Organ at risk dose comparison between gynaecological cancers of the endometrium and cervix using a combined external beam and brachytherapy boost treatment

Abstract

Gynaecological cancers (GCs) treated using external beam radiotherapy (EBRT) followed by a boost of brachytherapy (BT) reduces the overall treatment dose and gives a better treatment of the tumour compared to using EBRT or BT alone. However, with this combined treatment, there is growing concern for the increased dose to the Organs at Risk (OAR) as it increases the possibility of late toxicity effects and potentially reduces the patient’s quality of life (QoL). Using statistical analysis, the differences in dose delivered to the OAR for two GCs (endometrial and cervical) was investigated as well as other dose influencing factors (i.e. applicator insertion angle and size). This project involved 19 cervical patients: EBRT = 50.4 Gy, 28 fractions followed by BT = 21 Gy, 3 fractions; and 17 endometrial patients: EBRT = 45/46 Gy, 28 fractions and BT = 18 Gy 3 fractions. All patients had been treated with 3D-Conformal EBRT using 15 MV photon beams and BT with a Ir-192 GammaMed Plus system. Statistically significant differences (p-value < 0.05) between the OAR doses for the two GC treatments identified that cervical patients receive a higher dose to the bladder, sigmoid and small intestines, with a reduction in rectum dose due to the use of a rectum retractor in BT treatments. Total Reference Air KERMA (TRAK), a potential predictive factor for the biological effect of radiation on tissues, also showed that cervical treatments exhibited much higher TRAK values than when compared with endometrial treatments (p-value < 0.0001). Gynaecological cancers (GCs) treated using external beam radiotherapy (EBRT) followed by a boost of brachytherapy (BT) reduces the overall treatment dose and gives a better treatment of the tumour compared to using EBRT or BT alone. However, with this combined treatment, there is growing concern for the increased dose to the Organs at Risk (OAR) as it increases the possibility of late toxicity effects and potentially reduces the patient’s quality of life (QoL). Using statistical analysis, the differences in dose delivered to the OAR for two GCs (endometrial and cervical) was investigated as well as other dose influencing factors (i.e. applicator insertion angle and size). This project involved 19 cervical patients: EBRT = 50.4 Gy, 28 fractions followed by BT = 21 Gy, 3 fractions; and 17 endometrial patients: EBRT = 45/46 Gy, 28 fractions and BT = 18 Gy 3 fractions. All patients had been treated with 3D-Conformal EBRT using 15 MV photon beams and BT with a Ir-192 GammaMed Plus system. Statistically significant differences (p-value < 0.05) between the OAR doses for the two GC treatments identified that cervical patients receive a higher dose to the bladder, sigmoid and small intestines, with a reduction in rectum dose due to the use of a rectum retractor in BT treatments. Total Reference Air KERMA (TRAK), a potential predictive factor for the biological effect of radiation on tissues, also showed that cervical treatments exhibited much higher TRAK values than when compared with endometrial treatments (p-value < 0.0001).