Interfractional variation in position of the uterus during radical radiotherapy for cervical cancer

Uterus motion analysis for radiotherapy planning optimization. The innovative contribution of on-board hybrid MR imaging

Introduction

Organ motion (OM) and volumetric changes pose challenges in radiotherapy (RT) for locally advanced cervical cancer (LACC). Magnetic Resonance-guided Radiotherapy (MRgRT) combines improved MRI contrast with adaptive RT plans for daily anatomical changes. Our goal was to analyze cervico-uterine structure (CUS) changes during RT to develop strategies for managing OM.

Materials and methods

LACC patients received chemoradiation by MRIdian system with a simultaneous integrated boost (SIB) protocol. Prescription doses of 55-50.6 Gy at PTV1 and 45-39.6 Gy at PTV2 were given in 22 and 25 fractions. Daily MRI scans were co-registered with planning scans and CUS changes were assessed.Six PTVs were created by adding 0.5, 0.7, 1, 1.3, 1.5, and 2 cm margins to the CUS, based on the simulation MRI. Adequate margins were determined to include 95 % of the CUSs throughout the entire treatment in 95 % of patients.

Results

Analysis of 15 LACC patients and 372 MR scans showed a 31 % median CUS volume decrease. Asymmetric margins of 2 cm cranially, 0.5 cm caudally, 1.5 cm posteriorly, 2 cm anteriorly, and 1.5 cm on both sides were optimal for PTV, adapting to CUS variations. Post-14th fraction, smaller margins of 0.7 cm cranially, 0.5 cm caudally, 1.3 cm posteriorly, 1.3 cm anteriorly, and 1.3 cm on both sides sufficed.

Conclusion

CUS mobility varies during RT, suggesting reduced PTV margins after the third week. MRgRT with adaptive strategies optimizes dose delivery, emphasizing the importance of streamlined IGRT with reduced PTV margins using a tailored MRgRT workflow with hybrid MRI-guided systems.

MRI characterization of pelvic floor ligaments in nulliparous women: Technique development and morphometry within the 3D pelvic inclination correction system (3D-PICS)

PURPOSE

The aim of the MRI-study was to evaluate the visibility of the pelvic floor ligaments and to analyze the ligament morphometry in 3D space.

METHODS

Twenty-two nulliparous women underwent MRI with a ligament specific protocol. MR datasets were evaluated using the 3D Pelvic Inclination Correction System (3D-PICS). The round ligament (RL), sacrospinous ligament (SSL), sacrotuberous ligament (STL), urogenital diaphragm (UGD) and uterosacral ligament (USL) were analyzed. Qualitative and quantitative analysis was performed. 3D coordinates for origin and insertion points were determined relative to the symphysis; subsequently lengths and angles were calculated. Interrater reliability was calculated to validate the point determination method.

RESULTS

Moderate to good visibility was reported for the RL, the SSL, the STL and the UGD. Standard deviation of the points analyzed in the different dimensions vary from 1.5 mm to 21.3 mm. Origin and insertion points of the ligaments are found within a mean standard distance of 10.7 mm. The highest variability was seen in insertion points of RL, with a standard distance of 25.4 mm. The interrater reliability was good to very good (range of intraclass correlation coefficients (ICC) from 0.58 to 0.96), except for the UGD ventral points (ICC from 0.27 to 0.55).

CONCLUSIONS

This in-vivo MRI technique development study offers first exact data describing the pelvic floor ligaments in nulliparous women in 3D-PICS. Visibility, exact 3D coordinates of the origin and insertion points, lengths, angles and interrater reliability assessed for all parameters were evaluated morphometrically.

Prospects for daily online adaptive radiotherapy for cervical cancer: Auto-contouring evaluation and dosimetric outcomes

BACKGROUND

Training senior radiation therapists as "adapters" to manage influencers and target editing is critical in daily online adaptive radiotherapy (oART) for cervical cancer. The purpose of this study was to evaluate the accuracy and dosimetric outcomes of automatic contouring and identify the key areas for modification.

METHODS

A total of 125 oART fractions from five postoperative cervical cancer patients and 140 oART fractions from five uterine cervical cancer patients treated with daily iCBCT-guided oART were enrolled in this prospective study. The same adaptive treatments were replanned using the Ethos automatic contours workflow without manual contouring edits. The clinical target volume (CTV) was subdivided into several separate regions, and the average surface distance dice (ASD), centroid deviation, dice similarity coefficient (DSC), and 95% Hausdorff distance (95% HD) were used to evaluate contouring for the above portions. Dosimetric results from automatic oART plans were compared to supervised oART plans to evaluate target volumes and organs at risk (OARs) dose changes.

RESULTS

Overall, the paired CTV had high overlap rates, with an average DSC value greater than 0.75. The uterus had the largest consistency differences, with ASD, centroid deviation, and 95% HD being 2.67 ± 1.79 mm, 17.17 ± 12 mm, and 10.45 ± 5.68 mm, respectively. The consistency differences of the lower nodal CTVleft and nodal CTVright were relatively large, with ASD, centroid deviation, and 95% HD being 0.59 ± 0.53 mm, 3.6 ± 2.67 mm, and 5.41 ± 4.08 mm, and 0.59 ± 0.51 mm, 3.6 ± 2.54 mm, and 4.7 ± 1.57 mm, respectively. The automatic online-adapted plan met the clinical requirements of dosimetric coverage for the target volume and improved the OAR dosimetry.

CONCLUSIONS

The accuracy of automatic contouring from the Ethos adaptive platform is considered clinically acceptable for cervical cancer, and the uterus, upper vaginal cuff, and lower nodal CTV are the areas that need to be focused on in training.

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.

Effects of Interfraction Dose Variations of Target and Organs at Risk on Clinical Outcomes in High Dose Rate Brachytherapy for Cervical Cancer

Meeting dose prescription is critical to control tumors in radiation therapy. Interfraction dose variations (IDVs) from the prescribed dose in high dose rate brachytherapy (HDR) would cause the target dose to deviate from the prescription but their clinical effect has not been widely discussed in the literature. Our previous study found that IDVs followed a left-skewed distribution. The clinical effect of the IDVs in 100 cervical cancer HDR patients will be addressed in this paper. An in-house Monte Carlo (MC) program was used to simulate clinical outcomes by convolving published tumor dose response curves with IDV distributions. The optimal dose and probability of risk-free local control (RFLC) were calculated using the utility model. The IDVs were well-fitted by the left-skewed Beta distribution, which caused a 3.99% decrease in local control probability and a 1.80% increase in treatment failure. Utility with respect to IDV uncertainty increased the RFLC probability by 6.70% and predicted an optimal dose range of 83 Gy-91 Gy EQD2. It was also found that a 10 Gy dose escalation would not affect toxicity. In conclusion, HRCTV IDV uncertainty reduced LC probabilities and increased treatment failure rates. A dose escalation may help mitigate such effects.

Dosimetric and feasibility evaluation of a CBCT-based daily adaptive radiotherapy protocol for locally advanced cervical cancer

PURPOSE

Evaluate a cone-beam computed tomography (CBCT)-based daily adaptive platform in cervical cancer for multiple endpoints: (1) physics contouring accuracy of daily CTVs, (2) CTV coverage with adapted plans and reduced PTV margins versus non-adapted plans with standard-of-care (SOC) margins, (3) dosimetric improvements to CTV and organs-at-risk (OARs), and (4) on-couch time.

METHODS AND MATERIALS

Using a Varian Ethos™ emulator and KV-CBCT scans, we simulated the doses 15 retrospective cervical cancer patients would have received with/without online adaptation for five fractions. We compared contours and doses from SOC plans (5-15 mm CTV-to-PTV margins) to adapted plans (3 mm margins). Auto-segmented CTVs and OARs were reviewed and edited by trained physicists. Physics-edited targets were evaluated by an oncologist. Time spent reviewing and editing auto-segmented structures was recorded. Metrics from the CTV (D99%), bowel (V45Gy, V40Gy), bladder (D50%), and rectum (D50%) were compared.

RESULTS

The physician approved the physics-edited CTVs for 55/75 fractions; 16/75 required reductions, and 4/75 required CTV expansions. CTVs were encapsulated by unadapted, SOC PTVs for 56/75 (72%) fractions-representative of current clinical practice. CTVs were completely covered by adapted 3 mm PTVs for 71/75 (94.6%) fractions. CTV D99% values for adapted plans were comparable to non-adapted SOC plans (average difference of -0.9%), while all OAR metrics improved with adaptation. Specifically, bowel V45Gy and V40Gy decreased on average by 87.6 and 109.4 cc, while bladder and rectum D50% decreased by 37.7% and 35.8%, respectively. The time required for contouring and calculating an adaptive plan for 65/75 fractions was less than 20 min (range: 1-29 min).

CONCLUSIONS

Improved dose metrics with daily adaption could translate to reduced toxicity while maintaining tumor control. Training physicists to perform contouring edits could minimize the time physicians are required at adaptive sessions improving clinical efficiency. All emulated adaptive sessions were completed within 30 min however extra time will be required for patient setup, image acquisition, and treatment delivery.

Folic Acid Preconditioning Alleviated Radiation-Induced Ovarian Dysfunction in Female Mice

Radiological therapy/examination is the primary source of artificial radiation exposure in humans. While its application has contributed to major advances in disease diagnosis and treatment, ionizing radiation exposure is associated with ovarian damage. The use of natural products, either alone or as an adjunct, has become increasingly common for reducing the side effects of radiological therapy during disease treatment. Herein, we explored the protective effect of folic acid (FA), a widely used B vitamin, against radiation-induced ovarian injury and its mechanism of action. Female mice with normal ovarian function were randomly divided into control, FA, radiation, and radiation + FA groups. The intervention strategy included daily intragastric administration of FA (5 mg/kg) for 3 weeks prior to radiation exposure. Mice in the radiation and radiation + FA groups received a single dose of 5 Gy X-ray irradiation. Changes in the estrous cycle were then recorded, and ovarian tissues were collected. Pathophysiological changes as well as reproductive and endocrine-related indexes were determined via H&E staining, immunohistochemistry, Western blot, and ELISA. The reproductive performance and emotional symptoms of animals were also monitored. Our results indicated that FA intervention effectively alleviated ovarian damage, leading to more regular estrous cycles, lesser impairment of follicular morphology and endocrine status, as well as greater germ cell preservation. Reduced levels of oxidative stress, inflammation, and enhanced DNA repair were associated these changes. FA pre-administration improved the reproductive performance, leading to higher pregnancy rates and greater litter sizes. Further, the anxiety levels of animals were significantly reduced. Our results indicate that FA pre-administration significantly alleviates radiation-induced ovarian damage in rodents, highlighting its potential as a protective strategy against radiation exposure in the female population.

Comparison of survival, acute toxicities, and dose-volume parameters between intensity-modulated radiotherapy with or without internal target volume delineation method and three-dimensional conformal radiotherapy in cervical cancer patients: A retrospective and propensity score-matched analysis

BACKGROUND

To evaluate whether the use of the internal target volume (ITV) delineation method improves the performance of intensity-modulated radiotherapy (IMRT) and three-dimensional conformal radiotherapy (3DCRT) in terms of survival, acute toxicities, and dose-volume parameters.

METHODS

A total number of 477 cervical cancer patients who received concurrent chemoradiotherapy (CCRT) from January 2012 to December 2016 were retrospectively analyzed. They were divided into four groups: the non-ITV (N-ITV) + IMRT, ITV + IMRT, N-ITV + 3DCRT, and ITV + 3DCRT groups, with 76, 41, 327, and 33 patients, respectively. Survival analysis was performed with the Kaplan-Meier and the log-rank tests, and acute toxicity analysis was performed with the chi-squared test and the binary logistic regression test. Using the propensity score matching (PSM) method, 92 patients were matched among the four groups, and their dose-volume parameters were assessed with the Kruskal-Wallis method.

RESULTS

The median follow-up time was 49 months (1-119) for overall survival (OS). The 5-year OS rate was 66.4%. The ITV delineation method was an independent prognostic factor for OS (HR [95% CI]: 0.52 [0.27, 0.98], p = 0.044) and progression-free survival (PFS) (HR [95% CI]: 0.59 [0.36, 0.99], p = 0.045). The ITV + IMRT group had the lowest incidence rate (22%) and the N-ITV + IMRT group had the highest incidence rate of grade ≥3 hematological toxicity (HT) (46.1%) among the four groups. The pelvic bone marrow relative V10, V20, and V30 in the N-ITV + IMRT group was higher than those in the ITV + IMRT and N-ITV + 3DCRT groups (p < 0.05).

CONCLUSIONS

The use of ITV for IMRT treatment planning was associated with improved overall survival and progression-free survival, with lower HT rate.

To analyse target volume variations during SIB-IMRT of squamous cell carcinoma of uterine cervix

Purpose:

To assess volume variations in target site due to changes in bladder filling and rectal content including air bubbles during simultaneous-integrated boost intensity-modulated radiotherapy (SIB-IMRT) of patients suffering from squamous cell carcinoma of uterine cervix.

Materials and methods:

A total of ten patients of squamous cell carcinoma of uterine cervix were enrolled in this analysis. All patients were planned to undergo SIB-IMRT using 10 MV beam. Planning target volume of the tumour (PTVtumour) and PTVnodal were prescribed with 5,040 and 4,500 cGy doses, respectively. During planning, PTVtumour V95%, PTVnodal V95% and organs at risk (OARs) (bladder, rectum, femoral heads and small bowel) volumes were measured from initial CT planning scans taken with full bladder. CT scans were acquired once in a week over a treatment period of 5·5 weeks. Intra-treatment scans with full bladder were then fused with the planning scans to determine variations in the target volume and the OAR volume. Changes in radiation dose to the PTVtumour and the PTVnodal were also assessed by comparing intra-treatment scans with the planning (first) scans.

Results:

All patients showed intra-treatment bladder volume larger than the planning bladder volume. Difference between planning bladder and intra-treatment bladder volumes ranged from 4·5 to 49%. Rectal volume varied from 17 to 60 cc. A wide variation between planning and intra-treatment air volumes was found in most of the patients. When comparing initial and inter-fraction air volumes, the maximum difference was 366·67%. Due to bladder and rectal volume variations, PTVtumour V95% and PTVnodal V95% doses did not remain constant throughout the treatment. The maximum discrepancy between intra-treatment PTVtumour dose and planning PTVtumour dose was 12·15%. The maximum difference between planning and inter-fraction PTV V95% was 48·28%. PTVnodal dose observed from scan taken in last week of treatment was 12·87% less than planning PTVnodal dose analysed from planning CT scan. Maximum difference in planning and inter-fraction PTVnodal V95% was 57·78%.

Conclusion:

Inconsistent bladder and rectal volumes had a significant impact on target volume and dosage during an entire course of SIB-IMRT. For radiotherapy of gynaecological malignancies, data on variations in PTV should be acquired on daily basis to target radiation dose to the tumour site with accuracy.

Dosimetric Impact of Intrafraction Motion in Online-Adaptive Intensity Modulated Proton Therapy for Cervical Cancer

PURPOSE

A method was recently developed for online-adaptive intensity modulated proton therapy (IMPT) in patients with cervical cancer. The advantage of this approach, relying on the use of tight margins, is challenged by the intrafraction target motion. The purpose of this study was to evaluate the dosimetric effect of intrafraction motion on the target owing to changes in bladder filling in patients with cervical cancer treated with online-adaptive IMPT.

METHODS AND MATERIALS

In 10 patients selected to have large uterus motion induced by bladder filling, the intrafraction anatomic changes were simulated for several prefraction durations for online (automated) contouring and planning. For each scenario, the coverage of the primary target was evaluated with margins of 2.5 and 5 mm.

RESULTS

Using a 5- mm planning target volume margin, median accumulated D98% was greater than 42.75 Gy_RBE1.1 (95% of the prescribed dose) in the case of a prefraction duration of 5 and 10 minutes. For a prefraction duration of 15 minutes, this parameter deteriorated to 42.6 Gy_RBE1.1. When margins were reduced to 2.5 mm, only a 5-minute duration resulted in median target D98% above 42.75 Gy_RBE1.1. In addition, smaller bladders were found to be associated with larger dose degradations compared with larger bladders.

CONCLUSIONS

This study indicates that intrafraction anatomic changes can have a substantial dosimetric effect on target coverage in an online-adaptive IMPT scenario for patients subject to large uterus motion. A margin of 5 mm was sufficient to compensate for the intrafraction motion due to bladder filling for up to 10 minutes of prefraction time. However, compensation for the uncertainties that were disregarded in this study, by using margins or robust optimization, is also required. Furthermore, a large bladder volume restrains intrafraction target motion and is recommended for treating patients in this scenario. Assuming that online-adaptive IMPT remains beneficial as long as narrow margins are used (5 mm or below), this study demonstrates its feasibility with regard to intrafraction motion.

EANM/SNMMI practice guideline for [18F]FDG PET/CT external beam radiotherapy treatment planning in uterine cervical cancer v1.0

PURPOSE

The aim of this EANM / SNMMI Practice Guideline with ESTRO endorsement is to provide general information and specific considerations about [18F]FDG PET/CT in advanced uterine cervical cancer for external beam radiotherapy planning with emphasis on staging and target definition, mostly in FIGO stages IB3-IVA and IVB, treated with curative intention.

METHODS

Guidelines from related fields, relevant literature and leading experts have been consulted during the development of this guideline. As this field is rapidly evolving, this guideline cannot be seen as definitive, nor is it a summary of all existing protocols. Local variations should be taken into consideration when applying this guideline.

CONCLUSION

The background, common clinical indications, qualifications and responsibilities of personnel, procedure / specifications of the examination, documentation / reporting and equipment specifications, quality control and radiation safety in imaging is discussed with an emphasis on the multidisciplinary approach.

Dosimetric impact of variable bladder filling on IMRT planning for locally advanced carcinoma cervix

BACKGROUND

To evaluate the dosimetric impact of variable bladder filling on target and organ at risk (OARs) in cervical cancer patients undergoing chemoradiation. Forty consecutive patients with cervical cancer underwent radiotherapy planning as per the departmental protocol. All patients were asked to empty their bowel and bladder before simulation and catheterization was done. Normal saline was instilled into the bladder through Foleys till the patient had a maximal urge to urinate. Pelvic cast fabrication and CT simulation was done. Then, 30%, 50%, and 100% of the instilled saline was removed and rescans taken. Planning was done on full bladder (X) and the same plan applied to the contours with bladder volumes 0.7X (PLAN70), 0.5X (PLAN50), and empty (PLAN0). A dose of 50 Gy/25# was prescribed to the PTV and plans evaluated. Intensity-modulated radiotherapy plans with full bladder were implemented for each patient. Shifts in the center of mass (COM) of the cervix/uterus with variable bladder filling identified were noted. Statistical analysis was performed using SPSS software. A p value < 0.05 was considered significant.

RESULTS

Bladder volume in 70%, 50%, and empty bladder planning was 78.34% (388.35 + 117.44 ml), 64.44% (320.60 + 106.20 ml), and 13.63% (62.60 + 23.12 ml), respectively. The mean dose received by 95% PTV was 49.76 Gy + 1.30 Gy. Though the difference in target coverage was significant between PLAN100 and other plans, the mean difference was minimal. A decrease in bladder filling resulted in an increase in OAR dose. Variation in the increase in dose to OARs was not significant if bladder filling was > 78.34% and > 64.44% of a full bladder with respect to the bowel and rectal/bladder doses, respectively. Inconsistent bladder filling led to a maximal shift in COM (uterus/cervix) in the Y- and Z-axis.

CONCLUSION

Bladder filling variations have an impact on cervico-uterine motion/shape, thereby impacting the dose to the target and OARs. It is recommended to have a threshold bladder volume of at least 70-75% of optimally filled bladder during daily treatment.

TRIAL REGISTRATION

Institutional review board (IRB) registered by Drug Controller General (India) with registration number ECR/10/Ins/DC/2013. Trial Registration number - RGCIRC/IRB/44/2016, registered and approved on the 14th of May 2016.

Deformable image registration for dose mapping between external beam radiotherapy and brachytherapy images of cervical cancer

For locally advanced cervical cancer (LACC), anatomy correspondence with and without BT applicator needs to be quantified to merge the delivered doses of external beam radiation therapy (EBRT) and brachytherapy (BT). This study proposed and evaluated different deformable image registration (DIR) methods for this application. Twenty patients who underwent EBRT and BT for LACC were retrospectively analyzed. Each patient had a pre-BT CT at EBRT boost (without applicator) and a CT and MRI at BT (with applicator). The evaluated DIR methods were the diffeomorphic Demons, commercial intensity and hybrid methods, and three different biomechanical models. The biomechanical models considered different boundary conditions (BCs). The impact of the BT devices insertion on the anatomy was quantified. DIR method performances were quantified using geometric criteria between the original and deformed contours. The BT dose was deformed toward the pre-CT BT by each DIR method. The impact of boundary conditions to drive the biomechanical model was evaluated based on the deformation vector field and dose differences. The GEC-ESTRO guideline dose indices were reported. Large organ displacements, deformations, and volume variations were observed between the pre-BT and BT anatomies. Rigid registration and intensity-based DIR resulted in poor geometric accuracy with mean Dice similarity coefficient (DSC) inferior to 0.57, 0.63, 0.42, 0.32, and 0.43 for the rectum, bladder, vagina, cervix and uterus, respectively. Biomechanical models provided a mean DSC of 0.96 for all the organs. By considering the cervix-uterus as one single structure, biomechanical models provided a mean DSC of 0.88 and 0.94 for the cervix and uterus, respectively. The deformed doses were represented for each DIR method. Caution should be used when performing DIR for this application as standard techniques may have unacceptable results. The biomechanical model with the cervix-uterus as one structure provided the most realistic deformations to propagate the BT dose toward the EBRT boost anatomy.

EXclusion of non-Involved uterus from the Target Volume (EXIT-trial): an individualized treatment for locally advanced cervical cancer using modern radiotherapy and imaging techniques

Background

Definitive chemoradiotherapy is standard of care in locally advanced cervical cancer (LACC). Both toxicity and local relapse remain major concerns in this treatment. We hypothesize that a magnetic resonance imaging (MRI) based redefining of the radiotherapeutic target volume will lead to a reduction of acute and late toxicity. In our center, chemoradiotherapy followed by hysterectomy was implemented successfully in the past. This enables us to assess the safety of reducing the target volume but also to explore the biological effects of chemoradiation on the resected hysterectomy specimen.

Methods

The EXIT-trial is a phase II, single arm study aimed at LACC patients. This study evaluates whether a MRI-based exclusion of the non-tumor-bearing parts of the uterus out of the target volume results in absence of tumor in the non-high doses irradiated part of the uterus in the hysterectomy specimen. Secondary endpoints include a dosimetric comparison of dose on normal tissue when comparing study treatment plans compared to treatment of the whole uterus at high doses; acute and chronic toxicity, overall survival, local relapse- and progression-free survival. In the translational part of the study, we will evaluate the hypothesis that the baseline apparent diffusion coefficient (ADC) values of diffusion weighted MRI and its evolution 2 weeks after start of CRT, for the whole tumor as well as for intra-tumoral regions, is prognostic for residual tumor on the hysterectomy specimen.

Discussion

Although MRI is already used to guide target delineation in brachytherapy, the EXIT-trial is the first to use this information to guide target delineation in external beam radiotherapy. Early therapy resistance prediction using DW-MRI opens a window for early treatment adaptation or further dose-escalation on tumors/intratumoral regions at risk for treatment failure.

Trial registration

Belgian Registration: B670201526181 (prospectively registered, 26/11/2015); ClinicalTrials.gov Identifier: NCT03542942 (retrospectively registered, 17/5/2018).

Problems and solutions in IGRT for cervical cancer

The contribution of Image-guided Radiotherapy (IGRT) to modern radiotherapy is undeniable, being the way to bring into daily practice the dosimetric benefits of Intensity-Modulated Radiotherapy (IMRT). Organ and target motion is constant and unpredictable at the pelvis, thus posing a challenge to the safe execution of IMRT. There are potential benefits of IMRT in the radical treatment of cervical cancer patients, both in terms of dose escalation and decrease of toxicity. But it is essential to find IGRT solutions to control the aspects that can lead to geographic miss targeting or organs at risk (OAR) overdose. This review seeks to describe the problems and possible solutions in the clinical implementation of IMRT/IGRT protocols to treat intact cervical cancer patients.

Intensity-modulated radiotherapy reduces gastrointestinal toxicity in pelvic radiation therapy with moderate dose

This retrospective study was performed to evaluate and compare gastrointestinal (GI) toxicities caused by conventional radiotherapy (cRT) and intensity modulated radiotherapy (IMRT) in 136 cancer patients treated with pelvic radiotherapy (RT) with moderate radiation dose in a single institution. A matched-pair analysis of the two groups was performed; each group included 68 patients. Conventional RT was delivered using the four-field box technique and IMRT was delivered with helical tomotherapy. The median daily dose was 1.8 Gy and the median total dose was 50.4 Gy (range 25.2–56 Gy). Primary end point was GI toxicity during and after RT. Secondary end point was factors that affect toxicity. Patients treated with IMRT had lower incidence of grade ≥ 2 acute GI toxicity compared to the patients treated with cRT (p = 0.003). The difference remained significant in multivariate analysis (p = 0.01). The incidence of chronic GI toxicity was not statistically different between the two groups, but the cRT group had higher incidence of grade 3 chronic GI toxicity. Based on our results, IMRT can reduce GI toxicity compared to cRT in the treatment of pelvic radiotherapy even with moderate radiation dose and this will enhance patients’ quality of life and treatment compliance.

Predictive factors of uterine movement during definitive radiotherapy for cervical cancer

To determine the predictive factors affecting uterine movement during radiotherapy (RT), we quantified interfraction uterine movement using computed tomography (CT) and cone-beam CT (CBCT). A total of 38 patients who underwent definitive RT for cervical cancer were retrospectively analyzed. We compared pre-RT planning CT (n = 38) and intratreatment CBCT (n = 315), measuring cervical and corporal movement in each direction. Correlations between uterine movement and volume changes of the bladder and rectum on all CBCT scans were analyzed using Spearman rank correlation analysis. Relationships between the mean uterine movement and patient factors were analyzed using the Mann-Whitney test. The mean corpus movement was: superior margin (cranio-caudal direction), 7.6 ± 5.9 mm; anterior margin (anteroposterior direction), 8.3 ± 6.3 mm; left margin (lateral direction), 3.3 ± 2.9 mm; and right margin (lateral direction), 3.0 ± 2.3 mm. Generally, the mean values for cervical movement were smaller than those for the corpus. There was a significant, weak correlation between changes in bladder volume and the movement of the superior margin of the corpus (ρ = 0.364, P < 0.001). There was a significant difference in movement of the superior margin of the corpus between the subgroups with and without a history of previous pelvic surgery (P = 0.007). In conclusion, change in bladder volume and a history of previous surgery were significantly related to intrafractional corpus movement; however, our observations suggest that the accurate prediction of uterine movement remains challenging.

CTV to PTV in cervical cancer: From static margins to adaptive radiotherapy

Intensity-modulated radiotherapy (IMRT) is increasingly used in order to minimize the gastrointestinal, genitourinary, and hematological toxicity in cervical and uterine cancers. However, the benefit of this high-precision approach is detracted by the margins applied to the clinical target volume (CTV) to generate the planning tumor volume (PTV), taking into account tumor and surrounding organs movements, deformations, and volume changes. Adequate PTV margins should be large enough to prevent geographical misses, but not excessive, which might end the benefit from IMRT. The objectives of this review were: (a) to present the evidence available for the determination of CTV-PTV margin for uterine cancers; (b) to highlight the impact of these margins in the context of adaptive radiotherapy; and (c) to discuss the role of the PTV concept in intracavitary brachytherapy.

Prospective Validation of a High Dimensional Shape Model for Organ Motion in Intact Cervical Cancer

PURPOSE

Validated models are needed to justify strategies to define planning target volumes (PTVs) for intact cervical cancer used in clinical practice. Our objective was to independently validate a previously published shape model, using data collected prospectively from clinical trials.

METHODS AND MATERIALS

We analyzed 42 patients with intact cervical cancer treated with daily fractionated pelvic intensity modulated radiation therapy and concurrent chemotherapy in one of 2 prospective clinical trials. We collected online cone beam computed tomography (CBCT) scans before each fraction. Clinical target volume (CTV) structures from the planning computed tomography scan were cast onto each CBCT scan after rigid registration and manually redrawn to account for organ motion and deformation. We applied the 95% isodose cloud from the planning computed tomography scan to each CBCT scan and computed any CTV outside the 95% isodose cloud. The primary aim was to determine the proportion of CTVs that were encompassed within the 95% isodose volume. A 1-sample t test was used to test the hypothesis that the probability of complete coverage was different from 95%. We used mixed-effects logistic regression to assess effects of time and patient variability.

RESULTS

The 95% isodose line completely encompassed 92.3% of all CTVs (95% confidence interval, 88.3%-96.4%), not significantly different from the 95% probability anticipated a priori (P=.19). The overall proportion of missed CTVs was small: the grand mean of covered CTVs was 99.9%, and 95.2% of misses were located in the anterior body of the uterus. Time did not affect coverage probability (P=.71).

CONCLUSIONS

With the clinical implementation of a previously proposed PTV definition strategy based on a shape model for intact cervical cancer, the probability of CTV coverage was high and the volume of CTV missed was low. This PTV expansion strategy is acceptable for clinical trials and practice; however, we recommend daily image guidance to avoid systematic large misses in select patients.

A novel dynamic field-matching technique for treatment of patients with para-aortic node-positive cervical cancer: Clinical experience

AIM

To report outcomes for patients with para-aortic lymph node positive cervical cancer treated with a dynamic field-matching technique.

BACKGROUND

PET staging of cervical cancer has increased identification of patients with para-aortic lymph node metastasis. IMRT enables dose escalation in this area, but matching IMRT fields with traditional whole pelvis fields presents a challenge.

MATERIALS AND METHODS

From 2003 to 2012, 20 patients with cervical cancer and para-aortic lymph node metastasis were treated utilizing the dynamic field-matching technique. As opposed to single-isocenter half-beam junction techniques, this technique employs wedge-shaped dose junctions for the abutment of fields. We reviewed the records of all patients who completed treatment with the technique and abstracted treatment, toxicity, and disease-related outcome data for analysis.

RESULTS

Median prescribed dose to the whole pelvis field was 45 Gy and para-aortic IMRT field 50.4 Gy. All but 3 patients underwent HDR (13 pts) or LDR (4 pts) brachytherapy. All patients developed lower GI toxicity; 10 grade 1, 9 grade 2, and 1 grade 4 (enterovaginal fistula). Median DFS was 12.4 months with 1 and 2-year DFS 60.0% and 38.1%. One-year OS was 83.7% and 2-year OS, 64.4%. A total of 10 patients developed recurrence; none occurred at the matched junction.

CONCLUSIONS

The dynamic field-matching technique provides a means for joining conventional whole pelvis fields and para-aortic IMRT fields that substantially reduces dose deviations at the junction due to field mismatch. Treatment with the dynamic matching technique is simple, effective, and tolerated with no apparent increase in toxicity.

Short-course palliative radiotherapy for uterine cervical cancer

Purpose

The purpose of this retrospective study was to evaluate the efficacy and feasibility of short-course hypofractionated radiotherapy (RT) for the palliation of uterine cervical cancer.

Materials and Methods

Seventeen patients with cancer of the uterine cervix, who underwent palliative hypofractionated 3-dimensional conformal radiotherapy between January 2002 and June 2012, were retrospectively analyzed. RT was delivered to symptomatic lesions (both the primary mass and/or metastatic regional lymph nodes). The total dose was 20 to 25 Gy (median, 25 Gy) in 5 Gy daily fractions.

Results

The median follow-up duration was 12.2 months (range, 4 to 24 months). The median survival time was 7.8 months (range, 4 to 24 months). Vaginal bleeding was the most common presenting symptom followed by pelvic pain (9 patients). The overall response rates were 93.8% and 66.7% for vaginal bleeding control and pelvic pain, respectively. Nine patients did not have any acute side effects and 7 patients showed minor gastrointestinal toxicity. Only 1 patient had grade 3 diarrhea 1 week after completion of treatment, which was successfully treated conservatively. Late complications occurred in 4 patients; however, none of these were of grade 3 or higher severity.

Conclusion

Short-course hypofractionated RT was effective and well tolerated as palliative treatment for uterine cervical cancer.

The departmental impact of magnetic resonance imaging in the management of cervical cancer brachytherapy: a discussion paper

This discussion paper will explore the impact of using Magnetic Resonance Imaging (MRI) in the treatment of cervical cancer with brachytherapy. It is written from the perspective of current departmental practice in the UK and aims to highlight the issues associated with using MRI as a tool for image guided brachytherapy planning. To support the discussion, a literature review was undertaken focussing specifically on the use of MRI in brachytherapy treatment planning for cervical cancer. Results from planning case studies and clinical series were analysed, and the literature showed that image guided brachytherapy treatment planning is a promising development. MRI assisted planning could theoretically be implemented in centres that have access to a MRI scanner. Alternative brachytherapy technologies (e.g. Computed Tomography (CT) assisted planning), and alternative radiotherapy modalities (e.g. an external beam radiotherapy boost), were not found to be superior in effect or of implementation. Although MRI shows great promise, the evidence base for MRI in brachytherapy planning for cervical cancer is currently limited and therefore careful implementation and evaluation is required. It is suggested by the authors that new methods of working are devised to ensure consistency and quality in implementation and delivery, and that outcomes are measured and audited to evaluate efficacy.

Advances in clinical research in gynecologic radiation oncology: an RTOG symposium

There have been inexorable improvements in gynecologic radiation oncology through technologically advances, 3-dimensional imaging, and clinical research. Investment in these 3 critical areas has improved, and will continue to improve, the lives of patients with gynecologic cancer. Advanced technology delivery in gynecologic radiation oncology is challenging owing to the following: (1) setup difficulties, (2) managing considerable internal organ motion, and (3) responding to tumor volume reduction during treatment. Image guidance is a potential route to solve these problems and improve delivery to tumor and sparing organs at risk. Imaging with positron emission tomography-computed tomography and magnetic resonance imaging are contributing significantly to improved accuracy in diagnosis, treatment, and follow-up in cancer of the cervix. Functional imaging by exploiting tumor biology may improve prognosis and treatment. Clinical trials have been the greatest mechanism to improve and establish standards of care in women with vulvar, endometrial, and cervical cancer. There have been multiple technological advances and practice changing trials within the past several decades. Many important questions remain in optimizing care for women with gynecologic malignancies. The performance of clinical trials will be advanced with the use of consistent language (ie, similar staging system and criteria), eligibility criteria that fit the research question, end points that matter, adequate statistical power, complete follow-up, and prompt publication of mature results.

Risk factors related to interfractional variation in whole pelvic irradiation for locally advanced pelvic malignancies

PURPOSE

The goal of the present study was to demonstrate risk factors affecting the interfractional variation in whole pelvic irradiation.

PATIENTS AND METHODS

Daily image acquisitions of 101 patients with locally advanced pelvic malignancy were undertaken using a kilo-voltage orthogonal on-board imager. The baseline deviation (the shift between the initial treatment and each fraction; Value(Base)) and day-to-day variation (the shift between the previous treatment and each fraction; Value(DD)) were measured. The standard deviations (SD) along the x- (right-left), y- (cranial-caudal), and z- (anterior-posterior) axes (SD[x], SD[y], and SD[z], respectively), the 3D vector of the SD (SD[3D]), and the mean of 3D shift (mean[3D]) were calculated in each patient. Various clinical factors, lumbar pelvic balance and rotation, and the shift of 5 consecutive fractions from the initial treatment (Value(5Fx)) were investigated as risk factors.

RESULTS

The prone set-up showed a larger mean(Base)[3D] than in the supine position (p =0 .063). A body mass index (BMI) ≥ 30 kg/m(2) resulted in the largest mean(DD)[3D] (p = 0.078) and SD(DD)[3D] (p = 0.058). All the SD(5Fx) along the x-, y-, and z-axes had moderate linear relationships with SD(Base) and SD(DD) (p < 0.001). The SD(5Fx)[3D] also had a moderate linear relationship with the mean(Base)[3D], mean(DD)[3D], SD(Base)[3D], and SD(DD)[3D] (p < 0.001). In multivariate analysis, the SD(5Fx) had the same significant relationship with SD(Base) and SD(DD) (p < 0.001). A BMI ≥ 30 kg/m(2) was associated with the largest SD(DD)[x] (p = 0.003).

CONCLUSION

Close surveillance through high-quality and frequent image guidance is recommended for patients with extensive variations of the initial five consecutive fractions or obesity.

[Therapy of radiation enteritis--current challenges]

Radiation enteritis is one of the most feared complications after abdominal and pelvic radiation therapy. The incidence varies from 0.5 to 5%. It is not rare that the slowly progressing condition will be fatal. During a period of 13 years 24 patients were operated due to the complication of radiation enteritis. Despite different types of surgery repeated operation was required in 25% of cases and finally 4 patients died. Analyzing these cases predisposing factors and different therapeutic options of this condition are discussed. Treatment options of radiation induced enteritis are limited; however, targeted therapy significantly improves the outcome. Cooperation between oncologist, gastroenterologist and surgeon is required to establish adequate therapeutic plan.

[Surgical prevention of radiation enteritis: case report and review of literature]

Due to high morbidity and mortality rates, radiation enteritis is one of the most feared complications of abdominal and pelvic radiation therapy. Advances in radiation technology and radiation planning contributed to recent significant achievements. Surgical prevention provides further opportunities in decreasing the risk of radiation enteritis. A 75 year old male underwent transurethral resection for urothelial carcinoma of the bladder. Prior to initiation of radiation therapy, we performed Shouldice repair for bilateral inguinal hernias to prevent radiation injury to the fixed small intestines. Later our patient received 55 Gy of radiation therapy and two series of Carboplatin chemotherapy. Following radio-chemotherapy our patient did not developed radiation enteritis. In our report we discuss hernioplasty as an important method for prevention of radiation enteritis. We also review other options of surgical prevention.

Increasing treatment accuracy for cervical cancer patients using correlations between bladder-filling change and cervix-uterus displacements: proof of principle

PURPOSE

To investigate application of pre-treatment established correlations between bladder-filling changes and cervix-uterus displacements in adaptive therapy.

MATERIALS AND METHODS

Thirteen cervical cancer patients participated in this prospective study. Pre-treatment, and after delivery of 40 Gy, a full bladder CT-scan was acquired, followed by voiding the bladder and acquisition of 4 other 3D scans in a 1h period with a naturally filling bladder (variable bladder filling CT-scans, VBF-scans). For the pre-treatment VBF-scans, linear correlations between bladder volume change and displacements of the tip of the uterus (ToU) and the center of mass (CoM) of markers implanted in the fornices of the vagina relative to the full bladder planning scan were established. Prediction accuracy of these correlation models was assessed by comparison with actual displacements in CT-scans, both pre-treatment and after 40 Gy. Inter-fraction ToU and marker-CoM displacements were derived from the established correlations and twice-weekly performed in-room bladder volume measurements, using a 3D ultrasound scanner.

RESULTS

Target displacement in VBF-scans ranged from up to 65 mm in a single direction to almost 0mm, depending on the patient. For pre-treatment VBF-scans, the linear correlation models predicted the mean 3D position change for the ToU of 26.1 mm±10.8 with a residual of only 2.2 mm±1.7. For the marker-CoM, the 8.4 mm±5.3 mean positioning error was predicted with a residual of 0.9 mm±0.7. After 40Gy, the mean ToU displacement was 26.8 mm±15.8, while prediction based on the pre-treatment correlation models yielded a mean residual error of 9.0 mm±3.7. Target positioning errors in the fractioned treatments were very large, especially for the ToU (-18.5mm±11.2 for systematic errors in SI-direction).

CONCLUSIONS

Pre-treatment acquired VBF-scans may be used to substantially enhance treatment precision of cervical cancer patients. Application in adaptive therapy is promising and warrants further investigation. For highly conformal (IMRT) treatments, the use of a full bladder drinking protocol results in unacceptably large systematic set-up errors.

Automated weekly replanning for intensity-modulated radiotherapy of cervix cancer

PURPOSE

The adoption of intensity-modulated radiotherapy (IMRT) to treat cervical malignancies has been limited in part by complex organ and tumor motion during treatment. This study explores the limits of a highly adaptive, small-margin treatment scenario to accommodate this motion. In addition, the dosimetric consequences of organ and tumor motion are modeled using a combination of deformable registration and fractional dose accumulation techniques.

METHODS AND MATERIALS

Thirty-three cervix cancer patients had target volumes and organs-at-risk contoured on fused, pretreatment magnetic resonance-computed tomography images and weekly magnetic resonance scans taken during treatment. The dosimetric impact of interfraction organ and target motion was compared for two hypothetical treatment scenarios: a 3-mm margin plan with no replanning, and a 3-mm margin plan with an automated replan performed on the updated weekly patient geometry.

RESULTS

Of the 33 patients, 24 (73%) met clinically acceptable target coverage (98% of the clinical target volume receiving at least 95% of the prescription dose) using the 3-mm margin plan without replanning. The range in dose to 98% of the clinical target volume across all patients was 7.9% of the prescription dose if no replanning was performed. After weekly replanning, this range was tightened to 2.6% of the prescription dose and all patients met clinically acceptable target coverage while maintaining organ-at-risk dose sparing.

CONCLUSIONS

The dosimetric impact of anatomical motion underscores the challenges of applying IMRT to treat cervix cancer. An appropriate adaptive strategy can ensure target coverage for small-margin IMRT treatments and maintain favorable organ-at-risk dose sparing.

Dosimetric comparison study between intensity modulated radiation therapy and three-dimensional conformal proton therapy for pelvic bone marrow sparing in the treatment of cervical cancer

The objective was to compare intensity‐modulated radiation therapy (IMRT) with 3D conformal proton therapy (3DCPT) in the treatment of cervical cancer. In particular, each technique's ability to spare pelvic bone marrow (PBM) was of primary interest in this study. A total of six cervical cancer patients (3 postoperative and 3 intact) were planned and analyzed. All plans had uniform 1.0 cm CTV‐PTV margin and satisfied the 95% PTV with 100% isodose (prescription dose=45Gy) coverage. Dose‐volume histograms (DVH) were analyzed for comparison. The overall PTV and PBM volumes were 1035.9±192.2 cc and 1151.4±198.3 cc, respectively. In terms of PTV dose conformity index (DCI) and dose homogeneity index (DHI), 3DCPT was slightly superior to IMRT with 1.00±0.001,1.01±0.02, and 1.10±0.02,1.13±0.01, respectively. In addition, 3DCPT demonstrated superiority in reducing lower doses (i.e., V30 or less) to PBM, small bowel and bladder. Particularly in PBM, average V10 and V20 reductions of 10.8% and 7.4%(p=0.001 and 0.04), respectively, were observed. However, in the higher dose range, IMRT provided better sparing (>V30). For example, in small bowel and PBM, average reductions in V45 of 4.9% and 10.0%(p=0.048 and 0.008), respectively, were observed. Due to its physical characteristics such as low entrance dose, spread‐out Bragg peak and finite particle range of protons, 3DCPT illustrated superior target coverage uniformity and sparing of the lower doses in PBM and other organs. Further studies are, however, needed to fully exploit the benefits of protons for general use in cervical cancer.

PACS number: 87.55.D‐, 87.55.dk

Intrafraction motion in patients with cervical cancer: The benefit of soft tissue registration using MRI

BACKGROUND AND PURPOSE

During radiation delivery, target volumes change their position and shape due to intrafraction motion. The extent of these changes and the capability to correct for them will contribute to the benefit of an MRI-accelerator in terms of PTV margin reduction. Therefore, we investigated the primary CTV motion within a typical IMRT delivery time for cervical cancer patients for various correction techniques: no registration, rigid bony anatomy registration, and rigid soft tissue registration.

MATERIALS AND METHODS

Twenty-two patients underwent 2-3 offline MRI exams before and during their radiation treatment. Each MRI exam included four sagittal and four axial MRI scans alternately within 16min. We addressed the CTV motion by comparing subsequent midsagittal CTV delineations and investigated the correlation with intrafraction bladder filling.

RESULTS

The maximum (residual) motions within 16min for all points on the CTV contour for 90% of the MRI exams without registration, with rigid bony anatomy registration, and with rigid soft tissue registration were 10.6, 9.9, and 4.0mm. A significant but weak correlation was found between intrafraction bladder filling and CTV motion.

CONCLUSIONS

Considerable intrafraction CTV motion is observed in cervical cancer patients. Intrafraction MRI-guided soft tissue registration using an MRI-accelerator will correct for this motion.

Conformal and intensity-modulated radiotherapy for cervical cancer

Three-dimensional radiotherapy planning techniques, including conformal radiotherapy and intensity-modulated radiotherapy, have potential for improving outcomes in cervical cancer. Accurate target volume definition is essential in order to maximise normal tissue sparing while minimising the risk of a geographical miss. This reduction in toxicity provides the option of dose escalation, particularly with simultaneous integrated boost intensity-modulated radiotherapy. The evidence for the current use and potential applications of these techniques in the treatment of cervical cancer are discussed.

An assessment of interfractional uterine and cervical motion: implications for radiotherapy target volume definition in gynaecological cancer

PURPOSE

To assess interfractional movement of the uterus and cervix in patients with gynaecological cancer to aid selection of the internal margin for radiotherapy target volumes.

METHODS AND MATERIALS

Thirty-three patients with gynaecological cancer had an MRI scan performed on two consecutive days. The two sets of T2-weighted axial images were co-registered, and the uterus and cervix outlined on each scan. Points were identified on the anterior uterine body (Point U), posterior cervix (Point C) and upper vagina (Point V). The displacement of each point in the antero-posterior (AP), superior-inferior (SI) and lateral directions between the two scans was measured. The changes in point position and uterine body angle were correlated with bladder volume and rectal diameter.

RESULTS

The mean difference (+/-1 SD) in Point U position was 7 mm (+/-9.0) in the AP direction, 7.1 mm (+/-6.8) SI and 0.8 mm (+/-1.3) laterally. Mean Point C displacement was 4.1 mm (+/-4.4) SI, 2.7 mm (+/-2.8) AP, 0.3 (+/-0.8) laterally, and Point V was 2.6 mm (+/-3.0) AP and 0.3 mm (+/-1.0) laterally. There was correlation for uterine SI movement in relation to bladder filling, and for cervical and vaginal AP movement in relation to rectal filling.

CONCLUSION

Large movements of the uterus can occur, particularly in the superior-inferior and anterior-posterior directions, but cervical displacement is less marked. Rectal filling may affect cervical position, while bladder filling has more impact on uterine body position, highlighting the need for specific instructions on bladder and rectal filling for treatment. We propose an asymmetrical margin with CTV-PTV expansion of the uterus, cervix and upper vagina of 15 mm AP, 15 mm SI and 7 mm laterally and expansion of the nodal regions and parametria by 7 mm in all directions.

Online MRI guidance for healthy tissue sparing in patients with cervical cancer: an IMRT planning study

BACKGROUND AND PURPOSE

During cervical cancer treatment, target volumes change position and shape due to organ motion and tumour regression. An MRI-accelerator will provide information on these changes by online magnetic resonance imaging (MRI) guidance throughout each treatment fraction. The purpose of this intensity-modulated radiation therapy (IMRT) planning study is to assess the benefit of online MRI guidance in healthy tissue sparing.

MATERIALS AND METHODS

Weekly MRI scans of 11 cervical cancer patients were used. We created four IMRT plans per patient, based on these weekly MRI scans, to simulate an online-IMRT approach. We applied a primary and nodal planning target volume (PTV) margin of 4 mm. As reference, we created an IMRT plan based on the pre-treatment MRI scan (pre-IMRT) using a primary and nodal PTV margin of 15 and 10 mm. The weekly defined bladder, rectum, bowel, and sigmoid contours were evaluated on the online-IMRT and pre-IMRT dose distributions at six dose levels (V10(Gy), V20(Gy), V30(Gy), V40(Gy), V42.8(Gy), and V45(Gy)).

RESULTS

Online-IMRT compared to pre-IMRT significantly reduced the volume of healthy tissue irradiated to all dose levels, except V10(Gy).

CONCLUSIONS

Online MRI guidance reduces healthy tissue involvement in patients with cervical cancer.

Motion and deformation of the target volumes during IMRT for cervical cancer: what margins do we need?

BACKGROUND AND PURPOSE

For cervical cancer patients the CTV consists of multiple structures, exhibiting complex inter-fraction changes. The purpose of this study is to use weekly MR imaging to derive PTV margins that accommodate these changes.

MATERIALS AND METHODS

Twenty patients with cervical cancer underwent a T2-weighted MRI exam before and weekly during IMRT. The CTV, GTV and surrounding organs were delineated. PTV margins were derived from the boundaries of the GTV and CTV in the six main directions and correlated with changes in the volumes of organs at risk.

RESULTS

Around the GTV a margin of 12, 14, 12, 11, 4 and 8mm to the anterior, posterior, right lateral, left lateral, superior and inferior directions was needed. The CTV required margins of 24, 17, 12, 16, 11 and 8 mm. The shift of the GTV and CTV in the AP directions correlated weakly with the change in rectal volume. For the bladder the correlations were even weaker.

CONCLUSIONS

We used weekly MRI scans to derive inhomogeneous PTV margins that accommodate changes in GTV and CTV. The weak correlations with rectum and bladder volume suggest that measures to control filling status of these organs may not be very effective.

Inter- and intrafractional tumor and organ movement in patients with cervical cancer undergoing radiotherapy: a cinematic-MRI point-of-interest study

PURPOSE

Internal tumor and organ movement is important when considering intensity-modulated radiotherapy for patients with cancer of the cervix because of the tight margins and steep dose gradients. In this study, the internal movement of the tumor, cervix, and uterus were examined using serial cinematic magnetic resonance imaging scans and point-of-interest analysis.

METHODS AND MATERIALS

Twenty patients with Stage IB-IVA cervical cancer underwent pelvic magnetic resonance imaging before treatment and then weekly during external beam radiotherapy. In each 30-min session, sequential T(2)-sagittal magnetic resonance imaging scans were obtained. The points of interest (cervical os, uterine canal, and uterine fundus) were traced on each image frame, allowing the craniocaudal and anteroposterior displacements to be measured. The mean displacements and trends were analyzed using mixed linear models. Prediction intervals were calculated to determine the internal target margins.

RESULTS

Large interscan motion was found for all three points of interest that was only partially explained by the variations in bladder and rectal filling. The intrascan motion was much smaller. Both inter- and intrascan motion was greatest at the fundus of the uterus, less along the canal, and least at the cervical os. The isotropic internal target margins required to encompass 90% of the interscan motion were 4 cm at the fundus and 1.5 cm at the os. In contrast, smaller margins of 1 cm and 0.45 cm, respectively, were adequate to encompass the intrascan motion alone.

CONCLUSION

Daily soft-tissue imaging with correction for interfractional motion or adaptive replanning will be important if the benefits of intensity-modulated radiotherapy are to be maximized in women with cervical cancer.

Interfractional variation of uterine position during radical RT: weekly CT evaluation

PURPOSE

This study was performed to quantitate the positional change of the uterus during the period of radiotherapy (RT).

METHODS

For 13 patients who received RT with the use of small bowel displacement system (SBDS) for uterine cervix cancer, CT scans were taken before the beginning of RT. Three more weekly CT scans were subsequently performed during the RT period. The position of the uterus on each set of CT images was defined and compared to that on the initial CT images. The difference was quantified by measuring the parameters as follows: the change of uterus border in superior (D(S)), right lateral (D(R)), left lateral (D(L)), anterior (D(A)) and posterior (D(P)) direction measured on images taken before and during treatments. The change of uterus volume was also measured, and the correlation between the uterus volume reduction and uterus mobility was tested.

RESULTS

The most prominent interfractional positional changes were in the cranio-caudal direction. Among the three sets of comparisons, the largest mean values for D(S), D(R), D(L), D(A) and D(P) were -0.77+/-1.87, -0.29+/-1.02, -0.3+/-1.25, -0.20+/-1.13 cm, and -0.55+/-1.21 cm, respectively. The average target volume reductions were 6.4% (p=0.1335), 11.7% (p=0.0138) and 27.2% (p=0.0192) in the 1st, 2nd and 3rd week of treatment, respectively. Significant correlation between D(S) and uterus volume reduction (p=0.002) was found.

CONCLUSIONS

The average interfractional positional changes of the uterus with the use of SBDS were relatively small, while the inter-patient deviations were large. The significant target volume reductions and inter-patient deviations of uterus mobility need to be accounted for when conformal radiation therapy for cervical cancer is performed.

Interfractional dose variation during intensity-modulated radiation therapy for cervical cancer assessed by weekly CT evaluation

PURPOSE

To investigate the interfractional dose variation of a small-bowel displacement system (SBDS)-assisted intensity-modulated radiation therapy (IMRT) for the treatment of cervical cancer.

METHODS

Four computed tomography (CT) scans were carried out in 10 patients who received radiotherapy for uterine cervical cancer. The initial CT was taken by use of the SBDS, before the beginning of radiotherapy, and 3 additional CT scans with the SBDS were done in subsequent weeks. IMRT was planned by use of the initial CT, and the subsequent images were fused with the initial CT set. Dose-volume histogram (DVH) changes of the targets (planning target volume [PTV] = clinical target volume [CTV] + 1.5 cm) and of the critical organs were evaluated after obtaining the volumes of each organ on 4 CT sets.

RESULTS

No significant differences were found in PTV volumes. Changes on the DVH of the CTVs were not significant, whereas DVH changes of the PTVs at 40% to 100% of the prescription dose level were significant (V(90%); 2nd week: p = 0.0091, 3rd week: p = 0.0029, 4th week: p = 0.0050). The changes in the small-bowel volume included in the treatment field were significant. These were 119.5 cm3 (range, 26.9-251.0 cm3), 126 cm3 (range, 38.3-336 cm3), 161.9 cm3 (range, 37.7-294.6 cm3), and 149.1 cm3 (range, 38.6-277.8 cm3) at the 1st, 2nd, 3rd, and 4th weeks, respectively, and were significantly correlated with the DVH change in the small bowel, which were significant at the 3rd (V80%; p = 0.0230) and 4th (V80%; p = 0.0263) weeks. The bladder-volume change correlated to the large volume change (>20%) of the small-bowel volume.

CONCLUSIONS

Significant DVH differences for the small bowel can result because of interfractional position variations, whereas the DVH differences of the CTV were not significant. Strict bladder-filling control and an accurate margin for the PTV, as well as image-guided position verification, are important to achieve the goal of IMRT.

Recommendations from gynaecological (GYN) GEC ESTRO working group (II): concepts and terms in 3D image-based treatment planning in cervix cancer brachytherapy-3D dose volume parameters and aspects of 3D image-based anatomy, radiation physics, radiobiology

The second part of the GYN GEC ESTRO working group recommendations is focused on 3D dose-volume parameters for brachytherapy of cervical carcinoma. Methods and parameters have been developed and validated from dosimetric, imaging and clinical experience from different institutions (University of Vienna, IGR Paris, University of Leuven). Cumulative dose volume histograms (DVH) are recommended for evaluation of the complex dose heterogeneity. DVH parameters for GTV, HR CTV and IR CTV are the minimum dose delivered to 90 and 100% of the respective volume: D90, D100. The volume, which is enclosed by 150 or 200% of the prescribed dose (V150, V200), is recommended for overall assessment of high dose volumes. V100 is recommended for quality assessment only within a given treatment schedule. For Organs at Risk (OAR) the minimum dose in the most irradiated tissue volume is recommended for reporting: 0.1, 1, and 2 cm3; optional 5 and 10 cm3. Underlying assumptions are: full dose of external beam therapy in the volume of interest, identical location during fractionated brachytherapy, contiguous volumes and contouring of organ walls for >2 cm3. Dose values are reported as absorbed dose and also taking into account different dose rates. The linear-quadratic radiobiological model-equivalent dose (EQD2)-is applied for brachytherapy and is also used for calculating dose from external beam therapy. This formalism allows systematic assessment within one patient, one centre and comparison between different centres with analysis of dose volume relations for GTV, CTV, and OAR. Recommendations for the transition period from traditional to 3D image-based cervix cancer brachytherapy are formulated. Supplementary data (available in the electronic version of this paper) deals with aspects of 3D imaging, radiation physics, radiation biology, dose at reference points and dimensions and volumes for the GTV and CTV (adding to [Haie-Meder C, Pötter R, Van Limbergen E et al. Recommendations from Gynaecological (GYN) GEC ESTRO Working Group (I): concepts and terms in 3D image-based 3D treatment planning in cervix cancer brachytherapy with emphasis on MRI assessment of GTV and CTV. Radiother Oncol 2005;74:235-245]). It is expected that the therapeutic ratio including target coverage and sparing of organs at risk can be significantly improved, if radiation dose is prescribed to a 3D image-based CTV taking into account dose volume constraints for OAR. However, prospective use of these recommendations in the clinical context is warranted, to further explore and develop the potential of 3D image-based cervix cancer brachytherapy.