Page 1397 - Clinical Small Animal Internal Medicine

151 Soft Tissue Sarcomas 1335

margins and tumor grade. Both are necessary in deter- behind. Some advantages of postoperative radiation
VetBooks.ir mining whether further treatment, including additional include the following:
surgery or radiation therapy, is necessary. Following
wound complications are rare in tissues that are irradi-
●
removal of the tumor, surgical margins should be clearly
marked on the specimen and completeness of excision ated after the first inflammatory phase of wound
healing
should be evaluated. The resected tumor should be removal of a larger tumor with necrotic regions or
pinned out to the original dimensions to prevent shrink- ● infections may make the patient and patient’s family
age during formalin fixation. The following terminology more comfortable
is commonly used when evaluating surgical margins and postoperative treatment planning may be simpler than
considering additional treatment: ●
preoperative planning in patients in which the size or
incomplete margins – neoplastic cells are continuous shape of a tumor creates difficulty in achieving a uni-
●
with at least one surgical margin in any plane form dose distribution.
narrow margins – distance between surgically
● Disadvantages of postoperative radiation include
created tissue edge and neoplastic cells is less increased radiation field size, damage to vasculature,
than 5 mm
adequate margins – distance between surgically that may lead to local tissue hypoxia which decreases the
● effectiveness of radiation, and potential delays if post-
created tissue edge and neoplastic cells is ≥ 5 mm and surgical wound complications occur. Postoperative radi-
<10 mm
ideal margins – distance between surgically created ation is generally started within 7–14 days after surgery.
● The rationale behind preoperative radiation therapy is
tissue edge and neoplastic cells is at least ≥ 10 mm.
to decrease the number of tumor cells, thus reducing
Marginal and incomplete resection is associated with a contamination of the surgical site. Advantages include a
higher risk of local recurrence (26–60%). Further, dogs smaller radiation field, reduction in the size of the tumor,
with incomplete margins are 10.5 times more likely to making surgical excision with wide margins less difficult,
develop local recurrence than dogs with complete mar- and undisturbed tumor bed and blood supply, which
gins. Studies have also shown that the first surgery pro- increases the effectiveness of radiation. Disadvantages
vides the best opportunity for local tumor control. include the possibility of poor or delayed wound healing
Subsequent surgeries increase morbidity, treatment in the irradiated field.
costs, and the risk of further local recurrences, while Radiation therapy is commonly used as an adjunct to
decreasing survival time. If a second surgery is performed surgery. Radiation seems to have the greatest efficacy
after inadequate resection, a margin of healthy tissue of when it is used to treat remaining microscopic disease
3 cm in all directions surrounding the scar is recom- following surgical cytoreduction and is less effective
mended, including the removal of normal‐appearing when used to treat bulky, gross disease. Marginal surgi-
subcutaneous fat and underlying fascia. In a study evalu- cal resection combined with radiation therapy is an
ating scar reexcisions, local recurrence was reported in attractive alternative to limb amputation for a STS on an
15% of dogs and residual tumor was identified in 22% of extremity. It can also be used following a planned mar-
the resected scars. ginal resection when wide surgical resection is not pos-
Prior to the routine availability of radiation treatment, sible, such as with tumors of the head or neck. In these
radical and often disfiguring surgery was the mainstay of cases, removal of all grossly visible tumor is advised.
treatment and resulted in one‐year control rates of Radiopaque clips are often placed during surgery to
70–80%. Although STS have historically been consid- mark the lateral, proximal, and distal extent of the tumor
ered radiation resistant compared to other tumor types, to aid in radiation planning.
the multimodality approach of combining surgery with Several studies have evaluated radiation therapy for
radiation has been proven to help prevent local incompletely excised soft tissue sarcomas in dogs. They
recurrence. have shown that similar local control and survival rates
are attained with a better functional and cosmetic out-
Surgery and Radiation Therapy come by performing marginal surgical excisions plus
The sequencing of radiation and surgery is based on adjuvant radiotherapy compared to radical surgery
multiple factors and should be determined on an indi- alone. A prospective study evaluated 48 dogs with soft
vidual basis. There are several advantages and disadvan- tissue sarcomas treated with surgery to decrease tumor
tages to both preoperative and postoperative radiation size to <3 cm. This was followed by conventionally frac-
therapy. The rationale for administering postoperative tionated, full course radiation therapy to a total dose of
radiation therapy is that the radiation kills or prevents 63 Gy. The result was a five‐year survival rate of 76% and
the multiplication of any microscopic tumor cells left a recurrence rate of 16%. The median time to recurrence