Patterns of local residual disease and local failure after intensity modulated/image guided radiation therapy for sinonasal tumors in dogs

Abstract

Background: Most dogs with sinonasal tumors (SNT) treated with radiation therapy (RT) died because of local disease progression.

Hypothesis/objectives: Our hypothesis is that the majority of local failure and residual disease would occur within the radiation field.

Animals: Twenty-two dogs with SNT treated with RT.

Methods: Retrospective cohort study.

Inclusion criteria: dogs with SNT receiving 10 daily fractions of 4.2 Gy with intensity modulated radiation therapy (IMRT)/image guided radiation therapy (IGRT) and follow-up cone beam computed tomography (CBCT). Each CBCT was registered with the original radiation planning CT and the gross tumor volume (GTV) contoured. The GTV was classified as residual (GTVr) or a failure (GTVf). The dose statistic for each GTV was calculated with the original IMRT plan. For GTVf, failures were classified as "in-field," "marginal," or "out-field" if at least 95, 20-95, or less than 20% of the volume of failure was within 95% (D95) of the total prescription dose, respectively.

Results: There were 52 follow-up CBCT/CTs. Overall there was a GTVr for 20 dogs and GTVf for 16 dogs. The majority of GTVr volume was within the original GTV. GTVf analysis showed that 75% (12/16) were "in-field," 19% (3/16) were "marginal" and 6% (1/16) were "out-field."

Conclusion and clinical importance: In-field failures are the main pattern for local recurrence, and there is evidence of radioresistant subvolumes within the GTV.

Keywords: IGRT; IMRT; dosimetry; nasal tumor.

FIGURE 1

Gross tumor volume contouring. An example of the imaging GTV contouring in a dog. Transverse and sagittal images of CT/CBCT at different time point for the same dog. Original GTV is blue, CBCT‐3 months GTV is cyan, CBCT‐6 months GTV is green, CBCT‐9 months GTV is yellow, CBCT‐12 months GTV is purple. CT, computed tomography; CBCT, cone beam computed tomography

FIGURE 2

Nasal dosimetry structure. Transverse and sagittal CT images of the “nasal dosimetry” structure set from 8 dogs with sinonasal tumors treated with RT. Original GTV is blue, CBCT‐3 months GTV is cyan, CBCT‐6 months GTV is green, CBCT‐9 months GTV is yellow, CBCT‐12 or more months GTV is purple. CTV is Pink, PTV is red. CT, computed tomography; CBCT, cone beam computed tomography; CTV, clinical target volume; GTV, gross tumor volume; PTV, planned target volume

FIGURE 3

Progression‐free survival (PFS) in days for all 22 dogs

FIGURE 4

Overall survival time (OS) in days for all 22 dogs

FIGURE 5

Overall survival (OS) for all dogs based on gross tumor volume (GTV) (median: 33.35 cm³ or sphere equivalent diameter: 4 cm). <=less, > = more, HR, hazard ratio; 95% CI, 95% confidence interval

FIGURE 6

Spider plots of GTV volumes after treatment for all dogs. Time 0 GTV was GTV before radiation treatments and all other GTV during follow‐up were compared to this GTV. Each line is a dog, each point is an imaging GTV. Dotted line is from last imaging until death. † represents death. For dogs that are alive more than 18 months after RT, the number on the far right represent time of death in months from 1st RT. Underlined number is the censured dog. CR, complete response; GTV, gross tumor volume; PD, progressive disease; PR, partial response; RT, radiation therapy; SD, stable disease

FIGURE 7

Three dimensional (3D) images (dorsal and lateral view) of the GTVf from 3 different dogs (caudal aspect to the left) with marginal failure. A, Green volume is the GTVf and pink volume is CTV. B, The blue volume is the original GTV and was added to the other 2 volumes. CTV, clinical target volume; GTV, gross tumor volume; GTVf, gross tumor volume failure; Figure 8. Dog with out of field recurrence (GTVf) 1‐a CT transverse image, 1‐b sagittal CT image prior to RT with all CBCT volumes superimposed (blue = original GTV, cyan = CBCT‐3 month GTV, green = CBCT‐6 months GTV, yellow = CBCT‐9 month GTV, pink = CTV, Red = PTV) 2‐a/2‐b similar CT images at the time of recurrence 9 months after RT. 2‐c/2‐d 3D images of the GTVf (yellow volume), original GTV (blue volume) and the original CTV (pink volume). CBCT, cone beam computed tomography; CT, computed tomography scan; CTV, clinical target volume; GTV, gross tumor volume; GTVf, gross tumor volume failure; PTV, planned target volume; RT, radiation therapy

FIGURE 8

Dog with out of field recurrence (GTVf) 1‐a CT transverse image, 1‐b sagittal CT image prior to RT with all CBCT volumes superimposed (blue = original GTV, cyan = CBCT‐3 month GTV, green = CBCT‐6 months GTV, yellow = CBCT‐9 month GTV, pink = CTV, Red = PTV) 2a/2b similar CT images at the time of recurrence 9 months after RT. 2‐c/2‐d 3D images of the GTVf (yellow volume), original GTV (blue volume), and the original CTV (pink volume). CBCT, cone beam computed tomography; CT, computed tomography scan; CTV, clinical target volume; GTV, gross tumor volume; GTVf, gross tumor volume failure; PTV, planned target volume; RT, radiation therapy