Relationship of dose to vascular target volumes and local failure in pancreatic cancer patients undergoing neoadjuvant chemoradiation.

Objective: The objectives of this study were to evaluate whether dose to the vasculature is associated with local control after surgery in patients with borderline resectable (BLR) and resectable pancreatic cancer (PCA) receiving neoadjuvant radiation therapy (RT) and to identify a dose threshold for clinical use. Methods: Patients with BLR and resectable PCA treated with neoadjuvant RT were retrospectively reviewed. During this period, the institutional paradigm shifted from standard fractionation to hypofractionation/stereotactic body radiation therapy (SBRT). A vasculature clinical target volume (Vasc CTV) was contoured for each patient and defined as a 5-mm margin around the superior mesenteric artery (SMA) from its origin to the pancreatic head, the celiac artery from its origin to the level of the trifurcation and any involved vein. The Vasc CTV D95 was normalized to a 2-Gy equivalent dose to determine the optimal dose associated with optimal local failure-free survival (LFFS). Results: Forty-seven patients were included in the analysis. A Vasc CTV D95 of 32.7 Gy was the optimal cutoff for LFFS. Patients with Vasc CTV D95 Equivalent dose in 2 Gy per fraction (EQD2) >32.7 Gy had significantly longer LFFS compared to patients with Vasc CTV D95 EQD2 ≤32.7 Gy at 12 months (91% vs. 51%, respectively) and 24 months (86% vs. 12%, respectively). The median disease-free survival (DFS) for patients with EQD2 >32.7 Gy was 30.4 months compared to 14.0 months in patients with EQD2 ≤32.7 Gy (p = 0.01). There was no significant difference in overall survival (OS) between the two groups. Conclusions: During neoadjuvant treatment, dose to the Vasc CTV is associated with durability of local control (LC) after resection and should be intentionally included in the treatment volume with an EQD2 goal of 31-33 Gy.

Hematologic Toxicity Comparison of Intensity Modulated Proton Therapy and Intensity Modulated Radiation Therapy in Anal Cancer Patients.

PURPOSE: We hypothesize that hematologic toxicity will be lower in anal cancer patients treated definitively with intensity modulated proton therapy (IMPT) compared with patients treated with intensity modulated radiation therapy (IMRT). METHODS: Patients enrolled on a prospective feasibility trial assessing the use of IMPT for anal cancer were compared with contemporaneous patients treated with IMRT. Blood counts were collected during chemoradiation. Hematologic events were graded according to CTCAE version 5.0. Pelvic bone marrow (PBM) and positron emission tomography-defined active bone marrow (ABM) were defined and contoured for each patient. Toxicity rates, PBM and ABM dose metrics were compared between groups. RESULTS: Forty-one patients treated with definitive chemoradiation for anal cancer between 2015 and 2021 were included in this analysis. Of the evaluable patients, 14 patients were treated with IMPT and 27 were treated with IMRT. All PBM dose metrics were lower in patients receiving IMPT. Patients treated with IMPT versus IMRT also had a significantly lower ABM mean dose (1996 vs. 3073 Gy, P<0.01). However, there was no statistically significant difference in hematologic toxicity between the groups. Seventy percent of patients treated with IMRT had at least 1 grade ≥3 hematologic event compared with 86% in the IMPT group (P=0.48). CONCLUSION: Proton treatment reduced bone marrow doses but was not associated with lower hematologic toxicity when compared with IMRT.

The value of hybrid interstitial tandem and ring applicators for organ at risk dose reduction in small volume cervical cancer.

PURPOSE: Magnetic resonance imaging (MRI)-guided adaptive brachytherapy is the standard of care for cervical cancer. Hybrid intracavitary/interstitial applicators for bulky tumor (high-risk clinical target volume [HR-CTV] > 30 cc) dose escalation is recommended in the EMBRACE II trial. The value of hybrid applicators for smaller HR-CTV (< 30 cc) in organ at risk (OAR) sparing is less certain. MATERIAL AND METHODS: Twenty-seven patients with FIGO stage I-IVA cervical cancer treated with definitive chemoradiation and MRI-based brachytherapy using conventional tandem and ring (TR) applicators were re-planned using virtual needles. They were then summed with the external beam dose to evaluate target coverage and OAR dose using EQD2 summation. Target and OAR dose with/without hybrid applicator use were compared. RESULTS: Eighty-one percent had HR-CTV volumes < 30 cc, for which, hybrid TR applicators had significantly lower mean D2cc to all OARs without differences in target coverage. For HR-CTV < 30 cc, the bladder and rectal OAR goals per EMBRACE II were exceeded in significantly fewer patients with the hybrid TR applicators. No significant difference was found in the sigmoid D2cc dose goal. CONCLUSIONS: In small volume tumors (< 30 cc), hybrid applicators may offer improved OAR sparing compared with conventional tandem and ring applicators, and may increase the proportion of patients meeting EMBRACE II OAR goals.