Toward Optimal Fractionation Schemes in Nonuniform Radiation Therapy: Exploiting Helical Tomotherapy's Thread Effect...

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Biology

Background:

• Helical tomotherapy (HT) is a radiotherapy technique.
• Spatially fractionated radiotherapy (SFRT) aims to enhance tumor control while sparing normal tissues.
• The
• thread effect
• in HT can potentially be leveraged for SFRT.

Purpose of the Study:

• To optimize dose fractionation parameters for HT-SFRT in gynecological cancers.
• To exploit the
• thread effect
• to induce cohort effects for enhanced therapeutic outcomes.
• To evaluate the clinical efficacy and toxicity of the optimized HT-SFRT regimen.

Main Methods:

• In vitro optimization of HT-SFRT parameters (pitch, field width, modulation factor) using HeLa cells.
• Quantification of DNA damage (γ-H2AX) and cell viability to determine the cohort effect threshold.
• Clinical validation in 45 gynecological cancer patients comparing HT-SFRT with conventional HT and SBRT, including dosimetric analysis (BED, TCP, NTCP).

Main Results:

• Optimized HT-SFRT parameters (FW=5.048 cm, pitch=0.5, MF=2.0) maximized the peak-to-valley dose ratio (PVDR).
• An 8 Gy/fraction dose threshold was established for inducing cohort effects, significantly reducing cell viability.
• The 32 Gy/4F SFRT regimen demonstrated comparable tumor control to conventional HT, with an 84% reduction in treatment duration and significantly lower bladder NTCP.

Conclusions:

• The
• thread effect
• in HT can be effectively utilized for SFRT in gynecological cancers.
• The optimized HT-SFRT scheme (32 Gy/4 F) offers equivalent tumor control, shorter treatment duration, and acceptable normal tissue toxicity.
• HT-SFRT presents a promising alternative radiotherapy approach for gynecological cancers, warranting prospective clinical trials.