Newer Radiation Techniques
BEYOND CONVENTIONAL RADIOTHERAPY – SBRT, Radical treatment for Metastatic Cancers. Dr Swarupa Mitra. Senior Consultant Radiation Oncologist and Unit Chief, Rajiv Gandhi Cancer Institute And Research Centre, New Delhi
In 2008, doctors told a woman, now in her 80s, that she was not a candidate for surgery and there was nothing else they could do. Then she found her way to Yale and became one of the first patients here to be treated with stereotactic body radiotherapy (SBRT), which delivers high doses of radiation with pinpoint precision.
Just a few treatments wiped away her disease.
Advances in imaging and biological targeting have led to the development of stereotactic body radiation therapy (SBRT) as an alternative treatment of various metastatic sites with high dose. Key factors in SBRT are delivery of a high dose per fraction, immaculate patient positioning, target localisation, and management of breathing–related motion. This allows delivery of an ablative radiation dose with minimal toxicity, and may potentially improve local tumor control, and hence enhance clinical outcomes especially for tumours that are considered radio resistant.
We typically assume that metastases originate from the primary tumor but perhaps metastases can generate more metastases and so just leaving oligometastatic disease especially from some indolent tumours, alone when it appears stable may mean that we miss a window of opportunity for cure.
Some of such commonly occurring situations are as under.
Emerging Data on Image-Guided Ablative Therapy for Skeletal Metastasis —
In patients with only a limited number of metastases, and with good performance status, local therapy, besides causing pain control and preventing fractures, might definitively eradicate these areas and potentially convert the therapy to curative intent.
Both single- and multiple fractions SBRT for spinal metastasis is safe and feasible. Fractionated SBRT may be suitable in patients with a large tumor volume or when the dose to the spinal cord cannot meet the accepted dose constraint with single-fraction SBRT or in patients with recurrence in the area that was previously treated with radiation. Various dose schedules have been used in literatures.
SBRT of liver oligometastases
The liver is a common metastatic site for a variety of primary malignancies including colorectal, lung, breast, bladder, oesophageal, head & neck and pancreatic cancers, and cholangiocarcinoma. Surgery is still the standard of care for such lesions. SBRT has the advantage of delivering higher tumoricidal doses to the target and sparing uninvolved liver and surrounding critical organs, thus reducing the likelihood of RILD.
Follow-up of patients after liver SBRT is a challenge as the early treatment response (before 3 months) may be difficult to interpret on CT or MRI images because of radiation induced changes in the form of veno-occlusive diseases. But these changes are not associated with changes in overall liver functions.
SBRT of abdominal lymph node metastases (Local control and toxicity)
The rationale of administering abdominal SBRT with curative intent to patients with limited nodal metastatic disease is the same as for selected patients with liver or lung metastases. There is no consensus on optimal dose, number of fractions, or planning constraints. The highest dose in literatures has been upto 60 Gy while the number of fractions between 3 and 6.
PET CT OF A PATIENT OF LUNG CARCINOMA (TRIPLE MALIGNANCY)
Series showing the disease before SBRT. The top series shows PET CT taken 2 months Post SBRT. No side effects were seen. Stereotactic Body Radiotherapy as an Alternative to Brachytherapy in Gynecologic Cancer
Brachytherapy plays a key role in the treatment of most gynecologic cancers. However, some patients are unable to tolerate brachytherapy for medical or other reasons or unfavourable anatomy. For these patients, stereotactic body radiotherapy (SBRT) offers an alternative form of treatment which entails high doses of external radiation delivered in a very conformal fashion.
While SBRT is commonly used in medically unresectable early-stage lung cancer and has a growing use in other pathologies, there are very little data regarding the role of SBRT used in place of BB.
SBRT in reirradiation
Most of the recurrences occur in the previously irradiated field and it is impossible to deliver enough dose by conventional radiotherapy to control the disease. Surgery is often impossible due to the previous irradiation and the location of the recurrence. Reirradiation is often a complex situation and SBRT seems to be a safe and efficient option to treat tumor recurrences even if not in a curative intent. This is an attractive alternative in Recurrences in Head and Neck Carcinomas, pelvic carcinomas. In the latter, recurrence with lateral pelvic invasion or in proximity of the iliac vessel, local treatment cannot be achieved. Without treatment, local progression often causes pain and impacts the quality of life.
Set up of Respiratory gating for SBRT for a Lung metastasis patient (Courtesy-RGCIRC, Dept of Radiotherapy)
