A multicentre comparison of the dosimetric impact of inter- and intra-fractional anatomical variations in fractionated cervix cancer brachytherapy

Abstract

Background and purposeTo compare the dosimetric impact of organ and target variations relative to the applicator for intracavitary brachytherapy by a multicentre analysis with different application techniques and fractionation schemes.Material and methodsDVH data from 363 image/contour sets (120 patients, 6 institutions) were included for 1–6 fractions per patient, with imaging intervals ranging from several hours to ∼20 days. Variations between images acquired within one (intra-application) or between consecutive applicator insertions (inter-application) were evaluated. Dose plans based on a reference MR or CT image series were superimposed onto subsequent image sets and D2cm3 for the bladder, rectum and sigmoid and D90 for HR CTV were recorded.ResultsFor the whole sample, the systematic dosimetric variations for all organs at risk, i.e. mean variations of D2cm3, were found to be minor (<5%), while random variations, i.e. standard deviations were found to be high due to large variations in individual cases. The D2cm3 variations (mean ± 1SD) were 0.6 ± 19.5%, 4.1 ± 21.7% and 1.6 ± 26.8%, for the bladder, rectum and sigmoid. For HR CTV, the variations of D90 were found to be −1.1 ± 13.1% for the whole sample.Grouping of the results by intra- and inter-application variations showed that random uncertainties for bladder and sigmoid were 3–7% larger when re-implanting the applicator for individual fractions. No statistically significant differences between the two groups were detected in dosimetric variations for the HR CTV.Using 20% uncertainty of physical dose for OAR and 10% for HR CTV, the effects on total treatment dose for a 4 fraction HDR schedule at clinically relevant dose levels were found to be 4–8 Gy EQD2 for OAR and 3 Gy EQD2 for HR CTV.ConclusionsSubstantial variations occur in fractionated cervix cancer BT with higher impact close to clinical threshold levels. The treatment approach has to balance uncertainties for individual cases against the use of repetitive imaging, adaptive planning and dose delivery.

External beam techniques to boost cervical cancer when brachytherapy is not an option—theories and applications

“…For instance, inadequate placement and/ or displacement of ovoids reduced both local control (LC) and disease-free survival (DFS) rates, while inadequate packing reduced DFS (13). Even after adequate placement of applicator, significant inter-and intra-fraction variations can occur (14). Furthermore, there are additional aspects to the BT procedural requirements regardless of the skill of the clinician.…”

A review of the clinical experience in pulsed dose rate brachytherapy

“…81,82 In cervical cancer, the same results were found for the tandem/ovoid applicator. 83,84 Still PDR is only used in 16% of the brachytherapy centres in Europe. Moreover, the studies reviewed are only from a few centres across Europe or North America.…”

In vivodosimetry: trends and prospects for brachytherapy

“…However, recently, a number of investigations have been published, which improve the possibilities to describe BT uncertainty budgets that encompass the entire treatment workflow from source calibration to treatment delivery. 5,40 These investigations point towards the importance of geometric variations induced by organ and applicator movements, 41 which complicate and potentially compromise accumulated dose calculations in the organs. Interand intrafraction deformations of prostate, bladder and rectum have been studied, [42][43][44][45][46] and the dosimetric impact owing to more general anatomical variations has been evaluated in a multicentre comparison of cervix BT.…”

“…Interand intrafraction deformations of prostate, bladder and rectum have been studied, [42][43][44][45][46] and the dosimetric impact owing to more general anatomical variations has been evaluated in a multicentre comparison of cervix BT. 41 Organ-applicator movements occurring between patient imaging and treatment delivery stages have been identified as a major source of uncertainty 33,[47][48][49][50][51][52][53] and their impact further analysed. [54][55][56][57] In cervical cancer BT, inter-and intrafraction uncertainties owing to organ movements and deformations account for 20-25% of the D 2cm3 parameter (minimum dose to the most irradiated 2 cm 3 ) per fraction and is the most essential component in the uncertainty budget for OARs.…”