Volumetric Modulated Arc Therapy for Advanced Pancreatic Cancer

Abstract

Background: Intensity-modulated radiotherapy (IMRT) allows for improved sparing of organs at risk (OARs) in advanced pancreatic cancer. A planning study evaluated if volumetric modulated arc therapy (RapidArc™ [RA]) could be used as an alternative to IMRT in such cases. Patients and Methods: In ten patients, five-field IMRT (5f-IMRT) plans with fixed gantry positions were compared to RA plans using similar constraints for planning target volume (PTV) and OARs. PTV coverage, conformity indices (CI), and OAR doses were compared. One patient was treated using RA and calculated dose distributions were measured in coronal planes in a solid-water phantom. Results: RA plans showed superior mean CI of 1.09 ± 0.02 (± 1 SD [standard deviation]) versus 1.20 ± 0.10 in 5f-IMRT (p = 0.003). Both techniques achieved similar sparing of the right kidney, but RA significantly reduced left kidney doses with V 15 of 7.2% ± 5.3% and 15.9% ± 11.1%, respectively; p = 0.02. RA modestly decreased mean doses to liver (13.8 vs. 15.1 Gy; p = 0.003), stomach (16.7 vs. 17.9 Gy; p = 0.017), small bowel (19.8 vs. 22.1 Gy; p < 0.001), and duodenum (38.8 vs. 41.9 Gy; p = 0.004). Film dosimetry revealed excellent agreement between calculated and measured dose distributions. The delivery time for RA was < 3 min. Conclusion: RA planning achieved superior CI for pancreatic tumors compared to 5f-IMRT, and modestly reduced OAR doses. Fast treatment delivery using RA may decrease the risk of intrafractional organ motion. Ergebnisse: RA-Pläne zeigten einen günstigeren CI von 1,09 ± 0,02 (± 1 SD [Standardabweichung]) gegenüber 1,20 ± 0,10 bei 5f-IMRT (p = 0,003). Mit beiden Techniken gelang eine zufriedenstellende Dosisreduktion der rechten Niere, mittels RA konnten jedoch die V 15 der linken Niere signifikant reduziert werden (7,2% ± 5,3% vs. 15,9% ± 11,1% bei IMRT; p = 0,02). Geringer zeigte sich die Reduktion der mittleren Dosis der Leber (13,8 vs. 15,1 Gy; p = 0,003), des Magens (16,7 vs. 17,9 Gy; p = 0,017), des Dünndarms (19,8 vs. 22,1 Gy; p < 0,001) und des Duodenums (38,8 vs. 41,9 Gy; p = 0,004). Filmdosimetrische Überprüfungen zeigten hervorragende Übereinstimmungen bezüglich kalkulierter und tatsächlicher Dosisverteilung. Die Gesamtbestrahlungszeit betrug < 3 min. Schlussfolgerung: Mittels RA-Planung lässt sich im Vergleich zur 5f-IMRT sowohl ein günstigerer CI als auch moderate Dosisreduktion in den OAR erreichen. Durch die rasche Dosisapplikation vermindert sich das Risiko intrafraktionärer Bewegung der OAR.Schlüsselwörter: Pankreaskarzinom · "Volumetric modulated arc therapy" · Intensitätsmodulierte Radiotherapie · Planungsstudie · Risikoorgane

Volumetric Arc Therapy Seems More Promising for Sparing Organs at Risk in Adjuvant Postoperative Radiotherapy for Pancreatic Adenocarcinoma than Step-and-Shoot Intensity-Modulated Radiotherapy

“…[13] Also for locally advanced pancreas cancer, VMAT was shown to achieve similar dose levels for right kidney and significantly reduce doses for left kidney compared to 5 field IMRT. [12] In our analysis, VMAT plans revealed better overall sparing for right kidney and less amount of high dose regions for left kidney while no statistical difference was found in terms of mean dose and low dose areas for left kidney. Similar to our study design, Ali et al, analyzed 10 patients' dosimetric data and concluded that using double arc VMAT for curative or adjuvant radiotherapy for pancreas cancer patients, provides lower mean and V20-V15 doses of both kidney compared to IMRT, but other organ doses of both plans were found to be similar.…”

“…In another similar dosimetric study for evaluating the use of double arc VMAT for locally advanced pancreas tumors, reduced monitor units, bilateral kidney V15 dose, mean dose of liver, stomach and small bowel dose reported. [12] Kidney dose reduction was common in all the studies. In contrast to second study, high dose regions of liver and small bowel were reduced by VMAT in our study.…”

“…A "small-bowel region" was defined which consisted of the abdominal content after subtracting the PTV, all OARs and the vertebral bodies, with the posterior border extending to the dorsum of the lumbar vertebral body, but excluding the retroperitoneal space. [12] Liver was delineated at MinIP phase.…”

“…[10,11] As the motion is an important problem in radiotherapy planning of pancreas cancer, VMAT can decrease the risk of intrafractional organ motion by shortening treatment time. [12] In the dosimetric studies, comparing VMAT to Helical tomotherapy, IMRT and 3D-CRT, reduced organ at risk doses such as kidney and liver have a promising effect on reducing toxicity due to radiotherapy. [13,14] We aimed to define whether VMAT provides a superior dose distribution in comparison to Intensity modulated radiotherapy (Step and shoot: ssIMRT) based on 4D-CT target volume coverage and organs at risk (OAR) doses in adjuvant postoperative radiotherapy for pancreas adenocarcinoma patients.…”

Dosimetric and Clinical Toxicity Comparison of Critical Organ Preservation with Three-Dimensional Conformal Radiotherapy, Intensity-Modulated Radiotherapy, and RapidArc for the Treatment of Locally Advanced Cancer of the Pancreatic Head

“…By contrast, the V 35 was significantly higher with 3D-crt than with RapidArc (p = 0.007). In a comparative planning study of RapidArc and imrt conducted by Eppinga et al 19 in pcc, RapidArc was observed to modestly lower the mean dose to duodenum (p = 0.004). In our analysis, the mean dose to duodenum was similarly lower with RapidArc than with imrt (p = 0.034) or 3D-crt (p < 0.001).…”