Carpe Diem: Making the Most of Plan-of-the-Day for Cervical Cancer Radiation Therapy

The Current use of Adaptive Strategies for External Beam Radiotherapy in Cervical Cancer: A Systematic Review

AIMS

Variability in the target and organs at risk (OARs) in cervical cancer treatment presents challenges for precise radiotherapy. Adaptive radiotherapy (ART) offers the potential to enhance treatment precision and outcomes. However, the increased workload and a lack of consensus on the most suitable ART approach hinder its clinical adoption. This systematic review aims to assess the current use of adaptive strategies for cervical cancer and define the optimal approach.

MATERIALS AND METHODS

A systematic review of current literature published between January 2012 and May 2023 was conducted. Searches used PubMed/Medline, Cochrane Library, and Web of Science databases, supplemented with the University of Manchester, Google Scholar, and papers retrieved from reference lists. The review assessed workflows, compared dosimetric benefits, and examined resources for each identified strategy. Excluded were abstracts, conference abstracts, reviews, articles unrelated to ART management, proton therapy, brachytherapy, or qualitative studies. A narrative synthesis involved data tabulation, summarizing selected studies detailing workflow for cervical cancer and dosimetric outcomes for targets and OARs.

RESULTS

Sixteen articles met the inclusion criteria; these were mostly retrospective simulation planning studies, except four studies that had been clinically implemented. We identified five approaches for ART radiotherapy for cervical cancer: reactive and scheduled adaptation, internal target volume (ITV)-based approach using library of plans (LOP), fixed-margin approach using LOP, and real-time adaptation, with each approach reducing irradiated volumes without compromising target coverage compared to the non-ART approach. The LOP-based ITV approach is the most used and clinically assessed.

CONCLUSION

Identifying the optimal strategy is challenging due to dosimetric assessment limitations. Implementing cervical cancer ART necessitates strategic optimization of clinical benefits and resources through research, including studies to identify the optimal frequency, and prospective evaluations of toxicity.

Future of Multidisciplinary Team in the Context of Adaptive Therapy

The implementation and early adoption of online adaptive radiotherapy (oART) has required the presence of clinicians, physicists and radiation therapists (RTT) at the treatment console. The impact on each of them is unique to their profession and must be considered for safe and efficient implementation. In the short term future, widespread adoption will depend on the development of innovative workflows, and rethinking of traditional roles and responsibilities may be required. For the future, technologies such as artificial intelligence promise to change the workflow significantly in terms of speed, automation and decision-making. However, overall communication within the team will persist in being one of the most important aspects.

First Application of Demand-Triggered Online Adaptive Radiotherapy in the Treatment of Cervical Cancer: A Clinical Report

Gynecology cancers can reap significant benefits from adaptive radiation therapy (ART) for four major reasons: organ motion, organ deformation, density change, and cavity filling. There are three recognized types of adaptive radiotherapy: offline, online, and real-time. This balance of improved dosimetry versus clinic resources, as well as the optimal timing for adaptations, is still under investigation. The emergence of on-demand online adaptive radiotherapy (OART) can solve the above problems. In this context, we introduce two patients with cervical cancer who used on-demand OART for the first time. One patient with cervical cancer received radical radiotherapy on the United Imaging uCT-ART platform, and another patient with cervical cancer received postoperative adjuvant radiotherapy. The radiotherapy process used OART, which was triggered by senior radiotherapists, assisted by artificial intelligence, and guided by fan-beam computer tomography. Patient 1, who was 54 years old with cervical squamous cell carcinoma, International Federation of Gynecology and Obstetrics (FIGO) stage ⅢC1, underwent radical concurrent chemoradiotherapy. The target volume was reduced in the late stage of radiotherapy. The target volume coverage of the OART plan was better, and the bladder and rectum doses were lower than those of the image-guided radiotherapy plan. Patient 2, who was 56 years old with cervical adenocarcinoma, FIGO stage ⅡA1, underwent postoperative concurrent chemoradiotherapy. If the fractionated treatment during radiotherapy was carried out according to the original plan, treatment off-target would occur, while the OART plan could ensure target coverage. The acute toxic reactions that occurred in both patients during radiotherapy were patient-reported outcome Common Terminology Criteria for Adverse Events 1-2, and no toxic reactions of grade 3 or above occurred. This is the first description of the successful implementation of the uCT-ART-based OART system in EBRT for cervical cancer.

Implementing Plan of the Day for Cervical Cancer: A Comparison of Target Volume Generation Methods

Purpose

Owing to substantial interfraction motion in cervical cancer, plan-of-the-day (PotD) adaptive radiation therapy may be of benefit to patients. Implementation is limited by uncertainty over how to generate the planning target volumes (PTVs). We compared published methods on our own patients.

Methods and Materials

Forty patients each had 3 planning scans with variable bladder filling and daily cone beam computed tomographies (cone beam CTs) during radiation therapy; 5 to 11 cone beam CTs were selected to represent interfraction motion. Clinical target volumes (CTVs) and organs at risk were contoured following EMBRACE-II guidelines. A literature search identified 30 adaptive and nonadaptive solutions to PTV generation, which we applied to our patients. PTV sizes and mean coverage of the daily CTV were determined. For 11 patients, the clinically implemented, subjectively edited plan library was also investigated.

Results

Eleven studies assessed 15 PotD strategies against nonadaptive comparators on a median of 14 patients (range, 9-23). Some PotD approaches applied margin recipes to the CTV on each planning scan, some modeled the CTV against bladder volume, and others applied incremental isotropic margins to the CTV with a single planning scan. Generally, coverage improved as PTV size increased. The fixed isotropic margin required to provide 100% coverage of all patients was 44 mm, with a mean PTV size of 3316 cm3. The PotD strategy with the best coverage was a 2-plan library formed by modeling the CTV against bladder volume with extrapolation; it provided 98% mean coverage with 1419-cm3 mean PTV size. A 3-plan library consisting of the CTV on each planning scan with 10-mm margin provided 96% mean coverage with 1346-cm3 mean PTV size. The clinically implemented solution that employed subjective extrapolation had mean 100% coverage and 1282-cm3 PTV size on the 11-patient subset. Coverage provided by the best nonadaptive strategies was not statistically superior to the best PotD strategy (P = .13), but PTVs were larger (P = .02).

Conclusions

We identified a modeled 2-plan method and a simple 3-plan method, both of which provided excellent coverage with small PTVs compared with nonadaptive strategies.

Clinical Implementation of "Plan of the Day" Strategy in Definitive Radiation Therapy of Cervical Cancer: Online Adaptation to Address the Challenge of Organ Filling Reproducibility

PURPOSE

Definitive pelvic intensity modulated radiation therapy (IMRT) in cervical cancer is susceptible to geographic miss due to daily positional and volumetric variations in target and organs at risk. Hence, despite evidence of reduced acute and late treatment-related toxicities, implementation of image-guided IMRT (IG-IMRT) with a reasonable safety margin to encompass organ motion is challenging.

METHODS AND MATERIALS

In this prospective, nonrandomized phase 2 study, patients with cervical cancer International Federation of Gynecology and Obstetrics (2009) stage IB2-IIIB between the ages of 18 and 65 years were treated with definitive pelvic chemoradiotherapy with a prespecified organ (bladder and rectum) filling protocol. Reproducibility of organ filling was assessed along with the implementation of daily comprehensive adaptive image-guided radiotherapy (IGRT), with a library of 3 IMRT (volumetric modulated arc therapy) plans with incremental expansions of clinical target volume (CTV) to planning target volume (PTV) (primary) margins (small, 0.7 cm; adequate, 1 cm; and large, 1.5 cm) and a backup motion robust 3-dimensional conformal radiotherapy plan; the appropriate plan is chosen based on pretreatment cone beam computed tomography (CBCT) ("plan of the day" approach).

RESULTS

Fifty patients with a median age of 49 years (IQR, 45-56 years) received definitive radiation therapy (45-46 Gy in 23-25 fractions to pelvis, with simultaneous integrated boost to gross nodes in 15 patients) with the aforementioned IGRT protocol. In the analysis of 1171 CBCT images (in 1184 treatment sessions), the mean planning computed tomography (CT) and CBCT bladder volumes were 417 and 373 cc, respectively. Significant interfractional variation in bladder volume was noted with a mean absolute dispersion of 29.5% with respect to planning CT; significant influential random factors were postchemotherapy sessions (P ≤ .001), pre-CBCT protocol duration (P = .001), and grades of chemotherapy induced nausea vomiting (P = .001). Significantly higher variation in bladder filling was noted in patients with older age (P = .014) and larger planning CT bladder volume (P ≤ .001). Time trend analysis of fraction-wise bladder volume revealed an absolute systemic reduction of 16.3% in bladder volume means from the first to the fifth week. Variation in rectal diameter was much less pronounced, with 19.2% mean dispersion and without any significant factors affecting it. Although in 19% and 2% of sessions large IMRT PTV and 3-dimensional conformal radiotherapy were necessary to cover the primary target, respectively, reduction in treated volume was possible in 43% of sessions with small PTV selection instead of standard adequate PTV (36% sessions). Plan of the day selection had a moderate to strong correlation with nonabsolute dispersion of bladder filling (Spearman ρ =0.4; P = .001) and a weak (but significant) correlation with grades of acute toxicities. The planned protocol was well tolerated with no radiation-induced local grade 3 toxicity.

CONCLUSIONS

Interfractional variation in organ filling (especially bladder) is inevitable despite fixed pretreatment protocol in definitive settings (intact cervix). Despite the logistical challenges, adaptive IGRT in the form of plan of the day based on incremental CTV-to-PTV margins is a relatively simple and feasible strategy to minimize geometric uncertainties in radical IG-IMRT of cervical cancer.

Predicting cervical cancer target motion using a multivariate regression model to enable patient selection for adaptive external beam radiotherapy

Background and purpose

Interfraction motion during cervical cancer radiotherapy is substantial in some patients, minimal in others. Non-adaptive plans may miss the target and/or unnecessarily irradiate normal tissue. Adaptive radiotherapy leads to superior dose-volume metrics but is resource-intensive. The aim of this study was to predict target motion, enabling patient selection and efficient resource allocation.

Materials and methods

Forty cervical cancer patients had CT with full-bladder (CT-FB) and empty-bladder (CT-EB) at planning, and daily cone-beam CTs (CBCTs). The low-risk clinical target volume (CTVLR) was contoured. Mean coverage of the daily CTVLR by the CT-FB CTVLR was calculated for each patient. Eighty-three investigated variables included measures of organ geometry, patient, tumour and treatment characteristics. Models were trained on 29 patients (171 fractions). The Two-CT multivariate model could use all available data. The Single-CT multivariate model excluded data from the CT-EB. A univariate model was trained using the distance moved by the uterine fundus tip between CTs, the only method of patient selection found in published cervix plan-of-the-day studies. Models were tested on 11 patients (68 fractions). Accuracy in predicting mean coverage was reported as mean absolute error (MAE), mean squared error (MSE) and R2.

Results

The Two-CT model was based upon rectal volume, dice similarity coefficient between CT-FB and CT-EB CTVLR, and uterine thickness. The Single-CT model was based upon rectal volume, uterine thickness and tumour size. Both performed better than the univariate model in predicting mean coverage (MAE 7 %, 7 % and 8 %; MSE 82 %2, 65 %2, 110 %2; R2 0.2, 0.4, -0.1).

Conclusion

Uterocervix motion is complex and multifactorial. We present two multivariate models which predicted motion with reasonable accuracy using pre-treatment information, and outperformed the only published method.

Empirical analysis of a plan-of-the-day strategy to approximate daily online reoptimization for prostate CBCT-guided adaptive radiotherapy

PURPOSE

Adaptive radiotherapy (ART) can improve the dose delivered to the patient in the presence of anatomic variations. However, the required time, effort, and clinical resources are intensive. This work analyzed a plan-of-the-day (POD) approach on clinical patients treated with online ART to explore implementations that balance dosimetric benefit and clinical resource cost.

METHODS

Eight patients treated to the prostate and proximal seminal vesicles with 26 fractions of CBCT-guided, daily online ART were retrospectively analyzed. With a plan library composed of daily adaptive plans from the initial week of treatment and the original plan, the effect of a POD approach starting the following week was investigated by simulating use of these previously generated plans under 3- and 6-degree-of-freedom patient alignment. The plan selected for each treatment was that from the library that maximized the Dice similarity coefficient of the clinical target volume with that of the current treatment fraction. The resulting distribution of several target coverage and organ-at-risk dose metrics are described relative to those achieved with the daily online reoptimized adaptive technique.

RESULTS

The values of target coverage and organ-at-risk dose metrics varied across patients and metrics. The POD schemas closely approximated the reference values from a fully reoptimized adaptive plan yet required less than 20% of the reoptimization effort. The POD schemas also had a much greater effect on target coverage metrics than 6-degree-of-freedom registration did. Organ-at-risk dose metrics also varied considerably across patients but did not exhibit a consistent dependence on the particular schema.

CONCLUSIONS

POD schemas were able to achieve the vast majority of the dosimetric benefit of daily online ART with a small fraction of the online reoptimization effort. Strategies like this might allow for more practical and strategic implementation of ART so as to benefit a greater number of patients.