Proton Beam Therapy by Santosh Yajnik

Author:Santosh Yajnik
Language: eng
Format: epub
Publisher: Springer New York, New York, NY

Discussion and Future Directions

A diagnosis of lung cancer can be devastating for the patient and family members. Lung cancer remains the leading cancer killer in the USA. However, as we have seen in this chapter, the history of radiation therapy for lung cancer is not without significant advancements. For example, innovations in imaging including CT and PET scanning have been harnessed to better image and define the target volume to be treated with radiation therapy and better shield the normal tissues from the harmful effects of radiation. For early-stage patients, hypofractionated, stereotactic body radiation therapy has shown improvements in local control for the properly selected patients. For unresectable stage III patients with non-small cell lung cancer, concurrent chemotherapy with radiation has been shown to offer overall survival improvements compared with radiation therapy alone.

Proton beam therapy offers promise but also several unique dosimetric challenges as we evaluate its use in the management of non-small cell lung cancer. It is hoped that the unique physical characteristic of proton beam therapy, with Bragg peak and distal stopping of the proton beam, shall allow for improved dose distributions and less dose to normal tissues compared with photons. It is essential to account for tumor movement when planning for proton beam therapy, and the use of 4D CT scanning during simulation can help accomplish this. In addition, there may be a need for additional 4D CT scanning during the several week course of treatment to account for alterations in density along the proton beam’s path.

One area under active investigation is hypofractionation with proton beam therapy. Due to the improvements in dose distribution offered by proton beam therapy compared with photons, it may be possible to safely deliver a higher dose per fraction. For stage 1 patients, stereotactic body radiosurgery is being evaluated. For more advanced, unresectable stage III patient, a milder form of hypofractionation is being evaluated. We will await the results of these clinical trials to determine what role hypofractionated proton beam therapy plays in the management of non-small cell lung cancer.

Another concept under investigation is to leave the fraction size of the proton beam therapy as standard, but to take advantage of the improved shielding of normal tissues offered by proton beam therapy to intensify the systemic therapy. Systemic therapy can be intensified either by intensifying standard chemotherapy or adding novel-targeted therapies. Such trials are currently under way, and we will await the results of these studies to evaluate whether such intensification of systemic therapy offers an advantage to patients with non-small cell lung cancer.

Too often in emergency rooms and doctor’s offices today, the diagnosis of lung cancer is followed by a challenging treatment course. For unresectable stage 3 disease, we employ systemic chemotherapy and radiation therapy with modest improvements in survival, when what is really desired is a molecular switch that can turn off this dreaded disease. Until such a switch is available, radiation oncologists will continue to search for ways to improve dose delivered to the cancer while shielding critical normal tissues from the harmful effects of radiation.

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