The relationship of dose to nerve volume in predicting pain recurrence after stereotactic radiosurgery in trigeminal neuralgia.

OBJECTIVE Approximately 75%-92% of patients with trigeminal neuralgia (TN) achieve pain relief after Gamma Knife surgery (GKS), although a proportion of these patients will experience recurrence of their pain. To evaluate the reasons for durability or recurrence, this study determined the impact of trigeminal nerve length and volume, the nerve dose-volume relationship, and the presence of neurovascular compression (NVC) on pain outcomes after GKS for TN. METHODS Fifty-eight patients with 60 symptomatic nerves underwent GKS for TN between 2013 and 2015, including 15 symptomatic nerves secondary to multiple sclerosis (MS). High-resolution MRI was acquired the day of GKS. The median maximum dose was 80 Gy for initial GKS and 65 Gy for repeat GKS. NVC, length and volume of the trigeminal nerve within the subarachnoid space of the posterior fossa, and the ratio of dose to nerve volume were assessed as predictors of recurrence. RESULTS Follow-up was available on 55 patients. Forty-nine patients (89.1%) reported pain relief (Barrow Neurological Institute [BNI] Grades I-IIIb) after GKS at a median duration of 1.9 months. The probability of maintaining pain relief (BNI Grades I-IIIb) without requiring resumption or an increase in medication was 93% at 1 year and 84% at 2 years for patients without MS, and 68% at 1 year and 51% at 2 years for all patients. The nerve length, nerve volume, target distance from the brainstem, and presence of NVC were not predictive of pain recurrence. Patients with a smaller volume of nerve (< 35% of the total nerve volume) that received a high dose (≥ 80% isodose) were less likely to experience recurrence of their TN pain after 1 year (mean time to recurrence: < 35%, 32.2 ± 4.0 months; > 35%, 17.9 ± 2.8 months, log-rank test, χ2 = 4.3, p = 0.039). CONCLUSIONS The ratio of dose to nerve volume may predict recurrence of TN pain after GKS. Prospective studies are needed to determine the optimal dose to nerve volume ratio and whether this will result in longer pain-free outcomes.

Clinical correlation of previously undetected cancer-related incidental findings on CT planning scans for radiation therapy.

OBJECTIVE: The purpose of our study was to determine the management and cancer outcome of incidental cancer-related findings reported on CT radiation treatment planning scans. MATERIALS AND METHODS: We conducted a retrospective review of CT planning scans performed from 2004 to 2006 with diagnostic radiology reports. We previously found 45 (8%) cancer-related findings, defined as any previously unknown radiologic finding that could potentially change the staging or treatment of the cancer, in the 580 CT scans reviewed. This study further examines the cancer-related findings to identify their clinical significance, management, and cancer outcomes. RESULTS: Eight (18%) of the 45 cancer-related findings prompted additional imaging, with negative findings and no cancer failure at the site of the cancer-related findings. Three (7%) cancer-related findings resulted in changes in cancer management without further imaging, including initiating induction chemotherapy instead of localized radiation, increasing the radiation dose to identified lymphadenopathy, and changing the sequence of local management to initial surgery followed by radiation. Two of these findings had local recurrence at the site of cancer-related findings. The remaining 34 (76%) cancer-related findings did not result in any additional action. With a median follow-up of 17 months (range, 2-67 months) from CT, there was a similar failure rate at the site of cancer-related findings in the groups without (15%) and with (18%) additional action. CONCLUSION: In our series, cancer-related findings identified by diagnostic radiology review of radiation planning CT scans are associated with low incidence of cancer management changes and disease progression. However, the generalizability of this study is unclear because of the small number of cancer-related findings present.

Implications of previously undetected incidental findings on 3D CT simulation scans for radiation therapy.

PURPOSE: To determine the frequency of significant incidental findings on diagnostic quality simulation computed tomographic (CT) scans for radiotherapy planning. METHODS AND MATERIALS: An institutional review board--approved retrospective review of radiation simulation CT scans with diagnostic radiology reports, performed between 2004 and 2006, was conducted to identify incidental findings, defined as previously unreported findings. An incidental finding was classified as a cancer-related finding (CRF) if it could potentially change the staging and treatment of the cancer. Other nonmalignant findings, not likely caused by cancer, were classified as noncancer findings (NCFs). RESULTS: Of the 580 CT scans performed for radiation planning, 61 (11%) NCFs and 45 (8%) CRFs were identified. Common NCFs included degenerative bone changes (20%), diverticulosis (15%), and lung (11%), kidney (10%), thyroid (10%), and vascular (7%) abnormalities. Two of the vascular NCFs were thrombi requiring anticoagulation. The CRFs included suspected local recurrence (22%); lymphadenopathy (18%); significant progression of local disease (16%); distant metastasis to the liver (16%), bone (11%), and other sites (16%); and malignancy not evident (2%). Eight CRFs prompted additional workup, all with negative results, causing 2 treatment delays. Three CRFs warranted change of treatment without further imaging, including the use of induction chemotherapy before radiation, an increase in radiation dose, and proceeding with surgery up front followed by radiation. The remaining 34 CRFs did not require additional action because the abnormalities were already addressed by the planned treatment (33%), were believed to be benign with further review (29%), or would have been better evaluated by additional imaging that had been scheduled prior to radiation simulation (13%). Overall, 7 of 580 (1%) scans prompted treatment alterations, including 2 treatment delays. CONCLUSION: A comprehensive review of radiation planning CT scans by diagnostic radiologists resulted in a significant change in medical or cancer management in only a small percentage of cases.