Interfraction Motion of the Vaginal Apex During Postoperative Intensity Modulated Radiation Therapy: Are We Missing the Target?

Fiducial markers in adjuvant setting for a patient affected by endometrial cancer: a case report

Introduction

Intermediate-high and high-risk endometrial cancer often require adjuvant treatments such as radiotherapy (RT) or brachitherapy (BT) to reduce the risk of loco-regional relapse. Inter- and intra-fraction variability of internal pelvic anatomy are possibly the largest source of error affecting pelvic RT. The implantation of Fiducial Makers (FMs) in the vaginal cuff of patients receiving RT or BT could help patient daily setup, image guidance and intra-fraction detection of the radiation targets.

Clinical case

We have evaluated the case of an 80-year-old woman treated with surgery for endometrioid adenocarcinoma G2 (stage pT1b Nx LVSI+) who underwent adjuvant pelvic IMRT after the implantation of vaginal cuff FMs.

CT-simulation Treatment Planning and IGRT strategy

Patient underwent planning CT scan 10 days after FMs implantation. RT consisted of 45Gy in 25 daily fractions to pelvic lymph nodes and surgical bed with simultaneous integrated boost up to 52.5Gy to the vaginal cuff and the upper two-thirds of the vagina. Cone beam Computed Tomography (CBCT) was acquired prior to every RT fraction for IGRT. Bladder and rectum were re-contoured on every CBCTs. Bladder and rectal volumes and median shifts were reported on a prospective database to quantify the impact of the pelvic organ variations.

Results

The patient reported no discomfort during the FMs implantation, and no complications were seen. No evidence of FMs migration was reported. Bladder and rectal volumes planned contours were 245 and 55.3cc. Median bladder volumes for approved and "not acceptable" CBCTs were 222cc (range: 130-398) and 131cc (range: 65-326), respectively. Median rectal volumes for approved and "not acceptable" CBCTs were 75cc (range: 58-117) and 90cc (range: 54-189), respectively. The median values of the anterior-posterior, superior-inferior, lateral direction shifts were 3.4, 1.8 and 2.11 mm, respectively.

Conclusion

In our clinical case, the implantation of FMs in the vaginal cuff of a patient who underwent pelvic adjuvant RT was well tolerated and reported no complications. The use of IGRT procedures based on FMs surrogating the vaginal vault may reduce inter-observer variability and pave the way for adaptive strategies or stereotactic treatments as external beam pelvic boost in gynecological field.

Dosimetric impact of rotational setup errors in volumetric modulated arc therapy for postoperative cervical cancer

We aimed to evaluate the impact of rotational setup errors on the doses received during postoperative volumetric-modulated arc therapy (VMAT) for cervical cancer. Overall, 121 cone-beam computed tomography (CBCT) sets from 20 patients were rigidly registered to reference computed tomography (CT) sets based on bony landmarks. The rotational setup errors (pitch, yaw and roll) were calculated. Then, 121 CT sets involving rotational setup errors were created, and the dose distribution in these CT sets were recalculated. The recalculated dosimetric parameters for the clinical target volume (CTV) and organs at risk (OAR) were compared to the reference values, and the correlation coefficients between the dosimetric parameter differences and rotational setup errors were calculated. Only the pitch setup error was moderately correlated with CTV coverage (r ≥ 0.40) and strongly correlated with V45 for the bladder (r ≥ 0.91) and V40 for the rectum, small bowel and bone marrow (r ≥ 0.91). The maximum dosimetric difference in a single fraction and overall fractions was -1.59% and -0.69% in D98 for the CTV, 11.72% and 5.17% in V45 for the bladder and -8.03% and -4.68% in V40 for the rectum, respectively. In conclusion, rotational setup errors only slightly impact dose coverage during postoperative cervical cancer VMAT. However, the pitch setup error occasionally affected the doses received by the bladder or the rectum in the overall fraction when the error was systematic. Thus, rotational setup errors should be corrected by adjusting six-degree-of-freedom (DOF) couches to reduce dosimetric differences in the OARs.

Geometric and dosimetric evaluation of the differences between rigid and deformable registration to assess interfraction motion during pelvic radiotherapy

BACKGROUND AND PURPOSE

Appropriate internal margins are essential to avoid a geographical miss in intensity-modulated radiation therapy (IMRT) for endometrial cancer (EC). This study evaluated interfraction target motion using rigid and non-rigid approximation strategies and calculated internal margins based on random and systematic errors using traditional rigid margin recipes. Dosimetric impact of target motion was also investigated.

MATERIALS AND METHODS

Cone beam CTs (CBCTs) were acquired days 1-4 and then weekly in 17 patients receiving adjuvant IMRT for EC; a total of 169 CBCTs were analysed. Interfraction motion for the clinical target volume vaginal vault and upper vagina (CTVv) was measured using bony landmarks and deformation vector field displacement (DVFD) within a 1 mm internal wall of CTVv. Patient and population systematic and random errors were estimated and margins calculated. Delivered dose to the CTVv and organs at risk was estimated.

RESULTS

There was a significant difference in target motion assessment using the different registration strategies (p < 0.05). DVFD up to 30 mm occurred in the anterior/posterior direction, which was not accounted for in PTV margins using rigid margin recipes. Underdosing of CTVv D95% occurred in three patients who had substantial reductions in rectal volume (RV) during treatment. RV relative to the planning CT was moderately correlated with anterior/posterior displacement (r = 0.6) and mean relative RV during treatment was strongly correlated with mean relative RV at CBCT acquired days 1-3 (r = 0.8).

CONCLUSION

Complex and extensive geometric changes occur to the CTVv, which are not accounted for in margin recipes using rigid approximation. Contemporary margin recipes and adaptive treatment planning based on non-rigid approximation are recommended.

Inversely designed, 3D-printed personalized template-guided interstitial brachytherapy for vaginal tumors

Purpose

In this paper, we report cases of two patients with vaginal tumor who underwent interstitial brachytherapy (ISBT), using three-dimensional (3D)-printed personalized templates designed inversely from computed tomography (CT) or magnetic resonance (MR) images.

Material and methods

Patient 1 presenting with vaginal vault recurrence was planned to receive whole pelvis external beam radiotherapy (EBRT) followed by ISBT. The tumor invaded the paracolpium; thus, we planned to administer ISBT to include the tumor and vaginal membrane. A template was designed with holes for plastic needle applicator insertion considering the appropriate direction based on pre-treatment medical images. Patient 2 presenting with vaginal cancer was scheduled to receive EBRT and ISBT because of a paracolpium invasion. Before ISBT, MR imaging was performed with vaginal cylinder inserted in the patient’s vagina. By measuring the length of the tumor manually and projecting the tumor orthogonally to a plane parallel to the bottom surface of the cylinder applicator, a template was designed. Computer-aided design software was used for planning both templates. Polycarbonate/acrylonitrile-butadiene-styrene resin was selected as material of the templates.

Results

Patient 1 received 4-fraction ISBT one week apart. A mean of 10 applicators were inserted through the holes of the template in an average of 9 minutes (range, 5-15 minutes). All applicators were inserted toward the planned directions. Median minimum dose covering 90% (D_90%) of the clinical target volume (CTV) was 634 cGy. Patient 2 underwent three-fraction irradiation twice daily at 6-hour interval. All applicators were inserted through the inside of the template. The median D_90% of the CTV was 703 cGy. No grade 3 or higher toxicity were found in both series.

Conclusions

3D-printed templates designed using medical images are useful, especially for ISBT of vaginal tumors. Further verification of clinical indications, design of templates, and manufacturing process are needed.

Image-guided radiation therapy for post-operative gynaecologic cancer: patient set up verification with and without implanted fiducial markers

BACKGROUND

Intensity modulated radiotherapy (IMRT) is increasingly being used to treat gynaecological malignancies in the postoperative setting. The purpose of this study was to evaluate the use of image-guided radiotherapy (IGRT) using cone-beam computed tomography (CBCT) with fiducial markers for daily localization.

MATERIAL AND METHODS

A single institution study was performed of consecutive cervical or endometrial cancer patients receiving adjuvant external beam radiotherapy (n = 15). Patients were set up at treatment using daily CBCT and alignment of implanted fiducial markers. Image registration was retrospectively completed based on soft tissue matching and the resulting couch shifts from each IGRT method were compared (n = 122).

RESULTS

The median shift between IGRT methods was 2 mm, 1 mm and 1 mm in the anterior-posterior (A-P), superior-inferior (S-I), and lateral directions, respectively. The largest deviations were observed in the A-P direction; however, more than 90% were within 5 mm and 63.9% were within 2.5 mm.

CONCLUSIONS

IGRT based on soft tissue match provides a noninvasive convenient method for daily localization and is accurate within treatment uncertainty for the majority of cases.

Positional uncertainty of vaginal cuff and feasibility of implementing portable bladder scanner in postoperative cervical cancer patients

PURPOSE

To propose a geometrical margin for definition of the vaginal cuff PTV using only CT images of the full bladder (CT_full) in postoperative cervical cancer patients.

METHODS

Twenty-nine operated cervical cancer patients underwent volumetric arc therapy with a bladder filling protocol. This study assessed bladder filling using a portable bladder scanner and cone-beam computed tomography (CBCT) during the entire treatment period. The measured bladder volumes with a BladderScan® were compared with the delineated volume on CBCT. Titanium clips in the vaginal cuff were analysed to assess geometrical uncertainty and the influence of rectal and bladder volume changes.

RESULTS

BladderScan® showed good agreement with the delineated volume (R = 0.80). The volume changes in the bladder have a greater influence on the clip displacements than in the rectum. The 95th percentile of uncertainty of the clips in reference to CT_full in the right-left (RL), the superoinferior (SI), and the anteroposterior (AP) was 0.32, 0.65, and 1.15 cm, respectively. From this result and intra-fractional movements of the vaginal cuff reported by Haripotepornkul, a new geometrical margin was proposed for definition of the vaginal cuff planning target volume (PTV): 0.5, 0.9, and 1.4 cm in the RL, SI, and AP directions, respectively.

CONCLUSIONS

A new geometrical margin was proposed for definition of the vaginal cuff PTV based on CT_full, which will be needless of empty bladder at the planning CT scan. This method allows patients to reduce the burden and efficient routine CT scans can be improved.

Rectal balloon use limits vaginal displacement, rectal dose, and rectal toxicity in patients receiving IMRT for postoperative gynecological malignancies

Pelvic radiotherapy for gynecologic malignancies traditionally used a 4-field box technique. Later trials have shown the feasibility of using intensity-modulated radiotherapy (IMRT) instead. But vaginal movement between fractions is concerning when using IMRT due to greater conformality of the isodose curves to the target and the resulting possibility of missing the target while the vagina is displaced. In this study, we showed that the use of a rectal balloon during treatment can decrease vaginal displacement, limit rectal dose, and limit acute and late toxicities. Little is known regarding the use of a rectal balloon (RB) in treating patients with IMRT in the posthysterectomy setting. We hypothesize that the use of an RB during treatment can limit rectal dose and acute and long-term toxicities, as well as decrease vaginal cuff displacement between fractions. We performed a retrospective review of patients with gynecological malignancies who received postoperative IMRT with the use of an RB from January 1, 2012 to January 1, 2015. Rectal dose constraint was examined as per Radiation Therapy Oncology Group (RTOG) 1203 and 0418. Daily cone beam computed tomography (CT) was performed, and the average (avg) displacement, avg magnitude, and avg magnitude of vector were calculated. Toxicity was reported according to RTOG acute radiation morbidity scoring criteria. Acute toxicity was defined as less than 90 days from the end of radiation treatment. Late toxicity was defined as at least 90 days after completing radiation. Twenty-eight patients with postoperative IMRT with the use of an RB were examined and 23 treatment plans were reviewed. The avg rectal V40 was 39.3% ± 9.0%. V30 was65.1% ± 10.0%. V50 was 0%. Separate cone beam computed tomography (CBCT) images (n = 663) were reviewed. The avg displacement was as follows: superior 0.4 + 2.99 mm, left 0.23 ± 4.97 mm, and anterior 0.16 ± 5.18 mm. The avg magnitude of displacement was superior/inferior 2.22 ± 2.04 mm, laterally 3.41 ± 3.62 mm, and anterior/posterior 3.86 ± 3.45 mm. The avg vector magnitude was 6.60 ± 4.14 mm. For acute gastrointestinal (GI) toxicities, 50% experienced grade 1 toxicities and 18% grade 2 GI toxicities. For acute genitourinary (GU) toxicities, 21% had grade 1 and 18% had grade 2 toxicities. For late GU toxicities, 7% had grade 1 and 4% had grade 2 toxicities. RB for gynecological patients receiving IMRT in the postoperative setting can limit V40 rectal dose and vaginal displacement. Although V30 constraints were not met, patients had limited acute and late toxicities. Further studies are needed to validate these findings.

Should we customize PTV expansions for BMI? Daily cone beam computerized tomography to assess organ motion in postoperative endometrial and cervical cancer patients

AIM

A single-institution review assessing patient characteristics contributing to daily organ motion in postoperative endometrial and cervical cancer patients treated with intensity-modulated radiotherapy (IMRT).

BACKGROUND

The Radiation Therapy Oncology Group has established consensus guidelines for postoperative pelvic IMRT, recommending a 7 mm margin on all three axes of the target volume.

MATERIALS AND METHODS

Daily shifts on 457 radiation setups for 18 patients were recorded in the x axis (lateral), y axis (superior-inferior) and z axis (anterior-posterior); daily positions of the planning tumor volume were referenced with the initial planning scan to quantify variations.

RESULTS

Of the 457 sessions, 85 (18.6%) had plan shifts of at least 7 mm in one of the three dimensions. For obese patients (body mass index [BMI] ≥ 30), 75/306 (24.5%) sessions had plan shifts ≥7 mm. Odds of having a shift ≥7 mm in any direction was greater for obese patients under both univariate (OR 4.227, 95% CI 1.235-14.466, p = 0.021) and multivariate (OR 5.000, 95% CI 1.341-18.646, p = 0.016) analyses (MVA). Under MVA, having a BMI ≥ 30 was associated with increased odds of shifts in the anterior-posterior (1.173 mm, 95% CI 0.281-2.065, p = 0.001) and lateral (2.074 mm, 95% CI 1.284-2.864, p < 0.000) directions but not in the superior-inferior axis (0.298 mm, 95% CI -0.880 to 1.475, p = 0.619) exceeding 7 mm.

CONCLUSIONS

Based on these findings, the standard planned tumor volume expansion of 7 mm is less likely to account for daily treatment changes in obese patients.

Long-term outcomes using adjuvant pelvic intensity modulated radiation therapy (IMRT) for endometrial carcinoma

PURPOSE

We evaluated the long-term outcome and toxicity of adjuvant intensity modulated radiation therapy (IMRT) for high-risk endometrial carcinoma via a retrospective institutional review of patients treated in this setting with extended follow-up.

METHODS AND MATERIALS

Patients with endometrial cancer who underwent comprehensive surgical staging followed by adjuvant IMRT with or without sequential chemotherapy between 1999 and 2010 were reviewed. Median doses delivered with IMRT and brachytherapy were 45 Gy in 25 fractions and 10 Gy in 2 fractions; 10.2% received extended field and 94.5% received vaginal brachytherapy. Kaplan-Meier estimates are provided for rates of locoregional (in-field) relapse, distant metastasis, and disease-free survival, and overall survival. Gastrointestinal (GI) and genitourinary (GU) toxicity reported were graded with the Common Terminology Criteria for Adverse Events, version 4.03.

RESULTS

A total of 128 patients were identified. Median age at diagnosis was 64 years. Most patients (82.8%) had endometrioid adenocarcinoma followed by papillary serous (10.2%), clear cell (4.7%), and carcinosarcoma (2.3%). International Federation of Gynecology and Obstetrics staging distribution was as follows: IA, 13.3%; IB, 32.8%; II, 30.4%; IIIA, 5.5%; IIIC1, 9.4%; and IIIC2, 8.6%. Most (85.9%) underwent nodal dissections (28.1% pelvic only and 57.8% pelvic and para-aortic). Two patients (1.6%) experienced acute grade 3 GI toxicity; no other acute grade ≥3 GI/GU toxicities were noted. With a median follow-up of 57.0 months, 5-year locoregional relapse was 2.5%: vagina (n = 3), parametrium (n = 1), pelvic node (n = 1). Five-year estimates of distant metastasis, disease-free survival, and overall survival were 16.5%, 73.4%, and 77.4%, respectively. Five-year actuarial rates of late grade 3 GI and GU toxicities were 3.2% and 0.0%. The 5-year rate of symptomatic pelvic insufficiency fracture was 4.4%.

CONCLUSIONS

This study represents the largest cohort of endometrial cancer patients with extended follow-up receiving adjuvant IMRT. High rates of pelvic disease control and limited late toxicities demonstrate safety and efficacy of this approach in the setting of extended follow-up.

Internal target volume for post-hysterectomy vaginal recurrences of cervical cancers during image-guided radiotherapy

OBJECTIVE

The outcome of post-surgical recurrences of cervical cancer may be improved through radiation dose escalation, which hinges on accurate identification and treatment of the target. The present study quantifies target motion during course of image-guided radiotherapy (IGRT) for vault cancers.

METHODS

All patients underwent planning CT simulation after bladder-filling protocol. A daily pre-treatment megavoltage CT was performed. All translations and rotations were recorded. Post-registration displacement of gross tumour volume (GTV) and centre of mass (COM) of GTV was independently recorded by two observers for fractions one to seven. Day 1 image sets served as reference images against which the displacements of COM were measured. We calculated the displacements of common volume (CV) and encompassing volume (EV) of GTV for both the observers.

RESULTS

A total of 90 image data sets of 15 patients were available for evaluation. Individual patient GTV and average GTV by both the observers were comparable. The average shifts for EV were 2.4 mm [standard deviation (SD) ±1.2] in the mediolateral, 4.2 mm (SD ±2.8) in the anteroposterior and 4.0 mm (SD ±2.1) in superoinferior directions. Similarly, the average shifts for CV were 1.9 mm (SD ±0.6) in the mediolateral, 3.7 mm (SD ±2.7) in the anteroposterior and 4.4 mm (SD ±2.7) in superoinferior directions. Using Stroom's/van Herk's formula, the minimum recommended margins would be 4.5/5.2, 8.2/9.4 and 7.3/8.3 mm, respectively, for lateral, anteroposterior and superoinferior directions.

CONCLUSION

Differential directional internal margin is recommended in patients undergoing IGRT for post-surgical recurrence of cervical cancers.

ADVANCES IN KNOWLEDGE

Internal organ motion of vault cancers can be accounted for by a directional margin to the gross tumour.

Positioning accuracy during VMAT of gynecologic malignancies and the resulting dosimetric impact by a 6-degree-of-freedom couch in combination with daily kilovoltage cone beam computed tomography

Background

To improve the delivery of radiotherapy in gynecologic malignancies and to minimize the irradiation of unaffected tissues by using daily kilovoltage cone beam computed tomography (kV-CBCT) to reduce setup errors.

Methods

Thirteen patients with gynecologic cancers were treated with postoperative volumetric-modulated arc therapy (VMAT). All patients had a planning CT scan and daily CBCT during treatment. Automatic bone anatomy matching was used to determine initial inter-fraction positioning error. Positional correction on a six-degrees-of-freedom (6DoF) couch was followed by a second scan to calculate the residual inter-fraction error, and a post-treatment scan assessed intra-fraction motion. The margins of the planning target volume (M_PTV) were calculated from these setup variations and the effect of margin size on normal tissue sparing was evaluated.

Results

In total, 573 CBCT scans were acquired. Mean absolute pre-/post-correction errors were obtained in all six planes. With 6DoF couch correction, the M_PTV accounting for intra-fraction errors was reduced by 3.8–5.6 mm. This permitted a reduction in the maximum dose to the small intestine, bladder and femoral head (P = 0.001, 0.035 and 0.032, respectively), the average dose to the rectum, small intestine, bladder and pelvic marrow (P = 0.003, 0.000, 0.001 and 0.000, respectively) and markedly reduced irradiated normal tissue volumes.

Conclusions

A 6DoF couch in combination with daily kV-CBCT can considerably improve positioning accuracy during VMAT treatment in gynecologic malignancies, reducing the M_PTV. The reduced margin size permits improved normal tissue sparing and a smaller total irradiated volume.

Image-guided radiation therapy using surgical clips for localization of colonic metastasis from thyroid cancer

A 67-year old man with a history of papillary thyroid cancer (PTC) presented with metastatic disease to the left colon in the form of a 6.1x1.0 cm bleeding, ulcerated mass. Radiopaque surgical clips were used as fiducial markers to localize the gross tumor volume (GTV) as well as the corresponding clinical target volume (CTV) and planning target volume (PTV). Daily cone beam computed tomography (CBCT) image guidance was utilized to verify the tumor position. Inter- and intrafraction movement of the tumor mass was assessed. Gastrointestinal bleeding was controlled using palliative image-guided radiation therapy (IGRT).

Vaginal displacement during course of adjuvant radiation for cervical cancer: results from a prospective IG-IMRT study

OBJECTIVE

To compare internal target volume (ITV) generated using population-based displacements (ITV_study) with empty and full bladder scan fusion (ITV_EBFB) for organ-at-risk (OAR) doses during adjuvant intensity-modulated radiation therapy (IMRT) for cervical cancer.

METHODS

From January 2011 to October 2012, patients undergoing IMRT were included. CT simulation was carried out after inserting vault markers. Planning target volume (PTV)_EBFB received 50 Gy per 25 fractions. Pre-treatment megavoltage CT (MVCT) was performed. MVCTs were registered using bony landmarks with Day 1 MVCT. Displacement of the centre of mass of markers was measured along each axis. Directional ITV was calculated using mean ± 2 standard deviations (SDs) (ITV_study). Replanning was performed using PTV study, and OAR doses were compared with PTV_EBFB using Wilcoxon test.

RESULTS

A total of 348/386 data sets were evaluable for 16 patients. The median vaginal displacement was 1.2 mm (SD, 1.3 mm), 4.0 mm (SD, 3.5 mm) and 2.8 mm (SD, 3.3 mm) in the mediolateral, superoinferior and anteroposterior directions, respectively. The ITV margins were 4.1, 10.3 and 10.6 mm. ITV_study and ITV_EBFB were 115.2 cm(3) (87.7-152.2 cm(3)) and 151 cm(3) (95.7-277.1 cm(3)) (p < 0.0001), respectively. PTV_study and PTV_EBFB were 814 and 881 cm(3) (p < 0.0001), respectively. Median doses to the bladder were lower with the PTV_study (46.2 Gy vs 43.2 Gy; p = 0.0001), and a similar trend was observed in the volume of the small bowel receiving 40 Gy (68.2 vs 60.1 cm(3); p = 0.09).

CONCLUSION

Population-based PTV margins can lead to reduction in OAR doses.

ADVANCES IN KNOWLEDGE

Population-based ITV may reduce OAR doses while executing adjuvant IMRT for cervical cancer.