Dosimetric evaluation of manually and inversely optimized treatment planning for high dose rate brachytherapy of cervical cancer

Comparison of two inverse planning algorithms for cervical cancer brachytherapy

PURPOSE

To compare two inverse planning algorithms, the hybrid inverse planning optimization (HIPO) algorithm and the inverse planning simulated annealing (IPSA) algorithm, for cervical cancer brachytherapy and provide suggestions for their usage.

MATERIAL AND METHODS

This study consisted of 24 cervical cancer patients treated with CT image-based high-dose-rate brachytherapy using various combinations of tandem/ovoid applicator and interstitial needles. For fixed catheter configurations, plans were retrospectively optimized with two methods: IPSA and HIPO. The dosimetric parameters with respect to target coverage, localization of high dose volume (LHDV), conformal index (COIN), and sparing of organs at risk (OARs) were evaluated. A plan assessment method which combines a graphical analysis and a scoring index was used to compare the quality of two plans for each case. The characteristics of dwell time distributions of the two plans were also analyzed in detail.

RESULTS

Both IPSA and HIPO can produce clinically acceptable treatment plans. The rectum D_2cc was slightly lower for HIPO as compared to IPSA (P = 0.002). All other dosimetric parameters for targets and OARs were not significantly different between the two algorithms. The generated radar plots and scores intuitively presented the plan properties and enabled to reflect the clinical priorities for the treatment plans. Significant different characteristics were observed between the dwell time distributions generated by IPSA and HIPO.

CONCLUSIONS

Both algorithms could generate high-quality treatment plans, but their performances were slightly different in terms of each specific patient. The clinical decision on the optimal plan for each patient can be made quickly and consistently with the help of the plan assessment method. Besides, the characteristics of dwell time distribution were suggested to be taken into account during plan selection. Compared to IPSA, the dwell time distributions generated by HIPO may be closer to clinical preference.

Dosimetric comparison of manual forward planning with uniform dwell times versus volume-based inverse planning in interstitial brachytherapy of cervical malignancies

Aim

Dosimetic comparison of manual forward planning(MFP) with inverse planning(IP) for interstitial brachytherapy(ISBT) in cervical carcinoma.

Background

Brachytherapy planning by MFP is more reliable but time-consuming method, whereas IP has been explored more often for its ease and rapidness. The superiority of either is yet to be established.

Methodology

Two plans were created on data sets of 24 patients of cervical carcinoma who had undergone ISBT, one by MFP with uniform dwell times and another IP on BrachyVision 13.7 planning system with a dose prescription of 600 cGy. Isodose shaper was used for improving conformity & homogeneity. Dosimetric parameters for target and organs at risk (OARs) were recorded. Conformity index (COIN), dose homogeneity index (DHI), overdose index (OI), Coverage index (CI) and dose nonuniformity ratio (DNR) were calculated.

Results

Mean high risk clinical target volume: 73.05(±20.7)cc, D90: 5.51 Gy vs. 5.6 Gy (p = 0.017), V100: 81.77 % vs. 83.74 % (p = 0.002), V150: 21.7 % vs. 24.93 % (p = 0.002), V200: 6.3 % vs. 6.4 % (p=0.75) for IP and MFP, respectively. CI: 0.81(IP) and 0.83(MFP) (p = 0.003); however, COIN was 0.79 for both plans. D2cc of OARs was statistically better with IP (bladder 54.7 % vs. 56.1 %, p = 0.03; rectum 63 % vs. 64.7 %, (p = 0.0008).

Conclusion

Both MFP and IP are equally acceptable dosimetrically. With higher dose achieved to the target, for a similar OAR dose, MFP provides greater user flexibility of dwell positions within the target as well as better optimization. Isodose shaper may be carefully used for fine tuning. Larger sample sizes and clinical correlation will better answer the superiority of one over the other.

Influence of dwell time homogeneity error weight parameter on treatment plan quality in inverse optimized high-dose-rate cervix brachytherapy using SagiPlan

Purpose

Restricting the gradients of dwell times between adjacent dwell positions can potentially be beneficial in reducing the probability of unwanted hot/cold spots occurring, if the planned applicators/anatomy relative positions change before or during treatment. This constraint, however, may degrade plan quality. This study, for the first time, aims to quantify the impact of modulation restriction on plan quality indices in inverse optimization for cervix high-dose-rate (HDR) brachytherapy using the BEBIG SagiPlan treatment planning system.

Material and methods

Ten cervical cancer patient plans were optimized for treatment with a BEBIG SagiNova ⁶⁰Co HDR afterloader using the min/max inverse planning method, with dwell time homogeneity error weight (DTHEW) parameter values of 0 to 10. Dwell time homogeneity and gradients as well as various plan quality indices were analyzed.

Results

For DTHEW = 0, min/max-based optimization yielded higher HR-CTV D₉₀ values than the variance-based option (p < 0.001) and was therefore selected for this study. Averaging over all patients, selecting non-zero DTHEWs resulted in a general increase in dwell time homogeneity and decrease in mean and maximum adjacent dwell time gradients, especially between DTHEWs of 0 and 1. For DTHEW > 1, an increase of this parameter did not always result in more homogeneous dwell times or reduced gradients in individual patients. There was a negative correlation between DTHEW and both HR-CTV D₉₀ and V₁₀₀ (p < 0.001, r = –0.91). Increasing DTHEW also negatively affected conformity index (p < 0.001, r = –0.99). Changes in rectum and sigmoid colon D_2cc were insignificant. There was a strong positive relationship between bladder D_2cc and DTHEW (p < 0.001, r = 0.99).

Conclusions

Assuming a static geometry, statistically significant degradation of plan quality can result from restricting the dwell time homogeneity in min/max-based optimization of cervix HDR brachytherapy plans using SagiPlan. Therefore, setting DTHEW to zero is indicated for the type of patient plans considered in this study.

Comparison of graphical optimization or IPSA for improving brachytheraphy plans associated with inadequate target coverage for cervical cancer

Many studies have reported that inverse planning by simulated annealing (IPSA) can improve the quality of brachytherapy plans, and we wanted to examine whether IPSA could improve cervical cancer brachytherapy plans giving D₉₀ < 6 Gy (with 7 Gy per fraction) at our institution. Various IPSA plans involving the tandem and ovoid applicators were developed for 30 consecutive cervical cancer patients on the basis of computed tomography: IPSA1, with a constraint on the maximum dose in the target volume; IPSA1-0, identical to IPSA1 but without a dwell-time deviation constraint; IPSA2, without a constraint on the maximum dose; and IPSA2-0, identical to IPSA2 but without a dwell-time deviation constraint. IPSA2 achieved similar results as graphical optimization, and none of the other IPSA plans was significantly better than graphical optimization. Therefore, other approaches, such as combining interstitial and intracavitary brachytherapy, may be more appropriate for improving the quality of brachytherapy plans associated with inadequate target coverage.

Clinical efficacy and toxicity of radio-chemotherapy and magnetic resonance imaging-guided brachytherapy for locally advanced cervical cancer patients: A mono-institutional experience

BACKGROUND

To evaluate efficacy and toxicity of radio-chemotherapy (RCT) and MR-guided pulsed-dose-rate (PDR) adaptive brachytherapy (IGABT) for locally advanced cervical cancer (LACC).

MATERIAL AND METHODS

Between 2007 and 2014 85 patients with FIGO stage 1B1 N+ or ≥ 1B2 cervical cancer were treated with RCT+ IGABT. The treatment consisted of a pelvic± paraaortic external beam radiotherapy (EBRT) (45-50.4 Gy ± 10 Gy boost to primary tumor and/or to pathologic lymph nodes) with concurrent cisplatin followed by 25-35 Gy of PDR IGABT in 30-50 pulses. The ratio of 3D-CFRT/IMRT was 61/24 patients. Dose-volume parameters of high-risk clinical target volume (HR-CTV), intermediate-risk clinical target volume (IR-CTV) and D2cm(3) organs at risk (OARs) were reported. Local control (LC), cancer-specific survival (CCS) and overall survival (OS) were analyzed actuarially and morbidity crude rates were scored using CTCAEv4.0.

RESULTS

Mean follow-up was 36 months (range 6-94). The mean D90 and D98 for HR-CTV was 84.4 ± 9 Gy and 77 ± 8.1 Gy, while for IR-CTV was 69.1 ± 4.3 Gy and 64.8 ± 4.3 Gy, respectively. The mean D2cm(3) for OARs was the following: bladder: 77.3 ± 10.5 Gy, rectum: 65 ± 6.8 Gy, sigmoid: 63 ± 7.9 Gy and intestine: 64.0 ± 9.1 Gy. Three year LC, CSS and OS were: 94%, 85% and 81%. The three-year regional- and distant control rates were 95% and 74%. Node negative patients had significantly higher three-year CSS (100 vs. 72%, p = 0.016) and OS (92 vs. 72%, p = 0.001) compared to node positive ones. Three-year actuarial late Grade ≥ 3 morbidity was the following: GI: 8%, GU: 5%, Vaginal: 8%. The frequency of Grade ≥ 3 hematological toxicities including anemia/leukopenia/neutropenia/thrombocytopenia were 8.6%/34.7%/24.3%/24.3%, respectively.

CONCLUSION

This large mono-institutional experience builds up further evidences that IGABT in conjunction with RCT should be the standard of care for patients suffering LACC.

Impact of radiation dose and standardized uptake value of (18)FDG PET on nodal control in locally advanced cervical cancer

BACKGROUND

Despite local control now exceeding 90% with image-guided adaptive brachytherapy (IGABT), regional and distant metastases continue to curb survival in locally advanced cervical cancer. As regional lymph nodes often represent first site of metastatic spread, improved nodal control could improve survival. The aim of this study was to examine optimal volume and dose of external beam radiotherapy (EBRT) to maximize regional control including dose contribution from IGABT.

MATERIAL AND METHODS

In total 139 patients from the EMBRACE study were analyzed. Individual nodal dose was determined by dose-maps from EBRT and IGABT. All PET/CT scans were re-evaluated and nodal maximal standard uptake value (SUVmax) was determined. Nodal failures were registered to planning scans and related to boosted nodes and treated volume. Relation between SUVmax and nodal control as well as the pattern of regional nodal failure were analyzed.

RESULTS

Eighty-four patients were node positive. Nine patients had all metastatic nodes surgically removed. Seventy-five patients had 209 nodes boosted with EBRT. Median nodal boost dose was 62 Gy EQD2 (53-69 Gy EQD2). Median SUVmax was 6 (2-22). No patients had persistent nodal disease, but six patients recurred in a boosted node. SUVmax was significantly higher in nodes that recurred (p = 0.02). However, there was no correlation to nodal dose or volume. Twenty-one patients had a nodal failure including para-aortic nodal (PAN) metastases above the irradiated volume. Nine patients had a PAN-only failure. Patients receiving ≤ 4 cycles of weekly cisplatin had higher risk of nodal failure (p < 0.01).

CONCLUSION

Current RT practice provides a high level of control in both boosted nodes and the elective irradiated regional target. However, a high nodal SUVmax is a negative prognostic predictor for nodal control. Attention should be raised to administration of a complete schedule of concurrent chemotherapy as well as treatment of para-aortic nodes.

Evaluation of planning aims and dose prescription in image-guided adaptive brachytherapy and radiochemotherapy for cervical cancer: Vienna clinical experience in 225 patients from 1998 to 2008

BACKGROUND

To assess planning aims (PAs) and dose prescription in image-guided adaptive brachytherapy (IGABT) of cervical cancer and investigate potential impact on clinical outcome.

MATERIAL AND METHODS

Our study population consists of 225 consecutive cervical cancer patients (FIGO stages IB-IVA) treated between 1998 and 2008 at the Medical University of Vienna by external beam radiotherapy (EBRT) ± chemotherapy and IGABT. For this retrospective study, patients were stratified into two treatment groups: PA+ group, all dose constraints fulfilled for prescription; PA-, one or more dose constraints not fulfilled for prescription. The following dose constraints (EBRT+ IGABT) were applied: clinical target volume (CTV)HR D90 ≥ 85 Gy, D2cm3 Rectum < 70 Gy, D2cm3 Bladder < 90 Gy. Differences in patient, tumor and treatment characteristics and clinical outcome (event: local failure or grade 3 + 4 toxicity) were compared between Group 1 and 2. Further, the impact of learning period (1998-2000) and protocol period (2001-2008) on the fulfillment of PAs for dose prescription and clinical outcome was analyzed.

RESULTS

In the PA+ group there were 77 (34%) and in the PA- group 148 (66%) patients. In the PA- group, CTVHR D90 < 85 Gy was prescribed in 82 patients, D2cm3 bladder > 90 Gy was prescribed in 80 patients and D2cm3 Rectum > 70 Gy in 60 patients. Fulfillment of the PA for dose prescription improved from 4% in the learning period to 48% in the protocol period. The five-year event-free interval was 64% in the learning period and 84% in the protocol period (p = 0.008).

CONCLUSION

Fulfillment of all PAs for dose prescription is challenging - especially in patients with more advanced tumors. However, with growing experience fulfillment of PA for dose prescription can be significantly increased (learning and protocol period). Such increase in fulfilling PA for dose prescription is followed by a significant improvement in clinical outcome.

A novel two-step optimization method for tandem and ovoid high-dose-rate brachytherapy treatment for locally advanced cervical cancer

PURPOSE

To present a novel method allowing fast volumetric optimization of tandem and ovoid high-dose-rate treatments and to quantify its benefits.

METHODS AND MATERIALS

Twenty-seven CT-based treatment plans from 6 consecutive cervical cancer patients treated with four to five intracavitary tandem and ovoid insertions were used. Initial single-step optimized plans were manually optimized, approved, and delivered plans created with a goal to cover high-risk clinical target volume (HR-CTV) with D90 >90% and minimize rectum, bladder, and sigmoid D2cc. For the two-step optimized (TSO) plan, each single-step optimized plan was replanned adding a structure created from prescription isodose line to the existent physician delineated HR-CTV, rectum, bladder, and sigmoid. New, more rigorous dose-volume histogram constraints for the critical organs at risks (OARs) were used for the optimization. HR-CTV D90 and OAR D2ccs were evaluated in both plans.

RESULTS

TSO plans had consistently smaller D2ccs for all three OARs while preserving HR-CTV D90. On plans with "excellent" CTV coverage, average D90 of 96% (91-102%), sigmoid, bladder, and rectum D2cc, respectively, reduced on average by 37% (16-73%), 28% (20-47%), and 27% (15-45%). Similar reductions were obtained on plans with "good" coverage, average D90 of 93% (90-99%). For plans with "inferior" coverage, average D90 of 81%, the coverage increased to 87% with concurrent D2cc reductions of 31%, 18%, and 11% for sigmoid, bladder, and rectum, respectively.

CONCLUSIONS

The TSO can be added with minimal planning time increase but with the potential of dramatic and systematic reductions in OAR D2ccs and in some cases with concurrent increase in target dose coverage. These single-fraction modifications would be magnified over the course of four to five intracavitary insertions and may have real clinical implications in terms of decreasing both acute and late toxicities.