Dose response of a radiophotoluminescent glass dosimeter for TomoTherapy, CyberKnife, and flattening-filter-free linear accelerator output measurements in dosimetry audit

End-to-end dosimetry audit for three-dimensional image-guided brachytherapy for cervical cancer

BACKGROUND

End-to-end dosimetry audit for brachytherapy is challenging due to the steep dose gradient. However, it is an efficient method to detect unintended errors in actual clinical practice.

PURPOSE

We aimed to develop an on-site end-to-end test phantom for three-dimensional image-guided brachytherapy (IGBT) for cervical cancer.

METHODS

The test phantom we developed consisted of a water tank with an applicator/detector holder. The holder was designed to accommodate the applicator and insert an ionization chamber (PinPoint; PTW, Freiburg, Germany) to measure the dose at point A. Imaging and reconstruction were performed in the same way as performed for a patient. The feasibility of our test phantom was assessed in two different hospitals using tandem and ovoid (made of either metal or carbon) applicators that the hospitals provided.

RESULTS

The measured and calculated doses at point A were compared for each applicator. We observed that the values obtained using metal applicators were consistently lower, on an average by -2.3%, than the calculated values, while those obtained using carbon applicators were comparable to the calculated values. This difference can be attributed to the attenuation of the dose by the metal applicators, resulting in a lower dose at point A. The majority of treatment planning system, including the one used in this study, do not account for the material of applicator.

CONCLUSIONS

An end-to-end test phantom for IGBT was developed, tested, and applied in a dosimetry audit in hospitals and showed favorable results for evaluating the point A dose.

Evaluation of a New Method for CyberKnife Treatment for Central Lung and Mediastinal Tumors by Tracheobronchial Tracking

BACKGROUND

CyberKnife treatment for central lung tumors and mediastinal tumors can be difficult to perform with marker less.

PURPOSE

We aimed to evaluate a novel tracheobronchial-based method (ie, tracheobronchial tracking) for the purpose of minimally invasive CyberKnife treatment for central lung and mediastinal tumors.

METHODS

Five verification plans were created using an in-house phantom. Each plan included five irradiation sessions. The reference plan irradiated and tracked the simulated tumor (using the target tracking volume, TTV). Trachea plans tracked the simulated tracheo-bronchus and irradiated the simulated tumor and included two types of subplans: correlated plans in which the displacement of the simulated tracheobronchial and the simulated tumor were correlated, and non-correlated plans in which these factors were not correlated. Moreover, 15 mm and 25 mm TTVs were evaluated for each plan. The sin waveform and the patient's respiratory waveform were prepared as the respiratory model. Evaluations were performed by calculating the dose difference between the radiophotoluminescent glass dosimeter (RPLD)-generated mean dose values (generated by the treatment planning system, TPS) and the actual absorbed RPLD dose. Statistical analyses were performed to evaluate findings for each plan. Correlation and prediction errors were calculated for each axis of each plan using log files to evaluate tracking accuracy.

RESULTS

Dose differences were statistically significant only in comparisons with the non-correlated plan. When evaluated using the sin waveform, the mean values for correlation and prediction errors in each axis and for all plans were less than 0.6 mm and 0.1 mm, respectively. In the same manner, they were less than 1.1 mm and 0.2 mm when evaluated using the patient's respiratory waveform.

CONCLUSION

Our newly-developed tracheobronchial tracking method would be useful in facilitating minimally invasive CyberKnife treatment in certain cases of central lung and mediastinal tumors.