Dosimetry procedure to verify dose in High Dose Rate (HDR) brachytherapy treatment of cancer patients: A systematic review

Overview of treatment plan quality in a high dose rate prostate brachytherapy workflow

PURPOSE

High dose rate brachytherapy (HDR-BT) has been shown to be an effective treatment for prostate cancer, with treatment plan quality dependent on a number of factors. In this work, we report on the overall performance of our ultrasound (US)-based workflow and the impact of several treatment-specific variables.

METHODS AND MATERIALS

Patients who underwent HDR-BT (boost, monotherapy, and retreatment) using Varian Bravos/US from 2021 to 2023 were sampled for this study. Treatment plan quality was analyzed and plans were categorized with regard to a number of metrics, including: prostate volume, treating physician, planning physicist, number of needles included, estimated planning time, rectum-prostate separation, and bladder-prostate separation. The performance of this program was compared to the performance of our program using previously used modality combinations: Varian Varisource/US, Elekta microSelectron/CT.

RESULTS

Plan quality for our Bravos/US workflow was shown to be consistently above acceptability criteria for all personnel involved; on average: prostate V100%: 98.9% ± 0.1%, rectum V75%: 0.04 ± 0.01 cc, bladder V75%: 0.06 ± 0.01cc, urethra V125%: 0.00 ± 0.00 cc. Prostate coverage was statistically improved with this workflow compared to that using our previous modalities. There was a statistical correlation between organ-at-risk sparing/prostate coverage ratio and prostate volume, number of needles/prostate volume, bladder-prostate separation, and rectum-prostate separation. There was no correlation between plan quality and planning time.

CONCLUSIONS

Our US-based HDR-BT program led to target coverage and organ-at-risk sparing that exceeded department thresholds. Results were acceptable regardless of the personnel involved and improved plan quality was obtained using more needles/prostate volume and increased spacing between the prostate and the rectum and bladder.

Intercomparison and constancy check of brachytherapy well-type chambers as a means to improve the quality of measurements in Serbia

Source strength measurements are of critical importance for brachytherapy and are often performed in hospitals using well-type chambers. Quality assurance and quality control procedures should be implemented, but that may prove difficult in some hospitals due to the lack of equipment or metrological support. A study was conducted to investigate the status of the measurement equipment in Serbian hospitals and to organize an intercomparison campaign using a hospital 192Ir source. All the hospitals were able to measure the source strength with the required accuracy, but the quality assurance can be improved. Two hospitals performed stability checks, which were evaluated. Uncertainty budget was created during the exercise and is presented in this paper. The described methodology can be used to quickly assess the performance of brachytherapy centers, and can be easily adapted to calibration procedure.

High-dose rate endorectal brachytherapy for rectal cancer: A state-of-the-art review

Rectal cancer is a common malignancy that requires multidisciplinary treatment. By utilizing the dose-response relationship in rectal cancer radiotherapy, increasing the radiotherapy dose can improve clinical complete remission rates. High-dose rate endorectal brachytherapy (HDREBT) is a novel technique that delivers high doses of radiotherapy directly to the tumor via an endorectal applicator, sparing the adjacent normal tissues from excessive radiation exposure. HDREBT includes contact X-ray brachytherapy and high-dose-rate intracavitary brachytherapy. We introduce the latest developments in applicators and imaging techniques for HDREBT in rectal cancer and summarize the current evidence on the efficacy, safety, and feasibility of HDREBT as a neoadjuvant, definitive, or palliative treatment option for all stages of rectal cancer patients. We also discuss the potential advantages and challenges of HDREBT in achieving organ preservation and improving the quality of life of rectal cancer patients. HDREBT has shown promising results in achieving high complete response rates, enabling nonoperative management, improving organ preservation rates, and providing effective palliation in rectal cancer patients. More studies are needed to optimize its dose and fractionation schemes in different clinical scenarios.

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.

Quality assurance of six cylindrical and two parallel plate chambers by radioactive check device: Influence of chamber age to its performance

PURPOSE

To evaluate the performances of eight ionization chambers, (two types) manufactured in a time span of 14 years, with radioactive source devices and photon beams.

METHODS

The measurements were performed with six Farmer and two parallel plate ionization chambers with appropriate radioactive check devices and accompanying inserts. Some tests were performed with photon beams at linear accelerator. Physical visibility check, stability, linearity of response, directional dependence, determination of leakage current, ion recombination and polarity effect and influence of background radiation tests were conducted and analyzed.

RESULTS

The performance of all Farmer ionization chambers was in agreement to IEC standard as well as for parallel plate type chambers. Long-term stability of older planparallel chamber was somewhat worse than expected.

CONCLUSION

Radioactive check devices have proven to be easy to use in clinical environment. According to results of this work Farmer type ionization chambers showed good quality regardless of the time of production, which make them long-term suitable for clinical dosimetry in radiotherapy. Also, for parallel plate type of ionization chambers the results showed fine agreement with the IEC standard, except long-term stability for older chamber, which needs further investigation.