In vivo dosimetry with diodes in a radiotherapy department in Pakistan

Abstract

The International Commission of Radiological Units (ICRU) sets a tolerance of ±5 % on dose delivery, with more recent data limiting the overall tolerances to ±3 %. One of the best methods for accurate dose delivery and quality check is in vivo dosimetry, while radiotherapy is performed. The present study was carried out to test the applicability of diodes for performing in vivo entrance dose measurements in external photon beam radiotherapy for pelvic tumours and its implementation as quality assurance tool in radiotherapy. During November 2007 to December 2009, in 300 patients who received pelvic radiotherapy on a multileaf-collimator-assisted linear accelerator, the central axis dose was measured by in vivo dosimetry by p-Si diodes. Entrance dose measurements were taken by diodes and were compared with the prescribed dose. Totally 1000 calculations were performed. The mean and standard deviation between measured and prescribed dose was 1.26 ± 2.8 %. In 938 measurements (93.8 %), the deviation was <5 % (1.36 ± 2.9%); in 62 measurements (6.2 %) the mean deviation was >5 % (5.51 ± 2.3 %). Larger variations were seen in lateral and oblique fields more than anteroposterior fields. For larger deviations, patients and diode positional errors were found to be the common factors alone or in combination with other factors. After additional corrections, repeated measurements were achieved within tolerance levels. This study showed that diode-detector-based in vivo dosimetry was simple, cost-effective, provides quick results and can serve as a useful quality assurance tool in radiotherapy. The data acquired in the present study can be used for evaluating output calibration of therapy machine, precision of calculations, effectiveness of treatment plan and patient setup.

Quantifying inter- and intra-fraction variations of breast cancer radiotherapy with skin dose measurements

“…Mann-Whitney U test was used to compare between DIBH and FB groups in the systematic inter-fraction dose variations (in terms of MPE), random interfraction dose variations (in terms of SDs including SD total , SD MT , and SD LT ), and random intra-fraction dose variations (in terms of SD MT-LT ). The threshold of the IVD measurements for systematic dose variations was the relative difference between the measured and calculated dose, and it was set to 5% according to a previously published report [24]. While the threshold of IVD measurements for random dose variations was set to 5% (13.35 cGy) from the total dose per fraction (267 cGy).…”