Comparing the dosimetric impact of interfractional anatomical changes in photon, proton and carbon ion radiotherapy for pancreatic cancer patients

Abstract

Radiotherapy using charged particles is characterized by a low dose to the surrounding healthy organs, while delivering a high dose to the tumor. However, interfractional anatomical changes can greatly affect the robustness of particle therapy. Therefore, we compared the dosimetric impact of interfractional anatomical changes (i.e. body contour differences and gastrointestinal gas volume changes) in photon, proton and carbon ion therapy for pancreatic cancer patients. In this retrospective planning study, photon, proton and carbon ion treatment plans were created for 9 patients. Fraction dose calculations were performed using daily cone-beam CT (CBCT) images. To this end, the planning CT was deformably registered to each CBCT; gastrointestinal gas volumes were delineated on the CBCTs and copied to the deformed CT. Fraction doses were accumulated rigidly. To compare planned and accumulated dose, dose-volume histogram (DVH) parameters of the planned and accumulated dose of the different radiotherapy modalities were determined for the internal gross tumor volume, internal clinical target volume (iCTV) and organs-at-risk (OARs; duodenum, stomach, kidneys, liver and spinal cord). Photon plans were highly robust against interfractional anatomical changes. The difference between the planned and accumulated DVH parameters for the photon plans was less than 0.5% for the target and OARs. In both proton and carbon ion therapy, however, coverage of the iCTV was considerably reduced for the accumulated dose compared with the planned dose. The near-minimum dose ([Formula: see text]) of the iCTV reduced with 8% for proton therapy and with 10% for carbon ion therapy. The DVH parameters of the OARs differed less than 3% for both particle modalities. Fractionated radiotherapy using photons is highly robust against interfractional anatomical changes. In proton and carbon ion therapy, such changes can severely reduce the dose coverage of the target.

Dosimetric effects of anatomical changes during fractionated photon radiation therapy in pancreatic cancer patients

“…2). In particle therapy, changes in gastrointestinal gas can severely affect target dose coverage, as established for carbon ion and proton therapy in earlier studies of our group 17, 27. The observed limited effects of changes in gastrointestinal gas in our current study illustrate the inherent robustness of photon radiation therapy.…”

Dosimetric impact of gastrointestinal air column in radiation treatment of pancreatic cancer

“…On the other hand, our plans were all done with an IMRT technique, and IMRT offers the advantage of dose delivery based on beamlet segmentation. Similar findings were observed by Houweling et al 7 who compared photon, proton and carbon ion and concluded that photon beam is more robust to interfractional changes in pancreatic cancer using modulated beam. With beamlets, only a small fraction of the beam passes through at any given area of the air column and the air would thus have less potential impact on overall dose distribution.…”

“…Adaptive treatment approaches have been proposed for the changes in anatomical structures due to various parameters but have not exclusively pointed to changes in air column. 6,7 It is known that neither static CT nor 4DCT simulation scans will capture the potential variability of the air column that can be seen on a daily basis. 6,7 Air volume variability in the stomach and bowel is commonly observed in clinical practice on imaging studies and such variability in the air column can be seen during the course of radiation treatment for abdominal malignancies.…”

“…13 Concerns arise from the complexities in accurately treating pancreatic cancer due to factors such as gastric air column and related organ motion. 7,14 The anatomical position of the pancreas inside the abdominal cavity related to the aforementioned changes inevitably leads to movement in the target volume position and location of OARs with respect to isocentre location. Consequently, image guidance plays a key role in accurately treating pancreatic cancer with IMRT.…”

Density override in treatment planning to mitigate the dosimetric effect induced by gastrointestinal gas in esophageal cancer radiation therapy

“…There were only a few studies on the dosimetric effect induced by gas changes and its mitigation approach in RT of upper and middle gastrointestinal cancers [10][11][12][13]. For esophageal cancer, the focus was on dosimetric impact of gastric filling [14,15].…”