Film based verification of calculation algorithms used for brachytherapy planning-getting ready for upcoming challenges of MBDCA

Quantitative study on dose distribution of Freiburg flap for keloid high-dose-rate brachytherapy based on MatriXX

PURPOSE

To quantify the dose distribution effect of insufficient scattering conditions in keloid HDR brachytherapy with Freiburg fFlap (FF) applicator.

MATERIALS AND METHODS

A phantom composed of FF applicator, MatriXX and solid water slices was designed and scanned for treatment planning. Bolus with different thicknesses were covered to offer different scatter conditions. Planar dose distributions were measured by MatriXX. The maximum value (Max), average value (Avg) and γ passing rate (3 mm/3%) were evaluated by the software MyQA Platform.

RESULTS

The maximum and average doses measured by MatriXX were lower than the calculated values. The difference increased as field size decreased. The Max value, found at 0.86 cm level in the two tube case, was -20.0%, and the avg value was -11.9%. All the γ values were less than 95%. This difference gradually decreased with increasing bolus thickness and the γ values were significantly improved.

CONCLUSION

MatriXX could be used for dose verification of HDR brachytherapy with an FF applicator. When the FF applicator was applied for keloid, insufficient scattering conditions would cause an insufficient target dose. This difference could be reduced by covering the bolus with different thicknesses on the applicator. The smaller the field, the thicker the bolus required.

Advanced dose calculation algorithm in superficial brachytherapy - the impact of tissue inhomogeneity on treatment plan dosimetry

Purpose

Given tissue inhomogeneity and lack of backscatter media, superficial brachytherapy necessitates more accurate dosimetry than TG-43 formalism. However, the introduction of modern model-based dose calculation algorithms into clinical practice should be carefully evaluated. The aim of this work was to compare dose distributions calculated with TG-43 and advanced collapsed cone engine (ACE) algorithms for individual multi-catheter moulds, and investigate the impact of target size and the lack of bolus to differences between plans.

Material and methods

Eleven treatment plans for individual mould multi-catheter high-dose-rate brachytherapy (IMM HDR) were selected for retrospective analysis. All treatment plans were initially calculated with TG-43 formula and re-calculated using ACE algorithm. Plan re-calculation with ACE was repeated for each plan in order to assess the impact of bolus. To evaluate differences between TG-43 and ACE dose distributions, dose-volume histogram (DVH) parameters for each ROI were compared. D_max (maximal point dose), D_0.1cc, and D_2cc were calculated for each risk’s organ (OARs) and for external contour. For clinical target volume (CTV), D₉₈, D₉₀, D₅₀, CTV coverage (CTV-V₁₀₀), and dose delivered to reference point were compared between the plans.

Results

A significantly lower values (p < 0.05) of CTV parameters were observed for treatment plans calculated with ACE algorithm comparing to TG-43. Further analysis showed that differences between CTV-V₁₀₀ for ACE and TG-43 plans depended on CTV volume. Dosimetric parameters for OARs were significantly lower in ACE plans than those of TG-43. Only D_2cc for external and D_0.1cc for both eye lenses in ACE plans were insignificantly different comparing to TG-43 plans.

Conclusions

Results show that differences between dosimetric parameters are statistically significant. However, their clinical relevance is still undetermined. Careful re-evaluation of the clinical results based on long-term research on TG-43 is necessary to safely introduce modern algorithms to clinical practice.

Comprehensive methodology for commissioning modern 3D-image-based treatment planning systems for high dose rate gynaecological brachytherapy: A review

PURPOSE

Correct commissioning of treatment planning systems (TPSs) is important for reducing treatment failure events. There is currently no comprehensive and robust methodology available for TPS commissioning in modern brachytherapy. This review aimed to develop a comprehensive template for commissioning modern 3D-image-based brachytherapy TPSs for high dose rate (HDR) gynaecological applications.

METHODS

The literature relevant to TPS commissioning, including both external beam radiation therapy (EBRT) and brachytherapy, as well as guidelines by the International Atomic Energy Agency (IAEA), the American Association of Physicists in Medicine (AAPM), and the European Society for Radiotherapy and Oncology (ESTRO) were searched, studied and appraised. The applied relevant EBRT TPS commissioning tests were applied to brachytherapy. The developed template aimed to cover all dosimetric and non-dosimetric issues.

RESULTS

The essential commissioning items could be categorized into six parts: geometry, dose calculation, plan evaluation tools, plan optimization, TPS output, and end-to-end verification. The final template consists of 43 items. This paper presents the purpose and role of each test, as well as tolerance limits, to facilitate the use of the template.

CONCLUSION

The information and recommendations available in a collection of publications over many years have been reviewed in order to develop a comprehensive template for commissioning complex modern 3D-image-based brachytherapy TPSs for HDR gynaecological applications. The up-to-date and concise information contained in the template can aid brachytherapy physicists during TPS commissioning as well as devising a regular quality assurance program and allocation of time and resources.

Quality Assurance Procedures based on Dosimetric, Gamma Analysis as a Fast Reliable Tool for Commissioning Brachytherapy Treatment Planning Systems

Background

Fast and easily repeatable methods for commissioning procedures for brachytherapy (BT) treatment planning systems (TPS) are needed. Radiochromic film dosimetry with gamma analysis is widely used in external beam quality assurance (QA) procedures and planar film dosimetry is also increasingly used for verification of the dose distribution in BT applications. Using the gamma analysis method for comparing calculated and measured dose data could be used for commissioning procedures of the newly developed TG-186 and MBDCA calculation algorithms. The aim of this study was dosimetric verification of the calculation algorithm used in TPS when the CT/MRI ring applicator is used.

Materials and methods

Ring applicators with 26 and 30 mm diameters and a 60 mm intra-uterine tube with 60° angle were used for verification. Gafchromic® EBT films were used as dosimetric media. Dose grids, corresponding to each plane (dosimetric film location), were exported from the TPS as a raw data. Gafchromic® films were digitized after irradiation. gamma analysis of the data were performed using the OMNI Pro I’mRT® system, as recommended by the AAPM TG-119 rapport criterion for gamma analysis of 3%, 3 mm and a level of 95%.

Results

For the 26 mm and 30 mm rings, the average gamma ranged, respectively, from 0.1 to 0.44 and from 0.1 to 0.27. In both cases, 99% of the measured points corresponded with the calculated data.

Conclusions

This analysis showed excellent agreement between the dose distribution calculated with the TPS and the doses measured by Gafchromic films. This finding confirms the viability of using film dosimetry in BT.