A recent study compared the risk of having a second cancer after treatment using either intensity-modulated radiotherapy, 3-dimensional conformal radiotherapy, or proton beam radiotherapy.
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Having radiation therapy can be highly successful in treating cancer. Still, like every other treatment, it can come with side effects. One of the possible side effects can be the development of secondary cancer from the radiation treatment itself.
According to findings published in "Cancer", the risk of developing a second cancer diagnosis after primary cancer treatment was similar after intensity-modulated radiotherapy (IMRT) versus 3-dimensional conformal radiotherapy (3DCRT). At the same time, proton beam radiotherapy (PBRT) was correlated with a lower risk of a second cancer diagnosis.
How significant is this concern, and how do the risks compare among different types of radiation treatments?
"Our current results, although hypothesis-generating, are consistent with the conjectured reduction in second cancers with Proton Beam Radiation Therapy (PBRT), although the absolute benefit may be small in an unselected population because of the rarity of second cancers," the authors wrote. "Furthermore, we did not find evidence that the use of IMRT gives rise to more second cancers compared with 3DCRT, although additional follow-up is required."
For this study, the researchers used the National Cancer Database to identify pediatric and adult patients with an initial diagnosis of cancer between 2004 and 2015. These patients received either 3DCRT, IMRT, or PBRT treatment for several tumor types, including head and neck, gastrointestinal, gynecologic, lymphoma, lung, prostate, breast, bone/soft tissue, or brain/central nervous system.
The total study cohort identified 450,373 individuals, including 33.5% who received 3DCRT, 65.2% who received IMRT, and 1.3% who received PBRT.
The median follow-up after completion of radiotherapy was 5.1 years (range, 2-13.8 years) overall and 7.4 years among patients who had >5 years of follow-up. The cumulative follow-up period was 2.54 million person-years.
In a comparison between IMRT versus 3DCRT, there was no overall difference observed in the risk of developing a second cancer. The sole exception to this was head and neck cancer, which saw a modest decrease in second cancer risk with IMRT.
The researchers concluded that "In our study, the point estimates for second cancer risk favored PBRT across all age subgroups, including younger patients."
Notwithstanding these findings, the researchers noted that these study results should be interpreted in the context of several limitations, such as the lack of data regarding known cancer risk factors, such as smoking and obesity. Given that these results are only hypothesis-generating, the researchers highlighted the need for future studies to continue this research.
Because of the very high economic cost of PBRT, "future work is warranted to determine the cost-effectiveness of PBRT and to identify the patients best suited for this treatment," the authors concluded.
Reference:
Xiang M, Chang DT, Pollom EL. Second Cancer Risk After Primary Cancer Treatment With Three-Dimensional Conformal, Intensity-Modulated, or Proton Beam Radiation Therapy. Cancer. doi: 10.1002/cncr.32938.
