A dosimetric comparison of proton and photon therapy in unresectable cancers of the head of pancreas

Abstract

Proton therapy does not appear to reduce OAR volumes receiving high dose. Protons are able to reduce the treated volume receiving low-intermediate doses, however the clinical significance of this remains to be determined in future investigations.

Proton beam reirradiation for locally recurrent pancreatic adenocarcinoma

“…This is the case when the initial treatment was definitive chemoradiation to unresectable disease and there is duodenum close to or within the PTV for a second treatment course. We have previously described the dosimetric advantages of protons in lowering the volume of bowel and stomach treated in the low-dose region, however, due to decreased conformality of passively scattered protons, there can be an increased volume of duodenum in the high-dose region depending on the proximity to the target (6). In these cases, combined photon/proton plans may offer an advantage in lowering the high dose to the duodenum while still maintaining low dose to the other OARs.…”

“…Two patients were treated with definitive chemoradiation to unresectable disease as their initial therapy. Nine patients received adjuvant Gemcitabine following their initial treatment course for a median number of 4 months [2][3][4][5][6]. The median time from the prior radiation treatment course to local recurrence was 17.7 months .…”

“…One patient was treated with Gemcitabine/Abraxane and one patient was treated with FOLFIRINOX and then switched to Gemcitabine for continued progression. The median number of months of systemic treatment for local recurrence was 4 months [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] prior to PRT. The median number of months of observation from the time of recurrence to start of PRT for patients who did not receive chemotherapy for local recurrence was 1.7 months (1.2-10).…”

“…Eight patients developed metastatic disease in the liver and lungs with an indolent course and median survival of 8 months (0.5-27.8) from the diagnosis of metastatic disease. Only six patients were treated with chemotherapy following PRT for disease progression and the median chemotherapy-free interval in these patients was 7 months [4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”

“…Similarly, a locally recurrent esophageal cohort treated with proton reirradiation reported modest toxicities (maximum radiation attributed acute non-hematologic toxicity was grade 2), median overall survival (OS) of 14 months from the start of PRT, and excellent symptom palliation (5). A dosimetric comparison of proton beam radiation verses IMRT for unresectable pancreatic cancer showed decreased stomach, duodenum, and small bowel dose in the low-dose regions with proton radiation (6). In this dosimetric analysis, PRT yielded increased doses in the mid to high-dose regions to the duodenum in the intact setting, implying that patient selection may be necessary to avoid high dose to the duodenum when it is close to or included in the retreatment field.…”