Abstract
BackgroundTo compare volumetric-modulated arc therapy plans with conventional radiation therapy (3D-CRT) plans in pancreatic and bile duct cancers, especially for bilateral kidney preservation.MethodsA dosimetric analysis was performed in 21 patients who had undergone radiotherapy for pancreatic or bile duct carcinoma at our institution. We compared 4-field 3D-CRT and 2 arcs RapidArc (RA) plans. The treatment plan was designed to deliver a dose of 50.4 Gy to the planning target volume (PTV) based on the gross disease in a 1.8 Gy daily fraction, 5 days a week. Planning objectives were 95% of the PTV receiving 95% of the prescribed dose and no more than 2% of the PTV receiving more than 107%. Dose-volume histograms (DVH) for the target volume and the organs at risk (right and left kidneys, bowel tract, liver and healthy tissue) were compared. Monitor units and delivery treatment time were also reported.ResultsAll plans achieved objectives, with 95% of the PTV receiving ≥ 95% of the dose (D95% for 3D-CRT = 48.9 Gy and for RA = 48.6 Gy). RapidArc was shown to be superior to 3D-CRT in terms of organ at risk sparing except for contralateral kidney: for bowel tract, the mean dose was reduced by RA compared to 3D-CRT (16.7 vs 20.8 Gy, p = 0.0001). Similar result was observed for homolateral kidney (mean dose of 4.7 Gy for RA vs 12.6 Gy for 3D-CRT, p < 0.0001), but 3D-CRT significantly reduced controlateral kidney dose with a mean dose of 1.8 Gy vs 3.9 Gy, p < 0.0007. Compared to 3D-CRT, mean MUs for each fraction was significantly increased with RapidArc: 207 vs 589, (p < 0.0001) but the treatment time was not significantly different (2 and 2.66 minutes, p = ns).ConclusionRapidArc allows significant dose reduction, in particular for homolateral kidney and bowel, while maintaining target coverage. This would have a promising impact on reducing toxicities.
Highlights
To compare volumetric-modulated arc therapy plans with conventional radiation therapy (3D-CRT) plans in pancreatic and bile duct cancers, especially for bilateral kidney preservation
The administration of induction chemotherapy before RCT has been shown to be a promising strategy for selected patients with non progressive disease, which may help to define the subset of patients likely to benefit from RCT while sparing those with rapidly progressive disease from potentially toxic radiotherapy [4]
The volumetric-modulated arc therapy (VMAT) approach has a number of potential advantages compared to intensity modulated radiation therapy (IMRT) by significantly reducing the treatment time and the number of monitor units (MU), and improving normal tissue sparing while keeping the adequate target coverage [18,19,20]
Summary
To compare volumetric-modulated arc therapy plans with conventional radiation therapy (3D-CRT) plans in pancreatic and bile duct cancers, especially for bilateral kidney preservation. In the case of resectable pancreatic cancer, it is well established that RCT should be only considered in the adjuvant setting after insufficient pancreatic resection [5], whereas for bile duct malignancies, radiotherapy (RT) is likely to prolong survival in case of locally advanced disease as well as after R1 resection [6]. Recent data regarding the treatment of pancreatic disease are in favor of RCT without prophylactic irradiation of peripancreatic lymph nodes since the use of small radiation fields seems to provide similar local recurrence rates and lower gastrointestinal (GI) toxicity [7,8]. In addition to a favorable toxicity profile, the local control is not compromised with IMRT [15]
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