Applications and benefits of using gradient percentage depth dose instead of percentage depth dose for electron and photon beams in radiotherapy

Introduction: The aim of this study is to analyze the gradient of percentage depth dose for photon and electron beams of LINACs and to simplify the data set. Materials and Methods: Dosimetry measurements were performed in accordance with Technical Reports Series No. 398 IAEA. Results and discussion: The gradient of percentage depth dose was calculated and compared with the available published data. Conclusion: Instead of percentage depth dose for increasing and decreasing parts, the findings suggest using only two numbers for specific gradient of dose, separately. In this way, they can replace the whole set of the percentage depth dose (PDD).

Monitoring beam-quality constancy considering uncertainties associated with ionization chambers in Daily QA3 device

This study evaluates the changes occurring in the X-ray energy of a linear accelerator (LINAC) using a Daily QA3 detector system. This is accomplished by comparing the Daily QA3 results against those obtained using a water phantom. The X-energy levels of a LINAC were monitored over a duration of 1 month using the Daily QA3 system. Moreover, to account for the uncertainty, the reproducibility of the Daily QA3 ionization-chamber results was assessed by performing repeated measurements (12 per day). Subsequently, the energy-monitoring results were compared with the energy-change results calculated using the water-phantom percentage depth dose (PDD) ratio. As observed, the 6- and 10-MV beams experienced average daily energy-level changes of (-0.30 ± 0.32)% and (0.05 ± 0.38)%, respectively, during repeated measurements. The corresponding energy changes equaled (-0.30 ± 0.55)% and (-0.05 ± 0.48)%, respectively, when considering the measurement uncertainty. The Daily QA3 measurements performed at 6 MV demonstrated a variation of (2.15 ± 0.81)% (i.e., up to 3%). Meanwhile, the corresponding measurements performed using a water phantom demonstrated an increase in the PDD ratio from 0.577 to 0.580 (i.e., approximately 0.5%). At 10 MV, the energy variation in the Daily QA3 measurements equaled (-0.41 ± 0.82)% (i.e., within 1.5%), whereas the corresponding water phantom PDD ratio remained constant at 0.626. These results reveal that the Daily QA3 system can be used to monitor small energy changes occurring within radiotherapy machines. This demonstrates its potential for use as a secondary system for monitoring energy changes as part of the daily quality-assurance workflow.

Pemetaan Laju Dosis Radiasi-γ pada Pesawat Teleterapi 60Co

<p class="AbstractEnglish"><strong>Abstact: </strong>Radiotherapy ⁶⁰Co is a method of therapy cancer by radiation γ. Teletherapy ⁶⁰Co at RSUD Dr. Moewardi, the collimator opening area can be adjusted to (10 x 10) cm and the distance between source and surface target (SSD) is 80 cm. γ- radiation emitted by the ⁶⁰Co source will spread from the collimator to the target in a cone shape so that information about the dose rate receive by patient is needed to support the accuracy of the dose in radiotherapy. To support cancer radiotherapy at a certain depth, information is needed about the dose rate at various phantom depth, the average dose rate and the quality of the dose rate distribution. By using an ionization chamber detector placed at various phantom depth and positions, information can be recorded. PDD (percentage depth dose) of radiation with energy 1,3 MeV, the largest value is at a depth of 6,5 cm, at this depth the measured umbra area is (7,8 x 7,8)cm with an average dose rate of 0,6034 Gy/menit. As the depth of measuring instrument increases, the dose rate measured will decrease exponentially, while the umbra are at the phantom depth is relatively constant.</p><p class="AbstrakIndonesia"><strong>Abstrak: </strong>Radioterapi ⁶⁰co merupakan salah satu metode pengobatan kanker dengan cara menembakkan radiasi γ pada sel kanker. Pesawat teleterapi ⁶⁰Co di RSUD Dr. Moewardi, luas bukaan kolimator dapat diatur menjadi (10 x 10) cm dan jarak sumber dengan permukaan target (SSD) adalah 80 cm. Radiasi- γ yang dipancarkan oleh sumber ⁶⁰Co akan menyebar dari kolimator ke target dengan berbentuk konus sehingga informasi tentang laju dosis yang diterima pasien sangat diperlukan untuk mendukung ketepatan dosis dalam radioterapi. Untuk mendukung radioterapi kanker pada kedalaman tertentu, diperlukan informasi tentang laju dosis pada variasi kedalaman <em>phantom</em>, laju dosis rata-rata dan kualitas sebaran laju dosis. Dengan menggunakan detektor <em>ionization chamber </em>yang diletakkan pada berbagai kedalaman dan posisi <em>phantom,</em> informasi dapat direkam. PDD (<em>percentage depth dose</em>) dari radiasi-γ berenergi 1,3 MeV terbesar nilainya pada kedalaman 6,5 cm, pada kedalaman ini luas umbra yang terukur yaitu (7,8 x 7,8) cm dengan laju dosis rata-rata 0,6034 Gy/menit. Dengan bertambahnya posisi kedalaman letak alat ukur, laju dosis yang terukur akan menurun secara eksponensial, sedangkan luas umbra pada kedalaman fantom relatif tetap. </p>

Dosimetric Characterizations of Megavoltage Therapeutic Photon Beam

This paper presents the dosimetric parameters characterizations of a megavoltage therapeutic photon beam. The main focus of this study is to investigate and analyze the parameters of percentage depth dose (PDD) and tissue maximum ratio (TMR) due to the importance of treatment system. The depth dose characteristics of 6MV photon beam for different field sizes in water phantom has been measured, analyzed and found a robustness results. The results revealed that the depth dose variation from 0.067% to 1.812% and the TMR values varies from 0.501% to 2.111%. It seems the measured dosimetric quantities are clinically relevant for different field sizes and depths.

Depth dose measurement in water phantom for two X-ray energies (6MeV and 10MeV) in comparison with actual planning

The purpose of this study is to measure doses delivered at different depths in water phantom at vertical position in comparison with the actual planning in order to verify the dose delivered to the tumor in addition to the measurement of the effect penumbra dose to assess the dose leaking to the healthy soft tissue. Percentage depth dose (PDD) values was measured at field sizes (5×5,10×10,15×15, and 20×20) cm2, and the depth dose was measured between (0-16) cm deep at 4cm intervals, for both energies 6 MeV and 10 MeV X-ray beam. Other readings were taken at different distances 1cm and 2cm outside of the actual beam in orthogonal directions at depth of 4 cm. These measurements were designed to measure the penumbra dose produced outside the central beam. Results show that the high similarity between water phantom and actual tissue for this reason water is taken as phantom for Quality Assurance (QA) and calculation the depth dose. The similar results may appear strange as the actual planning depth dose is taken in the chest wall where there is bone and soft tissue. The increase in the field size, increases the percentage of surface dose, this could be caused by an increase in the amount of scattering in the larger fields. There is almost no difference in depth dose between homogenous and non homogenous planning also similar to the water phantom. Because of higher photon energy 6MeV and 10MeV the bone has no influence in absorption from the soft tissue. A slight change in the depth dose with increase in the field size may be caused by the scattered radiation.