Spot-scanning beam delivery with laterally- and longitudinally-mixed spot size pencil beams in heavy ion radiotherapy

The three-dimensional （3D） spot-scanning method is one of the most commonly used irradiation methods in charged particle beam radiotherapy. Generally, spot-scanning beam delivery utilizes the same size pencil beam to irradiate the tumor targets. Here we propose a spot-scanning beam delivery method with laterally- and longitudinally- mixed size pencil beams for heavy ion radiotherapy. This uses pencil beams with a bigger spot size in the lateral direction and wider mini spread-out Bragg peak （mini-SOBP） to irradiate the inner part of a target volume, and pencil beams with a smaller spot size in the lateral direction and narrower mini-SOBP to irradiate the peripheral part of the target volume. Instead of being controlled by the accelerator, the lateral size of the pencil beam was adjusted by inserting Ta scatterers in the beam delivery line. The longitudinal size Of the pencil beam （i.e. the width of the mini-SOBP） was adjusted by tilting mini ridge filters along the beam direction. The new spot-scanning beam delivery using carbon ions was investigated theoretically and compared with traditional spot-scanning beam delivery. Our results show that the new spot-scanning beam delivery has smaller lateral penumbra, steeper distal dose fall-off and the dose homogeneity （1-standard deviati^n/mean） in the target volume is better than 95%.

Carbon ion radiotherapy for synchronous choroidal melanoma and lung cancer: A case report

BACKGROUND Despite being the most common intraocular malignancy among adults,choroidal melanoma is a rare cancer type,even more so when accompanied by lung cancer.We report a patient with synchronous choroid melanoma and lung cancer treated with carbon ion radiotherapy(CIRT).CASE SUMMARY A 41-year-old woman was transferred to our center with a diagnosis of choroidal melanoma in her right eye.During the examination,we found a right lung tumor that was histologically diagnosed as lung cancer.The patient was treated with CIRT for both malignant neoplasms.The CIRT dose was 70 photon equivalent doses(GyE)in five fractions for the right eye choroidal melanoma and 72 GyE in 16 fractions for the right lung cancer.At 3 mo after CIRT,the choroidal melanoma completely disappeared,as did the right lung cancer 7 mo after;the patient was in complete remission.CONCLUSION CIRT may be an effective treatment for double primary lung cancer and choroid melanoma.

Active spot-scanning test with heavy ions at HIRFL-CSR

An active spot beam delivery system for heavy ion therapy has been developed based on the Cooling Storage Ring at HIRFL-CSR, where the pencil carbon-ion beams were scanned within a target volume transversely by a pair of orthogonal （horizontal and vertical） dipole magnets to paint the slices of the target volume and longitudinally by active energy variation of the synchrotron slice by slice. The unique techniques such as dose shaping via active energy variation and magnetic deflection constitute a promising three-dimensional conformal even intensity-modulated radiotherapy with heavy ions at HIRFL-CSR. In this paper, the verification of active energy variation and the calibration of steerable beam deflection are shown, as the basic functionality components of the active spot-scanning system. Additionally, based on the capability of creating homogeneous irradiation fields with steerable pencil beams, a radiobiological experiment like cell survival measurement has been performed aiming at comparison of the radiobiological effects under active and passive beam deliveries.