A dose homogeneity index for evaluating 192Ir interstitial breast implants

Interstitial Brachytherapy for Lip Cancer: Technical Aspects to Individualize Treatment Approach and Optimize Outcomes

Primary radiation therapy using interstitial brachytherapy (IBT) provides excellent local tumor control for early-stage squamous cell carcinoma of the lip. Technical aspects of treatment are important to optimize outcomes. In this report, we discuss patient selection criteria, procedural details, and dosimetric considerations for performing IBT for cancers of the lip. Catheters are inserted across the length of tumor entering and exiting approximately 5 mm beyond the palpable tumor extent. A custom mouthpiece is fabricated to facilitate normal tissue sparing. Patients undergo computed tomography imaging, the gross tumor volume is contoured based on physical examination and computed tomography findings, and an individualized brachytherapy plan is generated with the goals of achieving gross tumor volume D90% ≥ 90% and minimizing V150%. Ten patients with primary (n = 8) or recurrent (n = 2) cancers of the lip who received high-dose-rate lip IBT using 2.0- to 2.5-week treatment regimens are described (median prescription: 47.6 Gy in 14 fractions of 3.4 Gy). Local tumor control was 100%. There were no cases of acute grade ≥4 or late grade ≥2 toxicity, and cosmesis scores were graded as good to excellent in all patients. IBT represents an excellent treatment option for patients with lip squamous cell carcinoma. With careful attention to technical considerations furthered described in the present report, high rates of tumor control, low rates of toxicity, and favorable esthetic and functional outcomes can be achieved with IBT for lip cancer.

Dosimetric Evaluation of Different Optimization Algorithms Used in Interstitial Brachytherapy of Cervical Carcinoma

BACKGROUND

Conventional optimization techniques are based on the planning approach in which positions and weights are varied to generate the desired dose distribution. Inverse planning simulated annealing (IPSA) is an advanced optimization method developed to automatically determine a suitable combination of positions to design an acceptable plan.

OBJECTIVE

In this study, three optimization techniques namely IPSA, graphical optimization (GROPT), and geometrical optimization (GOPT) methods are compared in high-dose-rate interstitial brachytherapy of cervical carcinoma.

MATERIAL AND METHODS

In this retrospective study, twenty computed tomography (CT) data sets of 10 cervical cancer patients treated with Martinez Universal Perineal Interstitial Template-based interstitial brachytherapy were studied. The treatment plans generated were optimized using the IPSA, and GOPT methods. The prescribed dose was 24 Gy in 4 fractions. Plans produced using IPSA, GrOPT, and GOPT techniques were analyzed for comparison of dosimetric parameters, including target coverage, homogeneity, conformity, and organs at risk (OAR) doses.

RESULTS

V100 values for IPSA, GrOPT and GOPT plans were 95.81±2.33%, 93.12±2.76% and 88.90±4.95%, respectively. The mean D90 values for the IPSA, GrOPT, and GOPT plans were 6.45±0.15 Gy, 6.12±0.21 Gy, and 5.85±0.57 Gy, respectively. Significantly lower doses of OAR were in the IPSA plans that were more homogeneous (HI=0.66). Conformity was comparatively higher in IPSA-based plans (CI=0.75).

CONCLUSION

IPSA plans were superior and resulted in better target coverage, homogeneity, conformity, and minimal OAR doses.

Deep reinforcement learning for treatment planning in high-dose-rate cervical brachytherapy

PURPOSE

High-dose-rate (HDR) brachytherapy (BT) is an effective cancer treatment method in which the radiation source is placed within the body. Treatment planning is a critical component for a successful outcome. Almost all currently proposed treatment planning methods are built on stochastic heuristic algorithms, which limits the generation of higher quality plans. This study proposed a novel treatment planning method to adjust dwell times in a human-like fashion to improve the quality of the plan.

METHODS

We built an intelligent treatment planner network (ITPN) based on deep reinforcement learning (DRL). The network architecture of ITPN is Dueling Double-Deep Q Network. The state is the dwell time of each dwell position and the action is which dwell time to adjust and how to adjust it. A hybrid equivalent uniform dose objective function was established and assigned corresponding rewards according to its changes. Experience replay was performed with the epsilon greedy algorithm and SumTree data structure.

RESULTS

In the evaluation of ITPN using 20 patient cases, D₉₀, D₁₀₀ and V₁₀₀ showed no significant difference compared with inverse planning simulated annealing (IPSA) optimization. However, D_2cc of bladder, rectum and sigmoid, V₁₅₀ and V₂₀₀ were significant reduced, and homogeneity index and conformity index were significantly increased.

CONCLUSION

The proposed ITPN was able to generate higher quality plans based on the learned dwell time adjustment policy than IPSA. This is the first artificial intelligence system that can directly determine the dwell times of HDR BT, which demonstrated the potential feasibility of solving optimization problems via DRL.

American Brachytherapy Society (ABS) consensus statement for soft-tissue sarcoma brachytherapy

PURPOSE

Growing data supports the role of radiation therapy in the treatment of soft tissue sarcoma (STS). Brachytherapy has been used for decades in the management of STS and can be utilized as monotherapy or as a boost to external beam radiation. We present updated guidelines from the American Brachytherapy Society regarding the utilization of brachytherapy in the management of STS.

METHODS AND MATERIALS

Members of the American Brachytherapy Society with expertise in STS and STS brachytherapy created an updated clinical practice guideline including step-by-step details for performing STS brachytherapy based on a literature review and clinical experience.

RESULTS

Brachytherapy monotherapy should be considered for lower-recurrence risk patients or after a local recurrence following previous external beam radiation; a brachytherapy boost can be considered in higher-risk patents meeting implant criteria. Multiple dose/fractionation regimens are available, with determination based on tumor location and treatment intent. Techniques to limit wound complications are based on the type of wound closure; wound complication can be mitigated with a delay in the start of brachytherapy with immediate wound closure or by utilizing a staged reconstruction technique, which allows an earlier treatment start with a delayed wound closure.

CONCLUSIONS

These updated guidelines provide clinicians with data on indications for STS brachytherapy as well as guidelines on how to perform and deliver high quality STS brachytherapy safely with minimal toxicity.

Optimization in treatment planning of high dose-rate brachytherapy - Review and analysis of mathematical models

Treatment planning in high dose-rate brachytherapy has traditionally been conducted with manual forward planning, but inverse planning is today increasingly used in clinical practice. There is a large variety of proposed optimization models and algorithms to model and solve the treatment planning problem. Two major parts of inverse treatment planning for which mathematical optimization can be used are the decisions about catheter placement and dwell time distributions. Both these problems as well as integrated approaches are included in this review. The proposed models include linear penalty models, dose-volume models, mean-tail dose models, quadratic penalty models, radiobiological models, and multiobjective models. The aim of this survey is twofold: (i) to give a broad overview over mathematical optimization models used for treatment planning of brachytherapy and (ii) to provide mathematical analyses and comparisons between models. New technologies for brachytherapy treatments and methods for treatment planning are also discussed. Of particular interest for future research is a thorough comparison between optimization models and algorithms on the same dataset, and clinical validation of proposed optimization approaches with respect to patient outcome.

Dosimetric characteristics of accelerated partial breast irradiation by interstitial multicatheter brachytherapy with intraoperative free-hand implantation in the treatment of early breast cancer

Introduction

The aim of this study is to evaluate the characteristics of the dosimetry and the skin dose of interstitial brachytherapy by the use of the free‐hand implantation technique toward the treatment of early breast cancer.

Materials & Methods

Seventeen patients diagnosed with early breast cancer were selected for the study. The implantation of the catheters for postoperative interstitial brachytherapy was performed using the free‐hand technique. The total tumor dose to the tumor cavity plus 2 cm margin was 3400 cGy, twice daily for 10 fractions in 5 days. The dosage to the target and the organ at risk (OAR) were recorded for analysis. The skin dose of the patient and the phantom were measured with Gafchromic film (EBT3) and the results were compared with the skin dose calculated by the brachytherapy treatment planning system.

Results

The median conformal index is 94% (range 89%–99%), and the median homogeneity index is 71%. The median skin dose measured from the skin of the patients was 20.1% lower than the skin dose calculated from the treatment planning system and consistent with the phantom surface measurement experiment. There were no grade 3 or above acute toxicity recorded.

Conclusions

Interstitial brachytherapy by the use of the free‐hand implantation technique for early breast cancer is feasible and avoids the need for a second surgical intervention. The calculated skin dose was overestimated by at least 20%. The results of this study may help in building a modification model for the prediction of skin toxicity in any future study.

Dosimetric comparison of inverse optimisation methods versus forward optimisation in HDR brachytherapy of breast, cervical and prostate cancer

Objective

Dosimetric comparison of HIPO (hybrid inverse planning optimisation) and IPSA (inverse planning simulated annealing) inverse and forward optimisation (FO) methods in brachytherapy (BT) of breast, cervical and prostate cancer.

Methods

At our institute 38 breast, 47 cervical and 50 prostate cancer patients treated with image-guided interstitial high-dose-rate BT were selected. Treatment plans were created using HIPO and IPSA inverse optimisation methods as well as FO. The dose–volume parameters of different treatment plans were compared with Friedman ANOVA and the LSD post-hoc test.

Results

IPSA creates less dose coverage to the target volume than HIPO or FO: V100 was 91.7%, 91% and 91.9% for HIPO, IPSA and FO plans (p = 0.1784) in breast BT; 90.4%, 89.2% and 91% (p = 0.0045) in cervical BT; and 97.1%, 96.2% and 97.7% (p = 0.0005) in prostate BT, respectively. HIPO results in more conformal plans: COIN was 0.72, 0.71 and 0.69 (p = 0.0306) in breast BT; 0.6, 0.47 and 0.58 (p < 0.001) in cervical BT; and 0.8, 0.7 and 0.7 (p < 0.001) in prostate BT, respectively. In breast BT, dose to the skin and lung was smaller with HIPO and FO than with IPSA. In cervical BT, dose to the rectum, sigmoid and bowel was larger using IPSA than with HIPO or FO. In prostate BT, dose to the urethra was higher and the rectal dose was smaller using FO than with inverse methods.

Conclusion

In interstitial breast and prostate BT, HIPO results in comparable dose–volume parameters to FO, but HIPO plans are more conformal. In cervical BT, HIPO produces dosimetrically acceptable plans only when more needles are used. The dosimetric quality of IPSA plans is suboptimal and results in unnecessary larger active lengths.

Investigating the role of constrained CVT and CVT in HIPO inverse planning for HDR brachytherapy of prostate cancer

PURPOSE

The purpose of this study is to investigate the role of the centroidal Voronoi tessellation (CVT) and constrained CVT (CCVT) in inverse planning in combination with the Hybrid Inverse Planning Optimization (HIPO) algorithm in HDR brachytherapy of prostate cancer. HIPO implemented in Oncentra© Prostate treatment planning system, is used for three-dimensional (3D)-ultrasound-based intraoperative treatment planning in high dose rate brachytherapy. HIPO utilizes a hybrid iterative process to determine the most appropriate placement of a given number of catheters to fulfil predefined dose-volume constraints. The main goals of the current investigation were to identify a way of improving the performance of HIPO inverse planning; accelerating the HIPO, and to evaluate the effect of the two CVT-based initialization methods on the dose distribution in the sub-region of prostate that is not accessible by catheters, when trying to avoid perforation of urethra.

METHODS

We implemented the CVT algorithm to generate initial catheter configurations before the initialization of the HIPO algorithm. We introduced the CCVT algorithm to improve the dose distribution to the sub-volume of prostate within the bounding box of the urethra contours including its upper vertical extension (U-P). For the evaluation, we considered a total of 15 3D ultrasound-based HDRBT prostate implants. Execution time and treatment plan quality were evaluated based on the dose-volume histograms of prostate (PTV), its sub-volume U-P, and organs at risk (OARs). Furthermore, the conformity index COIN, the homogeneity index HI and the complication-free tumor control probability (P₊ ) were used for our treatment plan comparisons. Finally, the plans with the recommended HIPO execution mode were compared to the clinically used intraoperative pre-plans.

RESULTS

The plan quality achieved with CCVT-based HIPO initialization was superior to the default HIPO initialization method. Focusing on the U-P sub-region of the prostate, the CCVT method resulted in a significant improvement of all dosimetric indices compared to the default HIPO, when both were executed in the adaptive mode. For that recommended HIPO execution mode, and for U-P, CCVT demonstrated in general higher dosimetric indices than CVT. Additionally, the execution time of CCVT initialized HIPO was lower compared to both alternative initialization methods. This is also valid for the values of the aggregate objective function with the differences to the default initialization method being highly significant. Paired non-parametric statistical tests (Wilcoxon signed-rank) showed a significant improvement of dose-volume indices, COIN and P₊ for the plans generated by the CCVT-based catheter configuration initialization in HIPO compared to the default HIPO initialization process. Furthermore, in ten out of 15 cases, the CCVT-based HIPO plans fulfilled all the clinical dose-volume constraints in a single trial without any need for further catheter position adaption.

CONCLUSION

HIPO with CCVT-based initialization demonstrates better performance regarding the aggregate objective function and convergence when compared to the CVT-based and default catheter configuration initialization methods. This improved performance of HIPO inverse planning is clearly not at the cost of the dosimetric and radiobiologically evaluated plan quality. We recommend the use of the CCVT method for HIPO initialization especially in the adaptive planning mode.

An extended dose-volume model in high dose-rate brachytherapy - Using mean-tail-dose to reduce tumor underdosage

Purpose

High dose–rate brachytherapy is a method of radiotherapy for cancer treatment in which the radiation source is placed within the body. In addition to give a high enough dose to a tumor, it is also important to spare nearby healthy organs [organs at risk (OAR)]. Dose plans are commonly evaluated using the so‐called dosimetric indices; for the tumor, the portion of the structure that receives a sufficiently high dose is calculated, while for OAR it is instead the portion of the structure that receives a sufficiently low dose that is of interest. Models that include dosimetric indices are referred to as dose–volume models (DVMs) and have received much interest recently. Such models do not take the dose to the coldest (least irradiated) volume of the tumor into account, which is a distinct weakness since research indicates that the treatment effect can be largely impaired by tumor underdosage even to small volumes. Therefore, our aim is to extend a DVM to also consider the dose to the coldest volume.

Methods

An improved DVM for dose planning is proposed. In addition to optimizing with respect to dosimetric indices, this model also takes mean dose to the coldest volume of the tumor into account.

Results

Our extended model has been evaluated against a standard DVM in ten prostate geometries. Our results show that the dose to the coldest volume could be increased, while also computing times for the dose planning were improved.

Conclusion

While the proposed model yields dose plans similar to other models in most aspects, it fulfils its purpose of increasing the dose to cold tumor volumes. An additional benefit is shorter solution times, and especially for clinically relevant times (of minutes) we show major improvements in tumour dosimetric indices.

Calculation of dose volume parameters and indices in plan evaluation of HDR interstitial brachytherapy by MUPIT in carcinoma cervix

BACKGROUND

Evaluation of a HDR- interstitial brachytherapy plan is a challenging job. Owing to the complexities and diversity of the normalization and optimization techniques involved, a simple objective assessment of these plans is required. This can improve the radiation dose coverage of the tumour with decreased organ toxicity.

AIM

To study and document the various dose volume indices and parameters required to evaluate a HDR interstitial brachytherapy plan by Volume normalization and graphical optimization using MUPIT (Martinez Universal Perineal Interstitial Template) in patients of carcinoma cervix.

SETTINGS AND DESIGN

Single arm, retrospective study.

METHODS AND MATERIALS

35 patients of carcinoma cervix who received EBRT and HDR brachytherapy using MUPIT, were selected. The dose prescribed was 4 Gray/Fraction in four fractions (16Gy/4) treated twice daily, at least 6 hours apart. CTV and OARs were delineated on the axial CT image set. Volume normalization and graphical optimization was done for planning. Coverage Index (CI), Dose homogeneity index (DHI), Overdose index (OI), Dose non-uniformity ratio (DNR), Conformity Index (COIN) and dose volume parameters i.e. D2cc, D1cc, D0.1cc of rectum and bladder were evaluated.

STATISTICAL ANALYSIS

SPSS version 16 was used.

RESULTS AND CONCLUSION

CI was 0.95 ± 1.84 which means 95% of the target received 100% of the prescribed dose. The mean COIN was 0.841 ± 0.06 and DHI was 0.502 ± 0.11. D2cc rectum and bladder was 3.40 ± 0.56 and 2.95 ± 0.62 respectively which was within the tolerance limit of this organs. There should be an optimum balance between these indices for improving the quality of the implant and to yield maximum clinical benefit out of it, keeping the dose to the OARs in limit. Dose optimization should be carefully monitered and an institutional protocol should be devised for the acceptability criteria of these plans.

Inverse planning and inverse implanting for breast interstitial brachytherapy. Introducing a new anatomy specific breast interstitial template (ASBIT)

An innovative template, based on thoracic cage surface reconstructions for breast interstitial brachytherapy was developed. Hybrid-inverse-planning-optimisation-based implantations and brachytherapy plans, using three custom anthropomorphic breast phantoms, were utilised for its validation. A user independent, inverse planning and inverse implanting technique is proposed.

Successful salvage treatment of refractory recurrence of maxillary sinus carcinoma using image-guided high-dose-rate interstitial brachytherapy

This case report illustrates a treatment effect of image-guided high-dose-rate (HDR) interstitial brachytherapy for refractory recurrence of maxillary sinus carcinoma. A 61-year-old male was previously admitted to another hospital and received surgery because of left maxillary sinus squamous cell carcinoma (SCC) 6 years ago. Tumor regrowth was noted 2 years after the initial radical surgery. The patient accepted local excision again for the recurrence, followed by external beam radiotherapy. Despite salvage treatment with surgery and external irradiation, the lesion expanded as 4.8 × 4.4 × 4.0 cm³. Because the patient refused palliative resection, we recommended technique of image-guided HDR interstitial brachytherapy. The total doses of 42 Gy in 12 fractions were delivered to the whole recurrent tumor. Removal of the recurrent tumor was securely achieved by HDR interstitial brachytherapy, guided with ultrasound. The refractory tumor in the patient healed uneventfully after HDR interstitial brachytherapy without recurrence during 8 months of follow-up. This case is remarkable because the patient experienced complete remission by a safe and practicable method with image-guided HDR interstitial brachytherapy.

American Brachytherapy Society Task Group Report: Combined external beam irradiation and interstitial brachytherapy for base of tongue tumors and other head and neck sites in the era of new technologies

Irradiation plays an important role in the treatment of cancers of the head and neck providing a high locoregional tumor control and preservation of organ functions. External beam irradiation (EBI) results in unnecessary radiation exposure of the surrounding normal tissues increasing the incidence of side effects (xerostomy, osteoradionecrosis, and so forth). Brachytherapy (BT) seems to be the best choice for dose escalation over a short treatment period and for minimizing radiation-related normal tissue damage due to the rapid dose falloff around the source. Low-dose-rate BT is being increasingly replaced by pulsed-dose-rate and high-dose-rate BT because the stepping source technology offers the advantage of optimizing dose distribution by varying dwell times. Pulsed-dose and high-dose rates appear to yield local control and complication rates equivalent to those of low-dose rate. BT may be applied alone; but in case of high risk of nodal metastases, it is used together with EBI. This review presents the results and the indications of combined BT and EBI in carcinoma of the base of tongue and other sites of the head and neck region, as well as the role BT plays among other-normal tissue protecting-modern radiotherapy modalities (intensity-modulated radiotherapy, stereotactic radiotherapy) applied in these localizations.

Robustness of IPSA optimized high-dose-rate prostate brachytherapy treatment plans to catheter displacements

PURPOSE

Inverse planning simulated annealing (IPSA) optimized brachytherapy treatment plans are characterized with large isolated dwell times at the first or last dwell position of each catheter. The potential of catheter shifts relative to the target and organs at risk in these plans may lead to a more significant change in delivered dose to the volumes of interest relative to plans with more uniform dwell times.

MATERIAL AND METHODS

This study aims to determine if the Nucletron Oncentra dwell time deviation constraint (DTDC) parameter can be optimized to improve the robustness of high-dose-rate (HDR) prostate brachytherapy plans to catheter displacements. A set of 10 clinically acceptable prostate plans were re-optimized with a DTDC parameter of 0 and 0.4. For each plan, catheter displacements of 3, 7, and 14 mm were retrospectively applied and the change in dose volume histogram (DVH) indices and conformity indices analyzed.

RESULTS

The robustness of clinically acceptable prostate plans to catheter displacements in the caudal direction was found to be dependent on the DTDC parameter. A DTDC value of 0 improves the robustness of planning target volume (PTV) coverage to catheter displacements, whereas a DTDC value of 0.4 improves the robustness of the plans to changes in hotspots.

CONCLUSIONS

The results indicate that if used in conjunction with a pre-treatment catheter displacement correction protocol and a tolerance of 3 mm, a DTDC value of 0.4 may produce clinically superior plans. However, the effect of the DTDC parameter in plan robustness was not observed to be as strong as initially suspected.

Dosimetric advantages of using multichannel balloons compared to single-channel cylinders for high-dose-rate vaginal cuff brachytherapy

PURPOSE

To evaluate the dosimetric advantages of using multichannel balloons (MCBs) vs. single-channel cylinders (SCCs) for high-dose-rate vaginal cuff brachytherapy.

METHODS AND MATERIALS

A total of 91 consecutive high-dose-rate vaginal cuff brachytherapy including 45 MCB and 46 SCC treatments were reviewed. The clinical target volume (CTV) was defined as a 0.5-cm uniform expansion of the applicator surface from vaginal apex for 3 cm. For dosimetric comparison, we normalized prescription dose per fraction to 700 cGy and optimized each plan to cover at least 90% of CTV. CTV-1 cm, the true vaginal cuff volume, was defined as proximal 1 cm of CTV from vaginal apex. Four quality indices including conformity index (CI), dose homogeneity index, dose nonuniformity index, and overdose index were compared.

RESULTS

The CTV and CTV-1 cm were significantly larger for MCB cases compared to SCC cases. Evaluating CTV coverage, the mean dose homogeneity index and dose nonuniformity index were superior for MCB than SCC. No differences were noted regarding CI and overdose index between MCB and SCC cases. However, focusing on CTV-1 cm, the difference of CI became significant in favor of MCB cases. In addition, the mean point dose at 0.5-cm depth from the apex was significantly lower in SCC cases compared to cases by MCB treatment, indicating inadequate vaginal apex coverage by SCC treatment.

CONCLUSIONS

Compared to SCC, MCB treats a larger volume and offers a more conformal and homogeneous target coverage. In addition, a lower dose at the vaginal apex due to SCCs source anisotropy can be minimized.

Dosimetric comparison of volume-based and inverse planning simulated annealing-based dose optimizations for high-dose rate brachytherapy

The aim of this study was to compare the clinical benefits of inverse planning simulated annealing (IPSA)-based optimization over volume-based optimization for high-dose rate (HDR) cervix interstitial implants. Overall, 10 patients of cervical carcinoma were considered for treatment with HDR interstitial brachytherapy. Oncentra Master Plan brachytherapy planning system was used for generating 3-dimensional HDR treatment planning for all patients. All patient treatments were planned using volume-based optimization and inverse planning optimization (IPSA). The parameters V100, V150, and V200 for the target; D(2 cm³) of bladder, rectum, and sigmoid colon; and V80 and V100 for bladder, rectum, and sigmoid colon were compared using dose-volume histograms (DVHs). The conformity index (CI), relative dose homogeneity index, overdose volume index (ODI), and dose nonuniformity index (DNR) were computed from cumulative DVHs. Good target coverage for prescription dose was achieved with volume-based optimization as compared with IPSA-based dose optimization. Homogeneity was good with the IPSA-based technique as compared with the volume-based dose optimization technique. Volume-based optimization resulted in a higher CI (with a mean value of 0.87) compared with the IPSA-based optimization (with a mean value of 0.76). ODI and DNR are better for the IPSA-based plan as compared with the volume-based plan. Mean doses to the bladder, rectum, and sigmoid colon were least with IPSA. IPSA also spared the critical organs but with considerable target conformity as compared with the volume-based plan. IPSA significantly reduces overall treatment planning time with improved reduced doses to the organs at risk compared with the volume-based optimization treatment planning method.

Treatment planning methods in high dose rate interstitial brachytherapy of carcinoma cervix: a dosimetric and radiobiological analysis

Treatment planning is a trial and error process that determines optimal dwell times, dose distribution, and loading pattern for high dose rate brachytherapy. Planning systems offer a number of dose calculation methods to either normalize or optimize the radiation dose. Each method has its own characteristics for achieving therapeutic dose to mitigate cancer growth without harming contiguous normal tissues. Our aim is to propose the best suited method for planning interstitial brachytherapy. 40 cervical cancer patients were randomly selected and 5 planning methods were iterated. Graphical optimization was compared with implant geometry and dose point normalization/optimization techniques using dosimetrical and radiobiological plan quality indices retrospectively. Mean tumor control probability was similar in all the methods with no statistical significance. Mean normal tissue complication probability for bladder and rectum is 0.3252 and 0.3126 (P = 0.0001), respectively, in graphical optimized plans compared to other methods. There was no significant correlation found between Conformity Index and tumor control probability when the plans were ranked according to Pearson product moment method (r = −0.120). Graphical optimization can result in maximum sparing of normal tissues.

Head and neck (192)Ir HDR-brachytherapy dosimetry using a grid-based Boltzmann solver

Purpose

To compare dosimetry for head and neck cancer patients, calculated with TG-43 formalism and a commercially available grid-based Boltzmann solver.

Material and methods

This study included 3D-dosimetry of 49 consecutive brachytherapy head and neck cancer patients, computed by a grid-based Boltzmann solver that takes into account tissue inhomogeneities as well as TG-43 formalism. 3D-treatment planning was carried out by using computed tomography.

Results

Dosimetric indices D₉₀ and V₁₀₀ for target volume were about 3% lower (median value) for the grid-based Boltzmann solver relative to TG-43-based computation (p < 0.01). The V₁₅₀ dose parameter showed 1.6% increase from grid-based Boltzmann solver to TG-43 (p < 0.01).

Conclusions

Dose differences between results of a grid-based Boltzmann solver and TG-43 formalism for high-dose-rate head and neck brachytherapy patients to the target volume were found. Distinctions in D₉₀ of CTV were low (2.63 Gy for grid-based Boltzmann solver vs. 2.71 Gy TG-43 in mean). In our clinical practice, prescription doses remain unchanged for high-dose-rate head and neck brachytherapy for the time being.

Dosimetric comparison of optimization methods for multichannel intracavitary brachytherapy for superficial vaginal tumors

PURPOSE

Multichannel vaginal applicators allow treatment of a more conformal volume compared with a single, central vaginal channel. There are several optimization methods available for use with multichannel applicators, but no previous comparison of these has been performed in the treatment of superficial vaginal tumors. Accordingly, a feasibility study was completed to compare inverse planning by simulated annealing (IPSA), dose point optimization (DPO), and graphical optimization for high-dose-rate brachytherapy using a multichannel, intracavitary vaginal cylinder.

METHODS AND MATERIALS

This comparative study used CT data sets from five patients with superficial vaginal recurrences of endometrial cancer treated with multichannel intracavitary high-dose-rate brachytherapy. Treatment plans were generated using DPO, graphical optimization, surface optimization with IPSA (surf IPSA), and two plans using volume optimization with IPSA. The plans were evaluated for target coverage, conformal index, dose homogeneity index, and dose to organs at risk.

RESULTS

Best target coverage was achieved by volume optimization with IPSA 2 and surf IPSA with mean V100 values of 93.89% and 91.87%, respectively. Doses for the most exposed 2-cm(3) of the bladder (bladder D2cc) was within tolerance for all optimization methods. Rectal D2cc was above tolerance for one DPO plan. All volume optimization with IPSA plans resulted in higher vaginal mucosa doses for all patients. Greatest homogeneity within the target volume was seen with surf IPSA and DPO. Highest conformal indices were seen with surf IPSA and graphical optimization.

CONCLUSIONS

Optimization with surf IPSA was user friendly for the generation of treatment plans and achieved good target coverage, conformity, and homogeneity with acceptable doses to organs at risk.

Dosimetric analysis of radiation therapy oncology group 0321: the importance of urethral dose

PURPOSE

Radiation Therapy Oncology Group 0321 is the first multi-institutional cooperative group high-dose-rate (HDR) prostate brachytherapy trial with complete digital brachytherapy dosimetry data. This is a descriptive report of the data and an analysis of toxicity.

METHODS AND MATERIALS

Patients are treated with external beam radiation therapy at 45 Gy and 1 HDR implant with 19 Gy in 2 fractions. Implants are done with transrectal ultrasound guidance, and computed tomography (CT)-compatible nonmetallic catheters. HDR planning is done on ≤3-mm-thick CT slices. The "mean DVH" (dose-volume histogram) of the planning target volume (PTV), implanted volume (IP), and organs at risk are calculated. This includes the mean and standard deviation (SD) of the volume at 10-percentage-point intervals from 10% to 200% of the prescribed dose. The conformal index (COIN), homogeneity index (HI), catheters per implant, and patients per institution are calculated. Multivariate analysis and hazard ratios calculation of all the variables against reported grade ≥2 (G2+) genitourinary (GU) adverse events (Common Terminology Criteria for Adverse Events, version 3) are performed.

RESULTS

Dosimetry data are based on 122 eligible patients from 14 institutions. The mean of PTV, IP, catheters per implant, and patients per institution are 54 cc, 63 cc, 19 and 9, respectively. The mean of %V100PTV, V80Bladder, V80Rectum, and V120Urethra were 94%, 0.40 cc, 0.15 cc, and 0.25 cc, respectively. There are too few G2+ gastrointestinal adverse event (GI AE) for correlative analysis; thus, the analysis has been performed on the more common G2+ GU AE. There are positive correlations noted between both acute and late G2+ GU AE and urethral dose at multiple levels. Positive correlations with late AE are seen with PTV and IP at high-dose levels. A negative correlation is seen between HI and acute AE. A higher patient accrual rate is associated with a lower rate of G2+ acute and late AE.

CONCLUSIONS

Higher urethral dose, larger high-dose volumes, and lower dose homogeneity are associated with greater toxicities. A mean dose-volume histogram comparison at all dose levels should be used for quality control and future research comparison.

Accelerated partial breast irradiation using external beam radiotherapy-A feasibility study based on dosimetric analysis

AIM

To investigate the feasibility of using External Beam radiotherapy for accelerated partial breast irradiation by a comparative tumour and normal tissue dose volume analysis with that of high dose rate interstitial brachytherapy.

BACKGROUND

Accelerated Partial Breast Irradiation (APBI) is more clinically appealing because of the reduced treatment course duration and the irradiated area. Brachytherapy application is more dependent on the clinician's expertise when it is practised free hand without image guidance and a template. It happens to be an invasive procedure with the use of local anaesthesia which adds patient discomfort apart from its cost compared to External Beam Radiotherapy. But APBI with brachytherapy is more commonly practised procedure compared to EBRT owing to its previous reults. Hence in this research study, we intend to explore the use of EBRT with the radiobiological corrections for APBI in the place of brachytherapy. It is done as a dosimetric comparison of Brachytherapy treatment plans with that of EBRT plans.

MATERIALS AND METHODS

The computed tomography images of 15 patients undergoing ISBT planning were simulated with conformal photon fields. Various dose volume parameters of each structure were obtained from the DVH generated in the brachytherapy and the simulated external beam planning which can correlate well with the late toxicity. The plan quality indices such as conformity index and homogeneity index for the target volume were computed from the dosimetric factors. The statistical p values for CI, HI and normal tissue dosimetric parameters were calculated and the confidence levels achievable were analysed. The dose prescribed in brachytherapy was 3400cGy in ten fractions. The equivalent prescription dose for the external beam radiotherapy planning was 3000cGy in five fractions applied with radiobiological correction.

RESULTS

All the fifteen patients were with complete lung data and six were with left sided tumours having complete cardiac data. The lung dosimetry data and the cardiac dosimetry data of the patients were studied. Lower percentages of lung and cardiac V 20 and V 5 volumes were obtained with conformal planning. The conformity of radiation dose to the tumour volume was akin to the interstitial brachytherapy planning. Moreover the external beam planning resulted in more homogenous dose distribution. For the sampled population, the statistical analysis showed a confidence level of 95% for using EBRT as an alternate to multi catheter ISBT.

CONCLUSION

The EBRT planning for Accelerated Partial Breast Irradiation was found to be technically feasible in the institution where the interstitial brachytherapy happens to be the only available technique as evident from the dose volume parameters and the statistical analysis.

Consequences of dose heterogeneity on the biological efficiency of ¹⁰³Pd permanent breast seed implants

Brachytherapy is associated with highly heterogeneous spatial dose distributions. This heterogeneity is usually ignored when estimating the biological effective dose (BED). In addition, the heterogeneities of the medium including the tissue heterogeneity (TH) and the interseed attenuation (ISA) are also contributing to the heterogeneity of the dose distribution, but they are both ignored in Task Group 43 (TG43)-based protocols. This study investigates the effect of dose heterogeneity, TH and ISA on metrics that are commonly used to quantify biological efficiency in brachytherapy. The special case of 29 breast cancer patients treated with permanent (103)Pd seed implant is considered here. BED is compared to equivalent uniform BED (EUBED) capable of considering the spatial heterogeneity of the dose distribution. The effects of TH and ISA on biological efficiency of treatments are taken into account by comparing TG43 with Monte Carlo (MC) dose calculations for each patient. The effect of clonogenic repopulation is also considered. The analysis is performed for different sets of (α/β, α) ratios of (2, 0.3), (4, 0.27) and (10, 0.3) [Gy, Gy(-1)] covering the whole range of reported α/β values in the literature. BED is sometimes larger and sometimes smaller than EUBED(TG43) indicating that the effect of the dose heterogeneity is not similar among patients. The effect of the dose heterogeneity can be characterized by using the D(99) dose metric. For each set of the radiobiological parameters considered, a D(99) threshold is found over which dose heterogeneity will cause an overestimation of the biological efficiencies while the inverse happens for smaller D(99) values. EUBED(MC) is always larger than EUBED(TG43) indicating that by neglecting TH and ISA in TG43-based dosimetry algorithms, the biological efficiencies may be underestimated by about 10 Gy. Overall, by going from BED to the more accurate EUBED(MC) there is a gain of about 9.6 to 13 Gy on the biological efficiency. The efficiency gain is about 10.8 to 14 Gy when the repopulation is considered. Dose heterogeneity does not have a constant impact on the biological efficiencies and may under- or overestimate the efficacy in different patients. However, the combined effect of neglecting dose heterogeneity, TH and ISA results in underestimation of the biological efficiencies in permanent breast seed implants.

Assessment of dose homogeneity in conformal interstitial breast brachytherapy with special respect to ICRU recommendations

Purpose

To present the results of dose homogeneity analysis for breast cancer patients treated with image-based conformal interstitial brachytherapy, and to investigate the usefulness of the ICRU recommendations.

Material and methods

Treatment plans of forty-nine patients who underwent partial breast irradiation with interstitial brachytherapy were analyzed. Quantitative parameters were used to characterize dose homogeneity. Dose non-uniformity ratio (DNR), dose homogeneity index (DHI), uniformity index (UI) and quality index (QI) were calculated. Furthermore, parameters recommended by the ICRU 58 such as minimum target dose (MTD), mean central dose (MCD), high dose volume, low dose volume and the spread between local minimum doses were determined. Correlations between the calculated homogeneity parameters and usefulness of the ICRU parameters in image-based brachytherapy were investigated.

Results

Catheters with mean number of 15 (range: 6-25) were implanted in median 4 (range: 3-6) planes. The volume of the PTV ranged from 15.5 cm³ to 176 cm³. The mean DNR was 0.32, the DHI 0.66, the UI 1.49 and the QI 1.94. Related to the prescribed dose, the MTD was 69% and the MCD 135%. The mean high dose volume was 8.1 cm³ (10%), while the low dose volume was 63.8 cm³ (96%). The spread between minimum doses in central plane ranged from −14% to +20%. Good correlation was found between the DNR and the DHI (R²=0.7874), and the DNR correlated well with the UI (R²=0.7615) also. No correlation was found between the ICRU parameters and any other volumetric parameters.

Conclusions

To characterize the dose uniformity in high-dose rate breast implants, DVH-related homogeneity parameters representing the full 3D dose distributions are mandatory to be used. In many respects the current recommendations of the ICRU Report 58 are already outdated, and it is well-timed to set up new recommendations, which are more feasible for image-guided conformal interstitial brachytherapy.

Quality assessment of interstitial implants in high- dose- rate brachytherapy after lumpectomy in patients of early stage breast cancer

To assess the quality of high dose rate (H,D,R.) interstitial implants in breast cancer by using different volumetric indices and correlating them with skin and subcutaneous tissue toxicity. Out of 15 patients who were selected for interstitial implants after undergoing breast conservation surgery, five were treated radically with 34 Gy in 10 fractions in 5 days @ 3.4 Gy # twice daily and 10 patients recieved boost dose of 12 Gy in 4 fractions @ 3 Gy /# twice daily. The median follow up was 15 months. During each follow up assessment of late skin and subcutaneous tissue toxicity as per RTOG criteria was done . Various dosimetric indices were analysed. Dose Volume Histogram for dose per unit volume of skin for 10cc,5cc,2cc,1cc,0.1cc and 0.01cc was calculated. Best estimates and correlation of toxicity was revealed by assessment of Dose Nonuniformity Ratio(DNR) which also correlated well with geometry defining indices like Uniformity Index (UI).Volumetric assessment of skin dose for less than 2 cc correlated most with toxicity. DNR and UI can help us to assess and correlate late skin and subcutaneous tissue toxicity and thus serve useful to determine the quality of implant.

Three dimensional intensity modulated brachytherapy (IMBT): dosimetry algorithm and inverse treatment planning

PURPOSE

The feasibility of intensity modulated brachytherapy (IMBT) to improve dose conformity for irregularly shaped targets has been previously investigated by researchers by means of using partially shielded sources. However, partial shielding does not fully explore the potential of IMBT. The goal of this study is to introduce the concept of three dimensional (3D) intensity modulated brachytherapy and solve two fundamental issues regarding the application of 3D IMBT treatment planning: The dose calculation algorithm and the inverse treatment planning method.

METHODS

A 3D IMBT treatment planning system prototype was developed using the MATLAB platform. This system consists of three major components: (1) A comprehensive IMBT source calibration method with dosimetric inputs from Monte Carlo (EGSnrc) simulations; (2) a "modified TG-43" (mTG-43) dose calculation formalism for IMBT dosimetry; and (3) a physical constraint based inverse IMBT treatment planning platform utilizing a simulated annealing optimization algorithm. The model S700 Axxent electronic brachytherapy source developed by Xoft, Inc. (Fremont, CA), was simulated in this application. Ten intracavitary accelerated partial breast irradiation (APBI) cases were studied. For each case, an "isotropic plan" with only optimized source dwell time and a fully optimized IMBT plan were generated and compared to the original plan in various dosimetric aspects, such as the plan quality, planning, and delivery time. The issue of the mechanical complexity of the IMBT applicator is not addressed in this study.

RESULTS

IMBT approaches showed superior plan quality compared to the original plans and tht isotropic plans to different extents in all studied cases. An extremely difficult case with a small breast and a small distance to the ribs and skin, the IMBT plan minimized the high dose volume V200 by 16.1% and 4.8%, respectively, compared to the original and the isotropic plans. The conformity index for the target was increased by 0.13 and 0.04, respectively. The maximum dose to the skin was reduced by 56 and 28 cGy, respectively, per fraction. Also, the maximum dose to the ribs was reduced by 104 and 96 cGy, respectively, per fraction. The mean dose to the ipsilateral and contralateral breasts and lungs were also slightly reduced by the IMBT plan. The limitations of IMBT are the longer planning and delivery time. The IMBT plan took around 2 h to optimize, while the isotropic plan optimization could reach the global minimum within 5 min. The delivery time for the IMBT plan is typically four to six times longer than the corresponding isotropic plan.

CONCLUSIONS

In this study, a dosimetry method for IMBT sources was proposed and an inverse treatment planning system prototype for IMBT was developed. The improvement of plan quality by 3D IMBT was demonstrated using ten APBI case studies. Faster computers and higher output of the source can further reduce plan optimization and delivery time, respectively.

Dosimetric comparison of various optimization techniques for high dose rate brachytherapy of interstitial cervix implants

HDR brachytherapy treatment planning often involves optimization methods to calculate the dwell times and dwell positions of the radioactive source along specified afterloading catheters. The purpose of this study is to compare the dose distribution obtained with geometric optimization (GO) and volume optimization (VO) combined with isodose reshaping. This is a retrospective study of 10 cervix HDR interstitial brachytherapy implants planned using geometric optimization and treated with a dose of 6 Gy per fraction. Four treatment optimization plans were compared: geometric optimization (GO), volume optimization (VO), geometric optimization followed by isodose reshape (GO_IsoR), and volume optimization followed by isodose reshape (VO_IsoR). Dose volume histogram (DVH) was analyzed and the four plans were evaluated based on the dosimetric parameters: target coverage (V100), conformal index (COIN), homogeneity index (HI), dose nonuniformity ratio (DNR) and natural dose ratio (NDR). Good target coverage by the prescription dose was achieved with GO_IsoR (mean V100 of 88.11%), with 150% and 200% of the target volume receiving 32.0% and 10.4% of prescription dose, respectively. Slightly lower target coverage was achieved with VO_IsoR plans (mean V100 of 86.11%) with a significant reduction in the tumor volume receiving high dose (mean V150 of 28.29% and mean V200 of 7.3%). Conformity and homogeneity were good with VO_IsoR (mean COIN=0.75 and mean HI=0.58) as compared to the other optimization techniques. VO_IsoR plans are superior in sparing the normal structures while also providing better conformity and homogeneity to the target. Clinically acceptable plans can be obtained by isodose reshaping provided the isodose lines are dragged carefully.

PACS number: 87.53 Bn

Dose volume uniformity index: a simple tool for treatment plan evaluation in brachytherapy

Purpose

In radiotherapy treatment planning, dose homogeneity inside the target volume plays a significant role in the final treatment outcome. Especially in brachytherapy where there is a steep dose gradient in the dose distribution inside the target volume, comparing the plans based on the dose homogeneity helps in assessing the high dose volume inside the final treatment plan. In brachytherapy, the dose inhomogeneity inside the target volume depends on many factors such as the type of sources, placement of these radioactive sources, distance between the applicators/implant tubes, dwell time of the source, etc. In this study, a simple index, the dose volume uniformity index (DVUI), has been proposed to study the dose homogeneity inside the target volume. This index gives the total dose volume inhomogeneity inside a given prescription isoline.

Material and methods

To demonstrate the proposed DVUI in this study, a single plane implant (breast: 6 catheters), a double plane implant (breast: 9 catheters) and a tongue implant (5 catheters) were selected. The catheters were reconstructed from the CT image datasets in the Plato treatment planning system. The doses for the single, double and tongue implants were prescribed to the reference dose rate as per the Paris technique. DVUI was computed from the cumulative dose volume histogram.

Results

For a volume receiving a uniform dose inside the prescription isoline, the DVUI is 1. Any value of DVUI > 1 shows the presence of a relatively high dose volume inside the prescription isoline. In addition to the concept of DVUI, a simple conformality index, the dose volume conformality index (DVCI), has also been proposed in this study based on the DVUI.

Conclusion

The DVUI and the proposed DVCI in this study provide an easy way of comparing the rival plans in brachytherapy.

Accelerated Partial Breast Irradiation: Potential Roles following Breast-Conserving Surgery

Background

Multiple randomized trials comparing mastectomy to lumpectomy and whole breast irradiation (WBI) have shown equivalent survival outcomes in early-stage breast cancer. WBI requires a treatment course of several weeks, which has resulted in limited access to breast-conserving therapy in certain populations. A shorter accelerated course of partial breast irradiation (APBI) has been investigated recently.

Methods

This article reviews the current medical literature, including randomized trials and prospective institutional studies of APBI and the current recommendations regarding the use of this emerging technique.

Results

Several APBI techniques have been developed, including brachytherapy and external beam methods. The longest follow-up data are available for multicatheter interstitial brachytherapy, a technique that is not commonly used. Other methods, including balloon brachytherapy and external beam three-dimensional conformal techniques, have limited follow-up that shows similar local control rates to whole breast irradiation in highly selected patients. Guidelines for the appropriate use of APBI have been published.

Conclusions

While APBI may increase access to breast conservation therapy for some women with early-stage breast cancer, follow-up data demonstrating the efficacy of this relatively new treatment approach are limited. Therefore, strict evidence-based selection criteria should be applied when evaluating patients who may be appropriate for APBI.

Comparison of single and multiple dwell position methods in MammoSite high dose rate (HDR) brachytherapy planning

The purpose of this study is to dosimetrically compare two plans generated using single dwell position method (SDPM) and multiple dwell position methods (MDPM) in MammoSite high dose rate (HDR) brachytherapy planning for 19 breast cancer patients. In computed tomography (CT) image-based HDR planning, a surface optimization technique was used in both methods. Following dosimetric parameters were compared for fraction 1 plans: %PTV_EVAL (planning target volume for plan evaluation) coverage, dose homogeneity index (DHI), dose con-formal index (COIN), maximum dose to skin and ipsilateral lung, and breast tissue volume receiving 150% (V150[cc]) and 200% (V200[cc]) of the prescribed dose. In addition, a plan was retrospectively generated for each fraction 2-10 to simulate the clinical situation where the fraction 1 plan was used for fractions 2-10 without modification. In order to create nine derived plans for each method and for each of the 19 patients, the catheter location and contours of target and critical structures were defined on the CT images acquired prior to each fraction 2-10, while using the same dwell-time distribution as used for fraction 1 (original plan). Interfraction dose variations were evaluated for 19 patients by comparing the derived nine plans (each for fractions 2-10) with the original plan (fraction 1) using the same dosimetric parameters used for fraction 1 plan comparison. For the fraction 1 plan comparison, the MDPM resulted in slightly increased %PTV_EVAL coverage, COIN, V150[cc] and V200[cc] values by an average of 1.2%, 0.025, 0.5 cc and 0.7cc, respectively, while slightly decreased DHI, maximum skin and ipsilateral lung dose by an average of 0.003, 3.2 cGy and 5.8 cGy, respectively. For the inter-fraction dose variation comparison, the SDPM resulted in slightly smaller variations in %PTV_EVAL coverage, DHI, maximum skin dose and V150[cc] values by an average of 0.4%, 0.0005, 0.5 cGy and 0.2 cc, respectively, while slightly higher average variations in COIN, maximum ipsilateral lung dose and V200[cc] values by 0.0028, 0.2 cGy and 0.2 cc, respectively. All differences were too small to be clinically significant. Compared to the MDPM, the SDPM combined with a surface optimization technique can generate a clinically comparable fraction 1 treatment plan with a similar interfraction dose variation if a single source is carefully positioned at the center of the balloon catheter.

Anatomy-based inverse planning simulated annealing optimization in high-dose-rate prostate brachytherapy: significant dosimetric advantage over other optimization techniques

PURPOSE

To perform an independent validation of an anatomy-based inverse planning simulated annealing (IPSA) algorithm in obtaining superior target coverage and reducing the dose to the organs at risk.

METHOD AND MATERIALS

In a recent prostate high-dose-rate brachytherapy protocol study by the Radiation Therapy Oncology Group (0321), our institution treated 20 patients between June 1, 2005 and November 30, 2006. These patients had received a high-dose-rate boost dose of 19 Gy to the prostate, in addition to an external beam radiotherapy dose of 45 Gy with intensity-modulated radiotherapy. Three-dimensional dosimetry was obtained for the following optimization schemes in the Plato Brachytherapy Planning System, version 14.3.2, using the same dose constraints for all the patients treated during this period: anatomy-based IPSA optimization, geometric optimization, and dose point optimization. Dose-volume histograms were generated for the planning target volume and organs at risk for each optimization method, from which the volume receiving at least 75% of the dose (V(75%)) for the rectum and bladder, volume receiving at least 125% of the dose (V(125%)) for the urethra, and total volume receiving the reference dose (V(100%)) and volume receiving 150% of the dose (V(150%)) for the planning target volume were determined. The dose homogeneity index and conformal index for the planning target volume for each optimization technique were compared.

RESULTS

Despite suboptimal needle position in some implants, the IPSA algorithm was able to comply with the tight Radiation Therapy Oncology Group dose constraints for 90% of the patients in this study. In contrast, the compliance was only 30% for dose point optimization and only 5% for geometric optimization.

CONCLUSIONS

Anatomy-based IPSA optimization proved to be the superior technique and also the fastest for reducing the dose to the organs at risk without compromising the target coverage.