Volumetric and geometric changes in the parotid glands and target volume during image-guided radiotherapy for locally advanced oropharyngeal cancers.

PURPOSE: This study aimed to evaluate the volumetric and geometric changes in the parotid glands and target volume during image-guided radiotherapy (IGRT) for locally advanced oropharyngeal cancers. MATERIALS AND METHODS: Twenty patients receiving radiotherapy using IGRT at a dose of 70 Gy/35 fractions/7 weeks for locally advanced oropharyngeal cancers were accrued. Radiotherapy planning computed tomography (CT) scans were performed at pre-radiotherapy (RT), 20, 40, and 60 Gy for each patient. Volume changes in target and parotids along with shifts of parotids were assessed with respect to pre-RT scan after co-registration. In study scans, GTVp and GTVn were recontoured as per particular CT. CTV and PTV were copied from planning CT to study CT. CTV was edited from anatomical barriers, and PTV was edited only from the skin in the study CT. The parotids were recontoured on each study scan. The center of mass (COM) of C2 vertebral body was considered as the reference to evaluate its shifts. RESULTS: There was a statistically significant percentage regression of ipsilateral and contralateral parotid mean volumes at the rate of 0.85%/0.207 cc and 0.98%/0.26 cc per day, respectively. We observed the mean medial shift of center of mass of ipsilateral parotid of 2.23 mm (p = 0.011) and contralateral parotid of 2.67 mm (p = 0.069) at the end of 60 Gy. GTVp (mean) reduced from 41.87 cc at 0 Gy to 31.13 cc (25.65%) at 60 Gy (p = 0.003), while GTVn (mean) reduced from 19.98 cc at 0 Gy to 10.79 cc (45.99%) at 60 Gy (p = 0.003). There was a statistically significant reduction in CTV and PTV volumes at 60 Gy. CONCLUSION: Statistically significant volumetric and geometric changes occurred during intensity-modulated radiation (IMRT), which were most prominent after 40 Gy and were maximum at 60 Gy. There was a medial shift of parotid glands toward the high-dose region. This study can be useful to devise an adaptive radiotherapy strategy.

Coverage with dosimetric concordance index (CDCI): a tool for evaluating dosimetric impact of inter-observer target variability in brachytherapy.

PURPOSE: The aim of this study was to propose an index for evaluating dosimetric impact of inter-observer target delineation variability in brachytherapy. MATERIAL AND METHODS: The coverage with dosimetric concordance index (CDCI) is expressed as CDCIcommon and CDCIpair. The CDCIcommon is the mean coverage of target volume with common volume irradiated by prescription dose among all observers and represents the condition of worst target coverage. CDCIpair is the generalized form of CDCI, which is mean target coverage with common prescription volume obtained between all possible pairs of observers and represents more realistic coverage of target with dosimetric concordance. The index was used to evaluate the dosimetric impact of target delineation variability in optimized conformal plans on target volumes of five radiation oncologists for twenty patients of multi-catheter interstitial partial breast brachytherapy. RESULTS: The mean decline of 5.6 ±3.2% and 11.3 ±5.7% in CDCIpair and CDCIcommon, respectively, was observed comparing to coverage index (CI) of target volume in all patients due to inter-observer target variability. CDCIcommon and CDCIpair were found to have significant linear correlation (r = 0.964, p < 0.000). The difference between CDC and CI increased with the mean relative target volume among observers. Significant correlation (r = 0.962, p < 0.000) was also noted for the difference (Δ) in CDCIcommon and CDCIpair with CI of target volume. CONCLUSIONS: The recommended indices and difference between the dosimetric coverage of target volume (CI) with CDCI (ΔCDCI) can be used for evaluating dosimetric impact of the inter-observer target delineation variability.

Impact of inter-observer variations in target volume delineation on dose volume indices for accelerated partial breast irradiation with multi-catheter interstitial brachytherapy.

PURPOSE: To investigate dosimetric impact of inter-observer variation in clinical target volume(CTV) delineation for patients undergoing interstitial partial breast brachytherapy. METHODS: Five radiation oncologists delineated CTV in twenty patients who underwent multi-catheter partial breast brachytherapy. Five treatment plans for each patient were graphically optimized for CTV of all observers and evaluated using coverage index(CI), external volume index(EI), overdose volume index(OI) and conformal index(COIN). In addition, volume enclosed by prescription isodose(V100), its spatial concordance(CIcommon), mean coverage of all CTVs with common volume of prescription dose(V100_common) and mean CTV coverage for all pairs of observer with common prescription volume of respective pairs(V100_pair) were also computed. RESULTS: The mean ±â€¯standard deviation(SD) of CI and COIN ranged from 0.756 ±â€¯0.076 to 0.840 ±â€¯0.070 and 0.591 ±â€¯0.090 to 0.673 ±â€¯0.06 respectively. When a plan made for CTV of individual observer was evaluated on CTV of all observers, the maximum variations(ρ < 0.05) in the mean CI,COIN,OI and EI were 10.6%,11.4%,10.6% and 72.7% respectively. The observed mean ±â€¯SD of V100, CIcommon of V100, CTV coverage with V100_common and V100_pair was 160.7 ±â€¯52.1, 0.70 ±â€¯0.09, 73.1 ±â€¯8.1% and 77.9 ±â€¯7.3% respectively. CONCLUSION: Inter-observer variation in delineation of CTV showed significant dosimetric impact with mean CTV coverage of 73.1% and 77.9% by common and paired prescription dose volume respectively among all observers.

Change of target volume and its dosimetric impact during the course of accelerated partial breast irradiation using intraoperative multicatheter interstitial brachytherapy after open cavity surgery.

PURPOSE: To investigate the change of clinical target volume (CTV) and its dosimetric impact during the course of accelerated partial breast irradiation (APBI) using intraoperative multicatheter interstitial brachytherapy after open cavity surgery. METHODS AND MATERIALS: Twenty-two patients of APBI with intraoperative placement of catheters underwent computed tomography scans for the treatment planning before the first (CT1) and the last (CT2) treatment fraction. Delineation of lumpectomy cavity and CTV was done consistently on both CT data sets by one of the coauthors. Optimum plan (PCT1) was made on CT1. PCT1 was manually reproduced in CT2 which yielded plan PCT2. Plans were compared using coverage index (CI), dose homogeneity index (DHI), external volume index (EI), overdose volume index (OI) and conformal index (COIN). RESULTS: The mean ± SD volume of lumpectomy cavity and CTV was 78.5 ± 40.7 cm3, 156.4 ± 69.0 cm3 for PCT1, and 84.7 ± 50.1 cm3 (p = 0.11), 165.7 ± 82.8 cm3 (p = 0.15) for PCT2, respectively. CTV volume increase by ≥ 10% was observed in 9 cases however decrease of ≥10% was observed in 5 cases. Mean (SD) of absolute pairwise difference in CTV volume was found to be 13.2 (6.7) %. For cases with increase in CTV volume, significant (p < 0.05) decrease of 8.4%, 12.2%, and 5.5% was observed in CI, EI, and COIN of CTV respectively. However for cases with shrinkage of CTV, significant (p = 0.004) increase of 45% in EI was observed, whereas COIN reduced significantly (p = 0.001) by 13.5%. Overall 22 cases showed significant decrease of 5.8% and 8.1% in mean CI and COIN, respectively. CONCLUSIONS: The change of CTV during the course of APBI using intraoperative multicatheter interstitial brachytherapy after open cavity surgery was found patient specific and showed a significant impact on coverage and conformity.

Clinical outcome of high-dose-rate interstitial brachytherapy in vulvar cancer: A single institutional experience.

PURPOSE: With an aim to evaluate and report high dose date interstitial brachytherapy (HDR-ISBT) in vulvar cancers, we undertook this retrospective analysis. METHODS AND MATERIALS: Histologically proven vulvar cancers treated with HDR-ISBT between 2001 and 2016 were analyzed. Radiotherapy details, clinical outcome in terms of local control rates, survivals, and toxicities were evaluated. RESULTS: A total of 38 patients received HDR-ISBT, with definitive radiation in 29 (76.3%), adjuvant postoperative in six (15.8%) and salvage radiation in three (7.9%) patients. Of them, 29 patients received brachytherapy boost and nine patients ISBT alone. BT procedure included freehand plastic tube technique in 23 (single [n = 5] or multiple plane [n = 18]), 13 patients with template based and two patients combined approach. Patients with brachytherapy alone received median EQD2 of 38.4 Gy10 (35.5-46.7 Gy10), as boost received median 23.3 Gy10 (13-37.3 Gy10). At 3-month post-treatment response evaluation, 30 patients achieved clinically complete response, two patients partial response and six maintained postoperative status. With a median follow-up of 30 months, 29 (76.3%) were disease free, and 9 (23.7%) patients had relapsed disease with four patients expired due to disease and two died of other causes. The 5-year overall survival, disease free survival, and local control rates were 82%, 51%, and 77%, respectively. CONCLUSIONS: HDR-ISBT in vulvar cancer is a feasible and a viable option with acceptable and comparable outcomes.