Comparison of rectal dose in different techniques of prostate cancer external-beam radiotherapy based on TLD and XR type T GAFCHROMIC[R] film dosimetry

Radiotherapy of prostate carcinoma often results in high doses to surrounding structures, such as the rectum and bladder. Therefore, these organs should be closely monitored. The aim of this study is to evaluate the dose received by the target volume and rectum to compare two different methods of dose measurement with each other and to check the homogeneity of dose in the tumor volume. The dose distribution throughout a planned target volume and the rectum [OaR] in a phantom exposed to 9 MV photon beam, similar to treatment conditions were studied. Several techniques of external beam radiation therapy such as two-, three- and four-field have been planned. Dosimetry was performed using GAFCHROMIC film and TLD-100 chips. The rectal and cancer volume measured doses in treatment were similar to the prescribed doses. The results of two dosimetry types were compared with each other as well as with treatment planning. Rectal dose in three- and four-field [equal tumor dose and equal applied dose] techniques were respectively 23.15, 28.87 and 15.22% lower than the tumor dose. There was not a statistically significant difference between received and prescribed doses. So, this study showed that the Gafchromic film dosimetry can be used for fast dosimetric evaluations

Determining rectal dose through cervical cancer radiotherapy by 9 MV photon beam using TLD and XR type T GAFCHROMIC[R] Film

The goals of the present research were to investigate the rectal dose during four chosen techniques of cervical cancer radiotherapy and to examine how accurately the treatment planning represents dose measurements, and it's practicality for routine use as well as, to determine the homogeneity of dose in tumor volume. The study was carried out using a Nepton 10-PC unit and a Rando phantom. The equipments which were used for dose determination were a Radiochromic densitometer with GAFCHROMIC[R] film [XR type T], and a thermo-luminescent dosimeter [TLD] reader system with TLD chips for rectal and target volume dose determination. Several techniques of external beam radiation therapy such as two-field [AP-PA], three-field and four-field with equal tumor dose and with equal applied dose were planned. The maximum dose received by rectum was caused by two-field technique. The results of two dosimetry types were compared with each other as well as with the treatment planning, however, no statistically significant difference was observed between them [p > 0.05]. In three-field, four -field with equal tumor dose and four-field with equal applied dose, rectal dose was lower, respectively 26.17%, 33.75% and 16.47%, than tumor dose. This study showed that dosimetry using TLD and film during radiotherapy could have a useful role as a predictor of choosing appropriate technique for preventing future rectal complications. Dose limitation to the rectum could possibly be achieved by using three-field and four-field techniques with equal tumor dose while maintaining a high dose to the tumor

Assessment of variation of wedge factor with depth, field size and SSD for Neptun 10PC Linac in Mashhad Imam Reza Hospital

Background: In radiotherapy, wedge filters are used for optimizing the tumor dose distribution in patients. The attenuation in beam intensity due to the presence of wedge filter is compensated by means of a wedge factor measured at the central axis of the beam. The field size, depth and SSD dependence of wedge factor have been assessed for 9MV radiations of Neptun PC linear accelerator

Materials and Methods: Wedge factors [WF] at different SSD, field size [FS] and depth [d] in water were measured for 8 steel wedges with different sizes and angles of 15, 30, 45, and 60 degree. Experimental data were obtained using Neptun 10PC, Linac 9MV X-ray machine, a 3D water phantom, dosimeters and an electrometer. To study the effect of field size on WF, the wedge factor was measured for square field sizes from 5×5 to 20×20 cm, with 1 cm increment intervals for all wedges; and, at the depth of 10 cm, SSD of 100 cm with monitor unit [MU] of 80. Effects of depth on WF were studied by measurement in various depths from 3-19cm for all wedge angles at SSD of 100cm, field size of 10×10cm and 80 MU irradiation. Effects of SSD on WF were investigated by a variation of SSD from 90-110cm with 5cm increment intervals; while the dosimeter was set at depth of 10cm and field size of 10×10cm were irradiated for 80MU

Results: Linear dependence of WF with field size and depth of measurements were confirmed with 95% certainty. Shapiro-Wilk test, showed that the residual data of the regression tests have normal distributions [P>0.05]. There was also found no linear relationship between WF and SSD [P>0.05]

Conclusion: WF has linear dependence with field size and depth of measurements, but the rate of variations are less than 2.2% per 10cm variation in field size and less than 1.3% per 10 cm variation in depth of measurements, therefore, correction of WF for field size and depth of treatments in clinical trials is negligible