficial in patients with head and 30 and 85 years; diagnosis of cervical cancer that had
neck and lung tumors, 17-21 The Elekta Unity includes two been confirmed through histopathological examination;
adaptive planning strategies designed to address daily absence of any intestinal or metabolic diseases; and
anatomical variations using the MRI: Adapt-to-position adequate comprehension and communication ability of the
(ATP), which is also known as no-online adaptive patient. The following were the exclusion criteria: Severe
replanning. The ATP involves optimizing the reference cardiac, hepatic, or renal insufficiency; termination of
plan with an isocenter shift that is based on the alignment treatment due to significant complications during or after
between the daily MRI and reference image. Adapt-to- radiotherapy such as cardiac or pulmonary issues, severe
shape (ATS), also known as online adaptive replanning, infections, and hemorrhages; and refusal to participate in
involves generating a new treatment plan that is based on the study. This study was approved by the Ethical Review

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