HR-CTV Volume Research Articles

Impact of treatment time and dose escalation on local control in locally advanced cervical cancer treated by chemoradiation and image-guided pulsed-dose rate adaptive brachytherapy

PurposeTo report the prognostic factors for local control in patients treated for locally advanced cervical cancer with image guided pulsed-dose rate brachytherapy. Materials/methodsPatients treated with curative intent by a combination of external beam radiotherapy and pulsed-dose rate brachytherapy were selected. Local failure was defined as any relapse in the cervix, vagina, parametria, or uterus during follow-up. Prognostic factors were selected based on log rank tests and then analyzed with a Cox model. Dose/effect correlations were performed using the probit model. ResultsTwo hundred and twenty-five patients treated from 2006 to 2011 were included. According to the FIGO classification, 29% were stage IB, 58% stage II, 10% stage III, and 3% stage IVA; 95% received concomitant chemotherapy. Thirty patients were considered having incomplete response or local failure. Among the selected parameters, D90 for HR-CTV, D90 for IR-CTV, the overall treatment time, the TRAK, and the HR-CTV volume appeared significantly correlated with local control in univariate analysis. In multivariate analysis, overall treatment time >55days and HR-CTV volume >30cm3 appeared as independent. The probit analysis showed significant correlations between the D90 for both CTVs, and the probability of achieving local control (p=0.008 and 0.024). The thresholds to reach to warrant a probability of 90% of local control were 85Gy to the D90 of the HR-CTV and 75Gy to 90% of the IR-CTV (in 2Gy equivalent, α/β=10). To warrant the same local control rate, the D90 HR-CTV should be significantly increased in stage III–IV tumors, in case of HR-CTV >30cm3, excessive treatment time, or tumor width at diagnosis >5cm (97, 92, 105, and 92Gy respectively). ConclusionsOverall treatment time and HR-CTV volume were independent prognostic factors for local control. The D90 for HR and IR CTV were significantly correlated with local control, and D90 HR-CTV should be adapted to clinical criteria.

OC-0047: Dose painting under consideration of uncertainties of combined multiparametric functional images

Results: The overall mean sensitivity in D90 and D98 for all 15 plans was -0.3 ± 0.1 %/mm and -0.6 ± 0.3 %/mm respectively. This implies for instance that a 6mm error will give a mean reduction of 1.9 and 3.6 % in D90 and D98, respectively. The 2D colour maps visualized variations in spatial sensitivity between different patients, but a common angular patter was recognized showing an increased sensitivity in the right and anterior direction (table 1). The results also showed a negative correlation between HR-CTV volume and mean sensitivity that was more pronounced for treatments without needles (fig. 1).

Interfractional change of high-risk CTV D90 during image-guided brachytherapy for uterine cervical cancer

The purpose of this study was to evaluate interfractional changes of the minimum dose delivered to 90% of the high-risk clinical target volume (HR-CTV D90) and D2cc of the bladder and rectum during brachytherapy for uterine cervical cancer patients. A total of 52 patients received external beam radiotherapy and high-dose-rate intracavitary brachytherapy (ICBT). For each of four ICBT applications, a pelvic CT scan was performed and the HR-CTV was delineated. Retrospectively, these patients were divided into two groups: (i) the standard dose group with 6 Gy to point A in each ICBT, and (ii) the adaptive dose group with a modified dose to point A to cover the HR-CTV with the 6-Gy isodose line as much as possible. The HR-CTV D90 was assessed in every session, and analyzed as interfractional changes. In the standard dose group, the interfractional changes of the HR-CTV D90 showed a linear increase from the first to the third of the four ICBT (average 6.1, 6.6, 7.0 and 7.1 Gy, respectively). In contrast, those of the adaptive dose group remained almost constant (average 7.2, 7.2, 7.3 and 7.4 Gy, respectively). Especially, in the case of a large HR-CTV volume (≥35 cm3) at first ICBT, the total HR-CTV D90 of the adaptive dose group with brachytherapy was significantly higher than that of the standard dose group. There were no significant differences in total D2cc in bladder and rectum between the two groups. Image-guided adaptive brachytherapy based on interfractional tumor volume change improves the dose to the HR-CTV while keeping rectal and bladder doses within acceptable levels.

Feasibility of applying a single treatment plan for both fractions in PDR image guided brachytherapy in cervix cancer

PurposeThis study explores the feasibility of limiting dose optimisation to the first brachytherapy fraction (BT1) and applying the same plan for the second fraction (BT2). Material and methodsSeventy one consecutive patients were analysed. Pulsed dose rate (PDR) BT was initiated after about 4weeks of external beam radiotherapy (EBRT). Thirty eight patients had only intracavitary applicator (IC), and 33 had combined IC with interstitial needles (IC/IS). The optimised BT1 plan was copied to BT2 images with no further optimisation (single plan scenario) and dose volume histogram (DVH) parameters were compared with those of full dose optimisation for every fraction (optimised plan scenario). Results31/38 IC patients had similar applicator geometry in both fractions and mean DVH parameters were comparable between full optimisation and single plan. The mean HR CTV D90 in total EQD2 with optimisation was 94.5Gy and with single plan scenario was 94.4Gy (p=0.89). Organs at risk (OARs) planning aims were fulfilled with the single plan, although 5/31 patients would receive 3–10Gy extra to the D2cm3. The mean doses in total EQD2 for the D2cm3 of the bladder, rectum, sigmoid and bowel were respectively 68.5, 61.0, 64.9 and 60.6Gy for the optimised plan, and for the single plan scenario were 69.0, 61.3, 65.1 and 60.8Gy respectively. The difference was statistically not significant. The standard deviation (SD) of the difference between the single plan and the optimised plan was 3.2Gy for HR CTV and 2.9, 1.4, 1.2, 1.6Gy for the bladder, rectum, sigmoid and bowel D2cm3, respectively. Only 4/33 IC/IS patients had the same applicator geometry and single plan was therefore not feasible for the majority of these patients. ConclusionFor IC BT in small volume tumours (primarily stage IB-IIB) with mean HR CTV volume at BT1=24±12cm3, comparable mean DVH parameters resulted when applying a single plan, but with considerable variations in individual patients. Yet since in our population the applied target doses are high and the OARs doses are lower than the dose volume constraints these variations may not have considerable clinical consequences. Individual optimisation for each BT fraction is recommended when interstitial needles are used.

High resolution (3 Tesla) MRI-guided conformal brachytherapy for cervical cancer: consequences of different high-risk CTV sizes

PurposeTo evaluate conventional brachytherapy (BT) plans using dose-volume parameters and high resolution (3 Tesla) MRI datasets, and to quantify dosimetric benefits and limitations when MRI-guided, conformal BT (MRIG-CBT) plans are generated.Material and methodsFifty-five clinical high-dose-rate BT plans from 14 cervical cancer patients were retrospectively studied. All conventional plans were created using MRI with titanium tandem-and-ovoid applicator (T&O) for delivery. For each conventional plan, a MRIG-CBT plan was retrospectively generated using hybrid inverse optimization. Three categories of high risk (HR)-CTV were considered based on volume: non-bulky (< 20 cc), low-bulky (> 20 cc and < 40 cc) and bulky (≥ 40 cc). Dose-volume metrics of D90 of HR-CTV and D2cc and D0.1cc of rectum, bladder, and sigmoid colon were analyzed.ResultsTumor coverage (HR-CTV D90) of the conventional plans was considerably affected by the HR-CTV size. Sixteen percent of the plans covered HR-CTV D90 with the prescription dose within 5%. At least one OAR had D2cc values over the GEC-ESTRO recommended limits in 52.7% of the conventional plans. MRIG-CBT plans showed improved target coverage for HR-CTV D90 of 98 and 97% of the prescribed dose for non-bulky and low-bulky tumors, respectively. No MRIG-CBT plans surpassed the D2cc limits of any OAR. Only small improvements (D90 of 80%) were found for large targets (> 40 cc) when using T&O applicator approach.ConclusionsMRIG-CBT plans displayed considerable improvement for tumor coverage and OAR sparing over conventional treatment. When the HR-CTV volume exceeded 40 cc, its improvements were diminished when using a conventional intracavitary applicator.

Comparison of 3D MRI with high sampling efficiency and 2D multiplanar MRI for contouring in cervix cancer brachytherapy

BackgroundMRI sequences with short scanning times may improve accessibility of image guided adaptive brachytherapy (IGABT) of cervix cancer. We assessed the value of 3D MRI for contouring by comparing it to 2D multi-planar MRI.Patients and methodsIn 14 patients, 2D and 3D pelvic MRI were obtained at IGABT. High risk clinical target volume (HR CTV) was delineated by 2 experienced radiation oncologists, using the conventional (2D MRI-based) and test (3D MRI-based) approach. The value of 3D MRI for contouring was evaluated by using the inter-approach and inter-observer analysis of volumetric and topographic contouring uncertainties. To assess the magnitude of deviation from the conventional approach when using the test approach, the inter-approach analysis of contouring uncertainties was carried out for both observers. In addition, to assess reliability of 3D MRI for contouring, the impact of contouring approach on the magnitude of inter-observer delineation uncertainties was analysed.ResultsNo approach- or observer - specific differences in HR CTV sizes, volume overlap, or distances between contours were identified. When averaged over all delineated slices, the distances between contours in the inter-approach analysis were 2.6 (Standard deviation (SD) 0.4) mm and 2.8 (0.7) mm for observers 1 and 2, respectively. The magnitude of topographic and volumetric inter-observer contouring uncertainties, as obtained on the conventional approach, was maintained on the test approach. This variation was comparable to the inter-approach uncertainties with distances between contours of 3.1 (SD 0.8) and 3.0 (SD 0.7) mm on conventional and test approach, respectively. Variation was most pronounced at caudal HR CTV levels in both approaches and observers.Conclusions3D MRI could potentially replace multiplanar 2D MRI in cervix cancer IGABT, shortening the overall MRI scanning time and facilitating the contouring process, thus making this treatment method more widely employed.