Comparison of the IPSA and HIPO algorithms for interstitial tongue high-dose-rate brachytherapy

Inverse planning optimization with lead block effectively suppresses dose to the mandible in high-dose-rate brachytherapy for tongue cancer

PURPOSE

In this study, we developed in-house software to evaluate the effect of the lead block (LB)-inserted spacer on the mandibular dose in interstitial brachytherapy (ISBT) for tongue cancer. In addition, an inverse planning algorithm for LB attenuation was developed, and its performance in mandibular dose reduction was evaluated.

METHODS

Treatment plans of 30 patients with tongue cancer treated with ISBT were evaluated. The prescribed dose was 54 Gy/9 fractions. An in-house software was developed to calculate the dose distribution based on the American Association of Physicists in Medicine (AAPM) Task Group No.43 (TG-43) formalism. The mandibular dose was calculated with consideration of the LB attenuation. The attenuation coefficient of the lead was computed using the PHITS Monte Carlo simulation. The software further optimized the treatment plans using an attraction-repulsion model (ARM) to account for the LB attenuation.

RESULTS

Compared to the calculation in water, the D2 cc of the mandible changed by - 2.4 ± 2.3 Gy (range, - 8.6 to - 0.1 Gy) when the LB attenuation was considered. The ARM optimization with consideration of the LB resulted in a - 2.4 ± 2.4 Gy (range, - 8.2 to 0.0 Gy) change in mandibular D2 cc.

CONCLUSIONS

This study enabled the evaluation of the dose distribution with consideration of the LB attenuation. The ARM optimization with lead attenuation further reduced the mandibular dose.

Modern Tools for Modern Brachytherapy

This review aims to showcase the brachytherapy tools and technologies that have emerged during the last 10 years. Soft-tissue contrast using magnetic resonance and ultrasound imaging has seen enormous growth in use to plan all forms of brachytherapy. The era of image-guided brachytherapy has encouraged the development of advanced applicators and given rise to the growth of individualised 3D printing to achieve reproducible and predictable implants. These advances increase the quality of implants to better direct radiation to target volumes while sparing normal tissue. Applicator reconstruction has moved beyond manual digitising, to drag and drop of three-dimensional applicator models with embedded pre-defined source pathways, ready for auto-recognition and automation. The simplified TG-43 dose calculation formalism directly linked to reference air kerma rate of high-energy sources in the medium water remains clinically robust. Model-based dose calculation algorithms accounting for tissue heterogeneity and applicator material will advance the field of brachytherapy dosimetry to become more clinically accurate. Improved dose-optimising toolkits contribute to the real-time and adaptive planning portfolio that harmonises and expedites the entire image-guided brachytherapy process. Traditional planning strategies remain relevant to validate emerging technologies and should continue to be incorporated in practice, particularly for cervical cancer. Overall, technological developments need commissioning and validation to make the best use of the advanced features by understanding their strengths and limitations. Brachytherapy has become high-tech and modern by respecting tradition and remaining accessible to all.

Dose optimization comparison study of inverse planning simulated annealing [IPSA] and hybrid inverse planning optimization [HIPO] in interstitial brachytherapy of head and neck cancer

PURPOSE

This study was a retrospective dose optimization comparison of two commercially available inverse planning algorithms, the inverse planning simulated annealing (IPSA) and hybrid inverse planning optimization (HIPO) for head and neck cancer interstitial brachytherapy.

MATERIALS AND METHODS

Seven patients with head and neck cancer were selected (4 with tongue cancer, 2 with buccal mucosa cancer and 1 with carcinoma lip) who were previously treated with interstitial brachytherapy using a flexible nylon tube catheter and graphical optimization/geometric optimization technique. All seven patients were retrospectively re-planned using both IPSA as well as HIPO algorithms available in the Oncentra Brachytherapy Treatment Planning System (TPS) version V4.5.3.30. The dosimetric parameters [PTV-V₁₀₀, V₁₅₀, V₂₀₀, D₉₀; mandible-D2cc, parotid-D2cc, conformity index (CI), dose homogeneity index (HI), overdose volume index (ODI)] were chosen for evaluation in compliance with the objective function and organ at risk dose constraints.

RESULTS

Using the paired sample T test in chosen parameters (PTV-V₁₀₀, V₁₅₀, V₂₀₀, D₉₀; mandible-D2cc, CI, HI, ODI both the inverse planning algorithms), it was found that IPSA and HIPO were comparable.

CONCLUSIONS

Even though both IPSA and HIPO are largely comparable in most of the dosimetric parameters for inverse planning in brachytherapy of head and neck cancers, differences in the algorithms can be exploited to improve certain parameters in specific situations such as D2cc parotid.

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.

Does inverse planning improve plan quality in interstitial high-dose-rate breast brachytherapy?

Purpose

To investigate the effect of input parameters for an inverse optimization algorithm, and dosimetrically evaluate and compare clinical treatment plans made by inverse and forward planning in high-dose-rate interstitial breast implants.

Material and methods

By using a representative breast implant, input parameters responsible for target coverage and dose homogeneity were changed step-by-step, and their optimal values were determined. Then, effects of parameters on dosimetry of normal tissue and organs at risk were investigated. The role of dwell time modulation restriction was also studied. With optimal input parameters, treatment plans of forty-two patients were re-calculated using an inverse optimization algorithm (HIPO). Then, a pair-wise comparison between forward and inverse plans was performed using dose-volume parameters.

Results

To find a compromise between target coverage and dose homogeneity, we recommend using weight factors in the range of 70-90 for minimum dose, and in the range of 10-30 for maximum dose. Maximum dose value of 120% with a weight factor of 5 is recommended for normal tissue. Dose constraints for organs at risk did not play an important role, and the dwell time gradient restriction had only minor effect on target dosimetry. In clinical treatment plans, at identical target coverage, the inverse planning significantly increased the dose conformality (COIN, 0.75 vs. 0.69, p < 0.0001) and improved the homogeneity (DNR, 0.35 vs. 0.39, p = 0.0027), as compared to forward planning. All dosimetric parameters for non-target breast, ipsilateral lung, ribs, and heart were significantly better with inverse planning. The most exposed small volumes for skin were less in HIPO plans, but without statistical significance. Volume irradiated by 5% was 173.5 cm³ in forward and 167.7 cm³ in inverse plans (p = 0.0247).

Conclusions

By using appropriate input parameters, inverse planning can provide dosimetrically superior dose distributions over forward planning in interstitial breast implants.

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.

A 3D-printed patient-specific applicator guide for use in high-dose-rate interstitial brachytherapy for tongue cancer: a phantom study

A patient-specific applicator guide system (PSAG) for tongue-cancer high-dose-rate (HDR) interstitial brachytherapy (ISBT) was developed by utilizing a 3D printing technique. An effectiveness of the 3D-printed PSAG (3D-PSAG) was evaluated for HDR ISBT. Six patients with tongue cancer were retrospectively selected for this study. For each patient, a total of three virtual clinical target volumes (CTV) requiring the insertion of four catheters (CTV4), six catheters (CTV6), and eight catheters (CTV8) were defined. For each CTV, treatment plans were generated to deliver 45 Gy in nine fractions. The 3D-PSAG was fabricated using a 3D-printer and the patient's CT-images. The resulting 3D-PSAG took the form of a shell conforming to the patient's contours with tubes for catheter insertion. For each CTV, catheters were inserted into the phantom with and without the 3D-PSAG. After that, CT-images of the phantom with the inserted catheters were acquired. Differences between the planned positions and those of the actually inserted catheters were evaluated from the CT-images. Given the actual catheter insertion positions, the dose distributions were reconstructed and analyzed. The maximum positional errors with and without the 3D-PSAG were 0.2 mm and 4.5 mm, respectively. For CTV6, the D _90% values of the original plan, the reconstructed plan with the 3D-PSAG, and the reconstructed plan without the 3D-PSAG, were 48.8  ±  1.7 Gy, 49.0  ±  2.9 Gy, and 45.6  ±  3.3 Gy, respectively. The D _1cc values for the mandible were 51.3  ±  9.2 Gy, 61.6  ±  8.3 Gy, and 81.1  ±  16.7 Gy, respectively. The dose homogeneities in the CTVs into which the catheters had been inserted with the 3D-PSAG were always superior to those into which the catheters had been inserted without the 3D-PSAG. The present phantom study demonstrated the feasibility of more accurate interstitial tongue brachytherapy while simplifying the treatment process by utilizing the 3D-PSAG.