Abstract
PurposeRayStation treatment planning system employs pencil beam (PB) and Monte Carlo (MC) algorithms for proton dose calculations. The purpose of this study is to evaluate the radiobiological and dosimetric impact of RayStation PB and MC algorithms on the intensity‐modulated proton therapy (IMPT) breast plans.MethodsThe current study included ten breast cancer patients, and each patient was treated with 1–2 proton beams to the whole breast/chestwall (CW) and regional lymph nodes in 28 fractions for a total dose of 50.4 Gy relative biological effectiveness (RBE). A total clinical target volume (CTV_Total) was generated by combining individual CTVs: AxI, AxII, AxIII, CW, IMN, and SCVN. All beams in the study were treated with a range shifter (7.5 cm water equivalent thickness). For each patient, three sets of plans were generated: (a) PB optimization followed by PB dose calculation (PB‐PB), (b) PB optimization followed by MC dose calculation (PB‐MC), and (c) MC optimization followed by MC dose calculation (MC‐MC). For a given patient, each plan was robustly optimized on the CTVs with same parameters and objectives. Treatment plans were evaluated using dosimetric and radiobiological indices (equivalent uniform dose (EUD), tumor control probability (TCP), and normal tissue complication probability (NTCP)).ResultsThe results are averaged over ten breast cancer patients. In comparison to PB‐PB plans, PB‐MC plans showed a reduction in CTV target dose by 5.3% for D99% and 4.1% for D95%, as well as a reduction in TCP by 1.5–2.1%. Similarly, PB overestimated the EUD of target volumes by 1.8─3.2 Gy(RBE). In contrast, MC‐MC plans achieved similar dosimetric and radiobiological (EUD and TCP) results as the ones in PB‐PB plans. A selection of one dose calculation algorithm over another did not produce any noticeable differences in the NTCP of the heart, lung, and skin.ConclusionIf MC is more accurate than PB as reported in the literature, dosimetric and radiobiological results from the current study suggest that PB overestimates the target dose, EUD, and TCP for IMPT breast cancer treatment. The overestimation of dosimetric and radiobiological results of the target volume by PB needs to be further interpreted in terms of clinical outcome.
Highlights
Intensity‐modulated proton therapy (IMPT) is used for the treatment of breast cancer at many proton centers across the world
pencil beam (PB)‐PB, PB optimization followed by PB dose calculation; PB‐Monte Carlo (MC), PB optimization followed by MC dose calculation; MC‐MC, MC optimization followed by MC dose calculation; CTV, clinical target volume; LAD, left anterior descending artery; RBE, relative biological effectiveness. aP‐value for PB‐MC vs. PB‐PB. bP‐value for MC‐MC vs. PB‐PB
PB‐PB, PB optimization followed by PB dose calculation; PB‐MC, PB optimization followed by MC dose calculation; MC‐MC, MC optimization followed by MC dose calculation; CTV, clinical target volume; CW, chestwall; EUD, equivalent uniform dose; IMN, internal mammary nodes; SCVN, supraclavicular nodes; RBE, relative biological effectiveness. aP‐value for PB‐MC vs. PB‐PB. bP‐value for MC‐MC vs. PB‐PB
Summary
Intensity‐modulated proton therapy (IMPT) is used for the treatment of breast cancer at many proton centers across the world. Literature[1,2] has shown that proton therapy for breast cancer could potentially reduce normal tissue complication probability (NTCP) by reducing side effects such as cardiac and pulmonary toxicities. It is paramount that the reduction of NTCP must be accompanied by an increase in tumor control probability (TCP) to prevent tumor recurrence. Both the TCP and NTCP are calculated based on the absorbed dose in disease sites and normal tissues, respectively. RayStation (version 6.1.1.2; RaySearch Laboratories, Stockholm, Sweden) employs analytical pencil beam (PB) and Monte Carlo (MC) algorithms for proton dose calculations. Shirey et al.[6] showed better accuracy of MC compared to PB when treatment involves the range shifter and superficial lesions
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
