Position shifts and volume changes of pelvic and para-aortic nodes during IMRT for patients with cervical cancer

Pelvic target volume inter-fractional motion during radiotherapy for cervical cancer with daily iterative cone beam computed tomography

BACKGROUND

Tumor regression and organ movements indicate that a large margin is used to ensure target volume coverage during radiotherapy. This study aimed to quantify inter-fractional movements of the uterus and cervix in patients with cervical cancer undergoing radiotherapy and to evaluate the clinical target volume (CTV) coverage.

METHODS

This study analyzed 303 iterative cone beam computed tomography (iCBCT) scans from 15 cervical cancer patients undergoing external beam radiotherapy. CTVs of the uterus (CTV-U) and cervix (CTV-C) contours were delineated based on each iCBCT image. CTV-U encompassed the uterus, while CTV-C included the cervix, vagina, and adjacent parametrial regions. Compared with the planning CTV, the movement of CTV-U and CTV-C in the anterior-posterior, superior-inferior, and lateral directions between iCBCT scans was measured. Uniform expansions were applied to the planning CTV to assess target coverage.

RESULTS

The motion (mean ± standard deviation) in the CTV-U position was 8.3 ± 4.1 mm in the left, 9.8 ± 4.4 mm in the right, 12.6 ± 4.0 mm in the anterior, 8.8 ± 5.1 mm in the posterior, 5.7 ± 5.4 mm in the superior, and 3.0 ± 3.2 mm in the inferior direction. The mean CTV-C displacement was 7.3 ± 3.2 mm in the left, 8.6 ± 3.8 mm in the right, 9.0 ± 6.1 mm in the anterior, 8.4 ± 3.6 mm in the posterior, 5.0 ± 5.0 mm in the superior, and 3.0 ± 2.5 mm in the inferior direction. Compared with the other tumor (T) stages, CTV-U and CTV-C motion in stage T1 was larger. A uniform CTV planning treatment volume margin of 15 mm failed to encompass the CTV-U and CTV-C in 11.1% and 2.2% of all fractions, respectively. The mean volume change of CTV-U and CTV-C were 150% and 51%, respectively, compared with the planning CTV.

CONCLUSIONS

Movements of the uterine corpus are larger than those of the cervix. The likelihood of missing the CTV is significantly increased due to inter-fractional motion when utilizing traditional planning margins. Early T stage may require larger margins. Personal radiotherapy margining is needed to improve treatment accuracy.

Feasibility of using a dual isocentre technique for treating cervical cancer on the 1.5 T MR-Linac

Objective.Patients treated for cervical cancer exhibit large inter and intra-fraction anatomical changes. The Unity MR-Linac (MRL) can image these patients with MR prior to and during treatment which enables daily plan adaptation. However, the MRL has a limited treatment field in the sup/inf direction of 22 cm which can restrict the treatment of patients who require longer treatment fields. Here we explore potential adaptive workflows in combination with a dual isocentre approach, to widen the range of cervix patients that can benefit from this treatment.Approach.Ten cervical cancer patients were retrospectively planned with a dual isocentre technique to deliver 45 Gy in 25 fractions. 5 node-negative and 5 node-positive patients were planned using the EMBRACE II protocol. A 2 cm overlap region between the two isocentres was positioned entirely in the nodal region. A treatment workflow was simulated to account for inter-fraction anatomical change. Isocentre shifts of 3 and 6 mm were applied to investigate the effect of intra-fraction motion.Main results.Dual isocentre adapted plans ensured significantly better coverage than non-adapted (recalculated) plans with a larger benefit seen for the node-negative cases. The difference to the reference plan for the V4275 cGy to the ITV was -0.8 cGy and -8.2 cGy for the adapted and recalculated plans respectively. Movements superiorly did not affect the coverage of the ITV by more than 1%, but shifting it inferiorly caused the ITV coverage on the plan to reduce by ∼2.4% per mm.Significance.A dual isocentre technique for cervical cancer treatments and adaptive workflows have been demonstrated to recover the required plan quality for inter-fraction changes. This illustrates the feasibility of a dual isocentre technique for the MRL.

Prognostic factors of dose-response relationship for nodal control in metastatic lymph nodes of cervical cancer patients undergoing definitive radiotherapy with concurrent chemotherapy

Objective

Regional control is occasionally unsatisfactory in cervical cancer, with the optimal radiation dose for nodal metastases in definitive radiotherapy (RT) with concurrent chemotherapy (CRT) remaining controversial. We investigated dose-response relationship for nodal local control in cervical cancer.

Methods

We identified 115 patients with 417 metastatic nodes who received definitive CRT for cervical cancer with nodal metastases. External beam radiation therapy and brachytherapy plans were summated to determine total dose received by each node. Prognostic factors of nodal control and dose-response relationship were investigated using Cox-regression and restricted cubic spline function.

Results

The 2-year progression-free survival rate was 69.4%. Among 43 patients with failures, 17 patients (37.5%) had regional failure included in first failure sites of which all except one were in-field only regional failures. Total 30 nodes showed recurrence at initial metastatic site after treatment. Neutrophil-to-lymphocyte ratio (NLR) ≥3.1, total radiation dose (minimum dose received by 98% of the target volume in equivalent dose in 2 Gy per fractions), and initial nodal volume ≥5.29 mL were poor prognostic factors (all p<0.050) of nodal local control. Restricted cubic spline functions revealed strongest dose-response relationship in high NLR (NLR ≥3.1) and initial nodal volume ≥5.29 mL subgroup.

Conclusion

Initial nodal volume, radiation dose_, and NLR were significant factors of nodal local control in cervical cancer; a stronger dose-response relationship was seen in bulky nodes with high NLR. Clinicians may consider these factors when determining the RT dose and the need for boost to nodal metastases in cervical cancer.

One-third of cervical cancer with nodal metastases had regional failure as first failure, mostly in-field failures. Neutrophil-to-lymphocyte ratio (NLR) ≥3.1, radiation dose, and initial nodal volume ≥5.29 mL were significant factors of nodal control. The strongest radiation dose-response was found in bulky nodes with a high NLR.

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.

Mitigation on bowel loops daily variations by 1.5-T MR-guided daily-adaptive SBRT for abdomino-pelvic lymph-nodal oligometastases

PURPOSE

We report preliminary dosimetric data concerning the use of 1.5-T MR-guided daily-adaptive radiotherapy for abdomino-pelvic lymph-nodal oligometastases. We aimed to assess the impact of this technology on mitigating daily variations for both target coverage and organs-at-risk (OARs) sparing.

METHODS

A total of 150 sessions for 30 oligometastases in 23 patients were analyzed. All patients were treated with MR-guided stereotactic body radiotherapy (SBRT) for a total dose of 35 Gy in five fractions. For each fraction, a quantitative analysis was performed for PTV volume, V35Gy and D_mean. Similarly, for OARs, we assessed daily variations of volume, D_mean, D_max. Any potential statistically significant change between baseline planning and daily-adaptive sessions was assessed using the Wilcoxon signed-rank test, assuming a p value < 0.05 as significant.

RESULTS

Average baseline PTV, bowel, bladder, and single intestinal loop volumes were respectively 8.9 cc (range 0.7-41.2 cc), 1176 cc (119-3654 cc), 95 cc (39.7-202.9 cc), 18.3 cc (9.1-37.7 cc). No significant volume variations were detected for PTV (p = 0.21) bowel (p = 0.36), bladder (p = 0.47), except for single intestinal loops, which resulted smaller (p = 0.026). Average baseline V35Gy and D_mean for PTV were respectively 85.6% (72-98.8%) and 35.6 Gy (34.6-36.1 Gy). We recorded a slightly positive trend in favor of daily-adaptive strategy vs baseline planning for improved target coverage, although not reaching statistical significance (p = 0.11 and p = 0.18 for PTV-V35Gy and PTV-D_mean). Concerning OARs, a significant difference was observed in favor of daily-adapted treatments in terms of single intestinal loop D_max [23.05 Gy (13.2-26.9 Gy) at baseline vs 20.5 Gy (12.1-24 Gy); p value = 0.0377] and D_mean [14.4 Gy (6.5-18 Gy) at baseline vs 13.0 Gy (6.7-17.6 Gy); p value = 0.0003]. Specifically for bladder, the average D_max was 18.6 Gy (0.4-34.3 Gy) at baseline vs 18.3 Gy (0.7-34.3 Gy) for a p value = 0.28; the average D_mean was 7.0 Gy (0.2-16.6 Gy) at baseline vs 6.98 Gy (0.2-16.4 Gy) for a p value = 0.66. Concerning the bowel, no differences in terms of D_mean [4.78 Gy (1.3-10.9 Gy) vs 5.6 Gy (1.4-10.5 Gy); p value = 0.23] were observed between after daily-adapted sessions. A statistically significant difference was observed for bowel D_max [26.4 Gy (7.7-34 Gy) vs 25.8 Gy (7.8-33.1 Gy); p value = 0.0086].

CONCLUSIONS

Daily-adaptive MR-guided SBRT reported a significantly improved single intestinal loop sparing for lymph-nodal oligometastases. Also, bowel D_max was significantly reduced with daily-adaptive strategy. A minor advantage was also reported in terms of PTV coverage, although not statistically significant.

Dosimetric feasibility of hypofractionation for SBRT treatment of lymph node oligometastases on the 1.5T MR-linac

PURPOSE

At our department, MR-guided stereotactic body radiation therapy (SBRT) using the 1.5T MR-linac system (Unity, Elekta AB, Stockholm, Sweden) has been initiated for patients with lymph node oligometastases. Superior soft tissue contrast and the possibility for online plan adaptation on the Unity may allow for hypofractionated treatment. The purpose of this study was to investigate the dosimetric feasibility and compare the plan quality of different hypofractionated schemes.

METHODS AND MATERIALS

Data was used from 12 patients with single lymph node oligometastases (10 pelvic, 2 para-aortic), which were all treated on the Unity with a prescribed dose of 5x7 Gy to 95% of the PTV. Hypofractionation was investigated for 3x10 Gy and 1x20 Gy schemes (all 60 Gy BED α/β = 10). The pre-treatment plans were evaluated based on dose criteria and plan quality. If all criteria were met, the number of online adapted plans which also met all dose criteria was investigated. For pre-treatment plans meeting the criteria for all three fractionation schemes, the plan quality after online adaptation was compared using the four parameters described in the NRG-BR001 phase 1 trial.

RESULTS

Pre-treatment plans met all clinical criteria for the three different fractionation schemes in 10, 9 and 6 cases. 50/50, 45/45 17/30 of the corresponding online adapted plans met all criteria, respectively. Violations were primarily caused by surrounding organs at risk overlapping or adjacent to the PTV. The 1x20 Gy treatment plans were, in general, of lesser quality than the 5x7 Gy and 3x10 Gy plans.

CONCLUSION

Hypofractionated radiotherapy for lymph node oligometastases on the 1.5T MR-linac is feasible based on dose criteria and plan quality metrics. The location of the target relative to critical structures should be considered in choosing the most suitable fractionation scheme. Especially for single fraction treatment, meeting all dose criteria in the pre-treatment situation does not guarantee that this also applies during online treatment.

Target coverage and dose criteria based evaluation of the first clinical 1.5T MR-linac SBRT treatments of lymph node oligometastases compared with conventional CBCT-linac treatment

BACKGROUND AND PURPOSE

Patients were treated at our institute for single and multiple lymph node oligometastases on the 1.5T MR-linac since August 2018. The superior soft-tissue contrast and additional software features of the MR-linac compared to CBCT-linacs allow for online adaptive treatment planning. The purpose of this study was to perform a target coverage and dose criteria based evaluation of the clinically delivered online adaptive radiotherapy treatment compared with conventional CBCT-linac treatment.

MATERIALS AND METHODS

Patient data was used from 14 patients with single lymph node oligometastases and 6 patients with multiple (2-3) metastases. All patients were treated on the 1.5T MR-linac with a prescribed dose of 5 × 7 Gy to 95% of the PTV and a CBCT-linac plan was created for each patient. The difference in target coverage between these plans was compared and plans were evaluated based on dose criteria for each fraction after calculating the CBCT-plan on the daily anatomy. The GTV coverage was evaluated based on the online planning and the post-delivery MRI.

RESULTS

For both single and multiple lymph node oligometastases the GTV V_35Gy had a median value of 100% for both the MR-linac plans and CBCT-plans pre- and post-delivery and did not significantly differ. The percentage of plans that met all dose constraints was improved from 19% to 84% and 20% to 67% for single and multiple lymph node cases, respectively.

CONCLUSION

Target coverage and dose criteria based evaluation of the first clinical 1.5T MR-linac SBRT treatments of lymph node oligometastases compared with conventional CBCT-linac treatment shows a smaller amount of unplanned violations of high dose criteria. The GTV coverage was comparable. Benefit is primarily gained in patients treated for multiple lymph node oligometastases: geometrical deformations are accounted for, dose can be delivered in one plan and margins can be reduced.

Individual lymph nodes: "See it and Zap it"

BACKGROUND AND PURPOSE

With magnetic resonance imaging (MRI)-guided radiotherapy systems such as the 1.5T MR-linac the daily anatomy can be visualized before, during and after radiation delivery. With these treatment systems, seeing metastatic nodes with MRI and zapping them with stereotactic body radiotherapy (SBRT) comes into reach. The purpose of this study is to investigate different online treatment planning strategies and to determine the planning target volume (PTV) margin needed for adequate target coverage when treating lymph node oligometastases with SBRT on the 1.5T MR-linac.

MATERIALS AND METHODS

Ten patients were treated for single pelvic or para-aortic lymph node metastases on the 1.5T MR-linac with a prescribed dose of 5x7Gy with a 3 mm isotropic GTV- PTV margin. Based on the daily MRI and actual contours, a completely new treatment plan was generated for each session (adapt to shape, ATS). These were compared with plans optimized on pre-treatment CT contours after correcting for the online target position (adapt to position, ATP). At the end of each treatment session, a post-radiation delivery MRI was acquired on which the GTV was delineated to evaluate the GTV coverage and PTV margins.

RESULTS

The median PTV V35Gy was 99.9% [90.7-100%] for the clinically delivered ATS plans compared to 93.6% [76.3-99.7%] when using ATP. The median GTV V35Gy during radiotherapy delivery was 100% [98-100%] on the online planning and post-delivery MRIs for ATS and 100% [93.9-100%] for ATP, respectively. The applied 3 mm isotropic PTV margin is considered adequate.

CONCLUSION

For pelvic and para-aortic metastatic lymph nodes, online MRI-guided adaptive treatment planning results in adequate PTV and GTV coverage when taking the actual patient anatomy into account (ATS). Generally, GTV coverage remained adequate throughout the treatment session for both adaptive planning strategies. "Seeing and zapping" metastatic lymph nodes comes within reach for MRI-guided SBRT.

Prospective Study to Quantify Expansion Volumes Around the Involved Pelvic Lymph Nodes to Plan Simultaneous Integrated Boost in Patients With Cervical Cancer Undergoing Pelvic Intensity Modulated Radiation Therapy

PURPOSE

This study aimed to calculate the expansion margins around enlarged pelvic lymph nodes to encompass internal motion and setup errors during intensity modulated radiation therapy with simultaneous integrated boost for cervical cancer.

METHODS AND MATERIALS

Four-dimensional computed tomography scans were obtained for 19 patients with cervical cancer, and 32 fluorodeoxyglucose-avid pelvic lymph nodes were delineated in different respiratory phases to calculate respiratory displacement. Setup variations during daily treatments were estimated from on-board imaging. Descriptive statistics were used to quantify the expansion margins using Mc Kenzie and Van Herk formulas separately. An analysis of variance was used to analyze the volumetric impact of the margins.

RESULTS

Based on the McKenzie formula, an internal margin (internal target volume) of 3 mm and setup margin (planning target volume) of 5 mm was required to adequately encompass respiratory and setup uncertainties, respectively. Although the use of the Van Herk formula necessitated a single 6 mm expansion margin for all uncertainties, which resulted in a significant reduction in boost volume, inherent limitations in our methodology might pose a higher risk of target miss with such smaller margins.

CONCLUSIONS

An isotropic expansion margin of 3 mm for the internal target volume and 5 mm for the planning target volume is necessary for enlarged pelvic lymph nodes while planning intensity modulated radiation therapy with simultaneous integrated boost for cervical cancer.

Relations between dose cumulated in organs at risk and treatment based on different image-guidance strategies of cervical cancer

PURPOSE

In this study, relations between dose cumulated in organs at risk and treatment based on different image guidance strategies (IG) of cervical cancer were analyzed.

MATERIAL/METHODS

Thirty patients with cervical cancer were subjected to analysis. The first phase of the study involved analysis of shifts resulting from the registration process and calculations of margins based on shifts data. The margin was calculated for two imaging scenarios - based on the analysis of bones and soft tissues. The margins thus obtained were used in the second phase of the study where the VMAT and IMRT treatment plans were prepared and, in consequence, analyzed in the light of the dose distribution.

RESULTS

Using different IG implicates different margins for specified parts of the CTV. IG based on bones allows to establish margins for lymph nodes (CTV2) that are smaller than margins for the vagina/paravaginal tissues (CTV1). The opposite applies to the IG based on soft tissues, for which margins for CTV1 are smaller than for CTV2. While decreasing the margins for CTV1 reduces the doses in the bladder and rectum, doses cumulated in the bone marrow are independent of the size of the margin resulting from the type of IG used. Nevertheless, the average doses and the values of normal tissue complication probability in the bone marrow were smaller for VMAT than for IMRT.

CONCLUSION

The VMAT plan and image guidance based on soft tissue registration for the vagina/paravaginal tissues are recommended for radiotherapy of cervical cancer patients.

Evaluation of plan adaptation strategies for stereotactic radiotherapy of lymph node oligometastases using online magnetic resonance image guidance

BACKGROUND AND PURPOSE

Recent studies have shown that the use of magnetic resonance (MR) guided online plan adaptation yields beneficial dosimetric values and reduces unplanned violations of the dose constraints for stereotactic body radiation therapy (SBRT) of lymph node oligometastases. The purpose of this R-IDEAL stage 0 study was to determine the optimal plan adaptation approach for MR-guided SBRT treatment of lymph node oligometastases.

MATERIALS AND METHODS

Using pre-treatment computed tomography (CT) and repeated MR data from five patients with in total 17 pathological lymph nodes, six different methods of plan adaptation were performed on the daily MRI and contours. To determine the optimal plan adaptation approach for treatment of lymph node oligometastases, the adapted plans were evaluated using clinical dose criteria and the time required for performing the plan adaptation.

RESULTS

The average time needed for the different plan adaptation methods ranged between 11 and 119 s. More advanced adaptation methods resulted in more plans that met the clinical dose criteria [range, 0-16 out of 17 plans]. The results show a large difference between target coverage achieved by the different plan adaptation methods.

CONCLUSION

Results suggested that multiple plan adaptation methods, based on plan adaptation on the daily anatomy, were feasible for MR-guided SBRT treatment of lymph node oligometastases. The most advanced method, in which a full online replanning was performed by segment shape and weight optimization after fluence optimization, yielded the most favourable dosimetric values and could be performed within a time-frame acceptable (<5 min) for MR-guided treatment.

Simulated dosimetric impact of online replanning for stereotactic body radiation therapy of lymph node oligometastases on the 1.5T MR-linac

PURPOSE

Online 1.5T MR imaging on the MR-linac gives better target visualization compared to CBCT and facilitates online adaptive treatment strategies including daily replanning. In this simulation study, the dosimetric impact of online replanning was investigated for SBRT of lymph node oligometastases as a method for correcting for inter-fraction anatomical changes.

METHODS

Pre-treatment plans were created for 17 pelvic and para-aortic lymph nodes, with 3 and 8 mm PTV margins reflecting our clinical practice for lymph nodes with good and poor visibility on CBCT. The dose-volume parameters of the pre-treatment plans were evaluated on daily anatomy as visible on the repeated MRIs and compared to online replanning.

RESULTS

With online MRI-based replanning significant dosimetric improvements are obtained for the rectum, bladder, bowel and sigmoid without compromising the target dose. The amount of unintended violations of the dose constraints for target and surrounding organs could be reduced by 75% for 8 mm and 66% for 3 mm PTV margins.

CONCLUSION

The use of online replanning based on the actual anatomy as seen on repeated MRI compared to online position correction for lymph node oligometastases SBRT gives beneficial dosimetric outcomes and reduces the amount of unplanned violations of dose constraints.

The Potential Value of MRI in External-Beam Radiotherapy for Cervical Cancer

The reference standard treatment for cervical cancer is concurrent chemoradiotherapy followed by magnetic resonance imaging (MRI)-guided brachytherapy. Improvements in brachytherapy have increased local control rates, but late toxicity remains high with rates of 11% grade ≥3. The primary clinical target volume (CTV) for external-beam radiotherapy includes the cervix and uterus, which can show significant inter-fraction motion. This means that generous margins are required to cover the primary CTV, increasing the radiation dose to organs at risk and, therefore, toxicity. A number of image-guided radiotherapy techniques (IGRT) have been developed, but motion can be random and difficult to predict prior to treatment. In light of the development of integrated MRI linear accelerators, this review discusses the potential value of MRI in external-beam radiotherapy. Current solutions for managing pelvic organ motion are reviewed, including the potential for online adaptive radiotherapy. The impacts of the use of MRI in tumour delineation and in the delivery of stereotactic ablative body radiotherapy (SABR) are highlighted. The potential role and challenges of using multi parametric MRI to guide radiotherapy are also discussed.

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.

Clinical implementation of coverage probability planning for nodal boosting in locally advanced cervical cancer

PURPOSE

To implement coverage probability (CovP) for dose planning of simultaneous integrated boost (SIB) of pathologic lymph nodes in locally advanced cervical cancer (LACC).

MATERIAL AND METHODS

CovP constraints for SIB of the pathological nodal target (PTV-N) with a central dose peak and a relaxed coverage at the perimeter were generated for use with the treatment planning system Eclipse: PTV-N D98 >90%, CTV-N D98 >100% and CTV-N D50 >101.5% of prescribed dose. Dose of EBRT was 45Gy/25 fx with a SIB of 55-57.5Gy depending on expected dose from brachytherapy (BT). Twenty-five previously treated patients with 47 boosted nodes were analysed. Nodes were contoured on cone beam CT (CBCT) and the accumulated dose in GTV-N_CBCT and volume of body, pelvic bones and bowel receiving >50Gy (V50) were determined.

RESULTS

Nearly all nodes (89%) were visible on CBCT and showed considerable concentric regression during EBRT. Total EBRT and BT D98 was >57 Gy_EQD2 in 98% of the visible nodes. Compared to treatment plans aiming for full PTV-N coverage, CovP significantly reduced V50 of body, bones and bowel (p<0.001) CONCLUSION: CovP is clinically feasible for SIB of pathological nodes and significantly decreases collateral SIB dose to nearby OAR.

Quantifying target-specific motion in anal cancer patients treated with intensity modulated radiotherapy (IMRT)

Background and purpose

Intensity modulated radiotherapy requires all target areas to be treated by a single radiotherapy plan. In anal cancer, the pelvic nodes, inguinal nodes and primary tumour represent three different targets. We aim to calculate target-specific motion in anal cancer radiotherapy, when delivered using a single pelvic online auto-match.

Materials and methods

Twenty consecutive patients treated using IMRT at a single institution were studied. CBCTs were retrospectively re-matched around the inguinal nodes and primary tumour. Match values were recorded relative to origin, defined as pelvic CBCT auto-match. Systematic and random errors were quantified to determine target-specific motion and suggested margins calculated using van Herk formulae.

Results

The suggested margins to cover the independent motion of the inguinal and anal targets for LR, CC and AP set up around the inguinal nodes were 1.5 mm, 2.7 mm and 2.8 mm; and the primary tumour were, 4.6 mm, 8.9 mm and 5.2 mm respectively.

Conclusions

Target-specific set up will likely result in reduced treatment volumes and as such reduced toxicity. This is the first time a relationship has been described between pelvic bones, inguinal nodes and primary tumour. The PLATO study will prospectively assess the toxicity and outcomes of this target-specific margins strategy.

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.

[Clinical to planning target volume margins in prostate cancer radiotherapy]

The knowledge of inter- and intrafraction motion and deformations of the intrapelvic target volumes (prostate, seminal vesicles, prostatectomy bed and lymph nodes) as well as the main organs at risk (bladder and rectum) allow to define rational clinical to planning target volume margins, depending on the different radiotherapy techniques and their uncertainties. In case of image-guided radiotherapy, prostate margins and seminal vesicles margins can be between 5 and 10mm. The margins around the prostatectomy bed vary from 10 to 15mm and those around the lymph node clinical target volume between 7 and 10mm. Stereotactic body radiotherapy allows lower margins, which are 3 to 5mm around the prostate. Image-guided and stereotactic body radiotherapy with adequate margins allow finally moderate or extreme hypofractionation.

Whole pelvic intensity-modulated radiotherapy for gynecological malignancies: A review of the literature

Radiation therapy has long played a major role in the treatment of gynecological malignancies. There is increasing interest in the utility of intensity-modulated radiotherapy (IMRT) and its application to treat gynecological malignancies. Herein, we review the state-of-the-art use of IMRT for gynecological malignancies and report how it is being used alone as well as in combination with chemotherapy in both the adjuvant and definitive settings. Based on dosimetric and clinical evidence, IMRT can reduce gastrointestinal, genitourinary, and hematological toxicities compared with 3D-conformal radiotherapy for gynecologic malignancies. We discuss how these attributes of IMRT may lead to improvements in disease outcomes by allowing for dose escalation of radiation therapy, intensification of chemotherapy, and limiting toxicity-related treatment breaks. Currently accruing trials investigating pelvic IMRT for cervical and endometrial cancers are discussed.