Oct 7, 2011
ASTRO: studies in radiotherapy
The American Society for Radiation Oncology (ASTRO) annual meeting, held this week in Miami Beach, FL, saw over 1500 new research studies presented. Here is a selection of some of the radiotherapy-related results reported at this year's conference.
MLC proves promising for robotic radiosurgery
Researchers from Fox Chase Cancer Center (Philadelphia, PA) showed that multileaf collimator (MLC)-based CyberKnife delivery can be faster and spare more surrounding structures than conventional CyberKnife delivery. Jiajin Fan and his team created CyberKnife treatment plans for five patients with various tumours, using both the MLC and the original IRIS cone-shaped collimator. They also examined intensity-modulated radiotherapy (IMRT) plans.
All plans provided good target coverage. However, radiation doses fell off most sharply in the MLC plan, resulting in the greatest sparing of surrounding structures – such as the rectum and bladder for a prostate cancer treatment, for example. In addition, delivery of the MLC plan took only 10 minutes, roughly 10% of the total IRIS plan treatment time. This is primarily because the number of beams required is significantly less with the MLC technique.
"Using the MLC plan, we can deliver radiation therapy much faster compared to the current CyberKnife technique, and we can achieve much better target coverage and a much sharper dose fall off than a regular IMRT plan," Fan said. "Basically, we can spare the critical structures around tumours much better, providing the ability to treat the tumour to a higher dose without increasing the normal tissue toxicity."
IMRT reduces side effects for prostate cancer patients
Results of a randomized study reveal that men with localized prostate cancer treated with IMRT have fewer side effects than those who undergo 3D conformal radiation therapy (CRT). This study was a preliminary analysis of acute and late toxicity in men receiving high-dose radiotherapy as part of a phase III RTOG dose-escalation trial.
A group of 748 men were randomized to the high-dose arm of the trial. Of these, 491 were treated with 3D-CRT and 257 with IMRT. Median follow-up was 4.6 years and 3.5 years for 3D-CRT and IMRT patients, respectively. Results revealed that IMRT was associated with significant decrease in acute Grade 2+ rectal/bowel and urinary toxicity. There was also a 26% reduction in Grade 2+ late rectal and bowel side effects.
"This study supports the continued use of IMRT in the management of prostate cancer. It is a safe and very well tolerated therapy with fewer complications than 3D-CRT," said Jeff Michalski from Washington University Medical Center (St. Louis, MO), who presented the findings.
Higher dose of no benefit for treating lung cancer
A higher dose of radiation does not improve overall survival for non-small cell lung cancer that has spread to the lymph nodes, according to late-breaking results reported by Jeffrey Bradley from Washington University School of Medicine in St Louis. In a phase III trial, 423 patients were randomized to one of four treatment arms: standard-dose (60 Gy) versus high-dose (74 Gy) radiotherapy, and concurrent chemotherapy (paclitaxel and carboplatin) with or without Cetuximab.
The study's early findings showed that patients who received the higher dose of radiation did not have better survival rates than those receiving the standard dose; therefore, the two high-dose arms of the trial were closed to patient accrual.
"Although the optimal radiation dose for lung cancer patients has not been tested in a randomized phase III trial for over 30 years, most [radiation oncologists and lung cancer specialists] believed that higher doses of radiation cured more patients with lung cancer," said Bradley. "The trial provides class I evidence that the standard dose of radiation therapy for stage III lung cancer should remain at its existing level and doses as high as 74 Gy are not better in curing Stage III lung cancer," said Bradley.
Hypofractionation works just as well
A long-term study has demonstrated that hypofractionated radiotherapy is as effective a treatment for prostate cancer as conventional radiation therapy. The study involved 303 men with intermediate to high-risk prostate cancer who were randomized to receive either hypofractionated (70.2 Gy in 2.7 Gy fractions) or conventionally fractionated IMRT (76 Gy in 2.0 Gy fractions). Patients were followed for over five years to monitor cancer recurrence.
Although the hypofractionated treatment was hypothesized to be superior, the same tumour control rates were observed for both regimes. However, the benefit of hypofractionation was that comparable results were achieved in two and a half fewer weeks of treatment. In terms of side effects, rates were relatively low for both methods, but significantly higher bladder control was noted in the conventionally fractionated patients.
"Hypofractionation is rapidly gaining momentum for many types of cancers," said Alan Pollack, chairman of radiation oncology at the University of Miami Miller School of Medicine (Miami, FL). "The results presented here bring us much closer to effectively treating prostate cancer in a shorter period of time, with acceptable side effects."
About the author
Tami Freeman is editor of medicalphysicsweb.