RESUMO
Purpose: To compare dosimetric parameters of brachytherapy (BT) treatment plans made with or without active source positions of the ring/ovoid (R/O) applicator in locally advanced cervical cancer patients. Material and methods: Sixty patients with cervical cancer without vaginal involvement were selected for the study, who received intra-cavitary/interstitial BT. For each patient, two plans with and without active source dwell positions in R/O were created, using the same dose-volume constraints. EQD2 total doses from external beam and BT of target volumes and organs at risk (OARs) between the competing plans were compared. Results: There was no significant difference in the dose of high-risk clinical target volume (HR-CTV) and gross tumor volume (GTV) between the plans with inactive vs. active R/O. The mean D98 of intermediate-risk clinical target volume (IR-CTV) was significantly lower with inactive R/O; however, the GEC-ESTRO (EMBRACE II study) and ABS criteria were fulfilled in 96% in both plans. There was no difference in dose homogeneity, but conformity of the plans with inactive R/O was higher. Doses to all OARs were significantly lower in plans without R/O activation. While all the plans without R/O activation fulfilled the recommended dose criteria for OARs, it was less achievable with R/O activation. Conclusions: Inactivation of R/O applicator results in similar dose coverage of the target volumes with lower doses to all OARs, as activation of R/O in cervix cancer patients when HR-CTV does not extend to R/O applicator. The use of active source positions in R/O shows worse performance regarding the fulfilment of the recommended criteria for OARs.
RESUMO
PURPOSE: To compare image-guided adaptive interstitial brachytherapy (BT) and intensity-modulated arc therapy (IMAT) with conventional treatment techniques in cervical cancer using an alternative biological dose summation method. MATERIAL AND METHODS: Initially, 21 interstitial BT and IMAT plans of patients with cervical cancer were included and additional plans were created (inverse optimized interstitial, optimized intracavitary, non-optimized intracavitary BT plans, and conformal external beam radiotherapy [EBRT]). The most exposed volume of critical organs in BT were identified manually on EBRT CT images. Biological total doses (EQD2) were calculated and compared between each combination of BT and EBRT plans. This method was compared with uniform dose conception (UDC) in IMAT and conformal EBRT plans. RESULTS: The D90 of high-risk CTV and D2 of bladder and sigmoid were different in BT techniques only: p = 0.0149, < 0.001, < 0.001, respectively. The most advantageous values were obtained in the interstitial treatment plans and inverse optimized interstitial plans did not differ dosimetrically from these, while optimized intracavitary plans resulted in worse dose-volume parameters, and the worst of all were intracavitary plans without optimization. The D2 of rectum was significantly lower with IMAT than with conformal EBRT plans (p = 0.037) and showed the same trend in BT plans as the other parameters (p < 0.001). The UDC dose summation method overestimated D2 of bladder, rectum, and sigmoid (p < 0.001 for all). CONCLUSIONS: Although optimization improves the quality of conventional BT plans, interstitial plans produce significantly higher dose coverage of high-risk clinical target volume (HR-CTV) and lower doses to organs at risk (OARs). IMAT plans decrease the dose to the rectum. UDC overestimates OARs doses.
