A complication probability planning study to predict the safety of a new protocol for intracranial tumour radiotherapy in dogs

Relationship between radiation dose and cerebral microbleed formation in dogs with intracranial tumors

BACKGROUND

Cerebral microbleeds (CMBs) are a possible sequela in human brain tumor patients treated with radiation therapy (RT). No such association is reported in dogs.

OBJECTIVES

To investigate whether CMBs occur in dogs after radiotherapy, and if there is an association between number and dose, and an increase over time.

ANIMALS

Thirty-four client-owned dogs irradiated for primary intracranial neoplasia. ≥2 magnetic resonance imaging (MRI) scans including susceptibility-weighted imaging (SWI) were required.

METHODS

Retrospective, observational, single-center study. Cerebral microbleeds identified on 3 T SWI were counted within the entire brain, and within low- (<20 Gy), intermediate- (20-30 Gy), and high- (>30 Gy) dose regions. A generalized linear mixed-effects model was used to analyze the relationship between the CMBs count and the predictor variables (irradiation dose, time after treatment).

RESULTS

Median follow-up time was 12.6 months (range, 1.8-37.6 months). Eighty-three MR scans were performed. In 4/15 dogs (27%, 95% CI, 10%-52%) CMBs were present at baseline. ≥1 CMBs after RT were identified in 21/34 dogs (62%, 95% CI, 45%-77%). With each month, the number of CMBs increased by 14% (95% CI, 11%-16%; P < .001). The odds of developing CMBs in the high-dose region are 4.7 times (95% CI, 3.9-5.6; P < .001) greater compared with the low-dose region.

CONCLUSION AND CLINICAL IMPORTANCE

RT is 1 possible cause of CMBs formation in dogs. Cerebral microbleeds are most likely to occur in the peritumoral high-dose volume, to be chronic, and to increase in number over time. Their clinical relevance remains unknown.

Risk adaptive planning with biology-based constraints may lead to higher tumor control probability in tumors of the canine brain: A planning study

BACKGROUND

Classical radiation protocols are guided by physical dose delivered homogeneously over the target. Protocols are chosen to keep normal tissue complication probability (NTCP) at an acceptable level. Organs at risk (OAR) adjacent to the target volume could lead to underdosage of the tumor and a decrease of tumor control probability (TCP). The intent of our study was to explore a biology-based dose escalation: by keeping NTCP for OAR constant, radiation dose was to be maximized, allowing to result in heterogeneous dose distributions.

METHODS

We used computed tomography datasets of 25 dogs with brain tumors, previously treated with 10x4 Gy (40 Gy to PTV D50). We generated 3 plans for each patient: A) original treatment plan with homogeneous dose distribution, B) heterogeneous dose distribution with strict adherence to the same NTCPs as in A), and C) heterogeneous dose distribution with adherence to NTCP <5%. For plan comparison, TCPs and TCP equivalent doses (homogenous target dose which results in the same TCP) were calculated. To enable the use of the generalized equivalent uniform dose (gEUD) metric of the tumor target in plan optimization, the calculated TCP values were used to obtain the volume effect parameter a.

RESULTS

As intended, NTCPs for all OARs did not differ from plan A) to B). In plan C), however, NTCPs were significantly higher for brain (mean 2.5% (SD±1.9, 95%CI: 1.7,3.3), p<0.001), optic chiasm (mean 2.0% (SD±2.2, 95%CI: 1.0,2.8), p=0.010) compared to plan A), but no significant increase was found for the brainstem. For 24 of 25 of the evaluated patients, the heterogenous plans B) and C) led to an increase in target dose and projected increase in TCP compared to the homogenous plan A). Furthermore, the distribution of the projected individual TCP values as a function of the dose was found to be in good agreement with the population TCP model.

CONCLUSION

Our study is a first step towards risk-adaptive radiation dose optimization. This strategy utilizes a biologic objective function based on TCP and NTCP instead of an objective function based on physical dose constraints.

Treatment of intracranial neoplasia in dogs using higher doses: A randomized controlled trial comparing a boosted to a conventional radiation protocol

BACKGROUND

Local progression of intracranial tumors can be the consequence of insufficient radiation dose delivered. Dose increases in the brain must be made carefully so as not to risk debilitating adverse effects such as radiation necrosis.

HYPOTHESIS

A new protocol with 10 × 4 Gy + 11% physical dose increase limited to the macroscopic tumor volume results in a clinically better outcome compared to a 10 × 4 Gy protocol.

ANIMALS

Fifty-seven client-owned dogs with primary intracranial neoplasia.

METHODS

Randomized controlled trial. Twenty-eight dogs were assigned to the control protocol (10 × 4 Gy) and 29 to the simultaneous integrated boost (SIB) protocol with 4.45 Gy dose increase. Treatment groups were compared for outcome and signs of toxicity.

RESULTS

Mild, transient acute or early-delayed adverse radiation effects were observed in 5 dogs. Severe late adverse effects were not seen. Between the protocols, no significant differences were found for outcome (intention-to-treat analysis): overall time to progression (TTP) was 708 days (95% confidence interval (95% CI) [545,872]), in the control group it was 828 days (95% CI [401,1256]), and in the SIB group 627 days (95% CI [282,973]; P = .07). Median overall survival (OS) was 684 days (95% CI [516,853]), in the control group it was 724 days (95% CI [623,826]), and in the SIB group 557 days (95% CI [95,1020]; P = .47). None of the tested variables was prognostic in terms of outcome.

CONCLUSION AND CLINICAL IMPORTANCE

The dose escalation used with an 11% physical dose increase did not result in better outcome.

Can volumetric modulated arc radiation therapy reduce organ at risk dose in stage 4 sinonasal tumors in dogs treated with boost irradiation?

Intensity modulated radiation therapy (IMRT) introduced marked changes to cancer treatment in animals by reducing dose to organs at risk (OAR). As the next technological step, volumetric modulated arc therapy (VMAT) has advantages (increased degrees-of-freedom, faster delivery) compared to fixed-field IMRT. Our objective was to investigate a possible advantage of VMAT over IMRT in terms of lower OAR doses in advanced-disease sinonasal tumors in dogs treated with simultaneously-integrated boost radiotherapy. A retrospective, analytical, observational study design was applied using 10 pre-existing computed tomography datasets on dogs with stage 4 sinonasal tumors. Each dataset was planned with both, 5-field IMRT and 2 arc VMAT with 10x4.83 Gy to the gross tumor volume and 10x4.2 Gy to the planning target volume. Adequate target dose coverage and normal tissue complication probability of brain ≤5% was required. Dose constraints aspired to were D60 <15 Gy for eyes, D2 <35.4 Gy for corneae, and Dmean <20 Gy for lacrimal glands. OAR dose was statistically significantly higher in IMRT plans than in VMAT plans. Median eye D60% was 18.5 Gy (interquartile range (IQR) 17.5) versus 16.1 Gy (IQR 7.4) (p = 0.007), median lacrimal gland dose 21.8 Gy (IQR 20.5) versus 18.6 Gy (IQR 7.0) (p = 0.013), and median cornea D2% 45.5 Gy (IQR 6.8) versus 39.9 Gy (IQR 10.0) (p<0.005) for IMRT versus VMAT plans, respectively. Constraints were met in 21/40 eyes, 7/40 corneae, and 24/40 lacrimal glands. Median delivery time was significantly longer for IMRT plans than for VMAT plans (p<0.01). Based on these results, VMAT plans were found to be superior in sparing doses to eyes, lacrimal glands, corneae. However, not all ocular OAR constraints could be met while ensuring adequate dose coverage and restricting brain toxicity risk for both planning techniques.

Outcome After Radiation Therapy in Canine Intracranial Meningiomas or Gliomas

AIM

To characterize a group of dogs diagnosed with meningioma or glioma treated with radiation therapy and assess the clinical impact of diagnosis and radiation protocol on survival time.

PATIENTS AND METHODS

Canine patient records from a single veterinary referral hospital, between 2011 and 2015, were searched for intracranial tumour cases treated with radiation therapy, as a sole modality. Thirty-two dogs were included.

RESULTS

Median survival times were 524 days [95% confidence interval (CI)=287-677] in total, 512 days (95% CI=101-682) for the glioma group and 536 days (95% CI=249-677) for the meningioma group. No significant difference in survival was detected when using a definitive or a palliative protocol (p=0.130), nor other prognostic factors were found.

CONCLUSION

Our results highlight the efficacy of radiation therapy in the treatment of canine meningioma, as well as glioma, suggesting a change in the current perception of the response of glial tumours to radiation.

Canine presumed glial brain tumours treated with radiotherapy: Is there an inferior outcome in tumours contacting the subventricular zone?

Post-treatment outcome in canine glial tumours is described with a broad range of survival times between 2 and 28 months. After surgery or radiation therapy, the tumours may progress locally or spread within the central nervous system. It is unknown if tumour- or patient-specific factors influence prognosis. In humans, glioblastoma involving the subventricular zone has been found to recur distantly, with shortened time to progression and overall survival. We included 32 dogs irradiated for a presumptive primary glial brain tumour in this retrospective cohort study. Tumours were grouped relative to subventricular zone contact and overt ventricular invasion assessing pre-treatment magnetic resonance images. Median time to progression (TTP) for all cases was 534 days (95%CI, 310-758), with a significantly shorter TTP in dogs with lesions at the subventricular zone (median TTP, 260 vs. 687 days; p = .049). Tumours at the subventricular zone progressed more often (p = .001), and more likely as CNS-metastasis (52.9% vs. 13.3%, p = .028). Median overall survival (OS) was 489 days (95%CI, 147-831) and median tumour-specific survival 609 days (95%CI, 382-835). Involvement of the subventricular zone was significantly associated with a shorter tumour-specific survival (median, 306 vs. 719 days; p = .044). Glial tumours contacting the subventricular zone in dogs have a shorter tumour-specific survival and a higher rate of progression and CNS-metastasis. Despite local tumour control, metastasis must be considered and should prompt further treatment approaches.

CyberKnife stereotactic radiotherapy for treatment of primary intracranial tumors in dogs

Background

Limited data exist about the use, efficacy, and prognostic factors influencing outcome when CyberKnife is used to treat dogs with intracranial neoplasia.

Objectives

To determine the prognosis and associated prognostic factors for dogs that were imaged, determined to have primary intracranial tumors, and treated with CyberKnife radiotherapy.

Animals

Fifty‐nine dogs treated with CyberKnife radiotherapy for primary intracranial tumors.

Methods

Retrospective medical record review of cases from January 2010 to June 2016. Data extracted from medical records included signalment, weight, seizure history, tumor location, tumor type (based on imaging), gross tumor volume, planned tumor volume, treatment dates, radiation dose, recurrence, date of death, and cause of death.

Results

The median progression‐free interval (PFI) was 347 days (range 47 to 1529 days), and the median survival time (MST) was 738 days (range 4 to 2079 days). Tumor location was significantly associated with PFI when comparing cerebrum (median PFI 357 days; range 47‐1529 days) versus cerebellum (median PFI 97 days; range 97‐168 days) versus brainstem (median PFI 266 days; range 30‐1484 days), P = .03. Additionally, the presumed tumor type was significantly associated with MST (P < .001).

Conclusions and Clinical Importance

Use of Cyberknife and SRT might improve MST, compared with RT, in dogs with intracranial neoplasia.

Definitive-intent uniform megavoltage fractioned radiotherapy protocol for presumed canine intracranial gliomas: retrospective analysis of survival and prognostic factors in 38 cases (2013-2019)

Background

Radiotherapy (RT) is currently considered the treatment of choice for presumed canine intracranial gliomas. However, variable therapeutic responses are described, due to heterogeneous populations and different radiation methods or protocols. Only one study dedicated to intracranial suspected glioma highlighted prognostic criteria. Determination or confirmation of specific clinical and imaging prognostic factors may guide the therapeutic management of these tumours. The objectives were to provide data on long-term clinical outcome (including quality of life, QoL) and to determine specific prognostic factors associated with survival time. We report a single-institution retrospective study, including all dogs with suspected symptomatic primary solitary intracranial glioma, treated with a complete uniform fractionated megavoltage radiation protocol of 15x3Gy over 5 weeks, between January 2013 and February 2019. Thirty-eight client-owned dogs were included. Medical records were retrospectively evaluated for median overall survival time (MST), clinical and imaging responses. Prognostic factors on survival were researched in terms of signalment, clinical presentation, tumour imaging characteristics and response following RT. Finally, the RT’s impact on the dogs’ clinical signs and Qol were evaluated by the owners.

Results

The disease-specific MST was 698 days (95% CI: 598–1135). Survival at 1 and 2 years were respectively 74.2 ± 7.4% and 49.0 ± 9.8%. Initial clinical signs were related to survival, as well as tumour characteristics such as cystic-pattern, mass effect and Tumour/Brain volume ratio. No significant adverse effect or radiotoxicity was observed.

Conclusions

RT appears as a safe and effective treatment for canine intracranial gliomas, allowing long-term tumour control, improvement of life’s quality and management of associated clinical signs. The initial clinical signs and MRI characteristics (Tumour/Brain volume ratio, cyst-like lesion and mass effect) may help predict the prognosis.

Radiological protection of the patient in veterinary medicine and the role of ICRP

At the request of the Main Commission of the International Commission on Radiological Protection (ICRP), Task Group 107 (TG107) was set up to consider the issue of radiological protection of the patient in veterinary medicine. TG107, who authored this article, brought together information relating to the use of diagnostic imaging and radiation oncology in veterinary medicine. A number of specific areas were identified that appeared to be appropriate for attention by ICRP. These included the use of dose quantities and units, the need for re-evaluation of stochastic and deterministic risks from ionising radiation in animals, and the growing use of imaging and therapeutic equipment for animals that is little different from that available to humans. TG107 unanimously recommended that it was both appropriate and timely for ICRP to consider and advise on these issues, and the Main Commission agreed. This paper summarises the findings of TG107.

Definitive-intent intensity-modulated radiation therapy provides similar outcomes to those previously published for definitive-intent three-dimensional conformal radiation therapy in dogs with primary brain tumors: A multi-institutional retrospective study

Radiotherapy with or without surgery is a common choice for brain tumors in dogs. Although numerous studies have evaluated use of three-dimensional conformal radiotherapy, reports of definitive-intent, IMRT for canine intracranial tumors are lacking. Intensity-modulated radiation therapy has the benefit of decreasing dose to nearby organs at risk and may aid in reducing toxicity. However, increasing dose conformity with IMRT calls for accurate target delineation and daily patient positioning, in order to decrease the risk of a geographic miss. To determine survival outcome and toxicity, we performed a multi-institutional retrospective observational study evaluating dogs with brain tumors treated with IMRT. Fifty-two dogs treated with fractionated, definitive-intent IMRT at four academic radiotherapy facilities were included. All dogs presented with neurologic signs and were diagnosed via MRI. Presumed radiological diagnoses included 37 meningiomas, 12 gliomas, and one peripheral nerve sheath tumor. One dog had two presumed meningiomas and one dog had either a glioma or meningioma. All dogs were treated in the macroscopic disease setting and were prescribed a total dose of 45-50 Gy (2.25-2.5 Gy per fraction in 18-20 daily fractions). Median survival time for all patients, including seven cases treated with a second course of therapy was 18.1 months (95% confidence of interval 12.3-26.6 months). As previously described for brain tumors, increasing severity of neurologic signs at diagnosis was associated with a worse outcome. Intensity-modulated radiation therapy was well tolerated with few reported acute, acute delayed, or late side effects.

Ocular and periocular radiation toxicity in dogs treated for sinonasal tumors: A critical review

Visual impairment from radiation‐induced damage can be painful, disabling, and reduces the patient's quality of life. Ocular tissue damage can result from the proximity of ocular organs at risk to irradiated sinonasal target volumes. As toxicity depends on the radiation dose delivered to a certain volume, dose‐volume constraints for organs at risk should ideally be known during treatment planning in order to reduce toxicity. Herein, we summarize published ocular toxicity data of dogs irradiated for sinonasal tumors from 36 publications (1976‐2018). In particular, we tried to extract a dose guideline for a clinically acceptable rate of ocular toxicity. The side effects to ocular and periocular tissues were reported in 26/36 studies (72%) and graded according to scoring systems (10/26; 39%). With most scoring systems, however, toxicities of different ocular and periocular tissues are summed into one score. Further, the scores were mostly applied in retrospect and lack volume‐ and dose‐data. This incomplete information reflects the crux of the matter for radiation dose tolerance in canine ocular tissues: The published information of the last three decades does not allow formulating dose‐volume guidelines. As a start, we can only state that a mean dose of 39 Gy (given in 10 x 4.2 Gy fractions) will lead to loss of vision by one or both eyes, while mean doses of <30 Gy seem to preserve functionality. With a future goal to define tolerated doses and volumes of ocular and periocular tissues at risk, we propose the use of combined ocular toxicity scoring systems.

Using biologically based objectives to optimize boost intensity-modulated radiation therapy planning for brainstem tumors in dogs

Irradiated brain tumors commonly progress at the primary site, generating interest in focal dose escalation. The aim of this retrospective observational study was to use biological optimization objectives for a modeling exercise with simultaneously-integrated boost IMRT (SIB-IMRT) to generate a dose-escalated protocol with acceptable late radiation toxicity risk estimate and improve tumor control for brainstem tumors in dogs safely. We re-planned 20 dog brainstem tumor datasets with SIB-IMRT, prescribing 20 × 2.81 Gy to the gross tumor volume (GTV) and 20 × 2.5 Gy to the planning target volume. During the optimization process, we used biologically equivalent generalized equivalent uniform doses (gEUD) as planning aids. These were derived from human data, calculated to adhere to normal tissue complication probability (NTCP) ≤5%, and converted to the herein used fractionation schedule. We extracted the absolute organ at risk dose-volume histograms to calculate NTCP of each individual plan. For planning optimization, gEUD(a = 4)  = 39.8 Gy for brain and gEUD(a = 6.3)  = 43.8 Gy for brainstem were applied. Mean brain NTCP was low with 0.43% (SD ±0.49%, range 0.01-2.04%); mean brainstem NTCP was higher with 7.18% (SD ±4.29%, range 2.87-20.72%). Nevertheless, NTCP of < 10% in brainstem was achievable in 80% (16/20) of dogs. Spearman's correlation between relative GTV and NTCP was high (ρ = 0.798, P < .001), emphasizing increased risk with relative size even with subvolume-boost. Including biologically based gEUD values into optimization allowed estimating NTCP during the planning process. In conclusion, gEUD-based SIB-IMRT planning resulted in dose-escalated treatment plans with acceptable risk estimate of NTCP < 10% in the majority of dogs with brainstem tumors. Risk was correlated with relative tumor size.

Comparative evaluation of a novel, moderately hypofractionated radiation protocol in 56 dogs with symptomatic intracranial neoplasia

Background: Use of strongly hypofractionated radiation treatments in dogs with intracranial neoplasia did not improve outcomes and yielded increased rates of toxicosis.

Objectives: To evaluate safety and efficacy of a new, moderately hypofractionated radiation protocol of 10 × 4 Gy compared to a standard protocol.

Animals: Convenience sample of 56 client‐owned dogs with primary symptomatic brain tumors.

Methods: Retrospective observational study. Twenty‐six dogs were assigned to the control standard protocol of 20 × 2.5 Gy (group A) and 30 dogs to the new protocol of 10 × 4 Gy (group B), assigned on owners' informed consent. Statistical analysis was conducted under the “as treated” regime, using Kaplan‐Meier and Cox‐regression analysis. Treatment was delivered with technically advanced image‐guided radiation therapy. The 2 treatment groups were compared in terms of outcome and signs of toxicosis.

Results: Overall progression‐free interval (PFI) and overall survival (OS) time were favorable, with 663 (95%CI: 497;828) and 637 (95%CI: 403;870) days, respectively. We found no significant difference between the two groups: PFI for dogs in group A vs B was 608 (95%CI: 437;779) days and mean (median not reached) 863 (95%CI: 644;1083) days, respectively (P = .89), and OS for dogs in group A vs B 610 (95%CI: 404;816) and mean (median not reached) 796 (95%CI: 586;1007) days (P = .83).

Conclusion and Clinical Importance: In conclusion, 10 × 4 Gy is a safe and efficient protocol for treatment of primary intracranial neoplasia and future dose escalation can be considered.