Purpose: To better understand the normal tissue dose constraints for HDR brachytherapy (BT) in the treatment of locally advanced cervix cancer.
Methods: A retrospective analysis was performed for 9 patients that received EBRT via IMRT in accordance with the EMBRACE protocol (45 Gy in 25 fractions with concomitant chemotherapy). All patients received a concurrent or sequential EBRT nodal boost. Regions within BT influence were determined to be 1 cm, 2 cm, and 3 cm margins around the HR-CTV. D2cc values in the bladder, rectum, sigmoid and small bowel within these volumes were identified using Eclipse® Planning Station. D2cc in EQD2 were statistically analyzed using a paired t-test (H0: μ = 0) for two different DVH parameters: the overall D2cc used in accordance with EMBRACE protocol and the localized method for determining the D2cc within the treatment range of BT.
Results: Statistically significant differences (p < 0.05) are found for the bladder, sigmoid and small bowel. In several cases, the small bowel is found to be well outside the treatment range of BT.
Conclusion: The standard of treatment of locally advanced cancer is BT boost following EBRT and concomitant chemotherapy, with the following hard constraints for the prescribed dose: Bladder, D2cc < 80 Gy (α/β=3); Rectum, D2cc < 65 Gy (α/β=3); Sigmoid D2cc < 70 Gy (α/β=3); Bowel, D2cc < 70 Gy (α/β=3). The objective of this study was to assess the recommended DVH parameter against localized D2cc to OARs within 1 cm, 2 cm, and 3 cm volumes around the HR CTV. Our findings suggest that this revised DVH parameter may improve tumor control through better understanding the actual normal tissue dose limits.
HDR, Bioeffect Dose, Interstitial Brachytherapy