Clinical case study: Radiation oncolcogy in the treatment of pituitary macroadenoma

pituitary macroadenoma
Figure 1: Before radiotherapy

Over a period of about six weeks starting November 2017, Toastie, a 9-year-old male entire kelpie, became markedly lethargic and would yelp intermittently at random times. This was extremely unusual for Toastie, who is normally a very active dog. The lethargy and yelping appeared to coincide with the departure of the male owner who is primarily responsible for providing most of Toastie’s environmental enrichment at home, so it was initially thought that this was the cause of the behaviour change. 

In late December 2017, Toastie was assessed at another specialist referral hospital a week prior to the return of the male owner since the lethargy was becoming more pronounced, but he appeared normal on neurologic examination and there were no other symptoms or abnormal findings on baseline blood work, urinalysis, thoracic radiography, and abdominal ultrasonography. An MRI was discussed at that time to rule out intracranial causes for the behaviour change, but the owner elected to wait for her partner’s return to see if Toastie’s behaviour would change. 

Unfortunately, the symptoms persisted so they ultimately proceeded with an MRI scan of his brain roughly one month later which revealed a large, homogeneously contrast-enhancing mass in the pituitary fossa measuring 17 x 19 x 16mm, consistent with a pituitary macroadenoma (see image labeled ‘before radiotherapy’). 

pituitary macroadenoma
Figure 2: Four months after radiotherapy

Pituitary tumours in dogs can be either active/functional or inactive/nonfunctional in their biologic behaviour. If functional, they can lead to pituitary-dependent hyperadenocorticism (Cushings disease) at first, but if the pituitary nodule grows larger, it can potentially lead to neurologic symptoms due to the space-occupying nature of the growing mass putting pressure against the surrounding normal brain tissue and optic nerve tracts ventrally. Some patients with pituitary tumours may present with only acute blindness as the sole symptom, while others can present with vague intracranial signs (mental dullness, lethargy, behaviour changes, vocalisation, inappetence) or seizures. Radiation therapy is the primary treatment option for pituitary tumours causing neurologic symptoms. The main aim of radiotherapy is to reduce the tumour volume to decrease, and usually eliminate, the neurologic symptoms due to the space-occupying effects of the mass. Most patients will need to remain on medication for Cushings disease if their pituitary tumour is functional since radiotherapy is not likely to eliminate all the abnormal pituitary gland cells producing higher levels of ACTH. However, some patients may be able to come off their Cushings medication following radiotherapy. 

Toastie was referred to the Radiation Oncology service at BVSC and a radiation-planning CT scan was performed. Despite having already had an MRI done, which is a superior imaging modality than CT for the brain and spinal cord, a planning CT is still required in order to prepare the patient positioning devices needed for consistent positioning of the patient for each radiation treatment, and to complete the 3D treatment planning to deliver the high radiation dose safely and accurately into the tumour volume while sparing the normal surrounding tissues as much as possible. Using these patient positioning devices, 3D treatment planning, and our radiation dosing protocol, we are able to keep the risk of late radiation side effects to the normal surrounding brain tissue down to just 5%. With radiotherapy for brain tumours we do not typically see any external acute radiation side effects (such as hair loss, erythema or moist desquamation) due to the skin-sparing properties of our linear accelerator’s powerful megavoltage radiation beam. Toastie’s radiation protocol involved a daily (Monday through Friday) radiation treatment over 3 ½ weeks for a total of 18 radiation treatments. 

By the halfway point of his course of radiotherapy, Toastie began showing notable improvement in his mentation status and energy levels, he seemed much more settled, and the intermittent yelping stopped. He sailed through the remaining radiation treatments and completed the 18-dose protocol on 28 February.

We saw Toastie for regular follow-up visits after completion of radiotherapy to continue monitoring him, and he remained neurologically normal at each visit. We typically wait at least three months after completion of radiation before we anticipate having reached the maximum effect against the tumour, so a repeat brain MRI was performed in early July.

As you can see in the screenshots from the pre- and post-radiotherapy MRI scans, there has been a dramatic reduction in tumour size. On the pre-radiotherapy MRI, the tumour measured 17 x 19 x 16mm, while on the post-radiotherapy scan, the tumour shrank down to 6.3 x 9.9 x 7.8mm. This equates to a total reduction in tumour volume of approximately 87%, which is a truly remarkable response. At this point, no further MRI scans will be needed unless Toastie ever shows relapse of his neurologic symptoms, but we will continue to monitor him with a quarterly recheck examination and neuro assessment. 

Dr Elias Gumpel DVM Diplomate ACVR (RO)

 pituitary macroadenoma
Dr Elias Gumpel

Originally from Buenos Aires, Argentina, Dr Gumpel spent the first 31 years of his life in the state of Texas in the United States. He attended the University of Texas at Austin, where he graduated with the degree of Bachelor of Science in Biology (Ecology Evolution, Conservation). He was accepted to the Texas A&M University College of Veterinary Medicine in the year 2000 and graduated in May 2004 with the degree of Doctor of Veterinary Medicine. Following graduation, he worked as a general practitioner at Fry Road Animal Clinic on the outskirts of Houston from 2004-2008. 

Having always had an interest in oncology, Dr Gumpel was presented the opportunity to specialise in the field by starting an oncology internship at Gulf Coast Veterinary Specialists in Houston, Texas in July 2008. Upon completion of the internship, he accepted a position with GCVS as a radiation oncology resident. 

Dr Gumpel is a board-certified veterinary radiation oncologist with an onsite, dedicated LINAC for veterinary use. His expertise greatly contributes towards the improved care of veterinary cancer patients in Australia and surrounding countries.


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