Development and evaluation of an automatic interstitial catheter digitization tool for adaptive high-dose-rate brachytherapy.

PURPOSE: To develop and evaluate an automatic interstitial catheter digitization algorithm for use in adaptive high-dose-rate brachytherapy for gynecologic cancers using the Syed-Neblett template. METHODS AND MATERIALS: We developed an automatic catheter digitization tool, which uses a region growing algorithm in conjunction with a spline model of the catheters. Seed locations were selected in each catheter for the region growing algorithm. The region growing was constrained by a spline model of the catheters, which prevents intercatheter crossover or incorrect digitization due to air pockets. Plan reoptimization was performed on successive day computed tomography scans using dwell positions for the Day 1 computed tomography. This method was applied to 10 patients who had received high-dose-rate interstitial brachytherapy using the Syed-Neblett template. The prescribed dose was 18.75 or 20 Gy delivered in five fractions, twice daily, and more than 3 consecutive days. Dosimetric comparisons were made between automatically and manually digitized plans. RESULTS: The region growing algorithm was able to successfully digitize all catheters. The mean difference between automatic and manually digitized positions was 0.4 ± 0.2 mm. No significant difference was found in dosimetric parameters between the automatic and manually digitized plans. The mean D90% of the clinical target volume over all 3 days of treatment of the manual vs. reoptimized automatic plans was 94.3 ± 6.58% and 92.32 ± 8.34%, respectively (p = 0.50). CONCLUSIONS: The algorithm discussed in this article is the first developed for adaptive interstitial brachytherapy for a large number of catheters (14 on average). The algorithm has future potential in digitization quality assurance. A region growing algorithm was developed to automatically digitize interstitial catheters in high-dose-rate brachytherapy. This automatic digitization tool was shown to be accurate compared with manual digitization.

Dosimetric impact of interfraction catheter movement and organ motion on MRI/CT guided HDR interstitial brachytherapy for gynecologic cancer.

PURPOSE: To determine the dosimetric impact of catheter movement for MRI/CT image guided high dose rate (HDR) interstitial brachytherapy (ISBT) for gynecologic cancers. MATERIALS AND METHODS: Ten patients were treated with HDR ISBT. The CTV and organs at risk were contoured using a postimplant MRI and CT. 5 fractions were delivered twice daily on 3 consecutive days. The first fraction was delivered on day 1 (d1), fraction 2-3 on d2 and fraction 4-5 on d3. MRI/CT was acquired prior to the second and fourth fractions. Four scenarios were modeled. (1) The d1 plan was applied to the d2 and d3 CT, using the updated catheter positions. (2) Replanning was performed for d2 and d3. (3) We applied the dwell positions/times from the d2 replan over the d3 CT and compared with a d3 CT replan. (4) Based on daily MRI, target volumes were recontoured and replanned. Dosimetry was analyzed for each plan and compared to the d1 dose distribution. RESULTS: (1) When using the d1 plan on the d2 and d3 CT with the updated catheter positions, the mean CTV D90 was reduced from 93.4% on d1 to 89.3% (p=0.08) on d2 and to 87.7% (p=0.005) on d3. (2) Replanning on d2 and d3 compensated for catheter movement, mean CTV D90 of 95.4% on d2 and 94.6% (p=0.36) on d3. (3) When compared to the replan of d2 applied on the d3 CT vs the d3 replan, there was no significant difference in coverage, mean CTV D90 of 90.9% (p=0.09). (4) Reoptimization based on daily MRI, significantly improved the CTV coverage for each day. The mean D2cc for the rectum was significantly higher with model 1 vs model 3 59.1±4.7 vs 60.9±4.8 (p=0.04) Gy EQD2. There were no significant differences in D2cc of bladder and sigmoid between models. CONCLUSIONS: Interfraction dosimetric changes significantly decreased the CTV coverage of the third day. Rather than replanning on each day, replanning on the day 2 CT before the second or third fraction would give an optimal solution that would compensate for interfraction catheter displacement.

Hemithoracic radiotherapy after extrapleural pneumonectomy for malignant pleural mesothelioma: a dosimetric comparison of two well-described techniques.

INTRODUCTION: Extrapleural pneumonectomy (EPP) with adjuvant radiotherapy may be used to treat malignant pleural mesothelioma. Radiation pneumonitis, felt to be related to contralateral lung radiation dose, may affect patient mortality in this setting. Two standard therapeutic approaches currently used to deliver adjuvant radiotherapy were compared in this study: intensity modulation radiation treatment (IMRT) with a planned dose of 45 Gray (Gy) and a modified electron-photon technique delivering 54 Gy. METHODS: Treatment plans of 10 mesothelioma patients who underwent EPP and hemithoracic IMRT to a total dose of 45 Gy were analyzed. Plans using a combination of opposed anterior posterior radiation fields and electron supplementation (electron-photon technique [EPT]) to a total dose of 54 Gy were then generated and compared with IMRT plans. RESULTS: Dosimetric comparison revealed a significant reduction in contralateral lung dose with EPT versus IMRT, even with increased prescription dose used with EPT plans. Median heart and contralateral kidney doses were also significantly reduced with EPT versus IMRT. Dose coverage of planning target volume and doses to spinal cord, liver, and ipsilateral kidney were similar with use of the two techniques. CONCLUSIONS: Our data suggest that hemithoracic radiotherapy delivered after EPP using EPT may minimize dose to contralateral lung and other structures when compared with IMRT, without compromise of planning target volume coverage.