Fascinating article on IGRT and margins for prostate cancer from Japan by Itsuko Serizawa et al

Simul Parikh, Medical Director of OncoHealth, shared a post on LinkedIn about a recent paper by Itsuko Serizawa et al., commenting:

“Fascinating article on Image-Guided Radiation Therapy (IGRT) and margins for prostate cancer from Japan.

The TL;DR is that with fiducials and IGRT, one can reduce Planning Target Volume (PTV) margins and reduce toxicity. In this retrospective study they looked at,

• No IGRT.
• IGRT with same margins as no IGRT.
• IGRT with smaller margins.

No change in cancer outcomes was noted, while IGRT with smaller margins decreased toxicity compared to the other groups. And, this makes sense.

What I found more interesting was their volumes.

Their prostate gland Clinical Target Volume (CTV) was 3mm and the PTV was 5mm. Then, they subtract out the rectum from the PTV and call that PTV modified. This is what they prescribe to.

Typically, in our NRG studies, the gland itself is the CTV and the PTV margin is added to that can range from 3 to 10 mm, without subtracting out the rectum.

It seems that the NRG and American approach is ‘pure’ in that the PTV is not modified, but in the Japanese approach, they are accounting for a CTV in the space around the prostate.

My hunch is that because they do subtract out the rectum but do add a CTV, the rectal dose is probably very similar to ours.”

Clinical and Dosimetric Comparison between Non-Image-Guided Radiation Therapy and Fiducial-Based Image-Guided Radiation Therapy with or without Reduced Margin in Intensity-Modulated Radiation Therapy for Prostate Cancer published in Advances in Radiation Oncology.

Authors: Itsuko Serizawa, Takuyo Kozuka, Takashi Soyano, Kazuma Sasamura, Tatsuya Kamima, Hiroaki Kunogi, Nozomi Kurihara, Noboru Numao, Shinya Yamamoto, Junji Yonese, Yasuo Yoshioka.

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Source: Simul Parikh/LinkedIn