Tumor Regression with 5-Aminolevulinic Acid (5-ALA)-Mediated Radiodynamic Therapy (RDT) Using Different Megavoltage Energies

PURPOSE/OBJECTIVE(S)

5-aminolevulinic acid (5-ALA) accumulates in target tumor cells, where it is metabolized to a photosensitizer - protoporphyrin IX (PpIX). Cherenkov light induced by high-energy photon beams effectively activates the PpIX due to the Soret band. The activated photosensitizers lead to cellular toxicities to kill malignant tumor cells by converting surrounding tissue oxygens into singlet oxygens. Radiodynamic therapy (RDT) utilizes cellular damage caused by both radiation dose and activated photosensitizer. The emission of Cherenkov light was observed higher with higher energy irradiation in phantom and ex-vivo tissues. Therefore, using an in-vivo mouse model, this study aimed to investigate the efficacy and energy dependency of RDT combined with 5-ALA and different ranges of megavoltage photon irradiation.

MATERIALS/METHODS

In order to investigate individual and synergistic effects of 5-ALA administration and radiation treatment, the tumors (n = 344) were randomized into eight groups: control (untreated), 5-ALA only, 6-, 15-, and 45-MV conventional radiation treatment (RT) only, 6-, 15-, and 45-MV RDT. 4 Gy in a single fraction was delivered to the tumors using three different energy photons for RT only and RDT groups. 5-ALA was systemically injected into 5-ALA only and RDT groups at 100 mg/kg by tail-vein 4 hours before irradiation for endogenous PpIX accumulation in the tumor. Tumor growth was measured using a 1.5 T MR scanner on the day of treatment (prior to the treatment), 3, 7, and 14 days post-treatment. Two-way repeated ANOVA with Bonferroni correction was used to compare each treatment group to determine the statistically significant difference in tumor growth.

RESULTS

A total of 45 MV RDT resulted in the most significant decrease in tumor growth by 58.8 ± 3.4 %, 58.0 ± 3.0 %, and 55.0 ± 3.0 % compared to 5-ALA, 45 MV RT, and control group on 7 days post-treatment (P<0.001), respectively. Moreover, a synergistic effect of 45 MV RDT causes a 47.1-54.1 % additional decrease in tumor growth toward the effective treatment outcome. Compared to the different energies, 45 MV RDT resulted in a 52.2 ± 3.1 % and 19.7 ± 7.2 % decrease in tumor growth compared to 6 MV RDT and 15 MV RDT on 7 days post-treatment, respectively (P<0.001), whereas the conventional RT was not.

CONCLUSION

Radiodynamic therapy using 5-ALA administration and 45MV photon beam irradiation resulted in the most significant tumor growth control. A photon energy dependency was observed in radiodynamic therapy. 45MV photon beams showed greater in activating PpIX, improving the synergistic effects of radiation dose and activated photosensitizer than the other energies. The preliminary results provide a foundation for new innovative treatment strategies that have the potential to improve cancer treatment.

Investigation of Hydrogen Peroxide for 45MV 5-Aminolevulinic Acid-Mediated Radiodynamic Therapy

PURPOSE/OBJECTIVE(S)

Cytotoxicity caused by the reactive oxygen species (ROS), such as singlet oxygen species (1O2), superoxide radical (O2-), and hydroxyl radical (HO), is a mechanism for treating cancer cells in radiation therapy. 5-aminolevulinic acid (5-ALA)-mediated radiodynamic therapy (RDT) is more effective in killing tumor cells than conventional radiation therapy. ROS is produced not only by ionizing radiation but also by Cherenkov light-activated protoporphyrin IX (PpIX), which is metabolized endogenously from 5-ALA. Moreover, PpIX also catalyzes hydrogen peroxide to generate 1O2, and an enhanced catalytic yield of 1O2 was observed in X-ray irradiation in vitro. Therefore, using an in-vivo mouse model, this study aimed to investigate the effect of hydrogen peroxide as a coenzyme catalyst on a novel 45MV 5-ALA-mediated RDT.

MATERIALS/METHODS

A subcutaneous C57BL/6 mouse model of KP1 cell line was used. The tumors (n = 240) were randomized into six groups, consisting of untreated, conventional radiation treatment (RT), and RDT with or without hydrogen peroxide: 1. control (untreated), 2. hydrogen peroxide, 3. 45MV RT, 4. 45MV RT + hydrogen peroxide, 5. 45MV RDT, 6. 45MV RDT + hydrogen peroxide. For 45MV photon irradiation, a single fraction of 4 Gy was delivered to the tumors. 5-ALA was systemically injected at 100 mg/kg by tail-vein 4 hours before the treatment for endogenous PpIX accumulation in the tumor. Carbamide peroxide was used to deliver hydrogen peroxide to tissue and was administered at 60 mg/kg intratumorally into tumors ∼3-5 min before the treatment. The treatment effect of a single fraction of treatment was measured by calculating tumor growth, measured using a 1.5 T MR scanner on the day of treatment (prior to the treatment), 3 and 7 days post-treatment. Two-way repeated ANOVA with Bonferroni correction was used to compare each treatment group to determine the statistically significant difference in tumor growth.

RESULTS

A total of 45MV RDT with hydrogen peroxide was shown to significantly delay the tumor growth for the mouse model and cell line investigated in this work. 45MV RDT with hydrogen peroxide group resulted in a decrease in tumor growth by 51.3 ± 4.1 % and 56.1 ± 5.1 % compared to the control group on 3 and 7 days post-treatment, respectively (P<0.001), and 43.4 ± 0.8 % and 50.9 ± 0.8 % compared to 45MV RT alone on 3 and 7 days post-treatment, respectively. Moreover, the enhancement effect of hydrogen peroxide on 45MV RDT was 2.2-4.7 times greater on 45MV RT alone (P<0.05). Hydrogen peroxide did not contribute to tumor growth when administered alone.

CONCLUSION

A total of 45MV 5-ALA-mediated RDT with hydrogen peroxide resulted in the most significant tumor growth delay compared to the other groups. The catalytic effect of PpIX and hydrogen peroxide was observed in-vivo. These preliminary results demonstrate an effective cancer treatment modality.

Beam modeling and beam model commissioning for Monte Carlo dose calculation-based radiation therapy treatment planning: Report of AAPM Task Group 157

Dose calculation plays an important role in the accuracy of radiotherapy treatment planning and beam delivery. The Monte Carlo (MC) method is capable of achieving the highest accuracy in radiotherapy dose calculation and has been implemented in many commercial systems for radiotherapy treatment planning. The objective of this task group was to assist clinical physicists with the potentially complex task of acceptance testing and commissioning MC-based treatment planning systems (TPS) for photon and electron beam dose calculations. This report provides an overview on the general approach of clinical implementation and testing of MC-based TPS with a specific focus on models of clinical photon and electron beams. Different types of beam models are described including those that utilize MC simulation of the treatment head and those that rely on analytical methods and measurements. The trade-off between accuracy and efficiency in the various source-modeling approaches is discussed together with guidelines for acceptance testing of MC-based TPS from the clinical standpoint. Specific recommendations are given on methods and practical procedures to commission clinical beam models for MC-based TPS.

Dosimetric and delivery efficiency investigation for treating hepatic lesions with a MLC-equipped robotic radiosurgery-radiotherapy combined system

PURPOSE

The CyberKnife M6 (CK-M6) Series introduced a multileaf collimator (MLC) for extending its capability from stereotactic radiosurgery/stereotactic radiotherapy (SBRT) to conventionally fractionated radiotherapy. This work is to investigate the dosimetric quality of plans that are generated using MLC-shaped beams on the CK-M6, as well as their delivery time, via comparisons with the intensity modulated radiotherapy plans that were clinically used on a Varian Linac for treating hepatic lesions.

METHODS

Nine patient cases were selected and divided into three groups with three patients in each group: (1) the group-one patients were treated conventionally (25 fractions); (2) the group-two patients were treated with SBRT-like hypofractionation (5 fractions); and (3) the group-three patients were treated similar to group-one patients, but with two planning target volumes (PTVs) and two different prescription dose levels correspondingly. The clinically used plans were generated on the eclipse treatment planning system (TPS) and delivered on a Varian Linac (E-V plans). The multiplan (MP) TPS was used to replan these clinical cases with the MLC as the beam device for the CK-M6 (C-M plans). After plans were normalized to the same PTV dose coverage, comparisons between the C-M and E-V plans were performed based on D(99%) (percentage of prescription dose received by 99% of the PTV), D(0.1cm(3)) (the percentage of prescription dose to 0.1 cm(3) of the PTV), and doses received by critical structures. Then, the delivery times for the C-M plans will be obtained, which are the MP TPS generated estimations assuming having an imaging interval of 60 s.

RESULTS

The difference in D(99%) between C-M and E-V plans is +0.6% on average (+ or - indicating a higher or lower dose from C-M plans than from E-V plans) with a range from -4.1% to +3.8%, and the difference in D(0.1cm(3)) was -1.0% on average with a range from -5.1% to +2.9%. The PTV conformity index (CI) for the C-M plans ranges from 1.07 to 1.29 with a mean of 1.19, slightly inferior to the E-V plans, in which the CI ranges from 1.00 to 1.15 with a mean of 1.07. Accounting for all nine patients in three groups, 45% of the critical structures received a lower mean dose for the C-M plans as compared with the E-V plans, and similarly, 48% received a lower maximum dose. Furthermore, the average difference of the mean critical structure dose between the C-M and E-V plans over all critical structures for all patients showed only +2.10% relative to the prescription dose and the similar comparison finds the average difference of the maximum critical structure dose of only +1.24%. The estimated delivery times for the C-M plans on the CK-M6 range from 18 to 24 minutes while they are from 7 to 13.7 min for the E-V plans on the Varian Linac.

CONCLUSIONS

For treating hepatic lesions, for the C-M plans that are comparable to E-V plans in quality, the times needed to deliver these C-M plans on the CK-M6 are longer than the delivery time for the E-V plans on the Varian Linac, but may be clinically acceptable.